Yu. V. Yushkevich

Experimental complex to study nuclei far from the beta-stability line — ISOL-facility YASNAPP-2

Abstract A complex of physics installations (YASNAPP-2 complex) developed for spectroscopic investigations of short-lived isotopes in the proton beam of the JINR phasotron is briefly described. The complex consists of a proton line, a target unit, an electromagnetic mass separator, an ion beam transport system and different spectrometric installations. Some physics results of investigations of short-lived nuclides in the rare earth region are presented.

Ultra-pure 236Pu and 237Pu for environmental and biomedical research

Abstract Isotopically pure 236Pu (>99.999% by activity) has been produced by irradiating U (95% 235U) with 4He ions and refining the product by electromagnetic mass separation. Further developments in the production of 237Pu are also reported, giving material containing, by activity, only 3 × 10−6% 236Pu and probably only ∼ 10−5% 238Pu.

Extraction of ions from a plasma source and formation of beams

The current of ions extracted from a plasma source has been measured as a function of extraction voltage Ue. Comparison of the obtained characteristics to theoretical predictions has shown that the experimental data agree with the Child-Langmuir theory only within a certain range of Ue. The results of our measurements and computer simulation of the ion-beam profile allowed the assessment of the parameters of the ion-emitting surface and the average ion energy in the plasma of the source under study.

New neutron deficient isotopes with mass numbersA=136 and 145

Previously unobserved nuclei of136Sm (T1/2=42+4 s) and145Dy(t1/2=18+3 s) have been identified using an on-line mass separating facility, operating on a 1 GeV proton beam /1/.

Numerical Model for Extraction of Ions from Plasma

The ion-extraction process is investigated using the numerical model of a plasma ion source. The operating characteristics of the ion-optical system, such as the dependence of the plasma meniscus surface and the ion current on the extraction voltage, are found. In particular, it is shown that the ion current-extraction voltage characteristic is represented by the expression I = AU3/4, which differs from the well-known Child-Langmuir formula. Some new characteristics of the ion-optical system—its dynamic perveance and effective emitting area—are introduced.

Excited states of the doubly odd deformed nucleus 160Tm

Abstract The decay of 4.8 min 160 Yb has been investigated by means of Ge(Li) detectors, toroidal and magnetic-lens β-spectrometers and scintillation counters. The singles spectra of γ-rays and conversion electrons as well as prompt and delayed γ-γ and γ-ce coincidences have been measured. The 160 Tm level scheme is proposed including 94.5% of the total γ-ray intensity observed in the 160 Yb decay. The lifetimes of the 42.02, 174.40 and 215.78 keV states have been determined to be 1.6±0.3, 17±1 and 0.65±0.15 ns, respectively. From the analysis of the experimental data, the quantum characteristics of 160 Tm levels are proposed. Experimental γ-ray transition probabilities are compared with Weisskopf and Nilsson estimates, the latter also taking into account pairing correlations.

Plasma sources of ions of solids

Three variants of the design of ion sources are described: (1) with a hollow cathode and an anode-evaporator system in the rear part of the source, (2) with a cylindrical anode, and (3) with a hollow cathode and an anode in the front part. It is shown that these sources are most suitable for obtaining ion beams of solid-state elements and provide ion currents of ∼70–100 μA (for Al, Bi, As, Sb), 25 μA (Eu), and 15–30 μA (Fe, V, Cr, and doubly charged and molecular ions). Such sources are characterized by a relatively long operation time (tens of hours) and a low energy consumption level (300–400 W). The operational principle of ion sources is described with consideration for the differences in their designs. The experimental results are presented: the dependences of the ion currents on the discharge current, cathode current, and induction of the magnetic field of the source’s electromagnet, as well as the results of the computer simulations that are based on a numerical model of the ionization of atoms in the source.

Production of 237Pu with high radiochemical purity

Abstract 237 Pu (half-life 45.3 d) is a valid metabolic tracer for the long-lived isotopes of plutonium, but its use in human subjects has previously been restricted by difficulties in producing it with acceptable isotopic purity. These difficulties have been overcome by applying mass-separation techniques to the impure product of irradiating 235 U with 25-MeV 4 He + ions.

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.

Nuclear orientation study of the decay of 173Lu

Abstract A decay study of 173Lu oriented at low temperatures in a gadolinium host is carried out. Directional distributions of 12 γ-rays in 173Yb are measured using the high-resolution Ge(Li) detectors. The E2 M1 and M2 E1 multipole mixing ratios of mixed γ-transitions are deduced. The energies and structure of the rotational band levels in 173Yb, reduced E2 and M1 transition probabilities and E2 M1 mixing ratios are calculated in the framework of the semi-microscopic quasiparticle-phonon model with a Coriolis interaction included. In general, good agreement is obtained between the experimental results and theory.