Cross-sections for deuteron photo-disintegration from 139 to 832 MeV

The cross-sections for deuteron photo-disintegration have been measured at nine c.m. angles from 37 to 143 degrees. The minimum and maximum photon energies have been 139 and 832 MeV respectively. The results are in agreement with earlier data above 300 MeV, but are significantly larger below 200 MeV, the discrepancies being up to 50% at the lowest energies measured.     

Scattering of negative pions on helium

Differential cross sections for negative pion scattering on ⁴He have been measured at five pion kinetic energies between 110 and 260 MeV in the angular range from 5° to 180°. Total cross sections have also been measured at eleven energies between 67 and 285 MeV. The differential cross sections have been fitted with a phenomenological expression for the nuclear scattering amplitude. Conventional phase shifts have been reconstructed starting from the parameters of the fits.     

Photoproduction of high-energy neutrons in thick targets by electrons in the energy range 150 to 270 MeV

Photoneutron spectra with energies greater than 12 MeV produced by electrons incident on a thick lead target have been measured for primary electron energies between 150 and 266 MeV and at a fixed angle of 90 ° to the beam axis. Measurements of the neutron yield have furthermore been performed at a primary energy of 234 MeV as a function of target depth for the same lead target and as a function of the mass number for C, Al, Cu, Cd and Pb targets. The results were obtained with three independent neutron detectors: two proton recoil counters and one time-of-flight set-up. The high-energy regions of the spectra are compared with the predictions of the phenomenological quasi-deuteron model and a satisfactory agreement in shape and scale of the spectra is found. Additional high-energy neutrons from pion reabsorption processes were observed at electron energies of 234 and 266 MeV.     

Polarization of protons from the C(d,p)C reaction

The polarization of protons from the ¹²C(d, p)¹³C reaction has been measured for deuteron bombarding energies between 3.9 and 5.8 MeV. Angular distributions of the polarization for protons leaving ¹³C in its ground state have been measured for laboratory angles between 10° and 135° at several energies in the vicinity of a resonance at 4 MeV in order to determine the effect of that resonance on the polarization. Additional measurements were made at 0.4 MeV intervals throughout the energy range. These measurements demonstrate that the compound-nuclear resonances observed in the cross section do not significantly alter the polarization angular distributions except at back angles. The shape of the observed polarization angular distributions at all energies is quite similar to previous results obtained for deuteron bombarding energies up to 15 MeV.     

On the mechanism of the reactions24,25,26Mg(n,α)21,22,23Ne at neutron energies near 14 MeV

Differential cross sections of the reactions²⁴Mg(n,α)²¹Ne,²⁵Mg(n,α)²²Ne, and²⁶Mg(n,α)²³Ne have been measured at neutron energies of 13.19,13.93 and 14.33 MeV, at 13.93 and 14.33 MeV, and at 13.47 and 13.93 MeV, respectively. In forward direction, differential excitation functions of those reactions have been measured at energies between 12.67 and 16.05 MeV. The results are analysed in terms of direct-reaction and compound-nucleus theories.     

Scattering of fast neutrons on238U,average energy and angular distributions of fission neutrons

Angular distributions of neutrons elastically and inelastically scattered from²³⁸U have been measured with a time-of-flight spectrometer at seven incident neutron energies between 1.5 and 5.5 MeV. Inelastic angular distributions for groups of unresolved levels are given for incoming neutron energies of 1.5, 1.9 and 2.3 MeV. The corresponding neutron cross-sections were obtained relative to then-p scattering cross-sections. The average energies and angular distributions of the fission neutrons were extracted from the measured fission neutron spectra at 1.5,1.9 and 2.3 MeV. Cross-section calculations based on a spherical optical model have shown to be inadequate to describe the neutron-nucleus interaction in case of strong nuclear deformation. The experimental reality may be better approached, instead, if the calculations are made using a potential which takes into account the deformation of the target nucleus. Some of the present measurements are interpreted in this theoretical perspective.     

Fission of238U induced by136Xe for energies close to the Coulomb barrier

Excitation functions and angular distributions have been measured for fission of²³⁸U induced by¹³⁶Xe ions with bombarding energies between 4.5 and 5.9 MeV/N. Structures expected theoretically as characteristic for Coulomb fission have not been observed. The Q-value of ?(7.5±1.0) MeV measured for bombarding energies below 4.7MeV/N, however, appears to be compatible with inelastic scattering (e.g. Coulomb excitation) rather than subcoulomb transfer followed by fission. The total kinetic energy of deep inelastic events at 5.9 MeV/N is consistent with the current knowledge about mass diffusion, but also (for the highest excitation energies) with a fast fission process in the presence of the projectile.     

A MEASUREMENT OF THE ELASTIC SCATTERING FOR REACTION 12C+28Si AT ENERGIES 56MeV—69MeV

The angular distributions of the elastic scattering for reaction ¹²C+²⁸Si have been measured at the energies 69.5MeV, 66MeV, 59MeV, 56MeV using the large area position sensitive ionization chamber. The experimental data are fitted by use of the optical model. The probable reasons of the enhancement and oscillation of the elastic scattering angular distribution are discussed.     

Nuclear reactions between oxygen isotopes

Elastic and inelastic cross sections have been measured for the system ¹⁶O + ¹⁷O at c.m. energies from 12.5 to 15.5 MeV, and for ¹⁶O + ¹⁸O at c.m. energies from 12 to 20 MeV, at angles between 60° and 125°. Position-sensitive detectors were employed, using the kinematic coincidence technique. The data have been analyzed with particular attention to the contributions of multiple-exchange processes.     

Evaporation residue cross sections from reactions with argon ions

Evaporation residue cross sections have been measured in argon bombardments of Ni, Ge, Ag, and Sb at energies ranging from 167 to 296 MeV. Earlier Sb results appear to be in error in the energy range above 200 MeV. Results are compared with statistical model calculations which include rotating liquid drop fission barriers.     

Temperatures and Excitation Energies of Hot Nuclei in Reactions of 40Ar+natAg,209Bi at MeV/u

Coincidence measurements of fission fragment and light charged particle have been perfotrmed for the reactions of ⁴⁰Ar+^natAg,²⁰⁹Bi at E/A=25MeV using 4 PPAC and 11 sets of ΔE-E telescopes.Angular correlations of fission fragment were ploted as a function of the folding angle between the two detected fission fragments.The linear momentum transfer distributions were derived by measuring angular correlations.The backward spectra of light particles detected in coincidence with fission fragments having different average〈LMT〉are analyzed with Maxwell distribution.After some corrections the initial temperatures of the hot nuclei are determined from the energy spectra.The excitation energies corresponding to the different average〈LMT〉are obtained considering the reaction Q values and pre-equilibrum emission.In the central collision of the ⁴⁰Ar+^natAg,²⁰⁹Bi reactions,excitation energies are measured to be about 4.2MeV/u,2.4MeV/u and temperatures about 6.1MeV,5.5MeV,respecdvely.In semi-central collision,excitaionen energies are measured to be about 3.5MeV/u,1.9MeV/u and temperatures about 5.8MeV,4.8MeV respectively.     

Elastic scattering of 11B from 209Bi in the energy range 49.8 ⩽ E ⩽ 84.1 MeV

The elastic scattering of ¹¹B from ²⁰⁹Bi has been measured at laboratory energies of 49.8, 51.3, 52.2, 52.8, 54.3, 55.8, 59.8, 64.8, 69.8, 74.8 and 84.1 MeV. These data have been analyzed using a microscopic optical model and the energy dependence of the real and the imaginary parts of the optical potential at near barrier energies has been determined. The “threshold anomaly” observed in the real part of the potential is found to be consistent with the dispersion relation which connects the real and the imaginary parts of the potential. Inelastic scattering and transfer reactions have also been measured at energies of 51.3, 55.8, 59.8 and 74.8 MeV. DWBA calculations for the 3⁻ state in ²⁰⁹Bi are made. From the measured transfer probabilities, using a semiclassical approach the strength of the form factors have been obtained. The fusion cross sections have been derived at these energies from the corresponding quasi-elastic scattering angular distribution data. The fusion cross sections calculated using the energy dependent barriers extracted from the energy dependent real parts of the potential compare well with, that determined from quasi-elastic scattering data and are also in good agreement with simplified coupled channels calculation for fusion incorporating important inelastic and transfer channels.     

Asymmetric mass distribution from the fusion-fission reaction40Ar+243Am

The mass distributions and total c.m. kinetic energies of fission fragments formed in the reaction⁴⁰Ar+²⁴³Am at bombarding energies of 214, 222, 240 and 300 MeV have been measured using the angular correlation method. Angular distributions and anisotropy for 222 and 300 MeV have also been obtained. A symmetric mass distribution corresponding to the decay of a highly excited compound nucleus was obtained at 300 MeV bombarding energy. However, with decreasing bombarding energy the fission fragment mass distribution becomes asymmetric, the most probable heavy fragment mass being about 200–210 amu.     

Energy dependence of fission probabilities induced by negative pions in Sn,Au and Bi

Fission probabilities induced by negative pions in Sn, Au and Bi at different energies using variety of nuclear track detectors have been studied. The target-detector assemblies in 4π-geometric configuration were irradiated at the AGS facility of Brookhaven National Laboratory, USA. After etching the exposed detectors at appropriate etching conditions the detectors have been scanned for the tracks of fission fragments produced as a result of interaction of pions with the target nuclei. Based on the track counts, the values of fission cross sections have been measured and fission probabilities have been calculated using the reaction cross-section calculated with the help of the cascade-exciton model code CEM95. The values of fission probability based on experimental fission cross-sections have been compared with the theoretically calculated values of fission probabilities obtained using the CEM95 code. Theoretical values of fission probability have been computed for incident pion energy up to 2500 MeV in Sn, Au and Bi for comparison to fission data for high energy negative pions at 500, 672, 1068, 1665 MeV and 2300 MeV energies for the same targets. The values of fission probability based on the experimental fission cross section and theoretically calculated values of fission probability have been compared. Reasonable agreement has been observed among the experimentally measured and theoretically computed values of fission probabilities. A saturation of probabilities has been observed for Au and Bi at higher energies, but for Sn an increase of probability with the increase of pion beam momentum up to 1665 MeV has been observed.     

Angular distributions of photoprotons from 208Pb

Angular distributions of photoprotons following the (e, e′p) reaction in ²⁰⁸Pb have been measured at incident energies of 25.0 MeV and 40.0 MeV. The proton energy distributions were measured at several angles and the angular distributions were obtained for several proton energy ranges. Proton groups at around 11.0 MeV and 15.3 MeV are separated for the angular distributions and the results show almost isotropic distributions, which indicate that these proton groups are emitted through IAR. The angular distributions for other slowly varying parts of the proton spectra proved strongly asymmetrical, indicative of interference between E1 and E2 transition.     

Elektron-Photon-Kaskaden in Blei bei Primärenergien von 100, 200 und 400 MeV

Electron initiated showers in compact lead plates at primary energies of 100, 200 and 400 MeV have been measured by means of a propane bubble chamber. Cut-offenergies of the shower electrons were measured from 1.5 to 7.5 MeV by the range in propane. The wide-spread range distribution was related to energy by a Monte-Carlocalculation. The results are compared with shower calculations of Nagel. The electron numbers show good agreement at depths between 2 and 15 rad. length. Radial and angular distributions agree also but cannot be measured with the same precision as the numbers.     

Complete Fusion Excitation Function for the 16O+natS Reaction

The complete fusion excitation function for the ¹⁶O+^natS reaction has been measured in the range of 50-75 MeV with a step of 1.0MeV by using 1a position sensitive △E-E telescope system. The model parameters have been extracted from data analysis.The striking gross structure of the excitation function has been observed. The energies of peaks are at ECM=38,43 and 48 MeV respectively.     

Differential cross sections of proton Compton scattering in the energy range between 450 and 950 MeV

The differential cross sections of the proton Compton scattering around the second resonance have been measured at a c.m. angle of 90° for incident photon energies between 450 MeV and 950 MeV in steps of 50 MeV, and at an angle of 60° for energies between 600 MeV and 800 MeV. The results show that the peak of the 2nd resonance agrees with that of the pion photoproduction process. We also calculated the proton Compton scattering based on unitarity and fixed-t dispersion relations. The calculation describes well the data of the cross section and the recoil proton polarization.     

Measurement of the Angular Distributions of Fission Fragments from the Neutron-Induced Fission of 240Pu Nuclei in the Energy Range of 1–200 MeV and Their Model Analysis

JETP Letters - The measured angular distributions of fission fragments of 240Pu nuclei have been presented and theoretically analyzed. Measurements at energies above 10 MeV have been performed for...     

Spectroscopic study of neutron shell closures via nucleon transfer in the near-dripline nucleus 23O

Neutron single particle energies have been measured in 23O using the 22O(d,p)23O*-->22O+n process. The energies of the resonant states have been deduced to be 4.00(2) MeV and 5.30(4) MeV. The first excited state can be assigned to the nu d3/2 single particle state from a comparison with shell model calculations. The measured 4.0 MeV energy difference between the nu s1/2 and nu d3/2 states gives the size of the N=16 shell gap which is in agreement with the recent USD05 ("universal" sd from 2005) shell model calculation, and is large enough to explain the unbound nature of the oxygen isotopes heavier than A=24. The resonance detected at 5.3 MeV can be assigned to a state out of the sd shell model space. Its energy corresponds to a approximately 1.3 MeV sized N=20 shell gap, therefore, the N=20 shell closure disappears at Z=8 in agreement with Monte Carlo shell model calculations using SDPF-M interaction.