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We investigated the reaction dynamics induced by the 7Be,8B+208Pb collisions at energies around the Coulomb barrier. Charged particles originated by both the col- lisions were detected by means of 6 ΔE-Eres telescopes of a newly developed detector array. Experimental data were analysed within the framework of the Optical Model and the total reaction cross-sections were compared together and with the 6,7Li+208Pb colli-sion data. According to the preliminary results, 7Be nucleus reactivity is rather similar to the 7Li one whereas the 8B+208Pb total reaction cross section appears to be much larger than those measured for reactions induced by the other weakly-bound projectiles on the same target.

The scattering process of weakly-bound nuclei at Coulomb barrier energies provides deep insights on the reaction dynamics induced by exotic nuclei. Within this framework, we measured for the first time the scattering process of the short-lived Radioactive Ion Beam (RIB) 8B (S p = 0.1375 MeV) from a 208Pb target at 50 MeV beam energy. The 8B RIB was produced by means of the in-flight facility CRIB (RIKEN, Japan) with an average intensity on target of 10 kHz and a purity about 25%. Elastically scattering ions were detected in the angular range θc.m. = 10°-160° by means of the detector array EXPADES. A preliminary optical model analysis indicates a total reaction cross section of about 1 b, a value, once reduced, 2-3 times larger than those obtained for the reactions induced by the stable weakly-bound projectiles 6,7Li on a 208Pb target in the energy range around the Coulomb barrier.

Studies on nuclear reactions relevant for astrophysics have been performed using the radioactive-isotope (RI) beams at the low-energy RI beam separator CRIB, operated by Center for Nuclear Study (CNS), the University of Tokyo. A type of measurement to study astrophysical reactions at CRIB is by the elastic resonant scattering with the thick-target method in inverse kinematics. We introduce the α resonant scattering with 7Be beam, related to the astrophysical 7Be(α, γ) reactions, which is relevant in the hot p-p chain and νp-process in supernovae. Other α resonant scattering measurements with 30S, 10Be, 15O, and 18Ne beams have been performed at CRIB, using the thick-target method.

We investigated the reaction dynamics induced by the Radioactive Ion Beams 7Be and 8B on a 208Pb target at energies around the Coulomb barrier. The two measurements are strongly interconnected, being 7Be (Sα = 1.586 MeV) the loosely bound core of the even more exotic 8B (Sp = 0.1375 MeV) nucleus. Here we summarize the present status of the data analysis for the measurement of the elastic scattering process for both reactions and the preliminary results for the optical model analysis of the collected data.

In recent years gas-phase chemical studies assisted by physical pre-separation allowed for the investigation of fragile single molecular species by gas-phase chromatography. The latest success with the heaviest group 6 transactinide seaborgium is highlighted. The formation of a very volatile hexacarbonyl compound Sg(CO)6 was observed similarly to its lighter homologues molybdenum and tungsten. The interactions of these gaseous carbonyl complex compounds with quartz surfaces were investigated by thermochromatography. Second-generation experiments are under way to investigate the intramolecular bond between the central metal atom of the complexes and the ligands addressing the influence of relativistic effects in the heaviest compounds. Our contribution comprises some aspects of the ongoing challenging experiments as well as an outlook towards other interesting compounds related to volatile complex compounds in the gas phase.

Studies on nuclear astrophysics, nuclear structure, and other interests have been performed using the radioactive-isotope (RI) beams at the low-energy RI beam separator CRIB, operated by Center for Nuclear Study (CNS), the University of Tokyo. A typical measurement performed at CRIB is the elastic resonant scattering with the inverse kinematics. One recent experiment was on the α resonant scattering with 7Li and 7Be beams. This study is related to the astrophysical 7Li/7Be(α,γ) reactions, important at hot p-p chain and νp-process in supernovae. There have also been measurements based on other experimental methods. The first THM measurement using an RI beam has been performed at CRIB, to study the 18F(p, α)15O reaction at astrophysical energies via the three body reaction 2H(18F, α15O)n. The 18F(p, α) 15O reaction rate is crucial to understand the 511-keV γ-ray production in nova explosion phenomena, and we successfully evaluated the reaction cross section at novae temperature and below experimentally for the first time.

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, and the values were consistent with those determined from the evaporation residue cross sections.

Several alpha-induced astrophysical reactions have been studied at CRIB (CNS Radioactive Ion Beam separator), which is a low-energy RI beam separator at Center for Nuclear Study (CNS) of the University of Tokyo. Two major methods to study them are the α resonant scattering, and direct measurements of (α,p) reactions using an active or inactive helium gas target. Among the recent studies at CRIB, the measurement of 7Be+α resonant scattering is discussed.

Fragment mass distributions for fission after full momentum transfer were measured in the reactions of 30Si,34,36 S,31P,40Ar + 238U at bombarding energies around the Coulomb barrier. Mass distributions change significantly as a function of incident beam energy. The asymmetric fission probability increases at sub-barrier energy. The phenomenon is interpreted as an enhanced quasifission probability owing to orientation effects on fusion and/or quasifission. The evaporation residue (ER) cross sections were measured in the reactions of 30Si + 238U and 34S + 238U to obtain information on fusion. In the latter reaction, significant suppression of fusion was implied. This suggests that fission events different from compound nucleus are included in the masssymmetric fragments. The results are supported by a model calculation based on a dynamical calculation using Langevin equation, in which the mass distribution for fusion-fission and quasifission fragments are separately determined.

The influence of the nuclear structure of projectile and target nuclei on the capture cross-sections was investigated in the fusion reactions 34S+204,206,208Pb and 36S+204,206,208Pb. Capture cross-sections were deduced from the fission fragments measured with multi-wire proportional counters. Significantly enhanced capture-fission cross-sections were observed for the 34S induced reactions compared to 36S at beam energies below the interaction barriers. The experimental results were compared to a coupled-channel calculation. The enhancement was explained by strong couplings to vibrational states of the 34S with 204,206,208Pb. The capture and evaporation residue cross-sections of 34S+208Pb and 36S+206Pb reactions which lead to the same compound nucleus 242Cf are compared and discussed.

Abstract: A cryogenic gas target system was developed for the radioisotope (RI) beam production at CNS Radio Isotope Beam separator (CRIB). Hydrogen gas was cooled to 85–90K using liquid nitrogen and used as a secondary beam production target having a thickness of . An intense 7Be beam ( particles per second) was successfully produced using this target. We observed a density-reduction effect at the gas target for high-current primary beams with about 7.5W heat deposition. One main feature of the target system is forced circulation of the target gas. We have found that the circulation of the target gas at a rate of 55 standard liters per minute (slm) was effective in eliminating the density reduction. The extent to which the forced flow can prevent the density reduction had not been known well. In this work, the relation between the density reduction and the forced circulation rate was quantitatively studied. [Copyright &y& Elsevier]

A new method to produce spin-polarized radioactive nuclear beams has been developed, which takes advantage of the low-energy transfer reaction in inverse kinematics. The method provides beam energies of a convenient range so that they may be implanted in a thin stopper, yet allowing the stopper to be spatially separated from the production target. The presence of polarizations of sizes at least $\left|P\right|\sim 0.5 \%$ has been confirmed for a 17N beam obtained from 9Be(18O,17N) reaction at $\theta_{\rm Lab} \sim -1.7\,^{\circ}$ . [ABSTRACT FROM AUTHOR]

A new high-spin isomer in 150Dy has been observed at an excitation energy of 10.3 MeV by combining the inverse-kinematic reaction induced by a pulsed beam of 152Xe and the γ-ray recoil-shadow technique. The half-life of this isomeric state has been determined to be T⅛ = 1.6±0.6 ns using the conventional centroid-shift method with the 141Pr(16O, p6n)150Dy reaction at 165 MeV. The mechanism producing high-spin isomers in N = 83,84 isotones is qualitatively discussed in terms of the difference of the neutron particle-hole configuration between the high-spin isomer and the lower-lying state. [ABSTRACT FROM AUTHOR]

High-spin isomers were systematically studied in N = 83 isotones. These isomers are of stretch coupled configurations and have oblate shapes. High-spin isomers can be categorized to be high-spin shape isomer, as they are caused by the sudden shape change from near spherical to an oblate shape. These isomers are considered to be a good example of the nuclear Jahn-Teller effect. By the systematic study of high-spin isomers, several results were obtained, such as (1) change of Z = 64 sub-shell gap energy and (2) experimental pairing gap energy at high-spin states. The Z = 64 sub-shell gap energy was found to decrease from 2.4 to 1.9 MeV as the proton number decreases from 64 to 60. Paring gap energies of high-spin states were experimentally extracted by the three-point expression using binding energies and excitation energies of high-spin isomers. These pairing gap energies at high-spin states are as large as those of the ground states, even though isomers have oblate shapes( β ∼ - 0.19). [ABSTRACT FROM AUTHOR]