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.
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 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 (t½ = 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.
Statistical analysis has been performed on the gross alpha- and beta-activity measurements of surface waters collected at
the Atomic Weapons Establishment at Aldermaston (UK) during the period January 2002–September 2005. The results have been
found to follow a lognormal distribution and this has important applications when considering gross activity exemption thresholds.
This implies that the gross activity is the multiplicative product of many small independent factors, such as meteorology,
flow conditions and site operations. The influence of meteorological parameters has been investigated using linear regression,
and some correlation has been identified between gross beta-activity and parameters indicative of fine weather. Variations
in gross activity have been considered on monthly, weekly and daily timescales and characterised using the geometric mean
and geometric standard deviation in accordance with the properties of the lognormal probability density function.
Authors:K. Inn, Zhichao Lin, Zhongyu Wu, C. McMahon, J. Filliben, P. Krey, M. Feiner, Chung-King Liu, R. Holloway, J. Harvey, I. Larsen, T. Beasley, C. Huh, S. Morton, D. McCurdy, P. Germain, J. Handl, M. Yamamoto, B. Warren, T. Bates, A. Holms, B. Harvey, D. Popplewell, M. Woods, S. Jerome, K. Odell, P. Young, and I. Croudace
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.