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Title: Identification of Radiopure Titanium for the LZ Dark Matter Experiment and Future Rare Event Searches

The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon within a double-vessel cryostat. The large mass and proximity of the cryostat to the active detector volume demand the use of material with extremely low intrinsic radioactivity. We report on the radioassay campaign conducted to identify suitable metals, the determination of factors limiting radiopure production, and the selection of titanium for construction of the LZ cryostat and other detector components. This titanium has been measured with activities of $$^{238}$$U$$_{e}$$~$<$1.6~mBq/kg, $$^{238}$$U$$_{l}$$~$<$0.09~mBq/kg, $$^{232}$$Th$$_{e}$$~$$=0.28\pm 0.03$$~mBq/kg, $$^{232}$$Th$$_{l}$$~$$=0.25\pm 0.02$$~mBq/kg, $$^{40}$$K~$<$0.54~mBq/kg, and $$^{60}$$Co~$<$$0.02~mBq/kg (68\% CL). Such low intrinsic activities, which are some of the lowest ever reported for titanium, enable its use for future dark matter and other rare event searches. Monte Carlo simulations have been performed to assess the expected background contribution from the LZ cryostat with this radioactivity. In 1,000 days of WIMP search exposure of a 5.6-tonne fiducial mass, the cryostat will contribute only a mean background of $$0.160\pm0.001$(stat)$$\pm0.030$$(sys) counts.
Authors:
 [1]
  1. et al.
Publication Date:
Report Number(s):
arXiv:1702.02646; FERMILAB-PUB-17-069-AE-PPD; PNNL-SA-129064
Journal ID: ISSN 0927-6505; 1512771
Grant/Contract Number:
AC02-07CH11359; AC05-76RL01830; AC02-76SF00515; SC0012704; SC0010010; AC02-05CH11231; SC0012161; SC0014223; FG02- 13ER42020; FG02-91ER40674; NA0000979; SC0011702; SC0006572; SC0012034; SC0006605; FG02-10ER46709; NSF PHY-110447; NSF PHY-1506068; NSF PHY-1312561; NSF PHY-1406943; NSF PHY-1642619; ST/K006428/1; ST/M003655/1; ST/M003981/1; ST/M003744/1; ST/M003639/1; ST/M003604/1; ST/M003469/1; CERN/FP/123610/2011; PTDC/FIS-NUC/1525/2014; IE141517; UW PRJ82AJ; SC005336
Type:
Accepted Manuscript
Journal Name:
Astroparticle Physics
Additional Journal Information:
Journal Volume: 96; Journal ID: ISSN 0927-6505
Publisher:
Elsevier
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Orgs:
LZ Collaboration
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1354875
Alternate Identifier(s):
OSTI ID: 1395351; OSTI ID: 1419425