High-purity Germanium Gamma-ray Research Articles

Handling of high-volume High Purity Germanium gamma ray detector and repair with minimum resources – A case study

A High Purity Germanium (HPGe) detector is a high-resolution detector, used for gamma-ray spectroscopy. One such HPGe detector of our laboratory was showing poor resolution either due to malfunctioning of components or vacuum. This detector being a sophisticated instrument need to be operated in an environment with adequate cooling and humidity control. The optimum conditions such as maintaining liquid Nitrogen filling in Dewar at proper time and holding capacity of Dewar and humidity control environment could not be maintained due to lockdown conditions during the pandemic. This disrupted the functioning of the detector resulting in poor performance and poor resolution. One reason for such a behaviour is attributed to the condensation of moisture at the feed through points of High Voltage and failures of components such as preamplifier and Field Effect Transistor (FET). Transportation of the detector for repairs to France involves lengthy procedures, additional expenditure, custom clearance and safe transit. The possibility of performing the detector repair with the available facility on premise was explored. The repair involved breaking of vacuum in Clean room Facility, availability of Variac, Vacuum gauge, Dry Nitrogen, Helium leak detector, Liquid nitrogen, Temperature sensor with controller, Turbomolecular pump, Vacuum plunger etc. The diagnosis of cascading failure of components in the germanium detector and their rectification to restore its functionality with desired performance has been discussed in the present paper.

Radiological assessment in beach sediment of coastline, Ghana

The natural and artificial radioactivity in beach sediment sampled from the coastline of Ghana were analyzed using High Purity Germanium gamma ray detector. The overall average activity concentrations of 226Ra, 232Th, 40K and 137Cs were estimated to be 43 ± 6, 22 ± 1, 393 ± 74 and 8.4 ± 0.5 Bqkg−1, respectively. Apart from 226Ra the mean activity concentrations of the measured radionuclides were below the world averages of 32, 45, 412 and 18.2 Bqkg−1 respectively. High 137Cs mean concentration of 109.8 Bqkg−1 was observed for one of the locations, which might be due to the occurrence of a nuclear incidence or other factors. The evaluated radiological parameters also had values below world averages, except for some coastal areas which recorded Annual Gonadal Dose Equivalent (AGDE) values higher than the reference level of 300 μSvy−1. There was no significant risk associated with the radionuclide activities evaluated along the coast of Ghana. The correlation between the radionuclides and the radiological parameters were analyzed with the Pearson correlation matrix, cluster and PCA analysis, and they all showed similar outcomes. Spatial distribution maps were also created using ArcGIS software for a pictorial view of the distribution of radionuclides along the study area.

Neutron activation analysis of archeological artifacts using the ISIS pulsed neutron source

Archeological artifacts can be analyzed after neutron irradiation at the pulsed ISIS neutron and muon source, UK, using a newly installed high purity germanium gamma ray spectrometer to perform neutron activation analysis. In this work, the details of the measurement methods and data analysis are presented. In particular, it is explained how Monte Carlo calculations are necessary to evaluate the detection efficiency, taking into account self-shielding effects. The results for two certified bronze standards are presented. The good agreement between expected and measured compositions is promising for the use of this technique for archeological artifacts where the elemental concentration is often unknown. As an example, the analysis of a Chinese sword from the first or second century BC is presented.

The potential radio-immunotherapeutic α-emitter 227Th – part I: Standardisation via primary liquid scintillation techniques and decay progeny ingrowth measurements

Thorium-227 is a potential therapeutic radionuclide for applications in targeted α-radioimmunotherapy for the treatment of various types of cancer. To provide nuclear medicine departments involved in Phase I clinical trials traceability to the SI unit of radioactivity (Bq), a standardisation of a radiochemically pure 227Th aqueous solution has been performed at the National Physical Laboratory. This was achieved via two primary liquid scintillation (LS) techniques −4π(LS)-γ digital coincidence counting (DCC) and 4π LS counting. These absolute techniques were supported by the indirect determination of the 227Th activity via the measurement of the ingrowth and decay rate of the decay progeny by both ionisations chambers and high purity germanium (HPGe) gamma-ray spectrometry. The results of the primary techniques were found to be consistent, both with each other (zeta score = 1.1) and to the decay progeny ingrowth measurements. An activity per unit mass of 20.726 (51) kBq g−1 was determined for the solution. A procedure has been developed that provided an effective separation of the 227Th from its decay progeny, which was shown by the effective time zero of the 227Th-223Ra nuclear chronometer measured by HPGe gamma-ray spectrometry.

Pulse tube refrigeration for detectors

High purity germanium (HPGe) gamma-ray detectors are used for nondestructive assay. Liquid nitrogen (LN2), a cryogen, is commonly used to cool these detectors. Cryogen use is associated with several health risks and operational problems. This has prompted the development of cryogen-free refrigeration. A new generation of commercial pulse tube refrigerator (PTR) has been developed during the last decade. A unique feature of the PTR is the absence of cold moving parts. This significantly reduces the generated noise and vibration. In the following report, LN2, a modified Joule–Thompson cooler, and a PTR unit are examined and their cooling effectiveness with HPGe gamma-ray detectors compared. Overall, PTR is an engineering equivalent to LN2 and modified Joule–Thompson cooler systems used in gamma spectroscopy and eliminate the health and physical hazards associated with LN2 systems without adding hazards.

Risk reduction benefits of cryogen-free refrigeration

High Purity Germanium (HPGe) gamma-ray detectors are used at Los Alamos National Laboratory's Plutonium Facility (TA-55) for nondestructive assay. Liquid nitrogen (LN2), a cryogen, is commonly used to cool these detectors. Cryogen use is associated with several health risks and operational problems. This has prompted the development of cryogen-free refrigeration. Although the efficacy of the coolers has been proven for use with HPGe detectors, the health and safety aspect implications have not been studied. Both LN2 and mechanical coolers were examined and their application effectiveness on health and safety aspects in HPGe gamma-ray detector use at TA-55 was compared. Overall, cryogen-free refrigeration is an engineering equivalent to LN2 systems used in gamma spectroscopy and eliminates the health and physical hazards associated with LN2 systems without adding hazards.

Environmental radioactivity evaluation in the coastal stretch of Bay of Bengal from Pondycherry to Velanganni (South East coast of India)

Background: Since the Madras Atomic Power Station, Kalpakkam and Kudankulam Nuclear Power Plant, Kudankulam are sited in Bay of Bengal coast, radiological study of this coastal environment is imperative to assess the impact of operation of nuclear power plant, if any, on the radioactivity profile of the coast. Materials and Methods: In the present study the environmental radioactivity was evaluated by measuring activity concentrations of primordial radionuclides namely 238 U, 232 Th and 40 K. in the beach sand samples using high purity germanium gamma ray spectrometry. 10 sampling stations were fixed along a 290 km coastal stretch of Bay of Bengal from Pondycherry to Velangannni. Results: The activity concentration of 238 U is always much less than that of 232 Th and 40 K and it ranged from 9 Bq/kg (Pondicherry coast) to 93 Bq/kg (Karaikal coast). However, 232 Th concentration fluctuated from 12 Bq/kg (Pichavaram Mangrove) to 1075 Bq/kg (Karaikal coast). The activity concentration of 40 K varied within a narrow range from 162 Bq/kg to 474 Bq/kg. The distribution of primordial radioactivity was non-uniform along the entire stretch of Bay of Bengal. The elevated levels of 232 Th were recorded in Karaikal coast (S7) (1075 Bq/kg), Tirumullaivasal coast (S4) (215 Bq/kg), and Nagapattinam coast (S9) (146 Bq/kg) and attributed to the presence of thorium-rich monazite as beach placer in coastal sands. Conclusion: The total absorbed gamma dose contributed by the activity of 238 U, 232 Th, and 40 K varied between 29 nGy/h and 308 nGy/h with a GM value of 64.4 nGy/h. Similarly, the annual effective dose recorded for Bay of Bengal ranged from 0.04 mSv/year to 0.38 mSv/year, indicating that the Bay of Bengal, in general, falls under Normal Background Radiation Area.

RADIOACTIVE ROCK PHOSPHATE: THE FEED STOCK OF PHOSPHATE FERTILIZERS USED IN PAKISTAN

The existence of natural radioactivity in phosphate fertilizers originates from the rock phosphate that is used as a feed stock for the manufacturing of various types of phosphate fertilizers. Gamma ray activity mass concentrations have been determined in phosphate rock and fertilizer samples collected from different fertilizer manufacturing factories and suppliers in Pakistan. The technique of gamma ray spectrometry was applied using a HPGe (high purity germanium) gamma ray detector coupled with a personal computer (PC) based multichannel analyzer (MCA). The specific activity values of 40K, 226Ra, and 232Th were widely distributed in the rock and fertilizer samples. Activity mass concentrations of 238U (226Ra) in the rock phosphate from Jordan and Pakistan were 428 +/- 11 and 799 +/- 10 Bq kg(-1), respectively, and that in the triple-superphosphate fertilizer was 701 +/- 21 (-1), which was greater than the average values of 238U (226Ra) for other types of fertilizers under study. The concentrations of 40K and 232Th were of the order of background level on the Earth's crust. Chemical analysis for concentration of different constituents in rock phosphate was also carried out. The higher the concentrations of P2O5 and K2O were, the higher the specific activities of 226Ra and 40K were, respectively, in the rocks under study. The amount of radioactivity in the rock phosphate is a source of continuous exposure to radiation, which varies widely depending upon the origin and grade of rock; therefore, radiation dose rate has been estimated. The values of dose rate and other derived quantities were many folds larger than the limits specified for those quantities.

Natural environmental radioactivity and estimation of radiation exposure from saline soils

The study was conducted for the investigation of amount of radioactivity in the barren and cultivated soil of Bio saline Research Station in Pakka Anna, established by Nuclear Institute for Agriculture and Biology (NIAB) in 1990, 34 km. away from the city of Faisalabad, in the Punjab province of Pakistan. The studies were done on an area of about 100 hectares of two types of virgin and fertilized saline soils. The technique of gamma ray spectrometry was applied using HPGe (high purity germanium) gamma ray detector and a PC based MCA. Activity concentration levels due to 40 K, 137 Cs, 226 Ra and 232 Th were measured in 250 saline soil samples collected at a spacing of about 4 hectares at the depth level of 0–25 cm. with a step of 5 cm. depth. Activity concentrations ranges of the concerned radionuclides for both of the soils were as follows: 40 K, for virgin and cultivated saline soil was 500−610.2 and Bq/kg 560.2−635.6 respectively; 137 Cs, 3.57−3.63 and 1.98−5.15 Bq/kg 238 U, 26.3−31.6 and 30.3−38.7 Bq/kg, and 232 Th, 50.6−55.3 and 50.6−64.0 Bq/kg respectively. The absorbed dose rate in air lies in the region 63-73 nGyh -1 and 68-83 nGyh -1 for virgin and fertilized soils respectively. This indicates that this region lies in the area of higher radiation background, while comparing with the worlds’ average. The slightly higher value of dose in the fertilized farm may be due to the use of fertilizers for cultivation. Before the radiometric measurements, chemical analysis for concentration of Na, Ca and Mg was also carried out along with the measurement of electrical conductivity and pH of the soil samples.

Development of nuclear spectroscopy systems using high resolution semiconductor detector

Abstract Two kinds of spectrometers have been developed at Dalat Nuclear Research Institute. In this paper an XRF spectrometer and Compton suppression and pair spectrometers have been described. The XRF spectrometer consists of Si(Li) detector and Dalat Electronics. Compton suppression and pair spectrometers consist of a 20% high purity germanium gamma ray detector inserted into two large NaI(TI) shielding detectors, coupled with Compton suppression and pair electronics of Dalat. Improving the resolution of XRF spectrometer and increasing the peak to Compton ratio of gamma ray spectrometers have been done at Dalat Nuclear Research Institute. Block diagram of systems and results of testing spectroscopy systems have been given.

Position Sensitive Gamma Ray Detectors Using Resistive Charge Division Readout

The analysis of an orthogonal strip, two-dimensional position sensitive high purity germanium gamma ray detector is discussed. Position sensitivity is obtained by connecting each electrode strip on the detector to a resistor network and the ends of the network to charge sensitive preamplifiers. The difference of the voltage pulses at the output of each preamplifier is proportional to the position at which the charge entered the resistor network and the sum of the voltage pulses is proportional to the energy of the detected gamma ray. The results of the analysis of the energy and spatial signal noise show that the position resolution is proportional to the square root of the filter amplifier's output pulse time constant and that for energy measurement the resolution is maximized at the filter amplifier's noise corner time constant. The electronic noise filtering system and experimental noise measurement results are presented.

The noise analysis and optimum filtering techniques for a two-dimensional position sensitive orthogonal strip gamma ray detector employing resistive charge division

The analysis of an orthogonal strip, two-dimensional position sensitive high purity germanium gamma ray detector is discussed. Position sensitivity is obtained by connecting each electrode strip on the detector to a resistor network. Charge, entering the network, divides in relation to the resistance between its entry point and the virtual earth points of the charge sensitive preamplifiers located at the end of each resistor network. The difference of the voltage pulses at the output of each preamplifier is proportional to the position at which the charge entered the resistor network and the sum of the pulse is proportional to the energy of the detected gamma ray. The analysis of energy and spatial noise resolution is presented for this type of position sensitive detector. The results of the analysis show that the position resolution is proportional to the square root of the filter amplifier's output pulse time constant and that for energy measurement the resolution is maximized at the filter amplifier's noise corner time constant. The design of the electronic noise filtering system for the prototype gamma ray camera was based on the mathematical energy and spatial resolution equations. For the spatial channel a Gaussian trapezoidal filtering system was developed. Gaussian filtering was used for the energy channel. The detector noise model was verified by taking rms noise measurements of the filtered energy and spatial pulses from resistive readout charge dividing detectors. These measurements were within 10% of theory.

The Effect of Exposure to Various Gaseous Environments on the Subsequent Performance of High Purity Germanium Gamma Ray Detectors

Prior exposure to certain gases appears to largely determine the subsequent performance at LN2 temperatures of high purity germanium detectors with exposure temperature being a critical factor. These gases are hydrogen, water vapor and possibly oxygen. An optimum concentration of water vapor in the environment to which the detectors are exposed prior to cool down appears to be essential to achieving good performance and stable operating characteristics.