A calibration procedure for beta-gamma coincidence detector-systems using four radioxenon spikes.

The determination of activity concentrations of the CTBT-relevant radioxenon relies on a robust calibration method. A procedure is outlined using four radioxenon spikes for beta-gamma detector-systems with 4π geometry. Detection efficiencies of beta-gamma coincidences in the net count calculation method, including the interference matrix between radioxenon and radon, are determined by three measurement channels: beta singles, gamma singles and beta-gamma coincidences, without reference activity values.

Radium in New Zealand agricultural soils: Crop uptake and estimation of current and future ionising radiation dose.

Crop uptake of 226Ra over a range of key New Zealand agricultural and horticultural growing areas was analysed to establish the dietary implications of an increase in soil 226Ra activity concentrations. Thirty crop samples, covering both feed and food commodities, were quantified for 226Ra activity concentrations, and concentration ratio (CRs) from the soil activity were calculated. The calculated CRs correlated with international default values for estimating crop uptake. Variation in CRs established that there was no increase in the crop activity concentration, relative to soil 226Ra from pasture foliage at a fertiliser impacted site, with a gradient of soil 226Ra activity concentrations. Based on the calculated CRs, the upper bound of the theoretical range of dietary exposures to 226Ra was 78.1 µSv/yr for teenage boys. Future forecasting of the increased dietary dose of 226Ra that might occur at the current soil loading rate, based on current fertiliser activity concentrations, confirmed that long-term loading of soil with 226Ra is unlikely to present a dietary risk. The forecast model calculated that the increase in dietary ionising radiation burden is unlikely to reach thresholds requiring regulatory intervention for two millennia.

Radium in New Zealand agricultural soils: Phosphate fertiliser inputs, soil activity concentrations and fractionation profiles.

Phosphate ores can contain high levels of 238U and its decay products. Of these decay products 226Ra is an important environmental contaminant, while 228Ra from 232 Th day may also be present, albeit at lower activity concentrations. Acid processing of phosphate ore to triple superphosphate elutes a large proportion of the 226Ra from the final product. However, fertiliser production in New Zealand generally avoids acid processing and instead uses single superphosphate and reactive phosphate rock to maintain crop yields, meaning that 226Ra is retained in the final product. As a first step towards characterising the human health impacts from fertiliser-borne radium, research was undertaken to identify loading and long-term accumulation of 226Ra and 228Ra in New Zealand agricultural soils, as well as the fractionation of 226Ra into different soil phases. Activity concentrations for 226Ra of up to 1.6 kBq/kg were determined in phosphate-containing fertilisers used in New Zealand. In contrast, 228Ra did not exceed 75 Bq/kg. Analysis of 40 New Zealand soils, covering a range of agricultural uses, showed activities of between (27-88) Bq/kg 226Ra and (21-102) Bq/kg 228Ra. Unexpectedly, there was also a strong correlation between the two radium isotopes. In 13 of the agricultural soils, all with very high available phosphate levels, the fractionation profile of 226Ra was determined. These data indicated that 226Ra largely remains immobile in the residual phase of the soil. Calcium and available phosphate were significantly correlated with binding of 226Ra into labile and non-labile fractions. Barium is also hypothesised to play a significant role in co-precipitating 226Ra into non-labile soil fractions. While a high percentages of 226Ra immobile in the non-labile fraction would allow for marked accumulation over time it may limit the availability for uptake into crops and thus the ionising radiation dose for consumers.

Deterministic and Semiprobabilistic Modeling of the Committed Dose from Radionuclides and the Chemical Burden from Uranium in the New Zealand Diet.

To support New Zealand's food safety monitoring, estimates of the current population exposure to ionizing radiation through diet are needed. To calculate the committed dose from radionuclide activities in the food chain, dietary modeling was undertaken for different age and gender groupings of the New Zealand population. Based on a published survey of radionuclide activity concentrations in the New Zealand diet, deterministic and semiprobabilistic models were constructed to derive estimates of the effective dose via the diet. Deterministic estimated annual doses across the different age and gender groupings ranged from a minimum of 48 to 66 µSv/year for teenage girls to a maximum of 126 to 152 µSv/year for adult males. Polonium-210 was the main contributor to ingested dose, with anthropogenic radionuclides contributing very little. For adults, seafood represented the most important source of exposure, with the contribution from this source decreasing for younger age groups. Results of the semiprobabilistic model identified a range of possible ingested doses, with 2.5 to 97.5th percentile ranges of 0.01 to 1.44 µSv/day for adults and 0.02 to 1.84 µSv/day for children. Estimated doses to the New Zealand population show similarities to those of other countries and fall within the expected global range. The current level of exposure to ionizing radiation in the diet does not represent an elevated health risk.

Activity concentrations of (137)Caesium and (210)Polonium in seafood from fishing regions of New Zealand and the dose assessment for seafood consumers.

A study was undertaken to determine activity concentrations for (134)Caesium, (137)Caesium and (210)Polonium in New Zealand seafood, and establish if activity concentrations varied with respect to species/ecological niche and coastal region. Thirty seafood samples were obtained from six fishing regions of New Zealand along with a further six samples of two commercially important species (hoki and arrow squid) with well-defined fisheries. (134)Caesium was not detected in any sample. (137)Caesium was detected in 47% of samples, predominantly in pelagic fish species, with most activities at a trace level. Detections of (137)Caesium were evenly distributed across all regions. Activity concentrations were consistent with those expected from the oceanic inventory representing residual fallout from global nuclear testing. (210)Polonium was detected above the minimum detectable concentration in 33 (92%) of the analysed samples. Molluscs displayed significantly elevated activity concentrations relative to all other species groups. No significant regional variation in activity concentrations were determined. Two dose assessment models for high seafood consumers were undertaken. Dose contribution from (137)Caesium was minimal and far below the dose exemption limit of 1 mSv/year. Exposure to (210)Polonium was significant in high seafood consumers at 0.44-0.77 mSv/year (5th-95th percentile). (137)Caesium is concluded to be a valuable sentinel radionuclide for monitoring anthropogenic releases, such as global fallout and reactor releases, in the marine environment. (210)Polonium is of importance as a natural radionuclide sentinel due to its high contribution to dietary committed dose in seafood consumers.

Natural and anthropogenic radionuclide activity concentrations in the New Zealand diet.

To support New Zealand's food safety monitoring regime, a survey was undertaken to establish radionuclide activity concentrations across the New Zealand diet. This survey was undertaken to better understand the radioactivity content of the modern diet and also to assess the suitability of the current use of milk as a sentinel for dietary radionuclide trends. Thirteen radionuclides were analysed in 40 common food commodities, including animal products, fruits, vegetables, cereal grains and seafood. Activity was detected for (137)Caesium, (90)Strontium and (131)Iodine. No other anthropogenic radionuclides were detected. Activity concentrations of the three natural radionuclides of Uranium and the daughter radionuclide (210)Polonium were detected in the majority of food sampled, with a large variation in magnitude. The maximum activity concentrations were detected in shellfish for all these radionuclides. Based on the established activity concentrations and ranges, the New Zealand diet contains activity concentrations of anthropogenic radionuclides far below the Codex Alimentarius guideline levels. Activity concentrations obtained for milk support its continued use as a sentinel for monitoring fallout radionuclides in terrestrial agriculture. The significant levels of natural and anthropogenic radionuclide activity concentrations detected in finfish and molluscs support undertaking further research to identify a suitable sentinel for New Zealand seafood monitoring.

New determination of the electron's mass.

A new independent value for the electron's mass in units of the atomic mass unit is presented, m(e) = 0.000 548 579 909 2(4) u. The value is obtained from our recent measurement of the g factor of the electron in (12)C(5+) in combination with the most recent quantum electrodynamical (QED) predictions. In the QED corrections, terms of order alpha(2) were included by a perturbation expansion in Zalpha. Our total precision is three times better than that of the accepted value for the electron's mass.