Am-Be neutron source
1) Setups and source spectrum
| Setup with the standard PE moderator in light blue (X-Y) | X-Z |
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The borated PE is in yellow, and the air is in green, the crystal is magenta and sealed by the stainless steel. The same applies to the following sketches.
| Setup with the standard PE moderator and Lead in orange (X-Y) | X-Z |
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| Setup with the Copper in light blue (X-Y) | X-Z |
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2) Spectra measured among different setups
| Am-Be neutron measured with different setups |
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The background spectrum is measured from the 2.5 months data.
3) Optimization of the standard PE moderator
Based on the setup with the standard PE moderator and the Pb, the thickness of the PE moderator is adjusted. The optimal thickness would be the one with the largest neutron flux recorded in the GAGG detector, which is 6 cm.
| Neutron flux versus the PE thickness |
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4) Crystal size optimization
By varying height and radius of the GAGG crystal, the neutron flux in the crystal is simulated.
| Neutron recorded in the whole crystal volume versus crystal height |
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5) Comparison with the measurement
| setups | simulated flux [cts/cm2/source particle] | measured count rate [cts/h] | simulation_norm | measurement_norm |
|---|---|---|---|---|
| standard PE | 7.76e-05 | 84.14 | 1 | 1 |
| standard PE + Pb | 1.09e-4 | 116.68 | 1.41 | 1.39 |
| Cu | 2.35e-5 | 52.09 | 0.31 | 0.62 |
| No PE/Pb/Cu | 2.98e-5 | 0.37 |
The simulated flux is extracted from the simulated neutron energy spectrum;
The measured count rate is calculated from all the events above 5 MeV;
simulation_norm means it is normalized by the value of the setup with the PE, meaning each simulated neutron flux is divided by 7.76e-5;
measurement_norm means it is normalized by the value of the setup with the PE, meaning each measured count rate is divided by 84.14.
| Neutron spectra measured with different setups |
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6) Why is the simulation with the Cu smaller than the measurement?
- Geometry and material definition
- Cross-section of Cu interacting with neutrons
- Modify the Cu thickness (from 5 cm thick to 2.5 cm); Change Cu to air or Pb
| Cross-section of Cu (m5) and Air (m4) | Cross-section of Cu (m5), Air (m4) and Pb (m6) |
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| Comparison of neutron energy spectra at low energies | Comparison of neutron energy spectra at high energies |
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| setups | simulated flux [cts/cm2/source particle] |
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| 5 cm Cu | 2.35e-5 |
| Air | 2.97e-5 |
| 2.5 cm Cu | 2.51e-5 |
| Pb | 2.64e-5 |
Conclusion: at this point, it is hard to tell what caused the deviation between the simulation and the measurement with the Cu. The next step is to simulate the Am-Be measurements with LiI detector.