Simulations of mass attenuation coefficients for shielding materials using the MCNP-X code

In this paper,mass attenuation coefficients of concrete,bricks and cement plaster,as shielding materials,are calculated at 59.5,356,662,1173,1274 and 1333 keV by using the MCNP-X (version 2.4.0) code.The numerical simulation results are compared with previous Monte Carlo studies,experimental results and XCOM data.The effects of barite on mass attenuation coefficients are investigated.The mass attenuation coefficients increase with the barite content.Thus,our results agree well with experimental studies on gamma ray shielding of barite.It is flexible for the MN method to change the barite rates in material by small increments,which is experimentally difficult.Also,modeled geometry can be used for future approaches such as new designs and new structures especially in investigating new barite-containing materials to build nuclear reactors or high-energy radiation therapy facilities.     

SPECT的衰减校正

综述了常见的ＳＰＥＣＴ衰减校正方法,包括前、后校正法,本征法和迭代法。简要介绍了各种方法的基本原理并对各种方法的特点作了比较分析。从校正后图像的噪声特性、失真度、方法的运算速度有适用于何种脏器的重建等方面作了有关阐述。有助于系统理解不同的衰减校正方法,也对ＳＰＥＣＴ临床应用选择适当的衰减校正方法有所帮助。     

Observations on the experimental determination of mass attenuation coefficients

This article addresses certain aspects of planning, performing, analyzing and reporting experiments designed to determine mass attenuation coefficients. The aim is to encourage experimentalists to add value from the user’s perspective. For illustrative purposes two recent papers from this journal are taken as examples.     

能散X射线能谱数据分析中的基体修正系数最佳化

描述由标样中每个感兴趣元素的相互独立的基本修正系数导出相互关联的最佳基体修正系数的数学物理方法及其运算公式。最佳基体修正系数应用于能散Ｘ射线能谱分析可提高样品中每个感兴趣元素的分析精确度，特别对样品中低于或等于０．３％浓度感兴趣元素的分析，相对误差由２３％下降到１５％。     

Photon attenuation coefficients of concrete includes barite in different rate

The photon attenuation coefficients of barite and concrete produced with barite have been investigated. The linear attenuation coefficients have been calculated for 1 keV–1 GeV energy and compared with measurements performed using a gamma spectrometer that contains an NaI(Tl) detector and MCA at 662, 1173 and 1332 keV. The results have been compared with the corresponding property of lead as the standard shielding material.     

Gamma-ray attenuation coefficients of some building materials available in Egypt

Mass attenuation coefficients of various types of building materials were measured using a high-resolution HPGe spectrometer detector. Samples were irradiated by gamma-rays emitted from point sources of 241Am, 133Ba, 60Co and 137Cs. The results are in good agreement with the theoretical calculations of XCOM code. The effectiveness of building materials in shielding were determined over the range 50–3000 keV. Finally, the protection efficiency of walls and roofs from radiation exposure were determined. The effectiveness of all tested building materials was better than the internationally accepted limit, and they are therefore acceptable for use.     

穿透衰减校正改善成像质量的研究

对ＳＰＥＣＴ的穿透衰减校正装置进行模型和临床实验,结果显示穿透衰减校正能有效降低人体对γ射线的衰减影响,显著改善深部位置的图像对比度,提高诊断准确性。     

K and L X-ray mass attenuation coefficients for low-Z materials

X-ray mass attenuation coefficients for low-atomic-number elements, 6 ≤ Z ≤ 33, were obtained for characteristic K and L x rays of elements with 17 ≤ Z ≤ 94 by fitting a third degree polynomial to the values tabulated by Storm and Israel.     

Determination of mass attenuation coefficients, effective atomic and electron numbers, mean free paths and kermas for PbO, barite and some boron ores

The total mass attenuation coefficients, μ_m, for PbO, barite, colemanite, tincal and ulexite were determined at 80.1, 302.9, 356.0, 661.7 and 1250.0 keV photon energies by using NaI (Tl) scintillation detector. Effective atomic number, Z_eff, effective electron number, N_eff, total atomic cross-section, σ_t, total electronic cross-section, σ_e, mean free path, mfp, and kerma relative to air were determined experimentally and theoretically. The theoretical mass attenuation coefficients were estimated using mixture rule. The calculated values were compared with the experimental values for all samples.     

Scatter correction techniques in 3D PET: a Monte Carlo evaluation

In this work, a Monte Carlo software package, PET-EGS, designed to simulate realistic PET clinical studies, was used to assess three different approaches to scatter correction in 3D PET: analytical (gaussian fitting technique), experimental (dual energy window technique) and probabilistic (Monte Carlo technique). Phantom and clinical studies were carried out by 3D PET and simulated by PET-EGS. A clinical study (¹⁸F-FDG brain study) was simulated assuming PET emission/transmission multiple-volume images as a voxelised source object describing the distribution of both the radioactivity and attenuation coefficients and accounting for out-of-field activity and media. The accuracy of PET-EGS in modelling the physical response of a 3D PET scanner was assessed by statistical comparison between measured and total (scatter+unscatter) simulated distributions (probability for the two distributions to be the same distribution: p>0.95). The accuracy of the scatter models, for each scatter correction technique, was evaluated on sinograms by statistical comparison between the estimated and the simulated scatter distributions (agreement <1 σ). The accuracy of scatter correction was evaluated on sinograms by comparison between scatter corrected and simulated unscatter distributions, proving a comparable accuracy of all the considered scatter correction techniques for brainlike distributed sources     

Comparison of the simulated gamma-ray attenuation coefficients with the real measurements

The gamma-ray linear and the mass attenuation coefficients of Pb, Al, Cu, and plexiglass materials were calculated from both experimental and theoretical(simulation) methods. For the experimental results, a spectrometer, which was consisted of a Na I(Tl) inorganic scintillation detector, was used. The theoretical attenuation values were calculated by means of the FLUKA Monte Carlo(MC) and XCOM programs. Obtained attenuation coefficients from the experiment and the theoretical methods were compared with each other and literature values.     

A comprehensive study for mass attenuation coefficients of different parts of the human body through Monte Carlo methods

The gamma-ray mass attenuation coefficients of blood,bone,lung,eye lens,adipose,tissue,muscle,brain and skin were calculated at different energies(60,80,150,400,500,600,1000,1250,1500,and 2000 keV) by various theoretical methods such as FLUKA,GEANT4 Monte Carlo(MC) methods and XCOM program in this work.Calculated coefficients were also compared with the National Institute of Standards and Technology(NIST) values.Obtained results were highly in accordance with each other and NIST values.Our results showed that FLUKA was quite convenient in comparison to GEANT4 in the calculation of the mass attenuation coefficients of the used human body samples for low-energy photons(60,80,and 150 keV) when compared with the NIST values.     

Radiation dose estimation and mass attenuation coefficients of marble used in Turkey

In this study the natural radioactivity in marble samples used in Turkey was measured by means of gamma spectrometry. The results showed that the specific activities of ²²⁶Ra, ²³²Th and ⁴⁰K ranged from 10 to 92 Bq kg⁻¹, from 4 to 122 Bq kg⁻¹ and from 28 to 676 Bq kg⁻¹, respectively. The radiological hazards in marble samples due to the natural radioactivity were inferred from calculations of radium equivalent activities (Ra_eq), indoor absorbed dose rate in air values, the annual effective dose and gamma and alpha indexes. These radiological parameters were evaluated and compared with the internationally recommended values. The measurements showed that marble samples used in Turkey have low level of natural radioactivity; therefore, the use of these types of marble in dwellings is safe for inhabitants. Mass attenuation coefficients (μ/ρ) were obtained both experimentally and theoretically for different marble samples produced in Turkey by using gamma-ray transmission method. Experimental values showed a good agreement with the theoretical values.     

GA-based dynamical correction of dispersion coefficients in Lagrangian puff model

In atmospheric dispersion models of nuclear accident, the dispersion coefficients were usually obtained by tracer experiment, which are constant in different atmospheric stability classifications. In fact, the atmospheric wind field is complex and unstable. The dispersion coefficients change even in the same atmospheric stability,hence the great errors brought in. According to the regulation, the air concentration of nuclides around nuclear power plant should be monitored during an accident. The monitoring data can be used to correct dispersion coefficients dynamically. The error can be minimized by correcting the coefficients. This reverse problem is nonlinear and sensitive to initial value. The property of searching the optimal solution of Genetic Algorithm(GA) is suitable for complex high-dimensional situation. In this paper, coupling with Lagrange dispersion model, GA is used to estimate the coefficients. The simulation results show that GA scheme performs well when the error is big. When the correcting process is used in the experiment data, the GA-estimated results are numerical instable. The success rate of estimation is 5% lower than the one without correction. Taking into account the continuity of the dispersion coefficient, Savitzky-Golay filter is used to smooth the estimated parameters. The success rate of estimation increases to 75.86%. This method can improve the accuracy of atmospheric dispersion simulation.     

Energy and chemical composition dependence of mass attenuation coefficients of building materials

Total and partial mass attenuation coefficients of different building materials (glass, concrete, marble, flyash, cement and lime) have been computed over a wide energy range of 10 keV to 100 GeV. For the total mass attenuation coefficient, μ_total a significant variation is observed in low and high energy regions whereas there is no notable change in μ_total in the intermediate region. The results of μ_total have been discussed on the basis of obtained attenuation coefficients of different partial photon interaction processes.     

Alignment of dynamic cardiac PET images for correction of motion

A technique was developed to align images from dynamic cardiac N-13 ammonia positron emission tomography (PET) scans. Inaccurate alignment of images from these scans stems from breathing, motion of the heart within the thorax, and overall motion of the patient (particularly during pharmacologic stress). The images from these scans represent changing distributions, from high blood pool concentrations to predominantly myocardial uptake, and are generally noisy. In this technique, templates are defined from a long, late frame (5-10 min). These templates include a myocardial template, which matches late frames, a blood pool template, which matches frames in which the left ventricle blood pool is dominant, and a modified blood pool template, which reduces the effect of activity in the right ventricle. The correlation function is used as the maximized parameter over shifts between each three-dimensional image frame and the appropriate template. The technique was tested on phantom, human, and animal data with myocardial defects. Phantom data showed the technique to be reliable to within one voxel (1.7×1.7×4.2 mm³), and motion which was apparent in human data was reduced significantly. Blood flow values measured from corrected data showed two traits: higher values, due to better matching regions of interest to images, and better fits, due to smoother time-activity curves     

Measurements of linear attenuation coefficients of irregular shaped samples by two media method

The linear attenuation coefficient values of regular and irregular shaped flyash materials have been measured without knowing the thickness of a sample using a new technique namely “two media method”. These values have also been measured with a standard gamma ray transmission method and obtained theoretically with winXCOM computer code. From the comparison it is reported that the two media method has given accurate results of attenuation coefficients of flyash materials.