The LUMINEU (Luminescent Underground Molybdenum Investigation for NEUtrino mass and nature) project envisages a high-sensitivity search for neutrinoless double beta (0ν 2β) decay of <sup>100</sup>Mo with the help of scintillating bolometers based on zinc molybdate (ZnMoO<inf>4</inf>) crystals. One of the crucial points for the successful performance of this experiment is the development of a protocol for producing high quality large mass ZnMoO<inf>4</inf> crystal scintillators with extremely high internal radiopurity. Here we report a significant progress in the development of large volume ZnMoO<inf>4</inf> crystalline boules (with mass up to 1 kg) from deeply purified materials. We present and discuss the results achieved with two ZnMoO<inf>4</inf> samples (with mass of about 0.3 kg each): one is a precursor of the LUMINEU project, while the other one was produced in the framework of LUMINEU with an improved purification / crystallization procedure. The two crystals were measured deep underground as scintillating bolometers in the EDELWEISS dilution refrigerator at the Laboratoire Souterrain de Modane (France) protected by a rock overburden corresponding to 4800 m w.e. The results indicate that both tested crystals are highly radiopure. However, the advanced LUMINEU sample shows a clear improvement with respect to the precursor, exhibiting only a trace internal contamination related with <sup>210</sup>Po at the level of 1 mBq/kg, while the activity of <sup>226</sup>Ra and <sup>228</sup>Th is below 0.005 mBq/kg. This demonstrates that the LUMINEU purification and crystal-growth procedures are very efficient and leads to radiopurity levels which exceedingly satisfy not only the LUMINEU goals but also the requirements of a next-generation 0ν 2β experiment.
|Titolo:||Development and underground test of radiopure ZnMoO<inf>4</inf> scintillating bolometers for the LUMINEU 0ν2β project|
|Data di pubblicazione:||2015|
|Appare nelle tipologie:||Articolo su Rivista|