MEASUREMENT OF NARROW BEAM ATTENUATION COEFFICIENTS USING A BROAD-BEAM GEOMETRY CONFIGURATION FOR 145.4 KEV PHOTONS

Narrow beam attenuation coefficients, mu/rho, of 145.4 keV gamma-rays, emitted from the Ce-141 radioisotope have been measured in various hi gh Z materials such as Pb; (CH3COO)2. Pb.3H2O; Pb(NO3)2; PbO2; PbO; Na 2 WO4 . 2H2O; BiPO4 for the first time using a broad beam geometrical configuration, employing a 5. 10 cm x 2.54 cm NaI (Tl) detector spectr ometer system coupled to a 1 K multichannel analyser. The measured mu/ p values, in cm2/g for the above materials in the transmission range f rom 50% to 20% respectively are 2.12 +/- 0.02 (2.2); 1.25 +/- 0.03 (1. 27); 1.40 +/- 0.01 (1.43); 1.78 +/- 0.06 (1.92); 1.96 +/- 0.03 (2.05); 0.97 +/- 0.02 (1.04) and 1.52 + 0.03 (1.6). The corresponding theoret ical values estimated from the mixture rule using tabulated values of Hubbell (1982), are given in parentheses. It is observed that for high Z compounds at 145.4 keV energy, the exponential law of attenuation w ill be valid even for a broad beam geometry configuration in the trans mission range from 50% to 20%. The attenuation coefficients of element s derived from this method were compared with the tabulated narrow bea m attenuation coefficients indicating the validity of the mixture-rule in the above region of transmission.