TY - JOUR
T1 - Measurement of the delayed neutron fraction and correction of small angle scattering data from a pulsed spallation source
AU - Epperson, J. E.
AU - Carpenter, J. M.
AU - Thiyagarajan, P.
AU - Heuser, B.
N1 - Funding Information:
The use of fissionable materials as targets in pulsed spallation sources results in, in addition to the prompi pulses, a contribution from delayed neutrons . Certain precursor fission fragments undergo one or more steps of beta, decay followed by neutron emission, as has been discussed by Carpenter [1,2]. Energetic photons emitted from beta decaying products of fission and spallation processes can also induce delayed neutrons through (-y, n) reactions in such materials as 9 Be and 2 D which may be near the target . Delay half-lives [31 range from fractions of a second to a minute for precursor fission fragments and from a few seconds to several days for fission product gamma rays interacting with 9 Be . Since the intense pulsed neutron source (IPNS) at Argonne National Laboratory (ANL) normally operates with a pulse frequency of 30 Hz, the delayed neutrons are emitted at times not correlated with the generation of the prompt pulses . One may assume that the delayed neutrons are modera :PA and emerge in the collimat ,-d beam line ..ith approximatelythe same spectral distri- bution as in the prompt pulses . The result is an essen- tiâiiy steady source of delayed neutrons on which the prompt pulses are superimposed, as represented sche- matically in fig. 1. At the source, the prompt pulse of uninodulated neutronsis only some300ns in width; however, down- This work wasperformed under the auspices of the U.S. Department of Energy, Division of Materials Science, Office ofBasicEnergySciences,under Contract W-31-109-ENG-38.
PY - 1990/4/1
Y1 - 1990/4/1
N2 - The fraction of delayed neutrons in a moderated beam from the enriched uranium, pulsed spallation source at the intense pulsed neutron source at Argonne National Laboratory has been measured and found to be 0.0283 for 450-MeV protons. Delayed neutrons produce a sample-dependent background in time-of-flight instruments. Because of the distribution of neutron wavelengths in the prompt pulse, the significance of the delayed neutron contribution to the observed scattering profile is strongly dependent on the wavelength and therefore on the magnitude of the momentum transfer. This effect is demonstrated, and a general correction procedure in current use for small angle neutron scattering data is described.
AB - The fraction of delayed neutrons in a moderated beam from the enriched uranium, pulsed spallation source at the intense pulsed neutron source at Argonne National Laboratory has been measured and found to be 0.0283 for 450-MeV protons. Delayed neutrons produce a sample-dependent background in time-of-flight instruments. Because of the distribution of neutron wavelengths in the prompt pulse, the significance of the delayed neutron contribution to the observed scattering profile is strongly dependent on the wavelength and therefore on the magnitude of the momentum transfer. This effect is demonstrated, and a general correction procedure in current use for small angle neutron scattering data is described.
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U2 - 10.1016/0168-9002(90)90249-6
DO - 10.1016/0168-9002(90)90249-6
M3 - Article
AN - SCOPUS:0006934162
SN - 0168-9002
VL - 289
SP - 30
EP - 34
JO - Nuclear Inst. and Methods in Physics Research, A
JF - Nuclear Inst. and Methods in Physics Research, A
IS - 1-2
ER -