L. F. Hansen

Centrality dependence of kaon yields in Si + A and Au + Au collisions at the AGS

Charged kaon production has been measured in Si+Al and Si+Au collisions at 14.6 A GeV/c, and Au+Au collisions at 11.1 A GeV/c by Experiments 859 and 866 (the E--802 Collaboration) at the BNL AGS. Invariant transverse mass spectra and rapidity distributions for both K+ and K- are presented. The centrality dependence of rapidity-integrated kaon yields is studied. Strangeness enhancement is observed as an increase in the slope of the kaon yield with the total number of participants as well as the yield per participant. The enhancement starts with peripheral Si+Al and Si+Au collisions (relative to N+N) and appears to saturate for a moderate number of participating nucleons in Si+Au collisions. It is also observed to increase slowly with centrality in Au+Au collisions, to a level in the most central Au+Au collisions that is greater than that found in central Si+A collisions. The enhancement factor for

Ta181(p, n)W181 and Au197(p, n)Hg197 excitation functions between 4 and 13 MeV

K^+

Measurements of the neutron spectra from materials used in fusion reactors and calculations using the ENDF/B-III and -IV neutron libraries

production are 3.0 +-0.2(stat.) +-0.4(syst.) and 4.0 +-0.3(stat.) +-0.5(syst.), respectively, for the most central 7% Si+Au collisions and the most central 4% Au+Au collisions relative to N+N at the correponding beam energy.

Measurements and calculations of the leakage multiplication from hollow beryllium spheres

Excitation functions for the Ta/sup 181/(p,n)W/sup 181/ and Au/sup 197/ (p,n)Hg/sup 197/ reactions were measured for incident proton energies from 4 to 13 Mev. The stacked foil method was used. The activity of the foils was measured by counting the gamma rays and X-rays emitted when the product nuclei decay by electron capture. Absolute values of the cross sections were measured at several energies for these reactions and were compared with the cross sections for compound nucleus formation given by Shapiro. Threshold energies for the (p,2n) reactions were obtained by comparing the present data with neutron yields obtained from long counter measurements. The (p,2n) thresholds are 7.5 Mev for Ta/sup 181/ and 8.3 Mev for Au/sup 197/. The absolute (p,2n) cross section values were also obtained. The total reaction cross sections above 7 Mev are compared with optical model calculations. Results confirm the assumption of a surface absorption potential. (auth)

Study of the 22Ne(d, d)22Ne, 22Ne(d, p)23Ne, 22Ne(d, t)21Ne and 22Ne(p, d)21Ne reactions

Proposed fusion reactor blanket designs bring into focus a large number of problems dealing with the interaction of 14-MeV neutrons with different materials. Carbon, oxygen, aluminum, titanium, and iron are among the materials used in the blanket. To have confidence in fusion reactor blanket calculations, a necessary prerequisite is that the transport code correctly describes the interaction of 14-MeV neutrons with the materials of the blanket. Spherical assemblies of the above materials ranging from 1 to 5 mean-free-paths in thickness have been bombarded with a centered nominal 14-MeV neutron source. The emitted neutron energy spectra were measured using time-of-flight techniques (3-nsec full-width-at-half-maximum system resolution) in a geometry where the flight path (7 to 10 m) is long compared to the dimensions of the spherical targets. The spectra have been calculated with the Monte Carlo neutron transport code TART using the ENDF/B-III and -IV neutron libraries and compared with measurements.

The (α, n) cross sections on 17O and 18O between 5 and 12.5 MeV

Using the Pulsed-Sphere Method, the leakage spectra from hollow Be spheres of 4.5, 13.8 and 19.9 cm thickness have been measured. The predicted copious production of epithermal and thermal neutrons from the 13.8 and 19.9 cm spherical shells has been verified. A quantitative comparison of measured and calculated time-of-arrival count spectra over the energy range from thermal to ..integral.. 15 MeV indicates that the ENDL-84 library overestimates the leakage spectra between 2 and 10 MeV and in the epithermal and thermal energy regions. In the remaining regions, the leakage spectra are underestimated. Because of the above compensation the inferred leakage multiplication for the 19.9 cm Be is ..integral.. 3% higher than calculations. In the case of the 13.8 cm Be, the compensation is less exact and the inferred leakage multiplication is ..integral.. 9% higher than calculations.

Consistent folding model description of nucleon elastic, inelastic, and charge-exchange scattering from 6,7Li at 25–50 MeV

Abstract The nuclear reactions 22 Ne(d, d) 22 Ne, 22 Ne(d, p) 23 Ne and 22 Ne(d, t) 22 Ne induced with 12.1 MeV deuterons and 22 Ne(p, d) 21 Ne induced with 18.2 MeV protons have been studied by employing a gas target of enriched 22 Ne and beams accelerated in the Livermore variable energy cyclotron. The results have been analysed with the nuclear optical model and DWBA calculations. The neutron-transfer reactions have been compared with the predictions of the Nilsson model. The results for the pick-up reactions going to the first three levels of 21 Ne are in good agreement with the predictions of the Nilsson model. The RPC model (rotational and particle motion with Coriolis band mixing) modified for pairing effects was employed in an effort to obtain at least a qualitative explanation of the transitions leading to 23 Ne. There are certain large discrepancies consisting of strong transitions that are predicted theoretically under a wide range of assumptions but not seen experimentally. These results indicate that further detailed calculations are necessary to understand the structure of this nucleus.

Neutron and Gamma-Ray Spectra from 232Th, 235U, 238U, and 239Pu After Bombardment with 14-MeV Neutrons

Abstract The excitation functions for the (α, n) reaction on 17 O and 18 O have been measured from 5 to 12 MeV using long counters. Also, the neutron differential cross sections were measured at 9.8, 11.6 and 12.2 MeV, using the Livermore neutron time-of-flight facility. Neutron spectra were obtained every 15° between 3° and 135° with gas targets of enriched 17 O and 18 O. The angular distributions are roughly symmetric about 90°. Small forward peaking is observed at the higher bombarding energies for some of the states, mainly for the ground and first excited states.

System, centrality, and transverse mass dependence of two-pion correlation radii in heavy ion collisions at 11.6A and 14.6A GeV/c

Abstract The results of a consistent theoretical microscopic single scattering model study of nucleon elastic, inelastic, and charge-exchange scattering from 6,7 Li at E p(n) = 25–50 MeV are reported. A realistic effective nucleon-nucleon interaction, adopted from the work of Mahaux and collaborators and Bertsch and coworkers, has been employed in the model calculations. The density distributions needed to describe the structure of the mass 6 and 7 systems in the calculations are the same as those used in recent proton-nucleus scattering studies of these targets at E p = 200 MeV. The present, parameter-free model calculations provide an excellent description of the available low-energy nucleon-nucleus scattering data on 6,7 Li.

Study of the 18O(p,t)16O and 18O(p,d)17O reactions at Ep = 18.2 MeV

AbstractThe neutron and gamma-ray leakage spectra from pulsed spheres having a radius equal to 1.0 mean-free-path (mfp) for 14-MeV neutrons in 232Th, 235U (with radii of 0.7 and 1.5 mfp), 228U (with radii of 0.8 and 2.8 mfp), and 239Pu (with radii of 0.7 and 1.25 mfp) were measured by using time-of-flight techniques. The neutron spectra were measured between 0.9 and 15 MeV using stilbene and NE-213 scintillators. For the gamma rays, the electron recoil spectra were measured between 0.35 and 8 MeV with the NE-213 detector only. Pulse-shape discrimination and flight paths of ∼10 m were used in these measurements. The measured spectra are compared with calculations carried out with TARTNP, a coupled neutron-photon Monte Carlo transport code. The Lawrence Livermore Laboratory ENDL (neutron and photon cross sections) and ENDF/B-IV libraries were used in these calculations.In the region between 10 and 15 MeV, the calculated neutron spectra are in good agreement with the measurements (±5%). The maximum discrepan...