B. Remington

Particle identification via pulse-shape discrimination with a charge-integrating ADC

Abstract A charge-integrating ADC has been used to sample the intensity in two different time regions of a pulse and thus to sense the shape of the pulse. This idea has been applied to produce neutron/γ-ray discrimination from pulses in a liquid scintillation detector. Optimization of available parameters yields good pulse-shape discrimination for pulses greater than those produced by 100 keV electrons. The method uses only general purpose electronics.

Method for the study of neutron emission from light fragments in intermediate energy heavy-ion collisions

Abstract A procedure has been worked out for the study of neutron emission from the projectile-like fragments in intermediate energy heavy-ion collisions. We suggest presenting the collinear fragment-neutron coincidence data as relative velocity spectra. In 14 N + 165 Ho collisions at 35 MeV/u these spectra show that most of the neutrons are emitted via a few excited states of the light fragments. By comparison with Monte Carlo simulations which, in addition to the experimental details, take explicit account of kinematic effects, the excitation spectra for the major isotopes of Li, Be, B and C are explained.

Fragment production in 14N+C, Ni, Ho reactions at 35 MeV/nucleon

Abstract Inclusive fragment production from the collisions of 35 MeV/Nucleon 14 N with carbon, nickel, and holmium targets has been measured in the angular range of 7–23°. The energy spectra of many of the isotopes of Li, Be, B, C and N were determined. In an energy/nucleon representation the spectra at a given angle are similar for all fragments and all targets. The spectra contain contributions mainly from two components, quasielastic and deep inelastic, whose development can be followed as the fragment angle changes. The quasielastic structure, a broad peak, is most pronounced at high fragment energies and at the smaller angles. The deep-inelastic component falls off with fragment energy and becomes dominant at the large angles. The spectra for fragments with 6 ⩽ A ⩽ 12 were decomposed into these two components. The shape of the quasielastic component is consistent with a two-step model in which an early fragmentation is followed by a subsequent mass pick-up from the participant zone. The maxima and the average energies of the quasielastic distributions and the logarithm of the energy integrated quasielastic yields for the different light isotopes depend approximately linearly on angle for all three targets. The relative isotope yields indicate a slight dependence on the neutron/proton ratio of the target for the quasielastic component and a more pronounced one for the deep-inelastic component.

Comparison of the noncoplanar 6Li(p, pd)4He reactions at 120 and 200 MeV

Abstract The 6 Li(p, pd) 4 He reaction was studied at 200.2 MeV, at the quasi-free angle pair ( θ p , θ d ) = (54°, −48.9°), for noncoplanarity angles φ from 0° to 28°. 6 Li αd spectroscopic factors of 0.84 and 0.76 are deduced from our coplanar data at this energy and 120 MeV, respectively, for ground-state 2S Woods-Saxon wave functions. A recent microscopic three-body calculation predicts spectroscopic factors from 0.70 to 0.75; using the ground-state wave functions from this study, we deduce a factor of 0.76 from the 200 MeV data. DWIA calculations fit the measured integrated cross sections versus φ for spectator momenta P α ≲ 100 MeV/ c at both bombarding energies, but underpredict them for larger P α . Momentum form factors were better reproduced with 1S αd cluster wave functions for a soft-core bound-state potential than with the 2S Woods-Saxon wave functions, but the former wave functions generate unphysically large (∼1.25) spectroscopic factors.

Neutron emission from 14N + 165Ho collisions at 35 MeV/u

Abstract Neutron emission from 14 N + 165 Ho collisions has been studied at 25 MeV/u incident energy. Energy and angular distributions of the neutrons were measured in coincidence with projectile-like fragments (Li, Be, B, and C) emitted at angles of 10° and 30°. The spectra of neutrons at angles far from the angle of a coincident fragment have been satisfactorily parameterized in terms of a slowly moving, target-like source of temperature 2–3 MeV and a half-beam-velocity source of temperature about 7 MeV. The latter source accounts for about 20% of the detected neutrons for in-plane measurements. The out-of-plane cross sections are smaller. The relevant parameters of the moving-sources parametrization suggest a simple model which qualitatively explains the data in terms of the development of a hot participant zone and its subsequent mass exchange interactions with spectators in the projectile and target nuclei.

Excitation of discrete particle-unbound states in heavy-ion collisions

Abstract Neutron spectra in coincidence with fragments have been observed in 14 N- 165 Ho collisions at 490 MeV. Contributions to the spectra from excited light fragments are very pronounced when the fragments detector and the neutron detector are in colinear geomwtry. Relative velocity spectra then reveal that neutron decay of a single, well-known excited state dominates. In inclusive spectra of neutrons or protons these effects are still present and may not be disregarded.

The noncoplanar 6Li(p, pd)4He reaction at 120 MeV, and the 6Li cluster momentum wave function☆

Abstract The 6Li(p, pd)4He reaction was studied at 119.6 MeV, at the quasifree angle-pair (θp, θd) = (40°, 59°), for noncoplanarity angles 0° ⩽ φ ⩽ 36°. The deduced 6Li αd spectroscopic factor (0.75) and momentum distribution (73 MeV/c) FWHM) agree reasonably well with most other intermediate-energy measurements. A minimum and adjacent secondary maximum in the integrated cross section versus φ, predicted by the DWIA theory, was observed for the first time. Cross sections at large φ are about 2.5 times greater than the DWIA predictions, suggesting contributions of higher-order processes not included in the DWIA treatment of the reaction, or larger momenta than the cluster wave function contains.

Temperatures determined from neutron emission in nucleus-nucleus collisions

Abstract Most neutron spectra from 14N+165Ho collisions at 35 MeV/nucleon are described by two moving thermal sources, one at a temperature of ≈2.5 MeV and the other of ≈8 MeV. Resonances in gragment-neutron relative velocity spectra are used to determine a temperature from the relative populations of excited states of 13C nuclei. There is a discrepancy with the equilibrium assumption in that the fitted value, ≈1 MeV, does not match that of either thermal source.

The noncoplanar 7Li(p, pd)5He and 7Li(p, pt)4He reactions at Ep = 200 MeV, and evidence for deuteron clustering in 7Li

Abstract The 7Li(p, pd)5He reaction was studied at 200 MeV, at the quasi-free angle pair θ p θ d = 64° −47.4° , for noncoplanarity angles from 0° to 16°. Data were fitted with DWIA calculations, which gave a spectroscopic factor Cd of 1.1 for deuterons in 7Li if entrance-channel absorption was neglected, and 1.4 if it was not. The Cd deduced from plane-wave analysis (by comparison with 6Li(p, pd) data) is 0.9. The deuteron cluster momentum distribution is characterized, at small momentum, by an FWHM of 140 MeV/c. At large momentum there is an excess of measured cross section over predictions, as is true also for 6Li(p, pd) at intermediate energies. Cross sections for 7Li(p, pt)4He at the same experimental conditions are very small but are consistent with unit spectroscopic factor for t + α; these cross sections show the expected minimum at zero relative cluster momentum, and are adequately fitted by DWIA predictions.

Analysis of projectile fragmentation in intermediate-energy heavy-ion collisions

Abstract An analytical form is given for the entire energy range of quasielastic fragment spectra produced in intermediate-energy heavy-ion collisions. The fit parameters are related to physical quantities such as the probability of direct fragmentation versus damped fragmentation and the momentum width of the direct fragmentation peak. The formulation is applied to fragment spectra at 10° from the 14N+165Ho reaction at E/A = 35 MeV. It is suggested that Coulomb deflection and impact-parameter selection have a decisive effect on fragment spectra produced in peripheral collisions. The smaller the Z/A of the detected fragment at a given angle, the smaller the impact parameter of the reaction.