Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session JJ: Light Ion Reactions |
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Sponsoring Units: DNP JPS Chair: R. Jerry Peterson, University of Colorado Room: Ritz-Carlton Hotel Hawaii |
Thursday, September 22, 2005 9:00AM - 9:15AM |
JJ.00001: Measurement of deep hole states in $^{40}$Ca by 392 MeV (p,2p) reaction Yusuke Yasuda, Harutaka Sakaguchi, Satoru Terashima, Satoshi Kishi, Juzo Zenihiro, Tetsuo Noro, Tomotsugu Wakasa, Hidetomo Yoshida, Takashi Ishida, Shun Asaji, Takahisa Yonemura, Yohsuke Hagihara, Kichiji Hatanaka, Yasuhiro Sakemi, Masaru Yosoi, Yohei Shimizu, Kinihiro Fujita, Yuji Tameshige, Hiroyuki Takeda, Masatoshi Itoh, Takahiro Kawabata, Makoto Uchida We performed $^{40}$Ca($p,2p$) experiment with 392\,MeV polarized proton beam at RCNP Osaka University and measured recoil momentum distribution of cross section and analyzing power for low lying and deep hole states in $^{40}$Ca. The aim of this experiment is to obtain information on the spectroscopic factor and the width of the deep orbital states such as the $1s_{1/2}$ state of medium nuclei for understanding the nuclear structure and correlations in deep hole states. We analyzed deep hole states with L decomposition analysis method which disentangle the contributions of each orbital states from separation energy spectra.We will report the result of $^{40}$Ca measurements. [Preview Abstract] |
Thursday, September 22, 2005 9:15AM - 9:30AM |
JJ.00002: Neutron Density distributions in $^{204,206,208}$Pb observed via polarized proton elastic scattering at 300MeV Yoshihiko Iwao, Harutaka Sakaguchi, Testuya Murakami, Yusuke Yasuda, Satoru Terashima, Zyuzo Zenihiro, Takashi Emori, Masaru Yosoi, Hiroyuki Takeda, Masatoshi Itoh, Hidetomo Yoshida, Makoto Uchida Neutron skin thickness, the difference of root mean square radii of neutron and proton distributions, for $^{208}$Pb provide a key role to discern various effective interactions used in Skyrme Hartree-Fock (SHF) and Relativistic Mean Field (RMF) models. We performed an experiment of elastic scattering of 300MeV polarized protons off $^{204,206,208}$Pb at RCNP and extracted their neutron density distributions in the framework of the relativistic impulse approximation (RIA) with medium modified NN interactions . We will report the results of the neutron skin thicknesses together with the nuclear incompressibility. [Preview Abstract] |
Thursday, September 22, 2005 9:30AM - 9:45AM |
JJ.00003: An evaporation-based model of ternary fission John Lestone Large amounts of neutron-induced, spontaneous, and heavy-ion induced ternary-fission data are analyzed within the frame work of an evaporation-based model where the complexity of time-varying potentials are included in a simplistic fashion. A free parameter which controls the height above the rupture location beyond where quasi-evaporated particles become ejected ternary-fission fragments following the rapid collapse of the necking material is adjusted to reproduce ternary-fission emission probabilities. The observed dependence of this parameter on the mass and charge numbers of the light charged particles is consistent with a neck collapse time of $\sim $10$^{-22}$ s. Without any additional adjustment to model parameters, the observed trends in the energy spectra and angular distributions of the ternary-fission particles are reproduced. The calculated ratio of the first 2$^{+}$ to ground-state population probabilities for ejected $^{10}$Be ions is 0.155, in agreement with experiment. There are indications that the neck collapse time increases with nuclear temperature. The success of the model implies that ternary fission is caused by the evaporation of particles from a rapidly changing fluid. [Preview Abstract] |
Thursday, September 22, 2005 9:45AM - 10:00AM |
JJ.00004: Spin distribution effects in neutron induced preequilibrium reactions D. Dashdorj, G.E. Mitchell, P.E. Garrett, J.A. Becker, U. Agvaanluvsan, R.A. Macri, W. Younes, T. Kawano, M. Chadwick, M. Devlin, N. Fotiades, R.O. Nelson The preequilibrium reaction (PE) mechanism makes an important contribution to neutron induced reactions above about 10 MeV. PE has been studied exclusively via the characteristic high energy neutrons. We are expanding the study of PE through $\gamma$ ray spectroscopy. Cross sections of partial $\gamma$ rays following the neutron induced reaction on $^{48}$Ti for E$_n$ = 1 to 200 MeV have been obtained in an experiment using GEANIE array at LANSCE/WNR. Using the GNASH reaction code the effect of the spin distribution of the residual nucleus in preequilibrium reactions has been investigated. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). The FKK preequilibrium spin distribution was incorporated into the GNASH calculations and the $\gamma$-ray production cross sections were calculated and compared with experimental data. The difference in the partial $\gamma$-ray cross sections using spin distributions with and without preequilibrium effects is found to be significant. [Preview Abstract] |
Thursday, September 22, 2005 10:00AM - 10:15AM |
JJ.00005: Surrogate reactions for nucleosynthesis: $^{102,104}Ru(\alpha,\alpha')$ as surrogate reactions for $^{101,103}Ru(n,\gamma)$ J.A. Church, L.A. Bernstein, J.T. Burke, F. Dietrich, J. Escher, C. Forssen, E. Norman, J. Ai, L.W. Phair, R. Clark, P.A. Fallon, D. Lee, I.Y. Lee, A.O. Machiavelli, P. McMahan, S. Sinha, M. Stephens, E. R.-Vieitez, M. Wiedeking For two-step, neutron-induced reactions proceeding through an equilibrated intermediate state, an alternate, ``surrogate reaction'' technique (Cramer and Britt) is applicable. Measured decay probabilities for the intermediate nucleus formed via a light-ion reaction are combined with optical-model calculations for the formation of the same intermediate nucleus via the n-induced reaction, and result in the overall (n, $\gamma$/n/2n) cross sections. For the first time, we have extended this method to (n,$\gamma$) reactions important in nucleosynthesis. $^{102,104}Ru(\alpha,\alpha')$ were studied separately as surrogate reactions for $^{101,103}Ru(n,\gamma)$. The test, $^{101}Ru(n,\gamma)$, has been previously measured directly (EXFOR). The unknown, $^{103}Ru(n,\gamma)$, is a branch in the s-process. Energies of scattered $\alpha$ particles were detected in double-sided silicon detectors (STARS) over scattering angles of 42-60 degrees. Ge clover detectors (LiBerACE) were used to count $\gamma$-rays in coincidence with $\alpha$ particles scattered at energies corresponding to 0-3 MeV equivalent neutron energy in the desired (n,$\gamma$) reaction. Work performed under the auspices of the U.S. DOE by the Univ. of CA, LLNL contract W-7405-Eng-4, DOE grants DE-FG02-91ER-40609, and DE-FG03-03NA00081, and LDRD-04-ERD-057. [Preview Abstract] |
Thursday, September 22, 2005 10:15AM - 10:30AM |
JJ.00006: Study of {\it M1} Quenching in $^{28}$Si by a $p,p'$ Measurement at 0 Deg. H. Matsubara, A. Tamii, K. Fujita, H. Hashimoto, K. Hatanaka, M. Itoh, K. Nakanishi, Y. Sakemi, Y. Shimbara, Y. Shimizu, Y. Tameshige, T. Adachi, Y. Fujita, J. Carter, H. Fujita, F.D. Smit, T. Kawabata, L.A. Popescu, H. Sakaguchi, M. Yosoi, J. Zenihiro The quenching of $Gammow$-$Teller$($GT$) strengths with respect to the sum rule has been discussed as an opened problem. Similarly the $M1$ strengths may have the some quenching problem because the transition includes the same operator ``$\sigma \tau$'' with the $GT$ one. Since there are two type transitions in $M1$ strengths, $IS$($\Delta T$=0) and $IV$($\Delta T$=1), another aspect of the quenching can be found from their difference. The experiment was carried out at RCNP by applying both ``dispersion-matching technique'' and ``under-focus mode'' for high resolution measurements at 0$^{\circ}$. A 295 MeV unpolarized proton beam bombarded natural Si target. After detailed calibrations, an energy resolution of 20 keV and a scattering angle resolution of 0.5 $\sim$ 0.8$^{\circ}$ were achieved. Background events were subtracted reasonably. In order to select 1$^+$ states, angler distribution of each peak was compared with DWBA calculations. The comparison between the experimental results and theoretical predictions of $IS$ and $IV$ will be discussed. [Preview Abstract] |
Thursday, September 22, 2005 10:30AM - 10:45AM |
JJ.00007: The $^{237}$Np(n, f) cross section from E$_{n}$=10$^{-2}$ eV to 200 MeV Fredrik Tovesson, Tony Hill The fission cross section of $^{237}$Np relative to $^{235}$U was measured at the LANSCE spallation neutron source. This nuclear reaction data has been requested with a 1{\%} accuracy to support of the advanced fuel cycle initiative (AFCI). By combining measurements at both moderated and bare neutron producing targets, the differential fission cross section was obtained from thermal energies to 200 MeV. The fission detector consisted of a parallel plate ionization chamber, which has a near 100{\%} efficiency and is relatively insensitive to alpha particles. In order to reach the high precision requirement in the energy region of interest, detailed studies of the error sources were performed. The $^{238}$U(n,f) reaction was used to determine the level of low energy background, and a specially dedicated system was set up to monitor dark current effects from the accelerator. [Preview Abstract] |
Thursday, September 22, 2005 10:45AM - 11:00AM |
JJ.00008: Using the surrogate ratio method to determine the $^{237}$U(n,f) cross section. J.T. Burke, L.A. Bernstein, J.A. Church, F.S. Dietrich, J.E. Escher, E.B. Norman, L.W. Phair, P. Fallon, R.M. Clark, M. Descovich, M. Cromaz, M.A. Deleplanque, I.Y. Lee, A.O. Machiavelli, M.A. McMahan, L.G. Moretto, E. Rodriguez-Vieitez, S. Sinha, F.S. Stephens, H.C. Ai, C.W. Beausang, B. Cridder A collaboration of scientists at LLNL, LBNL, and Yale University have deduced the $^{237}$U(n,f) cross section over a neutron energy range of 0 to 20 MeV. The cross-section was determined from the relative fission probability of $^{238}$U($\alpha$,$\alpha$'f) compared to $^{236}$U($\alpha$,$\alpha$'f). Where $^{238}$U($\alpha$,$\alpha$'f) and $^{236}$U($\alpha$,$\alpha$'f) are surrogates for $^{237}$U(n,f) and $^{235}$U(n,f) respectively. The experiment was performed at the 88 Inch Cyclotron at LBNL using the Silicon Telescope Array for Reaction Studies (STARS) spectrometer developed at LLNL. In this talk I will present an overview of the measurement and present the surrogate ratio method. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Thursday, September 22, 2005 11:00AM - 11:15AM |
JJ.00009: Relativistic Effect and $\alpha -^{40}$Ca and $\alpha -^{48}$Ca Scattering Jeremy S. Scott, R. Tripathi, F. Bary Malik Past optical model calculations of elastic differential scattering cross sections of $\alpha $- particles incident upon $^{40}$Ca and $^{48}$Ca have been examined to illustrate the need for relativistic calculations at 1.37 GeV. Khoa et al. and Nakano et al$^{1}$. have constructed potentials that match the experimental data very well in the forward angles using Woods-Saxon and Mexican hat types of potentials using the non-relativistic Schroedinger equation. However, when the potentials are used in the relativistic Schroedinger equation (RSE) to produce scattering cross sections, the fits are no longer that good. At 1.37 GeV, the $\alpha $-particle momentum calculated relativistically differs significantly from the one determined from the non-relativistic energy-momentum relation. The new $\alpha -^{40}$Ca and $\alpha -^{48}$Ca potentials determined using RSE, differ from those of Khoa et al$^{1}$. and Nakano$^{2}$. et al. $^{1}$D.T. Khoa, M. Nakano et al., Phys. Rev. C. 65, 024611, 2002 $^{2}$ M. Nakano et al., Phys. Rev. C. 40, 1323, 1989. [Preview Abstract] |
Thursday, September 22, 2005 11:15AM - 11:30AM |
JJ.00010: Feeding of the 11/2$^{-}$ isomers in $^{191,193}$Ir and $^{197}$Au. N. Fotiades, R.O. Nelson, M. Devlin, J.A. Becker, P.E. Garrett, W. Younes The ($n,n^{\prime}\gamma$) reaction was used to study excited states and to measure absolute partial $\gamma$-ray cross sections in $^{191}$Ir, $^{193}$Ir and $^{197}$Au. The data were taken using the GEANIE spectrometer comprised of 26 high-purity Ge detectors with 20 BGO escape-suppression shields. The broad-spectrum pulsed neutron source of the Los Alamos Neutron Science Center's WNR facility provided neutrons in the energy range from 0.6 to 250 MeV. The time-of-flight technique was used to determine the incident neutron energies. The absolute partial cross sections for hundreds of $\gamma$-rays from several reaction channels were determined. The partial $\gamma$-ray cross sections of several transitions feeding directly the 11/2$^{-}$ isomers and ground states in $^{191,193}$Ir and $^{197}$Au were obtained. In the case of $^{197}$Au, where the structure above the 11/2$^{-}$ isomer was not known before, the partial $\gamma$-ray cross sections and the $\gamma$-$\gamma$ coincidence data were used to built the level scheme above the isomer up to $\sim$2~MeV excitation energy. The feeding of the 11/2$^{-}$ isomers, which originate from the odd proton occuping the h$_{11/2}$ orbital, was found in all three experiments to be very similar and it is compared to the feeding determined for the ground states of $^{191}$Ir, $^{193}$Ir and $^{197}$Au. \noindent This work was performed under the auspices of the U.S. Department of Energy by the University of California, Los Alamos National Laboratory under contract No. W-7405-ENG-36 and Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48. [Preview Abstract] |
Thursday, September 22, 2005 11:30AM - 11:45AM |
JJ.00011: Particle-$\gamma$ Coincidence Measurements of Neutron Transfer Reactions on Neutron-rich Nuclei Micah Johnson, A. Kronenberg, D.W. Bardayan, J.C. Blackmon, C.D. Nesaraja, D.C. Radford, M.S. Smith, J.A. Cizewski, K.L. Jones, S.D. Pain, J.S. Thomas, J.A. Howard, R.L. Kozub, B.A. Schwer, R.J. Livesay Neutron-transfer measurements with (d,p) reactions provide important nuclear structure information such as excitation energies, angular momenta and spectroscopic strengths for neutron single-particle states. Such information can also be used to inform neutron-capture rates for nuclei far from stability, where direct measurements of the (n,$\gamma$) reaction are not possible because of the short life-times. In particular, neutron-capture measurements on neutron-rich nuclei are important for understanding astrophysical phenomena such as $r$-process nucleosynthesis. Using inverse kinematics for (d,p) reactions enables neutron-transfer measurements to be made using beams of neutron-rich nuclei, which cannot be made into targets. Measurements of $\gamma$-rays using high-resolution $\gamma$-ray detectors in coincidence with (d,p) reaction protons enables more accurate energy determination of excitations and provides further information on $\gamma$-ray strengths, which are important when extracting direct contributions to neutron-capture rates. Prospects for (d,p$\gamma$) measurements in inverse kinematics with neutron-rich beams at the HRIBF at ORNL will be discussed. [Preview Abstract] |
Thursday, September 22, 2005 11:45AM - 12:00PM |
JJ.00012: Four-body CDCC analysis of $^6$He+$^{209}$Bi scattering near Coulomb barrier energies Tomoaki Egami, Kazuyuki Ogata, Takuma Matsumoto, Emiko Hiyama, Yasunori Iseri, Masayasu Kamimura, Masanobu Yahiro In 2003, Keeley et al. analyzed the elastic scattering of $^6 $He on $^{209}$Bi target at 19.0MeV and 22.5MeV by the continuum-discretized coupled-channels method (CDCC). In the analysis the $^2n$+$^4$He+$^{209}$Bi three-body model, where $^2n$ denotes dineutron, was adopted. This three-body CDCC analysis, however, failed to reproduce the experimental data of the elastic cross section of $^6$He+$^{209}$Bi. In the present paper, $^6$He+$^{209}$Bi system is described by $n$+$n$+$^4$He+$^{209}$Bi four-body model and the four-body CDCC analysis, including nuclear- and Coulomb-breakup channels explicitly, is carried out. The three-body ($n$+$n$+$^4$He) continuum states of $^6$He are discretized by the pseudostate method, i.e., pseudostates obtained by diagonalizing the internal Hamiltonian of $^6$He with Gaussian basis functions are assumed to be discretized-continuum states of $^6$He. We show that the four-body CDCC well reproduces the angular distribution of elastic scattering data and the total reaction cross section at the both incident energies. [Preview Abstract] |
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