Direct Neutron Capture for Magic-Shell Nuclei

In neutron capture for magic--shell nuclei the direct reaction mechanism can be important and may even dominate. As an example we investigated the reaction $^{48}$Ca(n,$\gamma)^{49}$Ca for projectile energies below 250\,keV in a direct capture model using the folding procedure for optical and bound state potentials. The obtained theoretical cross sections are in agreement with the experimental data showing the dominance of the direct reaction mechanism in this case. The above method was also used to calculate the cross section for $^{50}$Ca(n,$\gamma)^{51}$Ca.Comment: REVTeX, 7 pages plus 3 uuencoded figures, the complete uuencoded postscript file is available at ftp://is1.kph.tuwien.ac.at/pub/ohu/calcium.u

Experiments in the EXFOR library for evaluation of thermal neutron constants

E.J. Axton’s experimental database adopted in evaluation of thermal neutron constants by himself and also by a recent project to update the IAEA Neutron Standard was checked against the experimental literature and EXFOR library. We discovered that many data are found neither in the EXFOR library nor in the articles quoted by Axton due to various reasons. This paper summarizes the status of the experimental data cited by Axton in the experimental literature as well as in the EXFOR library

Ni elemental neutron induced reaction cross-section evaluation

A completely new evaluation of the nickel neutron induced reaction cross sections was undertaken as a part of the ENDF/B-V effort. (n,xy) reactions and capture reaction time from threshold to 20 MeV were considered for /sup 58/ /sup 60/ /sup 61/ /sup 62/ /sup 64/Ni isotopes to construct the corresponding reaction cross section for natural nickel. Both experimental and theoretical calculated results were used in evaluating different partial cross sections. Precompound effects were included in calculating (n,xy) reaction cross sections. Experimentally measured total section data extending from 0.7 MeV to 20 MeV were used to generate smooth cross section. Below 0.7 to MeV elastic and capture cross sections are represented by resonance parameters. Inelastic angular distributions to the discrete isotopic levels and elemental elastic angular distributions are included in the evaluated data file. Gamma production cross sections and energy distribution due to capture and the (n,xy) reactions were evaluated from experimental data. Finally, error files are constructed for all partial cross sections

INC (Intranuclear Cascade) model calculation of (. pi. /sup +/, p), (/bar p/, p) and (K/sup +/, p) spectra in the 1 GeV/c range

The proton inclusive spectra measured with 800 MeV/c ..pi../sup +/ beam (BNL) on light nuclei, and the 600 MeV/c /bar p/ beam (LEAR) on /sup 6/Li and /sup 63/Cu have been successfully interpreted in terms of the Intranuclear Cascade (INC) Model. According to the INC model predictions the /bar p/ induced reaction results in high pion yield for the light /sup 6/Li target case. This is attributed to the nonavailability of nucleons to be knocked out by the pions produced following the /bar p/ annihilation. While in the case of the heavier /sup 63/Cu target some of the internally produced pions are subsequently absorbed leading to thermal equilibration of the nuclear medium, resulting in a softer proton spectrum at the high energy end. Based on the INC model predictions, the K/sup +/ induced reactions could be studied to search for the ''true resonances'' beyond 1 GeV K/sup +/ energy. 10 refs., 7 figs

Deuteron breakup mechanism in the intermediate-energy region

In an earlier investigation, we have explored the possibility of explaining the deuteron breakup mechanism in terms of the Udagawa and Tannura (UT) formalism of the breakup-fusion process. The experimental doubly differential data were very well reproduced for the test case studies. However, the application of UT formalism of the spirit of DWBA involves the use of optical-model parameters for different nuclei and at different energies. The optical model parameters are not always unique. In the present study we investigate the deuteron breakup mechanism in terms of the semiclassical models of Serber (for the nuclear interaction part) and Dancoff (for the electromagnetic dissociation). In the case of Serber model the modification due to the finite range of the deuteron and the Glauber correction for the diffractive disassociation are considered. The modified deuteron breakup cross section either for the (d,p) or the (d,n) process is proportional to the product of the target radius and the deuteron radius (R{sub target} {center dot} R{sub deuteron}). The predicted proton/neutron spectrum is centered around 1/2 E{sub d} and forward peaked. The Coulomb dissociation of deuteron is attributed to the deuteron dipole excitation in the presence of the nuclear Coulomb field. The neutron/proton spectrum, resulting from the Coulomb breakup of the deuteron, is highly forward peaked and also centered around 1/2 E{sub d}. The systematics of the deuteron breakup neutron/proton spectra are investigated for medium to heavy target nuclei at 50--200 MeV deuteron energies. 10 refs., 4 figs

Some highlights in the evaluations of the thermal cross sections and resonance parameters of the actinides

The resonance parameters and thermal cross sections of /sup 235/ /sup 238/U and /sup 239/ /sup 240/ /sup 241/ /sup 242/Pu are reevaluated by considering the measurements carried out since 1973. Capture, scattering, fission cross sections as well as resonance integrals are calculated from the parameters and are compared with experimental values with the objective of achieving consistency between calculations and measurements. The Dyson-Metha ..delta../sub 3/ statistical analysis was applied in order to calculate average level spacings. Calculations of average radiative widths based on systematics are carried out and are compared with experimental values as well as with Moore's and Lynn's estimates

Least squares fit of thermal data for fissile nuclei

Since our previous paper was written, we have learned of one new set of measurements that would have been included had we known of it: Gwin, Spencer and Ingle's measurement of the nu-prompt ratios of the four fissile materials with respect to /sup 252/Cf. Their recently published paper reports revised final results for /sup 233/U, /sup 235/U and /sup 239/Pu and includes a measurement on anti nu/sub p/(241)/anti nu/sub p/(252) that was not attempted previously. In some of the fitted results reported here, we have replaced their earlier 1978/1981 values by the final 1984 set. The replacement has appreciable effect on some of the parameters. Another revised value that we have used here is Axton's 1984 revision (3.7509 +- 0.0107) of his 1982 /sup 252/Cf anti nu/sub p/ value (3.744 +- 0.021). The effect of including the revised result is not appreciable. Thermal constants for /sup 233/U, /sup 235/U, /sup 239/Pu, and /sup 241/Pu are given. 11 references. (WHK

Intranuclear cascade study of the hadron‐nucleus interactions at 1 GeV/c

The proton inclusive spectra measured with 800 MeV/c ..pi../sup +/ beam (BNL) on light nuclei, and the 600 MeV/c /bar p/ beam (LEAR) on /sup 6/Li and /sup 63/Cu have been successfully interpreted in terms of the Intranuclear Cascade (INC) Model. According to the INC model predictions the /bar p/ induced reaction results in high pion yield for the light /sup 6/Li target case. This is attributed to the nonavailability of nucleons to be knocked out by the pions produced following the /bar p/ annihilation. While in this case of the heavier /sup 63/Cu target some of the internally produced pions are subsequently absorbed leading to thermal equilibrium of the nuclear medium, resulting in a softer proton spectrum at the high energy end. Based on the INC model predictions the K/sup +/ induced reactions could be studied to search for the ''true resonances'' beyond 1 GeV K/sup +/ energy. 10 refs., 5 figs

Theoretical calculation of medium-energy proton-induced reactions on Al, Zr, and Pb

The intranuclear cascade model of nuclear reactions was used to calculate double differential cross sections for the (p,xn) reaction. The calculations were performed with a generalized version of the code VEGAS, CLUST. Model predictions are compared with recent experimental data. Calculated fast-particle spectral shapes at low angles are reproduced reasonably well for the experimental data. As one possible improvement to the model, the proton reaction cross sections were estimated independently using the prescriptions of Karol, and DeVries and Peng. The systematic trends that emerge from this analysis are discussed. 12 refs., 5 figs

Neutron cross sections

Neutron Cross SectionsIn addition to the extensive list of detailed individual resonance parameters for each isotope, this book contains thermal cross sections and average resonance parameters, as well as a short survey of the physics of thermal and resonance neutrons with emphasis on evaluation methods