Installation of a neutron bender-lens for spatially resolved prompt-gamma activation analysis

Journal Article · Tue Dec 31 04:00:00 EST 1996 · Transactions of the American Nuclear Society

OSTI ID:427058

Lindstrom, R M; Chen-Mayer, H H ^[1]; Sharov, V A ^[2]

---

1. National Inst. of Standards and Technology, Gaithersburg, MD (United States)
2. X-Ray Optical Systems, Inc., Albany, NY (United States); and others

The author have previously reported the focusing of a neutron beam by a lens composed of a bundle of glass capillary fibers using multiple grazing-angle reflection. The lens collects neutrons from a 45- x 50-mm beam from a {sup 58}Ni guide viewing a cold source and focuses them to a spot 0.53 mm full-width at half-maximum (FWHM) with a gain in flux of a factor of 80. Spatially resolved prompt-gamma activation analyses of boron, cadmium, and gadolinium have been demonstrated with submillimetre spatial resolution. The lens brings only a few percent of the incident neutrons to the focus. Because this lens is symmetrical, the high-intensity focal spot is in the shadow of the incident beam, which gives a high background. An object diaphragm of {sup 6}LiF (tapering to 1-mm aperture) is used just upstream from the sample to improve the contrast, but because this diaphragm and its support are necessarily located in the direct view of the gamma-ray detector, the gamma background is increased. Substantial background also comes from neutron scattering and capture in the lens itself, its mounting and positioning structure, and the surrounding shielding. Based on these measurements, a new neutron lens has been designed and constructed. Its installation was coordinated with a complete reconstruction of the prompt-gamma spectrometer in conjunction with the recent installation of a new liquid-H{sub 2} cold source at the NIST research reactor. To improve the signal-to-background ratio at the focal spot, a bent bundle of 3997 lead-glass fibers directs the neutrons to a focal spot 20 mm below the bottom edge of the incident beam. A motorized translation stage allows the lens to be remotely inserted into the neutron beam and removed when not needed.

• OSTI ID: 427058
• Report Number(s): CONF-961103--
• Journal Information: Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Vol. 75; ISSN TANSAO; ISSN 0003-018X
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
40 CHEMISTRY
DESIGN
FIBERS
INSTALLATION
LENSES
NBSR REACTOR
NEUTRON ACTIVATION ANALYSIS
NEUTRON GUIDES
PROMPT GAMMA RADIATION