Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session R13: Minisymposium: Precision Measurements in Nuclear Physics IFocus
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Sponsoring Units: DNP Chair: Hiro Iwasaki, Michigan State University Room: Roosevelt 5 |
Monday, January 30, 2017 10:45AM - 11:21AM |
R13.00001: Nuclear Excitation by Electronic Transition of U-235 Invited Speaker: Perry Chodash Nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that is theorized to exist in numerous isotopes. NEET is the inverse of bound internal conversion and occurs when an electronic transition couples to a nuclear transition causing the nucleus to enter an excited state. This process can only occur for isotopes with low-lying nuclear levels due to the requirement that the electronic and nuclear transitions have similar energies. One of the candidate isotopes for NEET, $^{235}$U, has been studied several times over the past 40 years and NEET of $^{235}$U has never been conclusively observed. These past experiments generated conflicting results with some experiments claiming to observe NEET of $^{235}$U and others setting limits for the NEET rate. If NEET of $^{235}$U were to occur, the uranium would be excited to its first excited nuclear state. The first excited nuclear state in $^{235}$U is only 76 eV, the second lowest known nuclear state. Additionally, the 76 eV state is a nuclear isomer that decays by internal conversion with a half-life of 26 minutes. In order to measure whether NEET occurs in $^{235}$U and at what rate, a uranium plasma was required. The plasma was generated using a Q-switched Nd:YAG laser outputting 789 mJ pulses of 1064 nm light. The laser light was focused onto uranium targets generating an intensity on target of order 10$^{12}$ W/cm$^2$. The resulting plasma was captured on a catcher plate and electrons emitted from the catcher plate were accelerated and focused onto a microchannel plate detector. Measurements performed using a variety of uranium targets spanning depleted uranium up to 99.4\% enriched uranium did not observe a 26 minute decay. An upper limit for the NEET rate of $^{235}$U was determined. [Preview Abstract] |
Monday, January 30, 2017 11:21AM - 11:33AM |
R13.00002: Precision measurement of the radiative beta decay of the free neutron Thomas Gentile A continuous spectrum of photons is emitted in the decay of the free neutron. We present the results of the RDK II experiment, in which radiative photons were detected in coincidence with the electrons and protons from neutron decay. The experiment was performed on the NG-6 fundamental physics neutron beam line at the National Institute of Standards and Technology Center for Neutron Research using two different photon detector arrays. An annular array of bismuth germanium oxide scintillators detected photons with energies between 14 keV and 782 keV and an array of large area avalanche photodiodes directly detected photons with energies between 0.4 keV and 14 keV . This experiment represents the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies. [Preview Abstract] |
Monday, January 30, 2017 11:33AM - 11:45AM |
R13.00003: Progress toward a new beam measurement of the neutron lifetime Shannon Fogwell Hoogerheide Neutron beta decay is the simplest example of nuclear beta decay. A precise value of the neutron lifetime is important for consistency tests of the Standard Model and Big Bang Nucleosynthesis models. The beam neutron lifetime method requires the absolute counting of the decay protons in a neutron beam of precisely known flux. Recent work has resulted in improvements in both the neutron and proton detection systems that should permit a significant reduction in systematic uncertainties. A new measurement of the neutron lifetime using the beam method is underway at the National Institute of Standards and Technology Center for Neutron Research. The projected uncertainty of this new measurement is 1 s. An overview of the measurement, its current status, and the technical improvements will be discussed. [Preview Abstract] |
Monday, January 30, 2017 11:45AM - 11:57AM |
R13.00004: Precision Measurement of Nuclear Electron Capture Decay David Koltick, Shih-Chieh Liu, Haoyu Wang, Jordan Heim, Jonathan Nistor The method of accurately measuring the radioactive decay constant of a isotope by measuring the decay rate as a function of time requires that both the detector and environment be stable over time periods comparable to the life-time of the isotope. In addition statistical accuracy requires initial counting rates be high but limited by the dead time capability of the data collection system and the detectors double-event resolving time. A High Purity Germanium (HPGe) spectrometer, sensitive to radiation from 3-KeV to over 3-MeV, has been built to measure radioactive decay constants to a level of 10$^{\mathrm{-5}}$ \textasciitilde 10$^{\mathrm{-6}}$ at a location only 6 meters from the core of the High Flux Isotope Reactor located at Oak Ridge National Laboratory. Such accuracy requires understanding of, background, signal-processing algorithms, and both the double and triple event pile-up in the observed spectrum. The approach taken is to fit the collected energy spectrum with invariant shapes, independent of event rate. By fixing the source-detector geometry and environmental conditions, the invariant shapes are (1) ideal energy spectrum without pile-up and background, (2) the ideal double event pile-up spectrum, (3) the ideal triple event pile-up spectrum, and (4) the stable background spectrum. A method is presented that finds these ideal shapes using the collected data in situ. Taking this approach the HPGe detector photopeak shape in the absence of background and pile-up is presented showing associated structure over a range of 7 orders of magnitude. [Preview Abstract] |
Monday, January 30, 2017 11:57AM - 12:09PM |
R13.00005: Precision Nuclear Beta Spectroscopy as a Probe for BSM Physics Aaron Sprow The shape of nuclear beta decay spectra is sensitive to new physics such as scalar and tensor currents, and weak magnetism. By selecting an appropriate nuclear species, it is possible to disentangle these effects. $^{45}$Ca, which undergoes a predominantly Gamow-Teller transition with an end-point energy of 256 keV, is an excellent probe for tensor couplings. Recently, the $^{45}$Ca beta decay spectrum was measured in the Caltech/UCNA $4\pi$ magnetic spectrometer instrumented with large, highly-pixelated Si detectors at the Los Alamos National Laboratory UCN facility. This detection system, in conjunction with an extremely thin foil source preparation, allows for a full reconstruction of events to build a precise spectrum. Preliminary results of the analysis of this data will be presented. [Preview Abstract] |
Monday, January 30, 2017 12:09PM - 12:21PM |
R13.00006: Precision Magnetometry and Systematic Effects in the Nab Experiment Jason Fry The Nab experiment will determine the electron-neutrino correlation parameter $a$ with a precision of $\delta a / a = 10^{-3}$ and the Fierz interference term $b$ to $\delta b = 3\times10^{-3}$ in unpolarized neutron $\beta$ decay. A long asymmetric spectrometer is optimized to achieve fast proton momentum longitudinalization and the required narrow proton momentum response function. A reliable relation of the measured proton TOF to $a$ requires detailed knowledge of the effective proton pathlength, which imposes requirements on the precision of the magnetic fields in the Nab spectrometer. The Nab magnetometry goals, associated systematics, and some initial results will be discussed. [Preview Abstract] |
Monday, January 30, 2017 12:21PM - 12:33PM |
R13.00007: ABSTRACT WITHDRAWN |
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