Rare-earth Isotopes Research Articles

Determination of radioisotopes of Ce, Eu, Pu, Am and Cm in low-level-wastes from power reactors

Long-lived isotopes of lanthanides and actinides are very important for the disposal of low-level radioactive wastes. These nuclides serve for risk calculations of accidents. Their determination requires radiochemical separation from high activity main nuclides. Supervision of waste vessels is done by direct non-destructive γ-spectrometry of the key nuclides:60Co for corrosion products and137Cs as for fission products as for transuranic elements. The activity ratios of the long-lived nuclides to the key nuclides are called scaling factors. They have to be determined radiochemically in the laboratory in representative samples of each waste type. They are used for activity calculations of long-lived nuclides in the waste vessels. The scaling factors determined are of the order of magnitude of 10−6 and due to the fact that we have used low-level measurement techniques, we could performe the necessary chemical separations in a laboratory not exceeding the 10-fold free-level limit.

Plutonium Incineration in LWR's by a Once-Through Cycle with a Rock-Like Fuel

AbstractPlutonium incineration in a uranium-free fuel by a once-through burning cycle in LWR’s followed by geological disposal of the rock-like material as a high level waste is discussed here. For burning plutonium of various origins, zirconium oxide is a promising candidate as inert matrix because it is stabilised by rare earth oxides (Er, Ho, Eu … Y) in a single phase solid solution with a stable cubic structure. In this material, selected rare earth isotopes can also act as burnable poisons. The spent fuel may be licensed as waste material on the basis of the inventory, the stability of the material and the behaviour of natural analogue material (e.g. baddeleyite). A fuel composed of 90-80% ZrO2, 7–14% PuO2 and 3–6% Er2O3 (At%), with potential addition of Y2O3 (as additional stabiliser), is suggested for experimental study. Such a fuel employed in LWR's could generate power effectively while transmuting about 95% of the 239Pu

Tracing emissions from coal-fired power plants with enriched rare earth isotopes

Tracing emissions from coal-fired power plants with enriched rare earth isotopes

Determination of rare earth elements in high purity rare earth oxides by liquid chromatography, thermionic mass spectrometry and combined liquid chromatography/thermionic mass spectrometry

A high-performance liquid Chromatographie (HPLC) method for the determination of rare earth elements in rocks has been modified and used for the determination of rare earth elements (REE) in high purity rare earth oxides. The detection limit was 1–1.5 ng or 2–3 mg kg when a solution corresponding to 0.5 mg of the rare earth oxide was injected. The REE determination was also carried out by adding a mixture of selected REE isotopes to the sample and analysing the collected HPLC-fractions by mass spectrometry (MS) using a thermionic source. Since the matrix element was not collected, interference from this element during the mass spectrometric analysis was avoided. Detection limits as low as 0.5 mg kg could then be obtained. Detection limits as low as 0.05 mg kg were possible by MS without HPLC-pre-separation, but this approach could only be used for those elements that were not affected by the matrix. Commercial samples of high purity Nd 2O 3, Gd 2O 3 and Dy 2O 3 were analysed in this study, and a comparison of results obtained by HPLC, combined HPLC/MS and direct MS are presented.

Tracing fly ash emitted from a coal-fired power plant with enriched rare-earth isotopes: An urban scale test

Artificially enriched isotopes of neodymium (Nd) were released from a 100 MW(e) coal-fired power plant at rates ranging from 40 to 61 mg h −1 in an experiment designed to test a new intentional particulate tracer technique. During each release, ambient samples of airborne particles with diameters < 2.5 μm were collected for 6 h at 13 locations along a 72° arc 20 km from the plant on 47-mm diameter Teflon filters operated at nominal flow rates of 130 l min −1. Samples collected when estimates of the meteorological dispersion parameter, X/ Q, ranged from 0.3 × 10 −10 to 350 × 10 −10 s m −3, were analysed for total Nd mass and excess 148Nd, the tracer isotope, by thermal-ionization mass spectrometry. Measured concentrations were in good agreement with predictions of ambient tracer concentrations made with a Gaussian plume model in which lateral and vertical plume dispersion parameters were derived from the standard deviation of the horizontal wind direction. The observed tracer concentrations correspond to signal-to-noise ratios ( S: N) of 150–450. The concentration of 148Nd measured in particles <0.65 μm in diameter corresponds to an S: N in excess of 4500.

Algebraic treatment of giant dipole resonances built on excited states.

An algebraic method for the description of giant dipole resonances built on discrete excited states of both spherical and deformed nuclei is presented within the framework of the interacting boson model. Applications to lanthanide and actinide isotopes are discussed and the effect of \ensuremath{\gamma} deformation is also investigated.

Evaporation techniques for preparing rare-earth targets used in heavy-ion nuclear physics

The preparation techniques for producing targets of rare-earth isotopes depend greatly upon the chemical and physical properties of the particular rare-earth element. In most cases the isotope is supplied in the oxide form requiring a reduction to the metallic form. Collection efficiencies will be discussed.

Organic matter and containment of uranium and fissiogenic isotopes at the Oklo natural reactors

SOME of the Precambrian natural fission reactors at Oklo in Gabon contain abundant organic matter1,2, part of which was liquefied at the time of criticality and subsequently converted to a graphitic solid3,4. The liquid organic matter helps to reduce U(VI) to U(IV) from aqueous solutions, resulting in the precipitation of uraninite5. It is known that in the prevailing reactor environments, precipitated uraninite grains incorporated fission products. We report here observations which show that these uraninite crystals were held immobile within the resolidified, graphitic bitumen. Unlike water-soluble (humic) organic matter, the graphitic bituminous organics at Oklo thus enhanced radionu-clide containment. Uraninite encased in solid graphitic matter in the organic-rich reactor zones lost virtually no fissiogenic lan-thanide isotopes. The first major episode of uranium and lead migration was caused by the intrusion of a swarm of adjacent dolerite dykes about 1,100 Myr after the reactors went critical. Our results from Oklo imply that the use of organic, hydrophobic solids such as graphitic bitumen as a means of immobilizing radionuclides in pretreated nuclear waste warrants further investigation.

Decay of the neutron-rich isotope 171Ho and the identification of 169Dy.

Neutron-rich rare-earth isotopes were produced in multinucleon transfer reactions between $^{170}\mathrm{Er}$ ions and $^{\mathrm{nat}}\mathrm{W}$ targets. On-line mass separation was used together with \ensuremath{\beta}- and \ensuremath{\gamma}-ray spectroscopy in these studies. At mass A=169, the heaviest known dysprosium isotope, 39(8) s${,}^{169}$Dy, was identified. It was observed to ${\mathrm{\ensuremath{\beta}}}^{\mathrm{\ensuremath{-}}}$ decay to the ground state of $^{169}\mathrm{Ho}$ or through a level at 1578 keV. In the A=171 mass chain, a partial decay scheme for 55(3)-s $^{171}\mathrm{Ho}$ was determined.

Investigation of neutron-rich rare-earth nuclei including the new isotopes 177Tm and 184Lu

Decays of neutron-rich isotopes in the rare-earth region were studied by means of on-line mass separation and β− γ spectroscopy using multinucleon-transfer reactions between beams of 136Xe (9 and 11.7 MeV/u), 186W (11.7 and 15 MeV/u) and 238U (11.4 MeV/u) and targets of natW and Ta. The higher beam energies appear to be advantageous for the production of such isotopes. Two new isotopes were identified: 177Tm with a half-life T 1 2 = 85 −15 +10 s , and 185Lu with T 1 2 ≈ 18 s . A new 47 s activity found at A = 171 is tentatively assigned to the decay of the new isotope 171Ho. The properties of the ground and excited states of neutron-rich lanthanide isotopes are interpreted within the shell model using the deformed Woods-Saxon potential. A change of the ground-state configuration for odd-mass neutron-rich lutetium isotopes from π 7 2 +[404] to π 9 2 −[514] is suggested, this change being due to the influence of a large hexadecapole deformation. The role of the possible isomeric state in 180Lu for the nucleosynthesis of 180mTa is discussed.

Zum Einbau von einigen Lanthaniden in Gd2Cl3 / Incorporation of Some Lanthanides into Gd2Cl3

Abstract Co-crystallization experiments with radioactive isotopes of lanthanides (Ce, Nd, Eu, Gd, Tb, Dy, Tm, Yb) show that only Tb is incorporated by Gd2Cl3 in a significant amount. The results are discussed in terms of the electronic configuration of Ln2+ ions as well as redox potentials E°(Ln3+/Ln2+).

Stable isotope enrichment techniques and ORNL separation status

The isotope separation program is described, emphasizing present state-of-the-art techniques utilized to achieve specific isotopic requirements. An interesting problem addressed here is the calutron enrichment of rare-earth isotopes where small quantities of feed (< 5 g) are available, and the unresolved feed is to be recovered and recycled. Conventional ion-source units using graphite and stainless steel deteriorate in the halogenating atmosphere or are permeable to rare-earth compounds, reducing the process efficiency. An ion source has been developed using boron nitride for containing the halogenating agent and rare-earth compounds. Tests have been successfully conducted using Lu 2O 3 and the in situ chlorinating technique with CCl 4. Collectively, 166 mg of 176Lu were recovered from two runs using 2.95 and 1.10 g of 44.5% 176Lu. Process efficiency of 10.5% was achieved, and 1.2 g of the unresolved feed were recovered. Material compatibility of the boron nitride, carbon tetrachloride, and lutetium compounds has been established.

Identification of new neutron-rich rare-earth isotopes produced in 252Cf fission.

New neutron-rich isotopes of several rare-earth elements have been identified using on-line mass separation. The observed decay rates of K x rays in the mass separated fractions for which 153\ensuremath{\le}A\ensuremath{\le}162, together with the associated \ensuremath{\gamma}-decay spectra, provided direct isotopic identifications. New isotopes observed, with values of their half lives given in parentheses, are $^{153}\mathrm{Pr}$ (4.3\ifmmode\pm\else\textpm\fi{}0.2 s), $^{155}\mathrm{Nd}$ (8.9\ifmmode\pm\else\textpm\fi{}0.2 s), $^{156}\mathrm{Nd}$ (5.47\ifmmode\pm\else\textpm\fi{}0.11 s), $^{157}\mathrm{Pm}$ (10.90\ifmmode\pm\else\textpm\fi{}0.20 s), $^{158}\mathrm{Pm}$ (4.8\ifmmode\pm\else\textpm\fi{}0.5 s), and $^{162}\mathrm{Eu}$ (10.6\ifmmode\pm\else\textpm\fi{}1.0 s). In addition, we have confirmed recent reports of the observation of $^{153}\mathrm{Nd}$ (28.9\ifmmode\pm\else\textpm\fi{}0.4 s), $^{154}\mathrm{Nd}$ (25.9\ifmmode\pm\else\textpm\fi{}0.2 s), $^{156}\mathrm{Pm}$ (26.70\ifmmode\pm\else\textpm\fi{}0.10 s), $^{159}\mathrm{Sm}$ (11.37\ifmmode\pm\else\textpm\fi{}0.15 s), and $^{160}\mathrm{Sm}$ (9.6\ifmmode\pm\else\textpm\fi{}0.3 s). These half-life values are compared to the reuslts of theoretical predictions.

A new ion source for fission-yield measurements of rare-earth isotopes

A new integrated target-ion source for fission-yield measurements of rare-earth isotopes has been developed for the Soreq on-line isotope separator (SOLIS). The source is heated by electron bombardment to a temperature of 2400° C and ionization takes place in a rhenium hot cavity. To overcome the problem of impurities which reduce the ionization efficiency, a ZrC disk was inserted in the cavity. Calculations show that because of its high thermionic emission, ZrC enhances ionization performance considerably. For example, in the presence of 10 −5 mbar of cesium impurity, the ionization efficiency of a rhenium hot cavity for the rare-earth terbium is 6%. However, with a ZrC disk, the efficiency increases to 97%.

Yields of rare earth fission products in the spontaneous fission of californium-252

Cumulative fission yields of rare earth isotopes have been determined in the spontaneous fission of252Cf by fast radiochemical separation and gamma-ray spectrometry. The determined yield values are compared with the available literature data. The yield values for147Nd,151Nd and151Pm differ from the reported values. The yield for145Ce is determined for the first time.

Operation of a high temperature ion source at the helium-jet on-line isotope separator facility HELIOS

The performance of a high temperature ion source coupled to a helium gas-jet transport system for an efficient mass separation of neutron-rich alkaline earth and lanthanide isotopes is reported and the results of overall efficiency measurements using different cluster materials in the gas-jet are given. A fast, microprocessor controlled tape transport system for γ-spectroscopic studies on short-lived isotopes is described. Some results on the decay of 3.8-s 152Pr are presented.

Quadrupolar interaction of gadolinium nuclei at the cubic sites of ferromagnetic GdAl 2

We show that unresolved quadrupolar splitting is the origin of the large width commonly observed for zero-field NMR lines of Gd on cubic sites in ferromagnetic intermetallic compounds such as GdAl 2. In contrast to earlier published results, this quadrupolar splitting could be well resolved in GdAl 2, even in powder samples provided they were appropriately prepared: e 2 qQ/h is 1.48 (1.34) MHz for 157Gd ( 155Gd) at 4.2 K. The main potential mechanisms for the quadrupolar splitting are discussed. The observed splitting is broken down into different contributions with the aid of their distinctive dependences on temperature and/or magnetization. We conclude that the largest of them, namely the isotropic relativistic quadrupolar interaction, cannot be disregarded in any metallic host. The results reported should also be taken into account for other compounds, rare-earth isotopes and measurement techniques if accurate results for the hyperfine interactions are to be obtained.

Beta-delayed proton emission observed in new lanthanide isotopes

The following new, beta-delayed proton emitters have been observed at the on-line isotope separator OASIS:120La (2.8±2s),122La (8.7±7s),123Ce (3.8±2s),141Dy (1.0±2s),141Gd, and143Dy (3.2±6s). Z-identification was achieved through observation of characteristic x-rays in coincidence with protons.

Nuclear moments and charge radii of rare-earth isotopes studied by collinear fast-beam laser spectroscopy

The collinear fast-beam laser technique is being used to measure systematically hyperfine structures and isotope shifts of unstable nuclides in the rare-earth region. This brief report gives a general survey of the results obtained for the even-Z elements64Gd,66Dy,68Er and70Yb, with emphasis on the nuclear spins and moments. They allow a rather complete mapping of the single-particle structure and the development of nuclear deformation in the N > 82 region. The spins, magnetic moments and spectroscopic quadrupole moments of159–169Yb are presented in detail.

The study of short-lived nuclei in the regionZ=59?68

β + -ray endpoint energies for mass-separated samples of neutron deficient Rare-Earth isotopes have been measured using an intrinsic germanium detector. QEC values have been obtained and new isomeric states have been identified for the first time.