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Abstract In order to monitor the intense neutron and gamma radiation, multi-element tissue equivalent proportional counters (TEPC) based on the standard gas electron multiplier (GEM) and ceramic thick GEM (THGEM) foils were designed and respectively tested by implanted 55Fe and 241Am sources which would also be used as calibration sources. The performance testing of GEM-TEPC/THGEM-TEPC detectors at various parameters showed that the detectors could work well. The THGEM-TEPC was also used to measure the linear energy spectra in 241Am–Be and intense (108 ncm−2s−1) neutron radiation fields. The results displayed that THGEM-TEPC was available to do microdosimetric research or be a dosimeter in intense neutron/gamma field. [ABSTRACT FROM AUTHOR]

Traditionally experimental microdosimetry has employed low pressure single cavity spherical Tissue Equivalent Proportional Counters (TEPCs). Multi-Element Tissue Equivalent Proportional Counters (METEPCs) with numerous cylindrical cavities have been constructed in order to increase sensitivity per unit volume; however existing METEPC designs are prohibitively complex and sensitive to motion and audible noise. This work proposes a novel hemispherical element with a wire-less anode ball as a solution to these issues. The gas gain characteristics of this hemispherical METEPC element were analyzed first for a single hemispherical TEPC to evaluate performance relative to current cylindrical and spherical counter designs that have been demonstrated experimentally to perform very well. This gain analysis evaluated relative avalanche size and the uniformity in maximum gain for electrons originating throughout the gas cavities of each of the three counters. Radial gas gain distributions for each counter were determined using both theoretical potential distributions as well as analytical equipotential distributions generated with ANSYS Maxwell (V. 14.0) to solve the Townsend equation. It was found that the hemispherical counter exhibits completely uniform gas gain for electrons approaching the anode from all directions and its avalanche region occupies only 3.5×10 −3 % of the entire gas cavity volume, whereas in the cylindrical and spherical counters the avalanche occupies 0.6% and 0.12% of the total respective gas cavity volumes. These analytical gas gain results are promising, suggesting that the hemisphere should exhibit uniform signal amplification throughout the gas cavity and if the recommended follow-up experimental work demonstrates the hemispherical counter works as anticipated it will be ready to be incorporated into an METEPC design. [ABSTRACT FROM AUTHOR]

Abstract: This study describes the measurement of lineal energy spectra carried out with a graphite walled proportional counter (GPC) simulating 1μm tissue equivalent (TE) site diameter in low energy neutron fields generated by employing the McMaster University 1.25MV double stage Tandetron accelerator. Experiments were carried out for neutron beams of mean energies extending from 34 to 354keV in direct neutron beams from the 7Li target using proton beam energies ranging from 1.89 to 2.56MeV. We have observed a continuously increasing trend in microdosimetric averages, and , and the ICRP 60 based quality factor, Q, with an increase in neutron energy. It is interesting to note that standard tissue equivalent proportional counters (TEPCs) give rise to a similar trend for these microdosimetric quantities of interest in the same energy range. Quantitatively, these quantities are also comparable to those obtained with standard TEPCs. This implies that at the microdosimetric level in the neutron energy range we employed in this study, the pattern of average energy deposited by ‘starter’ and ‘insider’ proton recoil events in the gas is similar to those generated cumulatively by ‘crosser’ and ‘stopper’ events originating from the counter wall plus ‘starter’ and ‘insider’ recoil events originating in the sensitive volume of a TEPC. This suggests that the average energy deposition per event in the wall of a TEPC counter is the same as in the counting gas itself, which confirms the similarity of the composition and mass stopping power of two media, i.e., TE wall and TE gas, used in neutron dosimetric measurements. [Copyright &y& Elsevier]

The Active Tissue Equivalent Dosimeter (ATED) is a low-cost, easy-to-use and compact tissue equivalent proportional counter designed for use aboard spacecraft, satellites, aircraft, unmanned aerial vehicles and high-altitude balloons. ATED was rigorously tested at particle accelerator facilities utilizing heavy ions of charge and energy similar to Galactic Cosmic Rays (GCRs). Upon completion of the ground-based testing and calibration, the ATED was operated aboard the International Space Station (ISS) during July–August of 2018. ATED measurements from the ISS were then analyzed in terms of time, latitude, longitude, and altitude in order to correlate with the radiation fields in the ISS orbit. When ATED measurements were correlated with orbital position, elevated absorbed dose rates due to the South Atlantic Anomaly (SAA) were clearly evident. ATED measurements were also separated based on their orbital location into three different regions. The results from the July–August 2018 flight show that ATED functioned as designed while onboard the ISS. The hypothesis that lineal energy and linear energy transfer can be used interchangeably with measurements by a TEPC in Low Earth Orbit (LEO) was tested by ATED measurements. Lastly, a direct comparison was made between linear energy transfer (LET) converted from lineal energy spectra from a spherical TEPC in LEO and model-calculated LET values. Such a comparison is highly challenging with the TEPCs with cylindrical geometry previously used in space. [ABSTRACT FROM AUTHOR]

Abstract: Beam tests were performed for a Micro Pixel Chamber (-PIC) with a detection volume of to investigate the response to heavy ions. The three-dimensional tracks of carbon, silicon, and iron beams were successfully observed and their track lengths were measured. Additionally, Linear Energy Transfer (LET) distributions of each ion were obtained, and the mean LET values were consistent with the theoretical calculation of mass stopping power within an error of . This detector is a candidate for an ideal dosimeter in space. [Copyright &y& Elsevier]

Abstract: For a passive scattering nozzle at the Proton Medical Research Center (PMRC), the distribution of the neutron dose equivalent in the direction transverse to the proton beam line was measured for 200MeV protons using a tissue equivalent proportional counter REM500. The neutron dose equivalent per Gray of proton-absorbed dose at the isocenter was approximately 2.3mSv/Gy. The neutron dose outside of the treatment field was approximately 2mSv/Gy, at maximum and it should be reduced as low as possible according to the ALARA principle. The aperture size of the multi-leaf collimator (MLC), which is a pre-collimator for shielding unwanted protons and mounted at a position upstream from the patient bolus and collimator, was varied in order to investigate its reduction effect on the neutron dose equivalent outside of the treatment field. We confirmed that the neutron dose equivalent outside of the treatment field can be limited depending on the aperture size of the MLC. This could be considered in future treatment planning optimization and patient treatment. MCNPX calculations showed good agreement with the measurements within 10%. [Copyright &y& Elsevier]

Abstract: A fast neutron irradiation field for biological studies was established at the cyclotron facility in the National Institute of Radiological Sciences. Neutron spatial distributions and absorbed dose distributions were measured to characterize the neutron field. By using a simple technique that an aluminum plate activated by neutrons was exposed to the imaging plates, the width of the neutron-irradiated area was measured to be 23.6cm with 2.5mm spatial resolution. The absorbed dose distributions of neutrons and rays were obtained separately by using a tissue-equivalent plastic- and a graphite-walled low-pressure proportional counter. The neutron absorbed dose in a tissue-equivalent plastic was measured to be 144.6 (Gy/C). It was confirmed that this neutron field has only 1.8% contamination of -ray dose and has good quality for neutron irradiation to biological samples. [Copyright &y& Elsevier]

By employing a Gas Electron Multiplier a new type of mini multi-element Tissue-Equivalent Proportional Counter (TEPC) has been designed and constructed. In this paper, we describe the design of this novel counter. The first pulse height measurements with this counter for both methane- and propane-based Tissue Equivalent gases are presented. These results show promising properties for application of this novel type TEPC in microdosimetric measurements. [Copyright &y& Elsevier]

We have studied the operation of two different Gas Electron Multiplier (GEM) structures in both methane and propane based Tissue-Equivalent (TE) gases at different pressures varying from 0.1 to 1 atm. This work was motivated to explore the possibility of using a GEM for a new type of Tissue Equivalent Proportional Counter. In methane based TE gas, a maximum safe GEM gain of 1.5×103 has been reached while in propane based TE gas this is 6×103. These maxima have been reached at different gas pressures depending on GEM structure and TE gas. Furthermore, we observed a decrease of the GEM gain in time before it becomes stable. Charge up/polarisation effects can explain this. [Copyright &y& Elsevier]

A comparison of two types of dose equivalent meters, a recombination chamber REM-2 and a tissue-equivalent proportional counter (TEPC) Homburg Area Neutron DosImeter (HANDI), were carried out at the CERN-EC high-energy reference field facility, CERF, in October 2001. Here, the mixed high-energy radiation field in commercial flight altitudes can be simulated with dose rates up to 2 orders of magnitude higher. The total absorbed dose and the dose equivalent have been measured at different radiation field intensities. Of particular interest for measuring in the CERF field is the assessment of the low LET-component, i.e. the γ and muon components of the field, which are not taken into account by existing Monte Carlo simulations modeling the radiation field. The new results for the estimation of the low LET-component are compared with previous ones delivered by REM-2 at CERF. The results show good agreement between the REM-2 chamber and the HANDI. [Copyright &y& Elsevier]

Microdosimetric parameters measured by a TEPC have been studied in the mixed radiation fields generated by the two D-T neutron generators developed at BARC and IGCAR facilities of DAE, India. These two generators differ in their sizes and designs. The present study reveals that the radiation fields by these two generators are significantly different. In the case of compact design (IGCAR generator) due to the significant contribution of bremsstrahlung photons in the total radiation field, the frequency and dose mean lineal energy, average quality factors are considerably less (factors of 3 to 6) than the BARC D-T generator. The study also reveals that the photon contribution to the total dose equivalent can be as high as 30% for compact D-T generator. • Measurement of microdosimetric parameters of neutrons produced by D-T generator using TEPC. • Average quality factor of the mixed radiation field of the D-T generator. • Microdosimetric spectra of high energy neutrons. [ABSTRACT FROM AUTHOR]