skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Journal Article · · Physical Review C
 [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
  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)
+ Show Author Affiliations

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.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Nuclear Physics (NP)
Grant/Contract Number:
AC05-00OR22725; SC0014664
OSTI ID:
1550769
Alternate ID(s):
OSTI ID: 1546456
Journal Information:
Physical Review C, Vol. 100, Issue 1; ISSN 2469-9985
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 5 works
Citation information provided by
Web of Science

References (28)

Neutron beta decay journal September 2009
The correct and incorrect generation of a cosine distribution of scattered particles for Monte-Carlo modelling of vacuum systems journal September 2002
The neutron and its role in cosmology and particle physics journal October 2011
Spin flip loss in magnetic confinement of ultracold neutrons for neutron lifetime experiments journal March 2017
Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection journal May 2018
Colloquium : The neutron lifetime journal November 2011
Storage of ultracold neutrons in the magneto-gravitational trap of the UCN τ experiment journal May 2014
A magneto-gravitational trap for absolute measurement of the ultra-cold neutron lifetime
  • Walstrom, P. L.; Bowman, J. D.; Penttila, S. I.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 599, Issue 1 https://doi.org/10.1016/j.nima.2008.11.010
journal February 2009
Neutron lifetime measurements with a large gravitational trap for ultracold neutrons journal May 2018
Neutron lifetime measurements using gravitationally trapped ultracold neutrons journal September 2008
The Neutron Enigma journal March 2016
Optimization and new applications of a magnetic trap for ultra-cold neutrons
  • Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 592, Issue 3 https://doi.org/10.1016/j.nima.2008.04.024
journal July 2008
The accuracy of symplectic integrators journal March 1992
On the measurement of the neutron lifetime using ultracold neutrons in a vacuum quadrupole trap journal July 2005
Chaotic scattering and escape times of marginally trapped ultracold neutrons journal July 2005
Reducing the Time Complexity of the Derandomized Evolution Strategy with Covariance Matrix Adaptation (CMA-ES) journal March 2003
Regular and Chaotic Dynamics book January 1992
Kolmogorov entropy and numerical experiments journal December 1976
A symplectic integration algorithm for separable Hamiltonian functions journal January 1991
ROOT — An object oriented data analysis framework journal April 1997
A new method for measuring the neutron lifetime using an in situ neutron detector journal May 2017
A multilayer surface detector for ultracold neutrons
  • Wang, Zhehui; Hoffbauer, M. A.; Morris, C. L.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 798 https://doi.org/10.1016/j.nima.2015.07.010
journal October 2015
New evaluation of neutron lifetime from UCN storage experiments and beam experiments journal January 2011
New evaluation of neutron lifetime from UCN storage experiments and beam experiments preprint January 2011
A multilayer surface detector for ultracold neutrons text January 2015
Spin flip loss in magnetic confinement of ultracold neutrons for neutron lifetime experiments text January 2016
Neutron lifetime measurements with the big gravitational trap for ultracold neutrons text January 2017
Neutron lifetime measurements using gravitationally trapped ultracold neutrons text January 2007

Figures / Tables (20)

FIG. 1(p. 2)figure FIG. 1
FIG. 2(p. 4)figure FIG. 2
FIG. 3(p. 5)figure FIG. 3
FIG. 4(p. 5)figure FIG. 4
FIG. 5(p. 5)figure FIG. 5
FIG. 6(p. 7)figure FIG. 6
FIG. 7(p. 7)figure FIG. 7
FIG. 8(p. 7)figure FIG. 8
FIG. 9(p. 8)figure FIG. 9
FIG. 10(p. 9)figure FIG. 10
FIG. 11(p. 9)figure FIG. 11
FIG. 12(p. 10)figure FIG. 12
TABLE I(p. 10)table TABLE I
FIG. 13(p. 11)figure FIG. 13
FIG. 14(p. 12)figure FIG. 14
FIG. 15(p. 12)figure FIG. 15
FIG. 16(p. 13)figure FIG. 16
FIG. 17(p. 14)figure FIG. 17
Fig. 18(p. 17)figure Fig. 18
Fig. 19(p. 17)figure Fig. 19

Similar Records

Storage of Ultracold Neutrons in the Magneto-Gravitational Trap of the UCN Experiment
Journal Article · Wed Jan 01 00:00:00 EST 2014 · Physical Review C · OSTI ID:1550769
+29 more
Status of the UCN τ experiment
Conference · Sun Dec 01 00:00:00 EST 2019 · OSTI ID:1550769
+2 more
On the measurement of the neutron lifetime using ultracold neutrons in a vacuum quadrupole trap
Journal Article · Fri Jul 01 00:00:00 EDT 2005 · Journal of Research of the National Institute of Standards and Technology · OSTI ID:1550769

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS