A polycapillary bending and focusing lens for neutrons

Abstract

A glass polycapillary lens that both bends and focuses a cold neutron beam has been designed and constructed. The bender focuser guides part of the incident beam away from its line of sight and focuses it to a spot of width 0.65 mm at a distance 95 mm from the lens exit and 20 mm below the bottom edge of the beam path, with a gain of 20 in neutron current density. The neutron transmission characteristics of the lens have been determined with two types of position-sensitive detectors, a charge injection device, and an imaging plate. The lens has been tested with prompt gamma measurements on a gadolinium shard and titanium foil.

Determination of Hydrogen in Semiconductors and Related Materials by Cold Neutron Prompt Gamma-ray Activation Analysis

“…In the future, the applicability of the technique may be enhanced by applying existing technologies and planned upgrades to the instrument. The application of a neutron lens 5,6 , that can focus the beam down to a spot size of 0.5 mm with minimum loss of flux, has made it possible to probe the elemental content of materials as a function of position. Future plans to bend the PGAA neutron beam away from the upper portion of neutron guide NG7 will permit mounting of larger samples in H2.2.4 the beam.…”

<title>Neutron imaging with Bragg mirrors</title>

“…Many neutron devices are being developed in this area but none has been yet designed for imaging. Polycapillary optics has shown exciting capabilities to focus neutrons at a submillimeter scale 17 . However, the devices designed on this principle have a modest transmission (less than 10%).…”

“…To study the image formation in that case it is necessary to add the TOF coordinate to the matrix formalism introduced before. The relation (7) corresponding to curved packets of wafers changes in a four dimensional formulation as follow: (17) where ∆t is the time deviation from the nominal value, v n is the average neutron velocity and M is the BM magnification as defined by (15). In this simple case the imaging conditions (12) - (14) (18) Considering the elastic (or quasi-elastic) scattering, the contributions of the horizontal angular deviation after scattering γ 0 , and of the relative wavevector deviation ∆k/k, to the final TOF relative deviation ∆t f /t f are given by: (19) where L SM is the distance from sample to BM and L T is the total flight path length from neutron source to detector.…”