Human lung ashes were collected in Vienna, Austria, during the early sixties of the last century in order to determine short-lived fission products from the nuclear test explosions by gamma-spectrometry (1). Later on in part of these samples also plutonium was determined by alpha-spectrometry (2).
Last year we started to investigate some of the remaining samples with regard to 236U (half- life 2.3∙107 years) which is produced via 238U(n,3n) by fast neutrons and by thermal neutron capture on 235U; the cross section for the latter reaction is about 1/6 of the 235U fission cross section.
The ash-samples were dissolved in half-concentrated nitric acid, a certain amount of 233U was added as a spike and uranium was then separated by anion exchange (UTEVA) and co-precipitated with Fe(OH)3. After calcination the samples were measured by accelerator mass spectrometry (AMS) at the VERA laboratory. The derived 236U/238U isotopic values were in the range of 10-8, as expected for global-fallout samples, corresponding to 107 atoms 236U per g of lung-ash. Although the values for individual samples from the same year scatter rather strongly, the calculated mean values clearly display the well-known bomb-peak. The new results will be discussed in connection with the old published data as well as with unpublished 137Cs data.
1) Schönfeld, T., Liebscher, K., Karl, F., Friedmann, Ch., Radiation fission products in lungs. Nature No. 4707 (January 16, 1960), 192-193.
2) Irlweck, K., Friedmann, Ch., Schönfeld, T., Plutonium in the lung of Austrian residents. Health Physics 39 (1980) 95-99.