Measurement of $\beta\beta$ Decay-Simulating Events in Nuclear Emulsion with Molybdenum Filling

TL;DR

This study investigates background events in nuclear emulsion with molybdenum to improve detection of neutrinoless double beta decay, showing that background suppression is feasible and does not limit sensitivity.

Contribution

It demonstrates the potential to suppress background events in nuclear emulsion experiments using molybdenum, enhancing the detection sensitivity for double beta decay.

Findings

Range of relativistic particles is about 0.60 μm, matching emulsion grain size.

Background from natural radioactivity can be significantly reduced.

Background does not limit the experiment's sensitivity with 1 kg of $^{100}$Mo.

Abstract

The measurement of positron--nucleus collisions was used to estimate the possibility of suppressing background events that simulate $\beta\beta$ decay in the emulsion region adjacent to molybdenum conglomerates. The range of the escape of two relativistic particles from the interaction was found to be $<d> = (0.60\pm 0.03) ~\mu$m, which approximately corresponds to the grain size of developed nuclear emulsion. No correlation of the values of d with the angle between two relativistic particles was observed. It was shown that it was possible to exclude $\beta\beta$ decay background from electrons emerging in the decay of elements of naturally occurring radioactive chains. The background from $\beta$ decays of $^{90}$Sr and $^{40}$K available in emulsion around Mo conglomerates was determined by the ratio of the volume $(\sim d^3)$ to the total volume of emulsion and was found to be $1.5\cdot 10^{-2}$. It was shown that the backgrounds from $^{40}$K, $^{90}$Sr and natural radioactivity could be significantly suppressed and would not limit the sensitivity of the experiment with 1 kg $^{100}$Mo.