Instruments and methods design, optimization and calibration of an automated density gauge for firn and ice cores

Abstract

A gamma-ray density gauge can provide high-resolution and high-precision density measurements of firn and ice cores. This study describes the design, gamma-ray energy optimization and mass attenuation coefficient calibration of the Maine Automated Density Gauge Experiment (MADGE), a portable, field-operable gamma-ray density gauge used on overland traverses in East Antarctica. The MADGE instrument uses a 241 Am gamma-ray source, a pulse-mode counting system and electronic core diameter calipers to collect high-precision (±0.004 g cm-3) density data from 3-8 cm diameter firn and ice cores. The data are collected at a 3.3 mm spatial resolution and an average throughput of 1.5 m h-1 for 5 cm diameter cores.