LXT. The determination of the internal conversion coefficient and branching ratio for the 80 kev γ-ray emitted by I131by means of X-ray-γ-ray coincidence measurements

Abstract

The investigation of primary and secondary electron spectra as a means of determining conversion coefficients becomes difficult at low γ-ray energies. A method relying on the measurement of the γ-rays emitted as a result of internal conversion does not suffer from this disadvantage. Such a method has been applied to the 80 kev γ-ray emitted by I¹³¹. This is believed to be in cascade with a 283 kev γ-ray, the two forming a branch parallel to the most intense γ-ray of 363 kev. X-rays arising from the conversion of the 80 kev γ-ray should be in coincidence with 283 kev γ-rays. Such coincidences were found, and the proportion of such x-rays in the total number measured. The relative number of these x-rays and unconverted 80 kev quanta gives 1·83±0·16 as the internal conversion coefficient, which places the 80 kev transition as magnetic dipole. It occurs in (4·3±0·6)% of the total number of disintegrations. Evidence for x-rays in coincidence with 638 kev γ-rays was also found. It is possible that these arise from the conversion of a γ-ray emitted in a transition between levels at 638 and 720 kev, of occurrence 0·3% per disintegration.