Radioactive contamination of SrI2(Eu) crystal scintillator

The interest in strontium iodide crystal increased in the last few years because of its high light output (> 100000 γ/MeV) and its good energy resolution (~3% at 662 KeV). An important advantage of SrI2(Eu) in comparison to other high resolution scintillators is the absence of natural long-living radioactive isotopes. This feature is interesting for searching for double β decay.

A scintillator crystal doped by 1.2% in Eu and with a nearly cylindrical shape (13 mm in diameter and 11 mm in length), was produced by using the Stockbarger growth technique. To investigate the scintillating properties of the crystal, first measurements have been performed in the low background set-up installed at sea-level in the Institute for Nuclear Research (INR, Kyiv, Ukraine). In particular, the detector has been irradiated with γ quanta using various sources. The otained energy resolution (FWHM) is 5.8%. at 662 KeV. Then, a backgrund measurement has also been performed at sea level, to firstly investigate the radioactive contamination of the crystal and to study its α/β discrimination capability. The measurements allowed the detection of the internal contamination of the scintillator by 226Ra and 228Th; limits on activities of 238U, 232Th, 210Pb, 210Po, 90Sr have also been obtained. The results are reported in the Table.