Efficiency Calibration Of Detectors Research Articles

A simple method for efficiency calibration of HPGe detectors in γ-spectrometric measurements

In this paper a simple, rapid and general method for γ-ray efficiency calibration of Ge detectors for environmental samples is presented. This method is based on the use of an active natural solid sample with several γ-emissions (in our case, 226Ra) as the calibrating matrix for determining the full energy peak efficiency (FEPE) ε c vs γ-emission energy E γ and the sample height h in a counting cylindrical geometry. The 226Ra activity concentration is determined by α-particle spectrometry, a method that has previously been validated.

Efficiency calibration of energy‐dispersive detectors for application in quantitative x‐ and γ‐ray spectrometry

AbstractA semi‐empirical method was used in a full‐peak efficiency calculation procedure; it was based on the measurements of characteristic x‐ray lines of pure elemental and compound samples and on the application of the fundamental parameter method (FPM) for the theoretical calculation of the characteristic x‐ray intensities. Radioactive standards were applied for the efficiency calibration of different semiconductor detectors [Si(Li), Si‐PIN and HpGe]. The efficiency curves were fitted to the characteristic intensities measured by a conventional Si(Li) and two Si‐PIN detectors, using 125I and 55Fe radioactive sources for x‐ray excitation in a ring‐shaped geometrical arrangement. Several quantitative applications in x‐ and γ‐ray spectrometry were carried out with these calibrated detectors: (i) x‐ray fluorescence (XRF) analysis of sediment samples [Si(Li)], (ii) determination of specific activity of 137Cs nuclide in sediment core samples originated from an oxbow area of the river Tisza, using γ‐spectroscopy (HpGe) with low‐background conditions, (iii) study of electrosorption phenomena at solid– liquid interfaces by making use of an in situ radiotracer method based on the application of low‐energy x‐ray emitting radionuclides (e.g. 65Zn), (iv) quantitative XRF analysis of ceramic glaze and (v) electron microprobe analysis of aerosol particles using an instrument equipped with a thin‐window Si(Li) detector. Copyright © 2001 John Wiley & Sons, Ltd.

Low level γ-ray germanium-spectrometer to measure very low primordial radionuclide concentrations

A new germanium spectrometer especially suited for large sample measurements is described in detail. It is operated in the Gran Sasso underground laboratory under shielding rock of 3300 m water equivalent, which reduces the muon flux by six orders of magnitude. The integral background counting rate in the energy range from 50 to 2750 keV is about 0.15 min−1. The low peak count rates of mostly less than 1 count per day together with a relative efficiency of 102% and the high sample capacity makes this spectrometer one of the most sensitive worldwide. Some sample measurements for the solar neutrino experiment BOREXINO and the detector efficiency calibration by the Monte Carlo method are discussed as well.

Solidang, a computer code for the computation of the effective solid angle and correction factors for gamma spectroscopy-based waste assay

Detection efficiency calibration of gamma spectroscopy for waste assay systems is a difficult and time-consuming task. Commonly, reference waste packages are used for efficiency calibration but these are sometimes difficult to build, are expensive and have limited use since there is large variability of parameters which influence the assay. Numerical calibrations, however, are an interesting alternative and have begun to find more and more application in waste assay. A dedicated computer code, Solidang, has been developed to compute detection efficiencies for gamma waste assay. Solidang uses the effective solid angle approach to derive detection efficiency and aims at improving and facilitating the calibration of gamma waste assay systems and at serving as a tool to investigate the influence of the many system and sample parameters involved.

Efficiency Calibration of Ge Detectors in Wide Energy Range with Natural Thorium and 137Cs

For the efficiency calibration of Ge detectors the 232Th natural radionuclide chain is suggested with a standard source of 137Cs which due to its long half-life requires a change of the calibrated standard only in about 30 to 50 years.

Efficiency calibration of low-energy electron detectors by means of β-ray emitters

The relative efficiency of a channel electron multiplier for 2–9 keV electrons was determined using the β-spectra of vacuum evaporated 241 Pu and 63 Ni sources. The results agreed within ±0.8% (1 σ). Conversion electron measurements of 57 Co and 169 Yb supported the result. The electron scattering and energy losses within the sources were taken into account by means of Monte Carlo simulations of individual elastic and inelastic collisions. The detector was calibrated in the same geometry as it works inside the cylindrical mirror analyzer.

A minimum biased shell-source method for the calibration of rad waste assay systems

This article outlines a simple experimental procedure to obtain the minimum biased detection efficiency calibration for gamma waste assay systems using the so called shell-source method in cylindrical waste drums. The conventional use of the shell-source method to simulate a homogeneous activity distribution in a cylindrical waste drum results in a systematic underestimation of the detection efficiency. The bias may be more then 30% at gamma energies of 59 keV and a waste density of 2 g/cm 3. Experimental evidence of this bias is given for the low level waste assay system, Q 2, and a simple measurement procedure to eliminate this bias is presented. The proposed method does not rely on data from computer simulations and is applicable to all types of waste matrices.

Absolute X-ray yields of light muonic atoms

The intensities of X-rays from muonic atoms formed in low pressure Ne, O2, N2, He, and H2 gas was measured. For the pressure chosen external electron refilling can be neglected. Absolute yields were extracted and compared to results of cascade calculations. Knowledge of the yields of the circular X-ray transitions allows an in situ efficiency calibration of X-ray detectors down to energies of 1.5 keV.

Decay of 89Sr and the emission probability of the 909.12 keV gamma-ray transition

Gamma-ray emission rates have been measured for highly pure sources of 89Sr. These sources were prepared with relative 85Sr activity ratios that ranged from less than 0.006% to undetectable, and had been previously standardized for radioactive concentration. Three such source materials were measured using Ge spectrometers, and the probability per decay of the 909.12 keV gamma ray was found to be 9.555×10 −5 with a relative expanded uncertainty of 1.26%. This result and other reported probabilities per decay have been evaluated according to the protocol of the International Atomic Energy Agency Coordinated Research Program on the Measurement and Evaluation of X-ray and Gamma-ray Standards for Detector Efficiency Calibration. This evaluation yielded a recommended value of 9.559×10 −5 with a relative standard uncertainty 0.47% for the probability per decay of the 909.12 keV gamma ray.

Absolute X-ray yields of light muonic atoms

The intensity of muonic X-rays was measured in Ne, O 2, N 2, He, and H 2 gas at low densities for which external electron refilling can be neglected. Absolute yields were extracted and compared to results of cascade calculations. Knowledge of the yields of the circular ( n + 1, l = n → n, l = n − 1) X-ray transitions allows an in situ efficiency calibration of X-ray detectors down to energies of 1.5 keV.

On self-attenuation corrections in gamma-ray spectrometry

In this paper we discuss and justify the dependence on the sample density and gamma energy of the self-attenuation correction factor, f, in the transmission method for the full energy peak efficiency calibration of Ge detectors. It is suggested as a method for the direct computing of f in the case that the sample composition in known.

Measurement of Radon Decay Products in Air by Alpha and Beta Spectrometry

A method for independently measuring the concentrations of 222 Rn decay products collected on a filter is described. The measurements utilise alpha and beta spectroscopy and use a special non-emanating source containing 2 26 Ra in equilibrium with its decay products for both energy and detection efficiency calibration. Internal conversion electrons from 137 Cs are used to establish the energy calibration for the beta spectrum to distinguish between 214 Pb and 214 Bi decays. The method has been applied to the investigation of self-absorption losses of alpha particles from 222 Rn decay products at different aerosol loading of the filters used to collect the 222 Rn progeny.

Si(Li) Detector Efficiency and Peak Shape Calibration in the Low-Energy Range Using Synchrotron Radiation

The efficiency and pulse distribution characterization of an Si(Li) detector (SLD) were obtained using the mono-chromatized Super-ACO (LURE, Orsay, France) synchrotron beam. The selected energies ranged from 700 to 7000 eV and the radiation intensity was successively measured with a proportional counter, used as a reference, then with the detector to be calibrated. More than 100 experimental points were recorded; steps as small as 1 eV were used to examine carefully the silicon and gold absorption edges. The SLD spectra were processed using the COLEGRAM deconvolution software, which fits different theoretical functions to experimental data. The processing includes a least-squares fitting with the Marquart–Levenberg algorithm and the use of a Hypermet-type function, the sum of a main Gaussian function with a low-energy tail. The proportional counter efficiency curve is calculated using attenuation coefficients for the polypropylene window and argon–methane counter gas. The complete SLD peak shape calibration was obtained: the variation of each fitting function parameter with energy is shown. The tailing parameters show sharp discontinuities that can be linked to different interaction points in the detector front end. This detector pulse distribution calibration obtained with monochromatized radiation could be used to process accurately usual X-ray spectra including several peaks and satellites. The uncertainty in the SLD efficiency calibration points is about 3%. The experimental values were fitted with a theoretical function describing the transmission through different absorbing layers. It is seen that the so-called silicon ‘dead layer’ acts as a partially active layer, the corresponding events being recorded in the peak tail. © 1997 John Wiley & Sons, Ltd.

Si(Li) Detector Efficiency and Peak Shape Calibration in the Low‐Energy Range Using Synchrotron Radiation

Si(Li) Detector Efficiency and Peak Shape Calibration in the Low‐Energy Range Using Synchrotron Radiation

HPGe detector efficiency calibration for extended cylinder and marinelli-beaker sources using the ESOLAN program

A personal computer based program ESOLAN has been developed for HPGe detector absolute-peak-efficiency calibration for various source-detector arrangements. The applicability of the previously developed program is limited to sources with diameter smaller than that of the detector active crystal. In this work, the ESOLAN program is modified to extend its application to sources with dimensions larger than the detector crystal, including extended cylinder and Marinelli-beaker sources.

Use of 169Yb as a calibration standard

The energies and intensities of the gamma and X-rays in the decay of 169Yb (32 d) have been measured with a low energy photon spectrometer (LEPS) and a high purity germanium (HPGe) detector. This source is recommended for use as a standard for low-energy efficiency calibration of such detectors. It is also proposed to use this source as a standard for conversion electrons, as the multipolarities and mixing ratios are well known for most strong transitions.

Gamma intensity standard from thermal neutron capture in 35Cl

Absolute emission probabilities of gamma-rays after thermal neutron capture in 35Cl were measured in the range 0.5–8.6 MeV. The intensities of 24 lines were determined with relative uncertainties below 3%. These data can usefully be employed as standards for efficiency calibration of gamma detectors and for the measurement of neutron capture cross sections by means of Ge detectors.

The Gender-Specific Chest Wall Thickness Prediction Equations for Routine Measurements of 239Pu and 241Am Within the Lungs Using HPGe Detectors

The current chest wall thickness prediction equation is not applicable to use in routine lung counting measurements for detection of low energy photons (17--60 keV) within the lungs of male and female subjects. The current chest wall thickness prediction equation was derived for the NaI-CsI "phoswich" detection system, which is not the routine detection system in use; the subject position was supine, which is not the routine position; the equation did not account for the intercostal tissue thicknesses of muscle and adipose which significantly attenuate low energy photons (17--60keV); it was derived from male subjects only and is used to predict the chest wall thickness of female subjects for whom it is not applicable. The current chest wall thickness prediction equation yields unacceptable percent errors in the HPGe detection efficiency calibration for 239Pu and 241Am (17- and 59.5-keV photons, respectively) relative to the gender-specific HPGe chest wall thickness prediction equations of this paper (+284% to --73% for 239Pu; (+)42% to --39% for 241Am). As a result, use of the current chest wall thickness prediction equation yields unacceptable percent errors (proportional in magnitude to the percent errors in the detection efficiency calibration) in the calculation of the minimum detectable activity (Bq) or in an initial assessment of a radioactive contamination exposure detected by a routine lung count measurement.

Use of activated samples to determine unknown components by gamma-ray spectrometry based on internal calibration

Calibration methods currently employed for the analysis of radioactive samples by γ-ray spectrometry apply reference sources and the accuracy of the final results is always limited by the unavoidable differences between the composition and the counting geometry of the samples and standards. Under suitable circumstances, described in this paper, the determination of elemental concentrations can be made by means of a relative detection efficiency calibration based on the spectra of multigamma-ray emitting nuclides generated by activation in the sample. The method of internal efficiency calibration may be applied to samples of different matrix composition and volume geometry to determine relative or absolute element concentrations by nuclear-induced activation reactions. Such an approach is only valid if the true coincidence effects are not significant; the criteria for selecting such γ-ray spectra are discussed. Experimental verification of the reliability of the method was carried out using certified materials analyzed by neutron activation.

An experimental/numerical method for the efficiency calibration of low-energy germanium detectors

Several radionuclides emit significant gamma rays at energies below 80 keV, which in many cases are essential for their detection in radioenvironmental assays. Gamma spectroscopic analysis at this energy region is conducted using planar Low Energy Germanium detectors, with high and almost constant efficiency in the energy region between 20 and 80 keV. In the analysis of solid and liquid samples, with these detectors, the count rate is highly affected by the intense self-absorption of the low energy photons. Thus, the difference in the absorption properties between the calibration source and the sample requires the introduction of an efficiency correction factor. A method applicable for cylindrical geometries was adapted for the determination of the above correction factor using a newly developed experimental-numerical technique and a Fortran program. This program, using as input the source-to-detector geometry and the values of the linear attenuation coefficient (μ) of both the calibration source and the material to be analysed, calculates the efficiency correction factor. The value of the linear attenuation coefficient (μ) needed for this calculation is being experimentally estimated for each material to be analysed. The technique has been cross-checked using standard materials. According to the results obtained, in the case of surface soil samples, lignite, and fly ash, the values of μ ranges from 0.2 to 0.9 cm −1. This leads to efficiency correction factors, for the geometry used and a 4M HCl mixed radionuclide calibration source, in the range of 0.5 to 1.2 for the photons emitted by 210Pb at 46.52 keV and 241Am at 59.54 keV. The correction factor for 185.99 keV photons is slightly lower than 1.0, even for the most absorbing of the materials analysed.