NIST liquid hydrogen cold source

Abstract

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Physics design of a cold neutron source for KIPT neutron source facility.

“…These results are different from the results of the National Institute of Standards and Technology (NIST) [3]. For 10-cm graphite column thickness of 10 cm, the neutron flux at the inner surface of the cold moderator sphere and at the end of cold channel are plotted for 100% para-LH 2 and 100% ortho-LH 2 in Figure 10 and 11.…”

“…Brightness, defined as d -s-meV-ster in terms of neutron energy. Specially, it's the brightness of cold neutrons with E < 5meV or λ > 4 Å, in the angles less than the critical angle for reflection from the Ni 58 coated surfaces within the guides [3]. The critical angle is θ c = 0.002 λ (Å) rad for Ni 58 [3].…”

“…Another reason is that only a very small fraction of neutrons generated in the target can reach the cold neutron moderator due to the long distance between the cold neutron channel and the target as well as the small cross section area of the cold neutron channel. To solve this problem, the cold neutron brightness is calculated in a two step process [3]. In the first step, a three-dimensional geometrical quarter model is used and a surface source file is being generated, using the SSW card of MCNPX, for neutrons and photons entering the cold source region.…”

“…Over the past two-three decades, structures with characteristic lengths of 100 Å and correspondingly smaller vibrational energies have become increasingly important for both science and technology [3]. The characteristic dimensions of the microstructures can be well matched by neutrons with longer vibrational wavelength and lower energy.…”

“…Its units are n/cm 2 -s-meV-ster, and its value should not depend on the distance of the tally surface from the cold source, if the tally surface is on the beam axis and is fully illuminated [3].…”