Speaker
Description
The underground ultra-low background laboratory STELLA (SubTerranean Low Level Assay) in the Laboratori Nazionali del Gran Sasso of the National Institute of Nuclear Physics (LNGS-INFN) is principally dedicated to material screening measurements for fundamental physics experiments installed in the underground laboratories. It uses ultra-low background (ULB) gamma-ray spectrometry, but has also alpha and beta spectrometry capabilities for selected samples. The high level of performance of the ULB detector systems allows for analysing extremely low concentrations of natural and man-made radioactivity in a wide range of materials down to a level of few $\mu$Bq $kg^{–1}$. Thanks to the extremely low background levels of the gamma-ray detection systems also basic physics results on rare radioactive decays are obtained.
The STELLA laboratory has recently been upgraded and moved to a new location in the Gran Sasso underground laboratories. It is now equipped with a combined shielding against neutrons (15 cm of water/polyethylene) and gamma-rays (5 cm of steel) that encloses the whole laboratory space with the most sensitive ULB-HPGe detectors. The improved performance will be laid out in detail including measurements of gamma-ray and neutron background in the new location with the improved shielding. The installations and experimental set-ups using ultra-low background techniques will be described shortly, and examples of significant measurements for both applications, material screening and basic physics, will be presented.