Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session DL: Nuclear Reactions: Heavy-Ions/Rare Isotope Beams II |
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Chair: Filomena Nunes, Michigan State University Room: Queens 6 |
Thursday, October 15, 2009 7:00PM - 7:15PM |
DL.00001: Statistical model of heavy-ion fusion-fission reactions John Lestone, Scott McCalla Methods commonly used to estimate the Bohr-Wheeler fission decay width are incorrect for several reasons. After making corrections to standard computational techniques, we find the cross-section and neutron-emission data from heavy-ion fusion-fission reactions are consistent with the fission of fully equilibrated systems with fission lifetime estimates obtained via a Kramers-modified statistical model. The strong increase in the nuclear viscosity above a temperature of $\sim $1.3 MeV deduced by others is an artifact generated by an inadequate model. [Preview Abstract] |
Thursday, October 15, 2009 7:15PM - 7:30PM |
DL.00002: Fusion of $^{124}$Sn with $^{40,48}$Ca A. Villano, H. Amro, F.D. Becchetti, J.J. Kolata, A. Roberts, D. Shapira, J.F. Liang, C.J. Gross, R.L. Varner, E. Chavez, W. Loveland Fusion of $^{124}$Sn with $^{40,48}$Ca near and below the barrier has been measured at ORNL. The ultimate goal is to compare with fusion of $^{132}$Sn on the same targets to study the effects of neutron excess and neutron-transfer Q-values on fusion. The Ca isotopes are ideal for this purpose since an identical $^{172}$Yb composite system is produced using two essentially spherical targets, thus reducing deformation effects on fusion. The $^{124}$Sn+$^{48}$Ca system displays weak sub-barrier fusion enhancement which is completely accounted for by coupling to the first 2$^+$ and 3$^-$ states in the target and projectile, but $^{124}$Sn+$^{40}$Ca fusion is strongly enhanced below the barrier. This effect appears to be related to the large positive Q-values for $^{124}$Sn+$^{40}$Ca neutron transfer reactions. The implications for $^{132}$Sn+$^{40,48}$Ca fusion will be discussed. [Preview Abstract] |
Thursday, October 15, 2009 7:30PM - 7:45PM |
DL.00003: Fast neutron-induced fission of Pu-240, Am-243 and W-nat A. Laptev, R. Haight, O. Shcherbakov, A. Vorobyev, A. Carlson The fast neutron-induced fission cross sections of Pu-240, Am-243, W-nat and Bi-209 have been obtained relative to the fission cross section of U-235 for incident neutrons from 1 MeV to 200 MeV in ``shape'' experiments. The measurements were done at the GNEIS facility simultaneously for each investigated isotopic target using two multiplate ionization chambers and the time-of-flight (TOF) technique on a 48-m flight path. The pulsed ``white spectrum'' neutron source GNEIS had an average intensity of 3 x 10$^{14}$ n/s, burst duration 10 ns and repetition rate 50 Hz. The statistical uncertainty of the measured cross section ratios for the actinide nuclei Pu-240 and Am-243 is about 2{\%} at neutron energies above fission threshold and is less than 10{\%} for the natW at energies above 150 MeV. The systematic error budget is discussed. In addition, the fission cross section of Bi-209 has been obtained to compare with results of previous experiments. The new fission cross section of U-235(n,f) from the international standards evaluation was used to convert the ratio data to fission cross-sections. Finally the shape fission cross section measurements were normalized using the new evaluations from the ENDF/B-VII.0 library for the actinides, while for the sub-actinides the normalization was done using the target thicknesses of investigated and reference (U-235) nuclei. The fission cross section of Am-243 above $\sim$40 MeV was measured for the first time and that of W-nat was measured for the first time with a ``white spectrum'' neutron source. [Preview Abstract] |
Thursday, October 15, 2009 7:45PM - 8:00PM |
DL.00004: Production of the Heaviest Elements Using RIBs Walter Loveland Previously we have evaluated quantitatively the prospects for the synthesis of transactinide nuclei using radioactive beams (PRC {\bf 76}, 014612 (2007)). We have revised these calculations to include current approaches to properly deal with the excitation energy dependence of shell and pairing corrections along with recent experimental advances in our understanding of the fusion probability, P$_{CN}$ and the capture cross sections for very neutron-rich systems. Using our simple formalism for calculating the complete fusion cross sections that reproduces the known heavy element production cross sections over six orders of magnitude, we calculate the production rates for transactinide nuclei with Z $\leq$ 120 using modern proposed radioactive beam facilities. All possible projectile and target combinations are evaluated. New possibilities for studies of the atomic physics, chemistry and nuclear spectroscopy of the heaviest elements exist at modern radioactive beam facilities. Examples of possible experiments at pre-FRIB facilities will be discussed. The synthesis of new heavy elements is best undertaken at stable beam accelerators. [Preview Abstract] |
Thursday, October 15, 2009 8:00PM - 8:15PM |
DL.00005: Estimating Super Heavy Element Event Random Probabilities Using Monte Carlo Methods Mark Stoyer, Roger Henderson, Jacqueline Kenneally, Kenton Moody, Sarah Nelson, Dawn Shaughnessy, Philip Wilk Because superheavy element (SHE) experiments involve very low event rates and low statistics, estimating the probability that a given event sequence is due to random events is extremely important in judging the validity of the data. A Monte Carlo method developed at LLNL [1] is used on recent SHE experimental data to calculate random event probabilities. Current SHE experimental activities in collaboration with scientists at Dubna, Russia will be discussed. \\[4pt] [1] N.J. Stoyer, et al., Nucl. Instrum. Methods Phys. Res. A 455 (2000) 433. [Preview Abstract] |
Thursday, October 15, 2009 8:15PM - 8:30PM |
DL.00006: Gamow-Teller transition strengths in the intermediate nucleus of the $^{116}$Cd double-$\beta$ decay by the $^{116}$Cd$(p,n)$ and $^{116}$Sn$(n,p)$ reactions at 300~MeV Masaki Sasano, Hideyuki Sakai, Kentaro Yako, Kenjiro Miki, Shumpei Noji, Tomotsugu Wakasa, Masanori Dozono, Kunihiro Fujita, Mark Greenfield, Kichiji Hatanaka, Takahiro Kawabata, Hironori Kuboki, Yukie Maeda, Hiroyuki Okamura, Yasuhiro Sakemi, Kimiko Sekiguchi, Yohei Shimizu, Yuji Tameshige, Atsushi Tamii, Tomohiro Uesaka, Yoshiko Sasamoto, Keisuke Itoh, Kazuo Muto Gamow-Teller (GT) transition strengths in the intermediate nucleus of the $^{116}$Cd double-$\beta$ ($\beta\beta$) decay, namely $^{116}$In have been studied by measuring the double differential cross sections for the $^{116}$Cd$(p,n)$ and $^{116}$Sn$(n,p)$ reactions at 300~MeV over a wide excitation-energy region including GT giant resonance (GTGR). A large amount of the strengths in the $\beta^+$ direction has been newly found in the GTGR region ($E_x=5$ to 20~MeV), which may indicate that a large part of the nuclear matrix element of the two-neutrino $\beta\beta$ decay comes from this region as well as the cancellation due to phase. [Preview Abstract] |
Thursday, October 15, 2009 8:30PM - 8:45PM |
DL.00007: Distinction between Proton- and Neutron-Density Distributions of Halo Nuclei at the Nuclear Surface via Reaction Cross Sections Daiki Nishimura, M. Fukuda, M. Takechi, M. Mihara, D. Ishikawa, K. Matsuta, R. Matsumiya, T. Kuboki, T. Suzuki, T. Yamaguchi, I. Hachiuma, K. Namihira, T. Ohtsubo, Y. Shinbara, Y. Ohkuma, T. Izumikawa, K. Tanaka, A. Ozawa, Y. Yasuda, T. Moriguchi, S. Momota, S. Fukuda, S. Sato, M. Kanazawa, A. Kitagawa The halo and skin structures at the nuclear surface have attracted much interest for their exotic nature. By utilizing the isospin asymmetry of nucleon-nucleon total cross sections in the intermediate energy region, in principle, the proton- and neutron-density distributions can be determined independently. To demonstrate this isospin asymmetric effect, we have studied ${\sigma_R}$ for the neutron-halo nucleus $^{11} $Be and the proton-halo nucleus $^{8}$B on proton targets. We measured ${\sigma_R}$ for $^{11}$Be and $^{8}$B on C and proton targets by the transmission method in the intermidiate energy region using HIMAC heavy ion synchrotron at NIRS. The present result for $^{11}$Be is consistent with that the tail of $^{11}$Be density consists of a neutron. On the other hand, the experimental result for $^{8}$B is in agreement with the calculation with a proton tail in $^{8}$B. Thus, the proton and neutron density distributions at the nuclear surface can be distinguished successfully by the ${\sigma_R}$ on C and proton targets. [Preview Abstract] |
Thursday, October 15, 2009 8:45PM - 9:00PM |
DL.00008: Important role of three-body forces effect on nucleus-nucleus elastic scattering Takenori Furumoto, Yukinori Sakuragi, Yasuo Yamamoto An analysis of nucleus-nucleus ($AA$) elastic scattering is made by the double-folding model (DFM) with a new complex G-matrix interactions called CEG07. The CEG07 interactions are derived from the free-space nucleon-nucleon interaction the Extended Soft Core model, including the three-body forces (TBF) contributions composed of the two parts of three-body repulsive and attractive forces. We have tested the present microscopic DFM optical potential with CEG07 in the $^{16}$O + $^{16}$O system at $E/A$ = 70 MeV. The TBF effect is clearly seen in the cross section and the folding model potential (FMP) calculated with TBF well reproduces the experimental data up to the backward angles. The role of each part of TBR and TBA are also demonstrated in the same system. The effect of TBF is very important not only for nuclear saturation properties but also proper understanding of $AA$ elastic scattering. Furthermore, the FMP with CEG07 was compared with one with CDM3Y6 that is one of the realiable and successful effective density-dependent $NN$ interaction to be used in the DFM. [Preview Abstract] |
Thursday, October 15, 2009 9:00PM - 9:15PM |
DL.00009: ABSTRACT WITHDRAWN |
Thursday, October 15, 2009 9:15PM - 9:30PM |
DL.00010: Astrophysical S-factors from reactions with exotic nuclei Carlos Bertulani, Kazuyuki Ogata Accurate nuclear reaction rates are needed for primordial nucleosynthesis and hydrostatic burning in stars. The relevant reactions are extremely difficult to measure directly in the laboratory at the small astrophysical energies. In recent years direct reactions have been developed and applied to extract low-energy astrophysical S-factors. These methods require a combination of new experimental techniques and theoretical efforts, which are the subject of this presentation. In this talk I will discuss the role of continuum states and their mutual coupling in extracting the nuclear astrophysical information from experimental data carried out at radioactive beam facilities. [Preview Abstract] |
Thursday, October 15, 2009 9:30PM - 9:45PM |
DL.00011: A Thick Target Method for Nuclear Astrophysics Roy J. Peterson Many years ago, a wide array of nuclear reaction rates relevant to stellar nucleosynthesis was developed, applied, and compiled for proton- [1] and alpha-induced reactions [2]. A recent thin-target study of the $^{12}$C(p,$\gamma )^{13}$N reaction [3] has confirmed the accuracy one of the important examples of these thick-target thermonuclear reaction rates. The thick-target method, stopping the beam in the sample and analyzing the subsequent radioactivity or prompt gamma radiation, has many advantages, especially since it is independent of the assumed reaction mechanisms and uses all of the beam. The method and its strengths will be reviewed, and a new extension to reactions induced by radioactive ion beams in reverse kinematics in a hydrogen-rich thick sample will be presented. This method may offer advantages for the use of sparse beams. \\[4pt] [1] N. A. Roughton \textit{et al}., At. Data and Nuclear Data Tables 23, 177 (1980) \\[0pt] [2] N. A. Roughton \textit{et al}., At. Dara and Nuclear Data Tables 28, 341 (1983) \\[0pt] [3] N. Burtebaev \textit{et al}., Phys. Rev. C 78, 035802 (2008) [Preview Abstract] |
Thursday, October 15, 2009 9:45PM - 10:00PM |
DL.00012: Application of Random Matrix Theory to low-energy heavy-ion reactions Shusaku Yusa, Koichi Hagino Coupled-Channels calculations taking into account collective excitations have been applied to the analysis of heavy-ion sub-barrier fusion as well as quasi-elastic scattering and have provided good descriptions of the experimental data. Recently, however, there arise some experimental data which cannot be accounted for by such a conventional coupled-channels approach. That is, the experimental quasi-elastic barrier distribution for e.g., $^{20}$Ne + $^{92}$Zr, is much more smeared than a theoretical barrier distribution. One of the possibilities to cure this problem is to take into account single-particle excitations in the coupled-channels calculation. In order to incorporate that kind of excitations, we employ random matrix theory. In this talk, we will present model calculations for penetrability for a one dimensional potential barrier. We will compare the results in the presence of only the collective excitation to those with both collective and single-particle excitations. Effects of single-particle excitations on barrier distributions and Q-value distributions will be also discussed. [Preview Abstract] |
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