| Popis: |
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 |
