A Ton-Scale NaI Detector to Measure Coherent Neutrino-Nucleus Scattering and the Charged Current Neutrino Interaction on Iodine

For the COHERENT Collaboration.  The COHERENT collaboration is measuring coherent elastic neutrino-nucleus scattering (CEvNS) on various nuclei in several detector systems located at the Spallation Neutron Source (SNS), in Oak Ridge National Laboratory (ORNL).  CEvNS is well calculated in the standard model with a predicted neutron number (N) dependence that will be compared to measured values. The CEvNS rate is important in supernova processes and serves as a background for direct dark-matter searches.  The collaboration plans to deploy a ton-scale NaI[Tl] scintillation crystal based detector and a larger array in the future.  The large-mass NaI[Tl] detector has the promise to simultaneously measure both CEvNS and the charged current neutrino interaction cross section on I-127, which is sensitive to g$_A$ quenching. Shielding requirements and space limitations constrain the modular detector design.  Measuring both high and low-energy signals requires a dual-gain phhotomultiplier tube base redesign. Extensive neutron background measurements, studies from the NaI-185kg prototype currently deployed at the SNS and multiple simulations contribute to the shielding design.  The ton-scale NaI detector development will be presented.