The cross section for the photodisintegration of helium-3 has been measured at gamma ray energies of 8.06 and 9.17 mev. The He³ (ɣ,p)D reaction cross section at 8.06 and 9.17 mev was found to be 0.493± 0.066 and 0.723± 0.087 millibarns respectively. The He³ (ɣ,n)2p reaction cross section at 9.17 mev was found to be 0.25± 0.13 millibarns. These results are compared with other experimental work on the photodisintegration of helium-3 and tritium. The photodisintegration reaction was observed in a cylindrical gridded ionization chamber using a helium-3, methane, and argon gas mixture. The C¹³ (p,ɣ) N¹⁴ reactions at proton bombarding energies of 0.554 and 1.75 mev were used as the source of gamma rays of well defined energy. The preparation of carbon-13 targets is discussed in detail. Theoretical calculations on the photodisintegration of mass 3 nuclei are summarized. Photodisintegration and electron scattering measurements are compared as methods of determining the nature of the ground state wave function of the mass 3 system. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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An atomic beam type of apparatus designed to produce a polarized He³ beam with an intensity of approximately one microampere and 90% polarization is described. He³ is a monatomic gas consisting of atoms with zero electronic magnetic moment and nuclear spin of ½. As no initial molecular dissociation is required, an intense, supersonic neutral beam can be produced with a miniature Laval nozzle cooled to liquid He⁴ temperatures. The velocity distribution of the particles in the Laval beam and the trajectories of these particles in a radially symmetric hexapole magnet have been computed. Sufficient separation of the two beams, consisting of particles in the two possible nuclear spin states, is achieved with a magnet in which the diameter of the gap between the pole pieces increases from 3mms at the entrance to 6mm in 15 cms and is then constant for 35cms. After ionization the nuclear polarization of the singly ionized particles depends upon the magnetic field strength at the position of the ion. Theoretical calculations show that field strengths of 6000 gauss at both the ionizer and target (in reaction studies) are sufficient to give 90% nuclear polarization. For an input gas temperature and pressure of 2.2°K and 15 mm.Hg. the Laval nozzle (throat diameter, 0.2 mm) has been designed to produce a supersonic beam of Mach number 4 with an intensity of 6.5x10¹⁵ particles/sec at the magnet entrance. Assuming 40% transmission through the magnet (one half of the beam being removed by the polarization process) and an ionization efficiency of 0.25%, the resulting ion beam intensity is 6.5x10¹² ions per second or approximately one microampere. The low temperature atomic beam source has been tested at liquid nitrogen temperature with a He⁴ beam. The measured beam intensity of 9x10¹³ particles/cm²/sec at the magnet exit, 76 cms from the nozzle, agrees favourably with the calculated intensity of 1.2x10¹⁴ atoms/ cm² sec under these operating conditions. The measured field gradient of 70,000 gauss/cm. near the pole tips of the hexapole splitting magnet is more than required for separating the atoms in the two nuclear spin states. A pulsed nuclear magnetic resonance method for measuring the nuclear polarization of the neutral He^ beam prior to ionization is described. The angular distribution and polarization of the protons produced by the D(He³,p)He⁴ reaction with an incident, polarized He³ beam of 150 Kev bombarding energy has been calculated, This angular distribution is isotropic. In the plane of the reaction, the proton polarization, which may be measured by a second scattering experiment, is -2/3 the incident He³ polarization. The angular distribution and polarization of the protons from this reaction has been calculated for the case of polarized and unpolarized He³ beams incident on a polarized deuteron target. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The cross section for the photodisintegration of a three body nucleus, helium-3, has been accurately measured for the first time. The He³( ɣ,p)D reaction cross section has been measured at gamma ray energies of 6.14, 6.97 and 7.08 Mev and found to be 0.104 ± .007, 0.298 ± .050 and 0.308±.024 milli-barns respectively. The photodisintegration cross section agrees with that calculated from the D(p,ɣ)He³ reaction using the principle of detailed balance to within the experimental errors. This is an accurate verification of this principle as applied to a direct nuclear-photon interaction. The photodisintegration reaction was observed in a cylindrical gridded ionization chamber using a helium-3, methane, and argon gas mixture. The F¹⁹(p, αɣ)016 reactions at proton bombarding energies of 873.5 kev and 935 kev were used as the source of gamma rays of well defined energy. The energy resolution of the chamber was adequately good to give a reasonable separation of the 642 kev photodisintegration reaction product peak from the electron background and the 765 kev peak from the He³(n,p)T reaction. It was necessary to reduce the tritium contamination in the helium-3 gas in order to reduce the background arising from the beta decay of the tritium; purification to less than 1 part tritium in 10¹⁰ parts helium was achieved. Proposed measurements of the photodisintegration cross section at higher gamma ray energies using ionization chambers and other types of detectors are discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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We have performed a careful measurement of the shape of the beta spectrum of He⁶. A detailed study of the phenomenon of electron scattering in our thin lens magnetic spectrometer enabled us to interpret the spectrum shape from the end point at Wₒ = 3.50 ± .02 Mev. down to 1/14 Wₒ = 0.250 Mev. The experimental shape has been compared with the theoretically predicted shape for allowed spectra. The influence of the pseudoscalar interaction on the shape of the He⁶ spectrum has also been considered. From these measurements we have been able to set limits on the Fierz interference in the Gamow-Teller interaction as well as on the magnitude of the pseudoscalar coupling constants. These limits have been interpreted in terms of the relative magnitudes of the axial vector, pseudoscalar, and tensor coupling constants using the two component theory of the neutrino and assuming that the complete beta decay Hamiltonian proposed by Lee and Yang is or is not invariant under time reversal. We have also calculated the effect on the spectrum shape of the production of inner Bremsstrahlung in beta decay and have shown this effect to be at the limit of experimental detectability.

The processes by which the three particle final state is formed in the He³(He³,2p)He⁴ reaction were investigated by observing the angular distribution of coincidence events between the two protons as a function of the angle between the protons. The reaction mechanism was determined by comparing the experimental distribution with those predicted for the various possible processes obtained from kinematic and phase space arguments. The reaction was found to proceed predominantly by sequential decays through unbound intermediate states and to a lesser extent by a direct instantaneous three body breakup. The majority of the two stage decays passed through the ground state of Li⁵ , The mean lifetime of this state was measured and found to be (1.0 ± .3) x 10⁻²¹ sec There was also good evidence of a sequential decay through the diproton state. In order to fit the shape of the observed distribution it was necessary to assume that a diproton system exists which is unbound by 600 keV and has a mean lifetime of 1.5 x 10⁻²² sec However another possible interpretation is that a direct breakup occurs and the angular distribution of the protons is distorted by an attractive final state two proton interaction similar to the scattering interaction, although whether this interaction would be strong enough to produce the observed distribution is not known. A more quantitative three body decay theory is therefore necessary in order to draw any firm conclusions about the existence of the diproton state. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The present work proposes trial wave functions for the three-body problem in nuclear physics taking into account the group theoretical classification of the states given by Derrick and Blatt and by Verde. We start from the Schroedinger equation in the internal variables (the interparticle distances) obtained by Derrick from a summation over the matrix elements for kinetic energy and potential energy extended over all variables except the internal variables. An “equivalent" Schroedinger equation is set up using a potential due to Eckart. This equation has the same form as the original Schroedinger equation in the region outside the range of the nuclear forces. The variables in this equation can be separated in a hyperspherical coordinate system and the resulting separate equations can be solved. Then using a superposition principle the solutions of the original equation are expanded in terms of solutions to the "equivalent" equation. The Rayleigh-Ritz variational procedure is used to determine the coefficients of the expansions with a given potential. Because of the computational labor involved significant approximation is made in allowing only the leading terms in the angular variables to appear in the expansions while keeping a sufficient number of radial terms to insure convergence. The present functions with a radial variable R = [formula omitted] give less than 1/2 of the binding energy predicted by Blatt, Derrick and Lyness (1962) who used a radial variable R = r₁₂ + r₂₃ + r₃₁. This shows that our approximation with the former radial variable is indeed too crude to predict a reliable value for the binding energy and that more angular terms must be included in the expansions, at least for the preponderent symmetric S-state. Wave functions derived by the Rayleigh-Ritz variational principle are used to calculate cross sections for the reaction D(p, γ)He³. The electric dipole cross section depends very sensitively on the potential used to derive the wave function and a comparison with experimental data provides a test of the various model assumptions used to describe the nuclear interaction. A realistic potential must contain a tensor potential plus a hard core in the central potential. The tensor interaction couples the S and D states and is necessary to explain the quadrupole moment of He³ while the hard core produced the required mixed-symmetry S-state. The experimentally observed isotropic component of the gamma ray yield is attributed to a magnetic dipole transition between a continuum quartet S-state and the mixed-symmetry component of the ground state wave function. For a range of the variable parameter used in the calculation comparison with experiment requires a 5% admixture of the mixed-symmetry S-state in the ground state wave function. / Science, Faculty of / Physics and Astronomy, Department of / Graduate