High-purity Germanium Spectrometer Research Articles

Full background decomposition of the CONUS experiment

The CONUS experiment is searching for coherent elastic neutrino nucleus scattering of reactor anti-neutrinos with four low-energy threshold point-contact high-purity germanium spectrometers. Excellent background suppression within the region of interest below 1 keV (ionization energy) is absolutely necessary to enable signal detection. The collected data also make it possible to set limits on various models regarding beyond the standard model physics. These analyses benefit as well from the low background level of sim 10 d^{-1} kg^{-1} below 1 keV and at higher energies. The low background level is achieved by employing a compact shell-like shield that was adapted to the most relevant background sources at the shallow depth location of the experiment: environmental gamma radiation and muon-induced secondaries. Overall, the compact CONUS shield including the active anticoincidence muon-veto reduces the background by more than four orders of magnitude. The remaining background is described with validated Monte Carlo simulations which include the detector response. It is the first time that a full background decomposition in germanium operated at a reactor site has been achieved. Next to the remaining muon-induced background, ^{210}Pb within the shield and cryostat end caps, cosmogenic activation and airborne radon are the most relevant background sources. The reactor-correlated background is negligible within the shield. The validated background model, together with the parameterization of the noise, is used as input to the likelihood analyses of the various physics cases.

CONRAD—A low level germanium test detector for the CONUS experiment

This proceeding presents the CONRAD high-purity germanium spectrometer with a large diode (2.2 kg mass) employing electrical cryocooling. The detector is an ideal tool to characterize background up to high energies of ∼12 MeV. The detector itself exhibits a high level of radiopurity. Due to the cryocooling the detector is flexible and of low maintenance effort. It can be deployed for example at nuclear reactors for site characterization such as for the CONUS experiment, which is looking for coherent elastic neutrino nucleus scattering.

A comparison of alpha-particle and gamma-ray spectrometry methods for determination of 235U, 238U and 226Ra activity concentration in samples of coal, slag and fly-ash

In order to compare alpha-particle and gamma-ray spectrometry, the activity concentrations of 235U, 238U and 226Ra in samples of coal, slag and fly-ash from the thermal power plant “Nikola Tesla A”, Serbia, were determined by these two methods. Methods were compared and discussed from the point of view of its precision, difficulty to apply and complexity. Gamma-ray spectrometry was performed with HPGe (High Purity Germanium) spectrometer, while alpha activity was measured by PIPS (Passivated Implanted Planar Silicon) detector. For the alpha-particle spectrometry, the chemical procedures applied were chromatographic resin extraction for uranium isotopes and micro-coprecipitation for 226Ra. Thin alpha sources were prepared by electrodeposition and filtration through polypropylene membrane filter for uranium determination, while filtration technique was performed for radium sources. For the evaluation of the statistical difference between individual measurement results obtained by application of two methods Z - test was used. In order to evaluate the difference between two methods used, paired samples t-test and F-test were applied. Results show that there is no statistical difference between two methods used and that gamma-ray spectrometry is a valid alternative to time consuming alpha spectrometry.

Natural Radioactivity in Soil and Bitumen in Al-Marj Spring and Abu-Jir Village, Anbar, Western Iraq

The aim of the present research is to illustrate γ-ray levels emitting from soil and bitumen producing from 238U, 232Th, and 40K along Abu-Jir Fault Zone. in the area extended from Al-Marj valley to Abu-Jir village using scintillometer device. Such study is important in environmental assessment to buildup data base about radioactivity. The concentration of natural radionuclides in the study area was determined to be occurring mostly in the clay minerals and organic matter. A high purity germanium spectrometer was used to detect the activity of these elements which ranged between 00.6±18.1- 1526±102, 0- 8.4±1.4, and 70.1±10.9- 328.2±73 in soil, and 28.2±5.6- 94±22.1, 0- 2.2±0.5, and 38.4±7.9- 70.1±10.9 in bitumen for 226Ra, 232Th, and 40K respectively. The anomaly of the Naturally occurring radioactive material was associated with hydrocarbon accumulation and springs. The source of 232Th and 40K came from the same source rock (illite), while 226Ra was associated with ascending fluids. The obtained results showed that the activity of 226Ra in soil has value above the world averages and other countries.

Determination of the gamma and X-ray emission intensities of erbium-169

The gamma and X-ray emission intensities of 169Er were determined using radionuclidically pure 169Er. The activity of the 169Er source was standardized by the triple-to-double-coincidence ratio technique. Three independent measurements were performed to measure the emission intensities using calibrated high-purity germanium spectrometers. The efficiencies were computed with the Monte Carlo method and validated using several experimental measurements. Final results present a large uncertainty reduction compared to previous evaluations. The emission intensities per decay of 169Er are reported as 1.401(40).10−5 for the 109.8 keV line and 1.513(19).10−6 for the 118.2 keV line. The values obtained for the X-ray lines show large discrepancies with the reference values.

Determination of the gamma and X-ray emission intensities of terbium-161

In this study, the gamma and X-ray emission intensities of 161Tb were determined using a high-purity germanium spectrometer. The samples used were previously standardised by coincidence counting and Triple to Double Coincidence Ratio (TDCR) methods. A total of 28 gamma-rays and 4 X-rays were measured and compared with previous measurements performed more than 30 years ago. Most of the lines are in agreement, while large discrepancies are observed for 5 lines. The uncertainties have been dramatically decreased with respect to previous measurements giving a better knowledge of the 161 Tb day.

In-situ gamma-ray background measurements for next generation CDEX experiment in the China Jinping Underground Laboratory

In-situ γ-ray measurements were performed using a portable high purity germanium spectrometer in Hall-C at the second phase of the China Jinping Underground Laboratory (CJPL-II) to characterise the environmental radioactivity background below 3 MeV and provide ambient γ-ray background parameters for next generation of China Dark Matter Experiment (CDEX). The integral count rate of the spectrum was 46.8 cps in the energy range of 60 to 2700 keV. Detection efficiencies of the spectrometer corresponding to concrete walls and surrounding air were obtained from numerical calculation and Monte Carlo simulation, respectively. The radioactivity concentrations of the walls in the Hall-C were calculated to be 6.8±1.5 Bq/kg for 238U, 5.4±0.6 Bq/kg for 232Th, 81.9±14.3 Bq/kg for 40K. Based on the measurement results, the expected background rates from these primordial radionuclides of future CDEX experiment were simulated in unit of counts per keV per ton per year (cpkty) for the energy ranges of 2 to 4 keV and around 2 MeV. The total background level from primordial radionuclides with decay products in secular equilibrium are 0.63 and 4.6×10−2 cpkty for energy ranges of 2 keV to 4 keV and around 2 MeV, respectively.

Preliminary investigation of the shutdown radioactivity for EAST based on gamma ray spectrometry

• The HPGe spectrometer system was placed inside the vacuum vessel to measure the characteristic γ-rays emission from radionuclides after EAST shutdown. • The identification and pathway analysis of radionuclides were discussed based on structural materials and radiation sources of EAST. • Activity of radionuclides and time evolution of dose rate, preliminary activation results, were discussed. Experimental Advanced Superconducting Tokamak (EAST) is capable of operating with long-pulse deuterium plasma, which will generate a lot of radiation such as fusion neutrons, gamma rays and hard X-rays. Since the structure material of the device was activated, work around and inside the tokamak would be limited from a radiation protection point of view after shutdown. Identification of radionuclides and evaluation of dose rate inside the vacuum vessel are needed to develop a guiding principle for radiation protection during maintenance. In this paper, a gamma ray spectrometer based on high purity germanium (HPGe) detector and digitizer was placed inside the vacuum vessel to measure the characteristic gamma ray emission from radionuclides. 7 Be, 46 Sc, 51 Cr, 54 Mn, 58 Co, 60 Co, 59 Fe, 88 Y, 91 Y, 91m Nb, 99 Mo, 124 Sb and 110m Ag produced by photonuclear reactions and neutron-induced reactions were identified. The activities of radionuclides was calculated respectively with the uncertainty not exceed 6.05 %. The dose rate for 10 days after shutdown was mainly contributed by 60 Co, 58 Co, 54 Mn, 110m Ag, 59 Fe, 51 Cr, 88 Y, 99 Mo, 7 Be and 124 Sb, total dose rate were 3.62 × 10 −9 Sv/h(Port E) and 3.40 × 10 −9 Sv/h(Port I).

Development of neutron activation system on EAST.

A neutron activation system (NAS) has been developed on the Experimental Advanced Superconducting Tokamak (EAST) for the investigation of time-integrated neutron yield. It is a robust neutron diagnostic with high precision and a wide dynamic range. Some high purity materials with a proper nuclear reaction energy threshold and cross section are tested as neutron detectors in the NAS, and they are delivered to the tokamak device by a pneumatic transfer system. The length of the pneumatic pipeline is about 50 m, and the transfer time ranges from 10 s to 20 s. The decay gamma rays of the activated samples are measured with a high-purity germanium spectrometer, and its detection efficiencies are 6.9% at 336 keV and 1.7% at 1779 keV, respectively. Indium and silicon samples with a reaction threshold of 0.3 MeV and 4.0 MeV, respectively, were successfully implemented in the diagnosis of DD and DT neutron yield in the EAST. The neutron flux of the NAS was compared with the count of the fission chamber in the EAST neutral beam injection experiment, and the DD neutron yield evaluated by the NAS ranges from 1.9 × 1012 n/shot to 5.9 × 1014 n/shot during recent experimental campaign.

Detection of background thermal neutrons in a modified low-background germanium gamma-ray spectrometer

The paper presents the detection of background neutrons using the 558.4 keV gamma line emitted from excited 114Cd nuclei after neutron induced processes. Stable cadmium and 60 L water moderator were placed inside low background shield of high purity germanium (HPGe) based spectrometer. The method was applied to study diurnal mean variation of background neutron flux. For this purpose 1 h gamma background spectra of modified HPGe spectrometer were collected subsequently for 50.5 days and then summed in 24-h-cycle. Results for the 558.4 keV line are presented along with those of main background lines. The total gamma-ray spectrum was also analysed and results are presented and discussed. No cyclic structure was noticed for all examited lines but 2223 keV, for which some day-night effect is suggested to exist. Test of another moderator made of 108 kg of graphite was done, but the results obtained with water are more promising.

Calibration of the gamma-ray measurement procedure in the EAST neutron activation system

A neutron activation system based on pneumatic transfer system has been employed to measure the time-integrated neutron yield for the Experimental Advanced Superconducting Tokamak (EAST). Those DD neutrons were detected by indium with the reaction of In115(n,n') In115m, the energy threshold of the reaction was 0.3 MeV which was capable of eliminating the interference of scatting neutrons. A small amount of DT neutron generated by the deuterium plasma was detected by silicon with the reaction of Si28n,pAl28, the energy threshold was 4 MeV so as to discriminate the DD neutron from DT neutron. The γ spectrum of activated samples was obtained with high purity germanium spectrometer. The efficiency for the measurement of fusion neutrons were calibrated by DD/DT neutron accelerator. The key coefficients using to calculate the neutron flux by characteristic γ peak counts have been obtained in this calibration. Furthermore, investigation of the thickness of samples in order to cover the wide range of neutron yields was performed. The neutron activation system was implemented to the measurement of fusion neutron yield in EAST from the experiment campaign of 2018, and obtained a linear with deviation less than ± 10% comparing with fission chamber.

Shutdown dose rate neutronics experiment during high performances DD operations at JET

A novel Shutdown dose rate benchmark experiment has been performed at Joint European Torus (JET) machine during the last high performance Deuterium–Deuterium (DD) campaign in preparation of future high Deuterium-Tritium experiment (DTE2). On-line continuous gamma dose rate measurements were performed for four months at two ITER relevant ex-vessel positions close to Radial Neutron Camera and on the top of ITER-like Antenna using high-sensitive ionization chambers. Decay gamma spectra at the shutdown were also collected using High Purity Germanium spectrometer to identify dominant radionuclides contributing to the dose. Neutron fluence measurements during operations were performed as well using activation foils assembly installed close to ionization chambers. The measurements are performed to validate shutdown dose rate tools used in ITER. This paper presents the experimental assembly and measurements analyses.

Improving sensitivity of a BEGe-based high-purity germanium spectrometer through pulse shape analysis

We performed Pulse Shape Analysis to separate single-scattered gamma energy deposition events from multiple-scattered photons in a high-sensitivity gamma -ray spectrometer. The spectrometer is based on a Broad Energy High Purity Germanium detector and the developed technique uses multivariate analysis by an application of the Multi-Layer Perceptron Neural Network. A very good separation of the single-site- and multi-site events was achieved leading to a significant reduction of the background level of the investigated spectrometer – the double escape peak, rich in single-site events, was reduced by 95%, while the full energy peaks lost at most 25% of their counts. The peak to Compton ratio, calculated for the 2614.5 keV gamma line from ^{208}Tl, was improved by 114.3%.

Nuclear spent fuel parameter determination using multivariate analysis of fission product gamma spectra

In this paper, we investigate the application of multivariate data analysis methods to the analysis of gamma spectroscopy measurements of spent nuclear fuel (SNF). Using a simulated irradiation and cooling of nuclear fuel over a wide range of cooling times (CT), total burnup at discharge (BU) and initial enrichments (IE) we investigate the possibilities of using a multivariate data analysis of the gamma ray emission signatures from the fuel to determine these fuel parameters. This is accomplished by training a multivariate analysis method on simulated data and then applying the method to simulated, but perturbed, data.We find that for SNF with CT less than about 20years, a single gamma spectrum from a high resolution gamma spectrometer, such as a high-purity germanium spectrometer, allows for the determination of the above mentioned fuel parameters.Further, using measured gamma spectra from real SNF from Swedish pressurized light water reactors we were able to confirm the operator declared fuel parameters. In this case, a multivariate analysis trained on simulated data and applied to real data was used.

Extended Stability of HPGe Spectrometer with Environmental Control at the High Flux Isotope Reactor

A High Purity Germanium (HPGe) spectrometer has been designed and constructed for making precision measurements over extended time periods at the High Flux Isotope Reactor (HFIR) located at Oak Ridge National Lab (ORNL). Toward the effort of achieving long-term system stability and high spectral resolution, local environment control is utilized as part of the system design. Further, the remote operation of the spectrometer is aided by live-streaming system conditions and automatic out-of-range alert messaging. System performance over the 7-month Phase I period is presented.

Low-level gamma-ray spectrometry for the determination of 210Pb

A well High purity germanium (HPGe) gamma spectrometer with NaI(Tl) Compton anticoincidence shield recently installed at DTU Nutech and specially designed for low-level measurements was used for the 210Pb determination in environmental samples. The system is compared to standard stand-alone HPGe spectrometers. The choice between high efficiency well and planar detectors as well as optimum sample size depending on available sample quantity are discussed. Results show that the only comparative advantage of the well anticoincidence system is when just small sample sizes are available.

Secondary radiation doses in IMRT techniques

Introduction The probability for developing the secondary cancer related to low peripheral doses during teleradiotherapy is nowadays of increasing interest. Among the components of the secondary dose photoneutrons and activated radionuclides should be discussed. Purpose Investigation of the secondary neutron and induced gamma radiation doses during intensity modulated radiation therapy employing Step&Shoot, sliding window and VMAT techniques. Materials and methods Elekta Synergy linacs with Agility MLC, working in 10 MV and 15 MV modes were used. Six plans with a 15 Gy fractional dose to PTV in mediastinum were studied and realized at anthropomorphic male phantom. Neutron flux was measured by the activation of indium 115 In foils. Neutron dosemeter LB 123N was also used. The induced gamma-activity of linac head was investigated using high-purity germanium spectrometer. Doses were assessed using fluence-to dose conversion coefficients. Results The dominant activation dose comes from 28 Al, 56 Mn and 187 W isotopes and may reach 2 μSv/h 10 cm from the linac head. Neutron flux densities are of the order of 10 3 –10 4 cm −2 s −1 for slow and 10 4 –10 5 cm −2 s −1 for fast neutrons. Additional doses connected with neutrons are ∼0.5 mSv/MU for 10 MV beam and within the range of 0.8–1.7 mSv/MU for 15 MV beam. Variation of neutron doses across the patient body is within 13%, for studied plans. Conclusion The neutron flux can be even 3.5 times lower whereas gamma-ray doses 5 times lower for 10 MV than for 15 MV beams in IMRT techniques. Disclosure No conflict of interest.

PRex: An Experiment to Investigate Detection of Near-field Particulate Deposition from a Simulated Underground Nuclear Weapons Test Vent.

A radioactive particulate release experiment to produce a near-field ground deposition representative of small-scale venting from an underground nuclear test was conducted to gather data in support of treaty capability development activities. For this experiment, a CO2-driven "air cannon" was used to inject (140)La, a radioisotope of lanthanum with 1.7-d half-life and strong gamma-ray emissions, into the lowest levels of the atmosphere at ambient temperatures. Witness plates and air samplers were laid out in an irregular grid covering the area where the plume was anticipated to deposit based on climatological wind records. This experiment was performed at the Nevada National Security Site, where existing infrastructure, radiological procedures, and support personnel facilitated planning and execution of the work. A vehicle-mounted NaI(Tl) spectrometer and a polyvinyl toluene-based backpack instrument were used to survey the deposited plume. Hand-held instruments, including NaI(Tl) and lanthanum bromide scintillators and high purity germanium spectrometers, were used to take in situ measurements. Additionally, three soil sampling techniques were investigated and compared. The relative sensitivity and utility of sampling and survey methods are discussed in the context of on-site inspection.

GIOVE: a new detector setup for high sensitivity germanium spectroscopy at shallow depth

We report on the development and construction of the high-purity germanium spectrometer setup GIOVE (Germanium Inner Outer VEto), recently built and now operated at the shallow underground laboratory of the Max-Planck-Institut für Kernphysik, Heidelberg. Particular attention was paid to the design of a novel passive and active shield, aiming at efficient rejection of environmental and muon induced radiation backgrounds. The achieved sensitivity level of $$\le $$ 100 $$\upmu $$ Bq kg $$^{-1}$$ for primordial radionuclides from U and Th in typical $$\gamma $$ ray sample screening measurements is unique among instruments located at comparably shallow depths and can compete with instruments at far deeper underground sites.

Simulation of background reduction and Compton suppression in a low-background HPGe spectrometer at a surface laboratory

High-purity germanium (HPGe) detectors are well suited to analyse the radioactivity of samples. In order to reduce the environmental background for an ultra-low background HPGe spectrometer, low-activity lead and oxygen free copper are installed outside the probe to shield from gamma radiation, with an outer plastic scintillator to veto cosmic rays, and an anti-Compton detector to improve the peak-to-Compton ratio. Using Geant4 tools and taking into account a detailed description of the detector, we optimize the sizes of these detectors to reach the design requirements. A set of experimental data from an existing HPGe spectrometer was used to compare with the simulation. For the future low-background HPGe detector simulation, considering different thicknesses of BGO crystals and anti-coincidence efficiency, the simulation results show that the optimal BGO thickness is 5.5 cm, and the peak-to-Compton ratio of 40K is raised to 1000 when the anti-coincidence efficiency is 0.85. In the background simulation, 15 cm oxygen-free copper plus 10 cm lead can reduce the environmental gamma rays to 0.0024 cps/100 cm3 Ge (50 keV-2.8 MeV), which is about 10−5 of the environmental background.