Study of 222−220Rn Measurement Systems Based on Electrostatic Collection by Using Geant4+COMSOL Simulation

New-designed measurement device for radon and thoron activity concentration based on gas direct detection

A new-designed measurement device for radon and thoron activity concentration is developed based on gas direct measurement to support their in-situ calibration. It consists of a 2000 mm2 Passivated Implanted Planar Silicon (PIPS) detector, a Multi-Channel Analyzer (MCA), a Micro Controller Unit (MCU), and a small electrostatic chamber with a volume of nearly 23 ml. The device records those alpha particles emitted from radon and thoron gas, and the detection efficiency and the crosstalk factor of 218Po/216Po are determined by Monte Carlo simulation. Measurement results have been compared with AlphaGUARD DF2000 in pure radon and thoron environments, respectively. Results show that the measurement results of the devices and the reference monitor agree well with each other, with an average relative deviation of 0.48% for radon gas from about 3300 Bq/m3 to 38 kBq/m3 and -3.25% for thoron gas from about 25 kBq/m3 to 70 kBq/m3. Uncertainty assessment has also been done, and a relative system uncertainty of radon is about 6.8%, while that of thoron is nearly 7.3%.

Optimizing some parameters of air-filled ion pulse ionization chambers for effective radon detection

Air-filled ionization chambers in pulse ion mode can provide precise low-level detection of indoor/outdoor radon. However, it suffers from relatively high collection duration of positive and negative charges as well as environmental changes. In order to overcome these shortcomings, the Garfield++ software which is a powerful toolkit to develop a realistic simulation framework for radiation detectors was applied. Also, Garfield++ interface to Magboltz was used to calculate the gas parameters for air at various humidity conditions for a wide range of electric field strengths in order to compare the results with other available data in the literature. The Garfield++ software was also used to calculate maximum charge collection duration for a wide range of tube radii, wire radii, and electric potentials which are the main parameters affecting the charge collection duration. Furthermore, the influence of environmental conditions including air pressure, temperature, and humidity on the charge collection duration was investigated. The results show that for an air-filled radon ionization chamber with a moderate size (e.g. 1 L) with a bias voltage of hundreds of volts, the time constant of the external circuit can be chosen to be less than 100 ms, which is much lower than the values used in other studies. Therefore, with a proper design of an ionization chamber and its electronic system, it is possible to determine radon activity concentrations of up to a few tens of kBq.m^-3 in pulse mode. In conclusion, the data obtained in this study assists in developing radon air-filled ionization chambers in order to determine chamber dimensions and bias voltage as well as designing the readout electronics according to the characteristics required in an intended application.

Experimental and Geant4 Simulation Study of MURA Mask for Scintimammography

Gamma rays have been extensively investigated for breast imaging using collimators; however, the coded-aperture technique needs to be investigated more. In this paper, we propose an experimental study and Geant4 simulations of MURA mask breast imaging. First, we compare the experimental data against the simulation results carried out using Geant4 (version 10.4) and accreditation phantom. Second, we virtually extend our work by changing the tumor-to-background (TBR) and lesion location parameters. We used 99mTc as a radioactive source. Good agreement has been seen for the benchmark stage, especially in terms of tumor localization. Moreover, the calculated full width at half maximum (FWHM) and contrast for decoded images (having average values of 8 and 3.5 for TBR between 2 and 10) permitted us to conclude that we can accurately localize small lesions up to lower TBR values by following the decoding procedure of deducing the image of a “blank phantom” (phantom with TBR = 1) every time within a matlab-based program. Hence, this work can be considered a continuously added value to previous investigations for scintimammography imaging.