Development of a device for measuring the vertical distribution of radioactivity in soil using photodiode

Abstract

Measurements of radiocaesium concentration profiles in a soil are very time-consuming and labor-intensive work. We developed a device for in-situ mea-surements of the vertical distribution of radioactivity in a soil using a photo diode sensor. Four photodiode sensors were separated by lead-shielded plates to increase direc-tivity at each depth. Because the directivity was relatively broad, we defined a leakage coefficient to compensate the broad directivity by introducing a matrix expression. With a field test of the device in an undisturbed rice field in Iitate Village, Fukushima, we confirmed that the vertical distri-bution of soil radioactivity was properly measured with the device developed.