Measuring the Cosmic Ray Muon-Induced Fast Neutron Spectrum by (n,p) Isotope Production Reactions in Underground Detectors

Abstract

While cosmic ray muons themselves are relatively easy to veto in underground detectors, their interactions with nuclei create more insidious backgrounds via: (i) the decays of long-lived isotopes produced by muon-induced spallation reactions inside the detector, (ii) spallation reactions initiated by fast muon-induced neutrons entering from outside the detector, and (iii) nuclear recoils initiated by fast muon-induced neutrons entering from outside the detector. These backgrounds, which are difficult to veto or shield against, are very important for solar, reactor, dark matter, and other underground experiments, especially as increased sensitivity is pursued. We used fluka to calculate the production rates and spectra of all prominent secondaries produced by cosmic ray muons, in particular focusing on secondary neutrons, due to their importance. Since the neutron spectrum is steeply falling, the total neutron production rate is sensitive just to the relatively soft neutrons, and not to the fast-neutron component. We show that the neutron spectrum in the range between 10 and 100 MeV can instead be probed by the (n, p)-induced isotope production rates 12C(n, p)12B and 16O(n, p)16N in oil- and water-based detectors. The result for 12B is in good agreement with the recent KamLAND measurement. Besides testing the calculation of muon secondaries, these results are also of practical importance, since 12B (T1/2 = 20.2 ms, Q = 13.4 MeV) and 16N (T1/2 = 7.13 s, Q = 10.4 MeV) are among the dominant spallation backgrounds in these detectors.

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• First calculation of cosmic-ray muon spallation backgrounds for MeV astrophysical neutrino signals in Super-Kamiokande
• Developing the MeV potential of DUNE: Detailed considerations of muon-induced spallation and other backgrounds
• Tagging Spallation Backgrounds with Showers in Water-Cherenkov Detectors
• Measurements of gamma ray, cosmic muon and residual neutron background fluxes for rare event search experiments at an underground laboratory
• A Neutron Multiplicity Meter for Deep Underground Muon-Induced High Energy Neutron Measurements
• Reconstructing the direction of reactor antineutrinos via electron scattering in Gd-doped water Cherenkov detectors
• Measurements using a prototype array of plastic scintillator bars for reactor based electron anti-neutrino detection
• Evaluation of the response of plastic scintillator bars and measurement of neutron capture time in non-reactor environment for the ISMRAN experiment
• Characterization of plastic scintillator bars using fast neutrons from D-D and D-T reactions
• On the Energy Spectrum of Cosmogenic Neutrons
• Measurement of Muon-induced High-energy Neutrons from Rock in an Underground Gd-doped Water Detector
• Neutron Tagging Can Greatly Reduce Spallation Backgrounds in Super-Kamiokande
• Gamma ray production in inelastic scattering of neutrons produced by cosmic muons in ${}^{56}$Fe
• New Spallation Background Rejection Techniques to Greatly Improve the Solar Neutrino Sensitivity of JUNO