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

Journal Article · Mon Sep 25 00:00:00 UTC 2017 · Astroparticle Physics

DOI: https://doi.org/10.1016/j.astropartphys.2017.09.002 · OSTI ID:1354875

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1. Michigan U.
2. Moscow Phys. Eng. Inst.
3. Wisconsin U., Madison
4. Imperial Coll., London
5. South Dakota Sch. Mines Tech.
6. Maryland U.
7. Rutherford
8. LBL, Berkeley
9. Fermilab
10. Edinburgh U.
11. UC, Berkeley; Yale U.
12. LLNL, Livermore
13. SLAC; KIPAC, Menlo Park
14. Oxford U.
15. Liverpool U.; Rutherford
16. LIP, Coimbra
17. Washington U., St. Louis
18. Liverpool U.
19. Alabama U.
20. SDSTA, Lead
21. Penn State U.
22. Brown U.
23. South Dakota U.
24. SLAC
25. Northwestern U.; Fermilab
26. University Coll. London
27. Rochester U.
28. UC, Davis
29. Brookhaven
30. UC, Santa Barbara
31. Massachusetts U., Amherst
32. Yale U.
33. UC, Berkeley
34. LBL, Berkeley; UC, Berkeley
35. Sheffield U.
36. IBS, Daejeon, CUP
37. SUNY, Albany
38. Texas A-M
39. UC, Berkeley; LBL, Berkeley
40. SUNY, Albany; LBL, Berkeley
41. Black Hills State U.
42. Northwestern U.
43. Yale U.; UC, Berkeley

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 ²³⁸U_e < 1.6 mBq/kg, ²³⁸U_l < 0.09 mBq/kg, ²³²Th_e = 0.28 ± 0.03  mBq/kg, ²³²Th_l = 0.25 ± 0.02  mBq/kg, ⁴⁰K < 0.54 mBq/kg, and ⁶⁰Co < 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. As a result, 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 ± 0.001(stat) ± 0.030(sys) counts.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); State University of New York, Albany, NY (United States); Univ. of California, Santa Barbara, CA (United States)
• Sponsoring Organization: USDOE; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
• Contributing Organization: LUX-ZEPLIN Collaboration; LZ; The LUX-ZEPLIN (LZ) Collaboration
• Grant/Contract Number: AC02-05CH11231; AC02-07CH11359; AC02-76SF00515; AC05-76RL01830; AC52-07NA27344; FG02-91ER40674; NA0000979; SC0004768; SC0006572; SC0006605; SC0010010; SC0010813; SC0011702; SC0012034; SC0012161; SC0012704; SC0014223; SC0015535
• OSTI ID: 1354875
• Report Number(s): FERMILAB-PUB--17-069-AE-PPD; LLNL-JRNL-825704; PNNL-SA-129064; oai:inspirehep.net:1512771; arXiv:1702.02646
• Journal Information: Astroparticle Physics, Journal Name: Astroparticle Physics Vol. 96; ISSN 0927-6505
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English