Effects of nuclear orientation on fusion and fission in the reaction using 238U target nucleus

Fission fragment mass distributions in the reaction of 30Si+238U were measured around the Coulomb barrier. At the above-barrier energies, the mass distribution showed a Gaussian shape. At the subbarrier energies, triple-humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at AL/AH ~ 90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections for 30Si+238U. The cross-section for 263Sg at the abovebarrier energy agree with the statistical model calculation which assumes that the measured fission cross-section originates from fusion-fission, whereas the one for 264 Sg measured at the sub-barrier energy is smaller than the calculation, which suggests the presence of quasifission

Design report of the KISS-II facility for exploring the origin of uranium

One of the critical longstanding issues in nuclear physics is the origin of the heavy elements such as platinum and uranium. The r-process hypothesis is generally supported as the process through which heavy elements are formed via explosive rapid neutron capture. Many of the nuclei involved in heavy-element synthesis are unidentified, short-lived, neutron-rich nuclei, and experimental data on their masses, half-lives, excited states, decay modes, and reaction rates with neutron etc., are incredibly scarce. The ultimate goal is to understand the origin of uranium. The nuclei along the pathway to uranium in the r-process are in "Terra Incognita". In principle, as many of these nuclides have more neutrons than 238U, this region is inaccessible via the in-flight fragmentation reactions and in-flight fission reactions used at the present major facilities worldwide. Therefore, the multi-nucleon transfer (MNT) reaction, which has been studied at the KEK Isotope Separation System (KISS), is attracting attention. However, in contrast to in-flight fission and fragmentation, the nuclei produced by the MNT reaction have characteristic kinematics with broad angular distribution and relatively low energies which makes them non-amenable to in-flight separation techniques. KISS-II would be the first facility to effectively connect production, separation, and analysis of nuclides along the r-process path leading to uranium. This will be accomplished by the use of a large solenoid to collect MNT products while rejecting the intense primary beam, a large helium gas catcher to thermalize the MNT products, and an MRTOF mass spectrograph to perform mass analysis and isobaric purification of subsequent spectroscopic studies. The facility will finally allow us to explore the neutron-rich nuclides in this Terra Incognita.Comment: Editors: Yutaka Watanabe and Yoshikazu Hirayam

Study of fission using multi-nucleon transfer reactions

Multi-nucleon transfer channels of the reactions of 18O+232Th, 18O+238U, 18O+248Cm were used to measure fission-fragment mass distribution for various nuclides and their excitation energy dependence. Predominantly asymmetric fission is observed at low excitation energies for all the studied cases, with an increase of the symmetric fission towards high excitation energies. Experimental data are compared with predictions of the fluctuation-dissipation model, where effects of multi-chance fission (neutron evaporation prior to fission) was introduced. It was shown that a reliable understanding of the observed fission fragment mass distributions can be obtained only invoking multi-chance fissions

Chemical Characterization of a Volatile Dubnium Compound, DbOCl3

The formation and the chemical characterization of single atoms of dubnium (Db, element 105), in the form of its volatile oxychloride, was investigated using the on-line gas phase chromatography technique, in the temperature range 350–600 °C. Under the exactly same chemical conditions, comparative studies with the lighter homologues of Group 5 in the Periodic Table clearly indicate the volatility sequence being NbOCl3 > TaOCl3 ≥ DbOCl3. From the obtained experimental results, thermochemical data for DbOCl3 were derived. The present study delivers reliable experimental information for theoretical calculations on chemical properties of transactinides

In-beam fission study for Heavy Element Synthesis

Fission fragment mass distributions were measured in heavy-ion induced fissions using 238U target nucleus. The measured mass distributions changed drastically with incident energy. The results are explained by a change of the ratio between fusion and qasifission with nuclear orientation. A calculation based on a fluctuation dissipation model reproduced the mass distributions and their incident energy dependence. Fusion probability was determined in the analysis. Evaporation residue cross sections were calculated with a statistical model in the reactions of 30Si + 238U and 34S + 238U using the obtained fusion probability in the entrance channel. The results agree with the measured cross sections for seaborgium and hassium isotopes

In-beam Fission Study at JAEA

Fission fragment mass distributions were measured in heavy-ion induced fissions using 238U target nucleus. The measured mass distributions changed drastically with incident energy. The results are explained by a change of the ratio between fusion and quasifission with nuclear orientation. A calculation based on a fluctuation dissipation model reproduced the mass distributions and their incident energy dependence. Fusion probability was determined in the analysis. Evaporation residue cross sections were calculated with a statistical model in the reactions of 30Si + 238U and 34S + 238U using the obtained fusion probability in the entrance channel. The results agree with the measured cross sections for seaborgium and hassium isotopes