Saturday, 11 July 2015

Beamtime fun at Diamond

I don't think I've been on this beamline since 2012 and the famous "which chocolate bar floats the best" experiment. On that visit we were looking at the calcium carbonate secreted by earthworms and it's pretty much the same system we're looking at on this visit, but in more exotic earthworms.

The reason we're at Diamond again is (or was) to investigate how earthworms deal with carbon dioxide. Specifically we're looking at earthworms from the Azores that live on the sides of mountains with high levels of carbon dioxide flowing through the soil that they live in. Normally these high levels would be sufficient to suffocate the earthworms but not in this case. There are two types of earthworm that we're looking at, Pontoscolex and Amynthus. Pontoscolex has a calciferous gland and so perhaps locks up the carbon dioxide by precipitating it as calcium carbonate whereas Amynthus doesn't have a calciferous gland. There is an enzyme, carbonic anhydrase, that moves carbonate around and contains zinc. Luis de Cunha, a postdoc. from Cardiff, has shown that zinc is concentrated in the skin of Amynthus, so we thought that perhaps that is where the carbonic anhydrase is as well and maybe Amynthus copes with the carbon dioxide by precipitating calcium carbonate in its skin. Two days in and we can say that this isn't the case which isn't particularly exciting but there you go.

The way this beamline works - i18, microfocus spectroscopy - is that first you section your sample which is a skill in itself, done on this occasion by John Morgan in Cardiff.
Thin section, about 6 cm x 3 cm. The faint white patches are slices through earthworms.

You then place these in the beamline and zap the section with X-rays to produce an XRF plot - this shows you the distribution of the elements you're interested in, e.g. calcium for us.

The top screen shows a close-up optical microscope image of our sample. The lower screen shows the XRF map. You can see a bright white diagonal line that indicates high calcium. From the optical image we can see this is associated with the earthworms chloragog - a liver like organ.

Once you have the map you can identify individual points that look like they have an interesting concentration of the element and do something called XANES (or EXAFS depending on precisely what you want to know). XANES is a fingerprinting technique - different forms of the element have different patterns and this allows you to work out what form your element is in.
Here, the lower screen shows a wiggle - this is a XANES spectrum, characteristic of the form that the calcium is present in the chloragog. By comparing with standards we can see that it looks like the calcium is present as a calcium phosphate. 

The controls look rather intimidating but as long as everything works there are relatively few buttons to press and we have had excellent instruction from the beamline scientist Tina Geraki.
Tina Geraki on the beamline.

i18 control screens
So we've shown that our hypothesis was incorrect - there isn't calcium carbonate concentrated in the Amnythus earthworm skin. We now have two more days beamtime so John Morgan and Stephen Short have high tailed it back to Cardiff to get some more samples so we can do a fuller comparison of calcium in calciferous glands.

Today has been a little odd as there is an Open day across the entire Harwell campus. True to the promises they made there were dinosaurs and volcanoes. Everyone seems to have had fun.
A dinosaur overlooks members of the public. Scientists use the synchrotron to investigate chemical traces in fossils.

and a model volcano - not sure what that was all about

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