Search for long-lived superheavy eka-tungsten with radiopure ZnWO$_4$ crystal scintillator

TL;DR

This study used a radiopure ZnWO$_4$ crystal scintillator to set new upper limits on the concentration of superheavy eka-tungsten (seaborgium) in the crystal, contributing to the search for long-lived superheavy elements.

Contribution

It provides the first experimental limit on eka-W concentration using scintillation detection and analyzes high-energy alpha spectra to search for decay signatures of superheavy elements.

Findings

Limit on Sg concentration: N(Sg)/N(W) < 5.5 × 10^{-14} atoms/atom

Limit on eka-Bi concentration: N(eka-Bi)/N(Bi) < 1.1 × 10^{-13} atoms/atom

Comparable sensitivity to recent experiments searching for superheavy elements

Abstract

The data collected with a radioactively pure ZnWO$_4$ crystal scintillator (699 g) in low background measurements during 2130 h at the underground (3600 m w.e.) Laboratori Nazionali del Gran Sasso (INFN, Italy) were used to set a limit on possible concentration of superheavy eka-W (seaborgium Sg, Z = 106) in the crystal. Assuming that one of the daughters in a chain of decays of the initial Sg nucleus decays with emission of high energy $\alpha$ particle ($Q_\alpha > 8$ MeV) and analyzing the high energy part of the measured $\alpha$ spectrum, the limit N(Sg)/N(W) < 5.5 $\times$ 10$^{-14}$ atoms/atom at 90% C.L. was obtained (for Sg half-life of 10$^9$ yr). In addition, a limit on the concentration of eka-Bi was set by analysing the data collected with a large BGO scintillation bolometer in an experiment performed by another group [L. Cardani et al., JINST 7 (2012) P10022]: N(eka-Bi)/N(Bi) < 1.1 $\times$ 10$^{-13}$ atoms/atom with 90% C.L. Both the limits are comparable with those obtained in recent experiments which instead look for spontaneous fission of superheavy elements or use the accelerator mass spectrometry.