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Final state interactions in the reaction T(He3, He4) np Beveridge, John Leslie

Abstract

Triple correlation cross sections have been measured for the reaction T(He³,He⁴)np in a complete experiment at a He³ bombarding energy of 1.5 MeV. Three similar experimental geometries were used which allow the observation of low relative energies in the n-p system, and energies of 0.96 MeV in the He⁴-n system. Therefore the n-p singlet and He⁵ (g.s.) final state interactions were observed. Events from the two body reaction channel T(He³,d)He⁴ and overlapping kinematic contours were eliminated by particle identification. A least squares fit to the experimental triple correlation cross section for one geometry was made using two approximate theories for three body reactions. These were the Watson, and Phillips, Griffy and Biedenharn (P.G.B.) final state interaction theories. Both theories give the theoretical cross section to be proportional to a density of states (D.O.S.) function. The P.G.B. theory gives two forms for this function (P.G.B.1 and P.G.B.2). The D.O.S. functions for the state of He⁵ and Li⁵ were calculated using only the P.G.B. 1 and Watson forms. The P.G.B.1 form gives an inadequate description of both the n-p singlet and He⁵(g.s.) final state enhancements. The He⁵(g.s.) enhancement is well described by the Watson form of the D.O.S. function. The triple correlation cross section, for high proton energies, was dominated by a sequential breakup through the ground state of He⁵ and by direct three body breakup. No evidence for contributions from the states of Li⁵ or for any well defined contributions from the first excited state of He⁵ were observed. The Watson and P.G.B.2 forms of the singlet n-p D.O.S. function gave indistinguishable predictions of the n-p singlet enhancement. The P.G.B. 2 form was used, for seven values of the n-p singlet scattering length, to fit the experimental data. The value of the singlet n-p scattering length extracted in the fitting procedure was [formula omitted]. The large experimental errors assigned were caused by the sensitivity of the extracted value on the background terms included in each fit.

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