Scintillation balloon for liquid scintillator base Neutrinoless double beta decay search experiments

TL;DR

This paper proposes using a scintillation film made of polyethylene naphthalate (PEN) as a mini-balloon in liquid scintillator experiments to improve background rejection in neutrinoless double beta decay searches.

Contribution

The study introduces a novel scintillation film material, PEN, for mini-balloons, enabling alpha-ray tagging to reduce background in neutrino experiments.

Findings

PEN film shows suitable transparency and emission spectra.

PEN has sufficient light yield and low radioactivity.

A test-sized scintillation balloon was successfully developed.

Abstract

A liquid scintillator base experiment KamLAND-Zen has set a lower limit on neutrinoless double beta decay half-life, and upgrade project KamLAND-Zen 800 has started in 2019. Unfortunately, this project expects some backgrounds, and one of the main backgrounds is beta/gamma-ray from 214Bi in container of xenon loaded liquid scintillator (mini-balloon). In order to reject the background, we suggest using scintillation film for the future mini-balloon. If we can tag alpha-ray from 214Po by scintillation detection, we can eliminate 214Bi events by delayed coincidence analysis. Recently, it was reported that polyethylene naphthalate (PEN) can be used as a scintillator with blue photon emission. PEN has chemical compatibility for strong solvent, thus it has a possibility to use in liquid scintillator. In this presentation, we will mention the results for feasibility studies about transparency and emission spectra, light yield, radioactivity, strength of film etc.. We also show the test-sized scintillation balloon with an 800-mm diameter and discussions about how to use the scintillation balloon in KamLAND.