Measurement of k0-Factors in Prompt Gamma-Ray Neutron Activation Analysis

The guided thermal neutron beam at 100 MW Dhruva research reactor facility of Bhabha Atomic Research Centre (BARC) was used to carry out prompt gamma-ray neutron activation analysis (PGNAA). The prompt k ₀-factors have been determined for the isotopes of the elements H, B, K, Co, Cu, Ca, Ti, Cr, Cd, Ba, Hg and Gd with respect to 1951 keV gamma-line of ³⁶Cl. The prompt k ₀-factors for H, Cl and Cu were also measured with respect to the 1381 keV gamma-line of ⁴⁹Ti. Different samples like NH₄Cl, Ti metal, cobalt chloride and other stoichiometric compounds and pure metals were used for this purpose. Prompt gamma-rays were accumulated using a 22% HPGe detector connected to a PC based 8k MCA in single mode counting. The energy calibration in the range of 100–8500 keV was carried out using gamma-rays from ¹⁵²Eu and ⁶⁰Co, and the prompt gamma-rays from ³⁶Cl whereas the absolute detection efficiency for this energy range was determined using ¹⁵²Eu and prompt gamma-rays from ³⁶Cl and ⁴⁹Ti.     

Relative efficiency calibration of Ge(Li) detector in low energy region

The relative gamma-ray intensities in the energy region between 122 and 411 keV in the decay of¹⁵²Eu were measured by using a Ge(Li) detector. Its efficiency calibration was carried out with the radioactive sources of²⁴¹Am,⁵⁷Co,²⁰³Hg,¹³⁷Cs,¹³³Ba,⁷⁵Se,¹⁶⁹Yb and¹⁹²Ir.     

High performance liquid chromatographic separation of <Superscript>228,229</Superscript>Th and <Superscript>232,233</Superscript>U and their estimation by α- and γ-ray spectrometry

The activities of ^228,229Th and ^232,233U from an irradiated ThO₂ sample were radiochemicaly separated by using high performance liquid chromatography. Plancheted sources of the separated samples were made and the amount of ^232,233U and ^228,229Th were estimated by using alpha and gamma-ray spectrometric techniques. These estimations are important for the Th–U fuel reprocessing cycle of advanced heavy water reactor and accelerator driven sub-critical system.     

Preparation and Pharmacokinetic Evaluation of Iodine-125 Labeled Alphamethyl-L-Tyrosine

A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of ⁶⁰Co and ¹⁵²Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120–1400 keV. Second, a PGNAA system consisting of a light-water moderated ²⁵²Cf (1.06 g) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the ²⁵²Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 g/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model.     

Rapid monitoring of gaseous fission products released from nuclear power stations

Rapid, in situ measurements were used for quantitative monitoring of gaseous fission products around the nuclear power stations in Taiwan. A portable high-resolution germanium detector with portable multichannel analyzer was used in the field monitoring work. The detecting unit was calibrated using activated Ar, Kr, and Xe isotopes dispersed in a large chamber to obtain absolute efficiency curve in terms of γ-counts per m³ versus gamma-ray energy. The calibrated detecting unit was brought to the nuclear power plants for in situ monitoring for both normal operation and nuclear accidental exercise. In a typical four-hour measurement, the detection limits for most Kr and Xe fission product isotopes were 0.0028%≈0.98% of the derived air concentration (DAC) imposed by the local authority. The dose rate caused by gaseous radioisotopes released from nuclear power stations and dispersed to the surroundings can be quantitatively monitored in a short period using this portable unit.     

Distribution and behavior of some radionuclides associated with the Trinity nuclear test

The activities of ¹³³Ba, ¹³⁷Cs, ¹⁵²Eu, ¹⁵⁴Eu, ¹⁵⁵Eu, ²³⁹Pu, and ²⁴¹Am were determined by gamma spectroscopy on the largest sample set (n = 49) of bulk trinitite to date. The range in activity for all isotopes is large. For example, the activity of ²⁴¹Am (normalized to the time of detonation) ranges between 1 and 42 Bq/g. Comparison of activities for isotopes derived from the device, ²⁴¹Am versus ¹³⁷Cs, ¹⁵⁵Eu, and ²³⁹Pu, indicate positive trends. Correlations were not observed between the activities of the soil-derived activation products ¹⁵²Eu and ¹⁵⁴Eu and the radioisotopes from the device. The calculated ratio of fission products (¹⁵⁵Eu/¹³⁷Cs) is 0.012 ± .006 (1σ, n = 3), which is lower than predicted for the thermal neutron-induced fission of ²³⁹Pu (~0.03). This discrepancy may be attributed to the spontaneous fission of the natural U tamper resulting in mixing between fission products from ²³⁹Pu and ²³⁵U. The spatial distribution of the trinitite samples relative to ground zero has been modeled based on the activity of ¹⁵²Eu. The calculated distances do not correlate with any of the activities for the radioisotopes investigated here, and suggest a relatively homogeneous distribution. However, trinitite samples with the highest activities for ¹³⁷Cs, ²³⁹Pu, and ²⁴¹Am yield the shortest calculated distances of 50–60 m away from ground zero.     

Simultaneous determination of Al,V, Mn and Cu from neutron-activated saline matrices by precipitation with poly-5-vinyl-8-hydroxyquinoline

Neutron Activation Analysis is a sensitive technique for the determination of more than seventy elements at the trace concentrations. The NAA analysis of biological and environmental matrices suffers from interferences caused by the presence of high concentrations of activated salts in these matrices. The high gamma-ray activities of these activated salts mask the low gamma-ray activities of short half-lived isotopes (e.g.,⁶⁶Cu,⁵⁶Mn,²⁸Al and⁵²V) necessitating the rapid separation of trace metals from high concentrations of salts. Poly-5-vinyl-8-hydroxyquinoline has been used to develop a new method to rapidly and quantitatively precipitate aluminum, copper, vanadium and manganese from neutron-activated biological and environmental matrices.     

Methodological advances for measuring low-level radium isotopes in seawater

A new approach for quantifying radium isotopes in seawater was developed in advance of the international GEOTRACES program, which has the goal of identifying processes and quantifying fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean. High-resolution water column samples were collected via a commercially available in situ pump modified to accept multiple filter media including a manganese-oxide (MnO₂) impregnated acrylic cartridge for extracting dissolved radionuclides from seawater. The modifications mitigated prefilter clogging and allowed for up to 1,800 L filtrations in 4 h of pumping. Different MnO₂ cartridge preparation methods were investigated to achieve maximum radium (Ra) extraction efficiency under high sample flow rates. Full-ocean depth profiles were measured for short-lived radium isotopes (²²³Ra and ²²⁴Ra) in shipboard laboratories using a delayed coincidence alpha scintillation counter (RaDeCC). Samples were reanalyzed 4 weeks and 2 months after collection for ²²⁸Th and ²²⁷Ac to correct for supported ²²⁴Ra and ²²³Ra, respectively. Finally, the cartridges were measured on a gamma-ray spectrometer for the long-lived radium isotopes (²²⁶Ra and ²²⁸Ra). Parallel 20 L samples at each pumping depth were collected from Niskin bottles and analyzed via alpha scintillation for ²²⁶Ra to determine radium extraction efficiencies for the cartridges. These modified methods will allow for increased sample throughput, and hence higher spatial resolution for radium isotopes in the ocean. Such resolution will greatly improve the determination of oceanic vertical and horizontal mixing rates over small and large scales, which in turn can be used to calculate fluxes of TEIs into the ocean.     

Excitation functions of neutrons induced reactions on terbium from threshold to 20 MeV

Cross-sections for (n,2n), (n,p), and (n,α) reactions have been measured on terbium isotopes at the neutron energies from 13.5 to 14.8 MeV using the activation technique in combination with high-resolution gamma-ray spectroscopy. Data are reported for the following reactions: ¹⁵⁹Tb(n,2n)^158m+gTb, ¹⁵⁹Tb(n,p)¹⁵⁹Gd, and ¹⁵⁹Tb(n,α)¹⁵⁶Eu. The cross sections were also estimated with the TALYS-1.4 nuclear model code, at neutron energies varying from the reaction threshold to 20 MeV. The results were discussed and compared with experimental data found in the literature, and with the comprehensive evaluation data in ENDF/B-VII.1 and JENDL-4.0 libraries.     

A two-point in situ method for simultaneous analysis of radioactivity in seawater and sediment

A new in situ radioactivity analysis method was developed to determine the fractional contributions of gamma-ray emitters in seawater and sediment from total measured counts. A semi-empirical formula to determine the fractional count contributions was derived using the variation characteristics of the gamma-ray attenuation rate and geometrical efficiency with the measurement points. The proposed method was employed to make in situ gamma-ray measurements using a CeBr₃ detector for radioactivity analysis of seawater and sediment at a coastal area with a relatively high tidal range. The full energy peak efficiency of the detector at measurement site was obtained using the GEANT4 simulation code. The radioactivity concentration of ⁴⁰K in seawater and sediment was determined using the proposed method and laboratory analysis with sampling. The MDA of the in situ measurement for ¹³⁷Cs and ¹³¹I was also estimated assuming they were deposited on the sediment surface-layer. The validation of this method was demonstrated by comparing with the sampling analysis results.

     

Prompt k 0-factors and relative gamma-emission intensities for the strong non-1/v absorbers 113Cd, 149Sm, 151Eu and 155,157Gd

Prompt k ₀-factors relative to chlorine and relative g-emission intensities were determined for the strong non-1/v absorbers ¹¹³Cd, ¹⁴⁹Sm, ¹⁵¹Eu,¹⁵⁵Gd and ¹⁵⁷Gd. Measurements were performed using the SNU-KAERI prompt gamma activation analysis (PGAA) facility at the Korea Atomic Energy Research Institute (KAERI). For proper experimental determination of the prompt k ₀-factors, the effective g-factor and cadmium ratio were taken into account, in consideration of the effects from the non-1/v capture cross section and neutron spectrum in the thermal and epithermal energy region. By using the actual spectrum of the neutron beam in this study, the effective g-factor was obtained by calculation, and the influence of epithermal neutrons on the capture rate was corrected by measuring the cadmium ratio for each non-1/v target isotope. The measured prompt k ₀-factors were used to check the consistency between the existing dataset of the absolute g-emission intensity and the 2200 m/s capture cross section for these isotopes.     

Titrating apparatus for the detection of soft β-emitting isotopes

The measuring devices reported in the literature allow only radiometric titrations indicated by hard β or γ-radiating isotopes. The authors developed an apparatus also suitable for the detection of soft β-emitting isotopes. In the course of the analysis, the activities are measured in a scintillation system in which the great surface of a mass of anthracene crystals provides excellent contact with the active solution. In studies on the linearity of the scintillation system the sources of error and their elimination were also examined. The sensitivity of the scintillation system was determined with³H,¹⁴C,³⁵S,⁴⁵Ca,³⁶Cl and³²P isotopes, frequently applied in organic chemical practice. The method of adjusting the specific activities of reagent solutions prepared from the various isotopes is discussed. The apparatus makes it possible to extend the applications of radiometric titration in the analysis of organic compounds.     

Distribution of plutonium isotopes in sediments of Melanesian Basin,Central Pacific

The anthropogenic plutonium isotopes are important geochemical tracers for environmental studies. The distributions and sources of the Pu isotopes in water column or sediments of the North Pacific have been intensively studied. However, knowledge on the distribution of Pu isotopes in sediments of the Central Pacific, when available, is limited. To study the composition of Pu isotopes in the ocean, thus to identify the sources of radioactive pollution, sediment core samples were collected in the Central Pacific by R/V Hakuho Maru in the KH-04-5 cruise. The activity concentrations of ^239+240Pu and the ²⁴⁰Pu/²³⁹Pu atom ratio were determined using a sector-field inductively coupled mass spectrometry (SF-ICP-MS) combined with a high efficiency sample introduction system (APEX-Q). Possible sources and sedimentation behavior of Pu isotopes are discussed.     

Further developments of a robust absolute calibration method utilizing beta/gamma coincidence techniques

Performing accurate and verifiable measurements is often the most challenging goal for any radiation detector and is especially challenging for the radio-xenon detectors deployed by the International Monitoring System (IMS) of the Preparatory Commission of the Comprehensive Test Ban Treaty Organization (CTBTO). Often the accuracy of the measurement is directly tied to how well the detector is calibrated, in both energy and efficiency. Standard methods often rely on using certified sealed sources to determine the absolute efficiency. Similarly, efforts to calibrate the absolute efficiency of radioactive gas cell detectors utilize a number of methodologies which allow adequate calibration but are time consuming and prone to a host of difficulties to determine uncertainties (McIntyre et al, J Radioanal Nucl Chem 282(3):755–759, 2009; Anderson et al, Stat Probab Lett 77(88):769–773, 2007). Utilizing methods developed in the 1960s for absolute measurements of activity with beta–gamma detector systems it has become clear that it is possible to achieve higher precision results that are consistent across a range of isotopes and activities (National Council on Radiation Protection and Measurement, A handbook of radioactivity measurements procedure NCPR report, 1985). Even more compelling is the ease with which this process can be used on routine samples to determine the total activity present in the detector. Additionally, recent advances in the generation of isotopically pure radio-xenon samples of ^131mXe, ¹³³Xe, and ¹³⁵Xe allow these measurement techniques to achieve much better results than have previously been possible when using mixed isotopic radio-xenon sources (Haas et al, J Radioanal Nucl Chem 282(3):677–680, 2009). This paper will discuss the beta/gamma absolute detection efficiency techniques of direct measurement of the efficiencies and the extrapolation method and compare the results using modeled and measured pure sources of ¹³³Xe and ¹³⁵Xe.     

Co-precipitation of plutonium(IV) and americium(III) from nitric acid–oxalic acid solutions with bismuth oxalate

This study presents analytical methods for the determination of gross beta, ⁹⁰Sr, ²²⁶Ra and Pu isotopes using samples in the IAEA-TEL-2015-04 ALMERA Proficiency Test exercise. Samples for gross beta were prepared by evaporation and then analyzed using a gas proportional counter. ⁹⁰Sr in the liquid sample was concentrated as SrCO₃ precipitates and purified by Sr resin. Pu isotopes and ⁹⁰Sr in the soil sample were extracted from the sample by mineral acid leaching and separated using TEVA and Sr resin, respectively. Pu isotopes were determined by alpha spectrometry and ⁹⁰Sr were determined with a liquid scintillation counter. Radium in the soil sample was extracted by LiBO₂ fusion, and the radon-emanation method using LSC was applied for the determination of ²²⁶Ra.     

(α, pxn) reactions on natural samarium

A stack of natural samarium was bombarded with 87 MeV -particles. Cumulative cross sections for the production of¹⁴⁵Eu,¹⁴⁶Eu,¹⁴⁷Eu,¹⁴⁸Eu,¹⁵⁰Eu,¹⁵²Eu and¹⁵⁴Eu have been studied using gamma-ray spectroscopy. The data are compared with the theoretical results provided by equilibrium and pre-equilibrium reaction models, for this purpose we used the code ALICE of Blann.     

Fission product yields in the fast-neutron fission of238U

The fission yields of 38 fission products in the fast-neutron induced fission of²³⁸U have been determined using a rapid, multiscaling gamma-ray spectroscopic method. To obtain absolute yields for fission products having half-lives ranging from 32 s to 40 d, a total of 56 multi-scaling gamma-ray spectra were collected using various irradiation and cooling periods. Gamma-rays and photopeak areas of interest were assigned to the fission products by their energies and half-lives. Fission product activities were evaluated from spectral data using growth and decay calculations and fission yields were determined by normalizing the¹⁴⁰Ba yield to the average value from reported data. The depleted uranium target, covered with a boron-cadmium thermal neutron shield, was used to keep interference from the fission of²³⁵U minimal. Results for the cumulative fission yields, including 17 mostly short-lived fission products measured for the first time, are compared with previous measurements and with the recommended yields in recent evaluations. The agreement, and some discrepancies, in the comparisons are discussed. No explicit even-odd pairing effects are observed in the fission yield data for fast-neutron induced fission of²³⁸U.     

Sample geometry and efficiency determination of bremsstrahlung radiation of 90Sr on gamma detection systems

Summary The bremsstrahlung radiation energy spectra were produced by hard beta-emitters the ⁹⁰Sr-⁹⁰Y contaminated tea sample sources placed in a copper cylinder (cylinder counting geometry) and encapsulated in two Cu discs (sandwich counting geometry). These energy spectra were directly measured by using two separate gamma-ray spectrometers with a coaxial 110% efficient HpGe detector and a 110 cm³ HpGe well-type detector. The minimum detectable activity and the absolute efficiency of beta-activity for the sandwich and cylinder geometries were found to be 23 Bq ^. kg^-1 and (1.67±0.04)% and 55 Bq ^. kg^-1 and (2.61±0.05)%, respectively. These results indicate that the bremsstrahlung radiation counting method can be applied to some environmental studies when high efficient HpGe detectors, especially well-type HpGe are used.     

Evaluation of radioactivity induced in the accelerator building and its application to decontamination work

For decommissioning of the cyclotron and electron synchrotron facilities, the residual radioactivity in surface and core samples of concrete, collected from various parts of buildings, was determined by gamma-ray spectrometry. It was found that the concrete samples were activated mainly by neutrons and that the major radioisotopes were ¹⁵²Eu, ⁶⁰Co, ¹³⁴Cs, ²²Na and ⁵⁴Mn. The maximum activity induced by thermal neutron capture was observed at the depth of 10 cm in the concrete wall near the deflector of the cyclotron. Tritium was also produced by the neutron reaction, because its concentration was proportional to the activities of ¹⁵²Eu and ⁶⁰Co. The surface dose rates inside the accelerator room were also monitored to define the decontamination area. The surface dose rate was proportional to the residual radioactivity, such as ⁶⁰Co. A careful evaluation was very useful in order to minimize the radioactive waste during decontamination.     

Preparation and characterisation of synthetic mixtures of lithium isotopes

Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterised, isotopically enriched, Li₂CO₃ compounds. The starting materials, 99.9981% enriched ⁶Li, and 99.9937% enriched ⁷Li, were purified by ion exchange, and the purified materials converted from LiOH to Li₂CO₃ by reaction with CO₂. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li₂CO₃ carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g^–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(⁶Li)/n(⁷Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2 · 10^–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned.