Measurement of mesitylene moderator efficiency @COSY,FZJ

The organic compound mesitylene combines an easy handling and a high hydrogen density. These properties qualifies the substance to be used in cold moderator systems. The performance of a mesitylene based cold moderator system has been investigated during a beamtime at the COSY facility of Forschungszentrum Jülich, where a tantalum target irradiated by a 45 MeV pulsed proton beam has been used to produce neutrons in a (p,n)-reaction. The mesitylene moderator system, cooled by a coldfinger cryocooler to temperatures between 22K and 300K, moderated the neutrons to long wavelength up to 40 Å. These cold neutron spectra has been measured by a 3He detector system in time-of-flight mode. In this talk the experimental setup and results will be presented

Monte Carlo simulation of a mesitylene based cold moderator system foraccelerator-driven compact neutron sources

The organic compound mesitylene has been proposed as a suitable material for cold neutron generationalongside liquid ortho/para H2 and solid CH4 at cryogenic temperatures because it has a high hydrogendensity, enables a safe operation. To investigate the neutron moderation properties of mesitylene andits potential application in the High Brilliance Neutron Source (HBS) project, a mesitylene based coldmoderator system was set up in the Big Karl experimental hall at Forschungszentrum Jülich andperformed to determine the cold neutron spectrum at different moderator temperatures.In the experiment, primary neutrons are generated by the Ta(p,xn )W reaction using a pulsed 45 MeVproton beam and further moderated by polyethylene thermal moderator blocks. An extraction channelis built to gain the neutrons from the thermal maximum, and the cold mesitylene is placed in it. Themoderator vessel is a cylinder with a diameter of 60 mm and a height of 30 mm. The mesitylenemoderator system is cooled from 300 to 22 Kelvin by a cold finger cryocooler in about two hours. andmoderates the neutrons to a long wavelength of up to 40 Å. The moderated neutrons were extractedvia the flat side of the vessel and measured by TOF using a 7-meter neutron guide and 3He tubedetectors in TOF counter mode.Monte Carlo simulations of this mesitylene based cold moderator system were performed using theMCNP6.1 program package. The geometry for the simulation is converted from the three dimentionalCAD model of the experimental setup directly. The neutron spectra at different mesitylenetemperatures were calculated with respect to the gain of the cold neutrons compared to a spectrum atroom temperature. A broadening and shift of the cold moderator peaks to longer wavelengths withdecreasing moderator temperature is observed in both experimental data and simulation results. Whenthe mesitylene temperature decreases from room temperature to 22 Kelvin, the neutron spectrum peakshifts to a longer wavelength. Mesitylene has proven to be a proper moderator material for cryogenictemperatures around 20 K, which offers good performance

Determination of the neutron yield of Be, V and Ta targets irradiated with protons (22-42 MeV) by means of prompt gamma neutron activation analysis

The neutron yield for beryllium, vanadium and tantalum irradiated with 22, 27, 33 and 42 MeV protons is indirectly determined by Prompt Gamma Neutron Activation Analysis (PGNAA). The neutron-to-gamma conversion rate is measured with an AmBe calibration neutron source. Corrections by escaped neutrons are applied via MCNP simulations of the experiment using the ENDF/B-VII.1 database. The experimental results are in good agreement with the neutron yield obtained from simulations deviating by 0.4% to 13%

An intense source of very cold neutrons using solid deuterium and nanodiamonds for the European Spallation Source

The European Spallation Source (ESS), currently under construction, is based on a high-brightness, bi-spectral, low-dimensional moderator placed above a spallation target, intended to initially serve fifteen neutron scattering instruments. Within the upgrade path of ESS, the HighNESS project aims at designing a source complementary to this upper moderator, focusing on delivering a higher intensity and a colder spectrum of neutrons. We have investigated the use of solid ortho-deuterium at 5 K as a source of very cold neutrons (VCNs). This source performs competitively as a high-intensity cold-neutron moderator, while also showing an order-of-magnitude flux increase in the very cold range above 40 ̊ A compared to a liquid deuterium moderator of similar volume and shape, also designed within HighNESS. The long-wavelength performance of the source can be improved further by encasing it in a thin layer of nanodiamonds. The cooling of a solid deuterium moderator placed so close to the spallation target of a high-power neutron source like ESS is very challenging, but may be feasible by augmenting the heat conductivity with the addition of low-density metallic foam structures within the moderator vessel. Such a source could provide unprecedented opportunities in fundamental physics research and neutron scattering using VCNs.</p

The High Brilliance neutron Source (HBS): A project for a next generation neutron research facility

The High Brilliance neutron Source (HBS) is a project for a next generation neutron research facility, based on new concepts and recent technological advancements. As elementary processes it uses neither fission nor spallation, but instead low energy nuclear reactions in a very compact Target-ModeratorReflector (TMR) assembly. Our facility design results in very efficient production of neutron beams with high brightness. Key features of HBS are: (i) very competitive instrument performance, (ii) comparatively low construction and operation costs, (iii) resilience, (iv) sustainability, (v) flexibility, (vi) accessibility and (vii) scalability. Here we present the basic layout of the facility, elaborate on the mentioned key features and report on the commissioning of a small test setup