THE EARLY RESPONSE OF PIG SKIN TO FRACTIONATED DOSES OF 35 MeV P-Be FAST NEUTRONS IRRADIATION

The early responses of pig skin to fractionated doses of fast neutrons (35 Mev P→B) were determined. A neutron fractionation scheme comprised of 12 fractions in 42 days. The lowest doses of Ⅰ, Ⅱ, Ⅲ degree erythema of pig skin by Irradiation were 16. 38, 17. 32 and 19. 78 Gy respectively. The ED50 Values for moist desquamation was 23. 40 Gy. The mean latency of early pig skin damage was prolonged with the decreasing of total dose. The degree and the incidence of early pig skin damage were associated with total dose.These results for fast neutron therapy facility can be extrapolated to the human situation with a high degree of confidence, so that the neutron dose which would yield acceptable skin damage in patients may be determined using the data presented here.

THE LATE EFFECTS ON BONE MARROWS IN MICE AFTER TOTAL BODY IRRADIATION BY P(35) BE FAST NEUTRONS AND γ RAYS

Purpose: To understand the late effects on bonemarrow after widefield or total body irrdiation withvarious types of radiation.Materials and Methods: Total body irradiationwith single dose of P(35) Be fast Neutrons and γ raysrespectively have been used in this study. Kunming strainmice were irradiated by fast neutrons produced bybombardment of beryllium target with 35MeV protonsand the dose rate was 0.12 to 0.14 Gy/min. Nine doselevels were used in fast neutrons irradiation from 0.20 to3.50Gy. The dose rate of 60Co γ rays was 0.60Gy/min andirradiation was in the range of 0.25 to 9.00Gy. Sixteendose points were studied. All animals without anesthesiawere irradiated whole body with single doses by fastneutrons and γ rays respectively, One group withoutirradiation was regarded as control group. 90 days afterirradiation all animals were sacrificed. The nucleatedcells of bone marrow and the peripheral blood cellsincluding WBC and lymphocytes were counted.Results: our study shows that the number ofnucleated cells of bone marrow in both fast neutrons andγ ray groups decreased with increase of the doses. Thereare significant differences between irradiated groups andzero line (control group) and the slopes are -1.41 ±0.55(p=0.038) and -0.98 ± 0. 24(P= 0.0015) for fast neutronsand γ rays respectively. There is no significant differencebetween the two kinds of radiation (p>0.05). The lateeffects on peripheral blood cells (WBC and lymphocytes)in mice after irradiation with single doses of neutrons andγ rays were signincantly lower than unirradiated group(P< 0.05). However, the dependence of the values ofperipheral blood cells on doses is not found and there areno significant differences between neutrons and γ raysgroups.Conclusions: Total body irradiation with neutronsor γ rays can suppress marrow in mice in the long-term,and is more obvious with increase of doses. There is nosignificant difference between neutrons and γ rays for thelate effects studied.

FAST NEUTRON RADIOTHERAPY FOR OSTEOSARCOMA

Twelve patients with advanced osteosarcoma were treated with fast neutron at the Neutron Therapy Facllity, The High-Energy Physics institute, Chinese Academy of Sciences. Five patients were operated in our hospital after radiotherapy, three were accepted fast neutron aloue, others added ￣(60)Co. The doses ranged from 660ucGy to 2168ncGy. The pain was released, the size of tumour was smaller in almost of the patients.Only one case was found to be histologically free of viable tumour. The skin reactions was serious, all the patients were in poor function of keen joint.

Comparison of Experiment and Simulation of the triple GEM-Based Fast Neutron Detector

A detector for fast neutrons based on a 10 × 10 cm^2 triple gas electron multiplier （GEM） device is developed and tested. A neutron converter, which is a high density polyethylene （HDPE） layer, is combined with the triple GEM detector cathode and placed inside the detector, in the path of the incident neutrons. The detector is tested by obtaining the energy deposition spectrum with an Am Be neutron source in the Institute of Modern Physics （IMP） at Lanzhou. In the present work we report the results of the tests and compare them with those of simulations. The transport of fast neutrons and their interactions with the different materials in the detector are simulated with the GEANT4 code, to understand the experimental results. The detector displays a clear response to the incident fast neutrons. However, an unexpected disagreement in the energy dependence of the response between the simulated and measured spectra is observed. The neutron sources used in our simulation include deuterium-tritium （DT, 14 MeV）, deuterium-deuterium （DD, 2.45 MeV）, and Am Be sources. The simulation results also show that among the secondary particles generated by the incident neutron, the main contributions to the total energy deposition are from recoil protons induced in hydrogen-rich HDPE or Kapton （GEM material）, and activation photons induced by neutron interaction with Ar atoms. Their contributions account for 90% of the total energy deposition. In addition, the dependence of neutron deposited energy spectrum on the composition of the gas mixture is presented.

Fast neutron radiation inactivation of Bacillus subtilis:Absorbed dose determination

In this paper,fast neutron inactivation effects of Bacillus subtilis were investigated with fission fast neutrons from CFBR-Ⅱreactor of INPC(Institute of Nuclear Physics and Chemistry)and mono-energetic neutrons from the Van de Graaff accelerator at Peking University.The method for determining the absorbed dose in the Bacillus subtilis suspension contained in test tubes is introduced.The absorbed dose,on account of its dependence on the volume and the form of confined state,was determined by combined experiments and Monte Carlo method.Using the calculation results of absorbed dose,the fast neutron inactivation effects on Bacillus subtilis were studied.The survival rates and absorbed dose curve was constructed.

Contrast sensitivity in 14 MeV fast neutron radiography

Fast neutron radiography(FNR) is an effective non-destructive testing technique.Due to the scattering effect and low detection efficiency,the detection limit of FNR under certain conditions cannot be determined.In order to obtain the minimum detectable thickness by FNR,we studied the contrast sensitivity of FNR lead samples,both theoretically and experimentally.We then clarified the relationship between pixel value and irradiation time,and sample materials and thickness.Our experiment,using a4-cm-thick lead sample,verified our theoretical expression of FNR contrast sensitivity.

Investigation of enhancement in planar fast neutron detector efficiency with stacked structure using Geant4

Geant4 based Monte Carlo study has been carried out to assess the improvement in efficiency of the planar structure of Silicon Carbide(SiC)-based semiconductor fast neutron detector with the stacked structure. A proton recoil detector was simulated, which consists of hydrogenous converter, i.e., high-density polyethylene(HDPE) for generating recoil protons by means of neutron elastic scattering(n, p) reaction and semiconductor material SiC, for generating a detectable electrical signal upon transport of recoil protons through it. SiC is considered in order to overcome the various factors associated with conventional Si-based devices such as operability in a harsh radiation environment, as often encountered in nuclear facilities. Converter layer thickness is optimized by considering 10~9 neutron events of different monoenergetic neutron sources as well as ^(241)Am-Be neutron spectrum. It is found that the optimized thickness for neutron energy range of 1–10 MeV is ~400 μm. However, the efficiency of fast neutron detection is estimated to be only 0.112%,which is considered very low for meaningful and reliable detection of neutrons. To overcome this problem, a stacked juxtaposition of converter layer between SiC layers has been analyzed in order to achieve high efficiency. It is noted that a tenfold efficiency improvement has been obtained—1.04% for 10 layers stacked configuration vis-à-vis 0.112% of single converter layer detector. Further simulation of the stacked detector with respect to variable converter thickness has been performed to achieve the efficiency as high as ~3.85% with up to 50 stacks.

Defects Induced by Fast Neutron Irradiation in GaAs

Defects induced by 5 and 9.5 MeV fast neutron irradiations in N-type HB single crystal GaAsare studied by the positron annihilation lifetime technique.Mono-and di-vacancies are created for the neu-tron irradiation to a fluence of 1013 n/cm2 and only rnono-vacancies are produced for the neutron irradia-tion to a fluence of 1011～1012n/cm2.It is found that the higher the irradiating neutron energy and flu-ence,the higher the intensity of the produced defects.As a result the defect production rate becomes in-creasingly more sensitive to the neutron fluence than to the neutron energy.The annealing behavior of thedefects is also investigated up to 750℃.Tri-vacaneies are formed between 450 and 620℃ in GaAs irra-diated to 1013 n/cm2 by 9.5 MeV neutrons.Three annealing stages are observed for the mono-,di-andtri-vacancies.

A study of beryllium moderator thickness for a fission chamber with fast neutron measurements

The detection efficiency of the fission chamber(FC) is very important for studying the neutron flux measurement(NFM) system in ITER. In this article, we mainly focus our attention on the influence of the moderator. With the Monte Carlo particle transport simulation tool named Geant4, we make a simulation of FC detection efficiency with different levels of thickness of a beryllium moderator.Two manufactured FCs for ITER-NFM systems are then used to test the parameters and performance. The test results agree well with our simulation.

Application of global variance reduction method to calculate a high-resolution fast neutron flux distribution for TMSR-SF1

The solid fuel thorium molten salt reactor(TMSR-SF1) is a 10-MWth fluoride-cooled pebble bed reactor. As a new reactor concept, one of the major limiting factors to reactor lifetime is radiation-induced material damage. The fast neutron flux(E > 0.1 MeV) can be used to assess possible radiation damage. Hence, a method for calculating high-resolution fast neutron flux distribution of the full-scale TMSR-SF1 reactor is required. In this study,a two-step subsection approach based on MCNP5 involving a global variance reduction method, referred to as forward-weighted consistent adjoint-driven importance sampling, was implemented to provide fast neutron flux distribution throughout the TMSR-SF1 facility. In addition,instead of using the general source specification cards, the user-provided SOURCE subroutine in MCNP5 source code was employed to implement a source biasing technique specialized for TMSR-SF1. In contrast to the one-step analog approach, the two-step subsection approach eliminates zero-scored mesh tally cells and obtains tally results with extremely uniform and low relative uncertainties.Furthermore, the maximum fast neutron fluxes of the main components in TMSR-SF1 are provided, which can be used for radiation damage assessment of the structural materials.

Water equivalence of some 3D dosimeters:a theoretical study based on the effective atomic number and effective fast neutron removal cross section

Effective atomic numbers for photon energy absorption(ZPEA_(eff)) and their corresponding electron numbers (NPEA_(eff)), and effective macroscopic removal cross sections of fast neutrons(RR) were calculated for 27 different types of three-dimensional dosimeters, four types of phantom materials, and water. The values of ZPEA_(eff) and NPEA_(eff) were obtained using the direct method for energies ranging from 10 keV to 20 MeV. Results are presented relative to water, for direct comparison over the range of examined energies. The effect of monomers that are used in polymer gel dosimeters on the water equivalence is discussed. The relation between Σ_R and hydrogen content was studied. Micelle gel dosimeters are highly promising because our results demonstrate perfect matching between the effective atomic number, electron density number, and fast neutron attenuation coefficient of water.

Energy and angular distribution of recoil proton of fast neutron in scintillation fiber:a simulation study

Due to their low cost,big reaction cross-section with neutrons,flexibility,and convenience for long distance data transfer,plastic scintillation fibers(PSF)have been increasingly used as detectors or sensors for high-energy neutron radiography.In this paper,Geant4 Monte Carlo simulation tool was used to obtain some characteristics of energy and angular distributions of recoil protons in plastic scintillation fibers irradiated by fast neutrons.The plastic fiber with BCF-20 as the core and an acrylic outer cladding was used in the simulation.The results show that there is a big range of energy and angular distribution of recoil protons in energies varying inversely with the recoil angle.

^(40)Ar/^(39)Ar Fast Neutron Activation Ages of Quartz from the Jinman Vein Copper Deposit in Western Yunnan and Their Significance

Quartz samples collected from the Jinman vein copper deposit in the Lanping Basin of western Yunnan were determined by \{\}\+\{40\}Ar/\{\}\+\{39\}Ar fast neutron activation techniques, and the spectra are characterized as being saddle\|shaped. The samples yielded a plateau age of \{58.05\}±\{0.54\} Ma, a minimum appearance age of \{56.76\}±\{0.81\} Ma and an isochron age of \{54.30\}±\{0.15\} Ma, the three ages being close to each other, indicating that the ages of the quartz samples so far determined are true and reliable. The plateau age represents the time of formation of Cu\|bearing quartz veins, which is corresponding to Early Himalayan. This age is also consistent with the time at which a tectonically thermal event (60 Ma) took place within the Lanping Basin, Yunnan Province. In consideration of the fact that copper ore and other ore types in the vast area of western Yunnan are concentrated mainly in the Early Himalayan strata, the authors believe that there must have existed some indispensable key factors leading to metallogenesis on a large scale during the Early Himalayan period in western Yunnan and also constraining in union the formation of ore deposits there.

Experiments on mine-detection with fast neutron activation

Fast neutron activation of nitrogen and oxygen contained in the explosives used for simulated mine samples has been preliminarily carried out in our laboratory. By spectroscopic analysis of characteristic γ-rays emitted from activated nitrogen and oxygen, mine can be identified almost instantly. This technique integrated with robottes would be a method for mine scavenging.

The Role of Replacing CdO by Fe₂O₃on the Fast Neutron Removal Cross Sections in Cd-Boro Phosphate Glass Shield

This work deals with the application of [MERCSF-N] computer program in calculating the macroscopic effective removal cross-section of fast neutrons, ΣR (cm-1), for two different boro phosphate glass systems: (0.5 - x) CdO-x Fe2O3-0.4 P2O5-0.1 B2O3 and (0.5 - x) B2O3-x Fe2O3-0.1 CdO-0.4 P2O5 (with 0.05 ≤ x ≤ 0.5 by mole), to realize from the role of iron in the attenuation process and hence the usefulness of the glass containing iron as neutrons shielding material. The effect of replacing cadmium and boron oxides by iron oxide has been analyzed which proved that iron is more efficient than cadmium in attenuating and removing fast neutrons and that the presence of small amounts of B2O3 at least 0.1 mole fraction, with iron is needed to aid improving the removal cross-section of iron phosphate glasses. Experimental IR results are developed and used to trace the structural change and confirm the role of iron in the removal cross section.

Fast Neutron Radiation Efiects on Bacillus Subtili

To examine the sterilizing effect and mechanism of neutron radiation, Bacillus subtills var. niger, strain （ATCC 9372） spores were irradiated with the fast neutron from the Chinese fast burst reactor II（CFBR-II）. The plate-count results indicated that the D10 value was 384.6 Gy with a neutron radiation dose rate of 7.4 Gy/min. The rudimental catalase activity of the spores declined obviously with the increase in the radiation dose. Meanwhile, under the scanning electron microscope, no visible influence of the neutron radiation on the spore configuration was detected even if the dose was increased to 4 kGy. The content and distribution of DNA double-strand breaks induced by neutron radiation at different doses were measured and quantified by pulsed- field gel electrophoresis （PFGE）. Further analysis of the DNA release percentage （PR）, the DNA breakage level （L）, and the average molecular weight, indicated that DNA fragments were obvi- ously distributed around the 5 kb regions at different radiation doses, which suggests that some points in the DNA molecule were sensitive to neutron radiation. Both PR and L varied regularly to some extent with the increase in radiation dose. Thus neutron radiation has a high sterilization power, and can induce falling enzyme activity and DNA breakage in Bacillus subtilis spores

fast neutron absorption spectroscopy;laser plasma accelerator;photo-nuclear neutrons;single neutron count

Fast neutron absorption spectroscopy is widely used in the study of nuclear structure and element analysis. However,due to the traditional neutron source pulse duration being of the order of nanoseconds, it is difficult to obtain a high-resolution absorption spectrum. Thus, we present a method of ultrahigh energy-resolution absorption spectroscopy via a high repetition rate, picosecond duration pulsed neutron source driven by a terawatt laser. The technology of single neutron count is used, which results in easily distinguishing the width of approximately 20 keV at 2 MeV and an asymmetric shape of the neutron absorption peak. The absorption spectroscopy based on a laser neutron source has one order of magnitude higher energy-resolution power than the state-of-the-art traditional neutron sources, which could be of benefit for precisely measuring nuclear structure data.

Corrections on energy spectrum and scatterings for fast neutron radiography at NECTAR facility

Distortions caused by the neutron spectrum and scattered neutrons are major problems in fast neutron radiography and should be considered for improving the image quality. This paper puts emphasis on the removal of these image distortions and deviations for fast neutron radiography performed at the NECTAR facility of the research reactor FRM-II in Technische Universit/it Mfinchen （TUM）, Germany. The NECTAR energy spectrum is analyzed and established to modify the influence caused by the neutron spectrum, and the Point Scattered Function （PSeF） simulated by the Monte-Carlo program MCNPX is used to evaluate scattering effects from the object and improve image quality. Good analysis results prove the sound effects of the above two corrections.