Measurement and analysis of neutron spectra from a thick Ta target bombarded by 7.2A MeV 16O ions (original) (raw)
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Analysis of neutron emission spectra for 30–50 MeV α-particle induced reactions in thick targets
Physical Review C, 2003
Comparisons of calculated neutron yield distributions from ␣-particle induced reactions on thick targets are made with measured data to analyze the initial reaction process in the framework of the exciton ͑hybrid͒ model code ALICE91 ͑M. Blann, Lawrence Livermore National Laboratory Report UCID 19614, 1982͒. We have considered two reaction mechanisms: dissolution of the ␣ in the nuclear field, and preequilibrium processes initiated by ␣-nucleon collisions. Both these processes seem to contribute to the emitted neutron spectra in varying proportions depending on the incident ␣ energy and possibly on the target nucleus. Contributions from other processes appear to be non-negligible.
Neutron energy spectra at the forward direction produced from stopping-length thick graphite, aluminum, iron and lead targets bombarded by 250 MeV protons were measured at the neutron TOF course at RCNP of Osaka University. The experiments were performed by the time-of-flight technique with the flight path length of 11.4m and 67.8m, and neutron energy spectra were obtained in the energy range from 10 MeV to 250 MeV. To compare the experimental data, Monte Carlo calculations by PHITS, MCNPX, and JQMD+INC codes were performed. It was found that these calculation results at 0-degree generally underestimated the experimental data for all targets in the energy range above 20 MeV.
Physical Review C, 2000
The angular and energy distributions of neutrons produced by 400 MeV/nucleon Ar, Fe, and Xe, and 800 MeV/nucleon Si ions stopping in thick C, Al, Cu, and Pb targets were measured using the Heavy-Ion Medical Accelerator in Chiba of the National Institute of Radiological Science ͑NIRS͒, Japan. The neutron spectra in the forward direction have broad peaks which are located at about 60 to 70 % of the incident particle energy per nucleon due to breakup and knock-on processes, and spread up to almost twice as much as the projectile energy per nucleon. The resultant spectra were integrated over energy to produce neutron angular distributions. The total neutron yields for each system were obtained by integrating over the angular distributions, and we could estimate the total yields using a simple formula. The experimental results are compared with the calculations using the heavy-ion collision Monte Carlo code, and the calculated results rather agree with the measured results. The phenomenological hybrid analysis, based on the moving source model and the Gaussian fitting of the breakup and knock-on processes, could also well represent the measured thick target neutron spectra.
Neutron emission spectra and angular distributions at 25.7 MeV neutron bombarding energies
Nuclear Physics A, 1983
Inelastic scattering of 25.7 MeV neutrons to unresolved final states with excitation energies up to -13 MeV were measured for monoisotopic samples of "V, 56Fe, 65Cu, 93Nb and 209Bi. Time-of-fight spectra were taken at several angles between 25" and 14.5" using the beam swinger spectrometer. Double differential cross sections, angle-integrated spectra and energy-binned angular distributions are compared with the predictions of pre-equilibrium theory.
Neutron Production in Thick Targets Irradiated with High-Energy Ions
Physics Research International, 2011
The neutron production in thick targets irradiated with 1 GeV protons was studied experimentally, and results are well understood with model calculations, including MCNPX 2.7a. However, one observes very large neutron production rates in the interaction of 44 GeV 12C onto thick Cu-, Pb-, and U-targets beyond calculated rates. The experimental spallation product yield curve in a 20 cm thick Cu target irradiated with 72 GeV 40Ar also cannot be reproduced by several model codes, including MCNPX 2.7a. This may be due to secondary fragments produced in high energy ( GeV) heavy-ion interactions which destroy target nuclei more effectively than primary ions. These observed experimental facts constitute “unresolved problems” from a fundamental point of view. It may have an impact on radiation protection issues for future heavy-ion accelerators.
Systematics and empirical expressions for neutron emission from thick targets in α-induced reactions
Physical Review C, 2005
The effect of two initial exciton (particle-hole) configurations, namely 4p0h and 5p1h, on the angular distribution of neutron emission from α-induced reactions on various thick targets have been analyzed. In the angular distribution of emitted neutrons the relative contribution of the 4p0h configuration is found to vary as the cosine of the angle of emission. Using such dependence, empirical expressions are developed for the total neutron yield, energy spectra, and angular distribution of neutrons in α-induced reactions in the 25-200-MeV energy range. These expressions are based on empirical fits to the hybrid model calculations of neutron emission from target elements in the mass range 9 Be to 209 Bi. The results of these calculations are compared with experimental data showing fairly good agreement. The empirical expressions provide a simple, fast, and reliable tool for calculating neutron emission essentially required for radiation shield design and other applications.
Physical Review C, 1983
We measured neutron time-of-flight spectra from 90 MeV protons and 140 MeV alpha particles bombarding thin targets of Al, Ni, Zr, and Bi at laboratory angles between 20 and 135. The lowenergy (5 to 45 MeV) portions of the spectra were measured with 5 cm diameter by 5 cm deep NE-213 counters at 1 m flight paths with n-y pulse-shape discrimination. The high-energy (35 to 150 MeV) portions of the spectra were measured with 12.7 cm diameter by 10.2 cm deep NE-102 counters at flight paths of 2.0 to 5.0 m. The proton-induced measured neutron spectra reveal three distinct energy regions: a low-energy evaporation region, a high-energy region dominated by the quasifree scattering process, and an intermediate-energy region dominated by multistep, preequilibrium processes. In the latter two regions, the spectra show strong angular dependence. The alphaparticle induced neutron spectra show these same distinct energy regions plus an exponential falloff above the beam energy per nucleon. The neutron spectra are compared with earlier proton spectra produced also by 90 MeV protons and 140 MeV alpha particles. It is observed that the high-energy portions of the forward-angle neutron and proton cross sections are in ratios consistent with the idea that single nucleon-nucleon scattering dominates. For the heavy-mass targets, the low-energy evaporation regions show neutron yields larger than proton yields. The proton-to-neutron ratios observed in the high-energy continua are interpreted with a quasifree calculation fitted simultaneously to the proton and the neutron spectra. Preequilibrium calculations with the exciton model and the hybrid model reproduce the shape of the experimental angle-integrated energy spectra down to lower energies than the quasifree calculations. The exciton model calculations underestimate the magnitudes of the cross sections, while the hybrid model provides better absolute agreement. One of the preequilibrium calculations uses the method of Mantzouranis and Weidenmuller to predict angular distributions; we find that the predicted angular distributions overestimate the neutron yields at forward angles. The intranuclear-cascade model predicts proton-to-neutron ratios much smaller than experimentally observed in the high-energy forward-angle continua.
Nuclear Physics A, 2001
We present a three source analysis of velocity spectra of light c harged particles (LCP) and neutrons emitted in the reaction 40 Ar+ 27 Al at 44 A.MeV. The light particle (LP) velocity spectra are studied as a function of the detection angle (1.5 < <172 ) and of the charge of the forward detected projectile-like fragment (PLF). The temperature parameter, the velocity a n d t h e i n tensity of each source are extracted as a function of the PLF charge. While the temperature parameters for PLF and target-like f r a g m e n ts (TLF) are very similar and show a dependence on the PLF charge, the temperature parameter for the intermediate source is approximately 15 MeV, independent of the PLF charge. Comparison with temperature values extracted from double isotopic ratios, shows an agreement o n l y b e t ween the temperature values extracted Experiment performed at GANIL. 1 from formula involving 3 He, 4 He, d, t ratios and the PLF proton temperature parameter. The characteristics of the PLF sources are derived. Present results are discussed with regards to the degree of thermalization which c o u l d b e achieved in the PLF and TLF sources. Keywords: Intermediate energy, 40 Ar+ 27 Al reaction, E=44 A.MeV,
Annals of Nuclear Energy - ANN NUCL ENERG, 2008
In this study, by using equilibrium and pre-equilibrium reaction mechanisms, the (p,xn) cross-sections of the spallation neutron target nuclei 50,52,53,54 Cr and 63,65 Cu were investigated for incident proton energies up to 100 MeV. The excitation functions for pre-equilibrium reaction mechanisms were calculated by using a hybrid model, a geometry dependent hybrid model, the full exciton model and the cascade exciton model. Equilibrium effects were calculated according to the Weisskopf-Ewing model. The calculation results were also compared with the measurements in literature.