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Neutron Depth Profiling with the New NIST Cold Neutron Source
Author(s) -
Lamaze G. P.,
ChenMayer H.,
Langland J. K.,
Downing R. G.
Publication year - 1997
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/(sici)1096-9918(199703)25:3<217::aid-sia226>3.0.co;2-3
Subject(s) - neutron , neutron source , nuclear physics , neutron flux , neutron temperature , materials science , neutron capture , chemistry , analytical chemistry (journal) , radiochemistry , physics , chromatography
Neutron depth profiling (NDP) is a method of near‐surface analysis for isotopes that undergo neutron‐induced positive Q‐value charged particle reactions, e.g. (n, α) and (n, p). The method is based on measuring the energy loss of the charged particles as they exit the specimen. Depending on the material under study, depths of up to 10 μm can be profiled and depth resolutions of the order of 15 nm can be obtained. The most studied analytes via NDP at the National Institute of Standards and Technology (NIST) are boron, lithium and nitrogen. These analytes have been determined in a variety of matrices. The NIST research reactor has recently undergone a major upgrade, including the addition of a new liquid‐hydrogen cold source, which reaches a lower effective temperature and more fully illuminates the neutron guides. The cold neutron depth profiling (CNDP) facility has been placed on a curved super‐mirror guide. Because of the guide curvature, the NDP chamber does not directly view the reactor and its associated fast neutrons and gamma rays, and therefore a 13.5 cm thick sapphire filter used previously in front of the beam port is no longer necessary. The increase in the neutron fluence rate at the end of the guide leads to an improvement in detection limit of more than a factor of four over the previous depth profiling instrument. The reduction in the gamma‐ray background in the chamber will improve our ability to measure elements such as nitrogen. © 1997 by John Wiley & Sons, Ltd.