• Blog Stats

    • 73,666 hits
  • Archives

  • Enter your email address to subscribe to this blog and receive notifications of new posts by email.

    Join 152 other followers

  • Copyright notice

    This blog entry and all other text on this blog is copyrighted, you are free to read it, discuss it with friends, co-workers and anyone else who will pay attention.

    If you want to cite this blog article or quote from it in a not for profit website or blog then please feel free to do so as long as you provide a link back to this blog article.

    If as a school teacher or university teacher you wish to use content from my blog for the education of students then you may do so as long as the teaching materials produced from my blogged writings are not distributed for profit to others. Also at University level I ask that you provide a link to my blog to the students.

    If you want to quote from this blog in an academic paper published in an academic journal then please contact me before you submit your paper to enable us to discuss the matter.

    If you wish to reuse my text in a way where you will be making a profit (however small) please contact me before you do so, and we can discuss the licensing of the content.

    If you want to contact me then please do so by e-mailing me at Chalmers University of Technology, I am quite easy to find there as I am the only person with the surname “foreman” working at Chalmers. An alternative method of contacting me is to leave a comment on a blog article. If you do not know which one to comment on then just pick one at random, please include your email in the comment so I can contact you.

Trinitite

Dear Reader,

Recently I purchased off eBay a small lump of trinitite, now I had been warned that a lot of fake trinitite is being offered for sale. So I choose to take the step of examining the sample with gamma ray spectroscopy.

In less than a minute I had been a peak at 668 keV which could either be due to either 214Bi (665 keV from the beta branch) or 137Cs (662 keV from 137mBa) was seen. This peak suggested that some radioactivity was present in the sample. I did a quick check at 609 keV. The line at 665 is emitted during a small fraction (1.46) of beta decays of 214Bi, while the 609 keV photons are emitted by 46.1 of all decays. As a result it is clear that the sample contains some man made radioactivity.

trinitite1a

Next I looked at the low energy end of the spectrum, here is a log log view to allow you to see this part of the spectrum better. I found a strong peak at 66 keV. I suspect that this is 59.5 keV peak for americium, keep in mind that the energy calibration of the detector is a little off. It was over reporting the energy of the 137mBa, so it is not totally unreasonable for it to over report the energy of the 241Am. As americium is associated with plutonium this is a good sign that the rock is a true lump of trinitite.

trinitite2

I then looked for some of the other lines of this americum nuclide, I looked for 99 and 103 keV photons. I found peaks at 99, 101 and 105 keV. This suggests that some peaks were in this expected range. Maybe it could be americium present. At 81 keV we should expect a peak for 133Ba, in our spectrum we see peaks at 81.7, 83.8 and 87.7 keV.

Also at 128 keV the spectrum contains a peak which could be due to the 122 keV line from 152Eu.

trinitite3

The spectrum also contains at 1414 keV a line which could be due to the 1408 keV emission from 152Eu. Also this nuclide will emit at 964, 444 and 245 keV. In the high energy part of the spectrum we can also see a line at 1466 keV which corresponds to the 1461 keV emission of 40K (decaying into 40Ar).

trinitite5

In our spectrum we see a line at 969 keV which can be matched with the 964 keV emission of 152Eu.

trinitite6

We can go further into the problem, in the range of 400 to 500 keV it is hard to decide if a peak is present. The signal to noise ratio is too bad in this range.

trinitite7

Now if we try again in the range of 200 to 300 keV range, we can see a line at 251 keV which is a possible match to the 245 keV.

trinitite8

The section of the spectrum between 300 and 400 keV shows peaks at 358 and 362 keV one of which could be the 356 keV line for 133Ba.

trinitite4

I think that after seeing this evidence that we can come to the conclusion that the rock sample came from a place where a nuclear fission event occurred, so it is likely to be real trinitite.

We will come back to this later, what I hope to do next is to try to estimate the way in which the efficiency of the detector changes as a function of photon energy. We will try to match the different lines from different radionuclides to the graph.

Advertisements

2 Responses

  1. Analysis of Trinitite – That is very cool. I always wanted a small sample – the nuclear tests are such a massive human event – I didn’t know you could get it on Ebay though! Hah.

    • Dear Becky, If you want I can privately tell you the name of the person on ebay I bought it off. You need to be careful as some people have been selling fake tinitite either knowingly or after having been sold a fake by someone else. I think that the thing to do is to check the sample contains the right man made radioisotopes.

Go on, Have your say !

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: