Compton scattering of 662 keV γ-rays from the K-shell electrons of tantalum

A new approach to the measurement of doubly differential Compton cross-sections is presented. The doubly differential cross-section for Compton scattering of 662 keV gamma-rays from the K electrons of Ta has been measured. In the previous experiments there have been very large problems in correcting for random coincidences and except for the work of Wolff et al. (1989) there have been great difficulties in correcting for the continuum of radiation underlying the K X-ray gating peaks. In the current study we use a coincidence method employing two high resolution Ge detectors, one for Ta K X-rays and the other for measuring the scattered γ-rays. The data collected from the detectors together with the time between incoming data is stored in a multi-parameter pulse height analysis (MP-PHA) system, event-by-event in a list. This method allows the collection of all true and a range of random coincidences in a way that allows direct estimation of the contribution of random coincidences and the continuum in the K X-ray channel. We also adopt a novel non-planar detector arrangement, which allows the K X-ray detector to be very close to the target for high coincidence efficiency. Comparison of theoretical predictions of Bergstrom and co-workers (Suric, 1992; Bergstrom, 1993; Bergstrom et al., 1993) with these experimental results shows poor agreement for Compton scattering from the K-shell of Ta at forward scattering angles, indicating the need for further theoretical treatment.