Radiochemical measurement of <Superscript>237</Superscript>Np in a solution of mixed radionuclides: Experiences in chemical separation and alpha-spectrometry

A radiochemical procedure is described for the measurement of 0.1 Bq ²³⁷Np in a solution containing similar activity concentrations of Th, U, Pu and Am as well as activity concentrations of ⁶⁰Co, ⁹⁰Sr and ¹³⁷Cs one hundred times higher. A tracer of ²³⁹Np (milked from ²⁴³Am) was used as an isotopic spike for chemical yield determination. The relationship between gamma-counting geometries for ampoule (liquid) and NdF₃ (solid) ²³⁹Np sources was established so that Np chemical yields could be measured by a comparative method. Efficiencies of alpha-spectrometers for ²³⁷Np in NdF₃ sources were measured by a bootstrap technique. Two sets of experiments were designed and used to test out the procedure.     

Pilot measurements of <Superscript>237</Superscript>Np in forest litter from Poland

Described are results and the procedure for a pilot study on ²³⁷Np content in forest litter samples from Poland in relation to their plutonium activity. Neptunium was determined by inductively coupled plasma mass spectrometry (ICP-MS) and Pu by alpha spectrometry. Two samples originated from a location with pure global fallout and two others from a place with about 65% of the plutonium from Chernobyl. Plutonium activities were determined twice: at Krakow and in Monaco. The two results were consistent and ^239 + 240Pu activities ranged from about 1 to about 7 Bq/kg dry weight (dw). The chemical recovery for Np was between 27 and 89%. Results for ²³⁷Np activity concentrations were between 0.099 ± 0.005 and 2.21 ± 0.076 mBq/kg dw. Observed activity ratios were lower than expected and could be explained by fractionation of Np against Pu in forest litter.     

Fast determination of indoor radon (<Superscript>222</Superscript>Rn) concentration using liquid scintillation counting

The indoor ²²²Rn radionuclide was directly absorbed in typical 20 ml glass scintillation vials by passing ?3 dm³ of ambient air through 16 ml of water-immiscible non-volataile scintillation cocktail Ultima-Gold F for 10 min. The activity of radon and its two α-emitting daughters: ²¹⁸Po and ²¹⁴Po, was determined with the BetaScout low-background liquid scintillation counter. The limit of ²²²Rn detection is 9 Bq/m³, and the quantification limit with 20% relative accuracy is 28 Bq/m³. The results of the indoor Rn measurement in different houses showed good consistency with results obtained from a Sarad EQF 3220 device.     

Extraction chromatography for the separation of <Superscript>239</Superscript>Np from <Superscript>243</Superscript>Am

Summary An extraction chromatography method was developed for the separation of 239Np from ²⁴³Am in nitric acid solution. A sorbent based on aliphatic quaternary amine Aliquat-336 and hydrophobized silica gel was prepared. ²³⁹Np reduced to the oxidation state(IV) with ferrous sulfamate in 2M or 6M HNO₃ sorbs on the prepared silica gel column. After washing with 0.1M ferrous sulfamate in 2.5M HNO₃, ²³⁹Np is eluted with 0.1M HNO₃ containing 0.02M HF. The separation of ²⁴³Am from ²³⁹Np is very effective. The purity of ²³⁹Np was found to be better than 99.5%. The proposed ²³⁹Np milking procedure is suitable for the preparation of ²³⁹Np tracer that can be used for the determination of ²³⁷Np radiochemical yield.     

Determination of <Superscript>237</Superscript>Np, <Superscript>93</Superscript>Zr and other long-lived radionuclides in medium and low level radioactive waste samples

The majority of long-lived radionuclides produced in the nuclear fuel cycle can be regarded as “difficult-to-measure” nuclides, hence chemical separation is needed before the nuclear measurement of them. A combined radiochemical procedure that enables the simultaneous determination of some “difficult-to-measure” nuclides in medium and low level radioactive wastes has been developed in our laboratory. Recently, this method has been extended for determination of ²³⁷Np and ⁹³Zr. ²³⁷Np and ⁹³Zr are pre-concentrated by co-precipitation on iron(II) hydroxide and zirconium oxide, separated by extraction chromatography using UTEVA, and measured by inductively coupled plasma mass spectrometry (ICP-MS). As even traces of polyatomic ions and isotopes at m/z 237 or 93 cause considerable interferences during ICP-MS detection, a purification step by extraction chromatography was needed. Analyzing real samples (evaporation concentrates of a nuclear power plant) 66–99% and 31–99% chemical yields were achieved for Np and Zr, respectively.     

<Superscript>237</Superscript>Np in peat and lichen in Finland

Activity concentrations of ²³⁷Np in peat and lichen samples in Finland were determined and contributions from nuclear weapons testing in 1950–1960s and the Chernobyl accident were estimated. ²³⁷Np was determined with ICP-MS using ²³⁵Np as a tracer. Activity concentrations of ²³⁷Np in peat samples varied between 1.98 ± 0.05 and 14.1 ± 0.3 mBq/m². The contribution from the Chernobyl accident to the total ²³⁷Np deposition in peat was 0.1–13%, the Chernobyl-derived fraction of total ²³⁷Np in peat being much lower than the previously determined corresponding Chernobyl-derived fractions of ^239+240Pu, ²⁴¹Pu, ²⁴¹Am and ²⁴⁴Cm.     

Polymer-coated magnetic nanoparticles for rapid bioassay of <Superscript>90</Superscript>Sr in human urine samples

A rapid bioassay for ⁹⁰Sr was developed involving preconcentration of ⁹⁰Sr/⁹⁰Y from human urine samples with a cation exchange polymer (poly–acrylamido–methyl–propanesulfonic acid) coated onto magnetic nanoparticles, followed by selective elution of ⁹⁰Sr (over ⁹⁰Y) with phosphate for determination by liquid scintillation analysis. The minimum detectable activity for this method (4.9 ± 0.5 Bq/L) is lower than the required sensitivity of 19 Bq/L for ⁹⁰Sr in human urine samples, as defined in the requirements for radiation emergency bioassay techniques for the public and first responders based on the dose threshold for possible medical attention recommended by the International Commission on Radiological Protection. The relative bias was 9.2%, the relative precision was 3.2%, and the linear dynamic range covered 12–600 Bq/L. This simple and rapid bioassay method is found to be in compliance with the HPS ANSI N13.30 performance criteria for radiobioassay.     

Determination of <Superscript>93</Superscript>Zr and <Superscript>237</Superscript>Np in nuclear power plant wastes

A combined radioanalytical method for determination of ⁹³Zr and ²³⁷Np (as well as other actinoids) in radioactive wastes has been developed. Analytes were co-precipitated on iron(II)-hydroxide, separated and purified on UTEVA columns, and detected by inductively coupled plasma mass spectrometry. According to Zr and Np, 65 and 75% yields were achieved, respectively.     

Low level detection of <Superscript>135</Superscript>Cs and <Superscript>137</Superscript>Cs in environmental samples by ICP-MS

The measurement of fission product cesium isotopes ¹³⁵Cs and ¹³⁷Cs at low femtogram (fg) 10⁻¹⁵ levels in ground water by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is reported. To eliminate the natural barium isobaric interference on the cesium isotopes, in-line chromatographic separation of the cesium from barium was performed followed by high sensitivity ICP-MS analysis. A high efficiency desolvating nebulizer system was employed to maximize ICP-MS sensitivity ~10 cps/fg. The three sigma detection limit for ¹³⁵Cs was 2 fg/mL (0.1 μBq/mL) and for ¹³⁷Cs 0.9 fg/mL (0.0027 Bq/mL) measured from the standard with analysis time of less than 30 min/sample. Cesium detection and 135/137 isotope ratio measurement at very low femtogram levels using this method in a spiked ground water matrix is also demonstrated.     

Determination of Np,Pu and Am in high level radioactive waste with extraction-liquid scintillation counting

A new method for the determination of transuranium elements, Np, Pu and Am with extraction-liquid scintillation counting has been studied systematically. Procedures for the separation of Pu and Am by HDEHP-TRPO extraction and for the separation of Np by TTA-TiOA extraction have been developed, by which the recovery of Np, Pu and Am is 97%, 99% and 99%, respectively, and the decontamination factors for the major fission products (⁹⁰Sr,¹³⁷Cs etc.) are 10⁴–10⁶. Pulse shape discrimination (PSD) technique has been introduced to liquid scintillation counting, by which the counting efficiency of -activity is >99% and the rejection of -counts is >99.95%. This new method, combining extraction and pulse shape discrimination with liquid scintillation technique, has been successfully applied to the assay of Np, Pu and Am in high level radioactive waste.     

Direct low-energy measurement of <Superscript>37</Superscript>Ar and <Superscript>127</Superscript>Xe in a radiotracer gas using low-background proportional counters

A radiotracer gas with a blend of ³⁷Ar and ¹²⁷Xe was created for a gas migration experiment and was characterized at Pacific Northwest National Laboratory using ultra-low-background proportional counters. This paper describes the direct low-energy measurement of ³⁷Ar and ¹²⁷Xe in a dual-isotope sample. Using this low-energy technique, the dual-isotope radiotracer gas was determined to have activity concentrations of 483 Bq/cc and 1435 Bq/cc for ³⁷Ar and ¹²⁷Xe, respectively, and a ratio of 1:3 on the reference date of 7/11/2016.     

Determination of <Superscript>90</Superscript>Sr in environment of district Swat,Pakistan

Assessment of ⁹⁰Sr is of great interest owing to the fact that this artificially produced radionuclide has high radiological importance because of its high fission yield, chemical similarity to calcium and its relatively long biological and physical half-life. To assess the likely hazard to population, low level ⁹⁰Sr in environmental samples is determined using pre-equilibrated tri-butyl phosphate (TBP) solvent and extraction-liquid scintillation procedure. ⁹⁰Y is selectively extracted from nitric acid solution into TBP solvent and stripped into aqueous phase as oxalate. The activity is finally measured by low level liquid scintillation counter using Cerenkov radiation. The specific activity is found only in three vegetation samples with average value of 2.86±1.7 Bq·kg⁻¹ of dry weight. In all other samples analyzed, the activity is below the detectable limit, i.e., 0.03 Bq. Results obtained are comparable with other areas of Pakistan. The chemical recovery of ⁹⁰Y varies from 75 to 90% for soil, vegetation and water. The present study provides a general background of the detectable radionuclide for the surveyed area that will be helpful in any radiological emergency.     

Measurement of <Superscript>90</Superscript>Sr in primary coolant of pressurized water reactor

The present procedure for analysing ⁹⁰Sr combines the use of a non radioactive carrier with high pressure ion chromatography separation, conductivity detection of the carrier and optimized external counting by liquid scintillation. This improvement with respect to traditional methods led to a more rapid and efficient purification stage. The present work proves that activities of ⁹⁰Sr as low as 3 Bq/L can be measured in highly contaminated pressurized water reactor primary coolant matrix without any observed radiochemical interference. The approach shows promise for the analysis of other emitters of low energy radiation, or isotopes subject to high background or matrix effects in a PWR primary coolant.     

Simultaneous measurements of cosmogenic radionuclides <Superscript>32</Superscript>P, <Superscript>33</Superscript>P and <Superscript>7</Superscript>Be in dissolved and particulate forms in the upper ocean

A technique to determine concentrations of ³²P, ³³P and ⁷Be in dissolved and particulate forms, in the upper ocean was developed. By using a large volume in situ filtration and concentration system (LV-FiCS), several tons of seawater at different depths were filtered concurrently through two kinds of filters. The dissolved radionuclides were concentrated onto adsorbents in the LV-FiCS. The radionuclides obtained were further purified by precipitation and ion-exchange chromatography, and quantified by gamma-spectrometry and ultra-low level liquid scintillation counter measurements. The technique was used with good results in a coastal area of Ibaraki, Japan.     

Measurement of the <Superscript>231</Superscript>Pa/<Superscript>235</Superscript>U ratio for the age determination of uranium materials

The paper describes the age (production date) determination of uranium reference materials using the ²³¹Pa/²³⁵U ratio. Direct addition of ²³⁷Np in secular equilibrium with its ²³³Pa daughter was chosen instead of the regular milking of ²³⁷Np to avoid possible loss of Pa. Sample preparation consists of a fast, one-step procedure. The developed method using ICP-MS for the measurement of ²³¹Pa is more precise than alpha spectrometry and is applicable for freshly produced low-enriched uranium materials. The measured ages are in good agreement with the reported production dates, thus the ²³¹Pa/²³⁵U chronometer can be applied for validation of ²³⁰Th/²³⁴U in nuclear forensics and safeguards.     

Determination of <Superscript>241</Superscript>Am in urine using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS)

Quantification of ²⁴¹Am in urine at low levels is important for assessment of individuals’ or populations’ accidental, environmental, or terrorism-related internal contamination, but no convenient, precise method has been established to rapidly determine these low levels. Here we report a new analytical method to measure ²⁴¹Am as developed and validated at the Centers for Disease Control and Prevention (CDC) by means of the selective retention of Am from urine directly on DGA resin, followed by SF-ICP-MS detection. The method provides rapid results with a limit of detection (LOD) of 0.22 pg/L (0.028 Bq/L), which is lower than 1/3 of the C/P CDG for ²⁴¹Am at 5 days post-exposure. The results obtained by this method closely agree with CDC values as measured by liquid scintillation counting, and with National Institute of Standards Technology (NIST) Certified Reference Materials (CRM) target values.     

Determination of <Superscript>3</Superscript>H and <Superscript>14</Superscript>C in the Dry Active Wastes (DAW) generated from the Light Water Reactors (LWR) by a wet oxidation method

³H and ¹⁴C Measurements of the dry active waste (DAW), such as the cotton, paper, and vinyl, generated from a nuclear power plant (NPP) were conducted with wet oxidation using open vessel equipment based on simulation results. The recovery efficiency with the simulated samples was around 93% with a relative standard deviation (RSD) of 1–3%. A liquid scintillation counter (LSC) was used for counting and adjusted to a quenching correction curve. The counting value was evaluated for the minimum detectable activity (MDA), which was found to be about 4 × 10⁻¹ Bq/g for ³H and 2 × 10⁻² for ¹⁴C when approximately 5 g of the samples were measured. The measured DAW samples for the cotton, paper, and vinyl generated from NPP achieved of RSD values of 25, 25, and 60%, respectively, for ³H and 0–50% for ¹⁴C.     

Separation of <Superscript>142</Superscript>La from fission products by SISAK technique

A rapid separation system based on SISAK technique was established to isolate ¹⁴²La successfully from fission products. SISAK technique is often applied in the separation of nuclides with the half-life of seconds or minutes. Here it was used to separate the parent nuclide of ¹⁴²La, which the half-life is in the magnitude of several seconds. According to the separation procedure designed in the paper, the activity of ¹⁴²La acquired is more than 10⁴ Bq and the decontamination factors for most γ-emitters are higher than 10³.     

Primary activity standardization of <Superscript>134</Superscript>Cs

Cesium-134 has been measured by means of a new coincidence counting system which is equipped with a liquid scintillation detector to count β particles and a NaI crystal to detect γ-rays which are emitted simultaneously. In order to validate this new technique, additional measurements were carried out with an established 4πβ–γ-coincidence counting system with a proportional counter in the β channel. The coincidence counting experiments were complemented with measurements in further liquid scintillation counters with two and three photomultiplier tubes. The counting efficiencies for these systems were determined using CIEMAT/NIST efficiency tracing and the triple-to-double coincidence ratio (TDCR) method, respectively.     

Reduction of <Superscript>68</Superscript>Ge activity containing liquid waste from <Superscript>68</Superscript>Ga PET chemistry in nuclear medicine and radiopharmacy by solidification

PET with ⁶⁸Ga from the TiO₂- or SnO₂- based ⁶⁸Ge/⁶⁸Ga generators is of increasing interest for PET imaging in nuclear medicine. In general, radionuclidic purity (⁶⁸Ge vs. ⁶⁸Ga activity) of the eluate of these generators varies between 0.01 and 0.001%. Liquid waste containing low amounts of ⁶⁸Ge activity is produced by eluting the ⁶⁸Ge/⁶⁸Ga generators and residues from PET chemistry. Since clearance level of ⁶⁸Ge activity in waste may not exceed 10 Bq/g, as stated by European Directive 96/29/EURATOM, our purpose was to reduce ⁶⁸Ge activity in solution from >10 kBq/g to <10 Bq/g; which implies the solution can be discarded as regular waste. Most efficient method to reduce the ⁶⁸Ge activity is by sorption of TiO₂ or Fe₂O₃ and subsequent centrifugation. The required 10 Bq per mL level of ⁶⁸Ge activity in waste was reached by Fe₂O₃ logarithmically, whereas with TiO₂ asymptotically. The procedure with Fe₂O₃ eliminates ≥90% of the ⁶⁸Ge activity per treatment. Eventually, to simplify the processing a recirculation system was used to investigate ⁶⁸Ge activity sorption on TiO₂, Fe₂O₃ or Zeolite. Zeolite was introduced for its high sorption at low pH, therefore ⁶⁸Ge activity containing waste could directly be used without further interventions. ⁶⁸Ge activity containing liquid waste at different HCl concentrations (0.05–1.0 M HCl), was recirculated at 1 mL/min. With Zeolite in the recirculation system, ⁶⁸Ge activity showed highest sorption.