Non-destructive Gamma Spectrometry Research Articles

Comparison of Real and Generated by MCNP Simulation Spectrums for Validation of Neutron Activation Calculations

The objective for decommissioning planning, is to obtain a radiological understanding of the involved installation. The characterization at this stage could be carried out by means of: (a) neutron activation calculations based on reactor design and neutron flux; (b) dose rate measurements; (c) in-situ gamma spectrometry; (d) sampling for determination of the scaling factors in activated and contaminated components.Neutron activation calculations contains several uncertainties. These uncertainties are based on the input data - such as material data (composition and impurities), neutron flux and energy, nuclear data libraries - and on the methodology of the process and the simulation codes.Taking into consideration all these modeling uncertainties, this work is focused on the development of a technique for validation of the calculations. A non-destructive gamma spectrometry technique by using MCNP6 simulations is under development for interpretation of the resulting gamma-ray spectra of the radionuclides in activated components. In particular, a spectrum will be produced, based on the activities of the main radionuclides in the activated component and the results of MCNP6 simulations. This spectrum will be compared with the experimental spectrum.Furthermore, the radiological characterization of activated components, which appeared with surface contamination, is essential for the decision making process during decommissioning. The cutting techniques to be followed in order to reduce the production of secondary waste and limit the doses to personnel and the selection of decontamination techniques should be based on accurate determination of the radionuclides inside the material and/ or in the surface contamination. The proposed method could also be helpful in this case. The activities inside and on the surface of the components could be determined by comparing the experimental spectrum with that produced by MCNP6 simulations, using the arisen activities from the scaling factors and the dose rate measurements.

Measurement of natural radioactivity and radium equivalent activity for pottery making clay samples in Paraíba and Rio Grande do Norte – Brazil

High levels of environmental radioactivity are caused by the composition of minerals in the earth's crust and the impact of prospection and utilization of natural sources, mainly due to the presence of 40K and radionuclides of 238U and 232Th series. Radium equivalent activity (RaEq) was calculated to assess the risk associated with primordial radionuclides in areas with clay extraction and production of bricks and tiles for civil construction. Twenty-eight clay samples, collected from potteries in Paraíba and Rio Grande do Norte states, Brazil, were analyzed using a non-destructive gamma-spectrometry method. Results showed radium equivalent activity in the range of 85 to 748 (mean value of 334) Bq kg−1. Around 29% of the samples presented RaEq higher than the limit of 370 Bq kg−1, a value established for specific applications of the products, whose raw material must be assessed in the source of extraction to comply with the radioecological protection principles. The qualitative characterization confirmed that all the radionuclides found in samples are of natural origin, with elevated values for some clay deposits, leading to suggestions to guarantee the safety of using the raw material in civil construction.

Relative efficiency calibration for determining isotopic composition and age of HEU items by passive non-destructive gamma spectrometry

The observation of the 239 keV gamma line from 232U decay in high-enriched uranium (HEU) samples prompted us to utilize 232U (with main gamma energies of its daughters at 239, 583, 763, and 860 keV) as a mediator isotope for performing relative (intrinsic) efficiency calibration among 232U, 234U, 235U, 238U, and 214Bi isotopes. By this way, the isotopic composition and age of HEU samples can be derived from activity ratios constituted between pairs of these isotopes on the basis of a common relative efficiency calibration curve. The method proved to be a useful tool for γ-spectrometric characterization of HEU items, especially of weapon grade, shielded uranium material.

Detection of fallout 241Am in U.S. Atlantic salt marsh soils

We report the presence of the fallout radionuclide 241Am (t1/2 = 433 years) in salt marsh soils from two U.S. Atlantic estuaries and discuss its utility as a particle tracer and geochronometer. This work is motivated by the knowledge that 137Cs, the most widely used geochronometer in environmental studies, will decay to extinction during the next century. At the same time, levels of 241Am, produced by radioactive decay of fallout 241Pu, will continue to increase on Earth's surface as they have since the height of atmospheric nuclear weapons testing in the 1960s. Measurements of 241Am in soils at eighteen salt marsh locations were made by non-destructive gamma spectrometry and compared to activities of 137Cs in the same samples. Results indicate that decay of fallout 241Pu can explain the presence of 241Am in the soils, and that the activities are sufficiently high to provide meaningful chronological information with acceptable confidence limits. We achieved a detection limit of 0.28–1.47 Bq kg−1 using low-energy, planar germanium detectors and 11-55 g powderized samples. Activities of 241Am (0.08–6.44 Bq kg−1) were similar in mineral- and organic-rich marsh soils indicating that soil composition does not appear to influence the initial capture of 241Pu and retention of its 241Am progeny. Given its high affinity for fine particles, long half-life, and ease of measurement by non-destructive gamma spectrometry, 241Am has potential to serve as an alternative to 137Cs geochronometry in salt marshes and perhaps other estuarine and coastal environments.

Radiochemical characterization of produced water from two production offshore oilfields in Ghana

Produced water from two Ghanaian offshore production oilfields has been characterized using alpha spectrometry after radiochemical separation, non-destructive gamma spectrometry and ICP-MS and other complimentary analytical tools. The measured concentrations of main NORM components were in the range of 6.2–22.3 Bq.L−1, 6.4–35.5 Bq.L−1, and 0.7–7.0 Bq.L−1 for 226Ra, 228Ra and 224Ra respectively. A good correlation between several physico-chemical parameters and radium isotopes was observed in each production oilfield. The radium concentrations obtained in this study for produced water from the two oilfields of Ghana are of radiological importance and hence there may be the need to put in place measures for future contamination concerns due to their bioavailability in the media and bioaccumulation characteristics. The results will assist in critical decision making for future set up of appropriate national guidelines for the management of NORM waste from the emerging oil and gas industry in Ghana.

Extension of the energy range of experimental activation cross-sections data of deuteron induced nuclear reactions on indium up to 50 MeV

The energy range of our earlier measured activation cross-sections data of longer-lived products of deuteron induced nuclear reactions on indium were extended from 40MeV up to 50MeV. The traditional stacked foil irradiation technique and non-destructive gamma spectrometry were used. No experimental data were found in literature for this higher energy range. Experimental cross-sections for the formation of the radionuclides 113,110Sn, 116m,115m,114m,113m,111,110g,109In and 115Cd are reported in the 37–50MeV energy range, for production of 110Sn and 110g,109In these are the first measurements ever. The experimental data were compared with the results of cross section calculations of the ALICE and EMPIRE nuclear model codes and of the TALYS 1.6 nuclear model code as listed in the on-line library TENDL-2014.

Radiological exposure assessment from soil, underground and surface water in communities along the coast of a shallow water offshore oilfield in Ghana.

Radiometric determinations have been carried out to assess public exposure to radioactivity for communities along the coast of a shallow water offshore oilfield in Ghana (which started their operations recently) in order to establish baseline data using alpha spectrometry after radiochemical separation and non-destructive gamma spectrometry. The average activity concentrations of (234)U, (238)U, (230)Th and (232)Th by alpha-particle spectrometry and of (226)Ra, (228)Ra, (228)Th, (40)K, (210)Pb, (234)Th and (137)Cs by gamma-ray spectrometry were determined in the soil samples. The activity concentrations of (234)U, (238)U, (230)Th and (232)Th were determined in the water samples by alpha-particle spectrometry and of (226)Ra by liquid scintillation counting. The total annual effective dose to the public was estimated from the measured activity concentrations and this was clearly below the International Commission on Radiological Protection (ICRP) reference level of 1 mSv y(-1) for public exposure control. In addition, the estimated values of Raeq, Hex and Hin were all lower than the recommended acceptable values and the mean values of gross alpha and gross beta determinations performed for all the water samples give values that were all below the Ghana Standards Authority and World Health Organization recommended guideline values for drinking water quality. The results obtained show insignificant public exposure to radioactivity. However, this study provides important information for future studies on subsequent evaluations of the possible future environmental contamination due to activities of the oil industry in Ghana.

The analysis of uranium-232: comparison of radiochemical techniques and an improved method by alpha spectrometry

Uranium-232 is an isotope of interest for nuclear forensic studies because it can provide information on the irradiation history of a sample of uranium. The isotope is formed in uranium materials through several pathways and is typically found at ultra-trace levels (usually ng/g or smaller) in typical uranium materials. The low abundance of this isotope in irradiated materials makes it very difficult to measure accurately and precisely. Many different methods have been proposed for the analysis of 232U using radiochemical methods including alpha and gamma spectrometry. In this paper, literature methods will be discussed and an improved method using alpha spectrometry will be presented. Alpha spectrometry offers a direct analysis technique for measuring 232U, with few interferences that can be removed via separations. Results from our improved method will be presented and compared to results obtained from a non-destructive gamma spectrometry method that utilizes an indirect measurement. LA-UR-12-20186.

Investigation of radioactivity in selected drinking water samples from Maryland

In 2004, levels of radioactivity exceeding federal drinking water standards were found by state laboratories in two separate areas of Maryland through gross alpha and beta screening measurements. It was desired to know which radionuclides were responsible for the activity and what effect water softener systems installed in individual households had on the mitigating problem. Non-destructive gamma-spectrometry and gross alpha-beta liquid scintillation measurements, as well as chemical separations followed by measurements of 222Rn, 226Ra and 228Ra, uranium and thorium isotopes, 210Po, and 210Pb were carried out by National Institute of Standards and Technology (NIST). The results of the studies indicated disequilibrium among the decay products in the Th and U decay chains had a major influence on the radionuclide content. Unsupported 210Po was found to be the predominant radionuclide in drinking water at one of the locations. Furthermore, the influence of the use of water softeners was found to be much more effective for radium than for uranium.

Dating of sediments in the Biscay bay: Implication for pollution chronology

Important historical informations on the temporal changes of anthropogenic pollution in marine environment can be assessed using sediment analysis. Dating is a crucial prerequisite to reconstruct pollution events, to calculate fluxes, and thus to allow comparison between different sites. This work presents estimates of accumulation rates of sediments in the Bay of Biscay. Fives cores were collected during RIKEAU 2002 cruise on board o/v Thalia in order to study temporal changes in PAH and organohalogens compounds content of sediment. We compare chronostratigraphic estimates on cores derived from the natural radionuclide 210 Pb in excess with estimates from the known times of introduction of the artificial radionuclide 137 Cs to the environment. 210 Pb, 226 Ra and 137 Cs were measured directly by non-destructive gamma spectrometry using a well type γ-detector. Total 210 Pb and 226 Ra activities vary from 30 to 150 mBq g -1 , and 20 to 36 mBq g -1 respectively; 137 Cs presents lower levels (< 5 mBq g -1 ). Profiles of 210 Pbxs in three cores present a well mixed layer, from 2-3 to 10 cm, in the uppermost sediments, followed by an exponential decrease of activities, suitable for the determination of sedimentation rates. Under constant flux and sedimentation rate assumptions, vertical accretion rates derived from 210 Pbxs present a large range from nearly 0.1 cm yr -1 up to almost 0.3 cm yr -1 . Differences are mainly due to relative position of studied cores regarding the muddy patch. Although the moderate level of 137 Cs limits the accuracy of this dating method, profiles of 137 Cs with depth strengthen mean rates derived from 210 Pbxs data. The implication of this dating on pollutant inputs in sediments of the Bay of Biscay is briefly discussed.

Radionuclide dates and foraminiferal accumulation rates: examples from submarine canyons

Caesium-137, an anthropogenic radionuclide, has been present in the global environment for the past 40 years and may be detected in sediment using non-destructive gamma spectrometry. 137Cs peaks can be used to date layers within core material. The effect of bioturbation upon the dating results has been considered using X-radiography of the core material.Recent sedimentary material from submarine canyons cutting the Portuguese continental margin has been dated using 137Cs and this information, used in conjunction with foraminiferal assemblage data, has allowed benthic and planktic foraminiferal test accumulation rates to be calculated. Benthic foraminiferal accumulation rates range from 55 to 687 tests/yr/10 cm2 and planktic rates range from 51 to 1338 tests/yr/10 cm2 at water depths of 385 to 3400. Accumulation rates have been calculated for selected genera and Brizalina has the highest overall value.

Sedimentation patterns and accumulation rates in the Tasman Basin

Sediment accumulation rates determined by nondestructive gamma spectrometry on 22 piston cores taken in the Tasman Basin vary from 0·2 to 2·7 g cm −2 (1000 yr) −1. Near the South Tasman Rise, winnowing keeps the sedimentation rate of foraminiferal ooze low on the rise crests [0·15 to 0·90 g cm −2 (1000 yr) −1] while rates on the flanks and base of the rise are faster [1·4 to 2·0 g cm −2 (1000 yr) −1]. The rateson the Tasman abyssal plainand central basin are controlled by proximity to a sediment source area and local scour. The effect of submarine canyons off the Bass Strait is evident in the high rate of clly accumulation near the terminus of the canyons. Rates in the central basin are low [0·2 to 1·0 g cm −2 (1000 yr) −1] because of bottom currents. The 230Th balance is studied by relating the accumulation rate of 230Th ( = F a) to its rate of production from 230U in the water column ( = F p). Sediment settling through the water column scavenges 230Th to produce an ideal ratio of F atoF pof1·0. Winnowing and bottom transport can alter the F a/F p ratio. Cores from rise crest and the central basin have F a/F pratios< 1·0 while areas of high clay accumulation rate have F a/F p > 1·0. The region as a whole is in balance with respect to 230Th accumulation.

Transuranics and other radionuclides in Bikini Lagoon: Concentration data retrieved from aged coral sections1

X‐radiography and autoradiography of thin vertical sections were used to estimate the growth rate of a specimen of Favites virens from Bikini Lagoon. Discrete bands of radioactivity were identifiable with specific nuclear test series. The coral growth rate of 8.0 mm year−1 determined by autoradiography is in good agreement with the rate of 8.1 ± 2.2 mm year−1 derived from the “seasonal” alternating light and dark bands on X‐radiographs. With these bands as growth rate indicators, the coral was sectioned into yearly increments and analyzed by low‐level, nondestructive gamma spectrometry, radiochemical techniques, and mass spectrometry to reconstruct the variations in the concentration of transuranics and other radionuclides in the marine environment at Bikini since 1954. From the concentration data retained in this indicator species, the exchange rate of radionuclides between the lagoon and the open ocean is computed to be longer than exchange rates based on physical circulation data. There is no constant ratio of plutonium isotopes in the coral growth sections, suggesting that the redistributions of the several plutonium isotopes in the environment may be governed by different biogeochemical processes. Increased levels of 210Po (210Pb) were found in test‐year growth sections, contradicting previous arguments that no 210Pb has resulted from weapons testing.

Non-destructive gamma spectrometry measurement of 239Pu/ 240Pu and Pu/ 240Pu ratios

A new non-destructive gamma spectrometry technique for the measurement of 239Pu/ 240Pu and Pu/ 240Pu ratios was developed by determining the intensity ratio of the 645·9 keV line of 239Pu to that of the 642·3 keV gamma line of 240Pu. The main advantages of this technique are: (i) the high penetration power of those gamma rays and (ii) the fact that their energies are very close together. Therefore, this method can be applied for all kinds of unirradiated samples with a Pu content of 1 g or more. The technique was checked in a rather wide range of Pu samples with different chemical and isotopic compositions and weights. The experiments demonstrated that it is possible, using this technique, to determine the 239Pu/ 240Pu isotopic ratio with an accuracy of the order of 1 per cent.

Solar Proton Medium Flux Constancy over a Million Years

THE data of cosmogenic radionuclide activity measurements in lunar material from the Apollo 11 and 12 missions have now been published1–8. Unfortunately, the data concern chiefly the measurements of medium radioactivity of whole rock (by non-destructive gamma-spectrometry) or large volume samples (by radiochemical methods). The data provide no way to determine the overall depth distribution gradient of radionuclides, produced by galactic and solar cosmic rays, and so no information can be extracted about the intensity of cosmic rays. But ref. 1 describes how the radioactivities of some radionuclides have been measured as a function of depth in lunar sample 10,017. By analysing these data we have drawn a conclusion about possible constancy of solar proton medium flux for the last million years.