High-pressure xenon time projection Titanium chamber: a methodology for detecting background radiation in neutrinoless double-beta decay experiments

Abstract

The xenon time projection chamber (TPC) promises a novel detection method for neutrinoless double-beta decay (0ν ββ) experiments. The TPC is capable of discovering the rare 0ν ββ ionization signal of a distinct topological signature, with a decay energy Q ββ = 2.458 MeV. However, more frequent internal (within TPC) and external events are also capable of depositing energy in the range of the Q ββ -value inside the chamber, thus mimicking 0ν ββ or interfering with its direct observation. In the following paper, we illustrate a methodology for background radiation evaluation, assuming a basic cylindrical design for a toy titanium TPC that is capable of containing 100 kg of xenon gas at 20 atm pressure; we estimate the background budget and analyze the most prominent problematic events via theoretical calculation. Gamma rays emitted from nuclei of 214 Bi and 208 Tl present in the outer-shell titanium housing of the TPC are an example of such events for which we calculate probabilities of occurrences. We also study the effect of alpha-neutron (α-n)-induced neutrons and calculate their rate. Alpha particles which are created by the decay of naturally occurring uranium and thorium present in most materials, can react with the nucleus of low Z elements, prompting the release of neutrons and leading to thermal neutron capture. Our calculations suggest that the typical polytetrafluoroethylene (PTFE) inner coating of 1Corresponding author.