Benchmarks

Benchmarking

Several checks of the code have been performed with respect to analytical calculations and to other Monte-Carlo codes

• Analytic benchmaking
• Comparison with MCucn
• Comparison with GEANT4ucn

Analytic benchmaking

• Geometry : Two material foils witin a vaccum tube
  • Titanium (VF=-50neV), two 15µm foils
  • Aluminum (VF= 50neV), 30µm and 300µm foils


• Generation : Neutron beam normal to the foils with uniform velocity distribution
• Observable : Transmission of the neutron beam as a function of the energy.


Comparison with MCucn

MCucn is a ucn code developped for the PSI nEDM experiment. For this chack, an analytical solution is also available.

• Geometry : Closed cylinder, H=15cm, R=25cm, VF=230neV, d=0, η=0


• Generation : Neutron are generated uniformly on the bottom of the cylinder
• Observable : Position of the center of mass of the ucn gas at equilibrium is reached (a few tenth of seconds) as a function of the initial veritcal energy.


MCucn results, courtesy of Dr. Geza Zsigmund, PSI

Comparison with GEANT4ucn

GEANT4ucn is a GEANT4 module designed to deal with very low energy neutrons

• Geometry : U-shaped steel guide : height = 70cm, length = 30 cm, square section 5x5cm, VF= 200neV
• Generation : Neutrons are generated at the entrance of the guide~:
  • Uniform energy form 0 to 500 neV
  • Uniform position in the square section
  • Horizontal direction


• Observable : Energy distribution of the neutron at the end of the guide, normalized to the initial spectrum. this obserfable check both total transmission and energy spectrum deformations.

The results are given for several configuraton of the wall properties

• Transmission of the perfect guide. The initial cut off is due to the guide height.


• Additional effect from absorption on the walls. The total transmission is reduced and as the energy increases so does the number of wall collisions and the loss probability.


• Additional effect from diffuse reflection. Indepedently of the energy, diffusivity allows neutrons to go back out of the guide, reducing the total transmission.


GEANT4 results, courtesy of Mr. Fabien Lafont, ILL

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