Measurement of the Neutron Total Cross section on Argon in Energy Range of 30-70 keV Jingbo Wang on behalf of the ARTIE collaboration University of California, Davis The Argon Resonant Transport Interaction Experiment (ARTIE) was recently performed at the Time-of-Flight neutron beam at Los Alamos National Laboratory (LANL). ARTIE makes a new measurement of the total cross-section of neutrons on natural argon between 30-70 keV. This measurement is crucial for the Deep Underground Neutrino Experiment (DUNE) as it determines the feasibility of the neutron-based detector calibration technique and provides a deeper understanding of signals and backgrounds for the low energy physics programs. Abstract Neutron Total Cross Section Summary Motivation This work is supported by the Department of Energy, Office of Science and the National Nuclear Security Administration Acknowledgements The Deep Underground Neutrino Experiment (DUNE) is an upcoming US-based international long-baseline experiment for neutrino science. Screen Shot 2020-06-10 at 11.04.11 AM Design of Liquid Argon Target References [1] http://www.dunescience.org [2] R.R Winters, et al., Phys. Rev. C 43 492 (1991) [3] https://lansce.lanl.gov DUNE is the future flagship experiment of the Department of Energy. It will send a neutrino beam from Fermilab in Illinois to Sanford Underground Research Facility in South Dakota [1] The neutron transport in liquid argon is important: 1. Detector calibration: Can we use an external pulsed neutron source to calibrate the far detector? Neutron capture signal could be used as a standard candle energy. 2. Neutron shielding: How much shielding material is needed for suppressing the neutron backgrounds in supernova and solar neutrino programs. 3. Neutrino Physics: Are nearby neutrons useful to achieve better energy resolution during the reconstruction of the supernova neutrinos? ENDF vs Previous Measurement The Lujan Center at the Los Alamos Neutron Science Center (LANSCE) Experimental Setup at LANL Energy [eV] 20000 40000 60000 80000 Cross-section [barn] 1 - 10 1 10 ENDF Ar-nat Winters ARTIE’s target density is 3.5 atoms/barn: blind to high cross sections but sensitive to low-cross sections at 30-70 keV • 168 cm long, 1” OD stainless steel tube • Sealed by Kapton foil windows allowing neutrons to go through • Dry-nitrogen gas-flow-caps used to prevent ice formation on Kapton windows • Liquid level monitored by video cameras and temperature sensors • Thermal insulation provided by Polyurethane foam Need good understanding of neutron total cross section in the range of 30-70 keV • The ENDF prediction of the neutron total cross section on natural argon is ∼0.01 barn at 57 keV, which disagrees with a previous measurement of ~0.1 barn [2]. • Previous Measurement by Winters: o Neutron Transmission Measurement 2.216-meter long gaseous target with a density of 0.211 atoms/barn o Not sensitive to low cross section at energy range of 30-70 keV Liquid Argon Target Foam Insulation Liquid Argon fill Dewar Liquid Argon vent Dewar Gas Cap Gas Flow Gas Flow Gas Cap • Neutron energy determined using the Time-of-Flight technique • The total cross section is measured through neutron transmission TOF neutron detector Vacuum pipe Vacuum pipe Liquid argon target Neutron beam 𝜎! = − " #∗ln 𝑇! = − ! "∗ln #"#$%"# #$%&$%$%& 𝜎!: total cross section at energy bin i 𝑛∗: effective column density of the target 𝑇": transmission coefficient at energy bin i 𝐶"#: 𝑇𝑜𝑡𝑎𝑙𝑛𝑒𝑢𝑡𝑟𝑜𝑛𝑐𝑜𝑢𝑛𝑡for target-in run 𝐵"#: Background count for target-in run 𝐶$%&: 𝑇𝑜𝑡𝑎𝑙𝑛𝑒𝑢𝑡𝑟𝑜𝑛𝑐𝑜𝑢𝑛𝑡for target-out run 𝐵$%&: Background count for target-out run • Neutron beam: Flight Path 13 at Lujan Center at the Los Alamos Neutron Science Center (LANSCE) [3] Proton Target Liquid Argon Target At 30 meter Li-glass Neutron Detector at 65 m Target area at FP13 Measurement Strategy Transmission Measurements: • “Target-out” run with the target tube flushed by gaseous argon • “Target-in” run with the target tube filled with