| NSF Org: |
PHY Division Of Physics |
| Recipient: |
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| Initial Amendment Date: | September 4, 2015 |
| Latest Amendment Date: | June 9, 2020 |
| Award Number: | 1506084 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Allena K. Opper
aopper@nsf.gov (703)292-8958 PHY Division Of Physics MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | September 1, 2015 |
| End Date: | August 31, 2021 (Estimated) |
| Total Intended Award Amount: | $180,000.00 |
| Total Awarded Amount to Date: | $180,000.00 |
| Funds Obligated to Date: |
FY 2016 = $60,000.00 FY 2017 = $60,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
200 W WARD ST SPRINGFIELD OH US 45504-2120 (937)327-7930 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
OH US 45501-0720 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | NUCLEAR STRUCTURE & REACTIONS |
| Primary Program Source: |
01001617DB NSF RESEARCH & RELATED ACTIVIT 01001718DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.049 |
ABSTRACT
The research supported by this award will probe the limits of our understanding of the weak interaction, one of the four fundamental forces of nature. Among other things, the weak interaction is responsible for the type of radioactive decay called beta decay in which a nucleus is transformed into a different nucleus with the emission of an electron and a neutrino. The award will allow the two scientists to carry out experiments in which they precisely measure the energy of electrons emitted in four different nuclear beta decays. Three of these experiments will test key aspects of the Standard Model of the electroweak interaction, which is the theory that describes the unification of two of the fundamental forces, the weak interaction and the electromagnetic interaction. These precision beta decay measurements are complementary to particle collider experiments in the search for new physics. A fourth proposed experiment aims to resolve uncertainties in the beta decay of potassium-40, an important tool in geochronology. The research program has the further goal and benefit of training highly talented undergraduate physics students. Students involved will gain experience with state-of-the-art software and experimental techniques, and will learn to think independently and gain a variety of practical problem solving skills. The broader impact is felt when these students enter the workforce in STEM fields or in teaching.
The research program consists of several experiments involving the high precision measurement of the shapes of beta spectra. In two of the proposed experiments the goal is to provide a strong test of the Conserved Vector Current hypothesis in the electroweak sector of the Standard Model of particle physics. In a third experiment, the goal is to improve limits on non-Standard-Model contributions (Fierz terms) to the description of the weak interaction. A fourth experiment has the goal of resolving an uncertainty in the potassium-40 beta spectrum, which is relevant to applications in geochronology. Specifically, the carbon-14 beta spectrum will be measured using a new magnetic spectrometer at the University of Wisconsin-Madison. This spectrometer will be nearly identical in form to the superconducting spectrometer used to make the same measurement in oxygen-14, enabling reduced uncertainties arising from higher order matrix element contributions. Measurements in fluorine-20 and helium-6 will be carried out at the National Superconducting Cyclotron Laboratory using implantation into a scintillator detector, which will have significantly different systematic effects from the magnetic spectrometer measurements and will be important in achieving low thresholds. A fourth experiment has the goal of measuring the shape of the potassium-40 beta spectrum. Knowledge of this spectrum shape is important for a standard technique in radioactive dating of geologic samples, but a recent report suggests the shape may not be as well understood as had been thought. An important aspect of all these measurements is in assessing and correcting for systematic effects through measurement and computational modeling.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The supported work consisted of several projects, all with the goal of advancing the understanding of the type of radioactive decay known as beta decay. By making precise measurements of the properties of beta-decaying atomic nuclei, we learn about the fundamental forces involved, and obtain information useful in areas such as medicine and astrophysics.
In one project, we demonstrated the feasibility of measuring the decay properties of the radioactive nucleus 20F by accelerating a beam of these nuclei to high energy and implanting them directly into a detector. This method differs from the traditional experimental scheme where the radioactive sample is external to the detector. The ?external source? method has the problem that some of the radiation emitted by the radioactive source will scatter back out of the detector. That means not all of the energy of the radiation will be detected resulting in a distorted measurement. The implantation method takes advantage of the variety of high energy, high intensity beams of radioactive nuclei available at facilities such as the National Superconducting Cyclotron Laboratory (where the 20F data were taken) and going forward at the Facility for Rare Isotope Beams.
Through this implantation method, we were able to record the energy of individual electrons emitted by 20F nuclei as they decay?that is, the beta spectrum of 20F. Thus, we were able to measure precisely the distribution of these electrons given off in beta decay, which enables us to search for evidence of new physics beyond our current understanding. When our analysis is completed, it will allow us to put limits on the size of specific contributions (so-called Fierz interference terms) predicted by some theories of beta decay. With the implantation method, we also carried out and published a precise determination of the 20F decay half-life, which is important in astrophysics for understanding the evolution of certain types of stars.
In the 20F experiment as well in a related experiment in which 6He was implanted in a detector to study its beta spectrum, we carried out computer modeling of the physical processes that take place in the detector. In beta decay, there?s some probability that a fraction of the energy of an emitted electron may go to create a photon. For beta-decaying nuclei implanted in a detector, the electrons will be detected, but some of the photons may escape, causing a distortion in the energy spectrum. We have published a paper demonstrating that carrying out careful computer modeling (Monte Carlo simulations) is necessary in order to determine and correct for these types of distortions, and showed quantitatively what the effect is in the 6He case.
In another project, we have developed a new apparatus to make a measurement of the beta spectrum of the radioactive nucleus 14C. This measurement, complementing a previous measurement we made of the 14O beta decay spectrum, will quantitatively test the effects of so-called ?weak magnetism? on the spectrum shape. These weak magnetism effects are a prediction of the currently accepted theory of the unification of two of the fundamental forces of nature: the weak force and electromagnetism. Comparison of the measured spectra to the predictions will provide a test of the underlying theory of the unification and will put limits on (or possibly reveal) new physics. For this work, we designed, constructed, and commissioned a new beta spectrometer that uses magnetic fields to focus electrons emitted in the decay onto a sensitive detector. This spectrometer may also have applications in measuring the yield of low energy (Auger) electrons emitted by radiopharmaceuticals, which would enable improved dose calculations for radiopharmaceuticals used in cancer treatments.
Over the course of the supported work, these projects have provided research opportunity and training for 7 undergraduate students at Wittenberg University, including 2 women. These students subsequently went on to K-12 teaching; industrial R&D; and graduate programs in medical physics, physics/high performance computing, electrophysics, and computational biophysical chemistry.
Last Modified: 12/14/2021
Modified by: Paul Voytas
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