1. TO LOW ENERGY NEUTRONS AND TO LOW ENERGY NEUTRONS AND
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
RPC SENSITIVITY
TO LOW ENERGY NEUTRONS AND
GAMMA RAYS

2. OUTLINE OF THE TALK Motivation Experimental setup Results
Conclusions and outlook

3. 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).

4. THE SOURCE NEUTRON AND g SPECTRA OF 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

5. OUTPUT signals: LVDS to the counting electronics
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

6. FOUR CONFIGURATIONS:
No absorber between RPC and source
B) 6 cm Pb between RPC and source
6 cm Pb and 4 cm PE
D) 6 cm Pb and cm PE

7. Compare to simulation results
Experimental method:
RPC
Trigger AND Chamber OR16
Source
Trigger
BaF2 scintillators
 = (Triggers x OR16)/Triggers
e= efficiency to fission
= chamber acceptance
Compare to simulation results

8. Effective Neutron Interaction length Xeq
Experimental data
GAP oil
Xeq
Double Gap
GAP non oil eh
What we measure is
 = (Triggers x OR16)/Triggers
e= efficiency to fission
= chamber acceptance
Effective Neutron Interaction length Xeq
Xeq = XPb/lPb + XPE/lPE
l=interaction length

9. Experimental data vs simulation results
Xeq
Data contain contribution from:
Prompt g rays from source
Prompt neutrons from Source
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)

10. Gamma ray sensitivity (preliminary results)
Xeq
-oil
Secondary g rays
Prompt g rays

11. Neutron Sensitivity Results (preliminary)
Xeq
-oil
Sensitivity independent on oiling!

12. Summary of sensitivity results
CONCLUSIONS
Summary of sensitivity results
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) g g g g