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A measurement of high-energy neutron streaming was performed through a maze at the CERN (Conseil Européen pour la Recherche Nucléaire) High-energy AcceleRator Mixed-field (CHARM) facility. The protons of 24 GeV/c were injected onto a 50-cm-thick copper target and the released neutrons were streamed through a maze with several corridor-legs horizontally designed with the shield walls in the facility. Streaming neutrons were measured by using aluminum activation detectors placed at 10 locations in the maze. From the radionuclide production rate in the activation detectors, the attenuation profile along the maze was obtained for the reaction of 27Al(n,α)24Na. Monte Carlo simulations performed with two codes, the Particle and Heavy Ion Transport System (PHITS) and CERN FLUktuierende KAskade (FLUKA), gave good agreements with the measurements within a factor of 1.7 for the production rates ranging over more than 3 orders of magnitude.

To devise an activation technique for characterizing mixed radiation fields, secondary particles from a copper target irradiated by 24 GeV/c protons were measured at the CERN High-energy AcceleRator Mixed field facility (CHARM). Activation detector sets consisting of aluminum, niobium, indium, and bismuth, were placed at 30 cm from the target at angles of 15° to 160° with respect to the beam axis. The nuclides generated in these detectors due to irradiation by secondary particles were analyzed by γ -ray spectrometry, and the angular distributions of the production rates were obtained. The results of Monte Carlo calculations using FLUKA code was compared with the experimental results. The calculated results well agreed with the measured data at all angles. The influence of competitive reactions on the measured data were also evaluated by FLUKA. The following nuclear reactions, with low affectivity by competitive reactions, were identified as promising tools for characterizing mixed radiation fields: the 115In( n , n ′ ) 115 m In reaction for detecting neutrons emitted by the evaporation process, the 93Nb( γ , n ) 92 m Nb reaction for verifying the photon distribution generated by neutral-pion decay ( π 0 → 2 γ ), and the 209Bi( p , 4 n )206Po reaction, which detects secondary protons.

The BigRIPS in-flight fragment separator in the RIKEN Radioactive Isotope Beam Factory project has been operated for nine years. Intense beams of heavy ions up to uranium with the beam power of 1-13 kW and the energy of 230-45 MeV/nucleon were used to produce the radioactive isotope beams by the BigRIPS fragment separator. The first superconducting triplet quadrupoles (STQ1) is in close proximity of the production target in the BigRIPS fragment separator and has been exposed to high radiation. The STQ1 consists of three air-core NbTi coils, wound by the wet-winding method, assembled in the liquid-helium bath cryostat. Based on the operation records of the superconducting magnet and its cryogenic system, the accumulated dose to the coils is evaluated to be order of 1 MGy. The observed impurities in the helium gas, such as tritium and hydrocarbons in the STQ1 cryostat, are presented as a possible radiation effect. Based on the excitation data of training ramps, we discuss the movement of the coils and a possible degradation of coils. No distinct degradation in the coil performance can be observed after nine years of operation.

The angular distribution of neutrons produced from a 4-mm-thick beryllium target bombarded with a 345-MeV/u 238U beam was measured outside the target chamber using bismuth and aluminum activation detectors at angles of 4.5°, 10°, 30°, 60°, 70° and 90° from the beam axis. Following two hours of irradiation and photo-peak analyses, the production rates of the radionuclides were obtained for the 209Bi(n,xn)210-xBi(x = 4–12) and 27Al(n,α)24Na reactions. Using the Particle and Heavy Ion Transport code System (PHITS), a Monte Carlo simulation of the production rates was performed and the ratios of the calculated to the experimental results (C/E) ranged from 0.6 to 1.0 generally and 0.4 to 1.3 in worst cases.

Neutrons generated from thin beryllium target by 50 MeV/u 238 U beam were measured using activation analysis at 15, 30, 45, and 90 degrees from the beam direction. A 0.085 mm-thick Be stripper of RIBF was used as the neutron generating target. Activation detectors of bismuth, cobalt, and aluminum were placed out of the stripper chamber. The threshold reactions of 209 Bi(n, xn)210-x Bi(x=4~8), 59 Co(n, xn)60-x CO(x=2~5), 59 Co(n, 2nα)54 Mn, 27 Al(n, α)24 Na, and 27 Al(n,2nα)22 Na were applied to measure the production rates of radionuclides. The neutron spectra were obtained using an unfolding method with the SAND-II code. All of production rates and neutron spectra were compared with the calculated results using Monte Carlo codes, the PHITS and the FLUKA. The FLUKA results showed better agreement with the measurements than the PHITS. The discrepancy between the measurements and the calculations were discussed.

On March 15-17 and April 8, 2011, right after the accident at Fukushima nuclear power plant, γ-ray dose-rate distributions and spectra were measured on expressways in Fukushima and neighboring prefectures using an NaI(Tl) dosimeter and a LaBr3 spectrometer. A radioactive plume was observed near Koriyama-city on 15. Although the distributions of Te, I, Cs, Cs, and Cs resembled each other, the distribution of I was different from the others. The dominant radionuclides of dose rate were Te and I on March 15-17 and Cs and Cs on April 8. The initial distribution profile of the dose rate on March 15-17 remained on April 8, which showed the deposited radioactive material was not moved from the initial location and there was no additional effective deposition of radioactivity after March 15.

In Fukushima and neighboring prefectures, the distributions of dose rate and γ-ray count rate of radionuclides from the Fukushima Daiichi Nuclear Power Station were measured on expressways on March 15, 16, 17, and April 8, 2011, using an NaI(Tl) detector and a LaBr3 detector. A radioactive plume that contained 133Xe, 132Te, 132I, 131I, 134Cs, and 136Cs was observed at Koriyama on the afternoon of March 15. The plume arrived in the Nakadori region of Fukushima prefecture, which is surrounded by two mountain ranges, and most of the radioactivity there was deposited by rainfall. Although the distributions of 132Te, 132I, 134Cs, 136Cs, and 137Cs were similar, the distribution of 131I was different from the others. The effective nuclides for the dose rate measurement were 132Te and 132I on March 15-17 and 134Cs and 137Cs on April 8. The initial distribution profile of the dose rate on March 15-17 was retained on April 8 because the deposited radioactive material was not moved from the initial location and there was no additional effective deposition of radioactivity.

The RIKEN RI (radioactive isotope) Beam Factory is scheduled to commence operations in 2006, and its maximum energy will be 400 MeV u - 1 for ions lighter than Ar and 350 MeV u - 1 for uranium. The beam intensity will be 1 pμA (6 × 10 1 2 particles s - 1 ) for any element at the goal. For the hands-on-maintenance and the rational shield thickness of the building, the beam loss must be controlled with several kinds of monitors. Three types of radiation monitors will be installed. The first one consists of a neutron dose equivalent monitor and an ionisation chamber, which are commercially available area monitors. The second one is a conventional hand-held dose equivalent monitor wherein the logarithmic signal is read by a programmable logic controller based on the radiation safety interlock system (HIS). The third one is a simple plastic scintillator called a beam loss monitor. All the monitors have threshold levels for alarm and beam stop, and HIS reads all these signals.

Irradiation experiments were performed at the Heavy Ion Medical Accelerator in Chiba (HIMAC) facility, National Institute of Radiological Sciences. The radioactive spallation products in a thick Cu target were obtained for Ar(230, 400 MeV/nucleon), Si(800 MeV/nucleon), Ne(100, 230, 400 MeV/nucleon), C(100, 230, 400 MeV/nucleon), He(100, 230 MeV/nucleon), p(100, 230 MeV) ions. The gamma-ray spectra from irradiated Cu, C, Al, Cr, Fe, Ni, Pb samples inserted into the composite Cu target were measured with a HPGe detector. From the gamma-ray spectra, we obtained the reaction cross section data on the Cu, C, Al, Cr, Fe, Ni and Pb samples. The measured cross sections were fitted to a modified form of Rudstam’s semi-empirical formula in order to evaluate the cross sections of unmeasured nuclides. These estimated cross sections were added to the experimental yields for each mass number and the total mass-yield and isobaric charge distributions. We also calculated the cross sections for the production of residual nuclides by high-energy heavy ions by the particle and heavy-ion transport code system (PHITS) code and compared with measured results. The PHITS code provides good results on cross section calculations.

We measured activities of some kinds of aggregate of concrete irradiated by neutrons which were emitted from copper bombarded by 400MeV/nucleon neon beam. Through the gamma-ray spectrometry over a half of year, 36 radioactive nuclides were observed. Activities induced by neutrons were calculated by using the Monte Carlo simulation code NMTC/JAM, MCNP and DCHAIN-SP2001. We discussed differences between experimental results and calculated ones.

We measured angular and energy distributions of neutrons from an iron target bombarded by 210 MeV protons at angles of 0°, 7.5°, 15°, 30°, 60°, 90° and 110° using the RIKEN Ring Cyclotron . The measured results are compared with the calculations using the MCNPX and NMTC/JAM codes with several physics models. These calculations generally agree with the measurements except at forward angles. We also show the angular distribution and total neutron yield from 0° to 180°, integrated above 5 MeV , to compare with similar experiments in the medium energy region of projectile protons.

Irradiation experiments were performed at the HIMAC (Heavy Ion Medical Accelerator in Chiba) facility, National Institute of Radiological Sciences, Japan. The radioactivity distributions of spallation products in a thick Cu target were obtained by irradiating 230 and 100MeV/nucleon Ne, C, He, p and 230MeV/nucleon Ar ions. The gamma-ray spectra from thin irradiated samples of C, Al and Cu inserted into a Cu target were measured with a HPGe detector. From the gamma-ray spectra, we obtained the spatial distribution of radioactive yields of spallation products of about 40 nuclides in Cu sample in the Cu target. Our results agree with other experimental data. We also calculated the spatial distribution of residual radioactivities in the Cu target by the PHITS (Particle and Heavy-Ion Transport code System) code and compared with measured results. The PHITS code provides good results on residual activity calculations.

The radioactivities of spallation products in a Cu target were obtained by bombarding 230 and 100 MeV/nucleon Ne, C, He, p ions. Irradiation experiments were performed at the HIMAC (Heavy Ion Medical Accelerator in Chiba) facility, National Institute of Radiological Sciences. The gamma-ray spectra from irradiated samples were measured with a HPGe detector. From the gamma-ray spectra, we obtained the variation of radioactivities of nuclides produced in Cu sample with Cu target thickness and the mass-yield distribution of nuclides produced in Cu sample on the surface of Cu target. The results showed that the dependence of the cross sections on the projectile mass strongly depends on the mass number difference between Cu and produced nuclide.

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory (RAL), United Kingdom. ISIS is a 800 MeV–200 μA proton accelerator facility. Neutrons are produced from a tantalum target, and are shielded with approximately 3-m thick steel and 1-m thick ordinary concrete. On top of the shield, we measured the neutron flux attenuation through concrete and iron shields, which were additionally placed up to 120-cm and 60-cm thickness, respectively, using activation detectors of graphite and bismuth. The attenuation lengths of concrete and iron for high-energy neutrons above 20 MeV were obtained from the 12 C(n, 2n) 11 C reaction of graphite.

A quasi-monoenergetic neutron field was developed using a thin 7 Li target bombarded by protons in the energy range from 70 to 210 MeV at the RIKEN ring cyclotron facility. The neutron energy spectra were measured with an NE213 organic liquid scintillator using the TOF method. The absolute peak neutron yields were obtained by measurements of 478 keV γ-rays from 7 Be nuclei produced in a 7 Li target through the 7 Li( p,n) 7 Be (g.s.+0.429 MeV) reaction. Using the neutron field, the absolute values of the neutron response functions of a 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator were measured, and were compared with calculations using a Monte Carlo code developed by Cecil et al. The measured response functions without any wall-effect events were also obtained, and compared with calcualtions using a modified Monte Carlo code. Comparisons between a measurement and a calculation both with and without any wall-effect events gave a good agreement.

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory (RAL), UK. ISIS is an 800 MeV–200 μA proton accelerator facility. Neutrons are produced from a tantalum target, which is shielded with approximately 3-m thick iron and 1-m thick ordinary concrete in the upward direction. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2-m and 0.6-m thicknesses, respectively, using the activation detectors of graphite, bismuth, aluminum and the multi-moderator spectrometer inserted indium. The attenuation lengths of concrete and iron for high-energy neutrons above 20 MeV produced at 90° to the proton beam were obtained from the 12 C ( n ,2 n ) 11 C reaction rates of graphite. The neutron spectra through concrete and iron were obtained by the unfolding analysis of the reaction rates of the 12 C ( n ,2 n ) 11 C , 27 Al ( n , α ) 24 Na , 209 Bi ( n ,x n ) 210−x Bi (x=4–10) and 115 In ( n , γ ) 116m In in the energy range of thermal to 400 MeV.

The absolute values of the neutron response functions of a 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator were measured using a quasi-monoenergetic neutron field in the energy range of 66– 206 MeV via the 7Li(p,n)7Be reaction in the ring cyclotron facility at RIKEN. The measured response functions were compared with calculations using a Monte Carlo code developed by Cecil et al. The measurements clarified that protons escaping through the scintillator wall induced by high-energy neutrons increase from 6% for 66 MeV neutrons to 35% for 206 MeV neutrons, and that this wall effect causes a difficult problem for n–γ discrimination. Measured response functions without the wall-effect events were also obtained by eliminating the escaping-proton events in the analysis, and compared with calculations using a modified Monte Carlo code. Comparisons between the measurements and calculations both with and without any wall-effect events gave a good agreement, but some discrepancy in the light output distribution could be found, mainly because the deuteron generation process was not taken into account in the calculation. The calculated efficiencies for 10 MeVee threshold, however, also gave good agreement within about 10% with the measurements.

The deep penetration of neutrons through thick shield has become a very serious problem in the shielding design of high-energy, high-intensity accelerator facility. In the design calculation, the Monte Carlo transport calculation through thick shields has large statistical errors and the basic nuclear data and model used in the existing Monte Carlo codes are not well evaluated because of very few experimental data. It is therefore strongly needed to do the deep penetration experiment as shielding benchmark for investigating the calculation accuracy. Under this circumference, we performed the following two shielding experiments through concrete and iron, one with a 800 MeV proton accelerator of the Rutherford Appleton Laboratory (RAL), England and the other with a high energy heavy iron accelerator of the National Institute of Radiological Sciences (NIRS), Japan. Here these two shielding benchmark experiments are outlined.

In order to estimate the accuracy of calculation methods such as an empirical formula and Monte Carlo codes for neutron and gamma ray flux in a room with a Cu target irradiated by 68-MeV-proton, experimental analyses are carried out. The analyses reveals that (1) the NMTC/JAERI code is applicable to source neutron calculation, (2) the Patterson’s equation with Ishikawa’s parameter is useful and estimates thermal neutron flux conservatively and (3) the MCNP calculation underestimates the fast neutron scattered back from the wall of the room, consequently the secondary gamma ray from the wall.

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory. ISIS is an 800MeV-200 μ A proton accelerator facility. Neutrons are produced from a tantalum target, and are shielded with approximately 3m thick iron and 1 m thick ordinary concrete. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2 m and 0.6 m thicknesses, respectively, using activation detectors of carbon, aluminum and bismuth, and also indium-loaded multi-moderator spectrometer. The dose attenuation was simultaneously measured with the neutron and photon survey meters. The attenuation lengths of concrete and iron for high energy neutrons above 20MeV were obtained from the 12C(n,2n) reaction of carbon, and the neutron spectra penetrated through the additional shield and on the target shield top were obtained from the 12C(n,2n), 27Al(n,α) and 209Bi(...

We have measured angular and energy distributions of neutrons produced by 100 and 180 MeV/u He, 100, 180, 400 MeV/u C, 100, 180, 400MeV/u Ne, 400MeV/u Ar, 400MeV/u Fe, 400MeV/u Xe and 800MeV/u Si 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. The neutron spectra in the forward direction have broad peaks of about 60 to 70 % of the incident particle energy per nucleon due to the break-up process and spread up to almost the twice of the projectile energy per nucleon. The neutron spectra are similar for the same incident energy for different projectile particles. The experimental results are compared with the calculations using the HIC code, and the calculated results agree with the measured results within a factor of 2. 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...

Construction of the RIKEN RI Beam Factory is started, and the phase 1 will be finished by the end of March 2003. Two ring cyclotrons including one superconducting machine and two Big RIPSs will be constructed in the phase 1. Heavy ions of proton to uranium will be accelerated up to 400 MeV/u (A < 40) and 150 MeV/u for uranium at an intensity of 1013 pps.Neutron production by the 400-MeV/u 20Ne beam was measured at HIMAC of NIRS and it was used for the source term of the shielding calculations. The deep penetration of high-energy neutrons was calculated by using the ANISN code with the DLC-119/HILO86R group constants and also by using the HETC code. The ANISN results were modified by using the HETC results and the shielding experiment at ISIS, and they were fitted by a simple formula for practical use.High-energy neutron penetrations of slantwise injection and the reflection probabilities of iron slab were calculated with the HETC code, and these results were used for the estimation of the thickness for th...

Deep penetration calculations were performed using the intra-nuclear-cascade-evaporation Monte Carlo code, HETC-KFA2, and a one-dimensional Sn code, ANISN, combined with a DLC119/HIL086 multi-group cross section library to compare a shielding experiment at ISIS. In this experiment the reaction rates of 12C(n,2n) in graphite activation detectors have been measured outside the bulk shield, that is 284-cm thick iron and 94-cm-thick concrete, and also outside 119-cm diameter additional shields of 20~120cm thick concrete and 10~60cm thick iron which were newly added to the bulk shield.The secondary neutron spectrum at 90 degree from the tantalum target bombarded by 800 MeV protons was calculated with the HETC-KFA2 code and was used for the source neutrons for a deep penetration calculation. For the Monte Carlo calculation, the geometry of the bulk shield was divided into approximately 100-cm-thick slabs, and step-by-step calculations were carried out for deep penetration in good statistics. 12C(n,2n) reaction ...

In order to estimate the accuracy of calculation methods such as empirical formulas and Monte Carlo codes for neutron and gamma ray fluxes through a labyrinth connected with a room having a Cu target irradiated by 68-MeV-proton, experimental analyses are carried out. As results of the analyses, the followings are obtained. (l)The MCNP calculation is applicable to estimation of neutron and gamma ray dose equivalent rates in the labyrinth, although cross sections in the process of neutron thermalization and gamma ray production cross section should be modified for more precise estimation. (2)The empirical formulas are useful for estimation of neutron dose equivalent rate. However, an additional safety factor of 2 should be required to apply to the estimation of total dose equivalent rates, because the contribution of gamma ray dose equivalent rate increases with the distance in the labyrinth and becomes comparable to that of neutron dose equivalent rate at the distance longer than 20 m.

Following our preceding study on thick target neutron yields by He and C, we measured angular and energy distributions of neutrons produced by 100, 180 and 400 MeV/nucleon Ne ions stopping in thick carbon, aluminum, copper and lead targets using the heavy ion medical accelerator of the National Institute of Radiological Sciences. 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 break-up process and spread up to almost twice as much as the projectile energy per nucleon. The neutron spectra at all angles consist of two components of cascade neutrons and evaporation neutrons. The phenomenological hybrid analysis of the moving source model for these two components and the Gaussian fitting of break-up process could well represent the measured thick target neutron spectra. The experimental results are also compared with the calculations using the HIC code, and the calculated results generally agree with the meas...

In our previous work, we have measured the neutron spallation cross sections of 12C and 209Bi in the 20-to 150-MeV energy range. Here in this succeeding study, the neutron activation cross sections on spallation reactions for 59Co and natCu have been measured in the quasi-monoenergetic p-7Li neutron fields in the 40-to 120-MeV energy range which have been established at two cyclotron facilities of Takasaki Research Establishment of Japan Atomic Energy Research institute (TIARA) and the Institute of Physical and Chemical Research (RIKEN). The neutron spectrum has been measured with the TOF (Time of Flight) method using an organic liquid scintillator, and the absolute value of peak neutron fluence has been determined from the proton recoil counter telescope at TIARA and the activation method of lithium target at RIKEN. In this study, the following seventeen neutron activation cross section data are reported which produce 56Mn, 54Mn, 52Mn, 58Co, 57Co, 56Co, 55Co, 59Fe from 59Co reactions and 56Mn, 59Fe, 60Co...

A quasi-monoenergetic neutron field was developed using the 7Li(p, n)7Be reaction in the energy range from 70 to 210 MeV in the ring cyclotron facility at RIKEN. Neutrons were generated from a 10-mm-thick 7Li target injected by protons accelerated to 70, 80, 90, 100, 110, 120, 135, 150, 210 MeV. The neutron energy spectra were measured with an NE213 organic liquid scintillator using the TOF method. The absolute peak neutron yields were obtained by measurements of 478 keV c-rays from 7Be nuclei produced in a 7Li target through the 7Li(p, n)7Be (g.s.#0.429 MeV) reaction. Two relative neutron fluence monitors, which were calibrated to the absolute peak neutron fluences by the 7Be measurement, were equipped along the neutron beam line during an irradiation experiment. This high-energy neutron field is very useful for neutron cross-section measurements, response measurements of neutron detectors, and shielding experiments. ( 1999 Elsevier Science B.V. All rights reserved.

国内のいくつかの加速器施設に開発された数keVから200 MeVに至る広いエネルギー範囲の単色中性子場の特徴と,それを用いた検出器の特性測定,中性子核反応や放射化断面積の測定,遮蔽実験など様々な中性子実験の現状を紹介する。

A p-7Li quasi-monoenergetic neutron field for activation experiment has been developed at energies between 18 and 38 MeV. The absolute neutron intensity was accurately determined from the number of 7Be nuclei produced in the 7Li target which is equal to the number of the monoenergetic peak neutrons released in the 4π direction. The angular distribution function of the peak neutrons is necessary for the estimation of the monoenergetic neutrons emitted in the forward direction for the sample irradiation. The distribution function was measured for proton energies of 20, 30 and 40 MeV and was collected from papers for energies between 25 and 800 MeV to get the universal curve. Activation experiments of various natural and enriched samples were performed at this quasi-monoenergetic neutron field. Here we show the neutron activation cross sections of the 197Au(n, 2n)196Au, 197Au(n, 4n)194Au and 59Co(n, 2nα)54Mn reactions as examples.

We developed a new phoswich detector. The detector consists of an inner NE213 organic liquid scintillator and an outer thin CaF2(Eu) crystal which are coupled to a photomultiplier. The charged particles produced in the NE213 scintillator by the interaction of radiation with the detector either stop in the NE213 scintillator or pass through both the NE213 scintillator and the outer CaF2(Eu) crystal. The fast output pulses of a few ns from the NE213 scintillator can easily be separated from the slow output pulses of about 1 μs from the outer CaF2(Eu) scintillator. From this difference, the events that the charged particle stops inside NE213 scintillator can be separated out from the events that the charged particle escapes from the inside NE213 detector. The phoswich detector response functions for gamma rays and neutrons measured with the radioactive gamma-ray sources and the neutrons produced by a Be + Cu target bombarded by protons from the cyclotron, and compared with Monte Carlo calculations. It was found that the main characteristics of the NE213 scintillator were not degraded by assembling as a phoswich detector using the CaF2(Eu) crystal wall. The n-γ discrimination property is slightly degraded but neutrons can be separated from gamma rays. Further we used to test the phoswich detector for neutron measurements under the intense charged particles, mainly protons, with considering the possibility of neutron detection in space crafts. It was shown that the phoswich detector is capable of detecting neutrons in the mixed field.

Neutron activation cross sections between 15 and 40 MeV were measured by the activation method using a monoenergetic neutron field based on the 7Li(p,n)7Be reaction. Natural samples of carbon and c...

Applications of accelerators to fields other than nuclear physics have been increasing more and more. As the fields expand, a greater variety of ions with wider accelerating energies are being used in these accelerator facilities. The thick-target neutron yield (TTNY) is the base data used for the shielding design as well as for the application of these accelerator facilities to estimate the neutron production rate in the facilities. However, so far, very few data of differential TTNY have been measured except for protons. Even for alpha particles, the number of measurements is not enough. Because of the lack of measured data, a study on TTNY for heavy ions has not been done. A practical calculation method for estimating the data for heavy ions has still not been established. Here, generalized parameterization of the differential thick-target neutron yield (TTNY) is obtained by studying systematics in the differential TTNY based on moving source parameters deduced from experimentally obtained differential TTNYs for light and heavy ions. The yields of equilibrium neutrons (ENs) and nonequilibrium neutrons (NENs) are expressed by simplified expressions. The variation of the nuclear temperature of the EN is scaled with the excitation energy transferred to the target-like fragment. The nuclearmore » temperature of the NEN is reproduced fairly well by the Fermi gas model. The scaling of the velocity parameter of the EN is considered based on the breakup fusion mechanism. The velocity of the NEN component is compared with the corresponding data for the proton emission. The velocity is related to the relative speed between projectile and target nuclei at contact.« less

Measurements of the double-differential thick-target neutron yield are made for 75- and 120-MeV 12C5+, 153-MeV 16O5+, and 40-MeV alpha particles bombarding carbon, aluminum, copper, and lead target...

A systematic study was made on the equilibrium and nonequilibrium neutron production cross sections for heavy ions based on intranuclear cascade evaporation model calculations. The cross sections were estimated by the HIC code at 337 MeV/u for projectiles of α, 12 C, 20 Ne and 40 Ar and targets of 12 C, 56 Fe and 207 Pb. Using the calculated cross sections, simple expressions for the production cross sections of both the equilibrium and nonequilibrium neutrons, that were previously proposed at a lower energy range through the analysis of experimental data, were extended to higher energies. The extended formulae well reproduced the systematic behaviors of the cross sections with varying the projectile and the target nuclei. The extended expression of the equilibrium neutron cross section is further modified so that a separate component of the cross section for each of the target-like and projectile-like fragments is described. The obtained expression is tested by HIC calculated data, showing a good reproducibility of the cross sections for both the fragments.

The possibility of a crossed beam facility of slow neutrons capturing unstable nuclei is examined in connection with the Japanese Hadron Project. With a pulsed proton beam of 50 Hz repetition and with a 100 μA average beam current, one obtains a spallation neutron source of 2.4 × 10 8 thermal neutrons/cm 3 /spill over a 60 cm length with a 3 ms average duration time by using a D 2 O moderator. By confining radioactive nuclei of 10 9 ions in a beam circulation ring of 0.3 MHz revolution frequency, so that nuclei pass through the neutron source, one obtains a collision luminosity of 3.9 × 10 24 /cm 2 /s. A new research domain aimed at studying rapid processes in nuclear genetics in a laboratory will be created.

The electrochemical calorimetry of the electrolysis of D2O has been carried out using a Pd cathode in an undivided, open cell fashion, together with measuring the total volume of the evolved gases....

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.

A low background neutron measuring system has been constructed. The background neutron counting rate is 1.4 counts/h and the long term stability is within 0.1 counts/h over one year. The detection efficiency for fission neutrons from 252 Cf is 4.4%. The system is capable of measuring low rate neutron emission events with a half life of 10 20 yr. The rate of neutron production from copper and lead by cosmic-rays was measured in an underground laboratory. The system was used for an experimental test of neutron emission from the electrolysis of D 2 O. The results show no enhancement of neutron emission. No tritium production was observed.

Spectral measurements of intermediate-energy neutrons (i.e., En ≤ 65 MeV) transmitted through iron, lead, graphite, and concrete shields are described. Concurrently, transmitted spectra of associat...

Measurements of neutron response functions of a 3 in. × 3 in. NE-213 scintillator were made for neutron energies from 10 MeV to 73 MeV using neutrons from a quasi-monoenergetic neutron source of p- 7 Li and a white source from thick Be and Cu targets. Neutrons sampled into small energy bins by TOF signals were utilized in the response measurements. Response functions calculated by the Monte Carlo method were compared with the measured data, thus clearing problems in the calculation model. Based on the measured and calculated data, a new response matrix which covered from 0 to 76 MeV was constructed. The matrix was successfully applied to unfold a pulse-height spectrum of up to several tens of MeV neutrons that were transmitted through a 50 cm concrete shield.

Experimental data for the $^{27}\mathrm{Al}$(n,2n${)}^{26}$Al cross section have never been reported in the neutron energy range above 15 MeV, since the detection of the long-lived $^{26}\mathrm{Al}$ (half-life of 7.2\ifmmode\times\else\texttimes\fi{}${10}^{5}$ yr) necessitates an intense high-energy neutron source and highly sensitive detection method. We have measured the $^{27}\mathrm{Al}$(n,2n${)}^{26}$Al cross section in the energy range of 14--36 MeV by using a semimonoenergetic neutron beam from the Be(p,n) reaction. The activity of $^{26}\mathrm{Al}$ was measured by the accelerator mass spectrometry method and we found that the cross section has a maximum value of 95 mb in the neutron energy range of 20--24 MeV.

Particle radiotherapy using proton and heavy ion beams has shown improved clinical results and is a promising cancer therapy which is expected to gradually spread in Japan. There are, however, no special regulations for radiotherapy treatment facilities. They have been operated under the same safety regulations as for a research facility using a research accelerator. Significantly high-energy radiation is necessary for particle radiotherapy compared with conventional radiation therapy. The treatment facility, therefore, should have a large accelerator, which is installed in a room with a thick shield wall. Data on radiation protection for such high energy medical facilities is fragmentary and insufficient. In this study, we examined the necessity of other regulations for the safe operation of medical facilities for particle radiotherapy. First, we measured activation levels of the therapeutic devices and of patients. Next the safety level of the medical facility was evaluated from the viewpoint of radiation protection. We have confirmed the facilities can be safely operated by present regulations given in the Law Concerning Prevention from Radiation Hazards due to Radiation Isotopes, etc. or the Law for Health Protection and Medical Care.