Alpha-, beta-, conversion electrons-, X-ray-detection systems with gas flow proportional multiwire detectors

To develop surface radioactivity measurement methods for alpha and beta emitters, a set of three types of detectors was realized and tested. The window areas are: 250 cm2, 400 cm2 and 800 cm 2. The basic radiometric performances obtained are: detection efficiency 70% - 75% / 2π sr. for alpha particles (241 Am, 239 Pu, 244 Cm); detection efficiency 90% - 93% / 2π sr. for beta particles (90 Sr + 90 Y); background rate 0.005 counts/min·cm2 for alpha regime and 1.7 counts/min·cm2 background rate for beta regime; plateau length 300 V - 400 V for alpha regime and 200 V - 300 V for beta regime; plateau slope 1%/100 V for both regimes. These kind of detectors are used for measuring and monitoring radioactive contaminated surfaces inside controlled areas. The results are worldwide competitive. For surface studies using hyperfine interaction, a detector assembly for simultaneous conversion electron Moessbauer spectroscopy (CEMS), conversion X-rays Moessbauer spectroscopy (CXMS) and transmission Moessbauer spectroscopy (TMS) was realized and studied. Two proportional low counters combined are used for CEMS and CXMS. The incident 14.4 keV γ-rays are able to permeate the sample and are detected by a third proportional detector located behind the CEMS/CXMS detector. To test the performance of the system, Moessbauer measurements were carried out at room temperature on a 25 μm thick natural stainless steel sample (Amersham International Plc Co.). Simultaneous Moessbauer spectra, using aluminium filter, was obtained for the three methods (CEMS, CXMS and TMS). (authors)