Zirconium Isotopes Research Articles

Application of the isotope dilution technique for 93Zr determination in an irradiated cladding material by multiple collector-inductively coupled plasma mass spectrometry

The determination of 93Zr concentration, a long-lived radionuclide present in spent nuclear fuel and in the structural components of nuclear reactors, is a major issue for nuclear waste disposal purpose and to validate neutronic calculation codes. To measure 93Zr concentration in irradiated cladding material with a high precision, an analytical method based on the use of multiple collector-inductively coupled plasma mass spectrometer (MC-ICPMS) combined to isotope dilution technique was developed. First a radiochemical separation of zirconium from a zircaloy sample (a zirconium alloy used as a cladding material for nuclear fuel elements), has allowed to obtain a very pure zirconium fraction with no potential isobaric interferences for mass spectrometric measurements. Then as the determination of all zirconium isotope ratios in the sample is necessary for the isotope dilution method, a MC-ICPMS procedure was developed to perform these precise measurements. Finally, the determination of 93Zr concentration in the same sample was performed, after preparation and calibration of a 96Zr spike solution. The uncertainties obtained on isotope ratios of zirconium by MC-ICPMS were in the order of 0.1%. The final uncertainty obtained on the 93Zr concentration in the nuclear material used and after chemical purification was lower than 0.6%.

Measurement techniques for tracer kinetic studies with stable isotopes of zirconium

Biokinetic models are used in radiation protection to assess internal radiation doses. Experiments with stable isotopes as tracers can be performed to obtain characteristic parameters of these models. Two methods for the measurement of zirconium isotopes in human biological samples are presented--thermal ionisation mass spectrometry (TIMS) and proton nuclear activation analysis (PNA). Descriptions include sample preparation, operating conditions, relative uncertainties and method detection limits as well as important properties of both methods.

Decay study of neutron-rich zirconium isotopes employing a Penning trap as a spectroscopy tool

A new technique to produce isobarically pure ion beams for decay spectroscopy by using a gas-filled Penning trap was commissioned at the ion guide isotope separator on-line facility, IGISOL. β-decays of neutron-rich 100Zr, 102Zr and 104Zr isotopes were studied with this technique. In addition, the $\ensuremath Q_{\beta^{-}}$ values of 100,102,104Zr β-decays were determined from the direct mass measurements of zirconium and niobium isotopes performed with a high-precision Penning trap. The mass of 104Nb was directly measured for the first time and the obtained mass excess value for the longer-living (1+) state is -71823±10 keV. For the ground states of 100Nb and 102Nb the obtained mass excess values were -79802±20 keV and -76309±10 keV, respectively. The observed distribution of the β strength supports a prolate deformation assignment for 100,102,104Zr isotopes.

Measurement of fission neutron spectrum averaged cross sections of some threshold reactions on zirconium: Production possibility of no-carrier-added 90Y in a nuclear reactor

Summary Employing the activation technique in combination with radiochemical separations and high-resolution γ-ray spectroscopy fission neutron spectrum averaged cross sections were measured for several (n, p) and (n, α) reactions on isotopes of zirconium; our measurements constitute the first systematic study. The special interest was in the investigation of the 90Zr(n, p)90Y reaction for the production of no-carrier-added 90Y in a nuclear reactor. At a fast neutron flux density of 7.5 × 1013 cm−2 s−1 and an irradiation time of 120 h, using 100% enriched 90Zr target 0.548 GBq of no-carrier-added 90Y per batch could be produced. The method is thus suitable for medium-scale production of this radionuclide.

A COMPREHENSIVE DOSE RECONSTRUCTION METHODOLOGY FOR FORMER ROCKETDYNE/ATOMICS INTERNATIONAL RADIATION WORKERS

Incomplete radiation exposure histories, inadequate treatment of internally deposited radionuclides, and failure to account for neutron exposures can be important uncertainties in epidemiologic studies of radiation workers. Organ-specific doses from lifetime occupational exposures and radionuclide intakes were estimated for an epidemiologic study of 5,801 Rocketdyne/Atomics International (AI) radiation workers engaged in nuclear technologies between 1948 and 1999. The entire workforce of 46,970 Rocketdyne/AI employees was identified from 35,042 Kardex work histories cards, 26,136 electronic personnel listings, and 14,189 radiation folders containing individual exposure histories. To obtain prior and subsequent occupational exposure information, the roster of all workers was matched against nationwide dosimetry files from the Department of Energy, the Nuclear Regulatory Commission, the Landauer dosimetry company, the U.S. Army, and the U.S. Air Force. Dosimetry files of other worker studies were also accessed. Computation of organ doses from radionuclide intakes was complicated by the diversity of bioassay data collected over a 40-y period (urine and fecal samples, lung counts, whole-body counts, nasal smears, and wound and incident reports) and the variety of radionuclides with documented intake including isotopes of uranium, plutonium, americium, calcium, cesium, cerium, zirconium, thorium, polonium, promethium, iodine, zinc, strontium, and hydrogen (tritium). Over 30,000 individual bioassay measurements, recorded on 11 different bioassay forms, were abstracted. The bioassay data were evaluated using ICRP biokinetic models recommended in current or upcoming ICRP documents (modified for one inhaled material to reflect site-specific information) to estimate annual doses for 16 organs or tissues taking into account time of exposure, type of radionuclide, and excretion patterns. Detailed internal exposure scenarios were developed and annual internal doses were derived on a case-by-case basis for workers with committed equivalent doses indicated by screening criteria to be greater than 10 mSv to the organ with the highest internal dose. Overall, 5,801 workers were monitored for radiation at Rocketdyne/AI: 5,743 for external exposure and 2,232 for internal intakes of radionuclides; 41,169 workers were not monitored for radiation. The mean cumulative external dose based on Rocketdyne/AI records alone was 10.0 mSv, and the dose distribution was highly skewed with most workers experiencing low cumulative doses and only a few with high doses (maximum 500 mSv). Only 45 workers received greater than 200 mSv while employed at Rocketdyne/AI. However, nearly 32% (or 1,833) of the Rocketdyne/AI workers had been monitored for radiation at other nuclear facilities and incorporation of these doses increased the mean dose to 13.5 mSv (maximum 1,005 mSv) and the number of workers with >200 mSv to 69. For a small number of workers (n=292), lung doses from internal radionuclide intakes were relatively high (mean 106 mSv; maximum 3,560 mSv) and increased the overall population mean dose to 19.0 mSv and the number of workers with lung dose>200 mSv to 109. Nearly 10% of the radiation workers (584) were monitored for neutron exposures (mean 1.2 mSv) at Rocketdyne/AI, and another 2% were monitored for neutron exposures elsewhere. Interestingly, 1,477 workers not monitored for radiation at Rocketdyne/AI (3.6%) were found to have worn dosimeters at other nuclear facilities (mean external dose of 2.6 mSv, maximum 188 mSv). Without considering all sources of occupational exposure, an incorrect characterization of worker exposure would have occurred with the potential to bias epidemiologic results. For these pioneering workers in the nuclear industry, 26.5% of their total occupational dose (collective dose) was received at other facilities both prior to and after employment at Rocketdyne/AI. In addition, a small number of workers monitored for internal radionuclides contributed disproportionately to the number of workers with high lung doses. Although nearly 12% of radiation workers had been monitored for neutron exposures during their career, the cumulative dose levels were small in comparison with other external and internal exposure. Risk estimates based on nuclear worker data must be interpreted cautiously if internally deposited radionuclides and occupational doses received elsewhere are not considered.

Extraction of short-lived zirconium and hafnium isotopes using crown ethers: A model system for the study of rutherfordium

Summary The extraction of zirconium and hafnium from hydrochloric acid media was studied using the crown ethers dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DC18C6) and dicyclohexano-24-crown-8 (DC24C8) as extractants. The goal was to find an extraction system that exhibits a high selectivity between the members of group 4 of the periodic table and is suitable for the study of rutherfordium. It was found that Zr and Hf are both extracted using DB18C6, DC18C6 and DC24C8. The extraction yield increases with increasing acid concentration and increasing concentration of crown ether. The extracted species most likely consists of an ion-association complex formed between a Zr or Hf chloro complex and a hydronium crown ether complex. Conditions can be found for each extractant that provide for the separation of Zr from Hf. This selective separation between Zr and Hf makes the extraction with crown ethers from HCl well suited to study the extraction behaviour of Rf and compare it to the behaviour of Zr and Hf. These extraction systems can be used to determine whether the extraction behaviour of Rf is similar to Zr, similar to Hf or follows the trend established by the lighter homologs. The extraction kinetics are fast enough for the study of the 78-s isotope 261mRf.

A theoretical description of energy spectra and two-neutron separation energies for neutron-rich zirconium isotopes

Very recently the atomic masses of neutron-rich Zr isotopes, from $^{96}$Zr to $^{104}$Zr, have been measured with high precision. Using a schematic Interacting Boson Model (IBM) Hamiltonian, the evolution from spherical to deformed shapes along the chain of Zr isotopes, describing at the same time the excitation energies as well as the two-neutron separation energies, can be rather well reproduced. The interplay between phase transitions and configuration mixing of intruder excitations in this mass region is succinctly addressed.

Coordinate space Hartree-Fock-Bogoliubov calculations for the zirconium isotope chain up to the two-neutron drip line

We solve the Hartree-Fock-Bogoliubov (HFB) equations for deformed, axially symmetric even-even nuclei in coordinate space on a two-dimensional (2-D) lattice utilizing the basis-spline expansion method. Results are presented for the neutron-rich zirconium isotopes up to the two-neutron drip line. In particular, we calculate binding energies, two-neutron separation energies, normal and pairing densities, mean square radii, quadrupole moments, and pairing gaps. Very large prolate quadrupole deformations $({\ensuremath{\beta}}_{2}=0.42,0.43,0.470)$ are found for the $^{102,104,112}\mathrm{Zr}$ isotopes, in agreement with recent experimental data. We compare 2-D basis-spline lattice results with the results from a 2-D HFB code that uses a transformed harmonic oscillator basis.

2-D lattice HFB calculations for neutron-rich zirconium isotopes

Using the Hartree-Fock-Bogoliubov (HFB) mean-field theory in coordinate space, we investigate ground-state properties of the zirconium isotopes from the line of stability up to the two-neutron dripline ( 102-122Zr). In particular, we calculate two-neutron separation energies, quadrupole moments, and r.m.s. radii for protons and neutrons. We find large prolate ground-state deformations for the isotopes 102Zr through 112Zr, and the spherical shapes starting from 114Zr up to the dripline nucleus 122Zr.

Direct mass measurements of neutron-rich zirconium isotopes up toZr104

Atomic masses of radioactive zirconium isotopes from {sup 96}Zr to {sup 104}Zr have been measured with a relative accuracy of {<=}5x10{sup -7} using a Penning trap coupled to the ion guide isotope separator on-line system. The obtained two-neutron separation energies show strong local correlation in relation to the shape change and shape coexistence between N=58 and 60.

Giant dipole resonance and Jacobi transition with exact treatment of fluctuations

In a macroscopic approach to giant dipole resonance (GDR) in hot and rotating nuclei, the observables are related to the nuclear free energy surface with consideration of thermal shape fluctuations. This formalism is revisited with more exact methods. The Nilsson-Strutinsky (NS) method extended to high spin and temperature is used for free energy calculations. Various approaches to calculate shell corrections at finite temperature and spin are compared. The GDR built on the states determined by the NS method is studied with a macroscopic model comprising anisotropic harmonic oscillator potential with separable dipole-dipole interaction. Methods to parametrize the free energy, such as the Landau theory, for easier evaluation of thermal fluctuations, are discussed along with a scheme to evaluate thermal fluctuations exactly. The Landau theory is found to work well even in the extreme limits of spin, however, in the absence of strong shell effects. GDR as a probe for Jacobi transition leading to hyperdeformation is analyzed in the case of zirconium isotopes.

Hartree-Fock-Bogoliubov calculations in coordinate space: Neutron-rich sulfur, zirconium, cerium, and samarium isotopes

Using the Hartree-Fock-Bogoliubov (HFB) mean field theory in coordinate space, we investigate ground state properties of the sulfur isotopes from the line of stability up to the two-neutron dripline ($^{34-52}S$). In particular, we calculate two-neutron separation energies, quadrupole moments, and rms-radii for protons and neutrons. Evidence for shape coexistence is found in the very neutron-rich sulfur isotopes. We compare our calculations with results from relativistic mean field theory and with available experimental data. We also study the properties of neutron-rich zirconium ($^{102,104}Zr$), cerium ($^{152}Ce$), and samarium ($^{158,160}Sm$) isotopes which exhibit very large prolate quadrupole deformations.

Zirconium isotope evidence for incomplete admixing of r-process components in the solar nebula

Isotopic anomalies in Mo and Zr have recently been reported for bulk chondrites and iron meteorites and have been interpreted in terms of a primordial nucleosynthetic heterogeneity in the solar nebula. We report precise Zr isotopic measurements of carbonaceous, ordinary and enstatite chondrites, eucrites, mesosiderites and lunar rocks. All bulk rock samples yield isotopic compositions that are identical to the terrestrial standard within the analytical uncertainty. No anomalies in 92Zr are found in any samples including high Nb/Zr eucrites and high and low Nb/Zr calcium–aluminum-rich inclusions (CAIs). These data are consistent with the most recent estimates of <10−4 for the initial 92Nb/93Nb of the solar system. There exists a trace of isotopic heterogeneity in the form of a small excess of r-process 96Zr in some refractory CAIs and some metal-rich phases of Renazzo. A more striking enrichment in 96Zr is found in acetic acid leachates of the Allende CV carbonaceous chondrite. These data indicate that the r- and s-process Zr components found in presolar grains were well mixed on a large scale prior to planetary accretion. However, some CAIs formed before mixing was complete, such that they were able to sample a population of r-process-enriched material. The maximum amount of additional r-process component that was added to the otherwise well-mixed Zr in the molecular cloud or disk corresponds to ∼0.01%.

Validation of Minor Actinide Cross Sections by Studying Samples Irradiated for 492 Days at the Dounreay Prototype Fast Reactor—I: Radiochemical Analysis

Actinide samples irradiated in the Dounreay Prototype Fast Reactor for 492 effective full-power days were analyzed at Japan Atomic Energy Research Institute by radiochemical methods to measure the isotopic compositions of the fission products (molybdenum, zirconium, and neodymium isotopes) and of the actinides (uranium, neptunium, plutonium, americium, curium, and californium isotopes). In this first of two companion papers, procedures used for chemical analyses and the analyzed data are presented. There is good agreement between the current results and previous results obtained at Oak Ridge National Laboratory. Therefore, these analytical results could serve as a benchmark for future calculations and validation of nuclear data libraries. Such a validation is attempted in the companion paper.

Reconstruction of the inhalation dose in the 30-km zone after the Chernobyl accident.

Due to lack of measurements of activity concentrations in air, the assessment of the inhalation dose of the population evacuated from the 30-km zone after the Chernobyl accident is not possible from continuous filter measurements. Since the evaluation of the inhalation dose in each settlement of the zone is of great interest for epidemiological purposes, an approach was chosen that utilizes the available data on ground deposition of 137Cs, a recently performed best estimate of the radionuclide vector and its spatial distribution as well as the radionuclide dependent deposition velocity. The derived inhalation dose values in the 30-km zone range between 3 mSv to 150 mSv effective dose for adults depending on the distance to the reactor site and the day of evacuation. For 1-y-old infants the values range between 10 to 700 mSv. In Chernobyl town, an effective inhalation dose of 25 mSv until evacuation day was assessed. Thyroid doses due to inhalation ranged from 0.02 to 1 Sv for adults, for 1-y-old infants from 0.02 to 6 Sv. The inhalation dose in each settlement of the 30-km zone is approximately 8-13 times higher than the external exposure in each settlement if evacuation of the settlement occurred at an early stage. For settlements with evacuation at a later stage (day 10 or later) the inhalation dose was about 50-70% higher than the external dose. The dominant contribution to the effective inhalation dose comes from 131I (about 40%) and tellurium and rubidium isotopes (about 20-30%). Despite high zirconium and cerium ground depositions, zirconium and cerium isotopes contribute rather little to the inhalation dose which is mainly due to the great particle sizes to which they are attached. The relative contribution of short-lived radionuclides is, despite higher activities than at greater distances, less than 5%.

Radiochemical analysis of 93Zr

The zirconium isotope 93Zr is a long-lived pure β-particle-emitting radionuclide, which is produced by nuclear fission and neutron activation of the stable isotope 92Zr. This element is a constituent of the structural components of nuclear reactor vessels. A selective liquid–liquid extraction method for radiochemical separation of Zr, based on liquid–liquid extraction with 1-(2′-thenoyl)-3,3,3-trifluoroacetone in xylene and a subsequent stripping of 93Zr by an aqueous acid solution, has been developed. The method was utilised to separate Zr from other pure β-particle and β– γ emitters in different kinds of samples. Decontamination factors higher than 99% for the pure β-particle and β– γ emitters and an overall chemical yield of 80% were obtained. The sensitivity of the method allows the determination of the isolated 93Zr by liquid scintillation counting and the minimum detectable activity value obtained was 0.067 Bq over a counting period of 60 min.

Total Lead and Stable Lead Isotopes in Stockholm Sediments

Lead (Pb) in the environment is derived from both naturaland anthropogenic sources. The aim of this study is to estimate the isotopic signature of anthropogenic Pb in sediments from a highly contaminated area (Stockholm), to discuss the influence of different sources on this signature, and to suggest natural Pb background concentrations. Also distribution patterns and differences between different water areas in Stockholm have been studied, both by total Pb and stable Pb isotopes. In 1993, sediment samples were collected at 24 stations in the Stockholm area and analysed for total Pb, zirconium (Zr), scandium (Sc) and stable Pb isotopes (204, 206-208Pb). Total Pb data show that the Stockholm sediments are severely contaminated by Pb. The contamination seems to be rather local since the small lakes surrounding the central parts of Stockholm are much less effected than the central parts. Stockholm is clearly influenced by anthropogenic and natural sources, but in some of the small lakes also by Pb in zircons from the geological basement. The anthropogenic Pb in Stockholm has typical 207Pb/206Pb ratios of 0.85–0.89 and 208Pb/204Pb ratios of 36–38, which are distinct from natural sources. Pb/Sc ratios suggest that the natural background Pb concentration is 10–20 mg kg-1 d.w.

Cross sections of (n,p), (n, α) and (n,2n) reactions on some isotopes of zirconium in the neutron energy range of 10–12 MeV and integral tests of differential cross section data using a 14 MeV d(Be) neutron spectrum

Cross sections were measured for the 90Zr(n, α) 87mSr, 90Zr(n,2n) 89m,gZr, 91Zr(n,p) 91mY, 92Zr(n,p) 92Y, 94Zr(n, α) 91Sr and 96Zr(n,2n) 95Zr reactions over the neutron energy range of 11.4 to 12.4 MeV and for the 94Zr(n,p) 94Y reaction from 9.2 to 12.4 MeV. Nuclear model calculations were performed up to 16 MeV. The statistical model incorporating precompound effects reproduces excitation functions of the three major threshold reactions, namely (n,p), (n, α) and (n,2n), quite well. Spectrum–averaged cross sections were measured using a thick target Be(d,n) neutron field at E d=14 MeV. For the same neutron field averaged reaction cross sections were deduced using the excitation functions measured in this work as well as those given in the ENDF/B-VI, JEF−2, JENDL−3.2, BROND and ADL−3 data files. A comparison of the experimental and deduced integral data helped validating the differential data.

92Nb-(92)Zr and the Early Differentiation History of Planetary Bodies.

The niobium-92-zirconium-92 ((92)Nb-(92)Zr) extinct radioactive decay system (half-life of about 36 million years) can place new time constraints on early differentiation processes in the silicate portion of planets and meteorites. Zirconium isotope data show that Earth and the oldest lunar crust have the same relative abundances of (92)Zr as chondrites. (92)Zr deficits in calcium-aluminum-rich inclusions from the Allende meteorite constrain the minimum value for the initial (92)Nb/(93)Nb ratio of the solar system to 0.001. The absence of (92)Zr anomalies in terrestrial and lunar samples indicates that large silicate reservoirs on Earth and the moon (such as a magma ocean residue, a depleted mantle, or a crust) formed more than 50 million years after the oldest meteorites formed.

Application of realistic effective interactions to the structure of the Zr isotopes

We calculate the low-lying spectra of the zirconium isotopes Z=40 with neutron numbers from N=52 to N=60 using the 1p1/20g9/2 proton and 2s1d0g7/20h11/2 neutron sub-shells to define the model space. Effective proton-proton, neutron--neutron and proton-neutron interactions have been derived using 88Sr as closed core and employing perturbative many-body techniques. The starting point is the nucleon-nucleon potential derived from modern meson exchange models. The comprehensive shell-model calculation performed in this work provides a qualitative reproduction of essential properties such as the sub-shell closures in 96Zr and 98Zr.