In measurement of β-rays from14C with a silicon semiconductor detector, pulse height spectra are observed to change by insertion of absorbers between the source and the detector. An obvious broad peak appears in the spectra by the insertion. An increase in the absorber thickness reduces the peak height, and shifts the peak position to the higher energy side in the spectra. On the other hand, the increase in the distance between the source and the absorber also reduces the peak height, but does not move the position of the peak. The absorption curve derived from these results shows its particular shape corresponding to the respective position of the absorber. Therefore, the distortion of the pulse height spectrum for low-energy β-rays depends not only on the thickness of the absorber but also on its position between the source and the detector.
Radioactivity of137Cs of plant samples taken in former Semipalatinsk Nuclear Test Site (SNTS) was determined. The radioactivity ranged from 0.3 to 81.1 Bq/kg, most of them were under background level but the distribution was localized. Compared to the soil, the plants did not have strong radioactivity, suggesting a potential that plants in this site absorbs radiocesium from soil when the chemical situation of the soil might change, causing fixed Cs turn to be available.
Using ESR spectroscopy, we revealed various free radicals in a Japanese commercially available black pepper before and after γ-irradiation. The representative ESR spectrum of the pepper is composed of a sextet centered at g=2.0, a singlet at the same g-value and a singles at g=4.0. The first one is attributable to a signal with hyperfine interactions of Mn2+ion (7.4 mT) . The second one is due to an organic free radical. The third one may be originated from Fe3+ ion of the non-hem Fe in proteins. A pair of signals appeared in the black pepper after γ-irradiation. The progressive saturation behavior reconfirmed the signal identification for the radicals in the black pepper.