ISNAP Seminars - Abstracts 2009 Spring

Topic: Measurements of double-beta decay matrix elements: some surprises in nuclear physics

Professor Dr. Dieter Frekers ( University of Muenster, Germany ) / June 10, 2009

I will talk about high-resolution charge-exchange reactions of (n,p) and (p,n) type at intermediate energies, which directly connect to the nuclear matrix elements in double-beta (bb) decay. Here, the (n,p) type reactions are realized through (d,²He) reactions, where ²He refers to two protons in a single ¹S0 state and where both of these are momentum analyzed and detected by the same spectrometer and detector. These reactions have been developed and performed exclusively at KVI, Groningen (NL), using incident deuteron energy of 183 MeV with final state resolutions of about 100 keV. The (p,n) type (³He,t) reaction was developed at the RCNP facility in Osaka (JP) allowing measurements with a resolution of 30 keV at incident energies of 420 MeV. Using both reaction types one can extract the Gamow-Teller transition strengths B(GT⁺) and B(GT^-), which define the two “legs” of the 2vbb decay matrix elements. The high resolution available in both reactions allows a detailed insight into the excitations of the intermediate odd-odd nuclei and, as will be shown, some rather unexpected features are being unveiled. Special emphasis will be placed on the bb decay nuclei ⁷⁶Ge, ⁸²Se, ⁹⁶Zr and ¹⁰⁰Mo. It will further be argued that the intrinsic deformation of the ground-state wave functions of the mother and grand-daughter nuclei can have a profound effect on the 2vbb decay matrix elements.
I will also talk about future directions using ion traps at the TRIUMF radioactive beam facility to measure ground-state properties of the intermediate odd-odd nuclei, which also connect directly to the nuclear bb decay matrix elements.

Topic: Towards a better understanding of the r-process from studies of exotic nuclei in the A~120 region

Prof. Henryk Mach ( University of Notre Dame / Uppsala University ) / May 18, 2009

The nucleosynthesis r-process is responsible for the production of most of the heavy elements observed in nature. Its general features are well understood, but there is a considerable debate over many related issues. The modeling of the process requires an extensive body of data on the neutron-rich nuclei located predominantly beyond the reach of modern experiments, thus it relies on extensive use of nuclear models. The most accurate predictions are based on a model which stipulates a strong quenching of the N=82 neutron shell. However, current updates of the model imply a much weaker quenching, while the new experimental data firmly disprove earlier indications of shell quenching at N=82 in Cd. Experimentally the main battle ground is the mass A~120 region where there is prospect of utilization of new techniques and facilities to investigate directly a significant part of the r-process path. This presentation will focus on the fast timing gamma-ray studies of heavy Mn/Fe nuclei at A~65, on the A~120 region and on the exotic neutron-rich Sb isotopes.

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Topic: Symmetries in the Geometrical Collective Model

Dr. Stijn De Baerdemacker ( Ghent University / University of Toronto, Canada ) / April 20, 2009

Away from the shell closures, the dynamics of the constituent particles within the atomic nucleus will polarise the core, leading towards enhanced deformation modes at the atomic surface. The quantum mechanical treatment of these surface excitations gave rise to the Geometrical Collective Model (GCM), developped by Bohr & Mottelson, and which has recently witnessed a renewed interest from a theoretical as well as experimental perspective.
The present talk will discuss the symmetries of the GCM at the quadrupole level. A brief overview will be given of how principles of symmetries and Lie-algebras can be applied to nuclear structure physics in general and the quadrupole GCM in particular. It will be demonstrated how the recently developed Cartan-Weyl based treatment of the GCM can provide all necessary ingredients for the description of collective vibrational, rotational and more involved structures, such as e.g. triaxiality and shape coexistence.

Topic: First results from the new RNB facility RESOLUT and nuclear astrophysics with stable beams at FSU

Dr. Grisha Rogachev ( RESOLUT at Florida State University ) / April 6, 2009

The new radioactive nuclear beam facility RESOLUT at Florida State University has started its operation. The results from the first two experiments will be presented. The astrophysically important resonances in Si and the level structure of the proton drip line nucleus B were studied in these experiments. Plans and future developments for the radioactive nuclear beam program at FSU will be discussed.

The Asymptotic Normalization Coefficients (ANCs) for the near threshold states in O and O were determined using the sub-Coulomb a-transfer reactions C (Li,d), C(Li,d) and C(li,t). Implications of these measurements for the C(a,n), C(a,g) and O(a,p) astrophysical reaction rates will be reviewed.

Topic: Study of the Nuclear Dipole Resonance using the Monoenergetic and Polarized Gamma Beams at HIgS

Dr. Anton Tonchev ( Duke University, NC ) / March 30, 2009

The present experimental activity at High-Intensity-Gamma-Ray Source (HIgS) is focused on the study of dipole states in spherical nuclei near closed shells where large, mostly electric dipole transitions to the ground state, have been observed. This concentration of dipole states close to the neutron separation energies in the Ex ~ 4 – 9 MeV energy region, has been dubbed ‘Pygmy Dipole Resonance” (PDR) in comparison to the Giant Dipole Resonance that dominates the E1 response. The dipole strength distribution at the particle separation energies might affect reaction rates in astrophysical scenarios where photo-disintegration reactions are important, i.e., in hot stars and stellar explosions.

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Topic: Many-body Approach to Nuclear Pairing

Dr. Roman Sen'kov ( Michigan State University, MI ) / March 23, 2009

A new theoretical approach is presented that combines the mean field (Hartree-Fock) variational scheme with the exact solution of the pairing problem in the finite orbital space. Using this formulation in the sd-space as an example, we show that the exact pairing significantly improves the results for the ground state energy.

Topic: Role of Physicists on Wall Street

Dr. Boris Skorodumov ( Mitsui Energy Risk Management ) / March 9, 2009

The presentation will be about role of physicists on Wall Street: what is a quant (financial modeler) role on Wall Street, how to become a quant, what is a necessary knowledge each physicist need to know in order to qualify to be a quant, my personal transition from physicist to financial modeler, "to-do-list" for potential candidate in order to pass interview process for quant role for any Tier Bank on Wall Street, why it is harder to find a job nowadays on Wall Street, role of financial background to get a quant job, role of programming experience, role of mathematical background, who use quant models, why we should be careful in using any quant model.

Topic: ^11,12B (n,g) – The influence of r-process nucleosynthesis of light elements

Dr. Hye Young Lee ( ANL, IL ) / March 2, 2009

Core-collapse SN models predict enhanced heavy element abundances in the r-process by extending the reaction network to include light, neutron-rich nuclei (Z<10). Based on the sensitivity study, ^11,12B (n,g) ^12,13B are found to be important for the production of the carbon isotopes, which can immediately convert to heavier seed nuclei in the neutrino-driven wind model. We have measured the (d,p) reaction with radioactive ¹²B beam and stable ¹¹B beam using the ATLAS in-flight facility at ANL. The spectroscopic factors and the branching ratio from these measurements are used in determining the reaction rates that are compared with theoretical calculations. The astrophysical implications using the present reaction rates of ¹¹B(n,g) and ¹²B(n,g) will be discussed.

Topic: Real Life Applications of a Nuclear Physics Degree

Prof. Rebecca Detwiler ( University of Florida ) / February 23, 2009

A degree in Nuclear Physics can lead to a career utilizing your knowledge in a variety of real-life applications. In this discussion, interesting applications and techniques involving radiation detection and isotope identification for nuclear emergency response/homeland security applications that are used or being developed at the Remote Sensing Laboratory (Las Vegas, NV) and University of Florida’s Nuclear and Radiological Engineering Department will be presented. We will discuss gamma-ray spectroscopy in the field, neutron spallation and the "ship effect", testing of the peak rendering code ASEDRA developed at the UF NRE department Florida Institute for Nuclear Detection and Security (FINDS) Institute, and the design of a LaBr₃(ce) array for gammy-ray detection, identification and localization.

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Topic: Study of Nuclear Weak and Electro-Magnetic Responses by Using Intermediate-Energy Beams

Prof. Yoshitaka Fujita ( Osaka University, Japan ) / February 20, 2009

The Gamow-Teller (GT) transition is one of the most popular nuclear weak processes of spin-isospin (s t) type. It is of interest not only in the study of nuclear physics, but also in astrophysics since it plays an important role, for example, in supernova-explosions and nuclear syntheses. In addition, E1 transitions are the most important electro-magnetic processes in nuclear astrophysics. Limited information on the spin-isospin response can be obtained directly through the study of weak processes, such as b decay or neutrino induced reactions. However, it was found that (³He,t) charge-exchange reaction at intermediate energies (E = 140 MeV/nucleon) and at 0�‹ can selectively excite GT transitions extending the range of excitation energies as well as the range of accessible nuclei [1]. In addition, inelastic reactions, such as (p,p�Œ) at 0�‹ and intermediate incoming energies (150 . 300 MeV) is a good probe to study the E1 response by means of Coulomb excitation. The E1 response over a large energy range, from the low lying E1 states to the giant dipole resonance (GDR) at 15 . 20 MeV, can be studied without being affected by the opening of the neutron-decay channel [2,3]. We will show quantum number �gisospin�h plays important roles in such studies.

Topic: The Science of Poisonous Polonium-210

Dr. Patrick Regan ( University of Surrey, UK ) / February 11, 2009

In late 2006 the world became acutely aware of the mysterious substance polonium-210 in the notorious fatal poisoning of former Russian spy Alexander Litvinenko – but what is polonium-210, how is it made, and what does it do? Dr. Patrick Regan, reader in nuclear physics at the University of Surrey will reveal that in addition to the more macabre uses, this isotope is of major fundamental significance, not least in explaining why there is a limit to the stable elements which occur in nature. He will also discuss how one might detect this substance to avoid smuggling such material in the future and how much of this material you need to be exposed and harmed.

Topic: Development and implementation of a new technique to study (p, a) resonances

Brian Moazen ( University of Tennessee, TN ) / February 9, 2009

The accurate determination of the strengths and energies of (p,a) resonances are important for understanding the influence of reaction cycles to element synthesis in many astrophysical environments. Typically, (p,a) studies performed in inverse kinematics employ solid polypropylene targets. These are not always advantageous, especially when the energy loss of the incoming beam in the solid target is much larger than the resonance width. At the Holifield Radiactive Ion Beam Facility in Oak Ridge National Laboratory, we have developed a new technique for measuring the strengths and energies of (p,a) resonances and applied it to study resonances in ¹⁷O(p,a)¹⁴N, ³¹P(p,a)²⁸Si and ³⁵Cl(p,a)³²S. In this technique, a large, differentially pumped scattering chamber is filled with hydrogen gas at pressures up to 4 Torr. No windows or foils obstruct the incoming beam and reaction products are detected in coincidence by two silicon strip arrays. The vertex of the (p,a) reaction is determined from the relative kinematics of the recoil and alpha particle. The experimental setup and overviews of the ¹⁷O(p,a)¹⁴N, ³¹P(p,a)²⁸Si, and ³⁵Cl(p,a)S experiments will be presented.

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Topic: Octupole collectivity near N=126

Dr. Walter Reviol (Washington University, St. Louis, MO) / February 2, 2009

Recent experiments in the actinide region, using Gammasphere and the evaporation residue detector Hercules, have covered the territory between N = 126 and the center of static octupole deformation at N = 134. The ²²⁰Th nucleus (N = 130) shows a multi-phonon like behavior, over a large spin range (I > 20 h). It has been described as a tidal-wave mode for a reflection-asymmetric nuclear surface. The neighboring odd-mass isotopes show the following features. In ²¹⁹Th, an octupole structure coexists with structures due to particle-core couplings. In ²²¹Th, an off-yrast octupole band is newly observed. With these findings, a definite trend for parity doublets is established.

Topic: Evaluation of the influence of Solar Model parameters on the expected neutrino fluxes

Prof. Gianluca Imbriani, ( University Federico Secundo, Naples, Italy ) / January 29, 2009

The Solar neutrino detection in the Homestake mine was one of the most important events for physics in the last century. For the first time there was direct evidence that sun shines because of nuclear fusion reactions, as suggested in the pioneering work be Bethe. In the last forty years, other experiments (SAGE, GALLEX, SK, SNO and Borexino) have collected data in different energy windows.
In order to calculate the neutrino production rate in the Sun, to evaluate the solar neutrino experiments data, one needs to calculate a solar model. In the talk I will report on the current uncertainties due to the physics input in the solar model.

Topic: Neutron Physics for Nuclear Astrophysics at Los Alamos

Dr. Aaron Couture ( Los Alamos National Lab, New Mexico ) / January 26, 2009

Neutron induced reactions play important roles in such diverse astrophysical environments as low-mass AGB stars, helium burning in massive stars, and supernovae. In fact, the production of isotopes heavier than iron are almost completely driven by neutron induced reactions.
The Los Alamos Neutron Science Center (LANSCE) produces time-of-flight neutron beams from 25 MeV to in excess of 200 MeV. By coupling these neutron beams with modern detection arrays, we have the capability of performing a range of experiments on small, potentially radioactive samples. Other facilities are designed for neutron scattering, transmission, and charged particle emission. The neutron fluxes are among the highest in the world and enable first measurements on extremely small and potentially radioactive targets.
I will discuss some recent ongoing measurements performed for nuclear astrophysics, paying particular attention to the capabilities for performing measurements on unstable isotopes.

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