6. (a) Nuclear and subatomic particles decays and reactions. Activity and radiation dose. (c) Which of the four fundamental interactions do you expect to dominate in each of the following processes involving subatomic particles. Motivate your answers. Also check all processes for conservation of the baryon charge. (i) n p+e+ve H - e +ve+V p+p- - ++ n y+y (iii) (iv) [2 marks] (b) A 1 g sample taken from an organic artefact is found to have a count rate of 2.1 counts/min, which is assumed to originate from the decay of 4C (t/2 = 5715 yr). If the current abundance of carbon-14, which constitutes 1.2 x 10-12 of all carbon atoms in living matter, is assumed to have been stable in the timeframe of human existence, evaluate the approximate age of the artefact. Hint: Assume the mass of the sample is entirely due to carbon. [3 marks] 197 For a 10 MeV a-particle scattering elastically on a particular 9Au nucleus in a gold foil target with an impact parameter b = 0, estimate the recoil energy of the nucleus. [2 marks] Question 6(d) continued on next page (d) For the purposes of evaluating whole body effective doses after ingestion of radioactive sources, so-called effective half-life te,1/2 is introduced. This is related to the physical half-life of the source but also depends on biological factors (i.e. how the radioisotope is removed from the organism). Based on the radioactive decay law, the rate of accumulating a dose after ingestion is given by: (i) -(t) dt dD e-het, where he is the corresponding effective decay constant. Show that the total accumulated dose due to such an exposure is D = 1 do Ae dttmo (ii) In the case of tritium t/2 = 12.3 yr but te,1/2 = 3 d. Evaluate what total effective dose is received by a 70 kg - person after ingesting a 1 Ci (= 3.7 x 100 Bq) tritium source emitting beta particles with an average energy Ep = 6.2 keV which are assumed to be entirely absorbed in the body. [3 marks]