Stable 127I Research Articles

Mass-spectrometric determination of iodine-129 using O2-CO2 mixed-gas reaction in inductively coupled plasma tandem quadrupole mass spectrometry.

This paper presents a mass-spectrometric method for determining the radionuclide iodine-129 (129I) from the significant amount of interference in inductively coupled plasma tandem quadrupole mass spectrometry (ICP-MS/MS) using a dynamic reaction cell passing a mixture gas of O2 and CO2. Thus far, mass spectrometry analysis of trace amounts of 129I has been hampered by the presence of xenon-129 (129Xe) and the formation of polyatomic ions from excess amounts of stable isotope 127I. In this study, flowing a mixture gas of O2 and CO2 into the dynamic reaction cell (Q2) successfully removed both 129Xe interference and polyatomic interference (127IH2) in the analysis of 129I in ICP-MS/MS. The resulting ratio of (background noise of m/z 129)/127I was 4.6 × 10-10 ± 3.3 × 10-10, which enables the analysis of 10mBq/L of 129I in the presence of 100mg/L of stable 127I without chemical separation. The detection limit of this method was 0.73mBq/L (= 0.11ng/L) with an APEX-Q sample inlet desolvation device. For demonstration purposes, spike and recovery analysis of rainwater was performed, and good agreement between the spiked and recovered amounts was achieved.

Recycling and persistence of iodine 127 and 129 in forested environments: A modelling approach

Differences in the source and behaviour of 129I compared to 127I isotopes have been described for a variety of surface environments, but little is known about the cycling rates of each isotope in terrestrial ecosystems. We developed a compartment model of the iodine cycle in a forest ecosystem, with a labile and non-labile pool to simplify the complex fate of iodine in the forest floor and soil. Simulations were performed using atmospheric 127I and 129I inputs for sites differing in climate, vegetation, and soil. In general, considering dry deposition in addition to wet deposition improved model simulations. Model results support the view that soil is the sink for atmospheric iodine deposited in forest ecosystems, while tree vegetation has little influence on long-term iodine budgets. Modelling also showed that iodine cycling reaches equilibrium after a period of about 5000 years, mainly due to a gradual incorporation of iodine into the bulk stabilised soil organic matter. At steady state, this pool of non-labile iodine in soil can retain about 20% of total deposition with a mean residence time of 900 years, while the labile iodine pool is renewed after 90 years. The proportions of modern anthropogenic 129I in each modelled pool reflect those of stable 127I at least several decades after input to the forest; this result explains why isotopic disequilibrium is common in field data analysis. Volatilisation plays a central role in regulating iodine storage in soil and, therefore, its residence time, while drainage is a minor export pathway, except at some calcareous sites. Dynamic modelling has been particularly helpful for gaining insight into the long-term response of iodine partitioning to continuous, single or even varying deposition. Our modelling study suggested that better estimates of dry deposition of atmospheric iodine, weathering of parent rock, and volatilisation of the deposited iodine from soil and vegetation will be required for reliable predictions of iodine cycling in specific forests, because these processes remain insufficiently explored.

Analysis of 129I and 127I in soils of the Chernobyl Exclusion Zone, 29 years after the deposition of 129I.

The Chernobyl Exclusion Zone (CEZ) represents a unique natural laboratory that received significant 129I contamination across a range of soils and land-use types in a short time period in 1986. Data are presented on 129I and 127I in soil samples collected from highly contaminated areas in the CEZ in 2015. The geometric mean (GM) total concentration of stable iodine (127I) was 6.7 × 10-7 g g-1 and the (GM) total concentration of 129I was 2.39 × 10-13 g g-1, equivalent to 1.56 mBq kg-1. GM total 127I concentration is below the European average soil concentration of 3.94 × 10-6 g g-1, while 129I is significantly higher than the pre-Chernobyl activity concentration for 129I of 0.094 mBq kg-1. Significant differences were found in the extractability of native, stable 127I and 129I almost 30 years after the introduction of 129I to the soils. Both 127I and 129I were predominantly associated with alkaline-extractable soil organic matter, established using a three-step sequential extraction procedure. Whereas 127I was significantly correlated with gross soil organic matter (measured by loss on ignition), however, 129I was not. The ratio of 129I/127I was significantly lower in extracts of soil organic matter than in more labile (soluble and adsorbed) fractions, indicating incomplete equilibration of 129I with native 127I in soil humic substances after 29 years residence time in the CEZ soils. The initial physico-chemical form of 129I in the CEZ soils is unknown, but the widespread presence of uranium oxide fuel particles is unlikely to have influenced the environmental behaviour of 129I. Our findings have implications for long-term radiation dose from 129I in contaminated soils and the use of native, stable 127I as a proxy for the long-term fate of 129I.

Anthropogenic 129I in the sediment cores in the East China sea: Sources and transport pathways

With the increased numbers of nuclear power plants constructed along the east coast of China, it is important to know radioactive sources and transport pathways between land and sea, in order to better understand the impact of these nuclear facilities to the marine environment. Two sediment cores collected from the East China Sea dated to 1959–2010 were analyzed for long-lived radioactive 129I and stable 127I. It was observed that 129I levels (129I/127I ratio of (15.0–75.0) × 10−12) were significantly increased compared to the pre-nuclear value (129I/127I = 1.5 × 10−12). Some 129I peaks were observed in layers of 1959, 1966, 1971 and 1976 (1977), corresponding to the atmospheric nuclear weapon tests at Pacific Proving Grounds and Lop Nor. The high values of 129I after the late 1970s are attributed to the releases from the European reprocessing plants. In addition to ocean current transport, the atmospheric dispersion through the interaction of the Westerlies with East Asia monsoon is the important pathway of large-scale transport of pollutants from high latitude West Europe to middle latitude East Asia. Riverine input is the main transport pathway of radioactive pollutants released from Lop Nor to the East China Sea through the atmospheric dispersion, deposition and runoff processes.

Role of natural organic matter on iodine and 239,240Pu distribution and mobility in environmental samples from the northwestern Fukushima Prefecture, Japan

In order to assess how environmental factors are affecting the distribution and migration of radioiodine and plutonium that were emitted from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, we quantified iodine and 239,240Pu concentration changes in soil samples with different land uses (urban, paddy, deciduous forest and coniferous forest), as well as iodine speciation in surface water and rainwater. Sampling locations were 53–63 km northwest of the FDNPP within a 75-km radius, in close proximity of each other. A ranking of the land uses by their surface soil (<4 cm) stable 127I concentrations was coniferous forest > deciduous forest > urban > paddy, and 239,240Pu concentrations ranked as deciduous forest > coniferous forest > paddy ≥ urban. Both were quite distinct from that of 134Cs and 137Cs: urban > coniferous forest > deciduous forest > paddy, indicating differences in their sources, deposition phases, and biogeochemical behavior in these soil systems. Although stable 127I might not have fully equilibrated with Fukushima-derived 129I, it likely still works as a proxy for the long-term fate of 129I. Surficial soil 127I content was well correlated to soil organic matter (SOM) content, regardless of land use type, suggesting that SOM might be an important factor affecting iodine biogeochemistry. Other soil chemical properties, such as Eh and pH, had strong correlations to soil 127I content, but only within a given land use (e.g., within urban soils). Organic carbon (OC) concentrations and Eh were positively, and pH was negatively correlated to 127I concentrations in surface water and rain samples. It is also noticeable that 127I in the wet deposition was concentrated in both the deciduous and coniferous forest throughfall and stemfall water, respectively, comparing to the bulk rainwater. Further, both forest throughfall and stemflow water consisted exclusively of organo-iodine, suggesting all inorganic iodine in the original bulk deposition (∼28.6% of total iodine) have been completely converted to organo-iodine. Fukushima-derived 239,240Pu was detectable at a distance ∼61 km away, NW of FDNPP. However, it is confined to the litter layer, even three years after the FDNPP accident-derived emissions. Plutonium-239,240 activities were significantly correlated with soil OC and nitrogen contents, indicating Pu may be associated with nitrogen-containing SOM, similar to what has been observed at other locations in the United States. Together, these finding suggest that natural organic matter (NOM) plays a key role in affecting the fate and transport of I and Pu and may warrant greater consideration for predicting long-term stewardship of contaminated areas and evaluating various remediation options in Japan.

Correlation between iodine isotopes (129I and 127I) species and marine parameters in the Baltic Sea

Iodine is a bio-intermediate and redox-sensitive element in the oceans and understanding the relationship between transformation of iodine species promotes them as indicators of biochemical cycling in the ecosystems. To gain an insight into the transformation of iodine species, correlations between the iodine species (127IO3−, 127I−, 129I−, 129IO3−) and marine parameters (temperature, salinity, oxygen, total phosphorus, nitrate and ammonium) are assessed here for the Baltic Sea during different seasons. The datasets used cover the periods of August 2006, April 2007 and November 2009. The results indicate that the correlations between radioactive 129I, stable 127I species and marine parameters mainly response to their respective sources as well as oceanographic environments. Also, insignificant correlations of iodine species and nutrients data (total phosphorus, nitrate and ammonium) are observed, suggesting that transformation activity of iodine species in the Baltic Sea is not directly linked to biological production.

Is soil natural organic matter a sink or source for mobile radioiodine ( 129I) at the Savannah River Site?

129I is one of the three major radiation risk contributors to the public as a consequence of past nuclear processing activities at Department of Energy (DOE) facilities. Elevated levels of 129I are present in the surface soils of F-Area of Savannah River Site, which used to be an isotope separation facility for the production of nuclear weapons components. The 129I in soils is thought to be bound predominantly to soil organic matter (SOM). Measurements of stable 127I and radioactive 129I in humic acids (HAs) and fulvic acids (FAs) obtained by five successive alkaline, two glycerol and one citric acid–alkaline extraction, demonstrated that these extractable humic substances (HS) together account for 54–56% and 46% of the total 127I and 129I in the soil, respectively. The remainder was likely bound to residual SOM. The iodine content (μg-I/g-C) generally decreased with each subsequent extract, while 129I/ 127I increased concurrently. The coincident variations in chemical compositions, aromaticity (estimated by UV spectroscopy), functional groups (e.g., aliphatic), degree of humification, relative migration in the hydrophobic interaction column, and molecular weight indicated that: (1) iodine in different HAs was bound to a small-size aromatic subunit (∼10 kDa); (2) the large-size subunit (∼90 kDa), which likely linked the small-size unit through some weak chemical forces (hydrogen bonds, hydrophobic or electrostatic interactions), determined the relative mobility of iodine bound to organic matter; (3) from the strong correlation between iodine content and aromaticity in the HAs, we suggested that iodine incorporation into the SOM via covalent aromatic C–I bond is the key mechanism controlling iodine behavior in this system. However, this relationship is not universal for all fractions of organic matter as evidenced from the different slopes of this relationship at the two sampling sites, as well as from the different relationships for HAs and FAs, respectively. These differences in iodination are due to different SOM molecular sizes, compositions, and availability of preferred iodination sites. 129I in the soil downstream from the contaminated site and near a wetland abruptly dropped below our detection limit (0.5 pCi- 129I/g-soil), which suggests that the high SOM in the plume soil around the 129I-contaminated F-Area might be a natural barrier to scavenge radioiodine released from the nuclear waste repository by forming organo-iodine compounds. Soil resuspension experiments showed that mobile 129I was mostly associated with a low average molecular weight amphiphilic organic carrier (13.5–15 kDa). SOM clearly behaves as a sink for iodine at the Savannah River Site F-Area. However, this work demonstrates that a small fraction of the SOM can also behave as a source, namely that a small fraction that may be readily dispersible under some environmental conditions and presumably release iodine in the organic-colloidal form. This radioiodinated organo-colloid likely can get into the groundwater through infiltration or surface runoff where it might migrate further into the wetlands. Results from this study provide the geochemical basis for future 129I migration controls, remediation, and/or land–groundwater management strategies.

Determination of iodine concentration in aqueous solutions by proton activation analysis: preliminary results for digested human thyroids

The aim of our studies is to check the possibilities of using proton activation analysis as a competitive method over other analytical techniques applied for iodine determination. It is well known that long-term irradiation of biological samples leads to their decomposition and formation of gaseous radiolysis products, which increase the pressure inside the sample container. In case of using proton beam another problem with liquid samples appears. It is the production of 7Be via spallation reactions 16O(p, spall)7Be. The Compton effect from 7Be γ-line increases the detection limits for isotopes with low-energy γ-lines. AIC-144 cyclotron at The Niewodniczanski Institute of Nuclear Physics Polish Academy of Science can accelerate protons up to energy of 60 MeV which is sufficient for (p,5n) reaction needed to obtain 123I (T1/2 = 13.27 h, Eγ = 159 keV, I = 83%) from stable 127I, thus the Compton effect from 7Be was the main factor perturbing the analysis. Separation and removal of 7Be is required to improve the detection limit. The paper presents a method and an example of its application to the determination of iodine concentration in digested fragments of human thyroids obtained during surgical treatment of patients with different types of thyroid tumor.

A Novel Approach for the Simultaneous Determination of Iodide, Iodate and Organo-Iodide for 127I and 129I in Environmental Samples Using Gas Chromatography−Mass Spectrometry

In aquatic environments, iodine mainly exists as iodide, iodate, and organic iodine. The high mobility of iodine in aquatic systems has led to (129)I contamination problems at sites where nuclear fuel has been reprocessed, such as the F-area of Savannah River Site. In order to assess the distribution of (129)I and stable (127)I in environmental systems, a sensitive and rapid method was developed which enables determination of isotopic ratios of speciated iodine. Iodide concentrations were quantified using gas chromatography-mass spectrometry (GC-MS) after derivatization to 4-iodo-N,N-dimethylaniline. Iodate concentrations were quantified by measuring the difference of iodide concentrations in the solution before and after reduction by Na(2)S(2)O(5). Total iodine, including inorganic and organic iodine, was determined after conversion to iodate by combustion at 900 °C. Organo-iodine was calculated as the difference between the total iodine and total inorganic iodine (iodide and iodate). The detection limits of iodide-127 and iodate-127 were 0.34 nM and 1.11 nM, respectively, whereas the detection limits for both iodide-129 and iodate-129 was 0.08 nM (i.e., 2pCi (129)I/L). This method was successfully applied to water samples from the contaminated Savannah River Site, South Carolina, and more pristine Galveston Bay, Texas.

Time Series of129I and127I Speciation in Precipitation from Denmark

Environmental 129I mainly released from reprocessing plants at La Hague (France) and Sellafield (U.K.) provides a unique atmospheric and environmental tracer. This study deals with 129I and 127I speciation in precipitation collected in Denmarkduring 2001-2006 that indicates many newfindings. The concentrations of total 129I in precipitation vary from 0.28 to 5.63 x 10(9) atoms 129I L(-1) with an average of (2.34 +/- 1.43) x 10(9) atoms 129I L(-1), and the annual deposition flux of 129I is (1.25 +/- 0.30) x 10(12) atoms m(-2). Increased 129I levels in precipitation and 129I/ 127I ratio are attributed to the releases of 129I from the reprocessing plants at La Hague and Sellafield. Iodide is the major specie of 129I, which accounts for 50-99% of total 129I. The concentrations of total 127I vary from 0.78 to 2.70 microg iodine L(-1) with an average of 1.63 +/- 0.47 microg iodine L(-1), and annual deposition flux of 0.95 +/- 0.26 mg m(-2). Unlike 129I, iodate is the major specie of 127I, which accounts for 43-93% of total 127I. The 291I/ l27I atomic ratios for total iodine vary from 5.04 to 76.5 x 10(-8) with an average of (30.1 +/- 16.8) x 10(-8). These values are 10 times lower for iodate with an average of (2.95 +/- 3.13) x 10(-8). Seasonal variations of 129I/127 ml values and 129I concentrations are associated with highs in spring and lows in summer-autumn periods. Re-emission of 129 from the surface water of the English Channel, Irish Sea, North Sea, and Norwegian Sea, especially from the European continental coast areas, is evidently the major source of 129I in the precipitation, while stable 127I in the precipitation has multiple sources, i.e., marine, as well as terrestrial emission. This work shows that data on speciation of iodine isotopes can provide thorough indications about the sources and geochemical cycle despite the complicated atmospheric chemistry of iodine.

Organo-Iodine Formation in Soils and Aquifer Sediments at Ambient Concentrations

One of the key risk drivers at radioactive waste disposal facilities is radioiodine, especially 129I. As iodine mobility varies greatly with iodine speciation, experiments with 129I-contaminated aquifer sediments from the Savannah River Site located in Aiken, SC, were carried out to test iodine interactions with soils and aquifer sediments. Using tracer 125I- and stable 127I- additions, it was shown that such interactions were highly dependent on I- concentrations added to sediment suspensions, contact time with the sediment, and organic carbon (OC) content, resulting in an empirical particle-water partition coefficient (Kd) that was an inverse power function of the added I- concentration. However, Kd values of organically bound 127I were 3 orders of magnitude higher than those determined after 1-2 weeks of tracer equilibration, approaching those of OC. Under ambient conditions, organo-iodine (OI) was a major fraction (67%) of the total iodine in the dissolved phase and by implication of the particulate phase. As the total concentration of amended I- increased, the fraction of detectable dissolved OI decreased. This trend, attributed to OC becoming the limiting factor in the aquifer sediment explains why at elevated I-concentrations OI is often not detected.

I–Xe dating: From adolescence to maturity

The I–Xe chronometer is based upon decay of now-extinct 129I where the ratio of accumulated daughter 129Xe to stable 127I reflects the iodine isotopic ratio at closure of the host mineral. Since none of the parent remains, I–Xe is by nature a relative chronometer but, when referenced by a standard mineral of known age, the I–Xe system becomes an absolute chronometer reflecting true closure times. Most iodine hosts are secondary minerals so the I–Xe system is unique in providing details of post-formational chronometry not readily available with other chronometers. The short half-life of 129I gives it exceptional precision. However, the secondary nature of iodine host minerals, combined with the inherent precision of I–Xe, were responsible for a large database of “whole-rock” I–Xe ages that were not easily interpreted. As this problem evolved historically, doubts were cast upon the viability of the I–Xe system as a chronometer which persisted until it was tested against other chronometers in single-mineral systems. Properly calibrated, absolute I–Xe ages reflect the true closure time of the host minerals, and sequences of closure times in different hosts provide cooling rates for the parent object.

Determination of 129I/127I ratios in environmental samplesusing neutron activation analysis

Studies on the behavior of 129I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable 127I. The background ratios of 129I/127I of 10-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 100 and 10-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure 129I to below mBq concentrations. Therefore, where there are elevated concentrations of 129I it is possible to use a combination of neutron activation techniques to determine 129I/127I ratios. This paper describes how NAA is used to measure 129I/127I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both 129I and 127I where the ratio is between 100 and 10-3. A radiochemical procedure is used to measure 129I at ratios between 10-3 and 10-7, with a thermal neutron flux of 1016 m-2·s-1.

Impact of the high tyrosine fraction in complementarity determining regions: measured and predicted effects of radioiodination on IgG immunoreactivity

Although iodine-131 is the most widely used radionuclide for radioimmunotherapy, direct radiolabeling methods yield decreased immunoreactivity of the antibody as a function of increased iodine incorporation. We have studied the amino acid sequences of a therapeutic IgG (HuM195), and in particular its complementarity determining regions (CDR), in order to correlate the iodination of tyrosine residues in the antigen binding site with changes in immunoreactivity. The CDR contained an overabundance of tyrosines relative to an expected random distribution of amino acids. In contrast, lysine residues that can be used for ligand attachment were evenly distributed throughout the IgG. HuM195 was first trace labeled with 111In and then labeled with stable 127I at various specific activities. The immunoreactivity of each product was determined using the 111In tracer. The immunoreactivity measured after varying levels of iodination fit a theoretical curve that was generated based on the assumption that a single iodine incorporation anywhere on a tyrosine residue in a CDR destroys the immunoreactivity of the antibody. Similar theoretical curves for antibody fragments (F ab, F v) suggest an even faster decrease in immunoreactivity with increasing iodination. A review of the sequences of other therapeutic IgG shows that a similar overabundance of tyrosine residues is found in the CDRs. Using enzyme digestion, the distribution of iodine on different parts of the antibody was also studied. The iodinated residues were distributed non uniformly throughout the IgG, with the heavy chain variable region tyrosines having a higher propensity for iodine incorporation than tyrosines in the other regions of the IgG. The common abundance of tyrosine in the CDR of IgG and its correlation with loss of function have important implications for therapeutic use of high specific activity radioiodinated monoclonal antibodies or fragments.

Neutron Capture Cross Sections and Resonances of Iodine-127 and Iodine-129

Neutron capture by 127,129I has been measured using the Oak Ridge Electron Linear Accelerator as a pulsed neutron source. Neutron energies were determined by time-of-flight. Resonance peaks were parameterized for radioactive 129I up to 3400 eV and for stable 127I from 2660 to 4260 eV. Average capture cross sections were derived for 129I from 3 to 500 keV and for 129I from 3 to 2200 keV. Over the 3- to 100-keV range, the 129I cross sections average ∼70% of the corresponding 127I cross sections but show much more fluctuation as a function of energy. The greater fluctuation is attributed to the approximately three times wider level spacing.

Further decrease in thyroidal uptake and disappearance of endemic goitre in children after 30 years of iodine prophylaxis in the east of Finland.

Endemic goitre of moderate severity was mainly found in the east of Finland in the 1930's. Studies in the 1950's showed an average daily iodine intake of 65-70 micrograms in the west and 50-65 micrograms in the east of the country. The use of iodized salt was introduced in the late 1940's but added only 15 micrograms of iodine to the daily intake. In the late 1950's iodine prophylaxis was intensified and the use of salt containing 25 mg KI/kg was recommended. In 1978 about 95% of all household salt used in the Savonlinna area was iodized. This region in the east of Finland has been used as an area of surveillance and studies have been carried out there in 1959, 1969 and 1979. During this period the thyroidal uptake decreased from 67 to 23% in non-goitrous subjects and from 62 to 28% in goitre patients the difference between the two last figures being statistically significant. The goitre patients also had significantly higher serum thyroxine and triiodothyronine levels. During the same period the urinary excretion of stable 127I increased from 45 micrograms to about 250 micrograms a day. Concomitantly the goitre prevalence among school children has decreased. Having been in the early 1950's in most parts 15-30% it is generally now 1-4%. It seems that the iodine intake is now adequate and that the endemia is gradually subsiding.

CH 3I: Isotope shift for 129I in the v 6 band

The isotope shift in the v 6 band of CH 3I has been measured with high resolution for the radioisotope 129I (half-life = 1.6 × 10 7 y) with respect to the stable 127I, using tunable diode laser spectroscopy. The average shift obtained from 30 transitions, free from interference in the RQ(J, 3) and RQ(J, 4) branches, amounted to (-0.0135 ± 0.0006) cm -1. The abundance ratio 129I/ 127I in the gas mixture was determined spectroscopically on RQ(16, 3) and found to be (0.032 ± 0.003), as compared to a mass-spectrometric analysis of (0.030 ± 0.001). The self and air broadening coefficients measured on RR(6, 0) of CH 3 127I were (32 ± 3) MHz Torr -1 and (10.4 ± 1.5) MHz Torr -1 respectively. The line strengths for RQ(16, 3) were found to be (2.0 ± 0.2) × 10 -21 cm -1 mol -1 cm 2 for both CH 3 127I and CH 3 129I.

Determination of 129I using tandem accelerator mass spectrometry

Iodine-129, with a half life of 15.7Myr (ref. 1), is one of the longest lived of the cosmogenic radionuclides. Although the primordial supply of 129I is now extinct, 129I is continuously being produced in the atmosphere primarily by cosmic ray reactions on xenon2, in the Earth primarily by spontaneous fission of 238U (ref. 3), and in meteorites and the Moon primarily by proton and neutron induced reactions on Te and Ba (ref. 4). The relatively large quantity of 129I introduced into the environment from the nuclear age may be useful as a tracer in groundwater hydrology5. Fissiogenic 129I in large granite formations (batholiths) could be used to establish the suitability of these sites for long term nuclear waste storage, because groundwater movement would carry away the more soluble iodides and disturb the equilibrium 129I/238U ratio. The concentration of 129I in meteorites can be combined with results for shorter-lived radionuclides to provide information on the constancy of the galactic cosmic ray flux over longer time scales than previously possible and also on the preterrestrial history of meteorites. We have applied the new atom counting technique to 129I analysis with a sensitivity (the minimum number of atoms in the sample required to obtain a quantitative result) of less than 107 atoms of 129I in a 1-mg sample. An AgI standard with a known 129I/127I ratio of 10−11 was determined to ±10%, and the background contribution from a reagent grade AgI sample gave an upper limit to the ratio of about 3×10−13. We used a time-of-flight measurement to distinguish 129I from the stable 127I ions that were not separated by the mass analysis system. Our results for the meteorites Bruderheim and Dhajala represent the first direct (that is, not inferred6 from radiogenic Xe) determination of 129I in meteorites. A Xe molecular negative ion was discovered but we show that it is not a problem for 129I analysis.

Untersuchung des Jodgehalts der Schilddrüse durch Fluoreszenzanregung*

A procedure is described in which stable 127I in the thyroid is induced to fluorescence (28.5 keV) by 241Am (59.5 keV). The radiation is registered on a Si (Li) detector and can be used in order to obtain a scintigram or to determine the concentration of127I in the thyroid at any selected point. The apparatus is available commercially and has been adapted for use with a scanner. Measurements using collimation of 3.5 to 4 cm revealed a focus with a marked tomographic effect. The sensitivity of the apparatus was investigated by using solutions of varying iodine concentrations; calibration curves for determining iodine concentration in thyroid tissue were obtained. It is necessary to take account of the thickness of the thyroid gland and of the superficial tissues because of the marked attenuation of the radiation within the tissues. Radiation dose to the thyroid during the scintigram was about 0.1 mGy (10 mrd), i.e. about 5% of a conventional TC scintigram. There is no whole body irradiation.

Iodine-129 in thyroids of grazing animals.

A combination of neutron activation and mass spectrometry has been used to determine the concentrations of fissiogenic 129I and stable 127I in thyroids of grazing animals and in mineral iodine. The 129I/127I ratios are lowest in mineral iodine and in a given area lower in cow thyroids than in deer thyroids. Near saturation levels of mineral iodine in commercial feeds and salt licks may account for differences in the 129I levels of cows and deer. Values of the 129I/127I ratio in deer appear to vary inversely with the iodine concentration of the thyroid.