Upper limit of 83Rb release into the gas phase from a 83mKr calibration source for the XENON project

The isomer 83mKr with its half-life of 1.83 h is an ideal calibration source for a liquid noble gas dark matter experiment like the XENON project. For such a low counting experiment the possibility that traces of the much longer living mother isotop 83Rb (t1/2 = 86.2 d) contaminate the detector must be avoided. In this work the 83Rb release of a 1.8 MBq strong 83Rb source embedded in zeolite spheres has been investigated by searching for the characteristic 83Rb γ lines with the ultra-sensitive germanium detector Gator at LNGS after collecting a possible 83Rb release in a cryogenic trap for about 10 days. No signal has been found. The corresponding upper limit for the 83Rb release of 200μBq means, that such a 83Rb source as 83mKr generator can be used at the XENON project as well as for the KATRIN experiment. % without the danger of contaminating the detector with 83Rb. The germanium detector also allowed to set upper limits on the possible release of the isotopes 84Rb and 86Rb, which were produced during the 83Rb production at the Rez cyclotron to some amount.