Measurement methods for iodine-derived contamination in L-[¹¹C]methionine injection were evaluated. L-[¹¹C]Methionine injection and samples from the mock synthesis routes where iodine vapor was introduced with or without passing precolumns of sodium hydroxide-coated silica (Ascarite columns) were used. The contents of total iodine, iodide ion, and I₂ were determined by ICP-MS, HPLC-UV detection, and N,N-diethyl-1,4 phenylenediamine method, respectively. Total iodine contents measured by ICP-MS indicated the potentials of Ascarite columns for removing I₂ . The iodine-derived contamination existed as iodide ion in the L-[¹¹C]methionine injections. Accordingly, measurement of iodide ion by HPLC offers a rapid and useful means of controlling the manufacturing processes of L-[¹¹C]methionine injection.

In recent years, new method called “microdose study” has been developed to directly investigate pharmacokinetics in the human body using a limited amount of ¹⁴C labeled candidate compounds which is less than 100 µg or 1％ of the dose that yields pharmacological effects. Drug development costs are expected to be dramatically decreased by this new method. Since the required abundance sensitivity of ¹⁴C analysis in the microdose studies is 10⁻¹⁰–10⁻¹², Accelerator Mass Spectrometry (AMS) is presently used for this purpose. However, the high cost and limited throughput in ¹⁴C analysis by AMS may prevent from wide expansion of the microdose studies to drug development. As an alternative method, we are developing ¹⁴C detection system based on Cavity Ring-Down Spectroscopy (CRDS) for microdose studies.

It is important to understand potassium (K) behavior in soils since K fertilization is one of the most effective countermeasures to reduce the radiocaesium (RCs) uptake by crops. The K behavior in soils is highly influenced by the clay mineral composition. In this study, we investigated the K behavior for non-vermiculitic and vermiculitic nature of soils at Fukushima Prefecture in Japan. In the adsorption experiments, vermiculitic nature of soils exhibited more adsorption of K onto the soils as compared to non-vermiculitic nature of soil. One dimensional column transport experiments using ⁴²K as a radioisotope tracer showed that almost similar K mobility for all soils as supported by adsorption isotherms of K. However, percentage of exchangeable K in the total K retained in the soil was higher in non-vermiculitic nature of soil, while the percentage of fixed K was higher in vermiculitic nature of soils. Thus, the existence of vermiculite with high K fixation capacity was suggested to reduce K retention as an exchangeable form in vermiculitic nature of soils.

Search for cosmic dark matter is one of the most important tasks in both astrophysics and particle physics. Various types of highly sensitive radiation detectors have been applied to searching for dark matter in the world. The NaI(Tl) scintillator is well-known radiation detector: it has been applied to the studies of dark matter and rare processes of fundamental physics. One needs to purify the detector down to a few µBq/kg to search for dark matter because of extremely small expected event rate of dark matter candidate. The author describes the recent status of low background detectors for dark matter search and the project to search for dark matter by using highly radiopure NaI(Tl) scintillator.