Calibration of cylindrical detectors using a simplified theoretical approach

A novel analytical method to calibrate cylindrical side-hole type sodium iodide scintillation detectors

Geometrical and absolute efficiencies play a significant role in the calibration of radioactivity measuring systems, which are regularly complicated. A novel analytical method of efficiency calibration is proposed for cylindrical side-hole type sodium iodide scintillation detectors. Cylindrical side-hole type sodium iodide scintillation detectors have a cylindrical side-hole passing perpendicularly on the sodium iodide crystal axis, which is gathered in the aluminum cover. This detector is a setup for low-level gamma radiation measurement, because of the close 4π solid angle correlated with it, this setup is convenient when low-energy radiation requires efficient detection. Also, the 4π gamma-ray counting is an established way for direct activity measurements and is remarkably well suited for radionuclides with complex gamma-ray spectra. This novel approach depends on the calculation of two primary factors, the photon path length inside the detector active material, and the solid angle, delimited by the radiation source-detector system. In addition, the attenuation of photons by the sodium iodide crystal covering substance is also included by determining the photon path length through this substance. The novel analytical approach calculates the total and geometrical efficiencies of this kind of detector. In comparison, the differences with the published data in the literature indicate that the current approach is favorable in the efficiency measurement of the cylindrical side-hole type sodium iodide scintillation detectors.

Dead layer estimation of an HPGe detector using MCNP6 and Geant4

In this study, Monte Carlo simulations were used to calculate the full-energy peak efficiency of a p-type coaxial high-purity germanium (HPGe) detector. The HPGe detector was modeled using MCNP6 and Geant4, and the thickness of the dead layer of germanium crystals was estimated for an accurate simulation. The dead layer was divided into front and side components, where a point source and a Marinelli beaker source were used to estimate each dead layer thickness. The model was validated by comparing the simulated as well as experimental results for the standard sources of cylindrical and Marinelli beakers. The Geant4 results and experimental results matched up to 4% in the 59.54-1836.05 keV energy range, while MCNP6 matched up to 6% when adjusted for coincidence summing effects. HPGe detector modeled in Monte Carlo simulations can be utilized for experimental validation and experimental setup prior to using actual HPGe detectors.

Simulation of a HPGe Detector with GEANT4

Gamma spectroscopy is an analytic technique that identifies isotopes through gamma rays. Currently, gamma spectroscopy is widely used in several science fields, for instance, the study of the hydrodynamics of soils and other applications. Considering the development of computers, it has been developed Monte-Carlo simulation packages, in order to estimate the response of gamma spectroscopy detectors. This work aims to develop a GEANT4 application to estimate the full energy peak efficiency for a HPGe detector and determine the deviation with experimental data. It was carried out measurements of the next radioactive sources, Am-241, Eu-152, Cs-137, and Co-60. These measurements were made at different distances, they were at 0, 5, 10, 20, and 25 cm from the detector’s cover layer. Meanwhile, the simulation was carried out through user action classes to extract energy deposited in the sensitive detector. It was determined full energy peak efficiency of experimental data, through these results, it was estimated a detection factor that measures the deviation between experimental and simulated data. A reason for the deviation was that the simulation did not include the electronic chain of acquisition. Finally, it was suggested that future works should develop a more accurate simulation for multi-emitters isotopes.

New analytical approach to calibrate the NaI (Tl) detectors using spherical radioactive sources

A new theoretical approach was used to calibrate and calculate the full-energy peak efficiency of the NaI (Tl) detectors based on the direct statistical method proposed by Selim and Abbas for cylindrical detectors. In addition, the self-attenuation of the source matrix, the attenuation by the source container and the detector housing materials were considered in the mathematical treatment. Results were compared with those measured by a cylindrical NaI (Tl) detector with resolution (FWHM) at 662 keV equal to 7.5 %. (152)Eu aqueous radioactive spherical sources covering the energy range from 121 to 1408 keV were used. In comparison, the calculated and the measured full-energy peak efficiency values were in good agreement.

Probability correction for the analytical simulation approach to calibrating γ-ray cylindrical detectors for environmental measurements

Marinelli beakers increase geometric efficiency of detection in the γ-spectrometry of low-activity environmental samples by positioning the sample in close proximity to the detector. A probability correction has been introduced to the analytical simulation approach proposed previously (Nafee et al., 2009) for calculating detection efficiencies of γ-ray cylindrical detectors using extended low- and high-volume Marinelli beakers. Improved expressions for the self-attenuation and the coincidence summing effects at short source-detector distances have also been included in the analytical algorithm. A remarkable agreement between the measured and calculated efficiencies was observed as a result. Deviations of results calculated in this way from experimental values are twice as small as were observed with the previously reported analytical methods (Abbas, 2001; Nafee et al., 2009).

New numerical algorithm method to calibrate the HPGe cylindrical detectors using non-axial extended source geometries

The knowledge of the full-energy peak efficiency for a specific source-detector arrangement is often required in various fields of research and applications, such as the analysis of nuclear waste or environmental samples, where both require modeling because it is not practical to prepare a standard that matches the physical and nuclear properties of every waste or environmental item. Therefore, a new numerical algorithm method (NAM) is proposed in the present work to calibrate the co-axial HPGe cylindrical detectors. Cylindrical sources are used in the calibration process placed perpendicularly to the detector's axis. The self-attenuation and the coincidence summing effects at low source-detector distance are also included in the algorithm. A remarkable agreement between the measured and the calculated efficiencies is achieved with discrepancies less than 3%.

Calculation of total counting efficiency of a NaI(Tl) detector by hybrid Monte-Carlo method for point and disk sources

This paper presents results on the total gamma counting efficiency of a NaI(Tl) detector from point and disk sources. The directions of photons emitted from the source were determined by Monte-Carlo techniques and the photon path lengths in the detector were determined by analytic equations depending on photon directions. This is called the hybrid Monte-Carlo method where analytical expressions are incorporated into the Monte-Carlo simulations. A major advantage of this technique is the short computation time compared to other techniques on similar computational platforms. Another advantage is the flexibility for inputting detector-related parameters (such as source-detector distance, detector radius, source radius, detector linear attenuation coefficient) into the algorithm developed, thus making it an easy and flexible method to apply to other detector systems and configurations. The results of the total counting efficiency model put forward for point and disc sources were compared with the previous work reported in the literature.