We hold an annual course in radiation biology at Stockholm University, and we try to take the students to some cool places related to radiation (nuclear power plants, mines, radiotherapy departments, etc).
Starting last year,we started to go to the Ytterby mine outside Stockholm. Here, several elements have been discovered and 4 are named from the mine
The mine entrance is filled since many years (the mine shaft is over 150m deep), but there is a small "quarry" which is easily accessible and that proved to be plenty "hot".
We have also heard rumors about an entrance permitting entrance 70 m into the mine, but this remains to be seen.
I was asked this year to tag along, as my supervisors (the course directors) knew about my interest in radiation detection. As I recently got my Walkabout, I thought this would be a great opportunity to test the system in the field.
Said and done, we put the students on the bus for a 40 min trip into the Stockholm archipelago. The mine itself is located almost in the middle of the Ytterby village, so one just has to walk up a short (but steep) hill to reach the quarry.
The students were given geiger counters, and sent off to look for hot objects. It was my first visit to the mine, so I did not know what to expect in terms of activity. Immediately the students found a part of the quarry "wall" to be sizzling, we measured the dose rate to between 15-20 µSv/h depending on which detector we looked at.
Desperately, we tried to find some rocks on the ground that would also be hot, but we failed to find any hot rocks on the ground. Probably, this small quarry has seen plenty of visits throughout the last 70 years and the best rocks are gone.
Also, it was quite tricky to find small hot rocks close to the "hot" wall which I believe masked the readings from smaller medium/low activity rocks.
In any case, after measuring around for about one hour, I took a look at the accumulated geigerbot spectrum, and what stands out from the rich background is a peak close to 600 keV, strongly suggesting that the peak is at 609 keV from Bi-214, belonging to the U decay chain.
The spectrometer was calibrated the day before using a Ra-226 sample, but one needs to keep in mind the measurements at the quarry were performed without background shielding and in an environment with shifting temperature (direct sunlight, shade, outside temp being 25 C) so I am quite surprised we saw such a clear peak.
We did not bring rockhammers, but that might be something to take for the next visit. The mine is easily accessible so there will probably be more visits later on!
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