Planar HPGe Detector Research Articles

Experimental evaluation of the performance of a novel planar segmented HPGe detector for use in gamma emission tomography

The use of segmented HPGe detectors for gamma-ray tracking applications is well established. The spectroscopic capabilities of these detectors make them most suitable for such applications. For similar reasons, the use of such detectors in the tomographic measurement of irradiated nuclear fuel has also been envisioned. Especially, these detectors can facilitate faster fuel examination with excellent energy resolution. We have proposed and designed a novel planar segmented HPGe detector for use in gamma emission tomography. The design of the detector segmentation and the mode of operation is unique and offers six simultaneous detection channels for tomographic measurements. This work reports the first experimental evaluation of the performance of the detector. Important characteristics of the detector have been obtained, such as energy resolution of the segments in 1-fold (one segment) and 2-fold (two segments) modes, throughput curves, crosstalk energy corrections, and mislocalisation rate. Collimated source tests have been performed and the results have been compared with the MCNP simulations results. The obtained results are as expected and in good agreement with the simulation results, and it is estimated that using this detector can speed up the data collection by 3.2 times in comparison to an unsegmented detector of the same overall dimensions, in a tomographic application. Further improvements are foreseeable if scaling up to a larger detector with greater segmentation.

Characterisation of the charge collection properties in a segmented planar HPGe detector

Segmented germanium semiconductor detectors provide excellent γ-ray spectroscopic information whilst also being sensitive to the position of interactions within their active volume. Understanding the detector response to γ-ray interactions throughout its volume is required for interpreting the signal output. This work is the first assessment of the response and charge collection properties of an electrically-cooled Mirion Technologies-manufactured planar HPGe detector with boron implanted p+ and amorphous germanium based n+ strip contacts. The signal response of the detector as a function of γ-ray interaction position has been characterised by performing collimated beam scans with 59.5 keV and 661.7 keV γ-rays. A database of average signals, generated through the detector volume and across the detector surfaces, has been produced. A map of parameterised rise time response through depth has been generated and used to apply pulse shape analysis techniques, improving the position resolution within the detector.

CAESIUM RETENTION CHARACTERISTICS OF KNIFC-PAN RESIN FROM RIVER WATER.

The caesium retention characteristics of a potassium-nickel hexacyanoferrate resin in a polyacrylnitrile (KNiFC-PAN) matrix were tested in fresh water over the range of 2.5-400mLmin-1. The experimental setup used 2mL resin and 4-L aliquots of freshwater samples. The results showed nearly 100% retention at speeds below 10mLmin-1, above 80% up to 100mLmin-1, and approached 50% at 400mLmin-1. Using 100mLmin-1 flow rate and KNiFC-PAN resin in a well-type HPGe detector, the minimum detectable concentration was reduced to 3 mBq kg-1 for 4-L aliquots of water samples from the previous 15 mBq kg-1 achieved by Powdex ion-exchange resin and a planar type HPGe detector.

Https://ijbch.kaznu.kz/index.php/kaznu/article/view/423

The application of comparator instrumental neutron activation analysis combined with the internal standard method was considered to study rhenium content of the uranium raw material core samples collected in Chu-Sarysu uranium province in the Southern Kazakhstan. Iron content of the samples as the internal comparator was determined by X-ray fluorescence analysis with the help of a laboratory energy dispersive X-ray spectrometer. Rhenium was analyzed by its long-lived radionuclide 186Re using a planar type HPGe detector. Six certified reference materials of complex ores and non-ferrous metal concentrates were analyzed to verify the accuracy of the method. Rhenium and its main interfering elements were determined in the samples from three different sites of the uranium province. Due to reverse correlation dependence, selenium was found as a simple predictor of industrially significant rhenium contents. The method can be used to analyse rhenium mass fractions more than ≈0.02 ppm in the ores with uranium content of the samples not exceeding several hundreds ppm.

Synthesis, characterization and low energy photon attenuation studies of bone tissue substitutes

AbstractEpoxy composites with different weight percentages of calcium carbonate and calcium phosphate were synthesized as bone tissue substitutes (BTS) for internal dosimetry. The Fourier-transform infrared spectroscopy analysis confirmed that no chemical reaction occurred between the polymer and the fillers. Thermogravimetric analysis also showed improvement in the thermal properties of the composites due to the fillers. The uniform distribution of fillers in the epoxy matrix was established by X-ray radiography. The attenuation behavior of BTS was probed for low energy γ source 241Am (59.5 keV) using planar HPGe detector. The measured mass attenuation coefficients of BTS were found to match with the values calculated using XCOM software. The radiological properties derived for these composites were found to be on par with those of ICRU-44 cortical bone and B-100 bone equivalent plastic.

Branching ratio and [formula omitted]-ray emission probabilities in the decay of the [formula omitted] isomer in 197Hg

Gamma rays following the decay of the 197gHg and 197mHg radionuclides were measured using chemically-purified sources and a planar HPGe detector. In the case of 197mHg, precise values of 94.68 (9)% and 5.32 (9)% were determined for the IT and EC branches, respectively, the latter found to differ significantly from previously published data. The half-lives of 197gHg and 197mHg were also measured as 64.81 (24) h and 23.82 (4) h.

Characterization of different surface passivation routes applied to a planar HPGe detector

The effects of different passivation methods applied to the same planar high-purity germanium gamma radiation detector have been studied. By means of the scanning with a low-energy collimated gamma source, it has been found that the surface passivation gives rise to a dead layer below the intrinsic Ge surface, whose thickness and distribution are strongly dependent on the passivation type. Measured bulk detector properties like the peak-to-Compton ratio and efficiency have shown a dependence on the passivation and an influence of the passivation type on the depletion voltage, whilst the optimal energy resolution has been the same for all the passivations.

Ag K-shell ionization by electron impact: New cross-section measurements between 50 and 100keV and review of previous experimental data

Abstract We report the measurement of Ag K-shell ionization cross-section by electron impact in the range 50–100 keV and review the experimental data found in the literature. The sample consisted in a thin film of Ag evaporated on a thin C backing. The x-ray spectra generated by electron bombardment in the Sao Paulo Microtron were observed with a planar HPGe detector. The ratios between characteristic and bremsstrahlung x-ray yields were transformed to ionization cross sections with the help of theoretical atomic-field bremsstrahlung cross sections. The measured cross sections are compared with existing experimental values and calculations based on the semi-relativistic distorted-wave Born approximation. According to our experiment, the ratio of Ag K β to K α x-ray intensities is 0.2018(24).

Determination of the detection efficiency of a planar HPGe detector with a non‐uniform frontal dead layer

Peak efficiency of a non‐uniform frontal dead layer planar detector was simulated with the general purpose Monte Carlo radiation transport code PENELOPE. In a previous publication, using experimental data and an analytical model proposed by Seltzer, we found the structure and dimensions of the detectors dead layer. In this work, we used our previous results as input for a Monte Carlo simulation that considered a point source emitting specific photons from 13 to 122 keV, with the energies and emission probabilities of241Am,133Ba,207Bi,57Co,137Cs, and152Eu calibration sources, placed at 30 cm from the frontal surface of the detector. The geometry consisted of an amorphous Germanium cylinder, 2.5 cm in diameter and 1.0‐cm thick, a 0.025‐cm thick Be window and a 50‐μm Al foil used in the experimental setup for irradiations in the Microtron de São Paulo. The simulation model succeeded as well as the analytical model and can be applied to other arrangements. Copyright © 2015 John Wiley & Sons, Ltd.

A simple and economic method for accurate determination of the energy peak efficiency of 208 keV γ-ray of 237U based on 241Pu/237U secular equilibrium

A new method is developed for the determination of energy peak efficiency of 208 keV γ-ray of 237U based on 241Pu/237U secular equilibrium. Plutonium solution was purified to remove Am with Dowex 1 × 2 anion exchange chromatography and the concentration of 241Pu in the purified solution was determined using 242Pu isotope-dilution mass spectrometry on an inductively-coupled plasma mass spectrometry. The solution can be used as calibration source for the determination of energy peak efficiency of 208 keV γ-ray of 237U after 48 days. The method was validated for a planar HPGe detector at the 12 mm above the detector surface. The results showed that this is a simple and economic method for determining the energy peak efficiency of gamma detectors for 208 keV γ-ray of 237U.

Development of a radioxenon measurement system and its application in monitoring Fukushima nuclear accident

An HPGe gamma-ray spectrometry system for radioxenon isotopes detection has been developed. The system was comprised of two low-energy planar HPGe detectors that were horizontally and oppositely placed, and a gas source cell made of carbon fiber in both sides was used. The spectra obtained simultaneously by the two HPGe detectors were analyzed by summing spectrum method. After the radioactive concentration of 133Xe was determined with three internal gas proportional counters, the efficiency of 81keV gamma-ray for 133Xe was calibrated to be 0.50 (1), and the Minimum Detectable Activity (MDA) for 133Xe detection was determined to be 10mBq during 1 day measurement time. Finally, the system was applied in atmospheric 133Xe monitoring at Xi'an of China after the Fukushima nuclear accident.

High-Spin States and Level Structure in Stable Nucleus Strontium-84

High-spin states of 84Sr are populated through the reaction 70Zn (18O, 4n) 84Sr at the beam energy of 75 MeV. The measurements of excitation functions, γ-γ coincidences, directional correlations of oriented states (DCO) ratios and γ-transition intensities are performed using eight anticompton HPGe detectors and one planar HPGe detector. Based on the experimental results, we establish a new level scheme of 84Sr, in which 12 new states and nearly 30 new γ-transitions are identified in the present work. The positive-parity yrast band is extended to spin Iπ = 24+, while one negative-parity band is extended to spin Iπ = 19− and it is found that the even-spin and odd-spin members in high-spin states show the nature of signature staggering. The deformation of 84Sr is studied by calculating the total-Routhian-surfaces (TRS) of positive-parity yrast states in the cranked shell model formalism.

Monte Carlo model of HPGe detectors used in routine lung counting

An MCNP model of a pair of planar HPGe detectors (designated as: detector 3 and detector 4), that are used for routine lung counting at AECL, was developed. The model was benchmarked against experimental results, where a multi-line 152Eu source was counted in several different geometrical arrangements. The best agreement for both detectors was achieved when side and back dead layers (of both detectors) were quadrupled, with respect to the ones quoted by their manufacturer (Canberra). In the case of detector 4, the agreement between simulated and measured spectra was within 4%, throughout the whole γ-spectrum, spanning 70–1600keV. The same was true for detector 3 at the lower end of the γ-spectrum. However, at the high end of the γ-spectrum, the agreement was within 7% and 12% for 152Eu γ-lines at 778.9 and 1408.01keV.

An AMOC System with Two Detectors

In this work, a single scintillator detector setup for AMOC measurement is considered to improve coincidence efficiency. A planar HPGe detector provide both the timing signal of stop channel and the energy spectrum signal for an annihilation events of positronium. Experiment results show that the system can get a count rate ~20cps/μCi with a time resolution of 2.2ns.

Photon emission probabilities of 176Lu

An aqueous solution containing dissolved lutetium nitrate with a natural isotopic composition was measured by means of gamma-ray spectrometry to determine emission probabilities of photons which are emitted as a consequence of the decay of the primordial isotope 176Lu. The geometry and matrix of the sample were taken into account in terms of efficiency transfer factors computed with the aid of the upgraded Monte Carlo simulation software GESPECOR. A combination of these results, with the activity determination via liquid scintillation counting using the CIEMAT/NIST efficiency tracing method, yields absolute values of PX(54.61keV)=0.095(4), PX(55.79keV)=0.168(5), Pγ(88.36keV)=0.149(5), Pγ(201.83keV)=0.777(9) and Pγ(306.84keV)=0.929(9). In addition, the upper limit of the probability for a potential electron-capture decay of 176Lu was improved using additional high resolution gamma-ray spectra taken with a planar HPGe detector.

Standardization of 65Zn by sum-peak method

A commercial solution of 65Zn was standardized by the sum peak-method using a planar HPGe detector. The activity results were compared with measurements made with a well type 4πγ ionization chamber, which is traceable to BIPM.RI (II)-K2.Zn-65 key-comparison performed in 2002. The sum-peak value was 42.79kBq/g and the ionization chamber value was 42.74kBq/g both at the reference date. The uncertainty obtained in the sum peak standardization was 0.25% (k=1), and in the ionization chamber was 0.85% (k=1).The results showed that sum-peak method can be used in 65Zn standardization and this method is easier, simpler and more practical than others methods.

A novel [formula omitted] imaging method for the pulse-shape characterization of position sensitive semiconductor radiation detectors

A new technique for the pulse-shape characterization of γ ‐ ray position sensitive germanium detectors is presented. This method combines the pulse shape comparison scan (PSCS) principle with a γ ‐ ray imaging technique. The latter is provided by a supplementary, high performance, position sensitive γ ‐ ray scintillator detector. We describe the basic aspects of the method and we show measurements made for the study of pulse-shapes in a non-segmented planar HPGe detector. A preliminary application of the PSCS is carried out, although a more detailed investigation is being performed with highly segmented position sensitive detectors.

High spin states in stable nucleus 84Sr

High spin states of 84Sr were populated through the reaction 70Zn(18O, 4n)84Sr at 75 MeV beam energy. Measurement of excitation function, γ-γ coincidences, directional correlation from oriented state (DCO) ratios and γ-transition intensities were performed using eight anticompton HPGe detectors and one planar HPGe detector. Based on the measured results, a new level scheme of 84Sr was established in which 12 new states and nearly 30 new γ-transitions were identified in the present work. The positive-parity states of the new level scheme were compared with the results from calculations in the framework of the projected shell model (PSM). One negative-parity band was extended to spin Iπ=19− and it can be found that in the high spin states, the γ-transition energies show the nature of signature staggering. The negative-parity band levels are in good agreement with deformed configuration-mixing shell model (DCM) calculations.

Crystal rounding and the efficiency transfer method in gamma-ray spectrometry

The effect of failing to properly model the rounding of the crystal edges in the application of the efficiency transfer method to the measurement of environmental samples is investigated for coaxial and thick planar (BeGe) HPGe detectors. It is found that for lower energies proper modelling of the crystal rounding is necessary to achieve the accuracy of the computed efficiency usually required in this type of measurements.

Matrix formalism and singular-value decomposition for the location of gamma interactions in segmented HPGe detectors

Modern coaxial and planar HPGe detectors allow a precise determination of the energies and trajectories of the impinging gamma-rays. This entails the location of the gamma interactions inside the crystal from the shape of the delivered signals. This paper reviews the state of the art of the analysis of the HPGe response function and proposes methods that lead to optimum signal decomposition. The generic matrix method allows fast location of the interactions even when the induced signals strongly overlap.