Transcript RPC SENSITIVITY TO LOW ENERGY NEUTRONS AND GAMMA RAYS

EPS-HEP2001
Budapest, july 12-18, 2001
SERGIO P. RATTI
INFN and Dipartimento di Fisica Nucleare e Teorica – PAVIA
for the Pavia-Bari collaboration in CMS
RPC SENSITIVITY
TO LOW ENERGY
NEUTRONS AND
GAMMA RAYS
OUTLINE OF THE TALK
Motivation
Experimental setup
Results
Conclusions and outlook
Experimental setup
2 single gap/common readout RPC’s
1 gap oiled
1 gap not oiled
BaF2 scintillators
source
17 mCi 252Cf:
a-3% spontaneous fission;
b-97% a decay (irrelevant,
absorbed by the source’
container).
THE SOURCE
3.8 n/fission
Eav= 2.14 MeV
10.3 prompt g
per fission
80% E<1MeV
NEUTRON AND g SPECTRA OF THE SOURCE
Sensitive area: 35 cm x 35 cm
Gas mixture (97 % C2H2F4 – 3% iC4H10)
OUTPUT signals: LVDS to the
counting electronics
(Low Voltage Differential Signals)
16 strips
Pickup strips
RPCs Cross Section
FOUR CONFIGURATIONS:
A) No absorber
between RPC
and source
B) 6 cm Pb
between RPC
and source
C) 6 cm Pb and
4 cm PE
D) 6 cm Pb and
10 cm PE
Experimental method:
RPC
Source
Trigger
AND
Chamber
OR16
Trigger
BaF2 scintillators

= (Triggers x OR16)/Triggers
=
efficiency to fission
=
chamber acceptance
Compare to
simulation
results
Experimental data



GAP non oil
Xeq
What we measure is
GAP oil
Xeq
Double Gap
Xeq

= (Triggers x OR16)/Triggers
Effective Neutron
Interaction length Xeq
=
efficiency to fission
Xeq = XPb/lPb + XPE/lPE
=
chamber acceptance
l=interaction length
Experimental data vs
simulation results
Data contain contribution
from:
a) Prompt g rays from source
b) Prompt neutrons from
Source
Xeq
c) Secondary g rays from
neutron interactions within
the different absorbers
Simulation (with GEANT3.21) used to extract the
relative contribution of each component a) b) c)
Gamma ray sensitivity
(preliminary results)
Prompt g rays
-oil
Secondary g rays
-oil
Xeq
Xeq
Neutron Sensitivity Results
(preliminary)
Sensitivity independent on oiling!
-oil
Xeq
CONCLUSIONS
Summary of sensitivity results
Single Gap
Sensitivity <Energy>(MeV)
Prompt g
3,50E-03
0,84
"
7,50E-03
1,45
Secondary g
Neutron
6,50E-03
1,35
3,00E-04
2,1
Double Gap
Sensitivity <Energy>(MeV)
Prompt
6,00E-03
0,84
"
1,30E-02
1,45
Secondary g
1,10E-02
1,35
Neutron
5,30E-04
2,1
g
Poor measurements
of this parameter
Sensitivity (S)
less than 1%;
Sg10Sn;
Double gap doubles;
S independ
on surface treatment
(at least
at this
low energies
1 MeV)