Abstract The results of experiments and calculations for a solid-deuterium UCN source are presented. It was experimentally shown that the UCN yield is increased by a factor 3 at the solidification of liquid deuterium and a factor 10 at a temperature 10 K, with respect to the liquid phase. The gain factor for UCN yield with respect to hydrogen gas or deuterium gas at room temperature is equal to 1230.

A Solid Deuterium Source for Ultra-Cold Neutrons

The performance of the solid deuterium ultra-cold neutron source at the pulsed reactor TRIGA Mainz with a maximum peak energy of 10 MJ is described. The solid deuterium converter with a volume of V=160 cm3 (8 mol), which is exposed to a thermal neutron fluence of 4.5x10^13 n/cm2, delivers up to 550 000 UCN per pulse outside of the biological shield at the experimental area. UCN densities of ~ 10/cm3 are obtained in stainless steel bottles of V ~ 10 L resulting in a storage efficiency of ~20%. The measured UCN yields compare well with the predictions from a Monte Carlo simulation developed to model the source and to optimize its performance for the upcoming upgrade of the TRIGA Mainz into a user facility for UCN physics.

V2:Performance of the solid deuterium ultra-cold neutron source at the pulsed reactor TRIGA Mainz

Ultracold neutrons (UCN) form a tiny low-energy fraction of the Maxwellian spectrum of thermal neutrons in moderators of nuclear reactors and spallation sources Their energy is extremely low (∼10−7 eV), their velocity is a few meters per second, and their effective temperature is as low as ∼1 mK The specific feature of UCN is their nearly total elastic reflection by the nuclear-optical potential of many materials at any incidence angle, so that they could be stored in closed traps for many minutes, and used for extremely sensitive measurements The fraction of UCN in a thermal neutron flux is as low as 10−12–10−11, and serious efforts are under way all over the world to produce UCN in larger amounts UCN are widely used in precision particle physics experiments Applications of UCN are emerging in surface and nanoparticle physics Here we focus on recent advances in the field

/pdf/experiments-with-ultracold-neutrons-kd5r3a3co9.pdf

Experiments with ultracold neutrons

The aim of this short note is to present an option for a source of ultracold neutrons (UCNs), which could profit from the pulse time-structure of the future ESS spallation neutron source in Lund, and thus which could produce a very high UCN density and a rather high UCN flux simultaneously. In order to realize this idea one has to install a relatively thin solid-deuterium UCN source in a close vicinity to the spallation target and to couple it with an extraction UCN guide with an entrance membrane window, which is moving periodically and synchronously with the operation cycle of the spallation source, as explained in the text below. This proposal profits from the fact that all characteristic parameters of the problem, such as the pulse duration of the ESS spallation source, the typical thickness of solid deuterium source that could be easily realized, the typical time of generation of UCNs in solid deuterium, the length and diameter of the extraction neutron guide and the time diagram of the membrane motion that is still realistic, they all fit nicely to optimum desired parameters. The UCN density produced in such a way could approach 10^6 UCN/cm3.

An option of "UCN pump" for ESS

Ultracold neutrons (UCN) have been produced using the cold neutron (CN) beam FUNSPIN at SINQ on cryogenic oxygen (O2), tetradeuteromethane (C2H4), and deuterium (2H2) targets. The target cell (40 mm long, fiducial volume about 45 cm3) was operated between room temperature and 8 K and UCN were produced from gaseous, liquid and solid targets. UCN rates have been measured as a convolution of UCN production and transport out of the target and to the detector. At least within the accessible temperature range of this experiment, deuterium outperforms the other materials.

https://iopscience.iop.org/article/10.1209/0295-5075/95/12001/pdf

Production of ultracold neutrons from cryogenic 2H2, O2, and C2H4 converters

The feasibility studies for a new ultra cold neutron (UCN) source to be installed at the Institut Laue-Langevin (ILL) are underway. One of these studies concerns a source using solid deuterium (SD2) as a neutron moderator. During source operation the SD2 would be exposed to intense γ-ray and neutron fluxes. These may result in radiolysis in SD2. Our work has shown that this effect—if it is produced—is not incompatible with a normal operation of the source.

Investigation of the energy accumulation rate in solid deuterium irradiated with fast electrons

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Investigation of the energy accumulation rate in solid deuterium irradiated with fast electrons