Recent results on the low-pressure GEM-based TPC at an Accelerator Mass Spectrometer

TL;DR

This paper presents a novel low-pressure GEM-based TPC technique for distinguishing isotopes like $^{10}$Be and $^{10}$B in Accelerator Mass Spectrometry, improving isotope separation accuracy for geological dating.

Contribution

The paper introduces a new ion identification method using a low-pressure TPC with GEM readout, enhancing separation of isobaric ions in AMS applications.

Findings

Successfully measured ion track ranges and energies for $^{14}$C.

Demonstrated separation of boron and beryllium ions with over 5 sigma significance.

Proposed application of the technique for geochronology of the Cenozoic era.

Abstract

The Accelerator Mass Spectrometry technique makes it possible to measure rare long-lived isotopes such as $^{10}$Be, $^{14}$C, $^{26}$Al, $^{36}$Cl, $^{41}$Ca and $^{129}$I. The content of these isotopes can be at the level of 10$^{-15}$ of the total element content. The Accelerator Mass Spectrometer developed by Budker Institute of Nuclear Physics (BINP AMS) successfully measures the concentration of $^{14}$C relative $^{12}$C. However, there is a problem of separating the $^{10}$B isobaric background from $^{10}$Be. Beryllium-10 is used to date geological objects on a time scale from 1 thousand years to 10 million years. To solve this problem we have proposed a new technique for ion identification based on measuring both ion track ranges and ion energies in a low-pressure Time-Projection Chamber (TPC) with Gas Electron Multiplier (GEM) readout. We have developed the TPC with a dedicated thin silicon nitride window for an efficient passage of ions. To begin with, the characteristic of the low-pressure TPC were studied in isobutane at a pressure of 50 torr using alpha particle sources. In this work, we set up the low-pressure TPC on BINP AMS facility and successfully measured track ranges and energies of ions from samples containing $^{14}$C. At the next stage, we are going to carry out measurements with samples containing $^{10}$Be. However, using the obtained results and SRIM simulation we have already shown that the isobaric boron and beryllium ions can be separated by more than 5 sigma. This technique is proposed to be applied in AMS for dating geological objects, namely for geochronology of Cenozoic era.