Minimum Detectable Mass Fraction of Localised Changes in Biological Matrices Using Neutrons in Transmission

The value of the minimum detectable mass of an irregularity, which will change the neutron macroscopic cross section of a biological matrix by 1%, has been calculated by using neutron transmission technique. The biological matrices selected were ones in which neutron transmission provided better detection of elements than photon attenuation measurements. Best results were obtained, for the detection of bone marrow in bone (12.2 mg/g), Ca in bone (10 mg/g) and water in brain (6 mg/g). The minimum required number of neutrons and the exposure time required for the detection of irregularities in bone marrow have been calculated.     

Elemental analysis of biological matrices using tomographic techniques

Gamma-ray transmission tomography and neutron induced gamma-ray emission tomography (NIGET) where delayed gamma-rays from an activated sample are detected in a tomographic mode, were used to investigate the elemental composition and distribution of a salivary gland stone, nondestructively. Transmission tomography provided information about the distribution of the linear photon attenuation coefficient in the object and showed clearly the two regions of inorganic and organic material in a number of sections through it. In addition it was possible to derive from the data the concentration of Ca and the ratio of Ca to P in the stone. By using NIGET it was shown that the concentration of Ca and Na in the object can be mapped and quantitative measurements of these elements could be obtained in any particular location within the salivary gland stone. The spatial resolution which depends on detector collimation was 1 mm for transimission and 2 mm for emission measurements. Instrumental neutron activation analysis was also used to determine the concentration of five elements in the stone, as a whole.     

Chemical effects on Kβ/Kα X-ray intensity ratios of Mo,Ag, Cd,Ba, La,Ce compounds and total mass attenuation coefficients of Fe and Cu

The Kβ/Kα intensity ratios for pure Mo, Ag, Cd, Ba, La and Ce elements and for some of their compounds were investigated. The vacancies in the K shell were created by 59.5-keV γ-rays from a heavily filtered ²⁴¹Am radioactive source. K X-rays were measured using a Si(Li) detector with a resolution of 155 eV at 5.9 keV. We observed chemical effects on Kβ/Kα intensity ratios of Mo, Ag, Cd, Ba, La and Ce compounds. Detailed interpretation of data obtained from X-ray transmission measurements usually depends on the assumption that the contribution of each element is additive. This assumption yields the mixture rule for X-ray attenuation coefficients which is valid if molecular and chemical effects are negligible. We measured the total mass attenuation coefficients of Fe and Cu in various compounds. Self-absorption corrections were carried out on data for ligands in the different compounds. Our values were compared with the theoretical values for pure elements.     

A method for the correction of self-absorption of low energy photons for use in routine INAA

Practical application of oow energy gamma rays and X-rays in I.N.A.A. was restricted because of the complexity of the X-ray spectrum and sample self-absorption. This paper describes a method for the calculation of sample self-absorption on the basis of the actual sample spectra only, as measured with a high resolution semiconductor X-ray detector. In the 20–400 keV energy range, the attenuation coefficient can be represented by a three parameter function of photon energy. This was verified by measuring the transmission of photons of different energies through a range of materials. Experiments with neutron irradiated U.S.G.S. standard reference materials with known major oxide composition showed that self-absorption thus calculated from the observed spectra is in good agreement with the results of theoretical calculations based on known attenuation coefficients.     

Investigation of mass attenuation coefficients of water, concrete and bakelite at different energies using the FLUKA Monte Carlo code

The mass attenuation coefficients of water, bakelite and concrete sample defined in the simulation package were obtained using the FLUKA Monte Carlo code at 59.5, 80.9, 140.5, 356.5, 661.6, 1173.2 and 1332.5 keV photon energies. The results for the mass attenuation coefficients obtained by simulation have been compared with experimental and the theoretical ones and good agreement has been observed. The results indicate that this process can be followed to determine the data on the attenuation of gamma-rays with the several energies in other materials. Also, the deposited energy by 661.6 keV photons at several thicknesses of each media was determined as being an important data for radiation shielding studies.     

Chemical effect on total mass attenuation coefficients of V, Cr, Mn, Co and Ni

Detailed interpretation of data obtained from X-ray transmission measurements usually depends on the assumption that the contribution of each element is additive. This assumption yields the mixture rule for X-ray attenuation coefficients which is valid if molecular and chemical effects are negligible. We measured the total mass attenuation coefficients of V, Cr, Mn, Co and Ni in various their compounds. Absorption corrections were carried on data for ligands in the compounds. We found that V, Cr, Mn, Co and Ni have different total mass attenuation coefficients in the different compounds. We compared our results with theoretical values of Hubbell and Seltzer.     

Utilization of Geant4 Monte Carlo simulation method for studying attenuation of photons in normal and heavy concretes at high energy values

The mass attenuation coefficients, μ/ρ, the linear attenuation coefficients, μ and the mean free path, MFP of normal and heavy concretes; ordinary, hematite-serpentine, ilmenite-limonite, basalt-magnetite, ilmenite, steel-scrap and steel-magnetite have been investigated using Geant4 Monte Carlo method at photon energies 1.5, 2, 3, 4, 5 and 6 MeV. The mass attenuation coefficients, the linear attenuation coefficient and the mean free path for the concretes were found dependent upon chemical compositions, density and the photon energy. The linear attenuation coefficient values for the selected concretes increase with the density and decrease with the energy. The mean free path thickness for the all the concretes decrease with increase in iron content and increase with increase the photon energy. The Geant4 Monte Carlo simulation method results have been compared with experimental and theoretical XCOM data, and showed a very good agreement. Our investigation validates the utilization of the Geant4 Monte Carlo simulation method for high energy photon interactions.     

A new method for detecting hemoglobin directly in whole blood using photon attenuation techniques

The objective of the proposed work is focused on measuring iron concentration directly in whole blood as tool for estimating hemoglobin and anemic conditions in patients across the world. The investigated method depends on theory of photon attenuation through transmission of low energy in whole blood sample. The mathematical expressions for calculating hemoglobin and iron deficit on blood using photon attenuation are derived. Calculations are carried out for estimating concentration of iron in blood samples taken from children, adults and old patients and therefore measuring their hemoglobin and iron deficit from normal values. Theoretical mass attenuation coefficient values were obtained using the XCOM program. A high-resolution gamma-ray spectrometry based on high purity germanium detector was employed to measure attenuation of strongly collimated monoenergetic gamma beam through blood samples.     

Study of non-validity of mixture rule near K-absorption edges by X-ray spectrometric technique

X-ray spectrometric technique has been described to determine the X-ray mass attenuation coefficient, μ/ρ, of X-rays employing HPGe X-ray detector and radioactive sources. The photon intensity is measured by gating the channel of the spectrometer at FWHM/photo peak. Using the technique the “best value” values of μ/ρ were obtained for those thicknesses which lie in the transmission (T) range 0.5 ≥ T ≥ 0.02. Total attenuation cross sections for other elements and lead compounds were measured at photon energies from 17 to 88 keV to study the Bragg’s additivity law near the absorption edge of the lead. The measured values of mass attenuation coefficient values are compared with theoretical values obtained using Winxcom (programme). This study suggests that measured mass attenuation coefficient values at and near absorption edges differ from the theoretical value by about 17–23%.     

Large-sample neutron activation analysis: Present status and prospects

Neutron activation analysis is attractive for trace-element determinations in large samples. Facilities for reactor irradiation and -ray spectrometry of kilogram-size cylindrical samples are described. The thermal neutron flux is ca. 5·10¹²m^–2·s^–1 with a _th/ _epi>10⁴, so neutron self-thermalization can be neglected. The correction for the neutron attenuation within the sample is derived from measurement of the neutron flux depression just outside the sample. Correction for -attenuation in the sample is performed via linear attenuation coefficients derived via transmission measurements. Also the natural radioactivity in the sample is taken into account. Examples are given of materials to which large sample INAA has been applied successfully, and further lines of development and exploration are indicated.     

Measurement of total and photoelectric cross sections of rare earth elements present in compounds for 123.6 keV and 145.4 keV photons

A new, simple and direct method proposed earlier by us has been employed here to measure the total photoelectric cross section of rare earth elements in the range 58 Z 66 present in compounds at 123.6 keV and 145.4 keV photon energies. The K X-ray fluorescence intensities emitted by these elements, from irradiating their compounds by the photons of above energies, are measured using a NaI (Tl) spectrometer system in a 2π geometrical configuration. The K X-ray fluorescence cross sections of the rare earth elements are determined, from which the total photoelectric cross sections are evaluated. Total mass attenuation coefficients of compounds for the K X-ray and the incident radiations respectively have been measured and these values were compared with the corresponding theoretical values and a good agreement between them is obtained.     

X-ray attenuation coefficient measurements for photon energies 4.508-13.375 keV in Cu, Cr and their compounds and the validity of the mixture rule

To investigate the validity of the mixture rule which is used to compute the mass attenuation coefficients in compounds, the total mass attenuation coefficients for Cu, Cr elements and Cu₂O, CuC₂O₄, CuCl₂·2H₂O, Cu(C₂H₃O₂)₂·H₂O, Cr₂O₃, Cr(NO₃)₃, Cr₂(SO₄)₃·H₂O, Cr₃(CH₃CO₇)(OH)₂ compounds were measured at photon energies between 4.508 and 13.375 keV by using the secondary excitation method. Ti, Mn, Fe, Ni, Zn, Ge, As, Rb elements were used as secondary exciters. 59.5 keV gamma rays emitted from an annular source were used to excite the secondary exciters and Kα (K-L₃, L₂) rays emitted from the secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Our measurements indicate that the mixture rule is not a suitable method for the computation of mass attenuation coefficients of compounds especially at an energy that is near the absorption edge. Obtained values were compared with theoretical values.     

Study of the mass attenuation coefficients and effective atomic numbers in some gemstones

The total mass attenuation coefficients for natural beryl, corundum, garnet, pearl, and tourmaline gemstones were measured at 81, 356.5, 661.6, 1173.2, and 1332.5?keV photon energies. The samples were irradiated with ¹³³Ba, ¹³⁷Cs and ⁶⁰Co radioactive point sources using gamma ray transmission method. Total atomic and electronic cross-sections, effective atomic numbers and electron densities were determined experimentally and theoretically. The experimental values were compared with the calculated values for all samples. The calculations were extended for total photon interactions in a wide energy range (1?keV?C100?GeV) using WinXCom program of the most commonly irradiated gemstones with different sources of ionized radiation. The values of these parameters have been found to vary with photon energy and chemical composition of the gemstones. All variations of these parameters against energy are shown graphically for total photon interactions.     

Shielding design and detection of neutrons from medical and industrial electron accelerators--simple method of design calculation for neutron shielding

The neutron leakage from medical and industrial electron accelerators has become an important problem and its detection and shielding is being performed in their facilities. This study provides a new simple method of design calculation for neutron shielding of those electron accelerator facilities by dividing into the following five categories; neutron dose distribution in the accelerator room, neutron attenuation through the wall and the door in the accelerator room, neutron and secondary photon dose distributions in the maze, neutron and secondary photon attenuation through the door at the end of the maze, neutron leakage outside the facility-skyshine.     

Instrumental neutron activation analysis of large samples: A pilot experiment

A large sample INAA (LS-INAA) was conducted based on available experimental conditions. Four different materials, e.g., a quartz-sand and three wastes from an incineration plant were analyzed on sample size of 1 kg. The neutron flux spatial distribution was determined by irradiation of flux monitors in the sample. The gamma-ray apparent counting efficiency was evaluated based on the effective-solid angle concept, using linear attenuation coefficients calculated from an iteration process. The k ₀- and the modified monostandard methods were modified for the LS-INAA. To check the LS-INAA performance, a conventional small sample INAA was carried out for the quartz sand and a waste. All detected elements in the LS-INAA are presented and the discussion is conducted to explore the sources of errors in the LS-INAA. As a pilot experiment, the information from this work will be used in constructing irradiation and counting devices for the new FRM-II neutron source in Garching, Germany.     

Towards routine NAA of materials rich in heavy elements with iterative gamma-ray attenuation and neutron self-shielding calculations

Solids and powders can be analysed directly and with good accuracy by neutron activation analysis without sample preparation because of the excellent penetrating powers of neutrons and gamma rays. However, if the sample contains high concentrations of gamma-absorbing heavy elements or neutron-absorbing elements, the analysis results must be corrected for neutron self-shielding and gamma-ray attenuation. These effects are coupled and depend on the chemical composition of the sample, which is the final result of the analysis. Thus, the correction calculation must be iterative. In this work we performed the first coupled iterative corrections of the two effects. Six test samples were prepared by mixing powders containing compounds of Cd, a neutron absorber, and the rare-earth elements Ce, Pr and Nd with concentrations as high as 47 %. The samples were irradiated in the SLOWPOKE research reactor and counted with a germanium gamma-ray detector. In the samples with the highest heavy element concentrations, the uncorrected Neutron activation analysis results were in error by as much as 55 %. The results were corrected iteratively using the neutron self-shielding model coupled with the gamma-ray attenuation model, and the final corrected results were accurate to 5 % or better.     

A novel shielding material prepared from solid waste containing lead for gamma ray

Human beings are continuously exposed to cosmogenic radiation and its products in the atmosphere from naturally occurring radioactive materials (NORM) within Earth, their bodies, houses and foods. Especially, for the radiation protection environments where high ionizing radiation levels appear should be shielded. Generally, different materials are used for the radiation shielding in different areas and for different situations. In this study, a novel shielding material produced by a metallurgical solid waste containing lead was analyzed as shielding material for gamma radiation. The photon total mass attenuation coefficients (μ/ρ) were measured and calculated using WinXCom computer code for the novel shielding material, concrete and lead. Theoretical and experimental values of total mass attenuation coefficient of the each studied sample were compared. Consequently, a new shielding material prepared from the solid waste containing lead could be preferred for buildings as shielding materials against gamma radiation.     

Gamma-ray shielding and structural properties of barium–bismuth–borosilicate glasses

The attenuation coefficients of barium–bismuth–borosilicate glasses have been measured for gamma-ray photon energies of 662, 1173 and 1332 keV using a narrow beam transmission geometry. These coefficients were then used to obtain the values of mass attenuation coefficients, effective atomic number, effective electron density and mean free path. Good agreement has been observed between experimental and theoretical values of these parameters. From the obtained results it is reported here that from the barium–bismuth–borosilicate glasses are better shields to gamma-radiations in comparison to the standard radiation shielding concretes from the shielding point of view. The molar volume, FTIR and acoustic investigations have been used to study the structural properties of the prepared glass system. The obtained results reveal that the formation of non-bridging oxygens occurs at higher concentration of Bi₂O₃.     

Point defects in reduced strontium titanate

Strontium titanate single crystals have been carefully reduced at temperatures ranging from 1200 to 1400°C in oxygen partial pressures of 10^?7?10^?12 atm and quenched to room temperature where optical absorption coefficients, Hall coefficients, mass densities and lattice parameters were measured. (Optical absorption coefficients and Hall coefficients were also measured at 77 K). The predominant defects at room temperature were found to be doubly ionized oxygen vacancies and conduction band electrons. No evidence was found for singly ionized oxygen vacancies as has been suggested by some workers.Optical absorption in the visible and ultraviolet frequency region was found to be dependent upon the concentration of free carriers. For photon energies of 0.5 eV to about 1 eV, a free carrier absorption effect occurs which may be due to intraband transitions. Three peaks occur at photon energies of 1.66, 2.44, and 2.95 eV and may be due to phonon assisted interband transitions among the titanium d-like conduction bands.     

Estimation of trace elements in water matrix from photon attenuation coefficients

The method of elemental analysis based on the measurement of attenuation coefficient has been used to estimate the impurity introduced in a water matrix using a scintillation detector with a single channel analyser. For a 2% change in the mass attenuation coefficient the minimum detectable fractions of impurities were estimated to be of the order of 625–1250 μg/g for uranium and thorium compounds at photon energies 32.1 and 59.5 keV.