Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session KM: Mini-Symposium on Technological Developments for Low-Radioactivity Background Experiments |
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Chair: Alan Poon, Lawrence Berkeley National Laboratory Room: Kona 5 |
Saturday, October 11, 2014 9:00AM - 9:30AM |
KM.00001: Overview of detector technologies in low-radioactivity-background experiments Invited Speaker: Ryuta Hazama It will discuss the current status of low-radioactivity-background detectors, in terms of low background counting techniques, such as alpha/beta/gamma spectroscopy, Rn emanation assay, and mass spectrometry and also, in terms of background reduction techniques to realize the detectors to catch rare signals. These techniques will be common issues, especially for experiments on solar neutrinos, dark matter, double beta decay and long half-life phenomena. Thus, several international cooperation/collaboration to share its knowledge and to create the database is in progress. [Preview Abstract] |
Saturday, October 11, 2014 9:30AM - 9:45AM |
KM.00002: The LBNL Low Background Facility - Services and Recent Updates Keenan Thomas, Alan Smith, Eric Norman, Yuen-Dat Chan, Alan Poon, Kevin Lesko The Low Background Facility (LBF) at Lawrence Berkeley National Laboratory (LBNL) in Berkeley, California provides low background gamma spectroscopy services to a wide array of experiments and projects. The analysis of samples takes place within two unique facilities; locally within a carefully-constructed, low background laboratory on the surface at LBNL and at a recently established underground location (4300 m.w.e) at the Sanford Underground Research Facility (SURF) in Lead, SD (relocated from Oroville, CA). These facilities provide a variety of gamma spectroscopy services to low background experiments primarily in the form of passive material screening for primordial radioisotopes (U, Th, K) or common cosmogenic/anthropogenic products; active screening via neutron activation analysis for U,Th, and K as well as a variety of stable isotopes; and neutron flux/beam characterization through the use of monitors. A general overview of the facilities, services, and sensitivities will be presented. Recent activities and upgrades will also be described in detail including an overview of the recently installed counting system at SURF. The LBF is open to any users for counting services or collaboration on a wide variety of experiments and projects. [Preview Abstract] |
Saturday, October 11, 2014 9:45AM - 10:00AM |
KM.00003: Study of $^{180}$Ta$^{\mathrm{m}}$ Lifetime by using HPGe Detector at Kamioka Underground Observatory W.M. Chan, T. Kishimoto, K. Suzuki, K. Matsuoka, S. Umehara, S. Yoshida, M. Nomachi, T. Iida, K. Nakajima, N. Nakatani, H. Kakubata, W. Wang, V.T.T. Trang, T. Ohata, K. Tetsuno, D. Tanaka, T. Maeda For all nuclear isotopes that exist on the Earth, $^{180}$Ta$^{\mathrm{m}}$ has known as the only isotope that naturally occurring in metastable state with remarkable properties of long-lived isomeric state (T$_{1/2}$ \textgreater 1.2 $\times$ 10$^{15}$ y) and short-lived ground state (T$_{1/2} = $ 8.1 h). Many researchers have great concern about this isotope because of its interesting nuclear properties and puzzling nucleosynthesis mechanics. The half-life of $^{180}$Ta$^{\mathrm{m}}$ is yet to be confirmed up until now. Since July 2013, we have developed a new ultra-low background gamma spectroscopy with HPGe detector at the Kamioka Underground Observatory (2700 m.w.e.) and started the observation of the decay of $^{180}$Ta$^{\mathrm{m}}$. Compare with other worldwide researches, Kamioka stands a good chance to conclude or impose a longer limit on the half-life of $^{\mathrm{180}}$Ta$^{\mathrm{m}}$ in the order of 10$^{17}$ years. With effort on background reduction such as shield design and pulse shape discrimination analysis, we have successfully improved the signal-to-noise ratio of the measurement. The result will be presented for the first time in this meeting. [Preview Abstract] |
Saturday, October 11, 2014 10:00AM - 10:15AM |
KM.00004: Neutron Activation Analysis for Low Energy Particle Physics Experiments Christopher Grant Particle physics experiments searching for new physics at or below a few tens of MeV are generally plagued with backgrounds from both natural and cosmogenic-induced radioactivity. The frequency of such signals from new physics is extremely rare. In the case of neutrino-less double beta decay, direct dark matter searches, and neutrinos from astrophysical phenomena, sufficient quantification and suppression of backgrounds is vital. The experimental neutrino and dark matter group at UC Davis has been developing dedicated neutron activation facilities to address backgrounds in future liquid Argon TPCs and low-background liquid scintillation detectors. I will summarize neutron activation studies performed both at the McClellan Nuclear Research Center and the Crocker Nuclear Laboratory 67.5 MeV proton cyclotron. Projected sensitivities for radio-assaying U, Th, and K in detector materials will be presented, along with measurements of fast neutron reaction cross-sections on Argon nuclei. [Preview Abstract] |
Saturday, October 11, 2014 10:15AM - 10:30AM |
KM.00005: Low background counting of 222Rn, 220Rn and 219Rn with electrostatic counters Brian Mong The radon counting technique based on electrostatic precipitation of progenies in gas followed by alpha spectroscopy has been applied to support the material selection programs of low background, neutrino and dark matter experiments with emphasis on EXO. An array of 8 counters operated by Laurentian University at SNOLAB and the Waste Isolation Pilot Plant have reached the sensitivity of 10 atoms/day in the uranium, thorium and actinium chains. Hardware improvements are underway to further increase the capacity and sensitivity in support of nEXO. [Preview Abstract] |
Saturday, October 11, 2014 10:30AM - 10:45AM |
KM.00006: Design of a low background cryostat for a 1.3 kg low-noise, high purity germanium gamma-ray spectrometer John Orrell, Craig Aalseth, Juan Collar, Jim Colaresi, Jim Fast, Todd Hossbach, Cory Overman, Brent VanDevender, Mike Yocum Recent progress on the development of very-low-energy threshold high-purity germanium ionization spectrometers has produced an instrument of 1.3 kg mass and noise performance of less than 100 eV full-width half-maximum for a peak generated with an electronic pulser as input. The detector was installed in a low-background cryostat intended for use in a low-mass WIMP dark-matter search. The integrated detector and low-background cryostat achieved noise performance of 98 eV full-width half-maximum for an electronic pulser-generated peak and gamma-ray energy resolution of 1.9 keV full-width half-maximum at the 60Co gamma-ray energy of 1332 keV. This presentation describes the low-noise and low-background design considerations employed, the thermal characterization of the low-background cryostat, the specifications of the newly prepared 1.3 kg p-type point contact germanium detector, and the baseline performance of the integrated detector and cryostat. [Preview Abstract] |
Saturday, October 11, 2014 10:45AM - 11:00AM |
KM.00007: Looking at Low-Background Nuclear Astrophysics Measurements using CASPAR Daniel Robertson, Manoel Couder, Uwe Greife, Hyo Soon Jung, Kiana Setoodehnia, Michael Wiescher, Doug Wells An accelerator laboratory (CASPAR) to be installed at the Sanford Underground Research Facility (SURF) is being constructed by a collaboration lead by South Dakota School of Mines and Technology. The study of alpha induced reactions of astrophysical interest in a quasi-background free environment is the goal of the laboratory. Specifically, neutron producing reactions for the s-process will be investigated. This process is responsible for the nucleosynthesis of half of the elements heavier than iron. An outline of CASPAR, its timeline and scientific goals will be presented. [Preview Abstract] |
Saturday, October 11, 2014 11:00AM - 11:15AM |
KM.00008: Background Studies of CANDLES for Double Beta Decays of $^{48}$Ca Hidekazu Kakubata An underground observatory is the most effective to perform low background experiments because an underground environment avoids cosmic muon. Backgrounds still remain in this environment, so to grasp their origin and intensity is necessary. We perform the CANDLES experiment in the Kamioka Underground Laboratory to search for $0\nu\beta\beta$ of $^{48}$Ca, which has the highest Q-value (4.27MeV) of all $\beta\beta$ nuclides. Here we must consider backgrounds in the energy region around the Q-value. On the CANDLES detector, internal backgrounds from radial contamination in CaF$_2$ crystal scintillators can be restrained to a level free from problems. However, other backgrounds were observed in the energy region higher than the Q-value and peak structure is found in 7$\sim$8MeV. We inferred that $\gamma$-rays emitted by neutron capture reactions on Fe is the main origin of backgrounds. To confirm this hypothesis, we carried out special run using $^{252}$Cf neutron source set outside the detector. As a result, we found that the source of these backgrounds is $\gamma$-ray from neutron capture on the surrounding material of the detector, especially on the rock and the stainless. For further background reduction, we plan to install additional passive neutron and $\gamma$-ray shields. [Preview Abstract] |
Saturday, October 11, 2014 11:15AM - 11:30AM |
KM.00009: A Time of Flight Background Rejection Technique for Low Temperature Calorimeters Johnny Goett Cryogenic bolometer detectors feature unmatched energy resolution, dynamic range and efficiency. In spite of these strengths, low energy alpha depositions introduce a continuum background below 5 MeV that present severe challenges to the advancement of precision low threshold spectroscopy. The indifference of the bolometer to different types of radiation, which goes hand in hand with what makes it such an excellent calorimeter, will limit the sensitivity of future macro-bolometer arrays to new physics. To develop new capabilities with this technology, we are developing a research program that leverages the spectrum and time- of-flight of ballistic phonon modes in the bulk of the material to introduce discrimination capabilities between alpha, beta and gamma radiation in a single detector. Applications in both pure physics research and materials assay will be discussed. [Preview Abstract] |
Saturday, October 11, 2014 11:30AM - 11:45AM |
KM.00010: Design of a Low Background Liquid Scintillation Counter for a Shallow Underground Laboratory John Orrell, Craig Aalseth, Bruce Bernacki, Matt Douglas, Jennifer Erchinger, Erin Fuller, Martin Keillor, Shannon Morley, Crystal Mullen, Mark Panisko, Sarah Shaff, Glen Warren, Michael Wright Pacific Northwest National Laboratory operates a 35-meter water-equivalent overburden, shallow underground laboratory for measuring low-concentration radioactive isotopes in environmental samples collected. A low-background liquid scintillation counter is under development. Liquid scintillation counting is useful for beta-emitting isotopes without (or low) gamma ray yields. The high-efficiency beta detection in a liquid scintillation cocktail coupled with the low-background environment of a shield located in a clean underground laboratory provides for increased-sensitivity measurements to a range of isotopes. Benchmarked simulations have evaluated the shield design requirements to assess the background rate achievable. Assay of shield construction materials provides the basis for the shield design development. The low background design is informed by efforts in experimental design of neutrinoless double beta decay experiments, direct detection dark matter experiments, and low energy neutrino detection experiments. In this vein a background budget for the instrument is presented with attention to low background methods directed toward applications of nuclear measurements. [Preview Abstract] |
Saturday, October 11, 2014 11:45AM - 12:00PM |
KM.00011: Nuclear Physics Backgrounds for Liquid Argon Neutrino Detectors Victor Gehman, Kelsey Oliver-Mallory, Kate Scholberg We present an analytic calculation of the radioactive backgrounds in neutrino detectors using liquid argon as their active medium, using the proposed LBNE far detector as a concrete example. These radioactive backgrounds are one of the main factors that will set the low-energy threshold of such a detector and will play an important role in its overall data rate. The presence or absence of these backgrounds will also determine the ultimate sensitivity of a liquid argon based neutrino detector to astrophysical neutrino signals, most importantly, those from galactic supernova bursts. The radioactive backgrounds in this study fall into two categories: intrinsic radioactivity from detector construction materials ($^{232}$Th, $^{238}$U, $^{60}$Co, $^{40}$K, $^{85}$Kr, and $^{39}$Ar), and cosmogenic backgrounds originating from {\it in situ} activation of the argon. We include neutron and proton flux as a function of detector overburden, both in terms of direct energy depositions and for cosmogenic activation. We then use this depth dependent background model to study the sensitivity of a large liquid argon detector to supernova burst neutrinos using both analytic and Monte Carlo techniques. [Preview Abstract] |
Saturday, October 11, 2014 12:00PM - 12:15PM |
KM.00012: Large-size germanium crystal growth for rare event physics Dongming Mei, Guojian Wang, Hao Mei, Yutong Guan, Gang Yang, Jayesh Govani Cosmogenic production in germanium crystals grown on the surface can limit the sensitivity for the next generation deep underground experiments in searching for rare event physics beyond the Standard Model. One of the best solutions to eliminate unwanted cosmogenics is to produce the germanium crystals and detectors in an underground environment. The goal of this project is to create state-of-the-art detectors to advance neutrinoless double-beta decay and dark matter exploration research and technology while simultaneously paving the way for infrastructure to support an underground laboratory for zone refining, crystal growth, and detector fabrication. The greatest challenge in the growth of germanium crystals is a lack of precise control of individual crystal properties such as the impurity distribution, the dislocation density, and the crystalline structure. With knowledge gained from the pioneers in the field of crystal growth, the researchers have developed a novel technique to grow detector-grade crystals. In this paper, we will report detector-grade large-size germanium crystal growth at the University of South Dakota. [Preview Abstract] |
Saturday, October 11, 2014 12:15PM - 12:30PM |
KM.00013: Study Well-Shaped Germanium Detectors for Low-background Counting Wenzhao Wei, Dongming Mei, Chao Zhang Radiogenic particles are known as the main sources of background for all ultra-low background experiments in the detection of dark matter and neutrino properties. In particular, the radiogenic gamma rays from PMTs are a main component of the observed backgrounds in the noble liquid detectors such as XENON100 and LUX. This suggests a more accurate screening of PMTs is needed for the next generation experiments such as LUX-Zplin or Xenon1T. Hence, we propose to develop well-shaped germanium detectors for a better understanding of the radiogenic background from PMTs. A well-shaped germanium detector array and PMT (R11410MOD) have been designed in a Geant4-based Monte Carlo simulation, in which three radiogenic background sources from $^{238}$U, $^{232}$Th and $^{40}$K have been studied. In this work, we show the detector performance including the detector efficiency, energy resolution and the detector sensitivity for low-background counting in the detection of rare event physics. [Preview Abstract] |
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