Variability of the fast neutron field
in underground environment
A. Borio di Tigliole
Laboratorio per l’Energia Applicata (LENA) dell’Università di Pavia
E. Calligarich, R. Dolfini, A. Rappoldi, G.L. Raselli
INFN sezione di Pavia
A. Cesana, L. Garlati, M. Terrani,
Dipartimento di Ingegneria Nucleare del Politecnico di Milano
A. Giuliani, M. Pedretti
Dipartimento di Fisica e Matematica dell’Università dell’Insubria
The Baradello Laboratory
Castel Baradello (Como)
Depth 100 m (300 m water eq.)
Area of Laboratory 10 m2
The aqueduct ACSM
Volume of Laboratory 380 m3
Laboratory Characterization
The Laboratory was characterized in 2002 for
what concerns the background radioactivity
(gamma rays, cosmic rays, radon, neutrons).
Two data-taking periods were dedicated to the
measurement of the flux intensity and energy
spectrum of the fast neutron fields:
• may – september 2002;
• april 2003 – january 2005.
“Characterization of an underground site in Northern Italy in view of
low radioactivity measurements” C. Brofferio et al., J. Environm.
Radioact., 71 (2004) 159.
The Neutron Detector
4 liquid scintillator cells
300 cc BC501A (tot. 1300 cc)
Pulse Shape Discrimination
Sensitivity 120 MeV
The detector will be upgraded
with two new 2000 cc scintillator
cells (tot. 4600 cc)
Neutron Flux
I = (1.9  0.8)  10-5 cm-1 s
-1
Long-period fluctuations (about 20%) are present
in the data above 3.5 MeV.
Neutron Field Variability
Correlation between the acquisition rate and
the rain intensity in the Baradello area
during the period 2002-2003
R = 0.08
R = - 0.73
30 days shift
Neutron Field Variability
30 days shift
Conclusions
• A strong correlation between neutron flux and
other environmental parameters has been
pointed out in the Baradello Laboratory.
• Il is important to verify the presence of such a
phenomenon in other underground laboratories.
• In the Gran Sasso Laboratory we plan to move
an upgraded version of the neutron detector in
the early months of 2005.
“Variability of fast neutron yield in underground environment” A. Borio
di Tigliole et al., Europhys. Lett., 67 (2004) 1049.