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Title: Monte Carlo simulations of trapped ultracold neutrons in the UCN τ experiment

Abstract

We report that in the UCNτ experiment, ultracold neutrons (UCN) are confined by magnetic fields and the Earth's gravitational field. Field-trapping mitigates the problem of UCN loss on material surfaces, which caused the largest correction in prior neutron experiments using material bottles. However, the neutron dynamics in field traps differ qualitatively from those in material bottles. In the latter case, neutrons bounce off material surfaces with significant diffusivity and the population quickly reaches a static spatial distribution with a density gradient induced by the gravitational potential. In contrast, the field-confined UCN—whose dynamics can be described by Hamiltonian mechanics—do not exhibit the stochastic behaviors typical of an ideal gas model as observed in material bottles. In this report, we will describe our efforts to simulate UCN trapping in the UCNτ magnetogravitational trap. We compare the simulation output to the experimental results to determine the parameters of the neutron detector and the input neutron distribution. The tuned model is then used to understand the phase-space evolution of neutrons observed in the UCNτ experiment. Lastly, we will discuss the implications of chaotic dynamics on controlling the systematic effects, such as spectral cleaning and microphonic heating, for a successful UCN lifetime experiment to reachmore » a 0.01% level of precision.« less

Authors:
 [1];  [1];  [1];  [1]; ORCiD logo [2]; ORCiD logo [2];  [3];  [3];  [4];  [5];  [6];  [1];  [7];  [8];  [3];  [9];  [10];  [3];  [3];  [3] more »;  [3];  [11];  [3];  [12];  [3];  [13];  [3];  [3];  [1];  [6];  [3];  [3];  [3];  [3];  [5];  [5] « less
+ Show Author Affiliations
  1. Indiana Univ., Bloomington, IN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. North Carolina State Univ., Raleigh, NC (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  5. North Carolina State Univ., Raleigh, NC (United States)
  6. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)
  7. Institut Laue-Langevin, Grenoble (France)
  8. Univ. of California, Los Angeles, CA (United States)
  9. Tennessee Technological Univ., Cookeville, TN (United States)
  10. DePauw Univ., Greencastle, IN (United States)
  11. East Tennessee State University, Johnson City, TN (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  12. Univ. of Washington, Seattle, WA (United States)
  13. Joint Institute for Nuclear Research, Dubna, Moscow (Russia)
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP)
OSTI Identifier:
1550769
Alternate Identifier(s):
OSTI ID: 1546456
Grant/Contract Number:  
AC05-00OR22725; SC0014664
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 100; Journal Issue: 1; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Callahan, Nathan, Liu, Chen-Yu, Gonzalez, Francisco, Adamek, E., Bowman, James David, Broussard, Leah, Clayton, S. M., Currie, S., Cude-Woods, C., Dees, E. B., Ding, X., Fox, W., Geltenbort, P., Hickerson, K. P., Hoffbauer, M. A., Holley, A. T., Komives, A., MacDonald, S. W. T., Makela, M., Morris, C. L., Ortiz, J. D., Pattie, R. W., Ramsey, J., Salvat, D. J., Saunders, A., Sharapov, E. I., Sjue, S. K. L., Tang, Z., Vanderwerp, J., Vogelaar, B., Walstrom, P. L., Wang, Z., Weaver, H., Wei, W., Wexler, J., and Young, A. R. Monte Carlo simulations of trapped ultracold neutrons in the UCNτ experiment. United States: N. p., 2019. Web. doi:10.1103/PhysRevC.100.015501.
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Callahan, Nathan, Liu, Chen-Yu, Gonzalez, Francisco, Adamek, E., Bowman, James David, Broussard, Leah, Clayton, S. M., Currie, S., Cude-Woods, C., Dees, E. B., Ding, X., Fox, W., Geltenbort, P., Hickerson, K. P., Hoffbauer, M. A., Holley, A. T., Komives, A., MacDonald, S. W. T., Makela, M., Morris, C. L., Ortiz, J. D., Pattie, R. W., Ramsey, J., Salvat, D. J., Saunders, A., Sharapov, E. I., Sjue, S. K. L., Tang, Z., Vanderwerp, J., Vogelaar, B., Walstrom, P. L., Wang, Z., Weaver, H., Wei, W., Wexler, J., & Young, A. R. Monte Carlo simulations of trapped ultracold neutrons in the UCNτ experiment. United States. https://doi.org/10.1103/PhysRevC.100.015501
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Callahan, Nathan, Liu, Chen-Yu, Gonzalez, Francisco, Adamek, E., Bowman, James David, Broussard, Leah, Clayton, S. M., Currie, S., Cude-Woods, C., Dees, E. B., Ding, X., Fox, W., Geltenbort, P., Hickerson, K. P., Hoffbauer, M. A., Holley, A. T., Komives, A., MacDonald, S. W. T., Makela, M., Morris, C. L., Ortiz, J. D., Pattie, R. W., Ramsey, J., Salvat, D. J., Saunders, A., Sharapov, E. I., Sjue, S. K. L., Tang, Z., Vanderwerp, J., Vogelaar, B., Walstrom, P. L., Wang, Z., Weaver, H., Wei, W., Wexler, J., and Young, A. R. Mon . "Monte Carlo simulations of trapped ultracold neutrons in the UCNτ experiment". United States. https://doi.org/10.1103/PhysRevC.100.015501. https://www.osti.gov/servlets/purl/1550769.
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@article{osti_1550769,
title = {Monte Carlo simulations of trapped ultracold neutrons in the UCNτ experiment},
author = {Callahan, Nathan and Liu, Chen-Yu and Gonzalez, Francisco and Adamek, E. and Bowman, James David and Broussard, Leah and Clayton, S. M. and Currie, S. and Cude-Woods, C. and Dees, E. B. and Ding, X. and Fox, W. and Geltenbort, P. and Hickerson, K. P. and Hoffbauer, M. A. and Holley, A. T. and Komives, A. and MacDonald, S. W. T. and Makela, M. and Morris, C. L. and Ortiz, J. D. and Pattie, R. W. and Ramsey, J. and Salvat, D. J. and Saunders, A. and Sharapov, E. I. and Sjue, S. K. L. and Tang, Z. and Vanderwerp, J. and Vogelaar, B. and Walstrom, P. L. and Wang, Z. and Weaver, H. and Wei, W. and Wexler, J. and Young, A. R.},
abstractNote = {We report that in the UCNτ experiment, ultracold neutrons (UCN) are confined by magnetic fields and the Earth's gravitational field. Field-trapping mitigates the problem of UCN loss on material surfaces, which caused the largest correction in prior neutron experiments using material bottles. However, the neutron dynamics in field traps differ qualitatively from those in material bottles. In the latter case, neutrons bounce off material surfaces with significant diffusivity and the population quickly reaches a static spatial distribution with a density gradient induced by the gravitational potential. In contrast, the field-confined UCN—whose dynamics can be described by Hamiltonian mechanics—do not exhibit the stochastic behaviors typical of an ideal gas model as observed in material bottles. In this report, we will describe our efforts to simulate UCN trapping in the UCNτ magnetogravitational trap. We compare the simulation output to the experimental results to determine the parameters of the neutron detector and the input neutron distribution. The tuned model is then used to understand the phase-space evolution of neutrons observed in the UCNτ experiment. Lastly, we will discuss the implications of chaotic dynamics on controlling the systematic effects, such as spectral cleaning and microphonic heating, for a successful UCN lifetime experiment to reach a 0.01% level of precision.},
doi = {10.1103/PhysRevC.100.015501},
journal = {Physical Review C},
number = 1,
volume = 100,
place = {United States},
year = {Mon Jul 08 00:00:00 EDT 2019},
month = {Mon Jul 08 00:00:00 EDT 2019}
}
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Journal Article:
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Publisher's Version of Record
https://doi.org/10.1103/PhysRevC.100.015501
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Figures / Tables:

FIG. 1 FIG. 1: A cross-sectional view of the UCNτ magneto-gravitational trap. A illustrates an example UCN trajectory inside the trap. The lab coordinate system x-y-z and the local coordinate system ξ-η-ζ are shown. B shows a cross-section of rows of magnets with identical magnetization highlighted by the colored strips. Arrows indicatemore » the magnetization direction for each row of magnets. C shows the in-situ detector, referred as the dagger detector, which can be to moved vertically in and out of the trap volume. The beige-colored region is the active area of the neutron detector, coated with 10B, and the gray is the detector housing and support structure.« less
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