Bachelor exam by Esben Thomas & Camilla Larsen – Niels Bohr Institutet - Københavns Universitet

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Bachelor exam by Esben Thomas & Camilla Larsen

We report results of neutron flux and neutron activation of the concrete walls surrounding the cyclotron at Rigshospitalet. The cyclotron is used for production of radioactive isotopes, which are primarily used for PET scanning. The nuclear reactions producing these isotopes generate a huge flux of neutrons, which can be extremely hazardous. For this reason the cyclotron is contained underground in a vault with heavy concrete walls approximately 2 meters thick. 

The neutrons are absorbed by the materials surrounding the cyclotron, generating radioactive isotopes.  We analyze samples from the vault walls using gamma ray spectroscopic techniques. The current activity of the longer lived isotopes is estimated to be 12-16 MBq, and the future activity 35 years from now - the slated decommissioning date - should be around 16-18 MBq. We use foil stacking techniques in an attempt to determine neutron flux distributions under normal cyclotron operation, and discuss our results of using the Gold algorithm to unfold these spectra.

 

Primary supervisor: Holger J. Jensen, Rigshospitalet
NBI supervisor: Thomas Døssing
censor: Hans Fynbo, University of Aarhus