79Kr Calibration Source for He6-CRES Measurements

The He6-CRES collaboration aims to use cyclotron radiation emission spectroscopy (CRES) to probe beyond the standard model physics at the TeV scale by performing low-background and high-resolution ꞵ decay spectroscopy on the MeV scale with 6He and 19Ne (Phys. Rev. Lett. 131, 082502 (2023).) We are motivated to use 79K as a calibration source for He6-CRES due to: 1) it is a noble gas, which is appropriate for our setup; 2) the +decay from 79Kr(t1/2=35.04(10) h)(endpoint=604(3) keV); 3) monochromatic electron lines from 79mKr(t1/2=50(3) s) to characterize the CRES detection system. The first steps are to test the production rate, purity, and transport by using a 13-MeV proton beam from the CENPA tandem Van de Graff accelerator into a cell containing compressed potassium bromide. An initial bombardment followed by gamma-ray measurements indicated a high purity of 79Kr and appropriate production rates, consistent with calculations based on the known cross section. Our next step is to produce the activity in a manner that can be cleanly separated from any stable contaminant that may cause poor performance in the CRES measurement, which requires high vacuum. A connection between the target cell and a high-vacuum pipe has been built, installed and tested. We plan to soon measure the pressure before the connection to our high-vacuum systems as well as gamma ray spectra while under beam bombardment to determine the next steps. Data will be presented at the meeting.