Daiya Kaji

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.

Synthesis and detection of a seaborgium carbonyl complex

A carbonyl compound that tips the scales Life is short for the heaviest elements. They emerge from high-energy nuclear collisions with scant time for detection before they break up into lighter atoms. Even et al. report that even a few seconds is long enough for carbon to bond to the 106th element, seaborgium (see the Perspective by Loveland). The authors used a custom apparatus to direct the freshly made atoms out of the hot collision environment and through a stream of carbon monoxide and helium. They compared the detected products with theoretical modeling results and conclude that hexacarbonyl Sg(CO)6 was the most likely structural formula. Science, this issue p. 1491; see also p. 1451 A special apparatus enables synthesis of a compound with carbon bonds to a short-lived element produced via nuclear reaction. [Also see Perspective by Loveland] Experimental investigations of transactinoide elements provide benchmark results for chemical theory and probe the predictive power of trends in the periodic table. So far, in gas-phase chemical reactions, simple inorganic compounds with the transactinoide in its highest oxidation state have been synthesized. Single-atom production rates, short half-lives, and harsh experimental conditions limited the number of experimentally accessible compounds. We applied a gas-phase carbonylation technique previously tested on short-lived molybdenum (Mo) and tungsten (W) isotopes to the preparation of a carbonyl complex of seaborgium, the 106th element. The volatile seaborgium complex showed the same volatility and reactivity with a silicon dioxide surface as those of the hexacarbonyl complexes of the lighter homologs Mo and W. Comparison of the product’s adsorption enthalpy with theoretical predictions and data for the lighter congeners supported a Sg(CO)6 formulation.

First online multireflection time-of-flight mass measurements of isobar chains produced by fusion-evaporation reactions: Toward identification of superheavy elements via mass spectroscopy

P. Schury, 2 M. Wada, 2 Y. Ito, D. Kaji, P.-A. Söderström, A. Takamine, F. Arai, H. Haba, S. Jeong, S. Kimura, H. Koura, H. Miyatake, K. Morimoto, K. Morita, 5 A. Ozawa, M. Reponen, T. Sonoda, T. Tanaka, 5 and H. Wollnik Institute of Physics, University of Tsukuba, Ibaraki 305-8571, Japan RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198, Japan Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK), Ibaraki 305-0801, Japan Advanced Science Research Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan New Mexico State University, Las Cruces, NM 88001, USA (Dated: November 15, 2017)

Decomposition studies of group 6 hexacarbonyl complexes. Part 1: Production and decomposition of Mo(CO)6 and W(CO)6

Abstract Chemical studies of superheavy elements require fast and efficient techniques, due to short half-lives and low production rates of the investigated nuclides. Here, we advocate for using a tubular flow reactor for assessing the thermal stability of the Sg carbonyl complex – Sg(CO)6. The experimental setup was tested with Mo and W carbonyl complexes, as their properties are established and supported by theoretical predictions. The suggested approach proved to be effective in discriminating between the thermal stabilities of Mo(CO)6 and W(CO)6. Therefore, an experimental verification of the predicted Sg–CO bond dissociation energy seems to be feasible by applying this technique. By investigating the effect of 104,105Mo beta-decay on the formation of 104,105Tc carbonyl complex, we estimated the lower reaction time limit for the metal carbonyl synthesis in the gas phase to be more than 100 ms. We examined further the influence of the wall material of the recoil chamber, the carrier gas composition, the gas flow rate, and the pressure on the production yield of 104Mo(CO)6, so that the future stability tests with Sg(CO)6 can be optimized accordingly.

Development of a gas-jet-coupled multitarget system for multitracer production

Summary A new multitracer production system, which consists of a gas-jet-coupled multitarget system for short-lived radioactive tracers and a gas- and water-cooled target system for intense beam irradiations, has been installed on a beam line of the K540 MeV RIKEN Ring Cyclotron. The performance of the gas-jet system was investigated with 50 radionuclides of 18 elements produced in the 135 MeV nucl.-1– 14N induced reaction on natCu. The gas-jet efficiencies of the nuclides varying from 61Cu to 24Na, except for the chlorine isotopes, show a smooth variation as a function of the mass difference between a product and a target. The multitracers on the natAg and 197Au targets were also produced by the 135 MeV nucl.-1– 14N beam with the intensity of 0.7 pμA, which was more than seven times the limit of the previous system.

First Direct Mass Measurements of Nuclides around Z=100 with a Multireflection Time-of-Flight Mass Spectrograph

The masses of ^{246}Es, ^{251}Fm, and the transfermium nuclei ^{249-252}Md and ^{254}No, produced by hot- and cold-fusion reactions, in the vicinity of the deformed N=152 neutron shell closure, have been directly measured using a multireflection time-of-flight mass spectrograph. The masses of ^{246}Es and ^{249,250,252}Md were measured for the first time. Using the masses of ^{249,250}Md as anchor points for α decay chains, the masses of heavier nuclei, up to ^{261}Bh and ^{266}Mt, were determined. These new masses were compared with theoretical global mass models and demonstrated to be in good agreement with macroscopic-microscopic models in this region. The empirical shell gap parameter δ_{2n} derived from three isotopic masses was updated with the new masses and corroborates the existence of the deformed N=152 neutron shell closure for Md and Lr.

Decay properties of new isotopes 234Bk and 230Am, and even-even nuclides 234Cm and 230Pu

A neutron-deficient berkelium isotope of 234Bk produced via 197Au(40Ar,3n) reaction and the daughter product of 230Am were newly identified. Alpha-decay energies of eleven 234Bk were found at 7.62–7.96 MeV, and six fission events that correlated with the α-decay of 234Bk were observed. The half-lives of 234Bk and 230Am were determined to be \(19_{ - 4}^{ + 6}\) s and \(32_{ - 9}^{ + 22}\) s, respectively. The 234Cm followed by the β-decay of 234Bk was also identified.