ISNAP Seminars - Abstracts 2015 Spring

Topic: Investigation of transitional rare earth nuclei using light ion reactions: Nuclear Structure and Surrogates

Prof. Cornelius Beausang ( University of Richmond ) / January 19, 2015

For several years, the Richmond group has been investigating the low/medium spin structure of N ~ 90 rare earth nuclei utilizing light ion transfer reactions, such as (p,d), (p,t) and inelastic proton scattering: work relevant for both basic nuclear structure and for surrogate (n,γ) cross section measurements. Such light ion induced reactions populate a variety of states and structures from the ground state to very high excitation energies, up to and indeed beyond the neutron separation energy. Thus we are probing the relatively unexplored bound state quasi-continuum at high energy and medium spin. Our recent work has focused on Sm and Gd nuclei and on several aspects: Single particle structures of odd N nuclei: Measurements of the spin distribution in the high energy bound quasi-continuum: Precision cross section measurements for excited states: and the properties of a intense feature, called the peak-like-feature observed just above the pair gap in all five even-even Gd and Sm nuclei studied to date.

Topic: Stellar Neutron Sources and s-Process in Massive Stars

Rashi Talwar ( University of Notre Dame ) / January 26, 2015

Potential stellar neutron sources for the s-process in massive stars are associated with α-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the buildup of the neutron source 22Ne during the helium-burning phase in stars. A critical influence on these reactions is expected to come from low-energy resonances at stellar energies below 800keV. Direct measurements of capture reactions to study these resonances are handicapped by the Coulomb barrier. Also, it is possible that some of these resonances correspond to pronounced cluster structures near the α-threshold. Hence, inelastic α-scattering on 26Mg has been used as an alternative tool to probe into the level structure. Also α-transfer technique has been used to extract α-strength information. In reference to this, the experiments performed using the Grand Raiden Spectrometer at RCNP, Osaka will be discussed and results will be presented.

Topic: Low energy nuclear physics research at LLNL

Dr. Jason Burke ( Lawrence Livermore National Laboratory ) / February 3, 2015

The low energy nuclear physics program at LLNL consists of a myriad of accelerator based and table top experiments. Studies include nuclear structure, neutron induced cross section measurements, determination of cross sections using the surrogate reaction technique, nuclear-atomic plasma induced interactions and beta decay studies. In this seminar, I will provide an overview of our low energy nuclear physics research program at LLNL. These include efforts at the Texas A&M Cyclotron Institute, Argonne National Laboratory, Lawrence Berkeley National Laboratory and Los Alamos National Laboratory. The Hyperion, Hydra and NeutronSTAR detector systems will also be discussed in detail.

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Topic: Measurement of the plasma astrophysical S factor for the 3He(d, p)4He reaction in exploding molecular clusters

Dr. Marina Barbui ( Texas A&M University ) / February 9, 2015

The plasma astrophysical S factor for the 3He(d, p)4He fusion reaction was measured for the first time at temperatures of few keV, using the interaction of intense ultrafast laser pulses with molecular deuterium clusters mixed with 3He atoms. D2 or CD4 molecular clusters were produced in the adiabatic expansion in vacuum of high pressure (52.5 bar) and low temperature gas, through a supersonic nozzle. The temperature of the gas was 86 K in the case of D2 and 200-260 K in case of CD4. Different proportions of D2 and 3He or CD4 and 3He were mixed in the gas jet target in order to allow the measurement of the cross-section for the 3He(d, p)4He reaction. The Texas Petawatt laser delivered 90-180 J per pulse with 150 fs duration to irradiate the clusters. The Coulomb explosion of deuterium molecular clusters provided energetic D ions capable of drive fusion reactions. The energy distribution of the deuterium ions was obtained from their time of flight measured with a Faraday cup. The yield of 14.7 MeV protons from the 3He(d, p)4He reaction was measured in order to extract the astrophysical S factor at low energies. Results of the experiment performed at Center for High Energy Density Science at The University of Texas at Austin will be presented [PRL, 111, 082502]. The possibility to use the same technique to investigate other reactions of astrophysical interest will be also discussed.

Topic: Inelastic Neutron Scattering Studies Relevant to Neutrinoless Double-Beta Decay

Dr. Benjamin Crider ( NSCL/MSU ) / February 16, 2015

The search for neutrinoless double-beta decay (0νββ) is a large international effort, with hopes of discovering physics beyond the standard model. One candidate for 0νββ, the decay of 76Ge to 76Se, is the focus of two major experiments, GERDA and MAJORANA. In these experiments, the signature of 0νββ would appear as a sharp peak in the energy spectrum at 2039 keV. Due to the high sensitivity of such a measurement, knowledge of background γ rays is critical. One such concern is the 2040.70(25) keV γ ray from the 3951.70(14) keV level in 76Ge, found in a study of 76Ga β- decay. This level could be populated via cosmic-ray-induced inelastic neutron scattering in the large experiments searching for the 2039 keV signature of 0νββ. The neutron-induced cross section of this level was measured at the University of Kentucky Accelerator Laboratory (UKAL). In this seminar, I will discuss the capabilities of UKAL and how we are using this facility to investigate topics related to 0νββ searches in 76Ge, ranging from the structure of the parent and daughter nuclei to potential backgrounds from decays in 76Ge itself. In particular, we have found that the 2039 keV region of the γ-ray spectrum following neutron scattering in 76Ge is more complex than was previously thought.

Topic: Study of fission dynamics and nuclear viscosity using particle emission as a probe

Dr. Yogesh Gupta ( University of Notre Dame ) / February 23, 2015

Understanding of fission dynamics in a wide energy regime has been a topic of continued research interest. Among many other degrees of freedom, the nuclear viscosity plays a crucial role in governing the fission dynamics. Several probes have been employed previously to study the fission dynamics and hence the nuclear viscosity.
Study of near scission particle emission (ternary fission), is a very good probe to provide information about the nuclear motion during saddle to scission points. I will discuss the systematic study of pre-scission and near scission ?-particle emission made for various systems over a wide range of Z2/A and excitation energies. It is seen that nuclear collective motion exhibits a changeover from dynamical emission to statistical one in going from very low excitation energy to the higher one which is a result of variation of viscosity with energy. Detailed experimental, procedure and results would be presented.

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Topic: Proton-capture reactions in thermonuclear supernovae and the p process

Dr. Kerstin Sonnabend ( Goethe University Frankfurt, Germany ) / February 26, 2015

Most of the elemental abundances beyond the so-called iron peak of the solar abundance distribution are produced by neutron-capture reactions in the r and s processes. However, there are about 35 isotopes on the proton-rich side of the valley of stability that are shielded against these reaction chains. These isotopes are usually referred to as ρ nuclei and are thought to be produced by different mechanisms in a number of astrophysical scenarios. One of these scenarios is a thermonuclear or type Ia supernova explosion. Thermonuclear supernovae provide a hot scenario where the ρ nuclei can be synthesized by the γ process and also by a series of proton-capture reactions.
The reactions producing the most abundant p nucleus 92Mo and their experimental investigation will be presented, e.g., recent results on the investigation of the 90Zr(ρ, γ) reaction using high-resolution γ-ray spectroscopy at Cologne, Germany, and steps towards the study of the 91Nb(ρ, γ) reaction in direct kinematics at FRANZ, Frankfurt, Germany. Future possibilities at different experimental facilities will be discussed in a detailed outlook.

Topic: Beta decay of deformed nuclei with the proton-neutron finite amplitude method

Thomas Shafer ( University of North Carolina ) / March 2, 2015

In the last few years the finite amplitude method (FAM) has emerged as an efficient technique to calculate nuclear transitions. While formally equivalent to the quasiparticle random-phase approximation (QRPA), the FAM removes the need to construct and diagonalize the large Hamiltonian matrix usually required in the QRPA. As a result, calculations performed with the FAM are significantly faster than their QRPA counterparts, reducing computational burden and enabling larger-scale studies.
At UNC we have recently extended the FAM to calculate beta-decay rates and other charge-changing observables of axially-deformed even-even nuclei. In this talk I will review mean-field theory and the QRPA before discussing the finite amplitude method and its application to beta-decay rates important for r-process nucleosynthesis.

Topic: TBA

Prof. Justin Frantz ( Ohio University ) / March 16, 2015

Topic: TBA

Prof. Jaideep Singh ( NSCL/MSU ) / March 30, 2015

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Topic: TBA

Dr. Ania Kwiatkowski ( TRIUMF) / April 13, 2015

Topic: TBA

Prof. Anatoli Afanasjev ( Mississippi State University ) / April 20, 2015

Topic: The photonuclear cross section of Boron-10 from the No Core Shell Model

Dr. Michael Kruse ( Lawrence Livermore National Laboratory ) / April 27, 2015

In this talk I will outline how I have started to build a framework to calculate electroweak observables in the ab-initio No Core Shell Model. Electromagnetic probes provide stringent tests of the predictive power of our nuclear Hamiltonians and can be used to constrain potential models whereas weak observables can answer interesting questions about the nature of the universe. As a starting point, I have calculated the photonuclear cross section of Boron-10 using as input realistic nuclear interactions to determine the ground- and excited-states of the nucleus. By using the moment-generating method of Lanczos one is able to construct the electric-dipole strength function from which one can calculate the energy-weighted strength function. To determine the cross section one needs to take into account the finite width of the continuum states; in our case we use the physics of neutron-escape widths, which will be extensively discussed. Theoretical results are compared to experimental data and some results regarding the Brink hypothesis will be presented.

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Topic: TBA

Prof. Sandrine Courtin ( University of Strasbourg, France ) / May 4, 2015

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