Study of the effects induced by lead on the emulsion films of the OPERA experiment

TL;DR

This paper investigates how contact with lead affects emulsion films in the OPERA neutrino experiment, focusing on radioactivity and mechanical properties to optimize detector performance.

Contribution

It provides a detailed analysis of lead-emulsion interactions and proposes a lead alloy with suitable properties to minimize background noise in neutrino detection.

Findings

Adding chemical elements to lead increases radioactivity in emulsions.

A specific lead alloy with good mechanical properties reduces background tracks.

Optimized packing techniques improve detector performance.

Abstract

The OPERA neutrino oscillation experiment is based on the use of the Emulsion Cloud Chamber (ECC). In the OPERA ECC, nuclear emulsion films acting as very high precision tracking detectors are interleaved with lead plates providing a massive target for neutrino interactions. We report on studies related to the effects occurring from the contact between emulsion and lead. A low radioactivity lead is required in order to minimize the number of background tracks in emulsions and to achieve the required performance in the reconstruction of neutrino events. It was observed that adding other chemical elements to the lead, in order to improve the mechanical properties, may significantly increase the level of radioactivity on the emulsions. A detailed study was made in order to choose a lead alloy with good mechanical properties and an appropriate packing technique so as to have a low enough effective radioactivity.