[en] A double-layered target system and an identification method (target ID) for individual targets mounted on a rotating wheel using correlation with evaporation residues were newly developed for the study of superheavy elements (SHE). The target system can be used in three modes: conventional single-layered mode, double-layered mode, and energy-degrader mode. The target ID method can be utilized for masking a target, measuring an excitation function without changing the beam energy from the accelerator, and searching for SHE nuclides using multiple targets during a single irradiation

[en] In RIKEN (The Institute of Physical and Chemical Research) productions and decays of isotopes ²⁷¹110 and ²⁷²111 were studied using a gas-filled recoil ion separator (GARIS). The isotopes were produced by ²⁰⁸Pb + ⁶⁴Ni → ²⁷¹110 + n and ²⁰⁹Bi + ⁶⁴Ni → ²⁷²111 + n reactions, respectively. Fourteen α-decay chains have been assigned to be the decays originating from the isotope ²⁷¹110. The excitation function of the production cross section was measured. We have observed 14 α-decay chains that can be assigned to subsequent decays from ²⁷²111. The excitation function was also-measured. The results have provided good confirmations of productions and decays of both the ²⁷¹110 and ²⁷²111 reported by GSI group. New information on decay energies and lifetimes of the isotopes in the decay chains are also presented. Future plan of the facility is presented. (author)

[en] The upgrade Gas-Filled Recoil-Ion Separator (GARIS) has been operated in RIKEN with the high-intensity heavy-ion linac (RILAC).Three alpha-decay chains of ²⁷¹[110], which were produced by the ²⁰⁸Pb(⁶⁴Ni, n)²⁷¹[110] reaction, have been identified and thus confirmed the observation at GSI. The same system was used to observe a new isotope ²³⁴Bk by ¹⁹⁷Au(⁴⁰Ar, 3n)²³⁴Bk reaction. The data indicate a possible existence of two states in ²³⁴Bk. The decay product of ²³⁴Bk, ²³⁰Am decays mainly by β decay because no α decay has been observed. The estimated halflife of ²³⁰Am is 17⁺¹⁵_-12 s. We also report the results of search of Z=118 element. (author)

[en] The production and decay of ²⁷²111 has been investigated using a gas-filled recoil ion separator in irradiations of ²⁰⁹Bi targets with ⁶⁴Ni beam at 320, 323 and 326 MeV. We have observed 14 α-decay chains in total, that can be assigned, on the basis of their time correlations, to subsequent decays from ²⁷²111 produced in the ²⁰⁹Bi(⁶⁴Ni, 1n) reaction. The present result is the first clear confirmation for the discovery of ²⁷²111 and its α-decay products, ²⁶⁴Bh and ²⁶⁸Mt, reported previously by a GSI group. New information on their half-lives and decay energies as well as the excitation function is presented. (author)

[en] The convincing candidate event of the isotope of the 113th element, were observed, for the first time, in the ²⁰⁹Bi+⁷⁰Zn reaction at a beam energy of 349.0 MeV with a total dose of 1.7 x 1019. Alpha decay energies and decay times of the candidates, ²⁷⁸113, ²⁷⁴111, and ²⁷⁰Mt, 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_-45⁺¹⁵⁰ fb(10^-39 cm²). The experiment was performed at RIIKEN (The Institute of Physical and Chemical Research) Linear Accelerator (RILAC) Facility. The evaporation residues produced by the reaction with a ⁷⁰Zn beam provided by the RILAC and the bismuth targets, were separated by a gas-filled recoil separator (GARIS) from the beam particles and the target recoils, and collected at the focus of GARIS. We observed an event of implantation of an evaporation residue in the position-sensitive semiconductor detector followed by four consecutive alpha decays terminated by a spontaneous fission decay. Assignment of the event was based on genetic correlation of sequential alpha decays to the already known nuclides ²⁶⁶Bh and ²⁶²Db. The fourth alpha decay and the following spontaneous fission decay were assigned to be the decays of ²⁶⁶Bh and ²⁶²Db, respectively because of agreements of decay energies and decay times with the reported values. As a consequence, the preceding three alpha decays were assigned to be ones of ²⁷⁸113, ²⁷⁴111, and ²⁷⁰Mt.

[en] With the syntheses of elements up to oganesson (Z = 118), all the fusion evaporation reactions using the 48Ca beams on deformed actinide targets have already been performed. Due to the lack of target material beyond the californium, the use of 50Ti, 51V, and 54Cr is now becoming mandatory to access elements beyond the oganesson (Z = 118). In the SHE mass region, these beams have only been used in reaction on spherical Pb and Bi targets to produce neutron deficient Sg, Db, and Rf isotopes. In addition, the cross-section predictions for SHE elements past Oganesson are currently extrapolated from the reaction performed with 48Ca beams, resulting in a wide range of predictions depending on the model used. Thus, in addition to reaction parameter measurements [1,2], the precise systematic measurements of excitation functions of lighter systems based on deformed targets around lanthanide nuclei provide a suitable training dataset for training and improving the predictive power of existing models. These lighter systems are good substitutes for the deformed actinide targets used in the current search for new elements above Oganesson. They have similar deformation parameters, but at a much higher production rate (μb range). In addition, the simultaneous measurement of the barrier distribution and the excitation function allows for the direct correlation between the barrier distribution and the maximum cross-section of production. This correlation is an important part of the discussion in the selection of the optimal beam energy for the synthesis of superheavy elements [1,2]. The search for the new element Z = 119 is currently underway at RIKEN using the reaction 248Cm(51V,xn)299-x119 on the GARIS-III experimental setup [3]. The goal of this work is thus to extend the systematic study of reaction parameters with deformed targets using the 51V beam to see if the behavior observed in [1,2] can be reproduced with lighter surrogate systems. In this work, the effects of the beam energy and nuclear deformation in the reaction 159Tb(51V,xn)210-xRa have been studied by measuring both the barrier distribution and the detailed excitation functions. The goal is to extend the systematic study of the quasielastic (QE) barrier distribution with 51V and to compare it with the results obtained in [2,3] as well as theoretical prediction using the Couple Channel Calculation (CCFULL [4]). In addition, the production of the full and detailed excitation function for the xn, pxn and αxn, also allowed us to study the correlation between the barrier distribution and the maximum cross-section of production and compare it with prediction made using the Fusion-By-Diffusion model [5]. The experimental setup, analysis and preliminary results of both studies will be presented in this presentation. [1] M. Tanaka et al., J. Phy. Soc. Jpn, 91, 084201 (2022). [2] T. Tanaka et al., Phys. Rev. Lett. 124, 052502 (2020). [3] H. Sakai, H et al., Eur. Phys. J. A 58, 238 (2022). [4] K. Hagino et al., Comput. Phys. Commun. 123, 143 (1999). [5] T. Cap, M. Kowal, K. Siwek-Wilczy´nska, Eur. Phys. J. A (2022) 8:5231

[en] The half-life of the alpha emitter ¹⁴⁸Gd isotope has been measured by following the decay curve of a low activity ¹⁴⁸Gd- ²⁴¹Am mixed source. Based on two years of decay the preliminary result is T_((1)/(2)) 70.9 ± 1.0 y

[en] de021741792A 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. (orig.)

[en] Recently, we have installed a gas-jet-coupled multitarget system on the E3b beam line of RRC as an alternative to the falling ball system. In the first chamber, the 135 MeV/nucl. ¹⁴N (or ¹²C, ¹⁶O) beam from RRC passes through a HAVAR vacuum window of 6 μm thickness, and enters 30 multitarget of about 1 μm in thickness with 10 mm spacings. The recoiling multitracers are stopped in He gas, attached to aerosols such as NaCl, KCl, and C, and are continuously transported through a Teflon capillary to a hot laboratory, where the multitracers are collected on a glass filter. Then, the multitracer solutions are obtained simply by washing the filter with a suitable solution. Lastly, the ¹⁴N beam enters the thick metallic targets such as Ti, Ag, and Au, which are about 200 μm in thickness, in the second chamber. After the irradiation, the long-lived multitracers were chemically separated using the same procedure as applied previously. (orig.)

[en] An anion exchange in mineral acid and methanol system was examined in view of rapid chemical separation. An elution behavior of Bk in hydrochloric acid-methanol system was obtained using ²⁵⁰Bk. An elution behavior of Bk in nitric acid-methanol system was predicted from the relationship between an elution position and an ionic radius. The separation was completed for nitric acid-methanol system and for hydrochloric-methanol system within 40 and 25 min, respectively. (author)