measurements of the neutron background from rock at boulby mine eirini tziaferi university of...
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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