The use of pre-irradiation group separations with neutron activation analysis for the determination of the rare earths in silicate rocks

The radiochemical neutron activation technique used consists of five stages; viz. sample digestion, cation exchange chromatography, irradiation and counting. Silicate samples are decomposed using a conventional hydrofluoric/perchloric acid digestion followed by loading the solutions, as chlorides, onto cation exchange resin columns. The columns are eluted with 2M HCl to remove unwanted elements and the rare earth elements are subsequently desorbed with 6M HCI. A tracer,¹⁴⁴Ce, is used to monitor the chemical yields and studies show that no fractionation or loss of any REE occurs. The REE abundances of five reference samples (NIM-G, SY-2, MRG-1, JB-1 and BOB-1) show that the described procedure is capable of providing good accuracy and precision. The method has some advantages over conventional INAA and RNAA and these are described.     

Pre-concentration of short-lived radionuclides using manganese dioxide precipitation from surface waters

Rapid determination of ²²²Rn and ²²⁰Rn progeny (²¹⁴Pb, ²¹²Pb, ²¹⁴Bi, ²¹²Bi) is achievable using manganese dioxide (MnO₂) precipitation with analysis by γ-spectrometry. This is of interest to environmental monitoring programmes that utilise gross activity methods to screen for anthropogenic radionuclides. The contribution from these naturally occurring radionuclides (NOR) varies, and is difficult to experimentally measure due to short half-lives (t _½ = 19.9 m–10.64 h) and low environmental activity (<0.1 Bq L^?1). The extraction efficiency of the technique is above 90%, and above 80% for other nuclides (²³²Th, ²³⁸U, ²³⁵U, ²²⁸Ac, ²²⁶Ra, ²²⁴Ra, ²¹⁰Pb, ⁵⁴Mn). Short-lived NOR have been measured at two surface water locations, and indicates elevated ²¹⁴Bi activity of 4.0 ± 1.1 Bq L^?1.     

A reliable and accurate procedure for preparing low-activity efficiency calibration standards for germanium gamma-ray spectrometers

An empirical procedure is described which is readily capable of producing reliable and accurate efficiency calibration sources of low activity for high-resolution -ray spectrometers. Known activities of a multiisotopic solution are adsorbed onto a mixture of cation and anion-exchange resins and chromatographic-grade cellulose. The dried powder that results can be mixed with any desired solid natural matrix material to produce a homogeneous, extended geometry, efficiency calibration source. Results are presented which enable the method to be critically evaluated.     

Rapid measurement of 241Pu activity at environmental levels using low-level liquid scintillation analysis

A straightforward and rapid method has been developed for the determination of ²⁴¹Pu activities. Pu is chemically separated from the sample, purified and electrodeposited to produce a source for alpha spectrometric determination of ²³⁸Pu and ^239,240Pu. Pu is stripped from the disc with concentrated nitric acid and extracted into tri-octylphosphine oxide (TOPO)/toluene. The organic extract is then mixed directly with commercial liquid scintillation cocktail without any further purification procedures and the sample counted on a Wallac 1220 Quantulus liquid scintillation counter (LSC). ²⁴¹Pu activity is estimated via the ²⁴²Pu yield monitor acquired by alpha spectrometry measurement. Experimental results for the performance testing of a low-level liquid scintillation spectrometer and the data for the evaluation of the method using standard reference materials are presented.     

The NIST natural-matrix radionuclide standard reference material program for ocean studies

In 1977, the Low-level Working Group of the International Committee on Radionuclide Metrology met in Boston, MA (USA) to define the characteristics of a new set of environmental radioactivity reference materials. These reference materials were to provide the radiochemist with the same analytical challenges faced when assaying environmental samples. It was decided that radionuclide bearing natural materials should be collected from sites where there had been sufficient time for natural processes to redistribute the various chemically different species of the radionuclides. Over the succeeding years, the National Institute of Standards and Technology (NIST), in cooperation with other highly experienced laboratories, certified and issued a number of these as low-level radioactivity Standard Reference Materials (SRMs) for fission and activation product and actinide concentrations. The experience of certifying these SRMs has given NIST the opportunity to compare radioanalytical methods and learn of their limitations. NIST convened an international workshop in 1994 to define the natural-matrix radionuclide SRM needs for ocean studies. The highest priorities proposed at the workshop were for sediment, shellfish, seaweed, fish flesh and water matrix SRMs certified for mBq per sample concentrations of ⁹⁰ Sr, ¹³⁷ Cs and ²³⁹ Pu + ²⁴⁰ Pu. The most recent low-level environmental radionuclide SRM issued by NIST, Ocean Sediment (SRM 4357) has certified and uncertified values for the following 22 radionuclides: ⁴⁰ K, ⁹⁰ Sr, ¹²⁹ I, ¹³⁷ Cs, ¹⁵⁵ Eu, ²¹⁰ Pb, ²¹⁰ Po, ²¹² Pb, ²¹⁴ Bi, ²²⁶ Ra, ²²⁸ Ra, ²²⁸ Th, ²³⁰ Th, ²³² Th, ²³⁴ U, ²³⁵ U, ²³⁷ Np, ²³⁸ U, ²³⁸ Pu, ²³⁹ Pu + ²⁴⁰ Pu, and ²⁴¹ Am. The uncertainties for a number of the certified radionuclides are non-symmetrical and relatively large because of the non-normal distribution of reported values. NIST is continuing its efforts to provide the ocean studies community with additional natural matrix radionuclide SRMs. The freeze-dried shellfish flesh matrix has been prepared and recently sent to participating laboratories for analysis and we anticipate receiving radioanalytical results in 2000. The research and development work at NIST produce well characterized SRMs that provide the world's environment-studies community with an important foundation component for radionuclide metrology.     

A new bomb-combustion system for tritium extraction

Quantitative extraction of tritium from a sample matrix is critical to efficient measurement of the low-energy pure beta emitter. Oxidative pyrolysis using a tube furnace (Pyrolyser) has been adopted as an industry standard approach for the liberation of tritium (Warwick et al. in Anal Chim Acta 676:93–102, 2010) however pyrolysis of organic-rich materials can be problematic. Practically, the mass of organic rich sample combusted is typically limited to <1 g to minimise the possibility of incomplete combustion. This can have an impact on both the limit of detection that can be achieved and how representative the subsample is of the bulk material, particularly in the case of heterogeneous soft waste. Raddec International Ltd (Southampton, UK), in conjunction with GAU-Radioanalytical, has developed a new high-capacity oxygen combustion bomb (the Hyperbaric Oxidiser; HBO₂) to address this challenge. The system is capable of quantitatively combusting samples of 20–30 g under an excess of oxygen, facilitating rapid extraction of total tritium from a wide range sample types.     

Isolation and quantification of Fe and Ni in reactor effluents using extraction chromatography and liquid scintillation analysis

A novel extraction chromatographic resin based on diisobutyl ketone has been developed for the isolation of ⁵⁵Fe. This material has been used in conjunction with a dimethylglyoxime-based resin for the sequential separation of ⁵⁵Fe and ⁶³Ni and isolation of these radionuclides from associated contaminants. The preparation and characterisation of these resins is described along with an assessment of their performance for the isolation of ⁵⁵Fe and ⁶³Ni from a mixture of nuclear activation products. In addition, a refined approach for the measurement of these nuclides by liquid scintillation counting is discussed. The findings of these studies have been combined to develop a robust procedure for the analysis of ⁵⁵Fe and ⁶³Ni in reactor effluents which is now the preferred method for a number of UK analytical laboratories.