Takahiro Akiyama

Experiment on the Synthesis of Element 113 in the Reaction 209Bi(70Zn,n)278113

The convincing candidate event of the isotope of the 113th element, 278 113, and its daughter nuclei, 274 111 and 270 Mt, were observed, for the first time, in the 209 Bi + 70 Zn reaction at a beam energy of 349.0 MeV with a total dose of 1.7 ×10 19 . Alpha decay energies and decay times of the candidates, 278 113, 274 111, and 270 Mt, were (11.68 ±0.04 MeV, 0.344 ms), (11.15 ±0.07 MeV, 9.26 ms), and (10.03 ±0.07 MeV, 7.16 ms), respectively. The production cross section of the isotope was deduced to be 55 +150 -45 fb (10 -39 cm 2 ).

Observation of Second Decay Chain from 278113

RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198 Department of Physics, Saitama University, Saitama 338-8570 Center for Instrumental Analysis, Niigata University, Niigata 950-2181 Center for Nuclear Study, University of Tokyo, Wako, Saitama 351-0198 Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 Department of Chemistry, Niigata University, Niigata 950-2181 University of Tsukuba, Tsukuba, Ibaraki 305-8571 Department of Physics, Tohoku University, Sendai 980-8578 Department of Physics, Yamagata University, Yamagata 990-8560

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.

Experiment on Synthesis of an Isotope 277112 by 208Pb+70Zn Reaction

The production and decay of 277 112 have been investigated using a gas-filled recoil ion separator in irradiations of 208 Pb targets with a 70 Zn beam at 349.5 MeV. We have observed two α-decay chains that can be assigned to subsequent decays from 277 112 produced in the 208 Pb( 70 Zn,n) reaction. After emitting four consecutive α-particles, both the chains terminate by spontaneous fission decays of 261 Rf, and the decay energies and decay times of both the chains obtained in the present work agree well with those reported by a group at Gesellschaft fur Schwerionenforschung (GSI), Germany. The present result gives the first clear confirmation of the discovery of 277 112 and its α-decay product 273 Ds reported previously.

Characteristics of Superconducting series array tunnel junctions for heavy ions

Heavy ion detection experiments were carried out with superconducting series array tunnel junctions. /sup 40/Ar beam from linear accelerator was introduced to a cryostat and stopped in a substrate on which series array tunnel junctions were fabricated. An energy resolution of 4.2% was obtained for 191 MeV /sup 40/Ar, but linearity proved poor for energy ranges from 136 MeV to 191 MeV.

Startup of Superheavy Element Chemistry at RIKEN

Present status and perspectives of the superheavy element (SHE) chemistry at RIKEN are reviewed. A gas‐jet transport system for the SHE chemistry has been installed in the focal plane of the gas‐filled recoil ion separator GARIS at the RIKEN Linear Accelerator. The performance of the system was appraised using 206Fr and 245Fm produced in the 40Ar‐induced reactions on 169Tm and 208Pb, respectively. The α particles of 206Fr and 245Fm separated with GARIS and transported by the gas‐jet were clearly identified under desired low background condition with a rotating wheel system for α spectrometry. The high gas‐jet efficiencies over 90% are independent of the beam intensity up to 2 particle μA. A gas‐jet coupled SHE production system and a safety system for the usage of radioactive targets were also developed on the beam line of the RIKEN K70 AVF Cyclotron. The gas‐jet transport of 255No and 261Rf produced in the 238U(22Ne,5n)255No and 248Cm(18O,5n)261Rf reactions, respectively, was conducted for the future Sg ...

Experiments on synthesis of the heaviest element at RIKEN

In the Institute of Physical and Chemical Research (RIKEN), using high intensity heavy ion beams from the RIKEN Linear Accelerator, productions and decays of isotopes of the heaviest elements have been investigated by using the gas‐filled recoil separator, GARIS. The isotopes studied were 265Hs, 271Ds, 272Rg, 277112, and 278113, respectively. Based on the observed decay chains consisting of consecutive alpha decays connected to the previously known alpha decays or spontaneous fissions, assignments of the initially produced isotopes were done. Our data with the atomic number from 108 to 112, agree well with the data previously taken. The production cross section of the isotope 278113 of the 113th element have reached around 32 fb which shows the simple decrease of the cross section with the increase of the atomic number. The isotopes were produced, for the first time in the 1n evaporation channel from heavy‐ion induced fusion reaction.