Transportable calibration pads for ground and airborne gamma-ray spectrometers

Abstract

Sets of four transportable concrete pads 1 m x 1 m x 30 cm and weighing approximately 675 kg were constructed for calibrating portable gamma-ray spectrometers. Each set consists of a low radioactivity background pad, and three radioelement pads of potassium, uranium, and thorium which provide almost pure gamma-ray spectra. The potassium pads were manufactured using potassium feldspar and the thorium pads using britholite, a thorium-rich rare earth phosphate. Initial problems of radon loss from the uranium pad were overcome by using a uranium-rich slag of calcium silicate which was a byproduct from a phosphorus processing plant. Experiments with these small pads have shown that they give the same potassium, uranium, and thorium spectral shapes as the much larger aircraft calibration pads. These small transportable pads can therefore be used for calibrating large volume airborne systems as well as portable gamma-ray spectrometers.

In situ gamma radiation measurements in the Neoproterozoic rocks of Sirohi region, NW India

“…Transportable concrete pads of 1 m × 1 m × 30 cm size containing known amounts of potassium, uranium and thorium and a fourth pad with none of these three elements to measure the background as described in Grasty et al (1991) were used by Radiation Solutions to obtain the stripping ratios and sensitivity constants for the matrix calculations that are carried out inside the spectrometer for background correction and conversion to ppm (for U and Th) and % (for potassium). The sources of error that can occur, according to Radiation Solutions Inc. (2007), are statistical errors due to noise of the counting, that can be reduced by choosing longer counting times; calibration errors that become comparable to the statistical error if the counting time is extended above 2 min and if levels of K, U and Th exceed the calibration pad concentrations of 4% K, 25 ppm U and 70 ppm Th; a geometrical error, because the detector assumes a homogeneous half-space of material, which is almost never the case in nature, and errors due to the counting Grasty et al (1991) cross-interference needs to be taken into account as well, because for varying concentrations of one element, there are not only error components for that element but also for the remaining elements. The error needs to be calculated by taking the square root of the sum of the square of errors.…”

Airborne γ-ray spectrometric characteristics of lithological units and environmental issues in the Bahariya Oases area in the northern part of western desert, Egypt

“…One roentgen equivalent man is the dose from any radiation that produces biological affects in a man. The conversion from exposure rate (E) to dose rate (D) is as follows (Grasty et al 1991):…”

The Radiometric Map of Australia

“…The fixed CSIRO pads are thus tied to the global baseline. * Transportable calibration pads for calibrating both portable and airborne spectrometers (Grasty et al, 1991). These pads have dimensions 1 Â 1 Â 0.3 m, and because they are transportable, are easily used for estimating stripping ratios for airborne gamma-ray spectrometers, and both stripping ratios and sensitivities for portable spectrometers.…”

“…* Transportable calibration pads constructed by the CSIRO at North Ryde in the early 1990s. These have the same dimensions, and similar concentrations, to the pads of Grasty et al (1991), and were tied to the fixed CSIRO (2 m-diameter) pads during a cross-calibration exercise in 1995. These pads are thus also tied to the global baseline.…”