Coaxial High Purity Germanium Research Articles

Radiological hazards of TENORM in precipitated calcium carbonate generated as waste at nitrophosphate fertilizer plant in Pakistan

The NORM (naturally occurring radioactive material) in phosphate rock is transferred as TENORM (technologically enhanced naturally occurring radioactive material) to phosphatic fertilizers and to the waste generated by the chemical processes. The waste generated at the NP (nitrophosphate) fertilizer plant at Multan in Pakistan is PCC (precipitated calcium carbonate). Thirty samples of the PCC were collected from the heaps of the waste near the fertilizer plant. Activity concentrations of radionuclides in the waste samples were measured by using the technique of gamma ray spectrometry consisting of coaxial type HPGe (high purity germanium) detector coupled with a PC (personal computer) based MCA (multichannel analyzer) through a spectroscopy amplifier. Activity concentrations of 226Ra, 232Th and 40K in the waste samples were determined to be 273 ± 23 (173–398), 32 ± 4 (26–39) and 56 ± 5 (46–66) Bq kg −1 respectively. The activity concentration of 226Ra in the PCC waste was found to be higher than that in naturally occurring calcium carbonate (limestone and marble) and in worldwide soil. Radiological hazard was estimated from indoor and outdoor exposure to gamma rays from the PCC. Indoor annual effective dose was higher than 1 m Sv. Potential radiological pollution in the environment from TENORM in the PCC has also been addressed.

Focus on test and measurement

Focus on test and measurement

An investigation of the performance of a coaxial HPGe detector operating in a magnetic resonance imaging field

Nuclear medical imaging modalities such as positron emission tomography and single photon emission computed tomography are used to probe physiological functions of the body by detecting gamma rays emitted from biologically targeted radiopharmaceuticals. A system which is capable of simultaneous data acquisition for nuclear medical imaging and magnetic resonance imaging is highly sought after by the medical imaging community. Such a device could provide a more complete medical insight into the functions of the body within a well-defined structural context. However, acquiring simultaneous nuclear/MRI sequences are technically challenging due to the conventional photomultiplier tube readout employed by most existing scintillator detector systems. A promising solution is a nuclear imaging device composed of semiconductor detectors that can be operated with a standard MRI scanner. However, the influence of placing a semiconductor detector such as high purity germanium (HPGe) within or close to the bore of an MRI scanner, where high magnetic fields are present, is not well understood. In this paper, the performance of a HPGe detector operating in a high strength static ( B S ) MRI field along with fast switching gradient fields and radiofrequency from the MRI system has been assessed. The influence of the B S field on the energy resolution of the detector has been investigated for various positions and orientations of the detector within the magnetic field. The results have then been interpreted in terms of the influence of the B S field on the charge collection properties. MRI images have been acquired with the detector situated at the entrance of the MRI bore to investigate the effects of simultaneous data acquisition on detector performance and MRI imaging.

A novel HPGe detector for gamma-ray tracking and imaging

A novel, large-volume High Purity Germanium (HPGe) detector that will provide gamma-ray detection with both sub-mm position resolution and high efficiency is under development. This design is based on a coaxial HPGe geometry and employs a point contact along with segmentation of the outer electrode. Calculations indicate that this device will be capable of achieving values of position sensitivity which are approximately a factor of four or five greater than conventional gamma-ray tracking detectors.

Experimental and theoretical Compton profiles of Be, C and Al

The results of Compton profile measurements, Fermi momentum determinations, and theoretical values obtained from a linear combination of Slater-type orbital (STO) for core electrons in beryllium; carbon and aluminium are presented. In addition, a Thomas–Fermi model is used to estimate the contribution of valence electrons to the Compton profile. Measurements were performed using monoenergetic photons of 59.54 keV provided by a low-intensity Am-241 γ-ray source. Scattered photons were detected at 90° from the beam direction using a p-type coaxial high-purity germanium detector (HPGe). The experimental results are in good agreement with theoretical calculations.

Measurement of naturally occurring/fallout radioactive elements and assessment of annual effective dose in soil samples collected from four districts of the Punjab Province, Pakistan

Soil samples were collected from different localities of districts Jhelum, Chakwal, Rawalpindi and Attock, Punjab Province, Pakistan with an aim to measure naturally occurring radionuclides, namely 226Ra, 232Th, 40K and fallout 137Cs radionuclide using a P-type coaxial high purity germanium (HPGe) γ-ray spectrometer. Measured specific activities of 226Ra, 232Th and 40K in these soil samples ranged from 26.02 ± 7.11 to 93.54 ± 8.13 Bq kg−1, 29.34 ± 2.58 to 114.41 ± 2.80 Bq kg−1 and 348.15 ± 3.20 to 752.98 ± 4.20 Bq kg−1, respectively. Activity due to 137Cs was observed in some locations which ranged from 0.4 ± 0.2 to 7.8 ± 0.3 Bq kg−1. From the measured activity concentrations, radium equivalent activity concentrations were determined followed by calculations of mean absorbed dose rate and mean annual effective dose for the inhabitants of the studied area. The mean radium equivalent activity, internal and external hazard indices values came out to be 179.26 ± 11.93 Bq kg−1, 0.64 ± 0.05 and 0.48 ± 0.03, respectively. Indoors and outdoor average annual effective dose values were found to be 0.42 ± 0.03 and 0.10 ± 0.01 mSv, respectively. Present data have been compared with the published data for other parts of the world and found to be safe for public and environment.

HPGe detectors timing using pulse shape analysis techniques

In this work the Pulse Shape Analysis has been used to improve the time resolution of High Purity Germanium (HPGe) detectors. A set of time aligned signals was acquired in a coincidence measurement using a coaxial HPGe and a cerium-doped lanthanum chloride (LaCl 3:Ce) scintillation detector. The analysis using a Constant Fraction Discriminator (CFD) time output versus the HPGe signal shape shows that time resolution ranges from 2 to 12 ns depending on the slope in the initial part of the signal. An optimization procedure of the CFD parameters gives the same final time resolution (8 ns) as the one achieved after a correction of the CFD output based on the current pulse maximum position. Finally, an algorithm based on Pulse Shape Analysis was applied to the experimental data and a time resolution between 3 and 4 ns was obtained, corresponding to a 50% improvement as compared with that given by standard CFDs.

Determination of trace elements in Chinese medicinal plants by instrumental neutron activation analysis

Roots of Astragalus membranaceus, Angelica sinensis, Glycyrrhiza uralensis and Codonopsis pilosula, which were often used as herbs in traditional Chinese medicine, were analyzed by Instrumental Neutron Activation Analysis (INAA). The samples were collected in Gansu, northwest of China and irradiated at the 15 MW heavy water reactor in China Institute of Atomic Energy (CIAE). The induced activities were counted by a well calibrated low background γ-spectrometer equipped with a high efficiency coaxial high-purity germanium (HPGe) detector. The concentrations of eighteen trace elements (Ca, Fe, Na, Zn, Ba, Rb, Ce, Cr, La, Co, Th, Cs, Sb, Sc, Sm, Hf, Eu and Tb) in the herbs were determined. Possible links between pharmacological action of the herbs and content of some elements were also discussed in this paper. The measured results were compared with the reported values in literature.

The 124Sb activity standardization by gamma spectrometry for medical applications

This work describes a metrological activity determination of 124Sb, which can be used as radiotracer, applying gamma spectrometry methods with hyper pure germanium detector and efficiency curves. This isotope with good activity and high radionuclidic purity is employed in the form of meglumine antimoniate (Glucantime) or sodium stibogluconate (Pentostam) to treat leishmaniasis. 124Sb is also applied in animal organ distribution studies to solve some questions in pharmacology. 124Sb decays by β-emission and it produces several photons (X and gamma rays) with energy varying from 27 to 2700 keV. Efficiency curves to measure point 124Sb solid sources were obtained from a 166mHo standard that is a multi-gamma reference source. These curves depend on radiation energy, sample geometry, photon attenuation, dead time and sample-detector position. Results for activity determination of 124Sb samples using efficiency curves and a high purity coaxial germanium detector were consistent in different counting geometries. Also uncertainties of about 2% ( k=2) were obtained.

Cross section measurements via residual nuclear decays: Analysis methods

We develop an approach to calculating the pure cross section of the ground state of artificial radioactive nuclides that subtracts the effect of an excited state on the ground state. We apply a formalism to obtaining pure cross sections by subtracting the effect of excited states in the reactions $^{122}\mathrm{Te}$($n,2n$)$^{121}\mathrm{Te}$${}^{g}$ and $^{128}\mathrm{Te}$($n,2n$)$^{127}\mathrm{Te}$${}^{g}$, induced by neutrons of about $14$ MeV. The cross sections are measured by an activation relative to the $^{93}\mathrm{Nb}$($n,2n$)$^{92}\mathrm{Nb}$${}^{m}$ reaction and are compared with results that take into account the effect of the excited state. Measurements are carried out by $\ensuremath{\gamma}$ detection using a coaxial high-purity germanium (HPGe) detector. As samples, spectroscopically pure Te powder is used. The fast neutrons are produced by the $^{3}\mathrm{H}$($d,n$)$^{4}\mathrm{He}$ reaction. The neutron energies in these measurements are determined using the method of cross-section ratios between the $^{90}\mathrm{Zr}$($n,2n$)$^{89}\mathrm{Zr}$${}^{m+g}$ and $^{93}\mathrm{Nb}$($n,2n$)$^{92}\mathrm{Nb}$${}^{m}$ reactions.

Distribution of some natural and man-made radionuclides in soil from the city of Veles (Republic of Macedonia) and its environs

A systematic study of soil radioactivity in the metallurgical centre of the Republic of Macedonia, the city of Veles and its environs, was carried out. The measurement of the radioactivity was performed in 55 samples from evenly distributed sampling sites. The gross alpha and gross beta radioactivity measurements were made as a screening, using a low background gas-flow proportional counter. For the analysis of (40)K, (238)U, (232)Th and (137)Cs, a P-type coaxial high purity germanium detector was used. The values for the activity concentrations of the natural radionuclides fall well within the worldwide range as reported in the literature. It is shown that the activity of man-made radionuclides, except for (137)Cs, is below the detection limit. (137)Cs originated from the atmospheric deposition and present in soil in the activity concentration range of 2-358 Bq kg(-1) is irregularly distributed over the sampled territory owing to the complicated orography of the land. The results of gamma spectrometry are compared to the K, U, and Th concentrations previously obtained by the reactor neutron activation analysis in the same soil samples.

Evaluation of a Closed-End Coaxial High-Purity Germanium Cylindrical Detector Efficiency Using a Simplified Geometrical Approach

The full-energy peak (photopeak) efficiency and peak-to-total ratio of a closed-end coaxial high-purity germanium detector were calculated and compared with the experimental measurements in the energy range between 60 and 1863 keV. The attenuation of photons by the source itself (self-absorption), the source container, and the detector end cap materials is also included. Many experimental readings have been taken for the source-detector system used in this investigation. By comparison, the calculated and experimental full-energy peak efficiency and peak-to-total ratio values are in good agreement; the overall percentage error is <3%.

Measurement of natural radionuclides in phosphgypsum using an anti-cosmic gamma-ray spectrometer

Gamma-ray spectrometry measurements have been carried out to determine the activity of natural radionuclides in a phosphogypsum sample included in a specific tight container. The gamma spectrometer includes an N-type coaxial high-purity germanium (HPGe) detector equipped with an anti-cosmic system. This measurement required the determination of linear attenuation coefficients of phosphogypsum to calculate self-absorption correction between efficiency calibration conditions and measurement ones. The results are given for the three natural chains and for 40K, in term of specific activity/g of dry material, ranging from a few Bq kg −1 to a few hundreds Bq kg −1. The equilibrium within the different families and the 235U/ 238U ratio are discussed.

Natural radionuclide content in building materials and gamma dose rate in dwellings in Cuba

An extensive research project to investigate the radioactive properties of Cuban building materials was carried out because there is a lack of information on the radioactivity of such materials in Cuba. In the framework of this project 44 samples of commonly used raw materials and building products were collected in five Cuban provinces. The activity concentrations of natural radionuclides were determined by gamma ray spectrometry using a p-type coaxial high purity germanium detector and their mean values were in the ranges: 9–857 Bq kg −1 for 40K; 6–57 Bq kg −1 for 226Ra; and 1.2–22 Bq kg −1 for 232Th. The radium equivalent activity in the 44 samples varied from 4 Bq kg −1 (wood) to 272 Bq kg −1 (brick). A high pressure ionisation chamber was used to measure the indoor absorbed dose rate in 543 dwellings and workplaces in five Cuban provinces. The average absorbed dose rates in air ranged from 43 nGy h −1 (Holguín) to 73 nGy h −1 (Camagüey) and the corresponding population-weighted annual effective dose due to external gamma radiation was estimated to be 145 ± 40 μSv. This value is 51% lower than the effective dose due to internal exposure from inhalation of decay products of 222Rn and 220Rn and it is 16% higher than the calculated value for the typical room geometry of a Cuban house.

AN ASSESSMENT OF NATURAL RADIOACTIVITY OF SOILS AND ITS EXTERNAL RADIOLOGICAL IMPACT IN SOUTHWESTERN NIGERIA

Soil samples collected from five states in the southwestern part of Nigeria have been analyzed for activity concentration of gamma-ray emitters. The States were Oyo, Lagos, Ondo, Ogun, and Osun. Activity concentration measurement was carried out using a co-axial type high purity germanium (HPGe) detector. Spectral analyses were performed using spectrometry software. The activity concentration measured ranged from 0.03 +/- 0.2 Bq kg(-1) for 137Cs to 1,358.6 +/- 28.5 Bq kg(-1) for (40)K. (40)K accounted for most of the activity. The calculated absorbed dose rates in air at 1.0 m above the ground ranged from 6 to 303 nGy h(-1) with a mean and standard deviation of 60.5 nGy h(-1) and 63.2 nGy h(-1), respectively. Estimated annual outdoor effective dose equivalent varied from 8 to 370 mSv y(-1). The calculated collective dose equivalent values for the five states ranged from 87,000 person-Sv to 600,000 person-Sv. The estimated annual outdoor effective values were considerably higher than the world soil average value of 70 microSv y(-1) reported by the International Commission on Radiological Protection.

Cross sections for (n, 2n), (n, p) and (n, 〈alpha〉) reactions on osmium isotopes in the neutron energy range of 13.5–14.8 MeV

Cross sections for (n, 2n), (n, p) and (n, alpha) reactions on the osmium isotopes were measured in the neutron energies 13.5-14.8 MeV by the activation technique with the monitor reaction (93)Nb(n, 2n)(92 m)Nb. Our measurements were carried out by gamma-detection using a coaxial high-purity germanium (HPGe) detector. Natural high-purity osmium powder (99.9%) was fabricated as the samples. The neutron energies were determined by the cross-section ratios for (93)Nb(n, 2n)(92 m)Nb and (90)Zr(n, 2n)(89 m+g)Zr reactions. The fast neutrons were produced by the T(d, n)(4)He reaction. The results obtained were compared with previous data.

Natural radioactivity and trace metals in crude oils: implication for health

Crude oil samples were collected from six different fields in the central Niger Delta in order to determine their natural radioactivity and trace element contents, with the aim of assessing the radiological health implications and environmental health hazard of the metals, and also to provide natural radioactivity baseline data that could be used for more comprehensive future study in this respect. The activity concentrations of the radionuclides were measured using a well, accurately calibrated and shielded vertical cryostat, Canberra coaxial high-purity germanium (HPGe) detector system, and the derived doses were evaluated. The metal concentrations were determined by the graphite furnace atomic absorption spectroscopic (GFAAS) method. The radionuclides identified with reliable regularity belong to the decay series of naturally occurring radionuclides headed by (238)U and (232)Th along with the non-decay series radionuclide, (40)K. The averaged activity concentrations obtained were 10.52 +/- 0.03 Bq kg(-1), 0.80 +/- 0.37 Bq kg(-1) and 0.17 +/- 0.09 Bq kg(-1) for (40)K, (238)U and (232)Th, respectively. The equivalent doses were very low, ranging from 0.0028 to 0.012 mSv year(-1) with a mean value of 0.0070 mSv year(-1). The results obtained were low, and hence, the radioactivity content from the crude oils in the Niger delta oil province of Nigeria do not constitute any health hazard to occupationally exposed workers, the public and the end user. The concentrations of the elements (As, Cd, Co, Fe, Mn, Ni, Se and V) determined ranged from 0.73 to 202.90 ppb with an average of 74.35 ppb for the oil samples analysed. The pattern of occurrence of each element agreed with the earlier studies from other parts of the Niger Delta. It was obvious from this study and previous ones that the Niger Delta oils have low metal contents. However, despite the low concentrations, they could still pose an intrinsic health hazard considering their cumulative effects in the environment. Also, various studies on the impact of oil spillage and activities of oil exploration and production on organisms in the immediate environment suggest this.

Extending the dynamic range of nuclear pulse spectrometers

Using an innovative time-varying front-end electronics in conjunction with a bulky coaxial high-purity germanium detector, we were able to extend the range of the radionuclide spectra well beyond the analog to digital converter (ADC) saturation point. The electronics automatically conditions the signal for digital-filtering optimization if it is in the ADC voltage range and for time-over-threshold analysis if it exceeds the ADC range. A high spectroscopic resolution has been achieved in both operation ranges. An unprecedented wide energy range from 5 keV to 150 MeV of equivalent energy, or 90 dB, has been obtained using a single acquisition chain, while maintaining a high-energy resolution in the whole spectrum. For example, with an ADC range of 3 MeV a resolution has been obtained of 1.3/2.2 keV full width at half maximum on the 122/1332 keV gamma-ray lines of 57Co and 60Co, and of <0.4% in the time-over-threshold region, or for energy deposits beyond 3 MeV.

Monitoring of air radioactivity at the Jungfraujoch research station: Test of a new high volume aerosol sampler

The Swiss Federal Office of Public Health (SFOPH) is responsible for the surveillance of environmental radioactivity in Switzerland and for the protection of the public from ionizing and non-ionizing radiation. In order to improve the Swiss radioactivity monitoring network, a new high volume air sampler (DIGITEL DHA-80) was tested in Fribourg and at the Jungfraujoch High Altitude Research Station at 3454 m. The filters are analyzed in the laboratory by a high purity coaxial germanium detector. In the test period natural radio nuclides and traces of 137Cs, due to the Chernobyl accident of April 1986, were measured and are in good agreement with values from Germany and Poland. Albeit, the main purpose of this radioactivity monitoring network is to detect rapidly any input of artificial radioactivity, it is also helpful to understand transport of natural radio nuclides in the atmosphere, as for example the cosmogenic 7Be and the long-lived radon daughter 210Pb. The DIGITEL sampler proved to be sufficiently reliable for aerosol radioactivity monitoring even in extreme meteorological conditions at Jungfraujoch. A detection limit for artificial 137Cs of 2 μBq/m 3 is obtained.

Improvement of the Compton suppression ratio of a standard BGO suppressor system by a digital pulse shape analysis

We have applied a digital pulse shape analysis (DPSA) to Compton suppression for a high-purity coaxial germanium detector (HPGe) as a means of verifying the DPSA method that we have recently developed to extract information for the interaction positions of gamma rays in semiconductor detectors. Our DPSA method is based on chi-square fitting the measured pulse shapes to the calculated ones obtained by the weighting potential method. In order to investigate the performance of the Compton suppression technique using our DPSA method, we have extracted the experimental peak-to-total (P/T) ratios for 662-keV gamma rays emitted from a 137Cs standard source. The experimental P/T ratios were compared with the ones obtained by a conventional BGO suppressor system. Applying the Compton suppression technique using the DPSA method to the BGO suppression system, we could also improve the P/T ratios. The experimental results were in good accord with the ones obtained by a Monte Carlo simulation.