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.
We have developed the CANDLES detector system for the study of 48-Ca 0nbb decay. The 48-Ca has the highest Q value (4.3 MeV) among double beta decay nuclei. It means that the large decay rate for a given neutrino mass and the least background. We constructed a detector at the Kamioka underground laboratory. I will describe the current status of this research in the world and our experiment.

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.

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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 the LHC.
This talk will discuss two avenues of research I am pursuing to investigate the fundamental symmetries of the electroweak interaction. As part of the TRINT collaboration at TRIUMF, we are utilizing neutral atom trapping techniques with optical pumping methods to highly-polarize ( ≥ 99%) a very cold and localized ( ≤ 1mK and ≤ 1mm3 ) source of short-lived 37K atoms. Locally at the Cyclotron Institute, we are nearing completion of building the Texas A&M University Penning trap (TAMUTRAP) facility, which will be the world’s largest-diameter cylindrical ion trap of radioactive nuclei. The unprecedented open-area of TAMUTRAP is ideal for 4π collection of the delayed protons following the superallowed β decays of very proton-rich nuclei. I will describe both of these “tabletop” research programs and especially try to relay how they are fun, interdisciplinary approaches of answering fundamental questions about the nature of our universe.

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 (PRL, 109(2012)032505).
In order to further push the limit of sensitivity it is necessary to suppress the background (currently dominated by gamma rays) and increase the mass of the parent isotope. EXO has started the development of a multi-ton scale time-projection chamber (TPC). One option under development is the search for 0nbb in 136Xe using a TPC filled with high pressure gaseous xenon as source and detection material. This layout allows the unique opportunity to extract into vacuum and tag Ba-daughter ions. This tagging possibility, combined with enough energy resolution to separate 0nbb and 2nbb decays, allows one to dramatically reduce the background of the measurement to virtually zero.
A test setup is being developed at Stanford to demonstrate the feasibility of Ba-ion extraction from 10 bar Xe into an UHV environment. A supersonic nozzle combined with an extraction RF-funnel (see e.g. NIMA, 496(2003)286) can be used to accomplish this task. Gas dynamic and Monte Carlo simulations indicate Ba-ion transport efficiencies higher than 90%. A prototype of such a nozzle-funnel system is currently being developed. A 10 bar Xe chamber and a Xe recovery system as well as the RF-funnel and a downstream sextupole ion guide are operational at Stanford. First ions have been extracted from Xe gas and the development of a m/q identification is ongoing. The status of Ba-ion extraction from a high pressure Xe gas environment, along with the latest results from EXO-200 will be presented.

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.
This effort is important, since long-lived heavy radionuclides have wide application in environmental science, and there is also potential for the study of nuclear reactions and the determination of trace elements combining Accelerator Mass Spectrometry with Neutron Activation Analysis. The possibilities will be demonstrated in recent examples of research projects in these areas.

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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.
Nuclear astrophysics provides tools to determine the age of the Universe independent from astronomical observations. This history of the Universe is imprinted in the isotopic abundance pattern of stable and, in particular, long-lived unstable nuclei. If the half-life of such isotopes is comparable to the Hubble time, they can be interpreted as cosmo-chronometers.
A promising isotope is 87Rb, which decays on a time scale of 50 Gyr to 87Sr. The interpretation of this isotope as a cosmo-chronometer is currently hampered by the unknown neutron capture cross section of 85Kr, which decays with a half-life of 10 yr. The measurement of this cross section will soon be possible at the FRANZ facility at the Goethe University Frankfurt/Germany, which is currently under construction.

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.
With respect to neutron-induced fission cross section measurements, sensitivity studies have indicated a need for high-precision data, as uncertainties in nuclear data inputs propagate into uncertainties in key performance parameters for applications. To address this need, the Neutron Induced Fission Fragment Tracking Experiment collaboration has developed a fission Time Projection Chamber (TPC). Designed to address sources of systematic uncertainty that have plagued previous measurements, the fission TPC is based on well-established technology, miniaturized and modified for use in fission research.
Fission TPC experiments take place at the Los Alamos Neutron Science Center (LANSCE) Weapons Neutron Research facility, a spallation neutron source which provides a white neutron spectrum ranging from hundreds of keV to hundreds of MeV. During the 2012 LANSCE run cycle, the fission TPC was used to measure the 238U/ 235U (n,f) cross-section ratio. This ratio will be used to benchmark TPC performance.
An overview of the LANSCE-NS experimental program and the fission TPC project will be presented along with early performance results.

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.
In this talk I will present recent results from in-beam gamma-spectroscopy experiments using the GRETINA array at the NSCL. Detailed spectroscopy of neutron-rich nuclei around N=20 and 40 shed new light on the evolution of nuclear shell structure in exotic nuclei.

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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.
In this talk, a variety of experimental methods used for the investigation of explosive astrophysical reactions will be considered. Direct studies play a key role in this field, but equally important, are indirect methods that use both stable and radioactive ion beams. Such investigations often require innovative new techniques, coupled with the latest developments in detector technology, and highlight the close relationship between nuclear structure and astrophysics.

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.

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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.
The Wien filter specifications are similar for the two pairs: Operating E-field range ~5-45kV/cm, effective length ~1.5m, operating B-field range ~60-540G, with the difference between the two pairs reflected in their inter-electrode gap. The first device pair required a gap of 12cm and the second a gap of 8cm, thereby requiring the systems to be designed for +/-300 and +/-200kV respectively. Due to space considerations, the +/- 300kV system was designed with external power supply stacks + HV cables, whereas the +/-200kV system contained stacks internally integrated in the Wien filter.
To reliably commission these systems, many hard lessons were learned, with the most severe ones being revealed in the first +/-300kV system. Specific details on: i) Max e-field specifications; ii) power supply and cable issues; iii) feedthrough design; iv) triple point considerations; v) insulator design; vi) surface finish requirements; vii) conditioning and safety practices; and vii) cleanliness requirements will be discussed in the presentation.

Topic: TBA

Dr. Nicholas Scielzo ( Lawrence Livermore National Laboratory ) / May 5, 2014

Topic: TBA

Ms. Qian Li ( Univeristy of Notre Dame ) / May 12, 2014

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