Search for magnetic monopoles
The CR39 is the main component of the track-etch detector of the
MACRO experiment
(Monopole Astrophysics and Cosmic Ray Observatory) [1] at the
Laboratori Nazionali del Gran Sasso of
INFN (Istituto Nazionale di Fisica Nucleare) in Italy.
One of the main objectives of
MACRO is to search
for supermassive magnetic monopoles predicted by most GUT theories [2].
The CR39 material used in
MACRO is produced
by the INTERCAST EUROPE Company
of Parma, Italy.
The standard
INTERCAST CR39, that is mainly used for sun glasses, was improved
in order to achieve :
- low detection threshold,
- high sensitivity in a large range of energy losses,
- high quality of the post-etched surface after prolonged etching,
- stability of the sensitivity of the polymer over long periods of time
(several years),
- uniformity of sensitivity for mass-produced sheets.
In order to achieve these goals, a specific scientific line of production was
designed and implemented [3].
Two types of CR39 have been developed, containing different additives and using
different catalysts and curing cycles:
- the EN3 type, that was used in the first
MACRO supermodule,
- the L6 type, that was installed in all the other supermodules.
The bulk etching rates (vB) obtained in a 6N solution of NaOH at 70° C are
vB = (1.25 ± 0.02) microns/h for the EN3 polymer and (1.16 ± 0.02)
microns/h for the L6 type.
The corresponding rates in a 8N solutions at 80° C are (5.74 ± 0.57)
microns/h for EN3 and (4.12 ± 0.21) microns/h for L6.
Presently, the CR39 production is restricted to the improved L6 type only.
REFERENCES
[1] S. Ahlen et al., (MACRO Collaboration), First supermodule of the
MACRO detector at Gran Sasso. NIM A324 (1993) 337.
[2] G. 'tHooft, Nucl. Phys. B79 (1976) 276.
[3] S. Ahlen et al., (MACRO Collaboration), Improvements of the CR39
polymer for the MACRO experiment at the Gran Sasso Laboratory,
Nucl.Tracks Radiat.Meas. 19 (1991) 641.
For information : intercast@relay1.it.net
Last update: A.Margiotta - 26-Mar-1997
e-mail: margiotta@bo.infn.it
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