Space radiation dosimetry measurements have been made onboard the Space Shuttle STS-65 in the Second International Microgravity Laboratory (IML-2: 28.5° x 300 km: 14.68 days) and the STS-79 in the 4th Shuttle MIR mission (S⁄MM#4: 51.6° x 300-400 km: 10.2 days). In these measurements, three kinds of detectors were used; one is a newly developed active detector telescope called “Real-time Radiation Monitoring Device (RRMD-I for IML-2 and RRMD-II with improved triggering system for S⁄MM#4)“ utilizing silicon semi-conductor detectors and the other detectors are conventional passive detectors of thermoluminescence dosimeters (TLDs) and CR-39 plastic track detectors. The main contribution to dose equivalent for particles with LET > 5.0 keV⁄μm(IML-2) and LET>3.5. keV⁄μm (S⁄MM#4) is seen to be due to galactic cosmic rays (GCRs) and the contribution of the South Atlantic Anomaly (SAA) is less than 5%(IML-2: 28.5° x 300 km) and 15% (S⁄MM#4: 51.6° x 400 km) in the above RRMD LET detection conditions. For the whole LET range (> 0.2 keV⁄μm) obtained by TLDs and CR-39 in these two typical orbits (a small inclination x low altitude and a large inclination x high altitude), absorbed dose rates range from 94 to 114 μGy⁄day, dose equivalent rates from 186 to 207μSv⁄day and average quality factors from 1.82 to 2.00 depending on the locations and directions of detectors inside the Spacelab at the highly protected IML-2 orbit (28.5°x 300 km) , and also, absorbed dose rates range from 290 to 367 μGy⁄day, dose equivalent rates from 582 to 651 μSv⁄day and average quality factors from l.78 to 2.01 depending on the dosimeter packages around the RRMD-II “Detector Unit” at the S⁄MM#4 orbit (51.6° x 400 km). In general, it is seen that absorbed doses depend on the orbit altitude (SAA trapped particles contribution dominant) and dose equivalents on the orbit inclination (GCR contribution dominant). The LET distributions obtained by two different types of active and passive detectors, RRMDs and CR-39, are in good agreement for LET of 15 - 200 keV⁄μm and difference of these distributions in the regions of LET<15 keV/μm and LET >200 keV⁄μm can be explained by considering characteristics of CR-39 etched track formation especially for the low LET tracks and chemical etching conditions.
The distributions of linear energy transfer for LET (LET water ) in front of the 80-cm-thick concrete side shield at the CERN-EU high-energy reference field (CERF) facility were measured with a Si detector telescope named real-time radiation monitoring device-III (RRMD-III) covered with and without a 1 cm-thick acrylic plate. In these measurements, a difference of about 20% in the absorbed dose between the two LET water distributions was observed as a result of protons, deuterons and tritons recoiled by neutrons. The LET water distribution obtained using RRMD-III without the 1-cm-thick acrylic plate is compared with lineal energy distributions obtained using the dosimetric telescope (DOSTEL) detector under the same conditions. These dose equivalents are also compared with that obtained using HANDI TEPC which is used as the standard at the CERF facility.
Borak, T. B., Doke, T., Fuse, T., Guetersloh, S., Heilbronn, L., Hara, K., Moyers, M., Suzuki, S., Taddei, P., Terasawa, K. and Zeitlin, C. J. Comparisons of LET Distributions for Protons with Energies between 50 and 200 MeV Determined Using a Spherical Tissue-Equivalent Proportional Counter (TEPC) and a Position-Sensitive Silicon Spectrometer (RRMD-III). Radiat. Res. 162, 687–692 (2004).Experiments have been performed to measure the response of a spherical tissue-equivalent proportional counter (TEPC) and a silicon-based LET spectrometer (RRMD-III) to protons with energies ranging from 50–200 MeV. This represents a large portion of the energy distribution for trapped protons encountered by astronauts in low-Earth orbit. The beam energies were obtained using plastic polycarbonate degraders with a monoenergetic beam that was extracted from a proton synchrotron. The LET spectrometer provided excellent agreement with the expected LET distribution emerging from the energy degraders. The TEPC cannot measure the LET distribution directly. However, the frequency mean value of lineal energy, ȳf, provided a good approximation to LET. This is in contrast to previous results for high-energy heavy ions where ȳf underestimated LET, whereas the dose-averaged lineal energy, ȳD, provided a good approximation to LET.
We are developing a new type of photon detector for an experiment searching for muon decays to positron+gamma with a sensitivity of 10/sup -14/ branching ratio by using the world most intense continuous muon beam provided at PSI. In this experiment the photon detector utilizes liquid xenon as a scintillation material because of its fast response, large light output yield, and high density. Scintillation light emitted in liquid Xe is directly observed by photomultipliers (PMTs) located in a liquid without any transmission window in order not to lose light yield. To study the detector response to gamma rays we constructed a prototype with an active volume of 2300 cm/sup 3/ surrounded by 32 PMTs. The PMT was newly developed so as to be operated even in liquid Xe at 165 K. The energy, position, and timing resolution have been evaluated with gamma-ray sources from 320 keV to 1835 keV. The performance of the prototype is presented.
