Measurements of the neutron background from rock at Boulby mine Eirini Tziaferi University of...
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Transcript of Measurements of the neutron background from rock at Boulby mine Eirini Tziaferi University of...
Measurements of the neutron background
from rock at Boulby mine
Eirini TziaferiUniversity of Sheffield, UK
JRA1 meeting, ILIAS , Paris, 14/02/2006
nthermal + 155,157Gd → 156,158Gd* → 156,158Gd + γ´s
Detection Principle: 2 pulse signature
~ 0.01% Gd-loaded liquid scintillator
• Large thermal neutron capture cross section of the isotopes 155Gd, 157Gd
• Release of a high energy (8 MeV) gamma cascade after thermal neutron capture on Gd
LS+0.01%Gd
Sources of Background Correlated background: 238U (214Bi → 214Po → 214Pb)
214Po:t1/2 = 164 μs
τ = 237 μs
0.8 MeV(7.68 MeV)
Pulse shapeanalysis
Time delay distribution of the neutron background
no. of neutrons = 124 ± 50 rate = 1.01 ± 0.41 d-1
February – June 2005 July – October 2005shielded run
SimulationsFirst step:
Input → 238U, 232Th spectra from SOURCES
Output → Energy spectrum, position, momentum
of neutrons which pass the rock/lab boundary
Second step:Input → Energy spectrum, position, momentum of neutrons which pass
the rock/lab boundaryOutput → Proton recoil energy,
Captured energy, time delay distribution
In progress …
10 ppb U, 10 ppb Th
60ppb U, 130ppb Th