Coincidence Summing Research Articles

A dedicated LIMS for routine gamma-ray spectrometry

We developed a Microsoft® Access-based LIMS (Laboratory Information and Management Systems), γ-LIMS, for the management of our gamma-spectrometry laboratory, in which thousands of routine, but high-quality analyses are performed each year. This paper explains the main features of the γ-LIMS and puts special attention on the interfacing methods and solutions for using the Genie™2000 spectrometry software in conjunction with the EFFTRAN package, which serves for efficiency transfer calculations, coincidence summing corrections and a procedure for uncertainty estimation.

Efficiency calibration of BEGe and extended range detectors

Any approach to efficiency calibration of HPGe detectors sensitive to low-energy gamma-rays and X-rays has to deal with true coincidence summing. We developed a method based on the integration of the EFFTRAN code into the commercial Genie2K™ gamma-ray spectrometry software. EFFTRAN's role is to compute true coincidence summing corrections and to obtain satisfactory results for detectors sensitive to X-rays. EFFTRAN had to be upgraded to include a full simulation of the emission of X-rays. In this manner, efficiency calibrations were successfully set up for BeGe and XtRa detectors.

Response of Ge photon detectors to beta-rays and possible reduction of photopeak areas due to beta–gamma coincidence summing effects

In the use of photon detectors having sensitivity to β-rays or internal conversion electrons (CEs), β–γ and/or X–CE coincidence summing may arise. In particular, an n-type germanium detector has a thin dead layer and window, causing considerably higher sensitivity to β-rays and/or CEs especially when sources are located at a small source-to-detector distance. In the present research, reduction of the photopeak area due to β–γ or X–CE coincidence summing has been studied for three germanium detectors.

Experimental assessment of the coincidence summing corrections in gamma-ray spectrometry of bulk samples

This work presents an experimental approach for estimation of the true coincidence-summing (TCS) correction for volume sources on the basis of TCS dependence on the source-to-detector distance. Firstly, it is shown that the TCS dependence on the source-to-detector distance can be linearized for point source geometry. If this linear dependence is established then TCS correction for an arbitrary source-to-detector distance can be obtained. In the case of a volume source a representative parameter dV can be formulated as the distance at which the point-source summing effect is the same as the one for the volume-source. Then if the TCS dependence on the source-to-detector distance is established for the point-source case and the volume-source dV-value is known, the TCS correction corresponding to the volume-source measuring geometry can be estimated. Experimental method and results are presented in the work too.

Characterisation of cascade summing effects in gamma spectroscopy using Monte Carlo simulations

A GEANT4 based Monte Carlo simulation has been successfully utilised to calculate peak efficiency characterisations and cascade summing (true coincidence summing) corrections in two source geometries commonly used for environmental monitoring. The cascade summing corrections are compared with values generated using an existing (validated) system, and found to be in excellent agreement for all radionuclides simulated. The calculated correction factors and peak efficiencies were also tested by analysing well defined sources used in the operation of the International Monitoring System, which undertakes radionuclide monitoring for verification of the Comprehensive Nuclear-Test-Ban Treaty. All abundances of the radionuclides measured matched the values that were previously determined using proprietary software. Using GEANT4 in this way, cascade summing corrections can now be extended to complex detector models and source matrices, such as Compton Suppression systems.

A simplified technique to determine random coincidence summing of gamma rays and dead time count loss corrections

The loss in counts rate under the peak in gamma spectrum was studied using two techniques (complex spectrum and high active single isotope). The results showed that the loss was occurred when the integrated counting rate was more than 400 counts per second (CPS) up to 104cps, for energy range 20–2500keV. This was mainly due to the random summing effect in the detector′s volume. It was found that the probability of random summing has increased with the increase of the volume of detector′s crystal. The correction factor F(Ct) for the counts rate under the peak was determined experimentally.

Measurement of thermal neutron cross section and resonance integral for the 170Er(n, γ)171Er reaction by using a gold monitor

The thermal neutron cross section (σ0) and the resonance integral (I0) of the reaction 170Er(n,γ)171Er were measured by an activation method using a reaction 197Au(n,γ)198Au as a single comparator. The high-purity natural erbium (natEr) and gold (197Au) foils with and without Cd cover with the thickness of 0.5mm were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a well calibrated coaxial HPGe detector. The thermal neutron cross section for the 170Er(n,γ)171Er reaction has been determined to be σ0=7.80±0.35 barn, relative to the reference value of 98.65±0.09 barn for the 197Au(n,γ)198Au reaction. By assuming the cadmium cut-off energy of 0.55eV, the resonance integral for the 170Er(n,γ)171Er reaction is I0=40.4±2.8 barn, which is determined relative to the reference value of 1550±28 barn for the 197Au(n,γ)198Au reaction. In order to improve the accuracy of the experimental results the epithermal neutron spectrum shape factor (α) was determined, and the necessary corrections for the counting loss caused by γ-ray attenuation (Fg), the thermal neutron shelf-shielding (Gth), the resonance neutron self-shielding (Gepi) effects, the γ-ray coincidence summing effect, as well as neutron flux fluctuation. The present results are compared with the reference data and discussed.

Calibration of a low-level anti-Compton underground gamma-spectrometer by experiment and Monte Carlo

In this work we present the experimental and Monte Carlo calibration of the Compton-suppressed spectrometer of the IAEA's Environment Laboratories, Monaco. For this purpose the GESPECOR code was extended to include the specific geometry and to implement the veto logic, integrated with the coincidence summing module of the code. The simulation results are in good accordance with experimental calibrations. The code is fast and user-friendly, able to evaluate the efficiency and the correction factors for nuclides with arbitrary complex decay schemes.

Experimental and Simulated Effective Dose for Some Building Materials in France

The specific radioactivity of several building materials used in France, which is considered a direct exposure to radiation, has been assessed by γ-ray spectrometry. Corrected for coincidence summing and self-absorption effects, the values for 226Ra, 232Th and 40K were in the ranges 4 - 56, 3 - 72 and 9 - 1136 Bq·kg-1, respectively. The samples were found to have radium-equivalent activities between 5 and 245 Bq·kg-1. Values of 0.02 - 0.67 for the external and 0.03 - 0.82 for the internal hazard indexes were estimated. The calculated absorbed dose in air agrees closely with MCNPX simulations. The conversion of absorbed dose to annual effective dose gave values between 0.03 - 1.09 mSv·y-1. All these values are below action limits recommended by the International Commission on Radiological Protection. The materials examined would not contribute a significant radiation exposure for an occupant and thus are acceptable for construction.

A possible improvement of the determination of 133Ba activity and detection efficiency by the sum-peak method, by inclusion of the previously neglected transitions

In the treatment of 133Ba decay by the method of coincidence summing, the transitions to the first two excited states of 133Cs were ignored in former works. By applying the most accurate values for these transitions available in literature, we include them into the count rate equations and obtain solutions for the corresponding system. As a result of this more accurate forming of count rate equations, some terms, which contain previously ignored transition probabilities, turn out to be more significant than the conventionally included terms. We show that their inclusion in the system of count rate equations leads to fine improvements in the determinations of detection efficiencies and the activity of the 133Ba source.

EXPERIMENTAL STUDY ON THE POSSIBILITY OF REDUCING BACKGROUND FOR THE GAMMA COINCIDENCE SPECTROMETER WITH HIGH PURE GERMANIUM DETECTORS

Gamma coincidence spectrometers with HPGe detectors are used for environmental research, nuclear reactions (n, g), (n, 2g) due to Compton backgrounds of their gamma spectra are very low. In this work, three types of coincidence spectrometers such as gamma coincidence spectrometer, gamma coincidence spectrometers with TAC and sum coincidence spectrometer using HPGe are described. Some experimental results obtained by using gamma coincidence spectrometers are presented. Especially, taking advantages of the software and hardware of the sum coincidence spectrometer used for research of nuclear reactions (n, g), (n, 2g), we have converted the spectrometer to one with very low background level.

Measurements and model calculations of isomeric cross section for (n,α) reaction on 140Ce isotope around 14 MeV neutrons

In this work, cross sections were measured for the 140Ce(n,α)137mBa (T1/2=2.552min) reaction at neutron energies from 13.57 to 14.83MeV. The neutrons were produced via the 3H(2H,n)4He reaction on a neutron generator using a solid Ti–T target. The activation technique was used, and induced gamma activities were measured by a high resolution gamma-ray spectrometer. Corrections were made for the effects of gamma-ray attenuation, random coincidence (pulse pileup), coincidence summing, dead time, neutron flux fluctuations, and low-energy neutrons. The measured cross sections were compared with statistical model (TALYS code) calculation results and the experimental data in the available literature.

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry—part II (volume sources)

The second part of an intercomparison of the coincidence summing correction methods is presented. This exercise concerned three volume sources, filled with liquid radioactive solution. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing corrective factors for several energies of 152Eu and 134Cs, and different source-to-detector distances. They are presented and discussed.

Coincidence summing corrections applied to volume sources

The numerical calculation of coincidence summing corrections requires both the total and full-energy peak efficiencies to be included in the corrective factors. Moreover, in the case of volume sources, the coincidence probability depends on the position of the photon emission inside the radioactive sample, thus it is necessary to calculate the coincidence summing corrective factors by integrating the elemental contributions for the entire volume.The software ETNA calculates coincidence summing corrective factors according to a deterministic method, for volume sources, two approaches are included in the software: the “simplified” calculation uses directly the efficiency of the volume source like in the case of point source, and the “complete” calculation performs the volume integration. To assess the difference between these, different geometrical cases are tested for several radionuclides using both methods.

Simplified methods for coincidence summing corrections in HPGe efficiency calibration

Simple and practical coincidence summing corrections for n-type HPGe detectors are presented for the common calibration nuclides 57Co and 60Co using a defined “virtual peak” and accounting for the summing of gamma photons with x-rays having energies up to 40keV (88Y and 139Ce). These corrections make it possible to easily and effectively establish peak and total efficiency curves suitable for subsequent summing corrections in routine gamma spectrometry analyses. Experimental verification of the methods shows excellent agreement for measurements of different reference solutions.

Precise measurement and calculation of coincidence summing corrections for point and linear sources

Point sources of 60Co, 133Ba, 134Cs and 152Eu, calibrated at Physikalisch-Technische Bundesanstalt were measured in 13 positions on the axis of a 50% relative efficiency p-type detector. The peak and total efficiencies were calibrated using single photon emitting nuclides. Precise experimental values of the coincidence summing corrections were evaluated in each geometry. Synthetic linear source data, as well as the corresponding peak and total efficiency curves, were prepared using the dependence of the count rates on the position of the emitting point. The coincidence summing corrections for the linear sources were computed, analyzed with respect to different approximations and compared with simulations carried out with GESPECOR.

A digital Compton suppression spectroscopy without gamma-ray coincidence-summing loss using list-mode multispectral data acquisition

The study demonstrates the advantages of an innovative list-mode multispectral data acquisition system that allows simultaneous creation of several different single, summed, coincident and anticoincident spectra with a single measurement. One of the consequences of list-mode data file offline processing is a reconstructed spectrum with Compton continuum suppression and without any full-energy peak efficiency deduction owing to true coincidence summing. The spectrometer is designed to read out analogue signal from preamplifier of gamma-ray detectors and to digitalize it using DGF/Pixie-4 software and card package (XIA LLC). This is realized by converting an Ortec Compton suppression data acquisition system into an all-digital spectrometer. Instead of using its timing electronic chain to determine the coincidence event, the analog signals from primary and guard detectors were connected directly into the Pixie-4 card for pulse height and time coincident measurement by individually logging and time stamping each electronic pulse. The data acquired in list-mode included coincidence and anticoincidence events consisting of records of energy and timestamp from primary and guard detectors. Every event was stored in a text file for offline processing and spectral reconstruction. A sophisticated computer simulation was also created with the goals of obtaining a better understanding of the experimental results and calculating efficiency.

A recursive deterministic algorithm for treatment of true coincidence summing effects in gamma-ray spectrometry

Different algorithms exist that can be applied to the calculation of the effects of true coincidence summing in gamma-ray spectrometry. Some of these, however, are not capable of reproducing the count rates in all the pure sum peaks that a spectrum may contain. A recursive, easy-to-implement deterministic algorithm has been developed that overcomes this shortcoming.

A new matrix method for calculating coincidence summing effects for gamma spectroscopy

Abstract A new method for deriving counting rate equations describing coincidence summing of gamma and X-rays for germanium spectrometers is developed. It is applied to the decay of 139 Ce and 57 Co. It is shown that the results obtained using the proposed method are in complete agreement with the results obtained using other methods, however these results are achieved in a much clearer and simpler way.

Coincidence summing of X- and gamma rays of 75Se

A study of coincidence summing of X- and gamma rays of (75)Se has been presented in this paper. The computation of the (75)Se spectra was performed by application of the previously published theory by Novković et al. The method enables the treatment of all possible single and sum peaks of (75)Se. The calculation gave the 419 decay path outcomes, resulting in 84 peak count rate equations and also the total count rate equation. By HPGe spectrometers with 15% and 18% relative efficiency, 20 and 30 peaks were recorded, respectively. Some simplification of the decay scheme was introduced and existing metastable level had to be treated separately. Nevertheless, the experimental values of the peak count rates were in good agreement with the theoretical evaluation.