Full Energy Peak Efficiency Curves Research Articles

Characterization of a Novel CdZnTe Spectrometer for Measuring Radioactivity in the Marine Environment

The scope of this study is to characterize the response of a CdZnTe spectrometer to evaluate its performance for measuring radioactivity in the marine environment. CdZnTe semiconductor detectors have never been used before for such applications. More specifically, a spectrometer with a 4 cm3 CZT crystal was studied under various scenarios, by means of Monte Carlo simulations and lab measurements. Using the Monte Carlo code MCNP5, the effect of the water’s salinity on the detector’s efficiency, as well as the ability of the sensor to localize radioactive sources in the water were examined. Futhermore, the full energy peak efficiency curve and energy resolution of the spectrometer was calculated experimentally in air. Finally, the effective volume of the CdZnTe crystal was estimated through measurements using a collimated point source of 137Cs. First results are considered satisfactory, however additional scenarios should be examined in the near future to further characterize the response of the detector.

Efficiency calibration for HPGe detector by Monte Carlo efficiency transfer method

In this paper, the Monte Carlo efficiency transfer method was used to calibrate the full energy peak efficiency (FEPE) of a coaxial p-type HPGe detector. The gamma standard radioactive sources including 22Na, 54Mn, 57Co, 60Co, 65Zn, 109Cd,133Ba, 137Cs, 154Eu, 207Bi, 241Am were measured at different positions on-center of detector with the distance of 5, 10, 15, 20, 25 cm. Besides, a cylindrical sample containing standard mixed nuclides solution was also measured at surface of the detector. The experimental FEPE curves as function of gamma energy for these geometries were determined with the coincidence-summing corrections. A HPGe detector model based on the specifications of manufacturer was built to directly calculate the FEPE for the geometries by Monte Carlo simulations with MCNP6 code. However, these simulated FEPEs show a quite high discrepancy from experimental FEPEs. Then, the FEPEs were calculated by the efficiency transfer method with the efficiency curve for point source at distance of 25 cm as the reference data. A good agreement was obtained between the calculated results by the Monte Carlo efficiency transfer method and experimental results. The comparisons between experimental and calculated FEPE showed that the relative deviations were mostly within +/-4% in the energy range of 53-1770 keV.

Intercomparison of full energy peak efficiency curves for an HPGe detector using MCNP6 and GEANT4

This work is focused on studying the capabilities of different Monte Carlo tools to complement the Full Energy Peak Efficiency (FEPE) calibration procedures of the Environmental Radioactivity Laboratory of the Universitat Politècnica de València, UPV. In this frame, detailed models of a High Purity Germanium detector have been implemented using MCNP6 and GEANT4. Accordingly, an inter-comparison with experimental values ensures the model validation and improves the analysis of the physics phenomena involved. The validation of the models is determined by a quantitative comparison between the simulated and the measured efficiencies over the energy range under study (59.54–1836.01 keV). The results show discrepancies between both Monte Carlo tools for 139Ce, 88Y and 60Co as GEANT4 is able to simulate the coincidence summing effect of these radionuclides.

Determination of the HPGe detector efficiency in measurements of radioactivity in extended environmental samples

A combination of experimental measurements and Monte Carlo (MC) calculations was used to determine the full-energy peak efficiency of a HPGe detector employed in environmental measurements. The manufacturer-provided parameters of the detector were corrected by comparing measured values of the efficiency with those obtained by MC simulations. After the adjustment of the active volume of the detector, the simulated and experimentally measured efficiencies agreed within 1%. A full-energy peak efficiency curve for a new distance was obtained by simulation. The efficiency curve for volumetric samples in the 53–1408keV energy range was determined using the efficiency transfer method. Geometric and self-absorption correction factors were estimated by experimental measurements, MC calculations or a combination of the two. In addition, the density of two sediment samples was estimated by a transmission measurement experiment and data simulation. Finally, concentrations of 238U and 232Th in two sediment samples from the Caetité region of Brazil were determined with relative uncertainties of about 5%.

Calculation of Coincidence Summing Correction Factors for an HPGe detector using GEANT4

The aim of this paper was to calculate the True Coincidence Summing Correction Factors (TSCFs) for an HPGe coaxial detector in order to correct the summing effect as a result of the presence of 88Y and 60Co in a multigamma source used to obtain a calibration efficiency curve. Results were obtained for three volumetric sources using the Monte Carlo toolkit, GEANT4. The first part of this paper deals with modeling the detector in order to obtain a simulated full energy peak efficiency curve. A quantitative comparison between the measured and simulated values was made across the entire energy range under study. The True Summing Correction Factors were calculated for 88Y and 60Co using the full peak efficiencies obtained with GEANT4. This methodology was subsequently applied to 134Cs, and presented a complex decay scheme.

A trapezoid approach for the experimental total-to-peak efficiency curve used in the determination of true coincidence summing correction factors in a HPGe detector

In this work, a simple method for true coincidence correction is suggested for a voluminous source measured in close detection geometry for a HPGe detector. TrueCoinc program based on Sudár's algorithm was used to determine true coincidence summing correction (TCS) factors by using full energy peak (FEP) efficiency, and total-to-peak (TTP) efficiency curves in which experimental efficiencies are obtained from almost coincident-free radionuclides such as 54Mn, 57Co, 65Zn, 109Cd, 137Cs and 241Am. In order to calculate TTP efficiency curve three different approaches were tested. One of them is new and here called trapezoid approach which was used successfully in determining total count of spectrum for the TTP efficiency curves. According to different TTP determination methods, the changes in true coincidence factors are observed. The FEP efficiency curves are also established for a cylindrical source. Then, TCS factors were determined for the particular peaks of daughters of 226Ra, 238U, and 232Th using the suggested method. Those activities measured from some certified reference materials such as IAEA RGU-1 and RGTh-1 are used to validate the present TCS correction procedure.

Application of the Monte Carlo method for the calibration of an in situ gamma spectrometer

A MCNP model was developed for the efficiency calibration of an in situ gamma ray spectrometry system based on a high purity germanium (HPGe) detector. The detector active crystal volume was adjusted semi-empirically against experimental measurements. Calculated full energy peak efficiency curves, over the photon energy range between 50 keV and 5 MeV, are presented for surface and slab source configurations. The effect of different collimator apertures and the contribution of different HPGe crystal regions in the detector response are also shown.

Coincidence Summing Corrections in Gamma-Ray Spectrometry Using GEANT4 Code

In this paper coincidence summing corrections in gamma-ray spectrometry have been analyzed in depth. Experimental setup included a n-type germanium detector and two efficient geometries of measurement (Marinelli beaker and air filter) calibrated with multi gamma radionuclides in the energy range of 40-1500 keV. Monte Carlo simulations were carried out using the GEANT4 code in order to develop this work. Firstly an optimization of the detector dimensions was performed to obtain the full-energy peak efficiency curve. Next, the simulation of the decay schemes for involved multi gamma radionuclides were appended to the GEANT4 code including beta, alpha, EC decay, together with the subsequent relaxation process consisting of a cascade of fluorescent X-rays and Auger electrons. In order to test the simulations an comparison between an experimental and a calculated spectra of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">133</sup> Ba point source was carried out. Finally coincidence summing effects for gamma-ray emission and X-ray, Auger electron, beta and EC electron were studied in detail.

Efficiency curves of NIRR-1 gamma-ray spectrometry system at near and far geometries

The full-energy peak efficiency curves of the gamma-ray spectrometry for use with the Nigeria Research Reactor-1 (NIRR-1) have been determined by both theoretical and experimental at two source-detector positions for routine neutron activation analysis. Standard gamma ray sources were used to determine the efficiency curv-es in the energy range of 59.5 - 2240.1 keV and a semi-empirical approach was used to extend the efficiency data from 2204.1 to 4000 keV. The data were presented for source-detector positions of 1.0 and 5.0 cm, which were designated as H1 and H2 respectively. The semi-empirical method, which required the use of relatively long-lived radionuclides was been found to be accurate within experimental uncertainties. Journal of Applied Science and Technology Vol. 13 (1 & 2) 2008: pp. 34-36

Improved radioxenon gamma-spectrometry counting system and its efficiency calibration: Monte Carlo simulation and experimental results at enriched xenon counting environment

To give satisfactory efficiency both for X- and gamma-ray photon, an improved counting system has been developed in CTBT Canadian radioxenon laboratory. The counting system consists of a BEGe detector coupled with a thin carbon fiber window counting cell, that can perform a reliable and efficient radioxenon measurement. A semi-empirical calibration procedure was adopted, which is a combination of experimental measurement and mathematical simulation. Mathematical calibration tool is Monte Carlo simulation software named VGSL. Advanced gamma-spectrum analysis software, named Aatami, was used for gamma-ray peak shape fitting and X-ray multiplets deconvolution. The calculated full energy peak efficiency curve covers from 30 to 700 keV and agrees well with experimental data points within 2%. The efficiency curve can provide radioxenon analysis both for X-rays and gamma-rays with high quality. The efficiency distortion near xenon k-absorption edge of 35 keV, which is caused by high concentrated xenon in the counting cell, is also discussed.

Assessment of on-line burnup monitoring of pebble bed reactor fuel using passive gamma-ray spectrometry

An investigation was performed to assess the feasibility of passive gamma-ray spectrometry assay as an approach for on-line burnup determination for the Modular Pebble Bed Reactor (MPBR). In addition to its inherently safe design, a unique feature of this reactor is its multipass fuel cycle in which graphite fuel pebbles are randomly loaded and continuously circulated through the core until they reach their prescribed end-of-life burnup limit (/spl sim/80 000 MWD/MTU). Unlike the situation with conventional light water reactors, depending solely on computational methods to perform in-core fuel management will be highly inaccurate. As a result, an on-line measurement approach becomes the only accurate method to assess whether a particular pebble has reached its end-of-life burnup limit. The results of this investigation indicate that the fission products Cs-137 and Eu-154 have the potential to provide accurate and power-history-resistant signatures that can be directly correlated with burnup. Furthermore, depending on the fuel manufacturing process, artificially introduced dopants (e.g., Co) can provide gamma-ray lines that are usable for burnup monitoring. In fact, it was found that the relative activity of Co-60 to Cs-134 could form a burnup indicator that is resistant to power-history variations. In this case, the use of a relative indicator has several advantages, among them the elimination of the need for absolute knowledge of the detector full-energy peak efficiency curve and the establishment of a system quality-assurance figure of merit based on the peak area ratio of the Co lines.

Monte Carlo calculation of the efficiency response of a low-background well-type HPGe detector

Well-type HPGe detectors are well suited for the analysis of small amounts of environmental samples, as they can combine both low background and high detection efficiency. A low-background well-type detector is installed in the Modane underground Laboratory. In the well geometry, coincidence-summing effects are high and make construction of the full energy peak efficiency curve difficult with the usual calibration standard, especially in the high energy range. Using the GEANT code, taking into account a detailed description of the detector and the source, efficiency curves have been modelled for several filling heights of the vial. With a special routine, taking into account the decay schemes of the radionuclides, corrections have been computed for coincidence-summing effects that occur when measuring samples containing 238U, 232Th or 134Cs. The results are found to be in good agreement with experimental data. It is shown that triple coincidences effect on counting losses accounts for 7–15% of pair coincidences effect in the case of the 604 and 796 keV lines of 134Cs.

Monte Carlo calculation of the efficiency calibration curve and coincidence-summing corrections in low-level gamma-ray spectrometry using well-type HPGe detectors

Well-type high-purity germanium (HPGe) detectors are well suited to the analysis of small amounts of environmental samples, as they can combine both low background and high detection efficiency. A low-background well-type detector is installed in the Modane underground Laboratory. In the well geometry, coincidence-summing effects are high and make the construction of the full energy peak efficiency curve a difficult task with an usual calibration standard, especially in the high energy range. Using the GEANT code and taking into account a detailed description of the detector and the source, efficiency curves have been modelled for several filling heights of the vial. With a special routine taking into account the decay schemes of the radionuclides, corrections for coincidence-summing effects that occur when measuring samples containing 238U,232Th or 134Cs have been computed. The results are found to be in good agreement with the experimental data. It is shown that triple coincidences effect on counting losses accounts for 7–15% of pair coincidences effect in the case of 604 and 796 keV lines of 134Cs.

High accuracy measurements and Monte Carlo calculations of the relative efficiency curve of an HPGe detector from 433 to 2754 keV

The relative full-energy peak efficiency curve of a 280-cm 3 coaxial HPGe detector was determined to an accuracy of about 0.1% over the energy range from 433 to 2754 keV from pairs of gamma-ray lines whose emission probabilities are very accurately known. The curve was extended from previous studies by the addition of lines from 108 m Ag and 24 Na . Ratios of full- energy peak efficiencies were also determined by Monte Carlo calculations using the CYLTRAN code. The measured ratios and the Monte Carlo values were in excellent agreement (0.03–0.19%). The relative efficiency was defined by a pair of functions, one for 433–1332 and one for 614–2754 keV. Monte Carlo values were used to supplement the measured values, resulting in a more accurate fit. The stability of the relative efficiency curve for a 94-cm 3 HPGe detector was studied and it was found that there was no statistically significant change over a period of 3 years.

High-accuracy determination of the relative full energy peak efficiency curve of a coaxial HPGe detector in the energy range 700–1300 keV

A method for the high-accuracy determination of the relative full energy peak efficiency is established. Radionuclides that emit at least two gamma-ray lines for which the relative intensity can be found (from the decay scheme) to much better than ±0.1% were used as calibration standards. Specifically, the 889 and 1120 keV lines of 46Sc, the 983 and 1312 keV lines of 48Sc, the 1173 and 1332 keV lines of 60Co, and the 702 and 871 keV lines of 94Nb were implemented. The high-accuracy calibration was taken to extend from the lowest line of 94Nb at 702 keV to the highest line of 60Co at 1332 keV. An analytical expression, based on linear least-squares fitting, was developed to describe the behavior of the relative efficiency curve in that energy range. As a result, the ability of predicting relative full energy peak efficiencies to within ±0.1% (over most of the energy range) was demonstrated. The presented method is applicable in any measurement that requires the minimum calibration bias in the determination of reaction rate ratios. Applications in Neutron Activation Analysis (NAA) and in nuclear reactor dosimetry represent examples of such situations.

Empirical Relation for the Slope of Full Energy Peak Efficiency Curves of Germanium Detectors.

We have measured full energy peak efficiencies εp of many germanium detectors with different types, active volumes Va and relative efficiencies εr. The empirical relations for the slope S of εp, curves as a function of Va are reexamined. It is proved that the Vano's empirical rule is almost valid and calculated relation by Hnatowicz overestimates.A strong correlation between Va and εr is found to be Va=7.98εr0.810 and a new empirical formula between S and εr is represented as S=-0.494 log10εr+1.55.A simplified model for εp and εr is introduced with the concept of multiple Compton collisions terminated by photoelectric absorption. Calculated results are compared with the present empirical relations.

Spline techniques for fitting efficiency curves in gamma-ray spectrometry

Low order spline functions are used in a least-squares fitting procedure to establish full-energy peak efficiency curves for different kinds of semiconductor photon detectors (Ge(Li), Si(Li), HPGe) in the energy range from 2 keV to 3 MeV. The algorithm allows discontinuities in the efficiency curves due to absorption edges of the detector material to be represented. Uncertainties of the calculated efficiencies are evaluated from the covariance matrix of the experimental data, taking into account correlated data uncertainties.

Addendum to “efficiency determination for some standard type Ge(Li) detectors for gamma-rays in the energy range from 0.04 to 11 MeV”

The experimental full energy peak efficiency curve of a 5.8 cm 3 planar Ge(Li) detector is compared with the curve obtained from the corrected semi-empirical formula of Paradellis and Hontzeas.

Encapsulated germanium γ-ray spectrometers performance characteristics and operational experience

Hermetically sealed Ge(Li) diodes for γ-ray spectroscopy have now been manufactured and under study for approximately two years. During this time, 'planar' drifted encapsulated diodes have been increased in size from 2 cm2 × 2 mm deep (0.4 cm3) to ˜ 8 cm2 × 10 mm deep (8 cm3). Coaxially drifted diodes of 25 to 30 cm3 volume have also been encapsulated. Encapsulation details of both types of detector are given, together with performance characteristics. Measured intrinsic full-energy peak efficiency curves are given for four detector sizes. For an 8 cm3 planar diode this efficiency is 1.1% at 7 cm for 1 MeV γ-rays. The corresponding efficiency for a 27 cm3 coaxial diode is 3.1%. Voltage ratings of 1000 V/cm with leakage currents ⩽ 1 nA at operating voltage are achieved. Resolutions of 3.4 and 5.5 keV (fwhm) at 1173 keV γ-ray energy have been obtained with a 2 cm3 (5 mm deep) planar diode and a 27 cm3 coaxial detector respectively. Mounting and general application details are discussed.