Kazuo Shin

Transmission Through Shields of Quasi-Monoenergetic Neutrons Generated by 43- and 68-MeV Protons —I: Concrete Shielding Experiment and Calculation for Practical Application

The energy spectra of neutrons that penetrate 25- to 200-cm-thick concrete shields are measured using 40- and 65-MeV quasi-monoenergetic neutron sources at the 90-MeV AVF cyclotron of the Takasaki Ion Accelerator Facility for Advanced Radiation Application at the Japan Atomic Energy Research Institute.

Transmission through Shields of Quasi-Monoenergetic Neutrons Generated by 43- and 68-MeV Protons —II: Iron Shielding Experiment and Analysis for Investigating Calculational Method and Cross-Section Data

Neutron spectra in the energy range above 10{sup {minus}4} eV transmitted through iron shields succeedingly are measured with a BC501A liquid scintillation detector and the Bonner Ball detector using quasi-monoenergetic neutron sources generated via the {sup 7}Li(p,n) reaction by 43- and 68-MeV protons. Using the collimated source neutrons, the spectra are obtained on the neutron beam axis and at off-center positions. The calculations using the MORSE-CG and DOT3.5 codes with the DLC119 group cross-section data sets as well as the HETC-KFA2 code are carried out and compared with the measurements.

Neutron Production from Thick Targets of Carbon, Iron, Copper, and Lead by 30- and 52-MeV Protons

The energy spectra of neutrons emitted by thick targets of carbon, iron, copper, and lead at angles of 0, 15, 30, 45, 75, and 135 deg to the incident beam of 30- and 52-MeV protons were obtained by unfolding the pulse height distributions measured with an NE-213 scintillator. The angular distribution of neutrons above 3 or 4 MeV was obtained by integrating the measured spectra. The measured spectra were compared with a Monte Carlo calculation based on the Fermi free gas model of intranuclear cascades and evaporation. This comparison revealed that the calculated spectra are harder and stronger in the forward direction, but softer and weaker in the backward direction than are the experimental spectra. There is good agreement between the two at about 75 deg. This experimental result showed that the calculational model is not adequate in the energy region below about 100 MeV, where nuclear structure has a great influence on neutron production. The total neutron yield was obtained by estimating the neutron yield below a few million electron volts by fitting the spectra measured above that energy to the Maxwellian distribution and showed good agreement with other experimental results.

Propagation of Errors from Response Functions to Unfolded Spectrum

AbstractAn analysis was made on the propagation of errors from the response functions to the unfolded spectrum in the unfolding process from a pulse height distribution to an energy spectrum. In the derivation of formulas, the terms of high variance were ignored. Assumed errors of the response functions were limited to statistical errors in Monte Carlo calculations for the response functions. The unfolding processes used were the SIMPLE method and the FERDO method. The test calculations were done assuming typical spectra having a sharp peak and the 252Cf fission spectrum. The response errors can have a serious influence on the flux error, especially in the case of a sharply peaked spectrum.

A combined technique of nuclear reaction analysis and plasma-driven permeation for a quantitative study on deuterium trapping

Abstract A new method of the in-situ depth-profiling technique was developed, in which the deuterium depth profile by nuclear reaction analysis (NRA) and the deuterium permeation flux of the plasma-driven permeation (PDP) were observed at the same time for a sample membrane, one side of which was continuously exposed to a deuterium plasma. The dissolved deuterium concentration in the sample was known from the permeation flux of the PDP and the trapped deuterium concentration was obtained from NRA. The trapping energy for deuterium in nickel, which was prebombarded with 0.8 MeV 4 He ions, was determined from the observations at the steady state at sample temperatures of 398 to 685 K. It was 0.24 eV, which suggested that the traps were associated with vacancies produced by the 4 He bombardment. This was supported by the fact that the depth profile of the trapped deuterium agreed well with the estimated distribution of the displaced host atoms.

Simultaneous measurement of prompt neutrons and fission fragments for 239Pu(nth, f)

The multiplicity and energy of the prompt neutrons emitted from the fission fragments for 239Pu(nth, f) were measured as functions of the fragment mass and total kinetic energy. The results were compared with those for 233U(nth, f) and with the predicted values by the multi-channel fission theory with the random neck rupture model. The measured and predicted values of the neutron multiplicity, ⟨V⟩(m*), show the saw-tooth trend and agree with each other. The total neutron multiplicity decreases linearly with increasing total kinetic energy resulting in —d⟨TKE⟩/d⟨Vtot⟩=16.5±0.4MeV/neutron. The slope of the neutron multiplicity vs. the total kinetic energy, —d⟨V⟩/d⟨TKE⟩, was plotted against the fragment mass. Its shape agrees with that for 233U(nth, f). The average neutron emission energy, ⟨η⟩(m*), follows a bell shape about the symmetric fission accompanying higher values for very asymmetric fissions and agrees with that for 233U (nth, f). The total excitation energy (TXE)(m*) was determined by two manners: (1) neutron data and (2) Qmax—⟨TKE⟩. Both results satisfactorily agree with each other as the case of 233U( nth, f), and thereby the present derivation of ⟨TKE⟩ from the neutron data is confirned.

Application of the EGS4 Monte Carlo Code to a Study of Multilayer Gamma-Ray Exposure Buildup Factors of up to 40 mfp

Multilayer γ-ray exposure buildup factors of up to 40 mfp were calculated using an electron-photon cascade Monte Carlo code, EGS4, as a point isotropic source. A kind of splitting technique was used in the EGS4 calculations in order to obtain reasonable results at very deep penetration problems, such as 40 mfp. The double-layer γ-ray exposure buildup factors were calculated for combinations of water, iron and lead for 0.1, 0.3, 0.6, 1.0, 3.0, 6.0 and 10MeV γ-rays. The thickness of the first medium was set to 1, 5, 10 or 20 mfp. As typical triple-layered shields, the calculations were performed for 4 different configurations of water, iron and lead. The behavior of multilayer buildup factors for deep penetration problems was studied using the obtained results. Buildup factors after the bounday show the tendency to vary largely depending on the material combination and the source energy of γ-rays.

Thick-target neutron yield for charged particles

Applications of particle accelerators have been increasing in a variety of fields other than nuclear physics, namely, heavy-ion accelerators for medical therapy, light-ion accelerators for an intense neutron source, materials research, and radioactive waste incineration. The energy and ion species used in these facilities span a wide range. For the shielding design of the facilities, inclusive neutron production data, especially differential thick-target neutron yields (TTNYs), are fundamental to estimating source terms of the design calculation. Here, measurements of the double-differential thick-target neutron yield are made for 75- and 1,120-MeV{sup 12}C{sup 5+}, 153-MeV{sup 16}O{sup 5+}, and 40-MeV alpha particles bombarding carbon, aluminum, copper, and lead targets. The measured data are parameterized by using the two-component moving source model. The systematic variation of the equilibrium neutron (EN) yield with incident ions and targets is analyzed by using the thus-obtained moving source parameters, and a simple expression is proposed to describe the systematics in the EN yield. The systematic change in the nonequilibrium neutron (NEN) yield was formulated to a simple expression by using the local hot spot model. The proposed expression reproduced well the measured EN and NEN yields.

Deuterium Plasma-Driven Permeation in Heliotron E During Discharge Cleaning and in a Small Plasma Device

AbstractTwo experiments on the plasma-driven permeation (PDP) of deuterium through nickel membranes were conducted. One was an observation of the permeation during the discharge cleaning of Heliotr...

Light Charged-Particle Production in Proton-Induced Reactions on 12C, 27Al, 58Ni, 90Zr, 197Au, and 209Bi at 42 and 68 MeV

Double-differential cross sections (DDXs) have been measured for light-charged particle production in proton-induced reactions on 12C, 27Al, 58Ni, 90Zr, 197Au, and 209Bi at incident energies of 42 and 68 MeV. The measured DDXs for 12C, 27Al, and 58Ni are compared with the LA150 evaluation. Good overall agreement is found except for the (p, xd) reaction. The dependence of total yields of secondary charged-particles on target mass number is investigated.