Y. Uwamino

Measurements of Secondary Neutrons Produced from Thick Targets Bombarded by High-Energy Helium and Carbon Ions

The angular and energy distributions of neutrons produced by 100 and 180 MeV/nucleon He and 100, 180, and 400 MeV/nucleon C 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 (NIRS), Japan. The neutron spectra in the forward direction have broad peaks of {approximately}60 to 70% of the incident particle energy per nucleon due to the break-up process, and they spread up to almost twice the projectile energy per nucleon. The neutron spectra are similar for the same incident energy of 100 MeV/nucleon for both He and C ions. The phenomenological hybrid analysis, based on the moving source model and the Gaussian fitting of the break-up process, could well represent the measured thick target neutron spectra. The experimental results are also compared with the calculations using the heavy-ion code, and the calculated results agree with the measured results within a factor of 2 margin of accuracy. This systematic study on neutron production from thick targets by high-energy heavy ions is the first experimental work performed by NIRS and will be useful for designing the shielding for the high-energy heavy-ion accelerator facility.

Measurements of Neutron Spallation Cross Sections of 12C and 209Bi in the 20- to 150-MeV Energy Range

The neutron spallation cross sections of {sup 12}C and {sup 209}Bi have been measured in the quasimonoenergetic p-{sup 7}Li neutron fields in the 20- and 150-MeV energy range. The irradiation experiments were performed at four cyclotron facilities: (a) the Institute for Nuclear Study (INS), University of Tokyo; (b) the Cyclotron and Radioisotope Center, Tohoku University; (c) the Takasaki Research Establishment (TIARA), Japan Atomic Energy Research Institute; and (d) the Institute of Physical and Chemical Research (RIKEN). The neutron spectrum has been measured with the time-of-flight method using an organic liquid scintillator, and the absolute value of peak neutron fluence has been estimated from the activation method of lithium target at INS, RIKEN, and the proton recoil counter telescope at TIARA. The cross-section data of {sup 12}C(n,2n){sup 11}C and {sup 209}Bi(n,xn) (x = 3.12) reactions are reported. The experimental data were compared with other experimental data [only for {sup 12}C(n2n){sup 11}C and {sup 209}Bi(n,3n){sup 207}Bi reactions] and the ENDF/B-VI high-energy file data. The comparison showed good agreement between the authors data and others. Their data of {sup 209}Bi(n,xn) reactions above 20 MeV and of {sup 12}C(n,2n){sup 11}C reactions above 40 MeV are the first experimental data and will be applied tomorexa0» high-energy neutron spectrometry for the Bi spallation detector.«xa0less

Measurement of neutron activation cross sections of energy up to 40 MeV using semimonoenergetic p-Be neutrons

This paper discusses an intense semimonoenergetic neutron field which was made using a simple beryllium target system bombarded by protons of nine different energies between 20 and 40 MeV. Natural sodium, aluminum, vanadium, chromium, manganese, copper, zinc, and gold samples were irradiated at this field, and gamma rays from the samples were observed by a germanium detector. The production rates of 17 radionuclides were obtained for the nine different neutron fields, and the excitation functions of these 17 reaction channels of {sup 23}Na(n,2n){sup 22}Na, {sup 27}Al(n,{alpha}){sup 24}Na, {sup 51}V(n,{alpha}){sup 48}Sc, {sup 51}V(n,p){sup 51}Ti, {sup 50}Cr(n,3n){sup 48}Cr, {sup 50}Cr(n,2n){sup 49}Cr, {sup 55}Mn(n,p{alpha}){sup 51}Ti, {sup 55}Mn(n,4n){sup 52}Mn, {sup 55}Mn(n,2n){sup 54}Mn, {sup 63}Cu(n,3n){sup 61}Cu, {sup 63}Cu(n,2n){sup 62}Cu, {sup 65}Cu(n,p){sup 65}Ni, {sup 64}Zn(n,t){sup 62}Cu, {sup 64}Zn(n,3n){sup 62}Zn, {sup 64}Zn(n,2n){sup 63}Zn, {sup 197}Au(n,4n){sup 194}Au, and {sup 197}Au(n,2n){sup 196}Au were obtained for neutron energies up to 40 MeV by using the SAND-II and the NEUPAC unfolding codes and also least-squares fitting. The initial guess value for these methods was obtained primarily from calculations of the ALICE/LIVERMORE82 code.

Measurement and calculation of neutron leakage from a medical electron accelerator

The leakage neutron spectra and dose equivalent were systematically measured in the irradiation field, treatment room, maze, and outside the shielding door at the microtron medical electron accelerator facility of the National Cancer Center, Tokyo. For these measurements, we used two types of multimoderator neutron spectrometers (Bonner spheres containing indium activation detectors and 3He detector), an aluminum activation detector, and a commercially available neutron rem counter. The measured results were compared with the combined calculation of the one-dimensional ANISN and two-dimensional DOT3.5 discrete ordinates transport codes. The calculation was performed by using a measured source spectrum in the irradiation field and by computer modeling of the maze entrance. The calculation indicated good agreement in spectral shape and agreement with experiment within a factor of 2 in absolute dose-equivalent values. This transport calculation was systematically repeated for different geometrical and material parameters, and simple analytical formulas and their parameters applicable for shielding design of a medical electron accelerator facility were obtained in general form.

Two types of multi-moderator neutron spectrometers: Gamma-ray insensitive type and high-efficiency type

Abstract Two types of multi-moderator neutron spectrometers were developed; one is a gamma-ray insensitive type, and the other is a high-efficiency type. An indium activation detector is loaded in the former spectrometer, which can measure the photon-dominant pulsed neutron field such as in the primary photon beam of a high-energy medical electron accelerator. The latter, in which a 3 He counter is loaded, is so sensitive that it can measure leakage neutrons from a well shielded facility or even the skyshine neutrons. The response functions of the spectrometers were measured by thermal and mono-energetic neutron standard fields, and were also calculated by the one-dimensional discrete ordinates transport code, ANISN. The measured and calculated responses showed generally good agreement. A benchmark measurement of 252 Cf fission neutrons by using these two spectrometers agreed well with the calculated spectrum. The spectrometers were used in the measurements of neutrons produced by a medical electron accelerator and of skyshine neutrons from an intense 14 MeV neutron source facility.

A Method to Estimate the Fast-Neutron Fluence for the Hiroshima Atomic Bomb

A new method to estimate the fast-neutron fluence of the Hiroshima atomic bomb is proposed. 63 Ni produced by the 63 Cu(n, p) 63 Ni reaction provides a unique measure by which to estimate the fast-neutron fluence of the Hiroshima/Nagasaki atomic bombs, because the half-life of 63 Ni is 100 years and 70% of the 63 Ni produced in a copper piece presently exists after 50 years. Using the neutron spectrum given in DS86 and the estimated cross section, we found that a piece of copper of about 10 g which was exposed at a point around 100 m from the hypocenter gives a measurable amount of 63 Ni using a low-background liquid scintillation counter. For the measurement of 63 Ni, accelerator mass spectrometry also seems to be applicable.

Semi-monoenergetic neutron field for activation experiments up to 40 MeV

Abstract A semi-monoenergetic high-energy neutron field for activation experiments was developed at the SF cyclotron of the Institute for Nuclear Study, the University of Tokyo, using a simple Be target system bombarded by 20, 25, 30, 35 and 40 MeV protons. The 1 and 2 mm thick Be targets were cooled by a water flow of 12 and 11 mm thick layers, respectively, which works as a proton beam stopper at the same time. The neutron spectra were measured with an NE213 scintillation counter and the energy resolution at their high energy peaks was corrected by calculations. The intensity was 4×10 15 to 1.6×10 16 [n sr −1 C −1 ] for the total neutrons of energy above 3 MeV, and 2×10 15 to 7×10 15 [n sr −1 C −1 ] for the high-energy peak neutrons. The irradiation point for the activation experiment is at 20 cm from the target, and the beam current is about 5 μA. The 27 Al(n, α), 197 Au(n, 2n) and 197 Au(n, 4n) reaction rates at the irradiation point were measured and they were compared with the calculation performed with the corrected neutron spectra and the cross sections in references. For the former two reactions, the measured and calculated data agreed well with each other, and the 197 Au(n, 4n) reaction cross section data in the reference were found to be overestimated.

Spectral measurements of neutrons, protons, deuterons and tritons produced by 100 MeV/nucleon He bombardment

Abstract We measured angular and energy distributions of neutrons, protons, deuterons and tritons produced by 100xa0MeV/nucleon He ions stopping in thick carbon, aluminum, copper and lead targets using the HIMAC (Heavy Ion Medical Accelerator in Chiba) of NIRS (National Institute of Radiological Sciences), Japan by using the time-of-flight method coupled with the Δ E – E counter system. The Δ E counter of the NE102A plastic scintillator was used to discriminate charged particles from noncharged particles and to measure charged particle energy spectra. The E counter of the NE213 liquid scintillator was used to measure neutron energy spectra. The experimental spectra were compared with the calculation using the LCS code and the calculated spectra are generally in rather good agreement with the measured spectra of these four secondary particles.

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.

Measurements of High-Energy Neutrons Penetrated Through Concrete Shields Using Self-TOF, NE213, and Activation Detectors

Abstract Neutron energy spectra penetrated through concrete shields were measured using three types of high-energy neutron detectors: the Self-TOF detector, an NE213 organic liquid scintillator, and Bi and C activation detectors, which have been newly developed by a group at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) facility of the National Institute of Radiological Sciences, Japan. Neutrons were generated by bombarding 400 MeV/nucleon C ions on a thick (stopping-length) copper target. The neutron spectra were obtained through an unfolding code with their response functions and compared with LAHET and MCNPX calculations combined with the LA150 cross-section library. The calculations tend to overestimate with increasing the shielding thickness compared to the experimental results. The neutron fluence measured by the NE213 detector was simulated by the track length estimator in the MCNPX code, and the contribution of the room-scattered neutrons was evaluated. The neutron fluence attenuation length was obtained from the experiment for each detector and the calculation in the energy range of 20 to 800 MeV.