Background Study in NDBD Ming Shao

sources environmental gamma radioactivity cosmic rays Neutrons Radon contamination of materials which detectors and their shielding are made of …

methods Cosmic veto shielding Underground locations Detector construction using screened low- background materials Detector construction using electroformed copper Ultra-pure shielding materials Low-cosmic-ray exposure DBD material, and copper … DBD element enrichment Signal processing Detector segmentation …

Example: Majorana Germanium crystals Electroformed copper module Close-in part Thick shield of lead Neutron- absorbing blanket Active cosmic-ray veto shield

Background model Critical to the design and execution of the NDBD experiment –Guide the pre-commissioning efforts in detector –Acquisition system design Sensitivity calculation -> physical goal Depend on experiment method Combine empirical and theoretic data

Background reduction in Majorana Ge background –Cosmogenic backgrounds in Ge –Neutrons at Altitude –Enrichment Primordial (Potassium, Uranium and Thorium) Backgrounds in Cu –Cosmogenic Activities in the Copper Backgrounds in Pb Other Materials

Cosmogenic backgrounds in Ge

Neutrons at Altitude - rate calculation

Cosmogenic activation stages

Primordial radioactivity Uranium-238 Thorium-232 (Polonium-210) Characteristic Alpha peak can be used for background estimation

Cu superior material for ultra-low background –Cu electroplating Cosmogenic activation Natural activities ( 208 Tl and 214 Bi)

Pb Gamma reduction –Ultra-low background Pb in inner detector –Normal lead outside

Other materials Outer: low dust situation to prevent contamination of the inner shield during maintenance Inner: thermal insulators and structural parts (plastic), wires, electrical contacts (metalized plastic), and vacuum seals (indium) –Commercially purchased –screened and stored

| | ~35 meV