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Design and test of a multiwire proportional chamber for the SOFIA project


The Studies On Fission with Aladin – SOFIA project at GSI

Fig.1 : The SOFIA experiment

The aim of the SOFIA experiment consists in the study of the fission fragment yields and the neutrons production of exotic beams in Columbian excitation on a lead target at GSI. In particular the interest is focalized on the measure of the nuclear masses, the nuclear charges and the kinetic energies of each produced fragment in coincidence with the total neutrons multiplicity. To pursue this objective then the experiment should count of a double MUltiple Sampling Ionization Chamber (TWIN MUSIC) to measure Z, a time-of-flight and a fission fragment tracking for A and Ek measurements and a Large Area Neutron Detector (LAND) to measure the neutron multiplicity in coincidence with other measurements, as pictured in fig.1.


Design of the multiwire proportional chambers for SOFIA at the IPNO

Fig.2 : A 3D view of SOFIA

Fig.3 : An exploded view of SOFIA

In particular the R&D Detector group at IPNO is responsible for the design and test of the multiwire proportional chambers needed for the fission fragments tracking. The R&DD group has a well recognized expertise in the design of the proportional chambers that had developed over the years due to the participation at the ALICE collaboration for the construction of the ALICE muon tracking chambers.
Operational test on the multiwire proportional chamber at IPNO

Fig.4 : Example of a signal acquired on a single wire of the 200 mm x 200 mm chamber

In June 2011, the mechanic shop of the R&DD group completed to build the 200mmx200mm chamber for the SOFIA project. We then proceeded to check the proper operation of the chamber and to this aim we flew a mixture of 80% Ar and 20% CO2 in the chamber active gap and we applied the high voltage to establish the electric field. At first we simply checked the presence of ouput signals produced by the interaction of the cosmic rays with the gas present in the active region of the chamber (fig. 3), then we irradiated the detector with a 55Fe source to test the gain of the detector as a function of the applied HV and to finish we placed the 55Fe source in front of different areas of the chamber to control the uniformity of response.
 Simulation of the gas flow in the chamber 200x200 


Fig.5 : Simulation of the gas in the chamber

Some simulations were done to visualize the distribution of the gas in the chamber

  Electric discharge etching of thin metalized plastic films

Fig.6 : Example of a signal acquired on a single wire of the 200 mm x 200 mm chamber

In order to do the « strip » plans, we must perform the etching on a plastic film. To do that, etching we used a special machine. The film is connected to the mass and the aluminum part is connected to a negative voltage (-24V).

Contact  : G. Hull, J. Bettane

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UMR 8608 - CNRS/IN2P3

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