Speaker
Description
The Mu2e calorimeter is composed by two disks of 1348 un-doped parallelepiped CsI crystals of
34$\times$34$\times$200 mm$^3$ dimension, each one readout by two large area SiPM arrays.
We translated the calorimeter requirements in a series of technical specifications for the
crystals that are summarized by the following list:
(i) a well defined 3D crystal shape with $\pm$ 100 $\mu$m tolerance on the transversal dimension
and 100 $\mu$m tolerance on each plane flatness and on the parallelism and perpendicularity between
faces;
(ii) a light yield $>$ 100 p.e./MeV when readout with a UV extended 2" PMT;
(iii) a good longitudinal response uniformity (LRU) rms $<$ 5\% measured along the crystal axis;
(iv) a large ratio F/T $>$ 0.75 between the fast scintillating light component, integrated in 200 ns, and
the total light emitted within 3 $\mu$ sec;
(v) a good radiation resilience with a light output loss $<$ 65\% after a total ionization dose up to 100 krad and a neutron fluence up to
10$^{12}$ n/cm$^2$;
(vi) and a small contribution to the readout noise $< 0.6$ MeV related to the radiation induced fluorescence in the crystals.
A pre-production of 72 Mu2e crystals has been procured by three international firms (Amcrys, St. Gobain and Siccas). A detailed
quality assurance (QA) has been carried out on each crystal for the determination of its mechanical and optical parameters.
The measurement of the radiation hardness have been carried out on 2 (1) random sample for each firm for irradiation wit
ionization dose (neutrons). A summary of the techniques used and of the QA characterization of the crystals will be shown.
