Direct measurement of total and photoelectric cross sections of medium and high Z elements in the range 48 ⩽ Z ⩽ 83 present in compounds for 123.6 keV photons

Abstract

A new, simple and direct method proposed earlier by us for the measurement of total photoelectric cross sections of elements at 123.6 keV has been extended here to obtain fairly accurate total photoelectric cross sections of medium and heavy elements present in various compounds by measuring their K x-ray fluorescence intensities induced by 123.6 keV gamma rays using a NaI(Tl) spectrometer system attached to a 1 K MCA in a 2 π geometrical configuration. The compounds of various elements in the region 48 ⩽ Z ⩽ 83 have been employed in the form of circular pellets for measurements. The K x-ray fluorescence cross section σ K is determined by measuring the K x-ray fluorescence intensity, from which the total photoelectric cross section τ is obtained by using the theoretical value of K fluorescence yield of the element. From the measured total photoelectric cross section, the K-shell photoelectric cross section is evaluated. A 50–20% transmission region in the broad beam geometry configuration is identified for measuring reasonably accurate total mass attenuation coefficients for the incident and for the K x-ray radiations in the same target. The values agree fairly well with the corresponding mass attenuation coefficients obtained using a stringent narrow beam geometry configuration. The total mass attenuation coefficients μ i and μ e of high Z elements were derived from the measured attenuation coefficients μ i and μ e of compounds using the mixture-rule for the incident and for the K x-ray energies by assuming μ i and μ e values of low Z elements present in the compounds. All these parameters are compared with their corresponding theoretical values and good agreement between them is obtained.