W.R. Jackson

Three α-particle decay of C12

Abstract The reaction B11(p, 2α)He4 has been studied at proton bombarding energies of 2.0, 2.65, 3.25, 3.73, 4.00, 5.08 and 5.64 MeV. These energies excite several resonantstates in C12. The kinematics of the reaction were completely determined by detecting in coincidence two of the three final α-particles in solid-state detectors. This determination of the kinematics permitted discrimination between sequential two-body decay and direct three-body decay. The reaction mechanism was found to be sequential two-body decay involving the ground and the broad first-excited states of Be8, with events involving the latter showing strong interference effects. These interference effects were attributable to the identity of the three final particles and to the ambiguity of the order of their emission. Not more than 5 % of the experimental cross section could be attributed to the direct three-body decay mechanism; indeed, the contribution from the direct process is probably much smaller than the quoted 5 %. Hence, the conclusion must be that, for C12 with an excitation energy between 17 and 21 MeV, the decay mechanism is predominantly sequential two-body decay. Also the total cross section for this reaction is of the order of 100 to 200 mb; thus it is comparable to the geometric cross section. These two facts imply that, in this energy region, C12 has a strong cluster configuration of an α-particle plus a Be8 nucleus in either the ground or the first-excited state.

Three-body break-up in 7Li(d, nα)4He and 7Li(d, αα)n reactions

Abstract The reaction 7 Li(d, n α) 4 He has been studied detecting neutron-alpha coincidences. The energies of the detected particles were determined by means of time-of-flight measurement for neutrons and a silicon, surface-barrier detector for alphas. Simultaneously alpha-alpha coincidences from 7 Li(d, αα)n were detected using two solid-state detectors. The measurements were performed at bombarding energies from 2.6 to 4.0 MeV in steps of 0.2 MeV. In addition the reaction 7 Li(d, αα)n was studied separately at 4.0 and 9.0 MeV for several angular settings of the two solid-state detectors. The most important reaction mechanism is found to be sequential decay through intermediate 5 He and 8 Be states.

Three-body break-up in 7 Li(d, n α) 4 He and 7 Li(d, αα)n reactions

Abstract The reaction 7 Li(d, n α) 4 He has been studied detecting neutron-alpha coincidences. The energies of the detected particles were determined by means of time-of-flight measurement for neutrons and a silicon, surface-barrier detector for alphas. Simultaneously alpha-alpha coincidences from 7 Li(d, αα)n were detected using two solid-state detectors. The measurements were performed at bombarding energies from 2.6 to 4.0 MeV in steps of 0.2 MeV. In addition the reaction 7 Li(d, αα)n was studied separately at 4.0 and 9.0 MeV for several angular settings of the two solid-state detectors. The most important reaction mechanism is found to be sequential decay through intermediate 5 He and 8 Be states.

METHOD FOR NEUTRON DETECTION EFFICIENCY MEASUREMENTS AND NEUTRON--CHARGED PARTICLE COINCIDENCE DETECTION.

A simple and straightforward method for experimentally determining neutron time-of-flight detector threshold and efficiency as a function of neutron energy is presented. A procedure for neutron-charged particle coincidence studies is included also.

The 2H(p, 2p)n reaction at 9.0 and 10.5 MeV

Abstract The 2H(p, 2p)n reaction has been studied experimentally at bombarding energies of 9.0 and 10.5 MeV. The two protons in the final state were detected in coincidence and energy-analysed by use of a two-parameter, pulse-height analyser, thus completely specifying the kinematics of the reaction. The distinction between sequential and simultaneous decay for the three-nucleon system was investigated. The sequential decay of this system via the virtual deuteron was observed. A preliminary analysis of the data using the generalized densty-of-states technique appears to adequately describe the reaction at these bombarding energies.

The 11B(p, 2α)4He reaction at the 163 keV resonance

Abstract The 11 B(p, 2 α ) 4 He reaction has been studied at a bombarding energy of 163 keV to complement the previous measurements at energies of a few MeV. Many two-parameter spectra have been taken, both around the 8 Be ∗ recoil axes and at selected angles away from the recoil axes. Coplanar and non-coplanar cases for the three alpha particles have been studied. Analysis yields results similar to those found previously for the higher bombarding energies but in dis-agreement with the conclusions of Dehnhard. Strong sequential decay through the 8 Be ∗ states has been observed with very little or no evidence for simultaneous three-alpha decay.

FINAL-STATE INTERACTIONS IN THE

Abstract The 9 Be + p → d + 2α reaction has been studied at a proton bombarding energy of 9.0 MeV, by the coincident detection of pairs of reaction products. Mass identification of one detected particle has been accomplished using a time-of-flight technique. The reaction yield has been shown to be dominated by final-state interactions through states in 8 Be and 6 Li, with little or no yield from direct three-body disintegration. Theoretical fits to the data using the generalized density of states functions reproduce quite accurately the shapes of the spectra. Efforts to fit the angular dependence of the yield have met with limited success.

sup 9

Abstract The 9 Be + p → d + 2α reaction has been studied at a proton bombarding energy of 9.0 MeV, by the coincident detection of pairs of reaction products. Mass identification of one detected particle has been accomplished using a time-of-flight technique. The reaction yield has been shown to be dominated by final-state interactions through states in 8 Be and 6 Li, with little or no yield from direct three-body disintegration. Theoretical fits to the data using the generalized density of states functions reproduce quite accurately the shapes of the spectra. Efforts to fit the angular dependence of the yield have met with limited success.

Be + p

Abstract The 2 H(p, pn) reaction has been studied at a bombarding energy of 9.0 MeV and several coincidence detection angles using the Rice University tandem Van de Graaff accelerator and computer-analyzer system. The energies of the detected, coincident particles were determined using a solid-state surface barrier detector for the proton and time-of-flight measurement on the neutron. The contributions of the neutron-proton final state interaction and neutron-proton quasi-free scattering have been observed. The final state interaction contribution has been reproduced using Phillips, Griffy and Biedenharn theory. The shape of quasi-free scattering contribution spectrum is in reasonable agreement with simple impulse approximation prediction. The absolute value of cross section is smaller than predicted by spectator model calculations.