Neutron Optics: Towards Applications for Hot Neutrons

Schanzer, Christian; Schneider, Michael L.; Böni, P.

doi:10.1088/1742-6596/746/1/012024

Cited by 24 publications

(19 citation statements)

References 20 publications

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“…The dimensionless factor m, referred to as the "m-value" of a mirror coating, quantifies the deviation of the critical angle from the critical angle of Ni, i.e., θ c,m = mθ c,1 = mθ c (Ni). Later on, the development of supermirrors [7,8] has enabled a significant increase of the critical angle by up to m 8 times [9]. As a result, compared to Ni-coated surfaces, supermirror coated guides can transport neutrons emanating from ambient and even from hot moderators within a significantly increased solid angle, or "beam divergence", defined as twice the critical angle per lateral dimension.…”

Section: Operational Principle and Basic Implementations Of Nested El...mentioning

confidence: 99%

Nested mirror optics for neutron extraction, transport, and focusing

Herb¹,

Zimmer²,

Georgii³

et al. 2022

Preprint

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Neutron scattering is a well-established tool for the investigation of the static and dynamic properties of condensed matter systems over a wide range of spatial and temporal scales. Many studies of high interest, however, can only be performed on small samples and typically require elaborate environments for variation of parameters such as temperature, magnetic field and pressure. To improve the achievable signal-to-background ratio, focusing devices based on elliptic or parabolic neutron guides or Montel mirrors have been implemented. Here we report an experimental demonstration of a nested mirror optics (NMO), which overcomes some of the disadvantages of such devices. While even simpler than the original Wolter design, our compact assembly of elliptic mirrors images neutrons from a source to a target, minimizing geometric aberrations, gravitational effects and waviness-induced blurring. Experiments performed at MIRA at FRM-II demonstrate the expected focusing properties and a beam transport efficiency of 72 % for our first prototype. NMO seem particularly well-suited to i) extraction of neutrons from compact high-brilliance neutron moderators, ii) general neutron transport, and iii) focusing and polarizing neutrons. The phase space of the neutrons hitting a sample can be tailored on-line to the needed experimental resolution, resulting in small scattering backgrounds. As additional benefits, NMO situated far away from both the moderator and the sample are less susceptible to radiation damage and can easily be replaced. NMO enable a modular and physically transparent realization of beam lines for neutron physics similar to setups used in visible light optics.

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Section: Operational Principle and Basic Implementations Of Nested El...mentioning

confidence: 99%

Nested mirror optics for neutron extraction, transport, and focusing

Herb¹,

Zimmer²,

Georgii³

et al. 2022

Preprint

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show abstract

“…The nominal distance of the focal point of the parabolas is 80 mm away from the exit of the guide. The substrates are coated with supermirror m = 6 having an excellent reflectivity of R = 0.67 at the critical edge of the supermirror [5].…”

Section: Experimental Set-upmentioning

confidence: 99%

“…As already shown in previous works, elliptic mirrors [1]-[4] are well suited to focus neutron and xray beams at the sample. With the rather dramatic increase of the reflection angles of supermirrors exceeding m = 8 times the critical angle of reflection of Ni [5], neutrons encompassing a wide range of wavelengths and large divergence can be directed towards the sample position. While adjusting the beam size at the sample with Montel mirrors [6] is straightforward using an aperture at the focal point at the entrance of the mirror [6], the selection of the beam size using elliptic or parabolic guides is more complicated and essentially given by the design of the optics [7].…”

mentioning

confidence: 99%

Variable focusing system for neutrons

Schanzer¹,

Schneider²,

Filges

et al. 2018

J. Phys.: Conf. Ser.

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Abstract. We have developed a variable focusing system for neutrons that allows varying the vertical and horizontal beam size at the sample position independently. It is based on a focusing parabolic neutron guide coated with supermirror m = 6 times the critical angle of reflection of Ni. The divergence of the incident beam is adjusted by solid-state collimators with horizontally and vertically arranged absorbing blades. The performance of the prototype set-up has been benchmarked at the beamline BOA at SINQ confirming the expected behavior. In particular we show that the beam size at the sample position can be varied between 0.6 and 2 mm without exchanging the focusing guide or by introducing a beam-defining aperture between the exit of the guide and the sample, i.e. the beam size can be adapted more than half a meter away from the sample. IntroductionThe investigation of novel materials using neutron scattering techniques is challenging because these materials are often only available in small quantities, e.g. encompassing a volume of a few mm³. Moreover, special experimental conditions, e.g. high pressure, high/low temperatures and/or high magnetic fields can only be realized for small volumes. Confining the neutron beam to such small areas using slits reduces the number of neutrons delivered by the rather large neutron beams (e.g. 50-100 cm²) significantly because for the minimization of the background, the penumbra must be suppressed too, to reduce scattering of neutrons from the sample environment. Moreover, it would require an aperture that is placed close to the sample which is usually not compatible with the sample environment. Therefore, it is desirable to focus the neutrons precisely to an area corresponding to the given size of the sample. Ideally, the useful neutrons would be selected already far away from the sample area using neutron optical devices. As already shown in previous works, elliptic mirrors [1]-[4] are well suited to focus neutron and xray beams at the sample. With the rather dramatic increase of the reflection angles of supermirrors exceeding m = 8 times the critical angle of reflection of Ni [5], neutrons encompassing a wide range of wavelengths and large divergence can be directed towards the sample position. While adjusting the beam size at the sample with Montel mirrors [6] is straightforward using an aperture at the focal point at the entrance of the mirror [6], the selection of the beam size using elliptic or parabolic guides is more complicated and essentially given by the design of the optics [7]. In the following we propose a combination of a focusing parabolic guide with a variable collimation stage in front of the entrance of the guide that allows varying the size of the beam spot at the sample position in the horizontal and

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“…Thus, the higher the critical angle, the more efficient the supermirror is at reflecting neutrons. Recently, results have been reported where supermirrors have been fabricated with m = 8 [4].…”

Section: Introductionmentioning

confidence: 99%

Measurements of the neutron absorption in supermirror coatings

DiJulio,

Santoro,

Devishvili

et al. 2021

Preprint

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In this work we report on measurements of neutron absorption in supermirror coatings. The measurements were carried out using the SuperADAM instrument at the Institut Laue-Langevin and by measuring the gamma-ray production from m = 3 and m = 4 neutron supermirrors when illuminated by a beam of neutrons. The results provide a valuable validation for recent computational and theoretical work that can be used as input to Monte-Carlo radiation transport calculations for the design of the shielding of neutron scattering instruments.

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Neutron Optics: Towards Applications for Hot Neutrons

Cited by 24 publications

References 20 publications

Nested mirror optics for neutron extraction, transport, and focusing

Nested mirror optics for neutron extraction, transport, and focusing

Variable focusing system for neutrons

Measurements of the neutron absorption in supermirror coatings

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