Medicine, Faculty of
Non UBC
DSpace
Ray, Dwaipayan
Collister, Robert
Rasiwala, Hussain
Backes, Lucas
Balbuena, Ali V.
Brunner, Thomas
Casandjian, Iroise
Chambers, Chris
Cvitan, Megan
Daniels, Tim
Dilling, Jens
Elmansali, Ryan
Fairbank, William
Fudenberg, Daniel
Gornea, Razvan
Gratta, Giorgio
Iverson, Alec
Kwiatkowski, Anna A.
Leach, Kyle G.
Lennarz, Annika
Li, Zepeng
Medina-Peregrina, Melissa
Murray, Kevin
O’Sullivan, Kevin
Ross, Regan
Shaikh, Raad
Shang, Xiao
Soderstrom, Joseph
Varentsov, Victor
Yang, Liang
Neutrinoless double beta decay (0νββ) provides a way to probe physics beyond the Standard Model of particle physics. The upcoming nEXO experiment will search for 0νββ decay in 136Xe with a projected half-life sensitivity exceeding 1028 years at the 90% confidence level using a liquid xenon (LXe) Time Projection Chamber (TPC) filled with 5 tonnes of Xe enriched to ∼90% in the ββ-decaying isotope 136Xe. In parallel, a potential future upgrade to nEXO is being investigated with the aim to further suppress radioactive backgrounds and to confirm ββ-decay events. This technique, known as Ba-tagging, comprises extracting and identifying the ββ-decay daughter 136Ba ion. One tagging approach being pursued involves extracting a small volume of LXe in the vicinity of a potential ββ-decay using a capillary tube and facilitating a liquid-to-gas phase transition by heating the capillary exit. The Ba ion is then separated from the accompanying Xe gas using a radio-frequency (RF) carpet and RF funnel, conclusively identifying the ion as 136Ba via laser-fluorescence spectroscopy and mass spectrometry. Simultaneously, an accelerator-driven Ba ion source is being developed to validate and optimize this technique. The motivation for the project, the development of the different aspects, along with the current status and results, are discussed here.
Citation: Ray, D.; Collister, R.;Rasiwala, H.; Backes, L.;Balbuena, A.V.; Brunner, T.;Casandjian, I.; Chambers, C.;Cvitan, M.; Daniels, T.; et al. IonManipulation from Liquid Xe toVacuum: Ba-Tagging for a nEXOUpgrade and Future 0νββExperiments. Atoms 2024, 12, 71.https://doi.org/10.3390/atoms12120071Academic Editor: Chengjian LinReceived: 21 October 2024Revised: 19 November 2024Accepted: 29 November 2024Published: 19 December 2024Copyright: © 2024 by the authors.Licensee MDPI, Basel, Switzerland.This article is an open access articledistributed under the terms andconditions of the Creative CommonsAttribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).ArticleIon Manipulation from Liquid Xe to Vacuum: Ba-Taggingfor a nEXO Upgrade and Future 0νββ ExperimentsDwaipayan Ray 1,* , Robert Collister 2,*, Hussain Rasiwala 3,* , Lucas Backes 1,4, Ali V. Balbuena 5,Thomas Brunner 1,3 , Iroise Casandjian 1,4, Chris Chambers 1,3 , Megan Cvitan 1,4, Tim Daniels 5, Jens Dilling 6,†,‡,Ryan Elmansali 2, William Fairbank 7, Daniel Fudenberg 8,§, Razvan Gornea 2, Giorgio Gratta 8 , Alec Iverson 7,Anna A. Kwiatkowski 1,9, Kyle G. Leach 10,11 , Annika Lennarz 1,4, Zepeng Li 12, Melissa Medina-Peregrina 12 ,Kevin Murray 3,∥, Kevin O’Sullivan 8, Regan Ross 3, Raad Shaikh 2 , Xiao Shang 3,¶, Joseph Soderstrom 7,Victor Varentsov 13 and Liang Yang 121 TRIUMF, Vancouver, BC V6T 2A3, Canada2 Department of Physics, Carleton University, Ottawa, ON K1S 5B6, Canada3 Physics Department, McGill University, Montreal, QC H3A 2T8, Canada4 Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4L8, Canada5 Department of Physics and Physical Oceanography, University of North Carolina at Wilmington,Wilmington, NC 28403, USA6 Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada7 Physics Department, Colorado State University, Fort Collins, CO 80523, USA8 Physics Department, Stanford University, Stanford, CA 94305, USA9 Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada10 Department of Physics, Colorado School of Mines, Golden, CO 80401, USA11 Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI 48824, USA12 Department of Physics, University of California San Diego, La Jolla, CA 92093, USA13 Facility for Antiproton and Ion Research in Europe (FAIR GmbH), 64291 Darmstadt, Germany* Correspondence: dray@triumf.ca (D.R.); rcollister@physics.carleton.ca (R.C.);hussain.rasiwala@mail.mcgill.ca (H.R.)† Current address: Neutron Science Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.‡ Current address: Physics Department, Duke University, Durham, NC 27708, USA.§ Current address: Qventus Inc., Mountain View, CA 94043, USA.∥ Current address: Introspect Technology, Montreal, QC H3J 1M1, Canada.¶ Current address: Department of Materials Science and Engineering, University of Toronto,Toronto, ON M5S 3E4, Canada.Abstract: Neutrinoless double beta decay (0νββ) provides a way to probe physics beyond theStandard Model of particle physics. The upcoming nEXO experiment will search for 0νββ decay in136Xe with a projected half-life sensitivity exceeding 1028 years at the 90% confidence level using aliquid xenon (LXe) Time Projection Chamber (TPC) filled with 5 tonnes of Xe enriched to ∼90% inthe ββ-decaying isotope 136Xe. In parallel, a potential future upgrade to nEXO is being investigatedwith the aim to further suppress radioactive backgrounds and to confirm ββ-decay events. Thistechnique, known as Ba-tagging, comprises extracting and identifying the ββ-decay daughter 136Baion. One tagging approach being pursued involves extracting a small volume of LXe in the vicinityof a potential ββ-decay using a capillary tube and facilitating a liquid-to-gas phase transition byheating the capillary exit. The Ba ion is then separated from the accompanying Xe gas using a radio-frequency (RF) carpet and RF funnel, conclusively identifying the ion as 136Ba via laser-fluorescencespectroscopy and mass spectrometry. Simultaneously, an accelerator-driven Ba ion source is beingdeveloped to validate and optimize this technique. The motivation for the project, the developmentof the different aspects, along with the current status and results, are discussed here.Keywords: Ba-tagging; neutrinoless double beta decay; nEXO upgrade; linear Paul trap;laser-fluorescence spectroscopy; multi-reflection time-of-flight mass spectrometryAtoms 2024, 12, 71. https://doi.org/10.3390/atoms12120071 https://www.mdpi.com/journal/atomsAtoms 2024, 12, 71 2 of 231. IntroductionThe Standard Model (SM) of particle physics, which has been hugely successful indescribing and even predicting subatomic particles and their interactions, was devel-oped with the assumption that neutrinos are massless particles. Observation of neutrinooscillations [1], which necessitates a non-zero neutrino mass, points towards physics be-yond the SM. While their actual mass is still unknown, the limits set by experiments implythat neutrinos are at least six orders of magnitude smaller than electrons [2], which couldsuggest a different underlying mass-generation mechanism [3,4]. The fact that neutrinosare electrically neutral, massive particles opens the possibility that they are in fact Majoranaparticles, as proposed by E. Majorana [5]. The most promising approach to probe for theMajorana nature of neutrinos is through searching for a unique decay process called neu-trinoless double beta decay (0νββ) [6]. This 0νββ decay is expected to happen in additionto the SM-allowed two-neutrino double-beta decay (2νββ), which is a second-order weaknuclear process involving the simultaneous decay of two neutrons to two protons withthe release of two electrons and two electron-anti-neutrinos. This rare type of decay hasbeen observed in even-even nuclides where single β-decay is energetically forbidden [6]. Ifneutrinos are indeed Majorana particles, 0νββ will occur in these isotopes with the emissionof only the two electrons, leading to a violation of lepton number. This is required forleptogenesis [7] and subsequent explanation of the observed baryon asymmetry in theuniverse [8]. In addition, 0νββ could also be able to shed light on the actual neutrino massas well as elucidate the origin of such a small mass [5,6].The EXO-200 experiment [9,10] has probed for 0νββ decay in 136Xe using an activeliquid xenon (LXe) mass of 110 kg, enriched to 80.6% in the ββ-decaying isotope 136Xeat the Waste Isolation Pilot Plant (WIPP) underground facility in Carlsbad, NM, USA,between 2011 and 2018. The experiment discovered 2νββ decay in 136Xe [11] and providedone of the most sensitive limits on the half-life of the 0νββ decay (T1/2 > 3.5× 1025 yrat 90% confidence level (C.L.) [12]). To increase this sensitivity, it is necessary to furthersuppress backgrounds (currently dominated by γ rays) and increase the quantity of theparent isotope under observation. Based on the success of EXO-200, the next-generationexperiment nEXO is under development, which will use a single-phase LXe Time ProjectionChamber (TPC) approach with an active mass of 5 tonnes of Xe enriched to 90% in theisotope 136Xe [13]. The projected sensitivity of nEXO to 0νββ half-life in 136Xe is beyond1028 years (90% C.L.) for 10 years of livetime, based on background estimates and signalsfrom 2νββ decays [14].2. Barium Tagging for Future nEXO UpgradeWhile efforts continue to further reduce and suppress backgrounds in the nEXO experi-ment, parallel research is being conducted on new technologies and techniques, such as mul-tivariate analysis or using electroformed copper, to increase detector sensitivity [14]. Onesuch technique being developed for a potential future upgrade to nEXO is Ba-tagging [15],that is, extracting and identifying the daughter isotope of barium, 136Ba, from the ββ-decayof 136Xe. Since 136Ba is not produced in any of the γ-background events, Ba-tagging willeliminate all background events except those from 2νββ and will allow one to discriminateany event of interest as arising from a ββ decay or a background event. In other words,a 100% efficient tagging would allow a nEXO-type experiment to realize a sensitivityachievable in an almost background-free environment with just 2νββ decays, increasingthe projected sensitivity by a factor of 2–3 [14,16] without increasing the isotope mass.Due to the high reward from successful tagging, this technique is being pursued indifferent forms by several groups within the nEXO collaboration [17–21] and outside [22].Ba-tagging can be broadly divided into four main steps:1. Localisation: when a ββ-like event in an energy window around the end-point energy(Qββ ≈ 2.5 MeV) is detected, the position of the decay within the detector is located.2. Extraction: the Xe volume surrounding the event location is extracted from the detector.3. Separation: a potentially present 136Ba ion is separated from the background Xe.Atoms 2024, 12, 71 3 of 234. Identification: the isolated 136Ba ion is positively identified.Step 1 has been demonstrated at EXO-200, where decay events were localized to withina few millimeters [23]. Step 4 has been achieved for different forms of Ba, for example,Ba+ trapped in vacuum [18,24], Ba atoms and ions trapped in a Xe-ice matrix [19–21],and Ba++ trapped in a molecule with Single Molecule Fluorescence Imaging (SMFI) [22].Depending on the technology of choice in Step 2 and Step 4, Step 3 becomes optional. Thecurrent focus of Ba-tagging for nEXO is the demonstration of Step 2 (and 3 if necessary),and two main avenues are being investigated. Both comprise inserting a macroscopicexternal element, a cryoprobe in one and a capillary tube in the other approach, inside theLXe volume. The cryoprobe approach, pursued by collaborators at Colorado State Univer-sity, Fort Collins, CO, USA and the University of California, San Diego, CA, USA,entailstrapping a Ba ion in a Xe ice matrix frozen to the tip of the probe, removing the probe fromthe detector volume with the Xe ice, and then using similar techniques to Ref. [19–21] forpositive identification. The second extraction method involves flushing Ba ions out of thedetector along with some LXe through a capillary, with subsequent transition to gas phaseby heating the capillary exit. This technique is being developed at Carleton University,Canada. After extraction, the 136Ba ions are separated from the accompanying Xe gasusing a radio-frequency (RF) carpet and RF funnel [25,26] and identified via laser fluores-cence in a linear Paul ion trap (LPT) [27] and mass spectrometry using a multi-reflectiontime-of-flight mass spectrometer (MRTOF-MS) [28]. These are being developed at McGillUniversity, Canada. Once a potential 0νββ event is detected, a positive Ba-tagging willunambiguously validate that event as a ββ event; otherwise, the event will be rejectedas background. This allows for a virtually background-free search for 0νββ without anyγ-photon contributions. Thus, Ba-tagging, although challenging, holds great promise inproviding an irrefutable signal.The Ba-tagging approach involving extraction using a capillary tube, separation usingan RF carpet and an RF funnel, and identification using laser-fluorescence spectroscopyin an LPT and MRTOF-MS mass spectrometry is shown in Figure 1 and is the focus ofthis paper. Section 3 describes the individual aspects of this approach, from the extractionof the Ba ions to their detection. To demonstrate the feasibility of the entire procedure ofBa-tagging, a Ba ion source is required. An accelerator-driven ion source is currently beingdeveloped at TRIUMF, Canada, where radioactive ions will be stopped in LXe, extractedelectrostatically, and identified using γ spectroscopy. The details of this development isdiscussed in Section 4. The ion source will lead the way for future ion source developments,which will be used to optimize either the cryoprobe or the capillary approaches beforeeither is implemented in nEXO-type detectors in the future.MRTOFMass SpectrometerQuadrupolemass filterXe GasLiquid Xe Xe Gas (~2 bar) ~10−6 mbar ~10−7 mbarHe Buffer Gas (~10−2 mbar) <10−8 mbarRF Carpet RF FunnelnEXO TPCLinear Paul TrapLaserSpectroscopyLaser AblationIon sourceLaser AblationIon sourceDetectorLaser AblationIon Source in GasFigure 1. Schematic depiction of the Ba-tagging approach involving extraction using a capillarytube, separation using an RF carpet and an RF funnel, and identification using laser-fluorescencespectroscopy in an LPT and MRTOF-MS. The respective pressures are shown in each step.Atoms 2024, 12, 71 4 of 233. Progress on Ba-Tagging SubsystemsEach step of the Ba-tagging approach shown in Figure 1 will be discussed in detailin this section, highlighting recent progress in each area under development. The work ispresented in order of the steps a Ba ion would experience following a decay event. First, theprogress at Carleton University will be discussed, beginning with the LXe TPC for decayidentification. This will include the light and charge collection systems and the capillaryprobe for extracting individual ions from the TPC, along with the displacement device andheating system to control the phase change in the capillary. Second, the developmentsat McGill University will cover the RF funnels for separating the ion from the xenon gas,followed by the ion identification stages for mass filtering and time-of-flight spectrometry.Additionally, many of the tools developed to aid in these endeavors will be presented, suchas the ion cooler and buncher that are necessary to demonstrate the full resolving power ofthe MRTOF-MS.3.1. Ion Collection and Extraction from LXeIn a LXe TPC, the collection of light and charge in coincidence can measure the totalenergy of a decay. It can also locate the site of the decay based on where the charge iscollected and the time between the detected light and charge pulses. LXe is a high-yieldscintillator with a peak emission at 175 nm. In the EXO-100 TPC at Carleton, the Xescintillation light is wavelength-shifted by a tetraphenyl butadiene-coated Teflon reflectorto a blue spectrum peaked at 430 nm before being collected by four photomultiplier tubes(PMTs). The collection of this prompt light provides a t = 0 for the event. In modestelectric fields of approximately 500 V/cm, the electrons generated by the ionization tracktravel at 1.71 mm/µs [23] through the 170 mm diameter, 120 mm long cylindrical driftvolume. These electrons drift directly to the anode, where a pair of crossed wire planes(63 wires spaced 2 mm apart per plane) provide two coordinates for the location of theevent. The third coordinate is given by the drift time and drift velocity. The total energyof the event, given by the combined magnitudes of the charge and light pulses, as well asthe characteristics of the location information, e.g., the length of tracks and whether it is asingle-site or multiple-site event, determines the nature of the decay as well as the speciesinvolved. This determines if a decay event is of interest for ion extraction and where to aimthe probe to extract the daughter ion.The heart of the probe is a commercial stainless steel capillary with a nominal innerdiameter of 0.508 mm and a wall thickness of 0.2 mm. Laminar LXe flow up this capillarytransports the ion out of the TPC into the subsequent stages of the tagging scheme. Thiscapillary is encapsulated in a set of polyether ether ketone (PEEK) rods, providing therigidity necessary to precisely position the capillary tip in a desired location. Flow along thecapillary is controlled by manipulating the pressure differential across the inlet and outletof the capillary, the inlet being in the cryostat, immersed in LXe with the TPC, and the outletin a separate chamber either with a detector for initial development or the subsequentstages of the ion identification scheme. At the outlet, at a long distance from the LXe in theTPC, the capillary is heated to promote a phase change in the xenon from liquid to gas. Theprobe is mounted to a UHV Design brand WS40 wobble stick [29], which is manipulatedby a custom-built displacement device consisting of three stepper motors on an aluminumframe, with two motors controlling the XY stage to set the probe angle and the third motorhandling the insertion and retraction of the probe tip. The setup is shown in Figure 2.Once the device has been fed location information from online analysis of the TPC eventsignals, the displacement device is capable of positioning the probe tip anywhere withinthe accessible volume of the TPC within 15 s, with a precision of 0.11 mm on any axis. Wealso have a homing system consisting of six sets of pogo pins that allows calibration of theprobe position at known locations above the TPC.Atoms 2024, 12, 71 5 of 23Figure 2. (Left) CAD model of the TPC, probe, and detector chamber, without the displacementdevice. The stepper motors on the displacement device position the WS40 wobble stick. The internalshaft of the stick is magnetically coupled to its handle, enabling insertion and retraction of thecapillary probe through the holes in the TPC cathode. (Right) Photographs of the displacementdevice with WS40 in its test stand and the PEEK rod encapsulating the capillary. The copper cap onthe PEEK rod is part of the homing system to calibrate the probe position.COMSOL simulations were performed to study the xenon flow properties into,through, and out of the capillary. Laminar flow through the capillary is maintained aslong as the average LXe extraction velocity is lower than 760 mm/s, corresponding to aReynolds number below 2300. Above this, turbulence is introduced to the flow, which maydirect a transiting ion into the capillary wall, where it could be neutralized and lost to thedetection scheme. In laminar flow, the flow separates into layers, with a radial velocityprofile that follows a smooth trend with a lower fluid velocity at the walls of the capillaryand a larger fluid velocity in the center. This radial velocity profile is the critical boundarycondition for the COMSOL simulations that were performed to study the ion extractionfrom LXe. These simulations solve the computational fluid dynamics of LXe being drawnup our capillary and determine the trajectories of a diffuse ion cloud located below thecapillary tip in the LXe. From these simulations, it is found that only ions moving in thedrift field directly into the capillary opening will be captured by the flow up the capillary;lateral displacements on the order of 0.5 mm prevent the ion from being collected. This isdue to the distortion of the electric field by the conductive capillary; it redirects the fieldand drives the ions into the capillary walls. Alternative scenarios have been simulated,such as floating the capillary at a voltage or using a non-conductive PEEK capillary, butthe drift field always dominates the motion except in the small volume with the strongestflow immediately around the capillary inlet. This greatly limits the capture volume, i.e., thevolume of LXe where an ion must be located in order for it to be collected and carried upthe capillary under these flow conditions. Hence the drift field must be turned off duringion collection for an acceptable extraction efficiency.In this no-drift-field scenario, the size of the capture volume is determined by the flowrate against the random thermal drift of the ion. We conservatively estimate this randomAtoms 2024, 12, 71 6 of 23drift to be less than 0.2 mm/s based on Rn-Po coincidence measurements performed inthe EXO-200 TPC [30]; any ion inside the 0.2 mm/s flow region should eventually makeit to the capillary tip. The measured ion mobility from EXO-200 of 0.219 cm2/kVs maybe used with the Einstein–Smoluchowski equation to calculate a diffusion constant and,assuming isotropic diffusion, a random drift velocity. This gives a drift velocity roughly20 times smaller than the empirical value above. Since we are using radioactive ions inproof-of-concept measurements, capturing from a larger volume with slower flow nearits extremities gives the ion more time to decay and hence be lost to our detection schemebefore extraction. Thus we are content to use this empirical drift velocity to define ourvolume of interest. Figure 3 shows a slice of the capture volume for the typical operationof the ion extraction probe, with an average extraction velocity of 750 mm/s to maintainlaminar flow. This corresponds to an LXe flow of roughly 0.5 g/s, a negligible fraction of thetotal xenon volume of nEXO and easily replaced during recirculation. Also indicated is the1 cm3 volume where the diffuse cloud of regularly spaced ions is generated in simulationfor extraction, investigating the proximity of the capillary to the event of interest requiredfor efficient extraction. The outermost flow contour indicates where the flow has fallen to0.2 mm/s, showing the outer edge of the capture volume. All of the ions within the 1 cm3cloud are extracted by the capillary within 30 s of its arrival at the collection position, andthey are concentrated radially within the center 3/4 of the capillary. This indicates that ifthe probe tip is positioned within a few mm of the ion, the ion will be extracted regardlessof any thermal drift. Thermal currents in the LXe are not included in this simulation,but this could in principle be accounted for by a flow map and appropriately targetingthe probe tip.Figure 3. Simulation showing the flow map of the 0.508 mm inner diameter capillary encapsu-lated in the PEEK rod, with an inlet velocity of 750 mm/s and the electric drift field turned off,showing a slice of the flow field. The 10 mm square indicates the extent of the diffuse ion cloudgenerated for extraction studies. The contour indicates the 0.2 mm/s flow boundary at the edge ofthe capture volume.Simulations of the moving capillary probe, consisting of the capillary and enclosingPEEK rod as they are moved at 10 mm/s into the LXe and brought to rest at a target depth,show that the agitation of the LXe is minimal in the target 1 cm3. The largest introducedflow is immediately below the probe tip before it stops at the target position. At 1 mm belowthe probe tip, at the edge of the target 1 cm3, the motion is on the order of 1.5 mm/s. At thatposition, the extracting flow is over 100 mm/s in the opposite direction. Elsewhere, and onthe axes orthogonal to the probe’s motion, the agitation is at least an order of magnitudeAtoms 2024, 12, 71 7 of 23smaller than the extraction flow, always in the opposite direction. Thus, the agitationintroduced by the moving probe negligibly disrupts the target ion during extraction.3.2. Ion Transport Through a CapillaryThe next stage is the ion’s transport through the capillary, where the LXe is heated toundergo a phase transition to gas. By using a metal capillary, we are able to apply a currentthrough its body to deliver heat in a well-defined location, with regulation of the transferredheat by Proportional Integral Derivative (PID) control. The apparatus includes a pair ofcopper clamps, necessary to make a robust electrical connection to the thin capillary, andresistance temperature detectors (RTDs) epoxied to each clamp with their own connections.The temperature difference between the clamps is monitored to ensure the phase transitionis complete. This heated section of capillary is roughly 80 cm from the LXe in the TPC andon the other side of a nominally room temperature flange. LXe flowing up the capillaryover this distance prevents any heat transfer backwards to the LXe in the TPC.COMSOL computational fluid dynamics and heat transfer simulations inform if anion survives the journey up the capillary, including the phase transition, without touchingthe wall. We employ a mixture model where the xenon is treated as a dispersed phase (gas)in a continuous phase (liquid). For the heat transfer, the mixture is treated as a single fluidwith properties given by a linear combination of the gas and liquid fractions’ properties.For example, for the density ρ,µ = Xgρg + Xlρl, (1)where Xα is the phase fraction and ρα the phase’s density, with the subscript α = g,ldenoting the gas or liquid phase, respectively. Similarly, the thermal conductivity and heatcapacity are defined. Xenon transitions between phases by the balance of the evaporationand condensation rates, which are influenced by how much heat is added to the system.For the setup discussed here, 40 W are applied over a 0.1 m length immediately beforethe outlet of the capillary. However, in the simulation, an additional 0.1 m of capillaryare added after the heating region to observe how the mixture will continue to evolve.Only 0.05 m before the heat is applied is simulated; before this, in the leading section ofthe 1 m long capillary, there is only uniform laminar flow. Particle trajectories are tracedthrough the resulting flow map along the length of the capillary. Some results are shownin Figure 4.The temperature of the mixture at the exit of the capillary is roughly 190 K, well abovethe boiling point of LXe, suggesting that enough energy for a complete phase changewas provided. Once the mixture emerges into the relatively lower pressure of a detectorchamber, or the RF funnel of the tagging scheme, any remaining superheated liquid dropletsshould finish transitioning to gas. The particle trajectories produced by the simulation showsome ion loss from a small amount of turbulence introduced within about 0.02–0.03 mm ofthe capillary walls, indicative of boiling. Fortunately, the extraction simulations previouslydiscussed suggest that these layers of the flow will not be populated by ions if the probeis accurately targeted to a decay event in the TPC. Thus, this simulation suggests that iontransfer should be close to 100% efficient for our scheme once the ion is inside the capillary.Atoms 2024, 12, 71 8 of 23Figure 4. (Left) Image of the capillary showing one of the heating clamps with RTD.(Middle) COMSOL simulation result of the density, showing where the heat is applied and theresulting density gradient as the phase transition occurs. (Right) COMSOL simulation result ofthe mixture velocity, showing the last length of capillary, demonstrating that the flow does notsignificantly deviate from laminar as the phase transition occurs.3.3. Ion Extraction from Gaseous XenonIn liquid xenon, it is expected that the 136Ba++ would gain an electron from a xenonatom to become 136Ba+ due to the different ionization potentials [15]. Extraction of this 136Ba+using the capillary tube will result in the ion being in a high-pressure gaseous Xe (GXe)environment. In this condition, the motion of ions is dominated by collisions with theGXe. To facilitate the extraction and identification of 136Ba+, the Ba-tagging scheme usesan RF-only ion funnel to guide and separate the ions from the GXe [17,25]. RF funnels, orion funnels in general, are devices used to focus beams of ions; first devised for use withelectrospray ionization mass spectrometry (ESI-MS) [31] at a pressure of 30 torr. Since then,ion funnels have been used in several mass spectroscopy applications involving ionizationsources as well as gas-filled stopper cells at fragmentation facilities [32,33].The RF-only ion funnel for Ba-tagging, as shown in Figure 5, is designed to accept136Ba+ from the capillary in GXe pressures of up to 10 bar and transport it to a region ofhigh vacuum [34]. Stacked annular disc electrodes with tapering hole sizes, supplied withRF potential, radially confine ions by restricting motion away from the axis. Due to theRF-only design, there are no axial drift fields, and the ion propagation along the funnelaxis is carried out primarily through the residual gas flow near the axis. This reduces thepossibility of contaminants in the vacuum system by eliminating the need for componentssuch as resistor chains for a DC drag field.Atoms 2024, 12, 71 9 of 23Figure 5. Schematic diagram of the RF funnel setup. Ions are injected through the converg-ing–diverging nozzle at pressures of up to 10 bar. Injected ions are guided by the RF potentialsapplied to the annular disc electrodes of the RF funnel, while GXe is pumped out from between theelectrodes. Ions then propagate through the SPIG and past Aperture 2 to be finally detected. Differention detection setups were used downstream of Aperture 2. Taken from [25].The design and initial results of the RF funnel are reported in [25]. A 148Gd-drivenBa-ion source was used to generate Ba+ ions [35] upstream from a converging–divergingnozzle. The nozzle injects the ions with carrier gas (GXe) into the RF funnel, which islocated inside a cryopump chamber for recovery of the GXe. Ions from the RF funneltravel through a sextupole ion guide (SPIG) to a channel electron multiplier (CEM) wherethey are detected. The SPIG stage is required to reduce the pressure after the RF funnelstage further to achieve a 10−6 mbar pressure that is favorable for operating the CEM(see Figure 5). The GXe captured in the cryopump during this operation is recovered byand stored in a gas-handling system for future use. Figure 6 shows the initial RF funnelsetup at Stanford University.Figure 6. CAD model rendering of the RF funnel test setup. A 148Gd-driven Ba-ion source generatesions for supporting the commissioning. The RF funnel and other ion optics are located inside a cryop-ump chamber for Xe gas recovery, and turbomolecular pumps (TMP) evacuate chambers C and Din Figure 5. Taken from [34].Ion transmission efficiency as a function of RF potential at different pressures showedsimilarities in trends at high RF potentials across pressures from 2–10 bar when comparedwith simulations [25]. Although this setup was successful in validating the simulatedtransmission efficiencies, it lacked ion discrimination capability. This proved to be im-portant since the 148Gd-driven Ba-ion source also generated α-particles that ionized theXe atoms. Thus, to allow for the identification of the extracted ions, a commercial1 linearquadrupole ion trap (LTQ) was introduced [36,37]. Additionally, a 252Cf source was usedin place of the 148Gd source to achieve a higher ion flux for better calibration of the LTQ.Figure 7 shows ions extracted from the 252Cf source placed upstream of the nozzle in 2.1 barof Xe pressure. The spectrum is normalized to counts per second, binned to integer values,Atoms 2024, 12, 71 10 of 23and fit to the isotopic signatures of various molecular species. The natural abundance ofelements in these molecules is used to calculate their m/q value. The bin corresponding tothis value is 5% smeared into the adjacent bins to account for the spectrometer’s resolution.Fitting molecule signatures to the observed spectrum showed clear evidence of the presenceof singly charged Xe ions and molecules of xenon, such as XeXe (dimer), HXeOH (xenonhydride-hydroxide), HXe (xenon hydride), and less than 100 ions (≈1% of the total numberof ions detected) that could be 252Cf fragmentation products.XeXe (a) (b) (c)Figure 7. (a) The m/q spectrum of ionized entities extracted from a 252Cf source at 2.1 bar GXepressure. (b,c) Fits of this spectrum to possible singly charged molecular entities. Aside from noevidence of fission products, the spectrum shows the presence of singly charged Xe and moleculessuch as xenon dimers (XeXe), xenon hydride-hydroxide (HXeOH), and possibly xenon hydride (HXe).Taken from [37].The RF funnel setup is currently being recommissioned at McGill University, with theRF funnel now located in a dedicated vacuum chamber that is connected to the cryopumpfor Xe gas recovery. This was done to prevent thermal contractions of the RF funnel thatwere suspected as the cause for the observed capacitance changes when installed on top ofthe cryopump. A photograph of the setup is shown in Figure 8. The cryopump chambercouples to the RF funnel through a proportional gate valve for better control over theRF funnel backing pressure. The proportional gate valve will be operated with feedbackfrom pressure gauges installed on the RF funnel chamber for precise pressure control.This feedback control is currently being developed into a LabVIEW program and will befirst tested with Ar gas and later with GXe. The Ba-tagging scheme is further extendedto replace the LTQ with a custom-designed LPT [27] and an MRTOF-MS [28]. The LPTtraps ions to allow for Ba ion identification via laser fluorescence spectroscopy [18], whilethe MRTOF-MS will be used to achieve high mass resolving power (m/∆m ≈ 100,000) todiscriminate 136Ba+ from 136Xe+ (compared with m/∆m ≈ 800 from the LTQ) and performother systematic studies. Additionally, a quadrupole mass filter (QMF) is located upstreamfrom the LPT to filter any dominant background ions from the RF funnel to improveion trapping.Atoms 2024, 12, 71 11 of 23Figure 8. Picture of the Ba-tagging apparatuses being commissioned at McGill University for studyingion extraction from GXe. Vacuum system shown here houses the RF funnel, which connects to thecryopump chamber via a proportional gate valve. Located downstream from the RF funnel are theLPT and the MRTOF-MS.As an upgrade to the apparatuses shown in Figure 8, a design is being proposed fordeveloping an RF carpet, to be located upstream from the RF funnel. RF carpets are apopular choice for use in gas stopper cells [38], which are used in accelerator facilities tothermalize and collect ions. An application, similar to the one presented here, is beingexplored by the NEXT collaboration for Ba++ detection using the SMFI technique [39].The RF carpet will facilitate the transfer of 136Ba+ coming from the capillary to the RFfunnel. The incoming Ba ion (in GXe) drifts towards the RF carpet, which then guides theion towards the exit aperture. For ion propagation along the carpet, an ion-surfing modeis being investigated that utilizes a combination of an RF potential and a high-frequencypotential to repel and guide the ions, respectively, as described in [40]. Once developed,the RF carpet will support the efficient transfer of 136Ba+ from the capillary exit to the RFfunnel as shown in Figure 1.3.4. Ion IdentificationThe task of ion identification is divided between the LPT, where elemental identifica-tion of the Ba ion is performed using laser fluorescence spectroscopy, and the MRTOF-MS,where the mass of 136Ba+ is identified to be 136. Figure 9 shows the entire setup beingdeveloped for ion extraction from gas medium, including components used to facilitatetheir commissioning and testing.Atoms 2024, 12, 71 12 of 23Split electrodefor steeringIons fromIon sourceTo LPTIons fromRF funnelRF FunnelSPIGLPT LASQMFPrecoolerCooler/BuncherMRTOF LASMRTOFLPTCooler Wedge-shapedelectrodesEntrance/exitaperturesTo MRTOF-MSDri�-tubeCollimating apertureElectrostatic steerers and lenses1.2.3.4.5.Mass analyzerDrift tubeIon directionEntrance mirrorCF-252 sourceFigure 9. CAD model rendering of the Ba-tagging setup for 136Ba+ extraction from GXe. Shown arethe RF funnel, LPT, and MRTOF-MS going from top to bottom. Starting from pressures of up to 10 bar,ions pass through (1) the RF funnel and the SPIG to arrive in a high-vacuum environment in (2) the LPTLAS chamber. Lenses of this LAS allow the focusing and steering of ions, while the quadrupole benderallows selecting between ions from the LAS and the RF funnel. The QMF filters incoming ions basedon their m/q ratio and guides the ions to the LPT. The precooler gradually cools ions, which are thentrapped in (3) the cooler and buncher, which are used to cool and bunch the ions, respectively. Afterbunching, the ions are ejected to the MRTOF-MS, passing through the MRTOF-MS LAS bender, (4) ionoptics, and a collimating aperture. In the MRTOF-MS, ions are reflected several times between (5) twosets of electrostatic mirrors before being detected using a CEM to obtain a time-of-flight spectrum.Atoms 2024, 12, 71 13 of 233.4.1. Ion SourcesWhile the 252Cf source is currently used as an in-gas ion source, laser ablation ionsources (LAS) are positioned upstream of the LPT and the MRTOF-MS for ion transportoptimization and to provide calibrant masses for the MRTOF-MS.3.4.2. Quadrupole Mass Filter (QMF)A QMF acts as an ion guide in its quadrupole design and the use of RF potentialsbut can additionally allow selective propagation of ions of a specific (or range of) mass-to-charge ratio(s). The QMF is positioned downstream from the RF funnel (see Figure 9) toremove background ions such as the molecular species seen in Figure 7 that exit the RFfunnel. This will help improve the trapping efficiency of the LPT by reducing the numberof ions being trapped.There are three sets of quadrupole electrodes in the QMF, each supplied with a DC-coupled RF potential. The main purpose of the first and third sets of quadrupole electrodes(referred to as ramp segments in [41]) is to provide a delayed DC ramp and reduce potentiallosses due to fringing fields [42]. The RF potential is supplied through a transformer,which in turn is supplied by an RF power amplifier and function generator, similar tothe RF funnel. The RF frequency of the current operation is impedance matched for a100 Vpp sinusoidal signal at a frequency of 750 kHz. Initial tests performed using a cesiumthermal source demonstrated a mass resolving power, m/∆m ≈ 100 [41], of the QMF. Thisexceeds the design goal of m/∆m > 80 [27], which will allow the QMF to resolve mostof the background ions aside from 136Xe+. Future tests will be performed by replacingthe thermal source with a laser ablation ion source (LAS) using a multi-element target toproduce ions over a large mass range. The ablated ions will be supplied to the QMF usinga quadrupole bender and other focusing elements, as shown in Figure 9 (2).3.4.3. Ion Cooling and Bunching (ICB)Filtered ions from the QMF are subsequently guided into the LPT, where they firstpass through a precooler. The precooler is comprised of a quadrupole with a flow-limitingaperture that allows for differential pumping between the QMF and the cooler. Similarly,the cooler also has a quadrupole electrode structure, where ions are collisionally cooled andstored. Rather than using segmented electrodes, the quadrupole electrodes of the coolerare tapered along their length and are enclosed in a square tube [41]. The axial potentialgradient created due to this taper is used to store ions just upstream from the entranceaperture of the buncher. A constant flow of helium gas (25 sccm) is supplied by a mass flowcontroller to maintain a pressure of 0.1 mbar in the cooler for sufficiently cooling ions tokinetic energies of under 1 eV and storing them before being transferred to the buncher foridentification. As shown in Figure 9 (3), the buncher consists of three sets of wedge-shapedquadrupoles for axial and radial confinement of transferred ions and aperture electrodesto control loading and unloading of the buncher. Ions from the cooler are loaded intothe buncher during a 4 µs transfer period by switching the bias voltage of the entranceaperture to allow ions into the buncher. At the end of the transfer period, the entranceaperture bias voltage is switched back to prevent ions from escaping the buncher whilealso preventing other ions from entering. In the buncher, the ions are cooled over a ≈10 msperiod. Once trapped, the Ba ion will be identified using a combination of lasers to inducefluorescence that will then be detected by a charge-coupled device (CCD) camera [18,24].This spectroscopic identification method will be implemented in the LPT in the future.Bunched ions are ejected from the buncher by applying a forward potential gradient usingvoltage switches, similar to the entrance aperture, and accelerated into a pulsed drift tube.The pulsed drift tube is switched to a different potential while the ions are traveling inside,which accelerates them further when they exit the tube before they are injected into theMRTOF-MS [41]. The pulsed drift tube switching potentials define the kinetic energy of theion bunch.Atoms 2024, 12, 71 14 of 23Ion bunching is currently being studied using a CEM located downstream from thebuncher inside the MRTOF-MS LAS bender. Figure 10a shows an example of waveformreadout from the CEM during a test run using a CAEN DT5730 digitizer and a continuousCs ion beam from a thermal ion source installed upstream from the QMF. Samples thatare below the ADC threshold2 are recorded as ion hits on the CEM. The number of ionsdetected in a given ion hit is then inferred from the analog-to-digital converter (ADC)amplitude. Figure 10b shows the time distribution of ions averaged over 10,000 suchwaveforms. Operational parameters such as buffer gas pressure, cycle time for trappingand ejection, and buncher potentials are currently being optimized to reduce the timespread of the ion bunch since it has a direct impact on the mass resolving power of theMRTOF-MS [28]. Additionally, the thermal ion source will be replaced with a multi-elementtarget and used to study the operation of the LPT and the MRTOF-MS over a large massrange. This will also allow the detection of molecular ions such as [XeXe]+ and [BaXen]+that were observed in the previous RF funnel study [37] and a mobility study of Ba ions inGXe [43], respectively. Aside from [BaXen]+ detection, a combination of RF heating andcollision-induced dissociation using the helium buffer gas in the LPT may also be used toseparate the Ba ion from Xe.(a) Typical waveform of ion bunch at CEM. (b) TOF spectrum of ion bunch.Figure 10. Bunched ion spectrum and waveform from run using bunched cesium ions. (a) Typicalwaveform of one ion bunch recorded using a CAEN DT5730. (b) Histogram of samples above thesignal noise threshold, accumulated and averaged over 10,000 waveforms.3.4.4. Multiple Reflection Time-of-Flight Mass Spectrometer (MRTOF-MS)The MRTOF-MS accepts bunched ions from the LPT and performs mass spectrometryto identify 136Ba+ from a background of 136Xe+ as well as perform systematic studies. Inplace of the bunched ions from the LPT, for commissioning and testing, a LAS is used [44].A 349 nm Spectra Physics laser is focused onto a copper target to ablate material and in theprocess produce ions. Ions produced by the LAS travel through a quadrupole bender andother ion optics (see Figure 9 (4)) to reach the MRTOF-MS. The MRTOF-MS operates byreflecting ions several times between two sets of electrostatic mirrors, shown in Figure 9 (5).Since ions with the same kinetic energy but different mass-to-charge ratios travel at differentvelocities, multiple reflections greatly increase the difference in their time of flight andthus resolve the different mass peaks. Electrodes of the electrostatic mirrors are biasedusing two-state and three-state high-voltage switches3 to change potentials during the firstreflection after the injection of the ion bunch and the last reflection before detection.The MRTOF-MS commissioning was completed in 2022, and a mass resolving powerof 20,000 was demonstrated [28]. However, this was achieved using ions from the LASthat are not bunched but created in ablation with laser pulses. Simulation studies ofthe MRTOF-MS using bunched ions from the LPT showed a mass resolving power over100,000 can be achieved, which is sufficient to resolve 136Ba+ and 136Xe+. Thus, followingAtoms 2024, 12, 71 15 of 23the optimization of the buncher, bunched ions will be injected into the MRTOF-MS todemonstrate its resolving power.4. In-LXe Ion Source for Testing Ba Ion Extraction TechniquesA controlled and calibrated Ba-ion source is required for the definitive demonstration,final optimization, and quantification of Ba extraction from LXe with either the cryoprobe orthe capillary method. Research and development (R&D) efforts are currently ongoing to de-velop an accelerator-driven, radioactive ion source using rare isotope beams (RIB) from theIsotope Separator and Accelerator (ISAC) facility [45] at TRIUMF, Vancouver, BC, Canada.An apparatus previously employed at Stanford University, Stanford, CA, USA, for Ba-tagging developments using an internal, spontaneous fission 252Cf source and a depositionsubstrate for the Resonance Ionization mass Spectroscopy (RIS) technique [46–48] is beingrecommissioned for a proof-of-principle measurement. A beam of radioactive 139Cs ions(T1/2 = 9.27(5) m [49]) will be injected through a Be window and stopped in LXe, where thedecay-daughter 139Ba ions will be tagged by collecting and extracting them electrostaticallyand detecting them using γ spectroscopy. Once the concept is tested, further developmentswill be conducted to make future ion sources that will be suitable for the cryoprobe and thecapillary extraction techniques. For a final demonstration and determination of Ba-taggingefficiency, injecting 136Cs (T1/2 = 13.01(5) d [49]) with Qβ ≈ 2.5 MeV [50] and tagging itsdecay daughter 136Ba is also being considered.An engineering rendering of the apparatus, along with a picture of it being assembledat TRIUMF’s ISAC-II experimental facility, is shown in Figure 11. The apparatus includesthree main parts: an Injection Chamber (IC), a Measurement Chamber (MC), and anextraction probe that can be moved between the IC and the MC. The IC consists of an LXecell of volume 1 L with 1.9 cm thick copper walls, thermally coupled to a liquid nitrogen(LN2) reservoir with copper heat-transfer straps, and is suspended in a vacuum chamberfor thermal insulation. The high thermal conductivity of the copper straps means the LN2-enabled cooling system over-cools the IC. The copper straps are equipped with resistiveheaters controlled by a PID controller using temperatures measured with PT100 probes.Thus the cell is maintained at ∼165 K, and the Xe is kept in its liquid state. Four equallyspaced DN40 ports are placed radially around the LXe cell. These ports will be fitted witha beam entrance Be-window mount, a diagnostic Faraday cup detector opposite the Bewindow, and two side-view ports. The 25 µm thick beam entrance Be window will be metaldiffusion bonded on the front face of the nozzle of the mount to separate the LXe insidethe cell from the upstream beamline vacuum. The nozzle protrudes ∼8 cm into the LXe.This is shown on the inset of Figure 11. The MC is a small chamber above the IC with ahigh-purity Ge detector (HPGe) placed at a view port for γ spectroscopy. The extractionprobe, controlled by a linear actuator with a stepper motor, consists of a flat rod with theremovable copper target at its tip (also referred to as an electroprobe; see inset of Figure 11).Radioactive ions will be collected by biasing the target while it is placed in LXe in frontof the beam entrance window in the IC. For identification, the target will be positionedin front of the HPGe. The setup will be connected to a beamline in the high-energy RIBfacility ISAC-II (called the SEBT-I beamline) through a beam pipe and a gate valve.The LXe will be contained at a pressure of 1 bar inside the IC, which requires around3.1 kg of gaseous Xe (GXe). Given the cost associated with procuring this required quantityof Xe, a closed gas handling system (GHS) is being developed for deploying and recoveringGXe with minimal to no loss. The gas will be deployed from the GHS into the apparatusthrough two ports on either side of a gate valve separating the IC and the MC (labeled as“Gas deployment & recovery” in Figure 11) from a pre-filled gas bottle through a cold getterpurifier to ensure impurities are removed from the gas. The recovery will occur throughcryopumping GXe into a second gas bottle, which will act as the supply bottle for the nextdeployment cycle.Atoms 2024, 12, 71 16 of 23LXe cell and LN2 reservoir inside the vacuum jacketExtraction probeMeasurement ChamberGePumping stationGas deployment & recoveryBeam entrance windowBeam pipeGate valvePumping stationAt TRIUMF’s ISAC-II experimental hallISAC-IIbeamFaraday cupISAC-IIbeamProbe-tipEstimated LXe levelInjection chamberFigure 11. Ion source for Ba extraction tests at TRIUMF. (Left) An engineering rendering of the appa-ratus showing the IC enclosed by a vacuum jacket, the MC, and the extraction probe. (Inset) Zoomedview of the engineering rendering of the IC, labeling the beam entrance window, the probe tip (orelectroprobe), and the Faraday cup, and showing the estimated LXe fill level in a light blue line.(Right) Photograph of the setup being assembled at TRIUMF’s ISAC-II experimental hall. See textfor details.The radioactive ions will be produced at TRIUMF’s ISAC facility [45] by impinging a∼480 MeV proton beam of∼40 µA from the TRIUMF cyclotron [51] onto a uranium-carbide(UCx) target by fragmentation, spallation, and fission reactions. The 139Cs ions will besurface ionized before being extracted and mass separated at ISAC’s mass separator [52].The mass-separated beam will pass through the low-energy beam transport (LEBT) [53]electrostatic beam line and then through a radio-frequency quadrupole (RFQ) [54], whereits longitudinal emittance will be lowered, before being directed towards ISAC-II. Next, thebeam will pass through a charge state booster [55] before being reaccelerated using a drifttube linac (DTL) and superconducting linear accelerator (SC-linac) [54] and delivered tothe experiment at the SEBT-I beamline with an intensity of ∼105 particles per second (pps)at an energy of up to 10 MeV/u.At the start of the experiment, the probe will be inserted into the LXe cell using thelinear actuator, such that the collection tip lines up with the beam entrance window, asshown on the inset of Figure 11. GXe will be introduced into the system from the GHSand liquified in situ until the LXe reaches a set level (blue line on the inset of Figure 11),sufficiently submerging the probe tip. Note that the volume of the IC above the blueline and the MC will be filled with Xe vapor. An upstream beamline valve will then beopened, and a beam of 139Cs, with some contaminant 139Ba ions, with energies between2 and 10 MeV/u, will be injected through the Be window into the LXe. Monte Carlosimulations of the ions’ trajectories using Transport of Ions in Matter (TRIM) [56] with abeam of 139Cs in LXe, at 1 bar pressure and having a density of 3.1 kg/L, with one suchenergy (4 MeV/u) and through a 25 µm Be window, with a density of 1.845 kg/L, show animplantation depth of ∼35 µm from the window (Figure 12a). The straggling of the ionswith maximum possible energy of 10 MeV/u, obtained from Stopping and Range of Ionsin Matter (SRIM) [56], is shown in Figure 12b. Thus, upon stopping, the ions will be withina few millimeters of the probe tip. After a few half-lives of 139Cs, the beam implantationwill be stopped and a negative voltage will be applied on the probe tip to induce an electricfield in the LXe medium and initiate electrostatic collection.Atoms 2024, 12, 71 17 of 23(a)Range (X direction) [µm]Z direction [µm]0 100−5050LXeBe window4 MeV/u 139Cs beam stopped in LXe after passing through a 25 µm Be windowRange vs Z direction(b)Z direction [µm]Y direction [µm]Figure 12. Simulations of ion implantation inside LXe, at 1 bar pressure, having a density of 3.1 kg/L,after passing through a 25 µm Be window, with a density of 1.845 kg/L, using TRIM. (a) TRIMsimulations showing 139Cs ions with energy of 4 MeV/u being stopped in LXe. The white verticalline represents the boundary between the Be window and the LXe medium. (b) Lateral (in Y-direction)and longitudinal (in Z-direction) straggling of a beam of maximum possible energy of 10 MeV/u.The red cross around (0, 0) marks the hypothetical alignment point of the probe tip.The collection of the ions is simulated with COMSOL Multiphysics™, using theAC/DC, the computational fluid dynamics (CFD), and the Particle Tracing for Fluid Flowmodules. The simulation consists of a simplified copper vessel filled with LXe at 1 barand 165 K and an electroprobe, as shown in Figure 11 inset and Figure 13a. For this 3Dgeometry, COMSOL is used to solve electrostatics and fluid dynamics within the vessel’senvironment, as well as particle tracing for the singly charged ions released within the LXe.The electrostatics model starts with the negative voltage being applied to the electroprobewhile keeping the rest of the setup grounded. The LXe is taken as an ideal dielectric medium,which can be polarized by the electric field generated from the probe. The simulation thencomputes the induced electric field lines in the LXe and the electric force experienced bythe positive Ba ions by solving a modified version of Gauss’ law for dielectric media andFaraday’s law of electrostatics, since the field is irrotational. This is shown in Figure 13a.Each COMSOL run starts with inputting lateral and longitudinal straggling infor-mation, as adapted from SRIM for a beam of maximum possible energy (10 MeV/u)(Figure 12b), the ions’ mass, diameter, and charge. Next, the ions are released from differentinitial X positions between the window and the probe tip. With the initial conditions,the simulation solves ordinary differential equations for the velocity of each particle as ittravels through the LXe medium. It is assumed that the ions do not displace the fluid inwhich they are submerged. The motion of the Ba ions in LXe is dictated by the electric andthe drag forces, as solved by the electrostatics and the fluid-dynamics model. The collectionefficiency is calculated by comparing how many initially released ions are present on theboundary of the probe tip surface after a given amount of time. Figure 13b shows theamount of time required to collect all of the ions onto the probe (100% collection efficiency)from different starting positions for various probe biases. The results follow an expectedtrend of higher applied voltage leading to ions feeling a stronger pull and hence gettingcollected faster. These simulation results provide a reference for the experimental param-eters, namely probe bias and beam implantation and collection time, which will then beoptimized and finalized from initial runs during experimental campaigns. Ions may beneutralized by contaminants in the LXe and free charges generated when stopping thebeam. In parallel, the Qβ of the decays could again force the neutral atoms to be ionized tothe 1+ or 2+ states. These competing effects will give a non-zero probability of the finalAtoms 2024, 12, 71 18 of 23product being an atom, not an ion. We will be determining this neutralization fractionduring the commissioning campaigns.(a)VcmcmProbe tip(−500 V applied)−5 0 5−505−500 −250 0(b)Ion cloud distance [cm]Time for 100% efficient collection [s]Figure 13. Simulations of ion collection in LXe using COMSOL Multiphysics. The ions enter thevolume from the left side. (a) Electric potential in LXe generated by the application of −500 V onthe probe tip, with the field lines overlaid on top of that heat map. (b) The time required for 100%efficient collection for ions starting from different positions for different probe biases.After passage of an optimized collection time, the probe will be retracted using theactuator such that the tip moves from the IC to the MC and is placed in front of the HPGefor identification using γ spectroscopy. The decay scheme for 139Cs → 139Ba → 139La [57]is shown in Figure 14. The extracted sample would predominantly consist of ions of139Ba (T1/2 = 82.93(9) m [49]), which will decay to 139La, populating its first excited level166 keV (Jπ = 5/2+). Therefore, the primary goal is to detect the 166 keV γ photons emittedfrom internal transitions from this 166 keV level to its ground state (Jπ = 7/2+) [57]. Inaddition, some 139Cs ions could also get extracted, which will decay to 139Ba, populating its1283 keV level (Jπ = 9/2−) and 627 keV level (Jπ = 3/2−). As a result, we will also aim todetect the emitted γ photons from internal transitions from these levels to the ground state(Jπ = 7/2−). This will prove the extraction of Ba ions, either from the injected beam or fromthe decay of the injected Cs ions, which can be determined from the preestablished beamcomposition and intensity. Any unwanted extracted species, like isobaric contaminants,present in the beam can be differentiated by their distinct γ signatures.Simulations were conducted in Geant4 [58], where the experimental apparatus wasmodeled. The model consisted of three main parts: a probe tip implanted with a radioactiveion source; a GXe-filled chamber having the same dimensions as the MC in Figure 11 witha Be window of thickness 0.25 mm on one flange; and an HPGe, with a Ge crystal placed6.5 cm from the probe tip next to the Be window. The Ge crystal used was 6.68 cm inlength and 5.76 cm in diameter, obtained from the manual of the HPGe, and had a 2 mmthick inner copper shield and a 2 mm thick outer lead shield around it. This is shownin Figure 15a. The experimental hall’s photon background, as well as detector efficiencyand energy resolution, were obtained from past γ spectroscopy experiments using thesame HPGe detector. Figure 15b shows a simulated γ spectrum using a source containing107 ions of 139Cs and 139Ba in a ratio of 1:1 integrated over 90 min of data acquisition. TheHPGe will be recommissioned to obtain the current background, detector efficiency, andenergy resolution and will be used for initial tests of the ion source.Atoms 2024, 12, 71 19 of 235/2!7/2!1660.0166 keV(𝐼𝛾 = 23.76%)139La3/2"9/2"7/2"6270.01283627 keV(𝐼𝛾 = 1.5%)1283 keV(𝐼𝛾 = 7.1%)139Ba 29.68%69.98%< 0.02%84.5%6.2%𝑡!/# = 82.93 m139Cs7/2! 0.0𝑡!/# = 9.27 mStableFigure 14. Decay scheme for 139Cs → 139Ba → 139La showing the β-decay (in solid red arrows) andγ-decay (in solid blue arrows) branches for the relevant levels. The energies are in keV, and the levelsare not to scale. Data taken from Ref. [57].(b)0 200 400 600 800 1000 1200 1400Energy (keV)05001000150020002500300035004000Counts/keVSimulated time elapsed: 90 minutesAfter 90 min of data collection166 keVEnergy [keV]Counts / keV400 600 800 1000 1200 1400 1600Energy (keV)20406080100120140160Counts/keVSimulated time elapsed: 90 minutes627 keV 1283 keV6.5 cmProbe tipGe crystalBe window(a)Probe33 keVFigure 15. Geant4 simulations: (a) The model with the chamber hosting the probe tip, the Be window,and the Ge crystal of the HPGe detector. (b) Photon spectrum acquired over 90 min from a depositcontaining 107 ions of 139Cs and 139Ba in a ratio of 1:1. The 166 keV peak from internal transitionsin 139La is labelled. Also shown is a 33 keV X-ray peak. The inset is zoomed in on the energy rangebetween ∼310 keV and ∼1760 keV to show the 627 keV and 1283 keV peaks from internal transitionsin 139Ba.Initial tests will be conducted using gas media, including a commissioning run usinggaseous argon (GAr), followed by a run using GXe. Simulations have been repeated for GArand GXe at 1 bar pressure with densities of 1.784 g/L and 5.86 g/L. The major differencesbetween the gas and liquid media are the ions’ ranges being ∼100 times longer and thecollection times being ∼10 times faster in gas media. To accommodate these, a spacerwill be used to create an additional distance of ≈10 cm between the probe tip and thebeam entrance window. A proposal for an experiment using GAr has been approved withhigh priority by the Nuclear Physics Experiments Evaluation Committee at TRIUMF for9 RIB shifts. The campaigns using gas media will be used to optimize the GHS, beamintensities, implantation and ion collection durations, and detection procedures, includingAtoms 2024, 12, 71 20 of 23the HPGe-detector position and the necessary data-acquisition times, before the experimentwill be repeated with LXe. From a known beam intensity, beam composition, and numberof detected γ photons, one can determine the extraction efficiency. Detection of the 166 keVγ photons from ions extracted from LXe will demonstrate that an accelerator-driven ionsource is well suited for future testing and perfecting Ba ion extraction using the capillarytube or the cryoprobe techniques.5. Conclusions and OutlookThe Ba-tagging scheme outlined in this paper is a comprehensive approach to extractions from LXe, separate the ions from background gas, trap and probe the ions with laserspectroscopy, and then measure their mass using an MRTOF-MS. This involves preservinga single ion through several stages of an apparatus, over a change of eleven orders ofmagnitude in background pressure. The capillary extraction probe has been fabricated,and currently work is being conducted to demonstrate ion extraction, first in gas, then inLXe. The RF-driven ion separation stages have been refurbished and will soon demonstratehigh-efficiency ion guiding. The MRTOF-MS has demonstrated a mass resolving power of20,000 and is anticipated to exceed 100,000 in the near future. The online Ba-ion source atTRIUMF will soon be taking beam, with the first step to demonstrate ion collection andextraction from GAr, followed by similar experiments in GXe and finally LXe. Once all ofthe stages have been successfully demonstrated individually, they will be combined into asingle apparatus for demonstration of the entire technique using the online LXe ion source.Lastly, a ton scale demonstrator is considered for final proof of the technique. Ba-tagging isa powerful tool that has the potential to eliminate all non-ββ radioactive backgrounds in0νββ searches in Xe.Author Contributions: Conceptualization, T.B., T.D., J.D., W.F., R.G., G.G., A.A.K., K.G.L., A.L., V.V.and L.Y.; Data curation, D.R., R.C., H.R., I.C., M.C. and K.M.; Formal analysis, D.R., R.C., H.R., A.V.B.,C.C., M.C., R.E., D.F., K.M., R.S. and V.V.; Funding acquisition, T.B., T.D., J.D., W.F., R.G., G.G., A.A.K.,A.L. and L.Y.; Investigation, D.R., R.C., H.R., L.B., A.V.B., T.B., I.C., C.C., M.C., T.D., J.D., R.E., D.F.,R.G., G.G., A.A.K., A.L., M.M.-P., K.M., R.S. and V.V.; Methodology, D.R., R.C., H.R., L.B., A.V.B., T.B.,I.C., C.C., M.C., T.D., J.D., R.E., W.F., D.F., R.G., G.G., A.I., A.A.K., K.G.L., A.L., M.M.-P., K.M., K.O.,R.R., R.S., X.S., J.S. and L.Y.; Project administration, T.B., T.D., J.D., W.F., R.G., G.G., A.A.K., A.L. andL.Y.; Software, D.R., R.C., H.R., L.B., C.C., M.C., R.E., R.S. and V.V.; Supervision, D.R., R.C., H.R.,T.B., C.C., T.D., J.D., W.F., R.G., G.G., A.A.K., K.G.L., A.L., Z.L., K.M., V.V. and L.Y.; Validation, T.B.;Visualization, D.R., R.C., H.R., L.B., T.B., I.C., M.C., R.E. and R.S.; Writing—original draft, D.R., R.C.and H.R.; Writing—review and editing, L.B., A.V.B., T.B., I.C., C.C., M.C., T.D., J.D., R.E., W.F., D.F.,R.G., G.G., A.I., A.A.K., K.G.L., A.L., Z.L., M.M.-P., K.M., K.O., R.R., R.S., X.S., J.S., V.V. and L.Y. Allauthors have read and agreed to the published version of the manuscript.Funding: This work has been supported by the Natural Sciences and Engineering Research Council ofCanada (NSERC) under Grant No. SAPPJ-2019-00058 and SAPPJ-2024-00034, the Canada Foundationfor Innovation (CFI) through the John R. Evans Leaders Fund under Fund No. 35700, and the CanadaFirst Research Excellence Fund (CFREF) through the Arthur B. McDonald Canadian AstroparticlePhysics Research Institute. In the USA, support has been provided by the National Science Foundation(NSF) under Grant No. 2011948. The ion funnel device and parts of the ion transport system werefunded by NSF grant PHY-0918469 at Stanford University. The nEXO experiment is supported inCanada through NSERC Grant No. SAPPJ-2022-00021 and CFI Fund No. 43140 and 39881.Data Availability Statement: The data presented in this paper are available on request from thecorresponding authors.Acknowledgments: We would like to thank the nEXO collaboration. We thank M. Good, T. Koffas, S.Kravitz, P. Lu, M. P. Reiter, B. Schultz, P. Schury, A. Stockton and K. Twelker. D.R. would like to alsothank the TITAN group (TRIUMF) and the Detectors group (TRIUMF).Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the designof the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; orin the decision to publish the results.Atoms 2024, 12, 71 21 of 23AbbreviationsThe following abbreviations are used in this manuscript:0νββ Neutrinoless double beta decay2νββ Two Neutrino double beta decayββ Double beta decayCCD Charge coupled deviceCF ConFlatDTL Drift tube linacEXO-200 Enriched Xenon ObservatoryGHS Gas handling systemGXe Gaseous XeHPGe High-purity germanium detectorISAC Isotope Seprator and Accelerator facility at TRIUMFIC Injection chamberLAS Laser ablation ion sourceLEBT Low energy beam transportLPT Linear Paul ion trapLXe Liquid XeMC Measurement chamberMRTOF-MS Multi-reflection time-of-flight mass spectrometerPID Proportional integral derivativePMT Photomultiplier tubepps Particles-per-secondQMF Quadrupole mass filterRIB Rare isotope beamRIS Resonance ionization mass spectroscopyRF Radio-frequencyRTD Resistive thermal deviceSC Super conductingSM Standard model of particle physicsSRIM Stopping and Range of Ions in MatterT1/2 Half-lifeTPC Time projection chamberTRIM Transport of Ions in MatterNotes1 Thermo Finnigan LTQ-FT ICR, Thermo Fisher Scientific, Waltham, MA, USA.2 Threshold is set as the minimum (data without ions) − 5. Threshold in Figure 10a = 8140 − 5 = 8135.3 High-voltage three-state switches (http://madcow-elec.com, accessed on 14 November 2024).References1. Capozzi, F.; Lisi, E.; Marrone, A.; Montanino, D.; Palazzo, A. Neutrino masses and mixings: Status of known and unknown 3νparameters. Nucl. Phys. B 2016, 908, 218–234. [CrossRef]2. Aker, M.; Batzler, D.; Beglarian, A.; Behrens, J.; Beisenkötter, J.; Biassoni, M.; Bieringer, B.; Biondi, Y.; Block, F.; Bobien, S.; et al.Direct neutrino-mass measurement based on 259 days of KATRIN data. arXiv 2024, arXiv:2406.13516. [CrossRef]3. Aker, M.; Beglarian, A.; Behrens, J.; Berlev, A.; Besserer, U.; Bieringer, B.; Block, F.; Bobien, S.; Böttcher, M.; Bornschein, B.; et al.Direct neutrino-mass measurement with sub-electronvolt sensitivity. Nat. Phys. 2022, 18, 160–166. [CrossRef]4. Petcov, S.T. The nature of massive neutrinos. Adv. High Energy Phys. 2013, 2013, 852987. [CrossRef]5. Majorana, E. Teoria simmetrica dell’elettrone e del positrone. Nuovo Cim. 1924–1942 1937, 14, 171–184. [CrossRef]6. Dolinski, M.J.; Poon, A.W.; Rodejohann, W. Neutrinoless Double-Beta Decay: Status and Prospects. Annu. Rev. Nucl. Part. Sci.2019, 69, 219–251. [CrossRef]7. Buchmüller, W.; Di Bari, P.; Plümacher, M. Leptogenesis for pedestrians. Ann. Phys. 2005, 315, 305–351. [CrossRef]8. Canetti, L.; Drewes, M.; Shaposhnikov, M. Matter and antimatter in the universe. New J. Phys. 2012, 14, 095012. [CrossRef]9. Auger, M.; Auty, D.J.; Barbeau, P.S.; Bartoszek, L.; Baussan, E.; Beauchamp, E.; Benitez-Medina, C.; Breidenbach, M.; Chauhan, D.;Cleveland, B.; et al. The EXO-200 detector, part I: Detector design and construction. J. Instrum. 2012, 7, P05010. [CrossRef]Atoms 2024, 12, 71 22 of 2310. Ackerman, N.; Albert, J.; Auger, M.; Auty, D.; Badhrees, I.; Barbeau, P.; Bartoszek, L.; Baussan, E.; Belov, V.; Benitez-Medina, C.;et al. The EXO-200 detector, part II: Auxiliary systems. J. Instrum. 2022, 17, P02015. [CrossRef]11. Ackerman, N.; Aharmim, B.; Auger, M.; Auty, D.J.; Barbeau, P.S.; Barry, K.; Bartoszek, L.; Beauchamp, E.; Belov, V.; Benitez-Medina, C.; et al. Observation of Two-Neutrino Double-Beta Decay in 136Xe with the EXO-200 Detector. Phys. Rev. Lett. 2011,107, 212501. [CrossRef] [PubMed]12. Anton, G.; Badhrees, I.; Barbeau, P.S.; Beck, D.; Belov, V.; Bhatta, T.; Breidenbach, M.; Brunner, T.; Cao, G.F.; Cen, W.R.; et al. Searchfor Neutrinoless Double-β Decay with the Complete EXO-200 Dataset. Phys. Rev. Lett. 2019, 123, 161802. [CrossRef] [PubMed]13. Kharusi, S.A.; Alamre, A.; Albert, J.B.; Alfaris, M.; Anton, G.; Arnquist, I.J.; Badhrees, I.; Barbeau, P.S.; Beck, D.; Belov, V.; et al.nEXO Pre-Conceptual Design Report. arXiv 2018, arXiv:1805.11142. [CrossRef]14. Adhikari, G.; Kharusi, S.A.; Angelico, E.; Anton, G.; Arnquist, I.J.; Badhrees, I.; Bane, J.; Belov, V.; Bernard, E.P.; Bhatta, T.; et al.nEXO: Neutrinoless double beta decay search beyond 1028 year half-life sensitivity. J. Phys. G 2021, 49, 015104. [CrossRef]15. Moe, M.K. Detection of neutrinoless double-beta decay. Phys. Rev. C 1991, 44, R931–R934. [CrossRef]16. Albert, J.B.; Anton, G.; Arnquist, I.J.; Badhrees, I.; Barbeau, P.; Beck, D.; Belov, V.; Bourque, F.; Brodsky, J.P.; Brown, E.; et al.Sensitivity and Discovery Potential of nEXO to Neutrinoless Double Beta Decay. Phys. Rev. C 2018, 97, 065503. [CrossRef]17. Rasiwala, H.; Murray, K.; Lan, Y.; Chambers, C.; Cvitan, M.; Brunner, T.; Collister, R.; Daniels, T.; Elmansali, R.; Fairbank, W.; et al.‘Searching for a needle in a haystack’; A Ba-tagging approach for an upgraded nEXO experiment. Nucl. Instrum. Methods Phys.Res. B 2023, 541, 298–300. [CrossRef]18. Green, M.; Wodin, J.; DeVoe, R.; Fierlinger, P.; Flatt, B.; Gratta, G.; LePort, F.; Díez, M.M.; Neilson, R.; O’Sullivan, K.; et al.Observation of single collisionally cooled trapped ions in a buffer gas. Phys. Rev. A 2007, 76, 023404. [CrossRef]19. Mong, B.; Cook, S.; Walton, T.; Chambers, C.; Craycraft, A.; Benitez-Medina, C.; Hall, K.; Fairbank, W.; Albert, J.B.; Auty, D.J.; et al.Spectroscopy of Ba and Ba+ deposits in solid xenon for barium tagging in nEXO. Phys. Rev. A 2015, 91, 022505. [CrossRef]20. nEXO Collaboration. Imaging individual barium atoms in solid xenon for barium tagging in nEXO. Nature 2019, 569, 203–207.[CrossRef]21. Yvaine, M.; Fairbank, D.; Soderstrom, J.; Taylor, C.; Stanley, J.; Walton, T.; Chambers, C.; Iverson, A.; Fairbank, W.; Kharusi, S.A.;et al. Overcoming photobleaching in imaging of single barium atoms in a solid xenon matrix. Phys. Rev. Res. 2024, 6, 043193.[CrossRef]22. McDonald, A.D.; Jones, B.J.P.; Nygren, D.R.; Adams, C.; Álvarez, V.; Azevedo, C.D.R.; Benlloch-Rodríguez, J.M.; Borges, F.I.G.M.;Botas, A.; Cárcel, S.; et al. Demonstration of Single Barium Ion Sensitivity for Neutrinoless Double Beta Decay using SingleMolecule Fluorescence Imaging. Phys. Rev. Lett. 2018, 120, 132504. [CrossRef] [PubMed]23. Albert, J.B.; Auger, M.; Auty, D.J.; Barbeau, P.S.; Beauchamp, E.; Beck, D.; Belov, V.; Benitez-Medina, C.; Bonatt, J.; Breidenbach, M.;et al. Improved measurement of the 2νββ half-life of 136Xe with the EXO-200 detector. Phys. Rev. C 2014, 89, 015502. [CrossRef]24. Killick, R.S. Observation of Singly Charged Barium Ions in a Buffer Gas: Towards a Functional Barium-Tagging System for Use inthe Enriched Xenon Observatory. Ph.D. Thesis, Carleton University, Ottawa, ON, Canada, 2015.25. Brunner, T.; Fudenberg, D.; Varentsov, V.; Sabourov, A.; Gratta, G.; Dilling, J.; DeVoe, R.; Sinclair, D.; Fairbank, W., Jr.; Albert, J.B.;et al. An RF-only ion-funnel for extraction from high-pressure gases. Int. J. Mass Spectrom. 2015, 379, 110–120. [CrossRef]26. Brunner, T.; Winslow, L. Searching for 0νββ decay in 136Xe—Towards the tonne-scale and beyond. arXiv 2017, arXiv:1704.01528.[CrossRef]27. Lan, Y. A Linear Paul Trap for Barium Tagging of Neutrinoless Double Beta Decay in nEXO. Ph.D. Thesis, University of BritishColumbia, Vancouver, BC, Canada, 2020.28. Murray, K. Design and Commissioning of a Multi-Reflection Time-of-Flight Mass-Spectrometer for Barium Tagging with nEXO.Ph.D. Thesis, McGill University, Montreal, QC, Canada, 2023.29. UHV Design WS40 Wobble Stick Range. Available online: https://www.uhvdesign.com/products/wobble-sticks/ws40-range/(accessed on 14 November 2024).30. Albert, J.B.; Auty, D.J.; Barbeau, P.S.; Beck, D.; Belov, V.; Breidenbach, M.; Brunner, T.; Burenkov, A.; Cao, G.F.; Chambers, C.;et al. Measurements of the ion fraction and mobility of α- and β-decay products in liquid xenon using the EXO-200 detector.Phys. Rev. C 2015, 92, 045504. [CrossRef]31. Page, J.S.; Tang, K.; Kelly, R.T.; Smith, R.D. Subambient pressure ionization with nanoelectrospray source and interface forimproved sensitivity in mass spectrometry. Anal. Chem. 2008, 80, 1800–1805. [CrossRef]32. Wada, M. Genealogy of gas cells for low-energy RI-beam production. Nucl. Instrum. Methods Phys. Res. B 2013, 317, 450–456.[CrossRef]33. Varentsov, V. Review of Gas Dynamic RF-Only Funnel Technique for Low-Energy and High-Quality Ion Beam Extraction into aVacuum. Micromachines 2023, 14, 1771. [CrossRef]34. Brunner, T.; Fudenberg, D.; Sabourov, A.; Varentsov, V.; Gratta, G.; Sinclair, D.; EXO Collaboration. A setup for Ba-ion extractionfrom high pressure Xe gas for double-beta decay studies with EXO. Nucl. Instrum. Methods Phys. Res. B 2013, 317, 473–475.[CrossRef]35. Montero Díez, M.; Twelker, K.; Fairbank, W.; Gratta, G.; Barbeau, P.; Barry, K.; DeVoe, R.; Dolinski, M.; Green, M.; LePort, F.; et al.A simple radionuclide-driven single-ion source. Rev. Sci. Instrum. 2010, 81, 113301. [CrossRef] [PubMed]36. Schwartz, J.C.; Senko, M.W.; Syka, J.E. A two-dimensional quadrupole ion trap mass spectrometer. J. Am. Soc. Mass Spectrom.2002, 13, 659–669. [CrossRef]Atoms 2024, 12, 71 23 of 2337. Fudenberg, D. Improved Discrimination for Neutrinoless Double Beta Decay Searches with EXO-200 and nEXO. Ph.D. Thesis,Stanford University, Stanford, CA, USA, 2018.38. Wada, M.; Ishida, Y.; Nakamura, T.; Yamazaki, Y.; Kambara, T.; Ohyama, H.; Kanai, Y.; Kojima, T.M.; Nakai, Y.; Ohshima, N.; et al.Slow RI-beams from projectile fragment separators. Nucl. Instrum. Methods Phys. Res. B 2003, 204, 570–581. [CrossRef]39. Jones, B.; Raymond, A.; Woodruff, K.; Byrnes, N.; Denisenko, A.; Foss, F.; Navarro, K.; Nygren, D.; Vuong, T.; Adams, C.; et al.The dynamics of ions on phased radio-frequency carpets in high pressure gases and application for barium tagging in xenon gastime projection chambers. Nucl. Instrum. Methods Phys. Res. A 2022, 1039, 167000. [CrossRef]40. Bollen, G. “Ion surfing” with radiofrequency carpets. Int. J. Mass Spectrom. 2011, 299, 131–138. [CrossRef]41. Rasiwala, H. Development of a Linear Paul Trap for Ba-Tagging in a nEXO Upgrade. Master’s Thesis, McGill University,Montreal, QC, Canada, 2022.42. Dawson, P.H. Fringing fields in the quadrupole mass filter. Int. J. Mass Spectrom. Ion Phys. 1971, 6, 33–44. [CrossRef]43. Medina, J.C.B. Mobility and Fluorescence of Barium Ions in Xenon Gas for the Exo Experiment. Ph.D. Thesis, Colorado StateUniversity, Fort Collins, CO, USA, 2014.44. Murray, K.; Chambers, C.; Chen, D.; Feng, Z.; Fraser, J.; Ito, Y.; Lan, Y.; Mendez, S.; Peregrina, M.M.; Rasiwala, H.; et al.Characterization of a Spatially resolved multi-element laser ablation ion source. Int. J. Mass Spectrom. 2022, 472, 116763.[CrossRef]45. Ball, G.C.; Hackman, G.; Krücken, R. The TRIUMF-ISAC facility: Two decades of discovery with rare isotope beams. Phys. Scr.2016, 91, 093002. [CrossRef]46. Twelker, K.; Kravitz, S.; Díez, M.M.; Gratta, G.; Fairbank, W., J.; Albert, J.B.; Auty, D.J.; Barbeau, P.S.; Beck, D.; Benitez-Medina,C.; et al. An apparatus to manipulate and identify individual Ba ions from bulk liquid Xe. Rev. Sci. Instrum. 2014, 85, 095114.[CrossRef]47. Twelker, K. Surface Adsorption and Resonance Ionization Spectroscopy for Barium Identification in Neutrinoless Double BetaDecay Experiments. Ph.D. Thesis, Stanford University, Stanford, CA, USA, 2014.48. Kravitz, S. Identification of Single Barium Atoms with Resonance Ionization Mass Spectroscopy for the nEXO NeutrinolessDouble Beta Decay Experiment. Ph.D. Thesis, Stanford University, Stanford, CA, USA, 2017.49. Kondev, F.; Wang, M.; Huang, W.; Naimi, S.; Audi, G. The NUBASE2020 evaluation of nuclear physics properties. Chin. Phys. C2021, 45, 030001. [CrossRef]50. Mccutchan, E. Nuclear Data Sheets for A = 136. Nucl. Data Sheets 2018, 152, 331–667. [CrossRef]51. Bylinskii, I.; Craddock, M.K. The TRIUMF 500 MeV cyclotron: The driver accelerator. Hyperfine Interact. 2014, 225, 9–16.[CrossRef]52. Bricault, P.; Baartman, R.; Dombsky, M.; Hurst, A.; Mark, C.; Stanford, G.; Schmor, P. TRIUMF-ISAC target station and massseparator commissioning. Nucl. Phys. A 2002, 701, 49–53. [CrossRef]53. Sen, A.; Ames, F.; Bricault, P.; Lassen, J.; Laxdal, A.; Mjos, A. Extraction and low energy beam transport from a surface ion sourceat the TRIUMF-ISAC facility. Nucl. Instrum. Methods Phys. Res. B 2016, 376, 97–101. [CrossRef]54. Laxdal, R.E.; Marchetto, M. The ISAC post-accelerator. Hyperfine Interact. 2014, 225, 79–97. [CrossRef]55. Adegun, J.; Ames, F.; Kester, O. Improvement of the Efficiency and Beam Quality of the TRIUMF Charge State Booster. J. Phys.Conf. Ser. 2022, 2244, 012067. [CrossRef]56. Ziegler, J.F.; Biersack, J.P.; Ziegler, M.D. The Stopping and Range of Ions in Matter. SRIM. 2011. Available online: http://www.srim.org (accessed on 22 October 2024).57. Joshi, P.K.; Singh, B.; Singh, S.; Jain, A.K. Nuclear Data Sheets for A = 139. Nucl. Data Sheets 2016, 138, 1–292. [CrossRef]58. Agostinelli, S.; Allison, J.; Amako, K.; Apostolakis, J.; Araujo, H.; Arce, P.; Asai, M.; Axen, D.; Banerjee, S.; Barrand, G.; et al.Geant4—A simulation toolkit. Nucl. Instrum. Methods Phys. Res. A 2003, 506, 250–303. [CrossRef]Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individualauthor(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury topeople or property resulting from any ideas, methods, instructions or products referred to in the content.
Article
eng
Reviewed
Vancouver : University of British Columbia Library
Multidisciplinary Digital Publishing Institute
CC BY 4.0
Faculty
Researcher
Ba-tagging
neutrinoless double beta decay
nEXO upgrade
linear Paul trap
laser-fluorescence spectroscopy
multi-reflection time-of-flight mass spectrometry
Ion Manipulation from Liquid Xe to Vacuum: Ba-Tagging for a nEXO Upgrade and Future 0νββ Experiments
Text