Kazutaka Ozeki

New Result in the Production and Decay of an Isotope, 278113, of the 113th Element

An isotope of the 113th element, i.e., 278 113, was produced in a nuclear reaction with a 70 Zn beam on a 209 Bi target. We observed six consecutive α-decays following the implantation of a heavy particle in nearly the same position in the semiconductor detector under an extremely low background condition. The fifth and sixth decays are fully consistent with the sequential decays of 262 Db and 258 Lr in both decay energies and decay times. This indicates that the present decay chain consisted of 278 113, 274 Rg ( Z =111), 270 Mt ( Z =109), 266 Bh ( Z =107), 262 Db ( Z =105), and 258 Lr ( Z =103) with firm connections. This result, together with previously reported results from 2004 and 2007, conclusively leads to the unambiguous production and identification of the isotope 278 113 of the 113th element.

Production and decay properties of 264Hs and 265Hs

The decay properties of 264 Hs and 265 Hs produced in the 207,208 Pb( 58 Fe, x n ) ( x =1,2) reactions were studied using a gas-filled recoil ion separator at the linear accelerator facility of RIKEN. A total of six decay chains were assigned to 264 Hs. The cross sections of 264 Hs produced in the 208 Pb( 58 Fe,2 n ) and 207 Pb( 58 Fe, n ) reactions were measured to be 2.8 +6.5 -2.3 and 6.9 +4.4 -3.1 pb, respectively. The isotope 264 Hs decayed by α-particle emission (five events) and spontaneous fission (one event). The α-particle energy of 264 Hs was observed at 10.61 ±0.04 and 10.80 ±0.08 MeV.

New result on the production of 277Cn by the 208Pb + 70Zn Reaction

The production and decay properties of an isotope of the 112th element, 277Cn, were investigated using a gas-filled recoil ion separator by irradiation of 208Pb targets with 70Zn beams at 347.5, 351.5, and 355.5 MeV. The excitation function for this reaction was measured for the first time. We observed one decay event assigned to the decay of 277Cn at the beam energy of 351.5 MeV. The measured production cross section was 0.078+0.179 pb. The present result gives improved half-lives of 0.61+0.46 and 0.19+0.14 ms for 277Cn and 273Ds, respectively. At the other energies, no event was observed. The measured upper cross section limits were 0.25 and 0.15 pb at the beam energies of 347.5 and 355.5 MeV, respectively.

Production of 88Nb and 170Ta for chemical studies of element 105, Db, using the GARIS gas-jet system

A technology to utilize radioisotopes of Nb and Ta was developed for chemical studies of element 105, Db, by coupling a gas-jet transport system to the RIKEN gas-filled recoil ion separator (GARIS). 88Nb and 170Ta were generated via the natGe(19F, xn)88Nb and natGd(19F, xn)170Ta reactions, respectively. They were separated by GARIS and extracted by the gas-jet method to a chemistry laboratory under the almost same experimental conditions for 262Db produced in the 248Cm(19F, 5n)262Db reaction. Yields of 88Nb and 170Ta at the chemistry laboratory were optimized by changing the setting parameters of the GARIS gas-jet system, such as magnetic field of GARIS, energy degrader and shutter for recoil ions, and volume of the recoil transfer chamber.

Effect of Biased Disc on Brightness of Highly Charged Uranium Ions from RIKEN 28 GHz Superconducting Electron Cyclotron Resonance Ion Source

The emittance and beam intensity of highly charged heavy ions were measured as a function of the negative voltage of a biased disc. We observed that the brightness of the highly charged uranium ion beam generated by the RIKEN 28 GHz superconducting electron cyclotron resonance ion source was strongly influenced by the bias voltage.

Superheavy element nuclear chemistry at RIKEN

A gas‐jet transport system has been coupled to the RIKEN gas‐filled recoil ion separator GARIS to startup superheavy element (SHE) chemistry at RIKEN. The performance of the system was appraised using an isotope of element 104, 261Rf, produced in the 248Cm(18O,5n)261Rf reaction. Alpha‐particles of 261Rf separated with GARIS and extracted to a chemistry laboratory were successfully identified with a rotating wheel apparatus for α spectrometry. The setting parameters such as the magnetic field of the separator and the gas‐jet conditions were optimized. The present results suggest that the GARIS/gas‐jet system is a promising approach for exploring new frontiers in SHE chemistry: (i) the background radioactivities of unwanted reaction products are strongly suppressed, (ii) the intense beam is absent in the gas‐jet chamber and hence high gas‐jet efficiency is achieved, and (iii) the beam‐free condition also allows for investigations of new chemical systems.

Decay Properties of 266Bh and 262Db Produced in the 248Cm+23Na Reaction—Further Confirmation of the 278113 Decay Chain—

Decay properties of an isotope {sup 266}Bh and its daughter nucleus {sup 262}Db produced by the {sup 248}Cm({sup 23}Na,5n) reaction were studied by using a gas-filled recoil separator coupled with a position-sensitive semiconductor detector. {sup 266}Bh was clearly identified from the correlation of the known nuclide, {sup 262}Db. The obtained decay properties of {sup 266}Bh and {sup 262}Db are consistent with those observed in the {sup 278}113 chain by RIKEN collaboration, which provided further confirmation of the discovery of {sup 278}113.