A low background ionisation chamber for alpha-spectroscopy

The goal of designing a low background ionisation chamber is to measure long lived alpha-decay half-lives which might interfere with rare event searches. Such decays play a part in many fields in nuclear physics and are difficult to measure. A lot of Geiger-Nutall studies also depend on them. Among others the research is specifically aimed at the precision measurements of alpha emitters mainly within the Lanthanide region. The excellent energy resolution would also allow to search for excited states in alpha-decays. To achieve this goal a gridded ionisation chamber was constructed using the Frisch-Grid design. A background rate of only 10.9(6) counts per day has been achieved in the energy region of 1 MeV to 9 MeV and improvements are possible. This low background rate and size of the chamber allows precision measurements of long living alpha decays with half-lives in the region of 1 x 10(15) years.