Study of a multi-pinhole collimation system based small-angle neutron scattering instrument at the Compact Pulsed Hadron Source

Abstract

The neutron flux of the Compact Pulsed Hadron Source (CPHS) is about 2–3 orders of magnitude lower than that of large neutron sources, which means that the beam intensity should be improved to achieve good statistics. Multi‐pinhole collimation can be used to obtain a lower Q with an acceptable beam intensity in a very small angle neutron scattering (VSANS) instrument and a higher beam intensity for a larger sample size in a small‐angle neutron scattering (SANS) instrument. A new nine‐pinhole structure is used in a SANS instrument at CPHS to achieve an acceptable range and resolution of Q and a higher beam intensity compared to single‐pinhole collimation. The crosstalk issue associated with multi‐pinhole collimation is addressed using an optimized algorithm to achieve a higher safety margin and a larger pinhole size with a higher beam intensity at the sample. Different collimator aperture structures are compared on the basis of their noise production. Experiments are performed to verify the theory of calculating reflection noise from the inner surface of the collimator's aperture and parasitic noise from the beveled collimator structure. From a simulated SANS experiment using cold neutrons in the SANS instrument, it is clarified that multi‐pinhole collimators with an opening angle on the downstream side have better performance than those with an opening angle on the upstream side and straight‐cut collimators. Compared with a single‐pinhole collimation system, a nine‐pinhole collimation system increases the intensity at the sample by approximately sevenfold when the sample size is increased by 20‐fold for CPHS‐SANS, and the signal‐to‐noise ratio is improved by exploiting a specific collimator aperture structure. Our goal is to install a multi‐pinhole collimator based SANS instrument at CPHS in the future, and it is hoped that these results will serve to promote the utilization of multi‐pinhole collimation systems at other facilities.

The multi-slit very small angle neutron scattering instrument at the China Spallation Neutron Source

“…Reflection and scattering from the edges of the multi-slits may result in severe noise, especially close to Q min . A bevelled multi-slit structure is suggested (Wang et al, 2018) with a cutting angle of 5 � to alleviate this issue.…”

Design of a three-detector system on LUOSHU: a small-angle neutron scattering instrument at China Mianyang Research Reactor

“…The collimator system consists of an 18 m-long series of super-mirror neutron guides (m = 3), which consist of six 2.5 m-long and one 3 m-long neutron guides near the velocity selector side, and a 1.5 m-long retractable vacuum tube, which can be manually changed from 0.5 to 1.5 m. The four-knife slits are used to reduce the experimental background with adjustable size. Also, the four-knife slits can be switched with the multi-pinhole slits to obtain an acceptable neutron intensity for different experimental scenarios including the grazing incidence module (Wang et al, 2018). Therefore, different collimation modes are available through the selection of different slits and apertures.…”

The very small angle neutron scattering instrument at the National Institute of Standards and Technology

“…Spallation sources utilize broad neutron wavelength distributions via time of flight (TOF), but the broad wavelength range causes the chromatic aberration from refractive lenses and the gravity distortion to become unacceptably large. Recent developments have been made utilizing converging vertically oriented narrow slits for beam current amplification (Abbas et al, 2015;Wang et al, 2018). The current instrument design uses a combination of converging beams, refractive lenses and gravity-canceling prisms for beam current enhancement.…”