Search

Investigations of possibilities to determine /sup 90/Sr//sup 90/Y in environmental samples with Cherenkov radiation of /spl beta/-particles in silica aerogels are presented. The Cherenkov photon detection is performed with a multianode photomultiplier (Hamamatsu R5900-00-M16). With the signal from a thin wire chamber in coincidence, a background count rate of 2 events per hour has been acheived. Measurements of efficiencies for different /spl beta/-emitters are presented as well as the distributions of the number of detected Cherenkov photons per event. Possibilities for improvement of the sensitivity of the method are indicated.

A multiwire proportional chamber with CsI photocathode as a detector of Cherenkov photons has been studied. Cherenkov radiation has been produced in an NaF radiator by cosmic rays and by electrons from /sup 90/Sr. Results on the variation of the CsI quantum efficiency over a period of 500 days are presented. Some preliminary data concerning the production of CsI photocathodes and the regeneration of the quantum efficiency by heating are given. >

A summary of experimental studies of different photon detectors is presented. A CsI photocathode in a multiwire proportional chamber, a TMAE based gaseous photon detector and a new Hamamatsu multianode photomultiplier tube have been investigated in order to evaluate their suitability as photon detectors in the ring imaging Cherenkov counter of HERA-B. The results of the present work suggest that only the MA-PMT meets the demanding requirements of the HERA-B experimental environment. The CsI-MWPC cannot be routinely produced and maintained with sufficiently high quantum efficiency and the TMAE photon detectors lose gain as a result of relatively quick anode wire ageing.

The HERA-B RICH detector was installed in spring 1998, and has been in stable operation over the last two years. The design criteria, detector components and event analysis tools are reviewed, and the observed particle identification capabilities are presented. The performance was found to meet design expectations.

The highly radiotoxic /sup 90/Sr cannot be determined by /spl gamma/-spectrometry as /sup 90/Sr and its daughter /sup 90/Y are both pure /spl beta/-emitters. Cherenkov radiation of the relatively high energy /spl beta/-particles from /sup 90/Y (E/sub /spl beta///sup max/=2.27 MeV) allows for discrimination or at least for strong suppression of the lower energy /spl beta/-emitters. The contribution of both may then be determined from /sup 90/Y if their ratio is known. Measurements of efficiencies with a silica aerogel radiator (n=1.055), show a steep dependence on the /spl beta/ end-point energy above threshold (E/sub /spl beta///sup th/=1.09 MeV). Possible contributions from /spl beta/-emitters other than /sup 90/Y in the sample may be detected by the shape of the pulse height spectrum. Using a multiwire proportional chamber in coincidence and plastic scintillation counters in anticoincidence reduces the background, so environmental activities down to about 1 Bq of /sup 90/Sr//sup 90/Y may be detected in a few hours of measurement of a thin sample (air filter or sediment).