Measurement of $\beta\beta$ Decay-Simulating Events in Nuclear Emulsion   with Molybdenum Filling
  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. 
V.D. Ashitkov, A.S. Barabash, V.Ya. Bradnova, V.A. Ditlov, V.V.   Dubinina, N.P. Egorenkova, S.I. Konovalov, E.A. Pozharova,...
nucl-ex