Simulation of the transmission for four different filters

 

Filter Element

REAL Filter Thickness

Filter Thickness used FOR THE CALCULATION

W

0.8 mm

0.8 mm

Al

29.4 mm

30 mm

Ag

0.5 mm

0.3 mm

Mo

1 mm

1 mm

Unfortunately, there have been several versions of the thickness of the filters circulating around. In the first column of the table you will find the REAL values of the filters installed, while in the second column you will find the values used in the calculations.

The nTOF energy spectrum has been taken from Vasilis latest simulations (1/6/2002). The experimental data for the Fe measurements with filters have been provided by Cesar.

 

  1. W 0.8 mm thick filter
  2. As you can see, the average effect of the W filter is an attenuation of the neutron beam between 5% and 10%. In beam gamma rays are attenuated in a similar factor (Jose´s simulations GEANT3 for a realistic spectrum + Daniel´s simulations with MCNPX for a white spectrum). The main resonance is fully saturated and the neighbouring ones are also clearly visible.

    EXPERIMENTAL TOF SPECTRUM

  3. Al 30 mm thick filter
  4. The average effect of the filter is an attenuation of the neutron beam of 20% between 1 eV and 5 keV. The main resonance is not fully saturated but still clearly visible.

    The attenuation of the in-beam gamma rays should be also of 20% for a white spectrum (see Jose´s simulation for the simulated in-beam gamma ray spectrum attenuation).

    EXPERIMENTAL TOF SPECTRUM

  5. Ag 0.3 mm thick filter
  6. The average attenuation of the Ag filter is below 5%. The main resonance is fully saturated and the smaller ones at higher energies are also visible.

    EXPERIMENTAL TOF SPECTRUM

  7. Mo 1 mm thick filter

The attenuation of the neutron beam is below 10% above 1 keV. The resonances in the eV region are saturated and thus clearly visible.

EXPERIMENTAL TOF SPECTRUM

Some observations