The radiation physics group has different test devices for the measurement of α-spectra. One is a grid ionisation chamber where probes of activities from µBq up to Bq can be analysed. Further, there is a semiconductor chamber for activities between Bq and MBq.
Semiconductor chamber for α-spectrometry
open vacuum chamber
spectrum of a mixed probe
In the vacuum chamber, the pressure can be varied between normal pressure and fine vacuum (0.01 mbar). The detector is a PIPS-detector with an active surface of 300 mm2. In combination with a charge sensitive preamplifier and a pulse height analyser, an energy resolution of (15.4 ± 0.7) keV (FWHM) is achieved for an α-energy of 5,486 MeV.
The background is about 8 counts per hour between 2 and 6 MeV. Thus, it is possible to analyse the spectra of α-sources down to 0.1 Bq. The lower detection limit is about 0.01 Bq.
For the insertion of the probe, a probe wheel is installed at about 1 cm distance from the detector. It is possible to mount up to 5 sources and measure them one after the other. For larger probes or radiation sources, individual holders can be designed.
radiation field measurement with the semiconductor chamber
radiation field of an α-source at a distance of 7.5 mm
It is possible to analyse the radiation field of an α-source in defined distances. For this task, a collimator is positioned in front of the detector, and the source is shifted via an x-y-desk. The collimator size defines the spatial resolution.
For example, the picture to the right shows the radiation field of an 241Am-source in 7.5 mm distance (activity 3.4 MBq). The quadratic collimator is of 0.5 mm x 0.5 mm edge length. The measurement entire covered 2601 points for 160 s measurement time each. This provided a spatial resolution of 0.5 mm over a length of 2.5 cm with about 15 keV energy resolution.
For questions and remarks concerning this web page please send email to: PD Dr. J. Henniger
Last Update: 11. 12. 2015