B. N. Markov

Production, chemical and isotopic separations of the long-lived isomer 178Hfm2 (T1/2=31 years)

The nucleus 178Hf, with its long-lived (T1/2=31 y) high-spin isomeric state Ipi =16+, is a challenge for new and exotic nuclear physics studies. The authors describe the first experiments they have performed in order to produce a reasonable microweight quantity of this hafnium isomer with an isomeric to ground-state ratio as high as possible (here 5%). The reaction 176Yb (4He, 2n) using an enriched target has been studied by measuring the excitation functions and the isomeric to ground-state ratio. About 3*1014 isomeric atoms have been produced up to now in irradiations with high-intensity beams ( approximately=100 mu A) at the U-200 cyclotron in Dubna. Chemical separation methods could be checked using about 1013 atoms of the isomer. Isotopic separation experiments have been performed in Orsay and preliminary results are given for the separation efficiency.

On spontaneous fission of neutron-deficient isotopes of elements 103, 105 and 107

Experiments are described on the determination of the spontaneous fission probability for the isotopes of elements 103, 105 and 107 produced by bombarding Tl, Pb and Bi targets with 50Ti, 51V, 54Cr, 55Mn and 58Fe ions. The upper limit of the spontaneous fission probability is established to be 2% for the isotopes 252, 253103. A new isotope of element 105 with mass number 257(T12 = 5 s) has been produced. In bombardment of 209Bi with 54Cr ions a new spontaneous fission activity with T12 ≈ 1–2 ms has been observed. The experimental data permit identification of this activity as the isotope of the new element 107 with mass number 261, which mainly undergoes α-decay (≈ 80%) resulting in the formation of the isotope 257105. The values of the partial α-decay and spontaneous fission half-lives of the isotopes 257105 and 261107 are compared with the systematics of the properties of transfermium nuclei.

Nuclear charge radii changes of uranium and hafnium isotopes determined by laser spectroscopy

The present work reports measurements of isotope shifts and hyperfine structure in the optical spectra of two high-Z elements: Hf and U. The experiments are based on the observation of the resonance fluorescence in a well collimated atomic beam, excited by a tunable dye laser. The chains of the stable Hf isotopes and of233–236, 238U have been investigated and changes in ms nuclear charge radii have been deduced. The results have been discussed from the point of view of nuclear structure in the investigated regions.

Precise measurement of the hyperfine splitting and isotope shift of8S7/2→10P9/2 transition in241Am and243Am atoms

The hyperfine structure and isotope shift of8S7/2→10P9/2 atomic transition in241Am and243Am was measured with high-resolution by laser fluorescent spectroscopy method. The results concern nuclear moments and charge radii. We notice that the hyperfine structure for the actinide atoms are rather high compared with other elements. This offers ample scope for obtaining information about higher nuclear moments than Q and μ.

Production of spontaneously fissioning isomers 242Am and 344Am by slow neutron capture

Abstract The spontaneously fissioning isomers 242 Am and 244 Am were produced by slow neutron capture. The cross sections of isomer production were measured at different neutron energies. The correlation between isomer formation and prompt fission was observed. This correlation is discussed on the basis of the two-humped fission barrier hypothesis.

Isotope shifts and hyperfine splitting in HfI changes in nuclear charge radii of stable isotopes and182Hf

Isotope shifts and hyperfine structures in three optical transitions of HfI are investigated. Magnetic dipole coupling constant A and electric quadrupole coupling constant B of four atomic levels for both stable odd-even isotopes177Hf and179Hf are determined. Nuclear charge radii changesδ〈r2〉 of the stable Hf isotopes and182Hf (T1/2=9×106 y) are extracted using the standard semiempirical procedure. Strong deviation from muonic atom data onδ〈r2〉 is observed. The course of theδ〈r2〉 dependence on mass number indicates changes in nuclear deformation at A=174 and influence of higher order deformations on nuclear shape in this region.

Optical isotope shifts and changes in nuclear charge radii of stable Ti isotopes

Isotope shifts and hyperfine structures in three optical transitions of TiI have been investigated by using laser induced resonance fluorescence in a collimated atomic beam. From the isotope shifts data, changes of the mean square charge radii of the stable titanium isotopes have been determined for the first time. Using a combined analysis with muonic atom data on root mean square nuclear charge radii, improved model independent 〈r2〉1/2 values for the odd-even Ti isotopes have been obtained.

Hyperfine magnetic anomaly in isotopic pairs 151, 152Eu and 152, 153Eu

High-resolution laser spectroscopy measurements of optical hyperfine splitting on the 151, 152, 153Eu isotopes were performed on the atomic transition 4f76s28S7/2 → 4f76s6p6P5/2 at λ ≈ 564.58 nm. Values of the nuclear magnetic dipole and electric quadrupole moments are obtained from the measured hyperfine splitting and the magnetic hyperfine anomalies in the isotope pairs 151, 152Eu and 152, 153Eu are deduced. The absolute values of the hyperfine anomaly in both cases are unusually large: 5 (1)%. The possible sources causing these anomalies are discussed.

Hyperfine splitting constants of thea3F3 andz5G 3 0 HfI levels

The hyperfine structure and the isotope shifts in the optical transition of HfI with λ=5903 Å have been investigated using high resolution laser spectroscopy. The magnetic dipole and electric quadrupole hyperfine splitting constants of the lower 5d2 6s2a3F3 and upper 5d2 6s 6p z5G30 levels have been determined for the two stable odd hafnium isotopes177Hf and179Hf.

Study of the isomeric ratios in photonuclear reactions of natural indium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region

We have determined the isomeric ratios in 113In(γ, n)112m,g In and 113In(γ, 2n)111m,g In photonuclear reactions of natural indium induced by bremsstrahlungs with end-point energies in the giant dipole resonance (GDR) region. The investigated samples were irradiated at the electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna. The gamma spectra of the samples irradiated were measured with a spectroscopic system consisting of an 8192-channel analyzer and a high-energy resolution (180 keV at gamma ray 1332 keV of 60Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors. For both the mentioned reactions, the isomeric ratios in the bremsstrahlung energy range from 19 to 24 MeV in this work are new measurements.