Gamma-Ray Shielding Effectiveness of Some Alloys for Fusion Reactor Design

The gamma-ray shielding effectiveness of some oxide dispersion-strengthen (ODS) alloys by means of mass attenuation coefficients, mean free path, exposure buildup factors and energy absorption buildup factors have been investigated in the present study. The buildup factors were calculated using geometrical progression method for photon energy 0.015–15 MeV up to 40 mfp penetration depth. The mass attenuation coefficients were calculated by using XCOM program and Geant4 simulation methods and found a very good agreement. Our investigation signifies that the low iron content ODS alloys are superior shielding materials with the lower buildup factors. This study should be useful for selection of shielding materials for their applications in fusion reactors design and future nuclear reactor technologies.     

Calculation of photon attenuation coefficient and dose rate in concrete with the addition of SiO_2 and MnFe_2O_4 nanoparticles using MCNPX code and comparison with experimental results

One of the most important safety features of nuclear facilities is the shielding material used to protect the operating personnel from radiation exposure. The most common materials used in radiation shielding are concretes. In this study, a Monte Carlo N-Particle eXtended code is used to calculate the gamma-ray attenuation coefficients and dose rates for a new concrete material composed of MnFe_2O_4 nanoparticles, which is then compared with the theoretical and experimental results obtained for a SiO_2 nanoparticle concrete material. According to the results, the average relative differences between the simulations and the theoretical and experimental results for the linear attenuation coefficient(l) in the SiO_2 nanoparticle materials are 6.4% and 5.5%, respectively. By increasing the SiO_2 content up to 1.5% and the temperature of MnFe_2O_4 up to 673 K, l is increased for all energies. In addition, the photon dose rate decreases up to 9.2% and3.7% for MnFe_2O_4 and SiO_2 for gamma-ray energies of0.511 and 1.274 MeV, respectively. Therefore, it was concluded that the addition of SiO_2 and MnFe_2O_4 nanoparticles to concrete improves its nuclear properties and could lead to it being more useful in radiation shielding.     

Photon energy absorption and exposure buildup factors for deep penetration in human tissues

Using photons in therapeutic and diagnostic medicine requires accurate computation of their attenuation coefficients in human tissues.The buildup factor,a multiplicative coefficient quantifying the ratio of scattered to primary photons,measures the degree of violation of the Beer-Lambert law.In this study,the gamma-ray isotropic point source buildup factors,specifically,the energy absorption buildup factor (EABF) and exposure buildup factor,are estimated.The computational methods used include the geometric progression fitting method and simulation using the Geant4 (version 10.4) Monte Carlo simulation toolkit.The buildup factors of 30 human tissues were evaluated in an energy range of 0.015-15 MeV for penetration depths up to 100 mean free paths (mfp).At all penetration depths,it was observed that the EABF seems to be independent of the mfp at a photon energy of 1.5 MeV and also independent of the equivalent atomic number (Zeq)in the photon energy range of 1.5-15 MeV.However,thebuildup factors were inversely proportional to Zeq for energies below 1.5 MeV.Moreover,the Geant4 simulations of the EABF of water were in agreement with the available standard data.(The deviations were less than5%.) The buildup factors evaluated in the present study could be useful for controlling human exposure to radiation.     

Barium-borate-flyash glasses: As radiation shielding materials

The attenuation coefficients of barium-borate-flyash glasses have been measured for γ-ray photon energies of 356, 662, 1173 and 1332 keV using narrow beam transmission geometry. The photon beam was highly collimated and overall scatter acceptance angle was less than 3°. Our results have an uncertainty of less than 3%. These coefficients were then used to obtain the values of mean free path (mfp), effective atomic number and electron density. Good agreements have been observed between experimental and theoretical values of these parameters. From the studies of the obtained results it is reported here that from the shielding point of view the barium-borate-flyash glasses are better shields to γ-radiations in comparison to the standard radiation shielding concretes and also to the ordinary barium-borate glasses.     

辐射防护玻璃照射量累积因子的计算及分析

为研究γ放射源操作热室观察窗辐射防护玻璃的累积因子,开展高活度γ放射源热室观察窗的设计,本研究根据五种常用辐射防护玻璃的成分以及ANSI/ANS-6.4.3的数据,得到五种常用辐射防护玻璃的照射量累积因子G-P插值法参数,并利用这些参数计算五种辐射防护玻璃在60 Co、75 Se、137 Cs、192 Ir核素γ射线照...     

On the effective atomic number and electron density: A comprehensive set of formulas for all types of materials and energies above 1 keV

A comprehensive and consistent set of formulas is given for calculating the effective atomic number and electron density for all types of materials and for all photon energies greater than 1 keV. The formulas are derived from first principles using photon interaction cross sections of the constituent atoms. The theory is illustrated by calculations and experiments for molecules of medical and biological interest, glasses for radiation shielding, alloys, minerals and liquids.     

钨玻璃与铅玻璃对X射线辐射屏蔽效果的数值计算分析

通过 WINXCOM理论计算X射线能量在20~100 keV下,钨和铅硅酸盐玻璃的质量衰减系数、有效原子序数和半值层。结果发现,随着 WO3和PbO 含量的增加质量衰减系数增加。钨玻璃在70 keV能量下,由于光电效应发生突变,质量衰减系数突然增强。随后,利用 MCNP 5计算5种能量下钨玻璃的积累因子,以便进一步修正模拟结果以达到真实情况。     

钨玻璃与铅玻璃对X射线辐射屏蔽效果的数值计算分析

通过WINXCOM理论计算X射线能量在20~100keV下,钨和铅硅酸盐玻璃的质量衰减系数、有效原子序数和半值层。结果发现,随着WO_3和PbO含量的增加质量衰减系数增加。钨玻璃在70 keV能量下,由于光电效应发生突变,质量衰减系数突然增强。随后,利用MCNP 5计算5种能量下钨玻璃的积累因子,以便进一步修正模拟结果以达到真实情况。     

Gamma ray and neutron shielding properties of some concrete materials

Shielding of gamma-rays and neutrons by 12 concrete samples with and without mineral additives has been studied. The total mass attenuation and linear attenuation coefficients, half-value thicknesses, effective atomic numbers, effective electron densities and atomic cross-sections at photons energies of 59.5 and 661 keV have been measured and calculated. The measured and calculated values were compared and a reasonable agreement has been observed. Also the recorded values showed a change with energy and composition of the concrete samples. In addition, neutron shielding has been treated in terms of macroscopic removal cross-section (Σ_R, cm⁻¹) concept. The WinXCom and NXcom programs were employed to calculate the attenuation coefficients of gamma-rays and neutrons, respectively.     

基于MCNP对γ射线吸收剂量累积因子的计算与研究

使用蒙特卡罗程序MCNP计算了常用材料下的吸收剂量累积因子,计算时采用了较新的截面数据库MCPLIB04及介质材料的衰减参数数据库,并考虑了轫致辐射和相干散射等物理过程,同时将计算结果与相关文献给出的数据进行了比较,分析了造成差异的主要原因。结果表明:利用MCNP计算出的低Z材料的吸收剂量累积因子值在入射光子的中能区部分,平均比文献给出的数据偏小,在高能区部分平均比其偏大;而利用MCNP计算出的高Z材料的吸收剂量累积因子则普遍比文献给出的数据偏大。本文工作可为更新目前使用的较为陈旧的累积因子数据库提供参考。     

An investigation of the role of spectroscopic factors in the breakup reaction of ~(11)Be

The experimental elastic cross section data of the projectile11 Be on target12 C at 49.3 Me V/nucleon energy is analysed. The calculations for the elastic scattering are performed by the phenomenological optical model. The different optical potentials to include breakup effects into the calculations, which are neutron+12C, neutron+10Be and10Be+12C, are described with the aid of the global potentials for neutron interactions and fitted to experimental data for the core and target interaction. Also, the first analysis of the optical model for10 Be on target12 C at 39.1 Me V is done for building the interaction potential of the core and the target for11 Be. For investigating the effects of the spectroscopic factors, obtained factors from the direct capture process using the nuclear level density are compared with the previous cross section and spectroscopic factor results. Obtained results for the elastic cross section reproduce the experimental data very well and show the requirement of including spectroscopic properties such as, spectroscopic factors and density of the excited states, to explain this elastic cross section data.     

Calculation of photon shielding properties for some neutron shielding materials

The objective of the present study is to calculate photon shielding parameters for seven polyethylene-based neutron shielding materials. The parameters include the effective atomic number(Z_(eff)), the effective electron density(N_(eff)) for photon interaction and photon energy absorption,and gamma-ray kerma coefficient(kc). The calculations of Z_(eff)are presented as a single-valued and are energy dependent. While Z_(eff)values were calculated via simplistic powerlaw method, the energy-dependent Z_(eff)for photon interaction(Z_(PI-eff)) and photon energy absorption(Z_(PEA-eff)) are obtained via the direct method for energy ranges of 1 keV–100 GeV and 1 keV–20 Me V, respectively. The kccoefficients are calculated by summing the contributions of the major partial photon interactions for energy range of 1 keV–100 MeV. In most cases, data are presented relative to pure polyethylene to allow direct comparison over a range of energy. The results show that combination of polyethylene with other elements such as lithium and aluminum leads to neutron shielding material with more ability to absorb neutron and crays. Also, the kerma coefficient first increases with Z of the additive element at low photon energies and then converges with pure polyethylene at energies greater than 100 keV.     

某轻混凝土γ屏蔽积累因子的计算

使用蒙特卡罗程序EGS4计算了光子能量范围0.015~15MeV、屏蔽厚度达40个平均自由程的某核电厂中使用的轻混凝土的γ照射量积累因子,程序计算中考虑了轫致辐射、荧光效应和相干（瑞利）散射对积累因子的影响。使用G-P近似拟合公式对γ屏蔽积累因子计算结果进行拟合计算,给出了相应的积累因子G-P拟合公式的拟合参数。利用此方法可得到此种轻混凝土的任意光子能量和屏蔽厚度的γ屏蔽积累因子。     

Radiation shielding of concretes containing different lime/silica ratios

The shielding of γ-rays and fast neutrons by concrete has been studied for concretes containing different lime/silica ratios. Calculations were carried out for six different concrete samples. The total mass attenuation coefficients (μ/ρ, cm² g⁻¹) have been computed at photon energies of 1 keV to 100 GeV using the personal computer software package WinXCom. Also the macroscopic effective fast neutron removal cross-sections (Σ_R, cm⁻¹) have been calculated using MERCSF-N program and the removal cross-section database for all required elements. The obtained results showed that the lime/silica ratio of concrete has significant and insignificant effects on μ/ρ and Σ_R values, respectively.     

Determination of gamma and fast neutron shielding parameters of magnetite concretes

In this study, some gamma shielding parameters such as mass attenuation coefficient (μ_ρ), effective atomic number (Z_eff), electron density (N_el) and buildup factors have been investigated for concretes with and without magnetite aggregate. The measurements have been carried out using 1.25 MeV (mean energy of 1.1732 MeV and 1.3325 MeV photons of a ⁶⁰Co radioactive source) gamma photons. The theoretical values of μ_ρ have been calculated in the energy range from 1 keV to 100 GeV by WinXCom computer code and these values were used in order to calculate the values of Z_eff and N_el. And fast neutron shielding parameter namely effective removal cross-sections (Σ_R, cm⁻¹) have been calculated. In addition, Energy absorption buildup factors (EABF) and exposure buildup factors (EBF) values of concrete samples have been calculated for photon energy 0.015–15 MeV up to 40 mfp (mean free path) penetration depths. The results of this study showed that the magnetite concrete is more efficient than the ordinary concrete for fast neutrons and gamma rays.     

基于CENDL-3.2的宽群屏蔽数据库开发与验证

为开展反应堆屏蔽计算研究,使用NECP-Atlas和NECP-Shield程序,基于我国最新的评价核数据库CENDL 32开发了宽群屏蔽数据库NECL CP29,该数据库的中子能群结构采用基于粒子群算法优化的29群结构。为验证该数据库,使用国际屏蔽基准题库SINBAD中包括Iron 88、ASPIS NG和HBR 2等在内的屏蔽基准题进行了计算,计算结果不仅与实验测量值进行了比较,而且与国际主流屏蔽数据库BUGLE B7和BUGLE 96的计算结果进行了对比。验证结果表明,NECL CP29数据库的计算值与测量值吻合较好,计算精度整体上优于BUGLE B7和BUGLE 96,且优化的能群结构有效提升了计算效率。     

NXcom – A program for calculating attenuation coefficients of fast neutrons and gamma-rays

This work is concerned with a construction and use of NXcom computer program for calculating the removal and attenuation coefficients of transmitted fast neutrons and γ-rays, respectively, through mixtures, composites, concretes and compounds. The program uses only one input data file for neutrons and γ-rays calculations. For γ-ray attenuation, the program predictions were tested by comparing them with the well-known WinXcom program results and an excellent agreement was noticed. Also, it has been used for calculating the values of macroscopic effective removal cross-sections Σ_R (cm⁻¹) for five new published polyamide and anhydride composites designed for shielding mixed neutron and γ-rays. The obtained values for Σ_R using the program and the reported attenuation thicknesses which were based on the Monte Carlo N-Particle (MCNP) code showed the same trend. The NXcom program can be used as a preliminary effective tool for testing the shielding material against fast neutrons and γ-rays.     

Parametrization of the total photon mass attenuation coefficients for photon energies between 100 eV and 1000 MeV

A convenient way of generating mass attenuation coefficients for data analysis in various fields of X-ray spectroscopy is by means of semi-empirical schemes. However, the validity of most of the existing schemes is limited to relatively narrow energy intervals (typically 1–50 keV) and their accuracy is usually poor especially in regions near absorption edges. A few years ago, we use a new semi-empirical scheme that enabled us to fit, for the first time, photon data for all elements in the very wide energy range, i.e. between 0.1 and 1000 keV. The scheme was found flexible enough to provide excellent fit to the most recent compiled photon cross section data in the entire energy range. It was based on fitting data to an exponential function with the addition of a Klein–Nishina term to account for dominant incoherent scattering at higher energies. In the present work, our former scheme is extended beyond the pair-production threshold (1.02 MeV) all the way to 1000 MeV. An interactive MS Windows based computer program for generating, printing and displaying mass attenuation coefficients based on the proposed scheme has been developed.     

蒙特卡罗程序EGS4在γ照射量积累因子计算中的应用

使用蒙特卡罗程序EGS4计算了入射光子能量范围从0.015 MeV到15 MeV、屏蔽厚度达到40个平均自由程的普通混凝土的γ照射量积累因子,程序计算中使用的是PHOTX光子截面库、各向同性点源和无限均匀介质模型,针对深穿透问题采用了粒子分裂技巧,并考虑了轫致辐射、荧光效应和相干(瑞利)散射对积累因子的影响。并将本文的计算结果与相关文献进行了比较分析,表明本文使用EGS4计算的积累因子数据是可靠的,可以更广泛的使用蒙特卡罗方法来计算γ照射量积累因子。     

Chemical composition dependence of exposure buildup factors for some polymers

Exposure buildup factors for some polymers such as poly-acrylo-nitrile (PAN), poly-methyl-acrylate (PMA), poly-vinyl-chloride (PVC), synthetic rubber (SR), tetra-fluro-ethylene (Teflon) have been computed using the G.P. fitting method in the energy range of 0.015–15.0 MeV, up to the penetration of 40 mean free paths (mfp). The variation of exposure buildup factors for all the selected polymers with incident photon energy at the fixed penetration depths has been studied, mainly emphasizing on chemical composition (equivalent atomic number) of the selected polymers. It has been observed that for the lower penetration depths (below 10 mfp), the exposure buildup factor decreases with the increase in equivalent atomic number of the selected polymers at all the incident photon energies. However, at the penetration depth of 10 mfp and incident photon energy above 3 MeV, the exposure buildup factor becomes almost independent of the equivalent atomic number of the selected polymers. Further, above the fixed penetration depth of 15 mfp of the selected polymers and above the incident photon energy of 3 MeV, reversal in the trend has been observed, i.e., the exposure buildup factor increases with the increase in equivalent atomic number.