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.

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.

Measurement of fast neutrons with ^(238)U-coated fission chamber

Purpose Afission chamber with two layers of 238Ufissile materials has been developed for the measurements of fast neutrons.Methods The developed fission chamber has been tested by 60Co gamma source and 252Cf neutron source.Results The results have indicated that it is very easy to cut off the gamma rays from the neutrons by using a discriminator,when the fission chamber works in the pulse mode.The detector works well,even if the static air is used as the filling gas.Conclusion To discuss the application of the detector,Monte Carlo simulations have been performed by considering four 238U-coated fission chambers located outside the spallation target for the fast neutron measurement from spallation reaction.The simulation results have indicated that the detector can be used to measure the fast neutron flux and neutron flux ratio of four fission chambers.Furthermore,a 238U-coated fission chamber can be used within a reactor for longer time,in comparison with a 235U-coated fission chamber.

THE EARLY RELATIVE BIOLOGICAL EFFECTIVENESS OF SINGLE DOSE OF FAST NEUTRONS（35MeV_（p→Be）） FOR BONE MARROW IN MICE

The early RBE of the bone marrow in mice after studied irradiation with fast neutrons(35 MeVp→Be) was studied.60Co-γ ray was used for referent beams.Using the dos.making 50% loss of the nucleated cells of bone marrow in mice relative to control group mice to calculated the RBE value which was 2.13±0.18.Meanwhile,the relationship of the RBE values and the dose of neutrons was noted.On log-log plot the RBE values decrease with increasing dose of fast neutrons and it is consistent with a slope of -0.39± 0.10.The α/β ratios were estimated from linear-quadratic model of cell survival,they are 14.4±1.30 Gy for fast neutrons and 0.83±0.10 Gy for γ-ray,respectively.

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.

THE LATE RESPONSE OF PIG SKIN TO FRACTIONATED DOSES OF 35 MeV P→Be FAST NEUTRON IRRADIATION

The late damage in pig skin to fractionated doses of 35 MeV fast neutron was studied. Neutron fractionation scheme comprised of 12 fractions in 42 days. The latent period of late damage of 19. 8 , 22. 2 , 24. 6 and 27. 0 G y groups were 17. 00±1. 53, 13. 67±1. 45, 14. 00±2. 31 and 17. 00±2. 00 , weeks , respectively(P>0. 05). The ED50 value for late damage was 2 1 . 0 G y. The mean latency of late pig skin damage was not related to the total dose. However, the incidence of late damage was related to the total dose. The late damage in pig skin was characterized by a dusky/mauve erythema which could progress to dermal necrosis. The mean latency for the development of necroses was longer and it was harder to heal than the pig skin early reaction.

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.

A method of monitoring gas saturation in carbon dioxide injection heavy oil reservoirs by pulsed neutron logging technology

A method is proposed to characterize the fast neutron scattering cross-section ( s f) quantitatively by the combina-tion of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation of CO_(2)-injected heavy oilreservoirs based on the three-de tector pulsed neutron logging technology. Factors influencing of the evaluation effect of thismethod are analyzed and the effectiveness of this method is verified by a simulation example. By using the Monte Carlo simu-lation method and the physical model of bulk-volume rock, the relationship between s f and CO_(2) saturation is studied, and thesaturation interpretation model is established. The influences of formation temperature and pressure, heavy oil density, bore-hole fluid and reservoir methane content on the evaluation results of CO_(2) saturation are analyzed. The results show that thecharacterization of s f by the combination of secondary gamma information can eliminate the influence of formation lithology,borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO_(2) saturation, and the ef-fects of formation temperature and pressure and heavy oil density are negligible. The simulation example verified the feasibilityof the method for evaluating the CO_(2) saturation of CO_(2)-injected heavy oil reservoirs.

GENERALIZED THEORY OF NONLINEAR AND UNSTEADY MECHANICS AND APPLICATIONS TO PARTICLE PHYSICS

In this paper we consider that the momentum of a free particle motion withhigh-level speed presenting nonlinear effects may be expanded by using Laurent seriesand then obtain the complete expression of nonlinear and unsteady momentum. These nonlinear and unsieady phenoniena of high-level speed may further expand to the theory of kinematics and it may be determined by Fredholm's integral equation of the first kind. In addition, according to the nonlinear and unsteady momentum obtained the relations of the nonlinear mechanics equations .work and energy, mass and energymay be derived.Finaly .this paper also calculates those experimental results which done in particle physics for mu-mesons u±and fast neutrons n, these results are in agreement with data perfectly.

Micro-size picosecond-duration fast neutron source driven by a laser-plasma wakefield electron accelerator

A pulsed fast neutron source is critical for applications of fast neutron resonance radiography and fast neutron absorption spectroscopy.However,due to the large transversal source size(of the order of mm)and long pulse duration(of the order of ns)of traditional pulsed fast neutron sources,it is difficult to realize high-contrast neutron imaging with high spatial resolution and a fine absorption spectrum.Here,we experimentally present a micro-size ultra-short pulsed neutron source by a table-top laser-plasma wakefield electron accelerator driving a photofission reaction in a thin metal converter.A fast neutron source with source size of approximately 500μm and duration of approximately 36 ps has been driven by a tens of MeV,collimated,micro-size electron beam via a hundred TW laser facility.This micro-size ultra-short pulsed neutron source has the potential to improve the energy resolution of a fast neutron absorption spectrum dozens of times to,for example,approximately 100 eV at 1.65 MeV,which could be of benefit for high-quality fast neutron imaging and deep understanding of the theoretical model of neutron physics.

Influence of thermal and resonance neutron on fast neutron flux measurement by ^(239)Pu fission chamber

The ^239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a fiat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using ^10B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of ^239gpu are measured as 1.791 × 10^-16 2.350 × 10^-16 and 1.385×10^-15 per second for 15 mm thick ^10B cover, 0.5 mm thick Cd cover, and no cover respectively, while the fission reaction rate of 239pu is rapidly increased to 2.569×10^-14 for a 20 mm thick polythene covering fission chamber. The average 239pu fission cross-section of thermal and resonance neutrons is calculated to be 500 b and 24.95 b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30×10^6, 2.24×10^6 and 1.04×10^8 cm^-2·s^-1.

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.

The associated killing of hepatoma cells using multilayer drug-loaded mats combined with fast neutron therapy

Chemotherapeutic and radiation therapy have emerged as two most important treatment strategies to treat cancer in clinical practice;however,to improve anticancer efficacy,combination chemotherapy still remains challenge.Dichloroacetate(DCA)could produce significant cytotoxic effects in certain tumor cells through its distinct mechanism.Radiation therapy with fast neutrons(FNT)has high relative biolgical effectiveness compared to other radiotherapeutics.Herein,we reported the combination chemotherapy with FNT for effective tumor growth inhibition with the assistance of a multilayered nanofiber loading DCA and DCA derivatives.We first synthesized a biodegradable polylysine to condense DCA with negative charge,or to conjugate DCA by condensing synthesis,to obtain Ion-DCA and Co-DCA,respectively.DCA,Ion-DCA or Co-DCA was then loaded into fibers to form multilayer drug-loaded mats.Upon adhesion on the surface of subcutaneous and orthotopic liver tumors,the multilayer drug-loaded mats realized a controllable release of DCA,which reversed the Warburg effect and inhibited cancer cell proliferation.Meantime,irradiation of fast neutrons could seriously damage DNA structure.Combination of the controllable release of DCA and FNT resulted in synergistic cell apoptosis in vitro,and the tumor inhibition in vivo.This study thus provides a new approach to integrate chemotherapy and FNT with the assistance of biocompatible nanofiber for synergistic tumor therapy.

Study on the novel neutron-to-proton convertor for improving the detection efficiency of a triple GEM based fast neutron detector

A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier（GEM） detector, which, coupled with a novel multi-layered high-density polyethylene（HDPE） as a neutron-to-proton converter for improving the neutron detection efficiency, is introduced and tested with the Am-Be neutron source in the Institute of Modern Physics（IMP） at Lanzhou in the present work. First, the developed triple GEM detector is tested by measuring its effective gain and energy resolution with55 Fe X-ray source to ensure that it has a good performance.The effective gain and obtained energy resolution is 5.0×104and around 19.2%, respectively. Secondly, the novel multi-layered HDPE converter is coupled with the cathode of the triple GEM detector making it a high-efficiency fast neutron detector. Its effective neutron response is four times higher than that of the traditional single-layered conversion technique when the converter layer number is 38.

An MRPC for fast neutron detection

The possibility to detect fast neutrons with a multi-gap resistive plate chamber （MRPC） has been investigated. To detect fast neutrons, a thin polyethylene layer is coated on the surface of electrode glass as a fast neutron converter. The MRPC detects the charged particles generated by neutrons via the （n,p） reaction on hydrogen. A prototype detector has been developed and tested on fast neutron sources in order to evaluate its performance： good agreement between experimental results and simulation has been achieved. A detailed description of the detector and the experimental test results are presented.

An empirical formula for scattered neutron components in fast neutron radiography

Scattering neutrons are one of the key factors that may affect the images of fast neutron radiography. In this paper, a mathematical model for scattered neutrons is developed on a cylinder sample, and an empirical formula for scattered neutrons is obtained. According to the results given by Monte Carlo methods, the parameters in the empirical formula are obtained with curve fitting, which confirms the logicality of the empirical formula. The curve-fitted parameters of common materials such as 6 LiD are given.

Design of readout electronics based on peak-holding circuit and multiplexer for a fast neutron spectrometer

Background Fast neutron detection is meaningful in many research fields such as space environment monitoring.A scintillating fiber array model for fast neutron detection was proposed and developed in 1980s.Aerospace applications of the model require electronics in small size.Purpose To design a dedicated electronic system to readout and process the 384-channel signals from scintillating fiber array,and to use the designed system to fabricate a neutron detector for aerospace applications.Methods With the method of nuclear recoil,fast neutron is detected by tracking recoil proton of n–p scatter in scintillating plastic fibers.Using the peak-holding circuits and multiplexers,the system size and power consumption were reduced.Results The detector fabricated with the designed system,had 34 cm×34 cm×27 cm mechanical size,20.4 kg weight,and 30.05W power consumption.Comparing to traditional waveform sampling electronics,the designed electronics was highly integrated and had a small size.The readout electronics also gave a better energy resolution of 39%in neutron detection,while the energy resolution was 43%in previous version.Conclusion In this study,a highly integrated readout electronic system was designed and verified.The detector using the system gave good performance.The designed electronics had potential development in fast neutron detection and other high energy physics detection system.

Measurements of effective delayed neutron fraction in a fast neutron reactor using the perturbation method

A perturbation method is proposed to obtain the effective delayed neutron fraction βeff of a cylindrical highly enriched uranium reactor. Based on reactivity measurements with and without a sample at a specified position using the positive period technique, the reactor reactivity perturbation Ap of the sample in βeff units is measured. Simulations of the perturbation experiments are performed using the MCNP program. The PERT card is used to provide the difference dk of effective neutron multiplication factors with and without the sample inside the reactor. Based on the relationship between the effective multiplication factor and the reactivity, the equation βeff=dk/△ρ is derived. In this paper, the reactivity perturbations of 13 metal samples at the designable position of the reactor are measured and calculated. The average βeff value of the reactor is given as 0.00645, and the standard uncertainty is 3.0%. Additionally, the perturbation experiments for fleer can be used to evaluate the reliabilities of the delayed neutron parameters. This work shows that the delayed neutron data of 235U and 23SU froin G.R. Keepin＇s publication are more reliable than those from ENDF-B6.0, ENDF-B7.0, JENDL3.3 and CENDL2.2.

Thermal conductivity of boron carbide under fast neutron irradiation

Due to the complex products and irradiation-induced defects, it is hard to understand and even predict the thermal conductivity variation of materials under fast neutron irradiation, such as the abrupt degradation of thermal conductivity of boron carbide (B_(4)C) at the very beginning of the irradiation process. In this work, the contributions of various irradiation-induced defects in B_(4)C primarily consisting of the substitutional defects, Frenkel defect pairs, and helium bubbles were re-evaluated separately and quantitatively in terms of the phonon scattering theory. A theoretical model with an overall consideration of the contributions of all these irradiation-induced defects was proposed without any adjustable parameters, and validated to predict the thermal conductivity variation under irradiation based on the experimental data of the unirradiated, irradiated, and annealed B_(4)C samples. The predicted thermal conductivities by this model show a good agreement with the experimental data after irradiation. The calculation results and theoretical analysis in light of the experimental data demonstrate that the substitutional defects of boron atoms by lithium atoms, and the Frenkel defect pairs due to the collisions with the fast neutrons, rather than the helium bubbles with strain fields surrounding them, play determining roles in the abrupt degradation of thermal conductivity with burnup.