N. A. Lebedev

Low temperature nuclear orientation of nuclei far from beta stability Spin — Facility at JINR

The experimental facility for the study of the decay of oriented nuclei in a broad range of atomic and mass number and half-lives based on hyperfine interactions at ultralow temperatures — the SPIN facility at JINR — is described. High cooling power top loading 3He-4He dilution refrigerator of the system is capable of fast cooling of the sample inserted into the mixing chamber to the base temperature 10 mK for about 1–2 h. Detection system is designed for the study of angular distribution and temperature dependence of the anisotropy of gamma rays, linear polarisation of gamma rays and NMR/ON studies. Some results of nuclear orientation studies in off-line mode of radioactive nuclei with the half-live down to ∼1 h produced by spallation reaction with 660 MeV protons are presented. The project of nuclear orientation system on-line to the mass-separator and the new 600 MeV Dubna proton phasotron is described.

Production, concentration and deep purification of 111In radiochemicals

A new method of 111In separation from a silver target irradiated with 30 MeV alpha-particles is described. The 111In isolation from Ag and Cd is based on its co-precipitation with La(OH)3. The 111In separation from La(III) has been performed by the method of ion-exchange chromatography. A multi-stage purification technique was developed that allows the production of 111In radiochemicals in which the part of impurities of di-, tri-valent metal atoms is negligible.

Nuclear orientation of156Tb in gadolinium matrix

The anisotropy of the angular distribution of gamma-rays from the decay of156Tb, oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction in the range of temperatures from 14·6 to 68·4 mK. The temperature dependence of anisotropy was measured for the first time. The parameters of hyperfine magnetic dipole and electric quadrupole splittings have been determined and the values of the magnetic dipole moment ¦Μ156¦=(9·6±1·3)×10−27 J/T and the electric quadrupole momentQ156=(2·9±0·9)×10−28 m2 of the156Tb ground state have been calculated. Multipole mixing ratios andB(E2) branching ratios of many gamma-ray transitions occurring in156Gd have been found and the results have been discussed in terms of the rotational-vibration and pairing-plus-quadrupole models.

Separation of 90Nb from zirconium target for application in immuno-PET

Abstract Fast progressing immuno-PET asks to explore new radionuclides. One of the promising candidates is 90Nb. It has a half-life of 14.6 h that allows visualizing and quantifying biological processes with medium and slow kinetics, such as tumor accumulation of antibodies and antibodies fragments or drug delivery systems and nanoparticles. 90Nb exhibits a positron branching of 53% and an average kinetic energy of emitted positrons of Emean =0.35 MeV. Currently, radionuclide production routes and NbV labeling techniques are explored to turn this radionuclide into a useful imaging probe. However, efficient separation of 90Nb from irradiated targets remains in challenge. Ion exchange based separation of 90Nb from zirconium targets was investigated in systems AG 1 × 8 – HCl/H2O2 and UTEVA-HCl. 95Nb (t1/2 = 35.0 d), 95Zr (t1/2 = 64.0 d) and 92mNb (t1/2 = 10.15 d) were chosen for studies on distribution coefficients. Separation after AG 1 × 8 anion exchange yields 99% of 90/95Nb. Subsequent use of a solid-phase extraction step on UTEVA resin further decontaminates 90/95Nb from traces of zirconium with yields 95% of 90/95Nb. A semi-automated separation takes one hour to obtain an overall recovery of 90/95Nb of 90%. The amount of Zr was reduced by factor of 108. The selected separation provides rapid preparation (< 1 h) of high purity 90Nb appropriate for the synthesis of 90Nb-radiopharmaceuticals, relevant for purposes of immuno-PET. Applying the radioniobium obtained, 90/95Nb-labeling of a monoclonal antibody (rituximab) modified with desferrioxamine achieved labeling yields of >90% after 1 h incubation at room temperature.

Improved limits on β− and β−β− decays of 48Ca

New limits on 48Caβ− and β−β− decays to excited states of 48Ti have been obtained using a 400 cm3 low-background HPGe detector and an external source of 24.558 g enriched CaF2 powder (9.822 g of 48Ca). The limits for β− decay to the 6+ ground state and excited 5+ and 4+ states in 48Sc are 1.6×1020 yr, 2.5×1020 yr, and 1.9×1020 yr at the 90% confidence level. For the β−β− decay to 48Ti, the limits to the first 2+, second 2+, and first 0+ excited states are 1.8×1020 yr, 1.5×1020 yr, and 1.5×1020 yr, again at the 90% confidence level.

Nuclear orientation studies of the 51·5 min167Lu decay

Anisotropies of γ rays emitted in the decay of167Lu,T1/2=51·5 min, were measured. The167Lu was oriented by the hyperfine interaction when the lutetium activity was included in a gadolinium host which was cooled to 15 mK temperature. A top-loading3He∶4He dilution refrigerator capable of quickly cooling a short-lived sample was used. Multipole mixing ratios have been evaluated for many transitions. The spin assignments have been made for a number of levels in167Yb and their parities have been deduced. In particular, an unambiguous 11/2− assignment was made for the 571·5 keV level which was identified as the band head of the 11/2− [505] band observed by Lindblad. The rotational bands in167Yb are discussed.

Behavior of Actinium, Alkaline, and Rare Earth Elements in Sr-Resin/Mineral Acid Systems

In this work, the interactions between the divalent alkaline earth elements (AEE) (Sr, Ba, Ra), the trivalent rare earth elements (REE) (Ce-Lu, Y), and Ac(III) with Sr-resin were investigated in the presence of HNO3, HCl, HBr, HClO4, and HPF6. Distribution coefficients of these ions on the Sr-resin were determined under batch-loading conditions. Lastly, online column separations were performed to demonstrate the utility of these systems. Substantial differences in the behavior of the ions in solutions comprised of the five different acids were observed. These differences can partly be explained by a combination of ion exchange (primary) and extraction (solvation) mechanisms. From a practical point of view, the Sr-resin/HClO4 or Sr-resin/HPF6 systems were demonstrated to be effective for the separation and purification of the different groups of the elements.

Sorption of Rare-Earth Elements and Ac on UTEVA Resin in Different Acid Solutions

ABSTRACT The distribution of some rare-earth elements (REEs) on Uranium and TEtraValent Actinides (UTEVA) resin was determined from different concentrations of inorganic (HCl, HNO3, HClO4, HPF6) and one organic acid – CCl3COOH. Low sorption of all REEs in the range of 1 M–5 M HNO3 was observed. In more concentrated HNO3, a rapid increase of the distribution coefficients (Kd) was noticed with an increase in the atomic number of the lanthanides as well as in Y and Sc. The system UTEVA–CCl3COOH showed a higher selectivity for Eu(III). Chromatographic elution profiles were checked in order to confirm the obtained Kd values.

Development of a γ-γ-perturbed angular correlation one-detector method (1-PAC) for investigation of physico-chemical properties of matter

Abstract A new method of the perturbed angular γ – γ -correlation (PAC) measurements was developed using one HPGe detector only (1-PAC). For quantifying the perturbation factor, the ratio R γ 1 + γ 2 of the summing peak composed of two cascade γ -rays (the perturbation-affected parameter) to the summing peak composed of one γ -ray and one X-ray (the perturbation non-affected parameter) was used. This method was demonstrated for the radionuclides 111 In and 111m Cd, identifying the chemical status of the radionuclides in aqueous solutions.

Directional correlations of γ-rays in149Gd

Theγ-γ directional correlations for cascades observed in the 4.1 hour149Tb decay were measured on the multidetector system consisting of 7 Ge (Li) detectors. The results together with the experimental data on the internal electron conversion allowed a model-independent assignment of the spin values at a confidence level higher than 95% for three levels in149Gd: 325 keV 3/2−, 817 keV 3/2− and 1206 keV 1/2−. Multipole mixing ratios for sixγ-transitions were also derived.