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Radiometry
α-Spectrometry
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
offene Halbleiterkammer
open vacuum chamber
Alphaspektrum
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
Strahlungsfeld
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
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