Portable Gamma-ray Spectrometer Research Articles

Radiological characterization of the ancient Roman tuff-pozzolana underground quarry in Orvieto (Italy): A natural laboratory to revisit the interactions between radionuclides and aerosols

Orvieto (Italy) has a large network of underground tunnels quarried to extract tuff and pozzolana by Etruscans and Romans. One of these tunnels was chosen as natural laboratory to compare different radiation measurement and dose assessment methods. Indeed, tuff and pozzolana are very rich in natural radioactivity and are interesting from the radiation protection point of view since they are still used as building materials. In order to characterize this site an in situ experimental procedure was followed. It consisted in measurements carried out with different instruments: two portable gamma ray spectrometers, two gamma dose rate meters, two radon monitors and one two channel working level monitor. Samples of tuff and pozzolana stones were also collected to be measured with gamma spectrometry in laboratory. Due to the high content of 238U, 232Th (more than 200 Bq kg−1 for both radionuclides) and 40K (more than 2000 Bq kg−1) of tuff and pozzolana, elevated levels of exposure to natural radioactivity were found: indeed, with different instruments and approach, a gamma dose rate of about 1 μGy h−1 and an average radon concentration of about 10,000 Bq m−3, with a Potential Alpha Energy Concentration (PAEC) of 288 MeV cm−3, were measured. The radiological characteristics of Orvieto underground quarry make it a perfect site for “in field” intercomparisons of different measurement and dose assessment methods.

Natural radioactivity levels of the Egyptian phosphate rocks using BGO detector based portable gamma-ray spectrometer

Gamma-ray surveys are used in geological, geochemical, and environmental mapping for mineral exploration. Natural radioactivity levels for forty phosphate sample localities on the Eastern Desert, Nile Valley, and Western Desert, Egypt, were measured using a gamma-ray spectrometer with high accuracy. From the obtained results, the average values of the annual effective dose were 0.19, 0.28, 0.29, and 0.15 mSv/year for Safaga, Abu.Tartur, El-Sebaeya, and Hamrawayn, respectively. The measured values of natural radionuclides in the studied samples are higher than the world average activity values. This study could be useful as baseline data for radiation exposure to phosphate and their impact on human health.

Application of two geophysical methods to characterize a former waste disposal site of the Trabzon-Moloz district in Turkey

Radionuclide variations, the vertical and lateral extent of a waste mass in the former Trabzon municipal solid waste dumpsite were investigated by combining in situ gamma-ray spectrometric measurements with 2D resistivity imaging methods. In the first step, the natural radioelement concentrations on the surface of dumpsite were measured using a portable gamma-ray spectrometer. The average activity concentrations of 238U, 232Th and 40K in the dumpsite are 42.68, 49.88 and 417 Bq/kg, respectively. In addition, radiation hazard parameters were calculated and compared with the international standard values. As a result of the evaluation of the radiological data, it was found that there are no significant radiologic hazards for humans and the environment. In the subsequent stage, 2D electrical resistivity method, using Wenner array, was carried out in this area. The survey was conducted using a multi-electrode resistivity instrument and the measured resistivity profiles were interpreted using RES2DINV program. Electrical resistivity values were obtained from three parallel lines. Results of the resistivity survey show that the waste masses in the study area reach to depths of about 18 m, with very low resistivity values less than 20 Ωm. According to the 2D inverted resistivity sections, low resistivities ( 160 Ωm) in profiles B and C are associated with non-degradable waste materials, medical wastes and buried construction materials. Also, very high resistivity zone (874 and 2636 Ωm) in profile A are interpreted as landfill gases.

Surface radioactive anomalies at Srisailam sub basin, Cuddapah basin, India

Surface radioactive survey has been carried with portable gamma ray spectrometer (PGRS) about the 45 km2 around the Srisailam sub basin, the surface radioactive anomalies were found at Chennakesavula gutta in the Srisailam sub basin of Cuddapah basin in the age of meso-neo proterozoic, India. The integrated geochemical and radiometric surveys were conducted as part of research work in the Srisailam basin, it has resulted the locating of surface radioactive anomalies near the Chennakesavula gutta. Secondary uranium minerals are observed along with the fracture planes in the Archean basement granite in the proximity of unconformity contact of Srisailam quartzite. The granite underlies the Srisailam formation and forms the source for possible unconformity related uranium mineralisation in the Srisailam sub-basin evidence by the significant radioactive anomalies. The radioactivity recorded by PGRS reflected uraniferous nature of the radioactivity (Average total counts = 195 ppm; U = 202 ppm; Th = 22 ppm; %K = 4.1, n = 15).

Portable Gamma-Ray Spectrometer for High Intensity Beam Measuring

The paper presents the development of the Laboratory "X-ray Optics" of the Institute of Applied Physics and Technology of Tomsk Polytechnic University, a portable gamma-ray spectrometer, which dimensions are 50×20×30 mm. The device is able to count and analyze gamma quanta with energies from hundreds of keV up to units of MeV with loading up to 109 pulses/min. The problem has been solved by improving the known scintillation counters, using modern silicon photomultiplier tubes, selecting the optimal scintillators and developing original electronic scaler.

Gamma dose rate and 226Ra activity concentrations in the soil around a Mexican radioactive waste-storage center

The environmental gamma dose rate has been determined at the Mexican Storage Centre for Radioactive Waste (SCRW) and surrounding communities. The gamma dose rates were evaluated using thermoluminescent dosimeters and a portable gamma-ray spectrometer. The activity concentrations of 235U, 226Ra, 232Th, 40K, and 137Cs in soil samples were determined by gamma spectrometry. The gamma dose rates and the annual effective doses were higher at the SCRW and at border line, as compared with the surrounding communities. A site specific lineal model to describe the relationship between the outdoor gamma dose rate and the 226Ra activity concentrations in the soil is proposed.

Spatial distributions of radionuclides deposited onto ground soil around the Fukushima Dai-ichi Nuclear Power Plant and their temporal change until December 2012

Spatial distributions and temporal changes of radioactive fallout released by the Fukushima Dai-ichi Nuclear Power Plant accident have been investigated by two campaigns with three measurement schedules. The inventories (activities per unit area) of the radionuclides deposited onto ground soil were measured using portable gamma-ray spectrometers at nearly 1000 locations (at most) per measurement campaign. Distribution maps of the inventories of 134Cs, 137Cs, and 110mAg as of March, September, and December 2012 were constructed. No apparent temporal change of the radionuclide inventories was observed from March to December 2012. Weathering effects (e.g., horizontal mobility) were not noticeable during this period. Spatial dependence in the ratios of 134Cs/137Cs and 110mAg/137Cs were observed in the Tohoku and Kanto regions. The detailed maps of 134Cs and 137Cs as of September 2012 and December 2012 were constructed using the relationship between the air dose rate and the inventory.

Afyon-Sandikli-Şuhut Arasindaki Bölgenin Toryum Konsantrasyonunun Alansal Dağilimi

Although at least 20 elements are known as natural radioactive, only U (Uranium), Th (Thorium) and K (Potassium) are important elements in nuclear geophysics. Stable nucleus of 232Th is Pb and in this chain there are 10 isotopes. 208Tl decay chain produces characteristic gamma radiation (2.62 MeV). The 232Th concentrations have been measured using portable gamma-ray spectrometer, for about 180 seconds counting times at 1169 points with known geographical coordinates. The variation of eTh concentration has been mapped in Afyonkarahisar district (Sandikli, Suhut, Haydarli). eTh concentration values ranged between 0-80 ppm with different regional lithology. It should be noted that high concentration values were obtained in volcanic rocks and altered volcanic zones

Evaluation of occupational exposure to naturally occurring radioactive materials in the Iranian ceramics industry

Zircon contains small amounts of uranium, thorium and radium in its crystalline structure. The ceramic industry is one of the major consumers of zirconium compounds that are used as an ingredient at ∼10-20 % by weight in glaze. In this study, seven different ceramic factories have been investigated regarding the presence of radioactive elements with focus on natural radioactivity. The overall objective of this investigation is to provide information regarding the radiation exposure to workers in the ceramic industry due to naturally occurring radioactive materials. This objective is met by collecting existing radiological data specific to glaze production and generating new data from sampling activities. The sampling effort involves the whole process of glaze production. External exposures are monitored using a portable gamma-ray spectrometer and environmental thermoluminescence dosimeters, by placing them for 6 months in some workplaces. Internal routes of exposure (mainly inhalation) are studied using air sampling, and gross alpha and beta counting. Measurement of radon gas and its progeny is performed by continuous radon gas monitors that use pulse ionisation chambers. Natural radioactivity due to the presence of ²³⁸U, ²³²Th and ⁴⁰K in zirconium compounds, glazes and other samples is measured by a gamma-ray spectrometry system with a high-purity germanium detector. The average concentrations of ²³⁸U and ²³²Th observed in the zirconium compounds are >3300 and >550 Bq kg⁻¹, respectively. The specific activities of other samples are much lower than in zirconium compounds. The annual effective dose from external radiation had a mean value of ∼0.13 mSv y⁻¹. Dust sampling revealed the greatest values in the process at the powdering site and hand weighing places. In these plants, the annual average effective dose from inhalation of long-lived airborne radionuclides was 0.226 mSv. ²²²Rn gas concentrations in the glaze production plant and storage warehouse were found to range from 10 to 213 Bq m⁻³. In this study, the estimated annual effective doses to exposed workers were <1 mSv y⁻¹.

Usefulness of systematic in situ gamma-ray surveys in the radiometric characterization of natural systems with poorly contrasting geological features (examples from NE of Portugal)

This paper focuses on the starting point of various studies that are being carried out in two possible locations being considered to host a hypothetical site for a repository for low and intermediate level radioactive waste (LILW) produced in Portugal in compliance with international requirements on the long-term safety of this kind of repository. Previous studies concerning the geology of the much larger geographical areas where these locations are included were fundamental in the choice of these locations and for the design of the survey strategy. One of the fundamental assessment studies during the site-selection is the overall radiological characterization of the locations and its relation to the geology. This paper pretends to show the adequability of using a fast and reasonably inexpensive survey technique such as in situ gamma-ray portable detectors, to access the radiometric response of the systems in study by providing the radiometric mapping of the areas. The existence of adequate radiometric maps represents a critical pre-requisite to constrain both the number and spatial distribution of samples to be collected for further analysis, sustaining as well the subsequent extrapolation of results needed to fully characterise the surveyed system. Both areas were surveyed using portable gamma-ray spectrometers with NaI(Tl) detectors. In situ gamma-ray measurements have clearly shown not only the poorly contrasting geological features, but also their differences representing: (i) a deformed/metamorphosed ophiolite complex and (ii) a monotonous meta-sedimentary sequence. The radiometric maps obtained have show heterogeneities that reflect mostly changes in rock-forming mineral assemblages, even in the presence of small variations of gamma radiation. These maps support objective criteria about the number/distribution of samples to be collected for subsequent comprehensive studies and reinforce the valuable contribution of in situ gamma spectrometry to assess, in radiological terms, the prevalent geological features.

Mapping the inhomogeneity of the U and Th distributions — using sample size concept in the field conditions

Indigenously fabricated portable gamma-ray spectrometer (PGRS) is used for the measurement of gamma activity of 214Bi (1.76 MeV) and 208TI (2.62 MeV), under field conditions in Mohar area, Shivpuri Distt. (MP). The energies are discriminated by using a Nal (TI) crystal of size 1.75″ × 2″. PGRS used to map the primordial elemental distributions shows reversals of concentration of thorium and uranium (represented by radium group) in field and lab analysis in many samples, which is attributed to the inhomogenity of distribution of these elements in the area. The concept of difference in the volume of dish shaped field sample and the randomly picked up sample from the field grid point (400 gm in lab analysis) is utilized to interpret the inhomogenity of these elements. However interpretations are based on the assumption that these primordial elements (U, Th) are in secular equilibrium and the terrain has low topographic relief.

In situ radiation measurement and estimation of U/Th ratio to reflect on the uranium bearing potential zone in metamorphic rocks of Mahendragarh district, Haryana

Gross gamma radiation survey was carried out using Nal(Tl) scintillator based portable gamma ray spectrometer (PGRS) around areas of Gaonri, Dholera, Pachnota and Meghot in Mahendragarh district, Haryana. Geologically the area forms part of north Delhi fold belt comprising calc-silicate, quartz biotite schist, impure marble, quartzite and pegmatite rocks. Equivalent uranium (eU3O8) concentration in ppm was estimated in situ on a regular grid pattern of 500 m (E-W) × 1000 m (N-S) and grab samples were collected at grid locations for analyzing in the laboratory for estimating the contents of eU3Os Raeq, ThO2 and %K. A comparison with the laboratory analysed grab samples for eU308 data and in situ radiation measurements shows a good match of the two sets of data. The in situ measurements indicate higher concentration of eU3O8 in Chapra Bibipur in northeastern most corners, Maghot area in central part, Gaonri in western part and Pachnota in southwestern part of the study area.

Field gamma-ray spectrometer GS256: measurements stability

The stability of in situ readings of the portable gamma-ray spectrometer GS256 during the field season of 2006 was studied. The instrument is an impulse detector of gamma rays based on NaI(Tl) 311 × 311 scintillation unit and 256-channel spectral analyzer which allows simultaneous assessment of up to 8 radioisotopes in rocks. It is commonly used in surface geophysical survey for the measurement of natural 40 K, 238 U and 232 Th but also artificial 137 Cs quantities. The statistical evaluation is given of both repeated measurements - in the laboratory and at several field control points in different survey areas. The variability of values shows both the instrument stability and also the relative influence of some meteorological factors, mainly rainfalls.The analysis shows an acceptable level of instrument measurements stability, the necessity to avoid measurement under unfavourable meteorological conditions and to keep detailed field book information about time, position and work conditions.

Identification of early Llandovery (Silurian) anoxic palaeo-depressions at the western margin of the Murzuq Basin (southwest Libya), based on gamma-ray spectrometry in surface exposures

ABSTRACT Following the melting of the Gondwanan icecap and the resulting postglacial sea-level rise, organic-rich shales were deposited in shelfal palaeo-depressions across North Africa and Arabia during the latest Ordovician to earliest Silurian. The unit is absent on palaeohighs that were flooded only later when the anoxic event had already ended. The regional distribution of the Silurian black shale is now well-known for the subsurface of the central parts of the Murzuq Basin, in Libya, where many exploration wells have been drilled and where the shale represents the main hydrocarbon source rock. On well logs, the Silurian black shale is easily recognisable due to increased uranium concentrations and, therefore, elevated gamma-ray values. The uranium in the shales “precipitated” under oxygen-reduced conditions and generally a linear relationship between uranium and organic content is developed. The distribution of the Silurian organic-rich shales in the outcrop belts surrounding the Murzuq Basin has been long unknown because Saharan surface weathering has commonly destroyed the organic matter and black colour of the shales, making it complicated to identify the previously organic-rich unit in the field. In an attempt to distinguish (previously) organic-rich from organically lean shales at outcrop, seven sections that straddle the Ordovician-Silurian boundary were measured by portable gamma-ray spectrometer along the outcrops of the western margin of the Murzuq Basin. It was found that the uranium content of the shales remained largely unaltered by the weathering processes and could therefore be used as a valid proxy parameter to distinguish between pre-weathering organically rich and lean shales. It is now possible to identify and map-out the thickness and approximate organic richness of the black shale using measurement of uranium radiation. Five of the newly measured sections are characterised by uranium-enriched intervals, representing areas of earliest Silurian palaeo-depressions. Major uranium peaks are absent in the spectral gamma-ray curves of two other sections, which are interpreted to mark earliest Silurian palaeo-highs. The new data on the distribution of Silurian black shales from the outcrop belt was integrated with subsurface data from the Murzuq Basin. The resulting map of the distribution of black shales may help with predictions of the occurrence of this unit in less well-explored areas of the basin. Graptolite biostratigraphic data suggests that the anoxic event centred on the middle Rhuddanian, with more oxygenated conditions and onset of deposition of organically leaner shales having commenced sometime during the late Rhuddanian. The presence of anoxic palaeo-depressions during the earliest Silurian within the Ghat outcrop belt indicates that the Tihemboka High at the western margin of the Murzuq Basin could not have been a positive structure during this time.

A least squares procedure for calculating the calibration constants of a portable gamma-ray spectrometer

In this study, a least squares procedure for calculating the calibration constants of a portable gamma-ray spectrometer using the general inverse matrix method is presented. The procedure weights the model equations fitting to the calibration data, taking into account the variances in the counting rates and in the radioactive standard concentrations. The application of the described procedure is illustrated by calibrating twice the same gamma-ray spectrometer, with two independent data sets collected approximately 18 months apart in the same calibration facility.

A simple and rapid method to locate fault traces by measurements of214Bi in soils

A simple and rapid technique is presented to determine the relative counts of 214Bi in surface soils to locate active fault traces of the El Pilar Fault in the state of Sucre, Venezuela. The method employes a portable differential gamma-ray spectrometer on site with 300 seconds of measuring time. Three transects across the El Pilar fault of very different geological aspects were studied. One of the advantages of this technique in respect to determining 222Rn in soil-gas is that no soil-gas probes are required to be inserted in the soil and it is not necessary to know the appropriate depth. Finally, it has been suggested that measurements of 1000 seconds would be preferred rather than 300 seconds for future studies even though this would limit the number of measurements to about 20 per day.

Assessment of ambient dose equivalent rate: performance of an automatic survey meter as an instrument to quantify the presence of radiation in soils

Those who work in radiation protection are faced with various quantities that were created to account for the effects of ionizing radiation in the human body. As far as the experimental point of view is concerned, each available equipment is planned to measure a distinct quantity, for a specific radiation protection application, and it is not always clear which one it is. This paper shows a series of tests, planned and applied to a portable gamma ray spectrometer, in order to assure that the monitoring low dose levels of radiation with it is reliable. The equipment is fully automated and does not allow modifications of the conversion factors from counts to ambient dose equivalent. It is therefore necessary to assure that the values provided by the equipment are correct and refer to the actual situation one expects to find in practice. The system is based on an NaI(Tl) scintillation detector, mounted with its electronics in a portable case, suitable for field measurements. It measures ambient dose equivalent rate (Ḣ*(10) in Sv h−1), total counts in the spectrum (from 50 to 1670 keV) and number of counts per channel (128 channels). The tests presented here are: evaluation of the cosmic component, repeatability, check against standard extended sources, and performance with point sources (60Co or 137Cs) on the ground. The results show that the system can be used, with its built-in conversion coefficients, for in situ measurements, whether or not the ground contains only natural radiation or is additionally contaminated.

Spectral component analysis applied to portable gamma ray spectrometry

Spectral component analysis is commonly applied to airborne gamma ray spectral data to reduce statistical noise in the measurements of potassium, uranium and thorium. This technique has been applied to continuous 5-second ground measurements with a portable gamma ray spectrometer using a 7.6 cm ´ 7.6 cm (3 inch ´ 3 inch) sodium iodide detector. The results have shown that the reduction in statistical noise is much greater than for large airborne detectors. Even with a short sampling time of 5-seconds, continuous ground measurements have practical significance for both geological mapping and mineral exploration.

CONCEPTUAL STUDY OF SPECTRAL BLANKOUT TECHNIQUE ON INSPECTING OF SOME SURROGATED NUCLEAR WARHEADS

We built up a nuclear warhead verification system based on an Intranet platform. The hardware of the system consists of an Intranet server, two personnel computers and a portable high purity gerinanium gamma-ray spectrometer. The software, Blanking-out, is made of two modules designed for the inspecting and inspected parties respectively. Both modules are interactive and communicate through the Intranet. When the system operates, any sensitive information carried by the high resolution gamma-ray spectrum collected by the detector will be meddled by the inspected module before the package of spectral data is sent to the inspecting module to prevent a disclosure of sensitive information. After receiving the spectral data, the inspecting module will display on the screen of the inspecting PC terminal the verification results in a form of blankouted spectrum (spectral blanking-out form) or a form of a piece of phrase (phrase form). The guideline to the spectral blanking-out is that: for those ranges of energy obligated to be inspected, the inspected module should ensure that the inspecting module can display truly their objective spectrum; and for the other ranges of energy, the inspected module can blankout certain parts of the spectra based on the knowledge of sensitive information. Phrase form is rather straightforward, answering the question whether the inspected warhead is a “uranium-type”, “plutonium-type” or “non-nuclear type.” We conducted a demonstration on some surrogates for nuclear warheads to see whether the nuclear warhead verification system possesses the capability of identifying the type of a warhead and blanking-out sensitive spectral information. The demonstration was carried out successfully. Phrase form is especially recommendable due to its stronger capability to prevent sensitive information from disclosure and its higher verification credibility. The demonstration also disclosed some deficiencies of the system, such as too much disintegrated hardware components lower the integration of the system, the interactive operation of the inspected module and the spectral blanking-out form decrease the verification credibility and so on.

Rapid Measurement of the Gaseous41Ar Released from a Nuclear Reactor Using a Portable Spectrometer

method to monitor in situ the dose rate from the gaseous radionuclide 41 Ar is developed using a portable gamma-ray spectrometer. A high-purity germanium detector with a sensitivity of 0.358 nSv/h per count per minute is used to calibrate 1294-keV gamma rays emitted from radioactive 41 Ar. Field measurements are conducted both inside and outside of the containment of a nuclear reactor during full-power operation, and iso-dose rate contour curves are mapped. The in situ measurement can be readily performed at various locations near a nuclear reactor with a 14-kg portable spectrometric unit. The detection limit for a 1-h counting period is as low as 0.35 nSv/h for the gaseous 41 Ar. One can use the method and field measurements developed in this research to quantitatively determine the gaseous fission products of krypton and xenon dispersed from a nuclear power plant.