ELFT HÍRADÓ

[László Bottyán <bottyan.laszlo AT wigner.hu>]

English speakers please scroll down.

Tisztelt Kollégák,

A Budapesti Neutronközpont következő (angol nyelvű) szemináriumára

"Coupling neutron moderators and optics" címmel,

2024. május 9-én, csütörtök 14:00 órakor kerül sor a

KFKI kampusz XIX. épülete tanácstermében.

Előadó: Petr Konik (BNC HUN-REN EK, Budapest)

Az előadást on-line formában is közvetíteni fogjuk. Az előadásra, illetve 
utólag a videofelvételre mutató linkeket az old.bnc.hu/News oldalra 
kitett hirdetésben közöljük.

Minden személyes és on-line érdeklődőt szeretettel várunk.

Az előadás kivonatát lásd alább.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Dear Colleagues,

The next in-person (EN language) BNC seminar entitled:

"Coupling neutron moderators and optics"

to be given by

        Petr Konik (BNC HUN-REN EK, Budapest)

     on 9 May, 2024 (Thursday) 2 p.m. (KFKI Campus, Bldg 19)

The seminar is also planned to be streamed. Please find the link to the
MS Teams netmeeting and later to the recorded video in the old.bnc.hu/News 
announcement.

All in-person and on-line visitors are welcome.

Best regards,

László Bottyán

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ABSTRACT

Coupling neutron moderators and optics

        Petr Konik(1) and Alexander Ioffe(2)

(1) HUN-REN Centre for Energy Research, Budapest, Hungary
(2) Jülich Centre for Neutron Science (JCNS) at MLZ FZ Jülich GmbH, Germany

In the last decade, low-dimensional neutron moderators made from almost 
pure parahydrogen (pH2) have been introduced [1]. Thanks to large 
difference in scattering crosssections of thermal and cold neutrons in 
pH2, moderators in the form of tubes or disks provide significant 
brightness improvements over traditional voluminous cold moderators.

According to the study by the ESS [2], potential gains of up to 2-3 times 
in the useful neutron flux are possible when the moderator height is 
reduced from 12 cm to 3 cm, especially for high-resolution instruments 
that use well-collimated beams. However, the small size of the moderators 
in some cases makes it difficult to properly illuminate the sample, 
leading to non-uniform divergence profiles. Therefore, larger neutron 
moderators with reduced brightness are preferred for some instruments. To 
determine the optimal moderator size, we have developed a new approach 
that takes into account instrument parameters such as sample size and 
angular resolution.

It is based on phase space considerations and extensive Monte Carlo 
simulations have been conducted to validate it. This method is 
particularly useful for designing new neutron instruments and neutron
sources. We also present a new analytic approach to calculate the 
brightness of pH2 moderators. It is shown that the brightness gain is a 
near-the-surface effect, so that a narrow cold moderator shaped
as elongated rectangular parallelepiped provide a substantially higher 
cold neutron brightness. The obtained results are in excellent agreement 
with MCNP calculations.

REFERENCES
[1] K. Batkov et al., Nuclear Instr. Meth. A 729 (2013) 500.
[2] L. Zanini et al., J. Phys.: Conf. Ser. 1021 (2018) 012066