Quantifying K, U, and Th contents of marine sediments using shipboard natural gamma radiation spectra measured on DVJOIDESResolution

Abstract

During International Ocean Discovery Program (IODP) expeditions, shipboard-generated data provide the first insights into the cored sequences. The natural gamma radiation (NGR) of the recovered material, for example, is routinely measured on the ocean drilling research vessel DV JOIDES Resolution. At present, only total NGR counts are readily available as shipboard data, although full NGR spectra (counts as a function of gamma-ray energy level) are produced and archived. These spectra contain unexploited information, as one can estimate the sedimentary contents of potassium (K), thorium (Th), and uranium (U) from the characteristic gamma-ray energies of isotopes in the 40 K, 232 Th, and 238 U radioactive decay series. Dunlea et al. (2013) quantified K, Th, and U contents in sediment from the South Pacific Gyre by integrating counts over specific energy levels of the NGR spectrum. However, the algorithm used in their study is unavailable to the wider scientific community due to commercial proprietary reasons. Here, we present a new MATLAB algorithm for the quantification of NGR spectra that is transparent and accessible to future NGR users. We demonstrate the algorithm's performance by comparing its results to shore-based inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-emission spectrometry (ICP-ES), and quantitative wavelength-dispersive X-ray fluorescence (XRF) analyses. Samples for these comparisons come from eleven sites (U1341, U1343, U1366-U1369, U1414, U1428-U1430, and U1463) cored in two oceans during five expeditions. In short, our algorithm rapidly produces detailed high-quality information on sediment properties during IODP expeditions at no extra cost.

Indonesian Throughflow drove Australian climate from humid Pliocene to arid Pleistocene

“…The HNGS uses two bismuth germanate scintillation detectors and five‐window spectroscopy to determine concentrations of potassium (K, in weight percent [wt %]), thorium (Th, in parts per million [ppm]), and uranium (U, ppm) from the characteristic gamma ray energies of isotopes in the 40 K, 232 Th, and 238 U radioactive decay series (Text S2). The computation of the elemental abundances uses a least squares method of extracting U, Th, and K elemental concentrations from the spectral measurements and is supported by discrete analyses [ De Vleeschouwer et al ., ]. The HNGS filters out gamma ray energies below 500 keV, eliminating sensitivity to bentonite or KCl in the drilling mud and improving accuracy.…”

A New Seismic Stratigraphy in the Indian‐Atlantic Ocean Gateway Resembles Major Paleo‐Oceanographic Changes of the Last 7 Ma

“…Potassium (K) content derived from NGR (De Vleeschouwer et al, ) ranges from 0.11 to 0.86 wt% with an average of 0.46 wt% (Figure d). In the upper 30 m CCSF‐B, K values show the most pronounced variations, with high amplitude cyclic changes around 0.45 wt%.…”

“…A NGR Logger equipped with 8 Sodium Iodide (NaI) scintillator detectors, 7 shielding plastic scintillator detectors, 22 photomultipliers, and passive Lead shielding (Vasiliev et al, ) was used to measure gamma radiation emitted from the whole‐round core sections of Site U1475 at a resolution of 10 cm (Hall et al, ). Changes in NGR represent the total variation in activity of the radioactive elements 40 K (Potassium), 238 U (Uranium), and 232 Th (Thorium), and by integration of the NGR counts over the element‐specific energy intervals of the spectrum concentrations of U, Th, and K have been derived (De Vleeschouwer et al, ). K is common in many sediments which bear feldspar, mica, and clays, thus characterizing the terrigenous sediment fraction.…”

Site U1519

“…Natural gamma radiation (NGR) values range from 18 to 67 counts/s at Site U1519 and are relatively uniform through the cored intervals, with an average of 40 counts/s ( Figure F26). The NGR spectra were used to estimate 40 K, 232 Th, and 238 U concentrations using the algorithm presented by De Vleeschouwer et al (2017) (Figure F28). K, Th, and U concentrations are relatively uniform through the cored intervals.…”