1. We had a discussion with Flavio last Friday about testing the neutron source in ProtoDUNE:
(1) Flavio is writing a document on the ProtoDUNE after the beam time. He would add a few lines about the neutron source test.
(2) Flavio suggested that we could test only the DD generator with the existing beam plug as a neutron port (second cryostat barrier not removed)
(3) We requested engineering support from CERN. Marzio Nessi (CERN neutrino platform coordinator) is the person to talk to.
(4) If the test can't be done right after the beam time in 2019, probably it has to be postponed to 2020
2. We've proven that the neutron scattering measurement is not critical. The mean scattering length of the neutron in natural argon is dramatically dependent on Ar-36 and Ar-38. The following table shows the calculation of the mean elastic scattering length at 57 keV.
| |
elastic cross section (barn) |
abundance |
density (g/cm^3) |
interactions/cm |
length (m) |
| 40-Ar |
2.40E-04 |
0.996035 |
1.390374795 |
7.00775E-06 |
1426.992378 |
| 38-Ar |
1.00E+00 |
0.000629 |
0.000834126 |
1.84392E-05 |
542.3215338 |
| 36-Ar |
3.10E+00 |
0.003336 |
0.004191079 |
0.000303166 |
32.98524839 |
Effective length L_eff = 30.43 m
We change the cross-section of 40-Ar by orders of magnitude as the following:
40-A4 (2.4E-4 barn) => L_eff = 30.43 m
40-A4 (2.4E-3 barn) => L_eff = 25.53 m (see attached figure for neutron capture positions)
40-A4 (2.4E-2 barn) => L_eff = 9.87 m
As can be seen, within the change of two orders of manitude, the effective scattering length is still acceptable.