Abstract
To efficiently measure the radioactivity of radiocesium (137Cs) in samples from a forest ecosystem, we examined whether the following two measuring methods are acceptable by comparing them to a normal method that uses an U-8 container and a coaxial Ge detector for a powdered sample: 1) filling a Marinelli container sparsely with an unpowdered sample and 2) using a #737 container and a well Ge detector. The 137Cs activity determined by both methods showed no systematic errors. Additional random errors caused by the former method were estimated to be less than 7% and those caused by the latter method less than 6%. The measurements using a #737 container (well Ge) tended to produce smaller values when self-absorption of the gamma rays was corrected in the same way as for the U-8 container (coaxial Ge) but showed reasonable values when the self-absorption was corrected using the bulk density of a reference material or when the self-absorption was not corrected. In addition, we found that measuring only a part of the sample with a smaller-volume container than the sample volume itself resulted in relatively large errors even though the samples were powdered. Thus, it is important to select a measurement container matching the sample volume to achieve measurements that are efficient and have small errors.
