ISNAP Seminars - Abstracts 2014 Spring
Topic: Double beta decay and matter dominated universe
Prof. Tadafumi Kishimoto ( Research Center for Nuclear Physics, Osaka University, Japan ) / January 14, 2014
Study of neutrino-less double
beta (0nbb) decay becomes of particular importance after
the confirmation of neutrino oscillation which shows that
neutrinos have mass. They could then be Majorana particles
which violate lepton number conservation. Once lepton number
non-conservation is verified, we have a scenario to explain
how our matter dominated universe is realized dynamically.
It is the leptogenesys combined with CP violation in lepton
sector.0nbb decay is only a known process to verify Majorana
nature of neutrino.
Topic: Nuclear Structure Studies with the Active-Target Time-Projection-Chamber: Moving Towards Exotic Beams
Dr. Tan Ahn ( NSCL/Michigan State University ) / January 20, 2014
The use of radioactive beams allows for the study of many unstable nuclei and continues to yield important information on the evolution of nuclear structure as well as uncover unique nuclear phenomena such as clustering and halos. One of the main challenges of using radioactive beams is dealing with their low-intensities, especially for beams of nuclei far from stability. A new detector, the Active-Target Time-Projection-Chamber (AT-TPC), is being developed at the National Superconducting Cyclotron Laboratory (NSCL) that will allow us to overcome some of these low-intensity limitations. The AT-TPC does this by using its tracking gas simultaneously as a target, which maximizes luminosity without sacrificing good energy resolution. This opens up a new window for experiments with lower beam rates. I will discuss the use of the AT-TPC's Prototype in several experiments using secondary beams from Twinsol at the University of Notre Dame to study alpha-cluster states, fusion, and the decay of the Hoyle state. In addition, I will show results for a test experiment using the Prototype AT-TPC to study isobaric analog states of Sn isotopes at Argonne National Laboratory (ANL). Possibilities for future experiments with more exotic Twinsol beams as well as experiments with fission fragments at ANL and neutron-rich nuclei with the ReA3 accelerator and the AT-TPC at NSCL will be presented.
Topic: Ion Traps for Astrophysics
Dr. Jason Clark ( Argonne National Laboratory ) / January 27, 2014
The astrophysical r process is thought to be responsible for the creation of half of the elements heavier than iron. In an attempt to reproduce the observed distribution of element abundances in the universe, models are generated which inherently rely upon many nuclear physics inputs, including the masses of the nuclides involved and their beta-decay properties. However, the uncertainties in these nuclide properties are often too large and limit our understanding of heavy-element nucleosynthesis, yet more precise measurements of these properties are difficult to obtain since a large number of the nuclides involved in the astrophysical r process are often too challenging to produce at accelerator facilities. Recently the CARIBU facility, an upgrade to Argonne National Laboratory’s ATLAS facility, has started to provide intense beams of a number of these previously elusive neutron-rich nuclei. A program of mass measurements at CARIBU is now underway with the Canadian Penning trap mass spectrometer. In addition, a specially designed ion trap is currently being developed to facilitate a new program of beta-decay spectroscopy using nuclides produced by CARIBU. This new technique of using ion traps to perform beta-decay studies could significantly advance the field, just as ion traps had done in the field of mass spectroscopy. The ion trapping techniques and the results/implications of some of the first measurements will be presented.
Topic: Probing Properties of the Weak Interaction using Trapped Atoms and Ions
Prof. Daniel Melconian ( Texas A&M University ) / February 3, 2014
>Nuclear β decay has a long-standing
history of shaping and testing the standard model of particle physics,
and it continues to this day with elegant, ultra-precise low-energy nuclear
experiments. Experiments observing the (un)polarized angular correlations
between the electron, neutrino and recoil momenta following nuclear β
decay can be used to search for exotic currents contributing to the dominant
(V - A) structure of the weak interaction. Precision measurements of the
correlation parameters to ≤ 0.1% would be sensitive to (or meaningfully constrain)
new physics, complementing other searches at large-scale facilities like
Topic: Fishing in a sea of Xe – Barium-ion tagging for 136Xe double-beta decay studies with EXO
Dr. Thomas Brunner ( Stanford University ) / February 17, 2014
The nature of the neutrino, i.e., whether
it is a Dirac or Majorana particle, still remains a mystery. An experimental
approach to answering this question is through decay experiments searching
for the lepton-number violating neutrino-less double decay (0nbb). A positive
observation of this decay would determine the character of the neutrino
to be a Majorana particle. Furthermore, one could extract the effective
Majorana neutrino mass from the half-life of the decay. Several collaborations
worldwide are investigating bb decays in different isotopes. EXO-200 is
a bb-decay experiment searching for a 0nbb signal in the bb decay of 136Xe
to its daughter isotope 136Ba. This detector contains ~175
kg liquid Xe enriched to ~80.6% and is currently operational at the WIPP
site in New Mexico, USA. The best limit on the 0nbb decay half-life of
136Xe (t1/2=1.6x1025 years) has recently been published
Topic: Accelerator Mass Spectrometry of Heavy Isotopes
Dr. Stephan Winkler ( University of Vienna, Austria ) / February 18, 2014
Accelerator Mass Spectrometry is a technique with the best sensitivity for many radioisotopes and the technique of choice for long-established methods such as radiocarbon dating or exposure dating with Beryllium-10 and Aluminium-26. Over the past 15 years heavier isotopes have gained significant attention. Measuring these isotopes faces two challenges, the separation of interfering isobars and the suppression of isotopic interference from molecules and their break-up. Careful design of the spectrometer and an understanding of ion-beam and atomic physics are required to achieve the lowest detection limits.
Topic: Nuclear astrophysics constraining cosmology
Prof. René Reifarth ( Goethe-University Frankfurt am Main, Germany ) / February 20, 2014
The destiny of the Universe is strongly coupled
to the history of space and time. In particular the age of the Universe
allows to constrain our models about the future. If the expansion of the
Universe is accelerated it is currently older than if it would collapse
again at some point in the distant future.
Topic: Nuclear Data Measurements at LANSCE: The NIFFTE fission TPC
Dr. Rhiannon Meharchand ( Los Alamos National Laboratory ) / February 24, 2014
The Neutron and Nuclear Science Group at Los
Alamos National Laboratory (LANSCE-NS) has a diverse experimental program
aimed at measuring nuclear data: prompt fission neutron and gamma output;
fission fragment mass, charge, and energy distributions; cross sections
for direct and surrogate (n,γ), (n,2n), (n,X), and (n,f) reactions. These
data are fundamental to nuclear energy and defense applications, which
are increasingly dependent upon advanced simulation and modeling due to
testing restrictions and high development costs.
Topic: Modifications of the Nuclear Shell Structure: Spectroscopy in Islands of Inversion
Prof. Kathrin Wimmer ( Central Michigan University ) / March 3, 2014
One of the major successes in the description of the properties of atomic nuclei was the introduction of the nuclear shell model. The magic numbers associated with closed shells have long been assumed to be valid over the whole nuclear chart. In the last decades it was found that the well-known magic numbers for atomic nuclei can change locally when going from the valley of stability to nuclei with extreme N/Z ratios, leading to the disappearance of classic shell gaps and the appearance of new magic numbers. This evolution of the magic numbers is one of the major topics in both experimental and theoretical nuclear structure research. Modifications of the nuclear shell structure can lead to unexpected phenomena, such as the occurrence of deformed ground states in so-called "Islands of Inversion". These changes in nuclear structure have a vast impact on the binding energies of nuclei, their decay properties, as well as on their excitation-energy spectra. Understanding the underlying phenomena causing these changes is of great importance to be able to reliably extrapolate nuclear structure properties towards the drip-lines.
Topic: Advances in Explosive Nuclear Astrophysics
Dr. Gavin Lotay ( University of Surrey, UK ) / March 31, 2014
Breathtaking results from the Planck satellite mission and Hubble space telescope have highlighted the key role modern Astronomy is playing in our understanding of Big Bang Cosmology. However, not so widely publicized is the similar wealth of observational data now available on explosive stellar phenomena, such as X-ray bursts, novae and Supernovae. These astronomical events are responsible for the synthesis of almost all the chemical elements we find on Earth and observe in our Galaxy, as well as energy generation throughout the Cosmos. Regrettably, understanding the latest collection of astounding data is currently severely hindered by large uncertainties in the underlying nuclear physics processes that drive such stellar scenarios, impeding our ability to describe the chemical evolution of the Universe.
Topic: Isospin Invariant Energy Density Functional Approach
Dr. Javid Sheikh ( Oak Ridge National Laboratory ) / April 14, 2014
Recent studies have demonstrated that the existing energy density functionals have reached limits and significant changes to the form of the functional are needed to describe the experimental data with higher accuracy. As a step toward enriching the existing density functionals, we have generalized the Skyrme density functional by including all the densities as mandated by the isospin symmetry. In the standard density functionals, isoscalar and only single tz component of the isovector densities are considered; tx and ty or p-n mixed densities are completely neglected. Using the newly developed isospin invariant approach, results shall be presented for the isobaric analog states in A = 48 and 78 chains in the HartreeFock approximation. Recently, we have also extended the approach to include the isovector pairing and interesting coexistence of different pairing solutions shall be presented.
Topic: An Advanced Ion Guide for Beam Cooling and Bunching for Collinear Laser Spectroscopy of Rare Isotopes
Dr. Bradley Barquest ( NSCL, MSU ) / April 22, 2014
Collinear laser spectroscopy provides a means of determining nuclear magnetic dipole and electric quadrupole moments and mean square charge radii of rare isotopes through the measurement of hyperfine spectra. Measurements performed at projectile fragmentation facilities with gas stopping capability can complement the efforts of ISOL-based efforts. Collinear laser spectroscopy of rare isotopes requires efficient transport of pulsed beams with very low energy spread. To this end, a next generation beam cooler and buncher has been developed and commissioned at the NSCL to provide bunched, low energy spread ion beams for collinear laser spectroscopy of rare isotopes. The beam cooler and buncher features a novel electrode design intended to simplify construction and maintenance, as well as permit the use of large radiofrequency (RF) amplitudes for more efficient beam cooling, especially in the case of high beam currents. The cooler and buncher has been characterized with an offline ion source, and an online measurement of the hyperfine spectrum of the D1 transition of 37K has been performed. The results of commissioning measurements will be presented.
Topic: The TRIUMF experience with the Design, Fabrication and Commissioning of Large Gap Wien Filters
Dr. Syd Kreitzman ( TRIUMF, Canada ) / April 28, 2014
In recent years TRIUMF has built two surface Muon (29.5 MeV/c) beam-lines each of which contained dual large gap Wien Filters. These were designed with the dual purpose of particle separation and simultaneous muon spin rotation up to 90 degrees (thereby creating a clean beam with variable transverse polarization). To achieve these functions achromatically (i.e. with essentially 100% transmission for a Δp/p of 10%), a phase space inverting triplet separated the Wien filter pair.
Dr. Nicholas Scielzo ( Lawrence Livermore National Laboratory ) / May 5, 2014
Ms. Qian Li ( Univeristy of Notre Dame ) / May 12, 2014
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