Measurement Of Mass Attenuation Coefficients Research Articles

Effect of sample thickness on the measured mass attenuation coefficients of some compounds and elements for 59.54, 661.6 and 1332.5 keV γ-rays

Measurements have been made to determine γ-rays attenuation coefficients very accurately by using an extremely narrow-collimated-beam transmission method. The effect of the sample thickness on the measured values of the mass attenuation coefficients (μ/ρ) cm 2/ g of perspex, bakelite, paraffin, Al, Cu, Pb and Hg have been investigated at three different γ-ray energies (59.54, 661.6 and 1332.5 keV). It is seen that for these chosen materials ( μ/ ρ) remains constant in good agreement with the theoretical values up to 3 mean free paths and after that ( μ/ ρ) values for Cu, Pb and Hg decrease with further increase in the absorber thickness. This result may be attributed to the increase in the number of coherent small-angle scattering photons which reach the detector.

Measurement of mass attenuation coefficients of moderate-to-high atomic-number elements at low photon energies

Mass attenuation coefficients for 12 selected moderate-to-high atomic-number elements have been obtained from good-geometry measurements made at five 241Am photon energies of significant emission intensity. Particular interest focuses on measured values for photon energies close to absorption edges. Comparisons with renormalized cross-section predictions indicate agreement to within stated error limits for the majority of cases. Significant discrepancies (>10%) are noted for Ta at 17.8 and 26.3 keV and W at 59.5 keV. Some support for a discrepancy between measurement and theory for W in the region of 60 keV is found in the reported measurements of others.

Measurements of mass attenuation coefficients of yttrium with characteristic lines from elements excited by energetic protons

The characteristic X-rays from elemental or compound targets excited by a proton beam of tandem accelerator is a quasimonochromatic X-ray source. The mass attenuation coefficients of yttrium have been systematically measured in the region 3.3 keV to 29.1 keV by using this kind of X-ray source. The experimental uncertainties of mass attenuation coefficients have been reduced to ±1%. The coherent scattering cross sections have been calculated in accordance with the present experimental condition. The total photoelectric cross sections have been obtained by subtracting scattering cross section from the measured total cross sections.

Effect of absorber-source distance on the transmission of beta particles in Al and Cu

The transmission of 0.766 MeV beta particles from 204T through aluminium and copper as a function of the absorber to source distance, H AS are measured when the absorber foil is held just above the window of a proportional counter. The measured mass attenuation coefficient μ of beta particles varies considerably, with H AS showing maxima, and the range R evaluated at the transmissions T = 5, 1 and 0.1% shows clear minima at H AS = 3.5 and 2.3 cm for Al and Cu respectively. The effect of H AS on measured μ and R is more pronounced in Al than Cu. The measured values of μ and R are compared with recent theory and experimental results.

Self-Absorption Correction for Low-Energy Photons in Instrumental Photon Activation Analysis of Biological Materials

A simple and effective method has been proposed for self-absorption correction for low energy photons in instrumental photon activation analyses of biological materials. The method involves measurements of mass attenuation coefficients of a given sample by means of a standard source of low-energy photons, and the correction for self-absorption at a relevant energy to evaluate quantitative results. Agreements between theoretical and experimental attenuation coefficients were found to be excellent with respect to the biological materials with known elemental compositions. Validity of the method was verified by analyzing several biological standard reference materials: the Orchard Leaves, Bowen′s Kale, Horse Kidney and Lobster Hepatopancreas. Amounts of several elements in human liver and kidney tissues determined by the proposed method are given.

Photon attenuation coefficient study of some materials containing hydrogen, carbon and oxygen

New measurements of mass attenuation coefficients of γ rays in materials containing hydrogen, carbon, and oxygen in the energy range 0.054–1.333 MeV are reported. The hydrogen weight ratio ranges from 0.055 to 0.177. The experimental results are analyzed in terms of the total cross-sections, effective atomic numbers and electron densities. A comparison between the present mass attenuation coefficients and existing compilations is discussed.

Use of a modified natural-rubber phantom for radiotherapy dosimetry measurements

The utility of a phantom material, based on SMR(L) [Standard Malaysian Rubber] grade natural rubber and a formulation used for the proprietary rubber phantom-material, Temex, has been examined for the 1-MeV photon-energy range using γ radiation from a 60Co source. Measurement has also been performed with 60-keV photons using the radionuclide 241Am. At photon-therapy energy levels the measured response, when compared with tabulated central-axis percentage depth doses for the defined measuring conditions, produces everywhere (in the range 1–19 cm depth) better than 2% deviation. The favourable measured response characteristics combined with the ease of processing and casting the phantom material provide the basis for useful radiotherapy machine calibration and anthropomorphic dosimetry measurements. The measured mass-attenuation coefficient, at 60 keV, of 0.204 cm 2 g -1 (±3%) is in close agreement with tabulated values for water (0.2055 cm 2 g -1).

Measurement of Attenuation of 137Cs and 241Am Gamma Rays for Soil Density and Water Content Determinations

AbstractSoil density and water content can be determined concurrently by measuring the attenuation of two different gamma energies. A dual source containing 241Am and 137Cs was shown to be suitable for these measurements. Multichannel pulse‐height analyzers were evaluated to determine their accuracy under experimental conditions for simultaneous measurements of soil density and water content. NaI(Tl) and Ge(Li) detectors were also evaluated. The measurements were made with a collimated beam, 1 cm in diameter, of 662‐keV gamma rays and 59.6‐keV gamma rays from a source containing 70 mCi of 137Cs and 29 mCi of 241Am. Measured mass attenuation coefficients were 0.08565, 0.07803, and 0.07887 cm2/g for cesium gamma rays and 0.20493, 0.27100, and 0.33480 cm2/g for americium gamma rays with water, Cecil, and Houston Black soil, respectively. The higher resolution of the Ge(Li) detector and a 4096‐channel pulse‐height analyzer had no significant advantage with peaks as widely separated as 662 keV and 59.6 keV. A NaI(Tl) detector and a 400‐channel pulse‐height analyzer were satisfactory. With the multichannel pulse‐height analyzer, it was simpler to adjust the area under the americium peak for the Compton contribution from the cesium radiation than with a single channel pulse‐height analyzer. Water content and density changes in both a swelling and nonswelling soil illustrate the utility of the system.

Attenuation Coefficients of Gases for 4.5-145-keV Photons

Narrow beam mass attenuation coefficients were measured for air, hydrogen, helium, neon, argon, krypton and xenon. Radioisotope sources were used to provide photons whose energies were 4.508, 5.895, 9.243, 27.380, 44.229, 88.09 and 145.43 keV. Hydrogen and helium measurements were made only at 5.895 keV. Experimental errors were less than 2 % for most of the measurements. Introduction. In the energy region of 1 to 20 key, extensive measurements have been made of the attenuation coefficients of neon and argon [l-91. Above 20 keV very few experimental results are available [8], [9]. For photon energies greater than 3 keV relatively few attenuation coefficients have been measured for air [S], [6], [7], 1101, hydrogen [2], helium [2], krypton [g], [ll], [l21 and xenon [12]. Rau and Fano [l31 suggest that irregularities in photon cross sections are likely to occur with the interpolation of these cross sections with respect to Z for the noble gases. In an attempt to improve the present knowledge of gas photon cross sections, an experiment was designed wherin the narrow beam mass attenuation coefficients of air, neon, argon, krypton and xenon would be measured with an accuracy of + 1 to 2 % at seven energies between 4.5 and 145 key. Hydrogen and helium measurements would be made at 5.895 keV. The narrow beam mass attenuation coefficient pip, with units of cm2/g is defined by the relation where I/I, is the gas transmissivity and x is the sample thickness in g/cm2. Apparatus. The experimental arrangement is shown schematically in figure l. Since the measured mass attenuation coefficients ranged through four orders of magnitude, many different sample lengths and sample densities were required. Sample lengths (*) This work was performed under the auspices of the United States Atomic Energy Commission. This work is to be published in PIzys. Rev., 1970 and J. Appl. Phys., 1970. PRESSURE GAUGE

The effective atomic number and the calculation of the composition of phantom materials.

The formula for photoelectric absorption given by Walter (1926), used by Spiers (1946) for the calculation of an effective atomic number of a compound material, is adjusted to the values of the attenuation coefficients given by Grodstein (1957). The exponent of the atomic number has to be changed from 2·94 to 3·4 or higher. The coherent scattering is less dependent on the atomic number and is proportional to Z1·7. A description is given of a method of calculating a phantom material which takes both effects into account. Some measurements of mass attenuation coefficients of water and of a water equivalent material composed of boron oxide, paraffin and magnesium carbonate, indicate the accuracy of the formulae, which is about 5 per cent.