Low-level activity measurement of 131Xem, 133Xem, 135Xe and 133Xe in atmospheric air samples using high-resolution dual X–γ spectrometry

The NMIJ air kerma primary standard for high energy x-ray beams in 300-450 kV

Accurate radiation dosimetry is required for radiation protection in various environments. Therefore, dosemeters and dose-rate meters must be calibrated in standard radiation fields. The National Metrology Institute of Japan (NMIJ) expands the energy range of x-ray reference field measurement up to 450 kV using a cylindrical graphite-walled cavity ionization chamber. Departure from the condition of the Spencer-Attix cavity theory was evaluated by comparing the measurement results obtained using the cavity ionization and the free-air ionization chambers, which are used as the primary standard up to a tube voltage of 250 kV. The calibration coefficients found using the spherical ionization chamber were in good agreement with those obtained by the free-air ionization chamber within relative standard uncertainties (k = 1) for N-200 and N-250 x-ray fields. Consistent calibration coefficients were obtained in the energy range 300-450 kV.

Assessment of a compton-suppressed spectrometer for measurement of radioactive xenon isotopes

Airborne radionuclide monitoring is considered to be the most certain way to detect a clandestine nuclear weapon test. The activity concentration of radioxenon samples collected by the radionuclide stations of the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is generally performed at the low-level, hence it is necessary to improve the detection sensitivity of the radioactivity measuring apparatus for radionuclide monitoring. The Compton-suppressed spectrometer (CSS) has the advantage of reducing the background and improving the sensitivity in the environmental level measurement. Therefore, the measurement of the relevant radioxenon sample at the environmental level is feasible by using CSS. To assess the performance of CSS for radioxenon measurements, the Compton-suppressed and unsuppressed spectra of the ¹³³Xe and ¹²⁷Xe samples have been acquired, and subsequently, the information of the full energy peaks (FEP) in the spectra were compared. The assessment indicates that CSS can provide high sensitivity, simple operation, and straightforward activity determination, and it can be regarded as an appropriate apparatus in the radioxenon measurement.

Calibration of HPGe Detector Efficiencies With Self-Absorption Correction of Gas Sphere Sources

Several types of radioactive gases are released from the nuclear reactor. In order to measure the activity of such gases, it is necessary to calculate the accurate efficiency. Practically, efficiency calibration with gaseous sources is not very easy because of the low half-lives of the noble gases. For this purpose, Monte Carlo (MC) simulation was performed to study the full energy peak efficiency of two n-type high-purity Germanium (HPGe) detectors. Two spheres of xenon and krypton composition sources with two nuclides (Xe133 and Kr85) and two-point sources were simulated, covering the energy range from 81 keV to 604 keV. Self-absorption correction factors were calculated with GEANT4 for two gas sphere samples and obtained good efficiency agreement with the experimental results. The simulation was performed for various gas samples with different densities and observed their effects on the full energy peak efficiency value of two detectors. The corresponding self-absorption correction factors were calculated for each gaseous sample and investigated that the self-absorption correction factors not only depend on the sample characteristics but also on the detector geometry and source to detector distance. The dependence of the full energy peak efficiency on the side cap wall material and their thicknesses were also carried out for some particular photon energies.

Low-level laboratory measurement of xenon radionuclides: Electron-photon versus photon measurements

Radioactive xenon (mainly ^131mXe, ¹³³Xe, ^133mXe and ¹³⁵Xe) are tracked as markers of nuclear weapons testing. The CEA has developed the PIPSBox, a measurement cell able to detect electrons emitted by xenon nuclides. Combined with an ultra-low background γ spectrometer, electron detection capacities allow reaching minimum detectable activities (MDA) for a 3-day long measurement of about 0.5mBq for the four xenon radionuclides. Compared to a classical measurement cell, MDAs are improved by a factor of 2-4.

Performance assessment by Monte Carlo simulations of a prospective assembly of up to three HPGe detectors designed for superior detection efficiency and sensitivity

The present work reports on the results of Monte Carlo simulations performed with MCNP on an assembly of two HPGe detectors facing each other regarding detector efficiencies. Report is also made when a third detector is added to the previous configuration from below. Moreover cross talk between detectors is investigated and found of limited impact. The choice for an actual detector goes to the three detector configuration for accommodating most geometries while cost and engineering constrains remain acceptable.