arXiv subjects

V. Talanov

Publications and source records attributed to V. Talanov.

4 recordsLinked to original sources

arXiv2022

Characterization of ultracold neutron production in thin solid deuterium films at the PSI Ultracold Neutron source

We determined the ultracold neutron (UCN) production rate by superthermal conversion in the solid deuterium (sD$_2$) moderator of the UCN source at the Paul Scherrer Institute (PSI). In particular, we considered low amounts of less than $20\,$mol of D$_2$, deposited on the cooled moderator vessel surfaces in thin films of a few mm thickness. We measured the isotopic ($ c_\text{HD} < 0.2 \, \% $) and isomeric ($ c_\text{para} \le 2.7 \, \% $) purity of the deuterium to conclude that absorption and up-scattering at $5\,$K have a negligible effect on the UCN yield from the thin films. We compared the calculated UCN yield based on the previously measured thermal neutron flux from the heavy water thermal moderator with measurements of the UCN count rates at the beamports. We confirmed our results and thus demonstrate an absolute characterization of the UCN production and transport in the source by simulations.

physics.ins-det↗

arXiv2018

Solid deuterium surface degradation at ultracold neutron sources

Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment (`conditioning') of the sD_2. We show that, in addition to the quality of the bulk sD_2, the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D_2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD_2 frost formation on initially transparent sD_2 in offline studies with pulsed heat input at the North Carolina State University UCN source results in a consistent description of the UCN yield decrease.

physics.ins-det↗

arXiv2018

On the accuracy of Monte Carlo based beam dynamics models for the degrader in proton therapy facilities

In a cyclotron-based proton therapy facility, the energy changes are performed by means of a degrader of variable thickness. The interaction of the proton beam with the degrader creates energy tails and increases the beam emittance. A precise model of the degraded beam properties is important not only to better understand the performance of a facility already in operation, but also to support the development of new proton therapy concepts. The exact knowledge of the degraded beam properties, in terms of energy spectrum and transverse phase space, depends on the model used to describe the proton interaction with the degrader material. In this work the model of a graphite degrader has been developed with four Monte Carlo codes: three conventional Monte Carlo codes (FLUKA, GEANT4 and MCNPX) and the multi-purpose particle tracking code OPAL equipped with a simplified Monte Carlo routine. From the comparison between the different codes, we can deduce how the accuracy of the degrader model influences the precision of the beam dynamics model of a possible transport line downstream of the degrader.

physics.acc-ph↗

arXiv2014

Neutron production and thermal moderation at the PSI UCN source

We report on gold foil activation measurements performed along a vertical channel along the tank of the ultracold neutron source at the Paul Scherrer Institute. The activities obtained at various distances from the spallation target are in very good agreement with MCNPX simulations which take into account the detailed description of the source as built.

nucl-ex↗