L.C. Dennis

High momentum transfer RT,L inclusive response functions for 3,4He.

Inclusive electron scattering cross sections for {sup 3,4}He have been measured in the quasielastic region at electron energies between 0.9 and 4.3 GeV, and scattering angles of 15{degree} and 85{degree}. Longitudinal ({ital R}{sub {ital L}}) and transverse ({ital R}{sub {ital T}}) response functions have been extracted using a Rosenbluth separation at constant {vert bar}{bold q}{vert bar} of 1.050 GeV/{ital c}. The ratio of the longitudinal to the transverse reduced response functions in the negative {ital y} region reaches unity.

12C + 7Li Reaction measurements and the 12C(7Li, t)16O reaction

Abstract A measurement of the residues from the 12 C + 7 Li reaction has been obtained for 7 Li energies from 10 to 38 MeV. From these measurements the fusion cross sections and critical angular momenta for the 12 C + 7 Li system have been deduced. Cross sections for the 7 Li( 12 C, t) 16 O reaction have been obtained for 12 C energies from 54 to 62 MeV at θ lab = 2.7°. The critical angular momenta obtained from the fusion cross sections have been used to perform Hauser-Feshbach calculations for the 12 C( 7 Li, t) 16 O reaction. These calculations have been compared to measured angular distributions over a wide energy range. By comparing the fusion cross sections required by the Hauser-Feshbach calculations to fit the 12 C( 7 Li, t) 16 O(8.87 MeV) reaction and the measured residue cross section it is estimated that at least 80 % of the measured residues are fusion products. The calculations also indicate that direct processes dominate the population of many 16 O levels at forward angles and the 10.35 MeV state at backward angles. The necessity for using a critical angular momentum in Hauser-Feshbach calculations is discussed.

Projectile breakup and total reaction strengths in Li-induced reactions

Abstract Spectra and angular distributions have been measured for the light particles emitted from the reactions induced by 36 MeV 6 Li and 7 Li ions on targets of 12 C, 13 C and 27 Al. Some measurements were also performed at beam energies of 28 and 32 MeV. The spectra are dominated by broad peaks centered at energies corresponding to the beam velocity, a characteristic of projectile breakup. A simple breakup model roughly reproduces the shapes of the measured spectra and angular distributions. The total cross sections observed for projectile breakup average about 600 mb and are almost as large as the fusion cross sections. The 7 Li breakup yields are somewhat larger than those for 6 Li, the same trend that was previously observed for the Li-induced fusion cross sections on C. As a result the measured total reaction cross sections induced by 7 Li ions are about 200 mb larger than those of 6 Li on the same targets. This difference is not predicted by conventional optical model calculations.

The reaction: High-spin states, resonances and coherence widths

Abstract Excitation functions were measured for states of 21 Ne populated by the 12 C ( 13 C , α) reaction over the bombarding energy range E lab = 18.2–32.0 MeV (18.4–27.0 MeV) at θ lab = 7°(25°) in in 200 keV steps, and average coherence widths of states and the moment of inertia of the compound nucleus 25 Mg were obtained from these excitation functions. A statistical analysis of these data was performed. Angular distributions for states in 21 Ne to 10 MeV in excitation energy were measured at θ lab = 7°, 18°, 28° and 43° at bombarding energies from 29.0 to 31.0 MeV in 400 keV steps. These data along with Hauser-Feshbach predictions allow us to suggest spins for some states as well as to suggest possible candidates for rotational bands in 21 Ne.

A large solid angle, high stopping power Bragg curve spectrometer for coincidence measurements

Abstract A large acceptance, high stopping power, Bragg curve spectrometer has been developed for use in coincidence experiments with heavy ions. The electron collection fields are radial and position information is obtained from a resistive anode. The detector is 60 cm deep and operates at pressures of up to 2.5 atm of P-10 gas. It is mated to a scattering chamber which allows it to be moved out of plane during coincidence measurements. The detector design was aided by the results of computer simulations of the electron collection process in the detector, and of the signal processing in the electronics. The signals from the Bragg curve spectrometer are recorded in a waveform digitizer and the Bragg peak height, range, position and pileup rejection information are determined from software analysis of the recorded signals. Factors limiting the performance of the detector are discussed, and results obtained with the detector are presented.

Direct and compound nuclear contributions to the 13C(6Li, t) reaction at Elab = 25 MeV☆

Abstract The reaction 13 C( 6 Li, t) 16 O has been studied in the incident energy range 24–26 MeV. Complete angular distributions have been measured at E 6 Li , = 25 MeV in the angular range θ lab = 8°–172°, with the reaction 6 Li( 13 C, t) 6 O being used for the backward angle measurements. Cross sections for evaporation residues from the fusion of the 6 Li + 13 C system have been measured in the incident 6 Li energy range 9.2–35.1 MeV. Compound nuclear contributions to the transfer cross sections have been calculated using the Hauser-Feshbach statistical theory with the assumption that the compound-nucleus formation cross section is equal to the measured fusion cross section. By comparison of the compound nuclear calculations with backward angle data it is found that the sharp cutoff approximation commonly used to represent the initial angular momentum distribution of the compound nucleus is not adequate for the 13 C( 6 Li, t) 16 O reaction. Good fits to the backward angle data can be obtained by using a smooth cutoff approximation. The forward angle cross sections have been compared with exact finite-range distorted-wave Born approximation calculations to extract transferred angular momenta and spectroscopic strengths. The present results differ from those of an earlier study. These differences are due to the inclusion of forward angle data in the present study.

Search for resonances in 12C(9Be, α)17O

Abstract Excitation functions at 7° (lab) have been measured from E c.m. = 5.1 to 11.4 MeV in approximately 114 keV steps for 15 groups of final states in 17 O populated by the 12 C( 9 Be, α) reaction. Statistical tests have been used to locate possible non-statistical structure in the excitation functions. Possible anomalies were found near E c.m. = 6.3, 7.5, 8.9 and 9.7 MeV. Angular distributions were measured at E c.m. = 9.20, 9.71 and 10.23 MeV for the three lowest excited states in 17 O. The data have been compared with Hauser-Feshbach calculations in addition to the following reaction mechanisms: compound plus a single resonance, compound plus interfering resonances and compound plus direct reactions.

Resonances: Population of low-level density regions?

Abstract A simple explanation based primarily on the binding energies of nuclei in the entrance channel and level densities calculated with the shell model is proposed to explain the occurence of resonances in heavy-ion reactions for sd-shell nuclei.

Proton-inclusive cross sections from 600 MeV proton-nucleus reactions☆

Abstract Proton-inclusive cross sections were measured for 600 MeV proton bombardment of 27Al and 181Ta targets using the SREL synchrocyclotron. Proton energies were measured with a plastic scintillator time-of-flight system, and a 10.2 cm thick NaI detector was used for particle identification. The results of classical many-body and knock-on calculations are compared with the data.

Proton inclusive cross sections from 720 MeV α-nucleus reactions

Abstract Proton inclusive cross sections have been measured from 30°–150° (lab) for outgoing energies up to 500 MeV from the bombardment of 720 MeV α-particles on Al and Ta. An exhaustive survey of applicable models indicates that the intranuclear cascade and knock-out models provide the best description of the data. Single scattering mechanisms seem to be important, and there is some indirect evidence that high nuclear density effects occur.