SXR103 - Day 4

I'm really getting into the swing of things now so after a quick breakfast at Bramber House it's off to the lab for a day of rocks and radioactivity.
This was a mixture of geology and physics with a nice link between the two. We started by looking at several samples of different rock and have to sort them into igneous, sedimentary and metamorphic, before beginning to look at the rocks more closely and thinking about how and where they were formed. This was very much like book 2 of S104, only with more and larger samples. By the end of this we had a pretty good idea that there must be something below the surface of the Earth that provides the energy to melt igneous rocks as well as drive plate tectonics.

In steps radioactivity, nicely linked by the OU I think.

We then moved onto measuring the background radiation in the lab (not very much) followed by two different types of granite (more than I had expected). By this point it's time for lunch so we all left the Geiger counters running to get a better figure for background.

Lunch today was chicken covered in guacamole and boiled potatoes followed by chocolate muffin. Then it was time to return to see how much radiation we had detected.

With the mean background count over 1 minute calculated we moved onto some more reliable sources, starting with a uranium-rich mineral. It starts getting "serious" at this stage as we have to handle the source with tongs even though the sample is in an enclosure, but nothing to worry about. We got a nice count for radiation emitted by the sample over 1 minute (which was not much higher than for the granite) before switching to another source.

This one comes in a protective box!! However no one was donning lead-lined suits and the dosimeter hanging by the bench didn't seem too worried so neither were we. This sample was called a caesium/barium isotope generator and we first measured how much of the radiation (gamma radiation) would get through different thicknesses of lead sheet. Even with 2cm of lead between the Geiger counter and the source we were still getting readings (we used the background count we got earlier to eliminate this). We also had to calculate a figure for the uncertainty of this figure but even accounting for this the gamma rays were still getting through. Then we had to plot our figures on a graph (with an awful scale pre-printed by the OU) and so calculate the mean half-thickness for absorption.

The final practical of the day involved extracting the barium isotope from the generator we had just used, which has a very short half-life that we get to calculate. Because of the short half-life we get a sample by flushing the caesium/barium isotope generator with distilled water which will give us a sample. This had to be carried out with a tutor present to make sure that if we spill any of the radioactive water it can be dealt with safely. Goggles and gloves were added to the list of precautions here and everything had to be checked before we could proceed. Once we had taken readings over 15 minutes we plotted the values (this time the scale was better) and could then calculate a half-life value. All the class came pretty close which was satisfying.

Another enjoyable day over with and time for tea (jacket spud followed by a very nice rice pudding) a call home and a check through today's workbook to make sure I had completed everything before going to my selected 8:15 lecture.

Another one by James (my third in a row) and this time he was talking about drug design and synthesis. This was a very interesting talk from a seasoned organic chemist which I thoroughly enjoyed.

Tomorrow is the lab I've been looking forward to, the notional chemistry practical with a bit of physics thrown in.