Research update blog: Tracking down core samples for NeutronCT measurements.

A week before my official PhD start date, I gave a presentation to industry asking permission to use their core data from the NWS, Australia. One year later and the approval process is still ‘in progress!’ Meanwhile, I have an accepted proposal for ANSTO instrument beamtime (with a scholarship) to measure this core using a neutron CT instrument called ‘Dingo’. The instrument time is scheduled for November 2022. In October 2022, I still have no core. Luckily, after emailing around all the core store archives in Australia, we find someone who can verify their whereabouts. The catch is – they are uncurated and the inventory is ‘incomplete’ at best. A two-week trip to the Perth core store and full access to this undocumented treasure trove is a small weight off my shoulders.

There is lots of core  – but the precious 200m long core has been whittled down to just 14m! I photograph all the core and submit a sample request form for non-destructive analysis that gets approved within a day (those guys are great!). Back at UWA (University of Western Australia), where I am meeting my co-supervisor and giving research update presentations, I am handed a ’spare’ box of NWS core. This is some of the very core I have spent a year searching for. Sat in the dark dank corner of an office, I gratefully whisk the box back to Sydney. Four weeks remain until beamtime (which comes in at around $45k for 5 days operation!). Even more fantastic – the Perth core store guys cut the core and have it sent to University of Sydney within 5 days!

So, I fly to Sydney, collect the 5 boxes of core (Fig.1), and make my way to ANSTO. The ANSTO beamtime proposal (co-collaborators: Jody Webster, Joseph Bevitt, Gregory Webb and Luke Northdruft) believes that by bombarding core samples with neutrons, we can distinguish sections of pure aragonite from calcite in the fossil coral, which we can then use for U/Th dating. I spend three days in a SAS workshop (small angle scattering workshop) to learn the science behind this method. I am concerned that it might not work but am told that ‘neutrons don’t lie’. The next day we start beamtime and measure a proof-of-concept Porites fossil coral sample (Fig.2) from PNG that has previously had calcite and aragonite definitively defined using hyperspectral imaging (Murphy et al, 2017). We quickly process the raw data and bring up the image. It is broken and upside down – but it is clear – the method has worked. We see that the light section clearly corresponds to the aragonite, and the dark section corresponds to the calcite. SUCCESS! This is the first time the DINGO NeutronCT instrument (Fig.3) has been used in this way. The next three days is spent trying to measure the remaining 5 boxes of core (I also accidentally leave my phone in the neutron beam room – but luckily, far enough away from the beam exposure that it is not radioactive and I don’t have to put it in the nuclear waste pile!). We also find that because the neutrons are ‘water-loving’ we can correlate the subaerial exposure events (high clay/water content) and find that coral fragments and shells precipitate calcite from the inside out – which can be indicative of the type of diagenetic textures and meteoric environment (i.e., freshwater or seawater alteration in the vadose or phreatic zones (Patterson et al, 2008; McGregor and Abram, 2008)). This is excellent information that will go towards the third and fourth chapters of my thesis on forward stratigraphic modelling.

Onwards and upwards! Pictures below…

Merry Christmas GRG folk!

Carra

One response to “Research update blog: Tracking down core samples for NeutronCT measurements.

  1. Absorbing information and an excellently written blog. Keep posting your work. Thank you, and Merry Christmas.

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