Chemical states of iodine produced by the spontaneous fission of252Cf

The distributions of the chemical states of¹³¹I,¹³²I,¹³³I,¹³⁴I and¹³⁵I produced by the spontaneous fission of²⁵²Cf were investigated by the method of fractional precipitation separation in 6M NH₄OH solution followed by measurement of the X-ray spectrum of the samples with a Ge(Li) detector. The iodine fission fragments were separately collected in the matrices of NaNO₃, NaCl, dehydrated sodium sulfate, CH₃COONa·3H₂O, Na₃H₂IO₆, KI and NaIO₃ crystals. The results showed that the distribution of the chemical states was the function of the collection time, the nature of matrix materials and the type of iodine isotopes. The relative amount of the reduced states of¹³⁴I decreased with the increase of collection time in the matrix of NaNO₃. The ratio of the amount of reduced states to the total amount of the¹³⁴I was the highest (50.4%) in NaCl matrix and the lowest (9.4%) in Na₃H₂IO₆ matrix. The relative quantities of reduced states of¹³⁵I were the highest (58.5% and 97.7%) and that of¹³⁴I were the lowest (16.9% and 63.1%) in matrices of NaNO₃ and NaCl, respectively.     

Computerized on-line measurement the yield of short-lived bromine and iodine isotopes from thermal neutron fission of235U

The short-lived bromine and iodine isotopes from thermal neutron fission of²³⁵U have been separated from fission products by one step solvent extraction combined with an ion exchange fast chemistry system. The measured gamma spectra have been acquisited by an automatic computer on-line system. The results include experimental independent fission yields of⁸⁶Br,^134mI,^134gI,^136mI, and^136gI, the cumulative yields of⁸⁷Br,⁸⁸Br,¹³⁷I,¹³⁸I. The isomeric yield ratio of¹³⁴I and¹³⁶I has been determined and the iodine isotopic distribution curve has been constructed and analyzed.     

Distribution and behavior of long-lived radioiodine in soil

The concentration of¹²⁹I in soil in Japan was determined by neutron activation analysis. For the activation analysis, pre-irradiation chemical separation of the iodine was carried out by acid decomposition and distillation and post-irradiation treatment was performed by ion exchange and solvent extraction. The concentration of stable iodine and¹³⁷Cs were also determined and compared with the behavior of¹²⁹I in soil.Soil samples from Ibaraki, Fukui, Fukushima, and Nagasaki Prefectures were analyzed and¹²⁹I was detected in amounts ranging from 10^–7 to 10^–5 Bq/g soil in uncultivated surface soil. There are apparently small variations in the¹²⁹I concentrations in each of the regions analyzed.From depth profile studies in sandy soil, the iodide form of¹²⁹I was found to migrate downward at a relatively rapid rate while other species remain longer in the surface soil.     

Determination of129I and127I in environmental samples by neutron activation analysis (NAA) and inductively coupled plasma mass spectrometry (ICP-MS)

In order to assess the levels and behavior of¹²⁹I (half-life: 1.6×10⁷ y) and¹²⁷I (stable) in the environment, we have developed analytical procedures involving neutron activation analysis (NAA). Environmental samples collected around Tokaimura, Ibaraki Prefecture, Japan, have been analyzed using this method. Ranges of¹²⁹I and¹²⁷I concentrations in surface soil were 0.9–180 mBq kg^–1 and 1–60 mg kg^–1, respectively. Higher¹²⁹I concentrations were found in soil samples collected from coniferous forests, suggesting a contribution from tree canopies in the deposition of this nuclide. Most of the¹²⁹I in soil, was found to be retained in the first 10 cm. The¹²⁹I/¹²⁷I ratios in wheat fields were lower than those in rice paddy fields.A soil sample collected by IAEA from an area contaminated by the Chemobyl accident was also determined. The¹²⁹I concentration and the¹²⁹I/¹²⁷I ratio were 1.6 mBq kg^–1 and 1.7×10^–7, respectively. The¹²⁹I level in this sample was higher than the values obtained in areas far from nuclear facilities in Japan. It was suggested that the analysis of¹²⁹I in soils in the Chernobyl area may be useful in evaluating the¹³¹I levels at the time of the accident.Analyses of¹²⁹I and¹²⁷I by ICP-MS in water samples were also made. The analytical speed of this method was very high, i.e., 3 minutes for a sample. However, there is a sensitivity limitation for¹²⁹I detection due to interference from¹²⁹Xe with the¹²⁹I peak. The detection limits for¹²⁹I and¹²⁷I in water samples were about 0.5 mBq ml^–1 and 0.1 ng ml^–1, respectively.     

Experiences in the routine production of123I via the124Te(p, 2n)123I reaction with a low energy cyclotron

This paper deals with the results and experimental observations obtained in routine production of¹²³I via¹²⁴Te(p, 2n)¹²³I reaction, using the low energy cyclotron (protons, E_max=22 MeV) at the German Cancer Research Center in Heidelberg. The reaction was studied during the past 4 years using¹²⁴TeO₂ targets with various levels of enrichment. The purpose of the study was to determine which target material provided the highest quality and most economical production of¹²³I. A viable routine production was defined as one in which¹²³I could be conveniently and reproducably prepared in reasonable purity while maintaining a low cost for the entire process. Different methods of sublimation of¹²³I activity from the¹²⁴TeO₂ target were examined to determine the optimal conditions for recovery of radioactivity and recycling of target material. A rapid method is described which permits quantitative separation of¹²³I while allowing only a negligible loss of¹²⁴TeO₂.     

Self-radiolysis of iodobenzene labelled with125I

The radiolysis of iodobenzene labelled with¹²⁵I has been investigated at liquid nitrogen and room temperatures, in the presence and absence of oxygen. After various storage times the samples were analyzed by gas chromatography, and benzene, vinyl iodide, biphenyl, and iodobiphenyl were detected. Biphenyl, benzene, and iodobiphenyl were found to be formed as a result of local radiolytic effect of Auger electrons of¹²⁵I, and vinyl iodide was probably produced due to the decay effect of¹²⁵I in labelled iodobenzene molecules. At the site of¹²⁵I decay the Auger electrons are radiolytically effective within a spherical volume with diameter of about 30 . Outside this sphere the energy absorbed by iodobenzene molecules is not high enough to produce any radiolytical damage.     

Determination of129I in ambient air by inductively coupled plasma mass spectrometry (ICP/MS)

The detection of¹²⁹I by Inductively Coupled Plasma Mass Spectrometry (ICP/MS) in environmental samples can be used to determine anthropogenic release of this long-lived radionuclide, which is a definitive indicator of certain nuclear activities. By using selective precipitation techniques with on-line ICP/MS detection, low levels of¹²⁹I can be detected. The major interference for the ICP/MS detection of¹²⁹I is due the presence of natural¹²⁹Xe found in water samples at a concentration of about 1 ng/ml. This work will demonstrate a instrument detection of less than 50 fg¹²⁹I from environmental air samples and shows promise for a rugged ICP/MS technique to monitor¹²⁹I levels in ambient air for nonproliferation monitoring purposes.     

Chemical and nuclear interferences in neutron activation of129I and127I in environmental samples

A combination of neutron activation and gamma-ray coincidence counting technique is used to determine the concentration of both long-lived fission produced¹²⁹I and natural¹²⁷I in environmental samples. The neutron reactions used for the activation of the iodine isotopes are¹²⁹I(n, )¹³⁰I and¹²⁷I(n, 2n)¹²⁶I. Nuclear interferences in the activation analysis of¹²⁹I and¹²⁷I can be caused by production of¹³⁰I or¹²⁶I from other constituents of the materials to be irradiated, i.e. Te, Cs and U impurities and from the¹²⁵I tracer used for chemical yield determination. Chemical interferences can be caused by¹²⁹I and¹²⁷I impurities in the reagents used in the pre-irradiation separation of iodine. The activated charcoals used as iodine absorbers were carefully cleaned. Different chemical forms of added¹²⁵I tracer and¹²⁹I and¹²⁷I constituents of the samples can cause different behaviour of¹²⁵I tracer and sample iodine isotopes during pre-irradiation separation of iodine. The magnitude of the nuclear and chemical interferences has been determined. Procedures have been developed to prevent or control possible interferences in low-level¹²⁹I and¹²⁷I activation analysis. For quality control a number of biological and environmental standard samples were analyzed for¹²⁷I and¹²⁹I concentrations.     

Resonance activation analysis of iodine

Resonance neutron activation and gamma-ray spectrometry were used to determine traces of iodine in biological materials. The method developed is purely instrumental and fairly rapid. The major interfering activities of²⁴Na,³⁸Cl,³⁶Mn and⁸²Br were significantly reduced by irradiating the samples inside a shield of Cd, NaCl, MnBr₂ and MnO₂. Neutrons with energies close to the resonances of Na, Cl, Mn and Br were absorbed in the shield and did not activate the sample while neutrons with energies close to the resonances of iodine were not absorbed appreciably. Thus the activity of¹²⁸I was enhanced relative to the interfering activities. The 442 keV gamma of¹²⁸I (T=25 min) was measured using a high-resolution Ge(Li) detector and a multichannel analyzer. Sensitivity of 0.05 ppm was obtained.     

Separation of trace impurities of131I from99Mo obtained by extraction from fission products of uranium

The radioisotope⁹⁹Mo was separated from a mixture of²³⁵U fission products in the presence of Hg²⁺ by sorption on a chromatographic column filled with Al₂O₃ and elution with 1M NH₄OH. Trace impurities of¹³¹I in the molybdenum fraction were eliminated by selective sorption on silver iodide or by repeated sorption of⁹⁹Mo on Al₂O₃.     

Pure iodine-123 production by small cyclotron for medical use

For improvement of radionuclidic purity of¹²³I a method was elaborated to obtain highly enriched [¹²³Te] tellurium. Using this new TeO₂ target the optimum irradiation conditions have been investigated for the production of¹²³I via¹²³Te (p,n)¹²³I and the radionuclide impurity levels were also determined.     

Radiochemical separation of110mAg,210Pb,127Te and131I from aqueous nitric acid solution by bis-2-(butoxyethyl ether)

A bis-2-(butoxyethyl ether) (DBC) solvent extraction method has been developed for the radiochemical separation of^110mAg,²¹⁰Pb,¹²⁷Te and¹³¹I in varying concentrations of aqueous HNO₃. Various factors were examined to determine the optimum conditions of extraction. The effect of various masking agents has been studied. The extraction of¹³¹I is enhanced to 99% at 2.4M HNO₃ in the presence of KSCN.¹³¹I was stripped into aqueous sodium hydroxide from the oxygenated organic extractant. The method was then applied for the recovery of¹³¹I from neutron irradiated tellurium metal. The mechanism and reactivity of DBC with metal ions is described.     

Contribution of nuclear medicine procedures to global129I inventory

¹²⁹I content of batches of Na¹³¹I vials, used for nuclear medicine procedures, was estimated by neutron activation analysis. The average value of the¹²⁹I/¹³¹I activity ratio /corresponding to zero decay time of the latter/ was /4.98±2.8/x10^–9. It is concluded that the contribution of¹²⁹I from medical applications of¹³¹I in India is insignificant in relation to that from nuclear fuel cycle activities.     

Determination of I-129 and I-127 in soil and tracer experiments on the adsorption of iodine on soil

Neutron activation analysis of¹²⁹I and¹²⁷I in soil has been studied. The limit of detection for¹²⁹I in soil was about 0.05 mBq/kg or 1×10^–9 as¹²⁹I/¹²⁷I atom ratio. The range of¹²⁹I concentration in surface soils collected around Tokaimura (Ibaraki Prefecture) was 0.9–41 mBq/kg.Tracer experiments on the adsorption of iodine were also carried out, in order to obtain information on the behaviour of iodine in soil-water systems. Different adsorption patterns of iodide and iodate on soil were found. It was supposed that iodide was adsorbed by the soil fraction which became unstable at about 200° C and iodate by the fraction which was relatively stable to heating.     

Plutonium-244 fission xenon and primordial xenon in the Allende meteorite

The carbonaceous chondrite Allende contains (22±1)·10⁻¹² cm³STP/g of²⁴⁴Pu fission xenon and two kinds of primordial xenon: Type I and Type II. The former represents the isotopic composition of a primordial xenon, which resided in the vicinity of a supernova shortly before it exploded, while the latter represents that of the xenon, which resided in the supernova. The isotopic composition of xenon found in the pink inclusion of the Allende meteorite, corrected for the presence of very large excesses of²⁴⁴Pu fission xenon,¹²⁹Xe from the decay of¹²⁹I, and of¹²⁸Xe from the neutron-capture reactions on¹²⁷I, resembles that of Type-I primordial xenon. The isotopic composition of xenon found in the diamond inclusions of the Allende meteorite, on the other hand, represents that of Type-II primordial xenon and it resembles that of a mixture of Type-I primordial xenon whose isotopic composition is severely altered by a combined effect of (a) mass-fractionation, (b) spallation, (c) stellar-temperature neutron-capture reactions, and (d) the presence of a large excess of²⁴⁴Pu fission xenon.     

Some observations on the radionuclidic and radiochemical control of radiopharmaceuticals at the N.R.C. Democritos

In the production of¹³¹I, the presence of a contamination extractable with organic solvents has been detected and its source discovered. The influence of overheating was established in the preparation of^99m Tc by the extraction method. Finally, details are given of the procedure used for the estimation of¹⁹⁹Au present in¹⁹⁸Au.     

Preparation of99Mo,132Te isotopes and99mTc,132I generators

Adsorption and desorption of⁹⁵Zr−⁹⁵Nb,⁹⁹Mo,¹⁰³Ru,¹³²Te and²³⁹Np in a HCl-alumina system were studied in order to purify⁹⁹Mo and¹³²Te obtained by the cation-exchange separation of fission products and to prepare highly pure^99mTc and¹³²I generators.⁹⁹Mo and¹³²Te, of which radionuclidic purity was over 99.99% and 99.999%, respectively, could be obtained by passing the cation-exchange separated Mo and Te fractions through alumina columns, by washing with HCl and finally by eluting⁹⁹Mo with 1M NH₄OH and¹³²Te with 3M NaOH. In order to raise the recovery of⁹⁹Mo and¹³²Te from the alumina columns, they should be eluted as quickly as possible after the adsorption. The direct use of the alumina column containing⁹⁹Mo or¹³²Te as the generator allowed milking of^99mTc or¹³²I, of which radionuclidic purity was over 99.999%. Milking yields of^99mTc with 0.1M HCl and¹³²I with 0.01M NH₄OH were 77% and 90%, respectively. The latter value was much higher than that in usual performance of the generator.     

A study on the separation and distribution of the chemical forms of131I produced from thermal neutron-irradiated tellurium compounds by thin-layer chromatography

The separation and distribution of the chemical forms of¹³¹I produced from thermal neutron-irradiated tellurium compounds were investigated by thin-layer chromatography using alumina as adsorbent and water as developer as well as the effect of iodine carriers added on the distribution of different chemical forms of¹³¹I was studied. The effects of both atmospheric oxygen and light were investigated on the oxidation of carrier-free iodide on the thin-layer plate.     

Determination of iodine-129 and iodine-127 in environmental samples collected in Japan

Analytical method for the determination of¹²⁹I and¹²⁷I in environmental samples has been developed by using radiochemical neutron activation analysis. The¹²⁹I levels in the samples such as soil (0.9–41 mBq/kg), precipitation (0.002–0.11 mBq/kg), pine needles (1.2–32 mBq/kg) and seaweed (<0.1–17 mBq/kg) collected near the nuclear facilities in Tokaimura were higher than those from the other areas in Japan. The highest¹²⁹I concentration was found in surface soil (0–5 cm), and the highest¹²⁹I/¹²⁷I ratios were found in pine needles and precipitation. The¹²⁹I/¹²⁷I ratio was higher in rice paddy soil than those in wheat field soil collected around Tokaimura, while the concentration of¹²⁹I somewhat higher in wheat field soil.     

Dry deposition velocity of iodine-129 onto grass as obtained by field measurements in the environment of a nuclear fuel reprocessing plant

The deposition velocity of gaseous organic¹²⁹I species from the exhaust air stack of the Karlsruhe reprocessing plant onto pasture grass was measured by a field experiment. By simultaneously measuring the amount of¹²⁹I deposited per unit area of pasture grass and the time integrated mean air concentration of¹²⁹I a deposition velocity of V_g=5.8×10^–1 /cm s^–1/ onto pasture grass was determined.