A study on the range of non-validity of the Bragg's additivity law for compounds at photon energies below 10 keV

• Published in: International journal of radiation applications and instrumentation. Part A, Applied radiation and isotopes Applied radiation and isotopes, 1992, Vol.43 (7), p.893-898
• Main Authors: Kerur, B.R., Thontadarya, S.R., Hanumaiah, B.
• Format: Article
• Language: English
• ISSN: 0883-2889
• DOI: 10.1016/0883-2889(92)90151-4

An experimental study on the validity of the mixture rule for compounds is made using the characteristic x-rays of manganese from a 55Fe source with a weighted average energy value of 5.947 keV and characteristic x-rays of copper from a 65Zn source with the weighted average energy value of 8.118 keV. The compounds were selected in such a way that the absorption edges ( E b) lie on either side of the incident x-ray energy ( E x). The region of atomic numbers considered is 16 ⩽ Z ⩽ 30 to suit the incident photon energies. The experimental values of μ/ρ are compared with the values calculated according to the additivity law utilizing the published theoretical μ/ρ values for elements from the tables of Saloman et al. We found that for compounds with edges lying 1.9 keV below the incident energy, that is for ( E x − E b) ⩾ + 1.9 keV, and for compounds with edges lying 600 eV above the incident energy, that is ( E x − E b) ⩽ − 600 eV, the experimental values agree with the theoretical values. And for those with ( E x − E b) ⩽ + 1.5 keV and ( E x − E b) ⩾ − 100 eV, there are large deviations from the theoretical values; the deviation of the former is attributed to the fine structure above the edge and to environmental effects while for the latter the deviations are attributed to anomalous scattering. Thus the range of non-validity of the mixture rule is shown, for the first time experimentally, to extend beyond 1 keV above an edge.