DIRECT MEASUREMENT OF TOTAL AND PHOTOELECTRIC CROSS-SECTIONS OF MEDIUM AND HIGH Z-ELEMENTS IN THE RANGE 48 LESS-THAN-OR-EQUAL-TO Z LESS-THAN-OR-EQUAL-TO 83 PRESENT IN COMPOUNDS FOR 123.6-KEV PHOTONS

A new, simple and direct method proposed earlier by us for the measure ment of total photoelectric cross sections of elements at 123.6 keV ha s been extended here to obtain fairly accurate total photoelectric cro ss sections of medium and heavy elements present in various compounds by measuring their K x-ray fluorescence intensities induced by 123.6 k eV gamma rays using a NaI(Tl) spectrometer system attached to a 1 K MC A in a 2pi geometrical configuration. The compounds of various element s in the region 48 less-than-or-equal-to Z less-than-or-equal-to 83 ha ve been employed in the form of circular pellets for measurements. The K x-ray fluorescence cross section sigma(K) is determined by measurin g the K x-ray fluorescence intensity, from which the total photoelectr ic cross section tau is obtained by using the theoretical value of K f luorescence yield of the element. From the measured total photoelectri c 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 attenuatio n 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 geomet ry configuration. The total mass attenuation coefficients mu(i) and mu (e) of high Z elements were derived from the measured attenuation coef ficients mu(i) and mu(e) of compounds using the mixture-rule for the i ncident and for the K x-ray energies by assuming mu(i) and mu(e) value s of low Z elements present in the compounds. All these parameters are compared with their corresponding theoretical values and good agreeme nt between them is obtained.