Preparation of low level sealed 210Pb source for random pulse generator

We have developed the random pulse generator (RPG) that utilizes alpha-particle detection with pin photodiode (PPD). In order to support an expected large market of RPG, a steady production system of weak (about 100 Bq) alpha sealed source is necessary, and, for such alpha-source, 210Pb-210Po source is the best candidate on a viewpoint of environmental radioactivity impact. Two methods for such 210Pb-210Po sealed source preparation, namely direct deposition from isopropyl alcohol solution (IPA solution) of 210Pb-210Po nitrate (D-IPA method) and the 210Pb-210Po hydroxides precipitation (PPT method), were experimentally examined. In the former D-IPA method, an aliquot of IPA solution of 210Pb-210Po nitrate was directly dropped in a sealed cap for PPD and dried by heating. Then, a polycarbonate (PC) solution of 1/1 mixture of dichloromethane and dichloroethane was dropped on the source to make a thin (about 0.1 mg/cm2) film for radioactivity sealed. In the PPT method, 210Pb-210Po hydroxide was filtrated on a PC membrane filter (Nuclipore 0.1 μm) and the membrane filter was dissolved in a 1/1 mixture of dichloromethane and dichloroethane. The sealed 210Pb-210Po sources were prepared directly by dropping an aliquot of the solution into the PPD cap followed by its evaporation. The sealed sources thus prepared were subjected to 1m height fall-down test, air blowing test, and water immersion test. It was confirmed that no radioactive contaminants were coming off from the sealed source through these tests. (author)