Metal Container Instead of Glass Bulb in Tritium Measurement by Helium-3 Ingrowth Method

The performance of a mass spectrometric system for measurement of tritium by ³He ingrowth method is described. Preparation and measurement includes three steps. The first step is to pump the dissolved gas from the environmental water samples stored in special glass bulb. The second step is the storage of the degassed water for a few months. In the final step the helium-3 formed from tritium is measured by mass spectrometer. In the course of tritium measurement there were some difficulties with the glass bulbs, such as pre-treatment of the glass, storage of the samples in deep freezer, long storage time, O-ring sealing. To solve these problems metal bulbs were built and applied with volume of six litres. The metal bulb was equipped with a metal valve. Three litres of water can be filled into the metal bulb. The large volume of the bulb causes an increase of degassing time, and a decrease of the storage time. The degassing of three litres of water needs twice one and a half hours in two days. The storage time is only two months in contrast to the half-year storage time of glass bulb. The background, the helium penetration from the air is less than using glass bulbs, because the metal bulb can be fitted to the inlet system via copper gasket instead of elastic O-ring.