Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session JD: Nuclear Theory II: Heavy Nuclei |
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Chair: Mihai Horoi, Central Michigan University Room: Heritage |
Friday, October 28, 2011 2:00PM - 2:12PM |
JD.00001: New microscopic theory of low-energy collective motion in soft spherical nuclei Liyuan Jia, Vladimir Zelevinsky Many medium and heavy spherical nuclei clearly manifest strong collective motion of low frequency, mainly of quadrupole symmetry. In the absence of static deformation, this motion has a character of large amplitude collective vibrations. While the shell-model diagonalization is usually impossible in such cases, and anharmonic effects are crucial, we develop a method to go beyond standard Hartree-Fock-Bogoliubov mean field and random phase approximation. Considering typical frequencies of collective motion smaller than the pair breaking energy, we map the exact operator equations of motion onto the dynamics governed by the collective Hamiltonian. The parameters of this Hamiltonian (cubic and quartic anharmonicity) are determined self-consistently. After checking the approach by simple cases (Lipkin model and the model with factorizable forces), we discuss the realistic applications. [Preview Abstract] |
Friday, October 28, 2011 2:12PM - 2:24PM |
JD.00002: Exploring the fission barrier of superheavy nuclei in covariant density functional theory Hazem Abusara, Anatoli Afanasjev, Peter Ring Systematic calculations of the fission barriers with allowance of triaxial deformation have been performed within the covariant density functional theory for the super heavy region of the nuclear chart. Pairing is treated within the BCS approximation using seniority zero forces adjusted to empirical values of the pairing gap parameters. The analysis of the results showed that triaxiality doesn't lower the height of the inner fission barrier. The height of the inner fission barrier increases with increasing Z from 112 up to 120. The fission barrier height is around 5.5 -- 6 MeV in the Z=120 isotope chain. The doubly magic Z=120 N=172 nucleus has the largest value of the height of the inner fission barrier indicating its increased stability. [Preview Abstract] |
Friday, October 28, 2011 2:24PM - 2:36PM |
JD.00003: Brownian shape motion:\ Fission fragment mass distributions J. Randrup, P. Moller Exploiting the expected strongly damped character of nuclear dynamics, we treat the nuclear shape evolution in analogy with Brownian motion and perform random walks on five-dimensional fission potential-energy surfaces which were calculated previously and are the most comprehensive available. Test applications give good reproduction of a selection of diverse experimental mass yields. This novel general approach requires only a single new global parameter, the critical neck size at which the mass partition is frozen in, and the results are remarkably insensitive to its specific value. A deeper understanding of these results can be achieved by including the friction tensor for the shape motion which appears to have only a minor effect on the resulting mass partition. Relative to previously employed models, the present approach represents a significant advance with regard to predictive power. It can be readily employed in regions of the nuclear chart that are of special astrophysical interest and it may, for example, help to clarify the importance of fission recycling for the r-process. Taking explicit account of the equilibration process, the treatment extends in a natural way the compound nucleus concept and it builds directly on the general picture of low-energy nuclear dynamics as being dissipation dominated. [PRL 106 (2011) 132503] [Preview Abstract] |
Friday, October 28, 2011 2:36PM - 2:48PM |
JD.00004: Microscopic dynamic study of giant resonance excitation and fusion in $^{132}$Sn+$^{48}$Ca Volker Oberacker, A.S. Umar In connection with experiments at Radioactive Ion Beam Facilities, we study pre-compound giant resonance excitation and fusion in heavy-ion reactions within a microscopic dynamic theory. Calculations are carried out on a 3-D lattice using the density-constrained Time-Dependent Hartree-Fock (DC-TDHF) method [1,2]. For $^{132}$Sn+$^{48}$Ca, we calculate the time-evolution of giant resonance excitation and associated gamma-ray yield. Also, we calculate the heavy-ion interaction potential and total fusion cross section and compare the results to $^{124}$Sn+$^{40}$Ca. A comparison with recently measured fusion cross sections will be given.\\[4pt] [1] Umar and Oberacker, Phys. Rev. C 74, 021601(R) (2006)\\[0pt] [2] Oberacker, Umar, Maruhn and Reinhard, PRC 82, 034603 (2010) [Preview Abstract] |
Friday, October 28, 2011 2:48PM - 3:00PM |
JD.00005: Novel Indication for Non-Locality of the Optical Model for $^{12}$C George Rawitscher, Mohammed Hassan, Mahmoud Jaghoub In this work we consider the n - $^{12}$C elastic scattering data and fit the angular distributions in the energy range 12 to 20 MeV. Our fits are obtained by adding to the conventional optical model a new term which is real, velocity dependent and is assumed to represent the nuclear density. The fits reproduce well the detailed structure of the angular distributions including the prominent backscattering minima which depend sensitively on the incident energies. A sign of the presence of non-locality is manifested a) by the pronounced motion of the peak of the spin-orbit potential towards the nuclear interior as the incident energy increases, and b) the necessary presence of a velocity-dependent term, which is nearly stationary as the incident energy increases. All our potentials have the form of the conventional Woods-Saxon potential or its derivative. Possible explanations of the non-locality in terms of physical processes will be attempted. Non-localities in the nucleon - $^{16}$O optical potential were also previously found by Cooper [1] in the form of parity dependent potentials. \\[4pt] [1] S. G. Cooper, Nucl. Phys. A618 (1997), 87-106. [Preview Abstract] |
Friday, October 28, 2011 3:00PM - 3:12PM |
JD.00006: Do We Understand Physics of Non-Exponential Decay? Vladimir Zelevinsky, Alexander Volya In practical evaluations of the mean lifetime the exponential behavior of the survival probability is assumed. Quantum mechanics, however, predicts that the survival probability of the decaying state, given by the squared overlap of the initial wave function and the evolved wave function at a later time, cannot be strictly exponential. Although it is hard to observe experimentally, in a quantum system with the finite expectation values of energy and its mean square fluctuation, both the initial stage of decay and its long-time limit are non- exponential. Using an exactly solvable quantum model we show that even at intermediate times the decay is not strictly exponential. This could be due to interfering components in the decay wave function, interfering decay channels, recurrent returns of the system to the quasi-bound states including those different from the original one, and due to exchange terms in cluster decays. In the presence of intrinsic degrees of freedom coupled to different decay channels we observe the oscillations superimposed on the power tail in the long-time limit, which is similar to the so-called GSI oscillations. [Preview Abstract] |
Friday, October 28, 2011 3:12PM - 3:24PM |
JD.00007: Random Matrix Theory Approach for Unstable Nuclei Gavriil Shchedrin, Vladimir Zelevinsky Random Matrix Theory as a statistical approach for exploring energy spectra of complex quantum systems was pioneered by Wigner and Dyson in 1950's. This theory was successfully applied to excited states of complex nuclei and other mesoscopic systems evaluating statistical fluctuations and correlations in energy levels and corresponding wave functions. The standard random matrix approach was formulated only for closed systems with no coupling to the outside world. Later it was generalized for decaying systems with energies of unstable states in the complex plane. Recent precise experiments showed that the neutron width distribution in low-energy neutron resonances cannot be described by the standard Porter-Thomas distribution that follows from standard random matrix theory. We analyze the combined distribution function of resonance widths and energies in an unstable quantum system that follows from the statistical assumptions which agree with the general quantum requirements, such as unitarity of the scattering matrix. We show that such statistical theory indeed leads to the trend observed experimentally. [Preview Abstract] |
Friday, October 28, 2011 3:24PM - 3:36PM |
JD.00008: Random matrices, symmetries, and many-body states Calvin Johnson All nuclei with even numbers of protons and of neutrons have ground states with zero angular momentum. This is ascribed to the pairing force between nucleons, but simulations with random interactions suggest a much broader many-body phenomenon. I discuss how to project out random Hermitian matrices that have good quantum numbers and, computing the width of the Hamiltonian in subspaces, find ground states dominated by low quantum numbers, e.g. $J = 0$. [Preview Abstract] |
Friday, October 28, 2011 3:36PM - 3:48PM |
JD.00009: An improved nuclear mass model: FRDM (2012) Peter Moller We have developed an improved nuclear mass model which we plan to finalize in 2012, so we designate it FRDM(2012). Relative to our previous mass table in 1995 [1] we do a full four-dimensional variation of the shape coordinates EPS2, EPS3, EPS4, and EPS6, we consider axial asymmetric shape degrees of freedom and we vary the density symmetry parameter L. Other additional features are also implemented. With respect to the Audi 2003 data base we now have an accuracy of 0.57 MeV. We have carefully tested the extrapolation properties of the new mass table by adjusting model parameters to limited data sets and testing on extended data sets and find it is highly reliable in new regions of nuclei. We discuss what the remaining differences between model calculations and experiment tell us about the limitations of the currently used effective single-particle potential and possible extensions.\\[4pt] [1] ADNDT 59 (1995) 185 [Preview Abstract] |
Friday, October 28, 2011 3:48PM - 4:00PM |
JD.00010: Energy Released from Nuclear Radiation Han Yongquan If temperature is not taken into consideration (in fact, atomic nucleus temperature is far beyond the atom temperature), energy released from visible light---electromagnetic wave radiated by atomic nucleus can be calculated as follows: $\frac{1}{2}m\times v^2-m_1 \times c^2=\frac{1}{2}\times 0.91\times 10^{-30}\times \left({2.14\times 10^{14}} \right)^2-4.04\times 10^{-36}\left( {3\times 10^8} \right)\approx 0.8\times 10^{-2}$. Ignoring electromagnet's whole movement velocity in interior part of the object, we only calculate the revolving velocity of its electron pair and assume that both the revolving velocity of electromagnetic electron pair of visible light and its transmission velocity equal $3\times 10^8$ in the above calculation formula. If the influence of temperature is taken into consideration, the energy released from radiation is more than $0.8\times 10^{-2}$. Therefore, the energy released from nuclear radiation must be far beyond this value. It can easily explain why international prototype kilogram has lessened about 50 micrograms, which is a cylindrical casting made of platinum and iridium and having a history of 118 years. [Preview Abstract] |
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