Question

Yasser Arafat, former chairman of the Palestine Liberation Organization (PLO), died in November 2004, after a brief illness. Not surprisingly, his death aroused considerable suspicion, particularly given that his symptoms were somewhat consistent with acute radiation poisoning. In November 2012, samples of tissue were obtained from his corpse and tested—by three independent research groups—for evidence of poisoning by a highly radioactive isotope of Polonium. The results, though far from conclusive, suggest that Arafat died as a result of polonium-210 poisoning.

Polonium-210 is a short-lived isotope in the uranium decay series. Together with thallium-206, polonium-210 is a penultimate daughter product in the 238U → 206Pb decay series. Polonium-210 occurs in trace amounts in uranium ores; annually, about 100 grams of 210Po is produced (synthetically) in reactors. 210Po decays to 206Pb via alpha emission with a radiogenic half-life of 138 days. The ejected alpha particle has an energy of 5.3 MeV. The biological half-life of 210Po is about 40 days, i.e. it takes your body about 40 days to excrete half the amount of 210Po originally ingested. For the purposes of this class, the fatal internal dose (D50) of radiation from an ingested alpha emitter like 210Po is approximately 0.25 Joule of energy absorbed per kilogram of body mass. (Note: The D50 notation indicates the dosage that proves fatal for half of a population; D50 ~ 0.25 J/kg for 210Po.) For those interested in dosage units, 0.25 J/kg = 0.25 Gy = 5 Sv = D50 for an alpha emitter absorbed internally (Q factor of 20).

1 (20 pts.): Assuming access to a ‘fresh’ polonium source, i.e. straight from the reactor, would one microgram (1 μg) of ingested 210Po kill Arafat? (FYI: 1 μg of 210Po is equivalent to approximately one grain of silt.) If yes, then approximately what time interval was required to absorb a fatal dose? Note: There is typically a lag time of days to weeks between the time at which a fatal dose is absorbed and the actual time of death. Arafat died about two weeks after the onset of symptoms. Discuss very briefly some of the complications we might expect in analyzing Arafat’s corpse for signs of 210Po poisoning in 2012.

1) clear and concise explanations of your reasoning and 2) careful calculations using scientific notation. The answer should be presented clearly and logically.

Answer 1

Let us assume 1 mass of 210Po has entered into Arafat's body .

Let us find number of atoms N present in 1 of 210Po .

N = [ 6.02 1023 / 210 ] 10-6 = 2.867 1015

Activity (dN/dt) in 1 of 210Po is obtained as follows

(dN/dt) = N = ( ln2 ) N / T1/2

where is decay constant and T1/2 is half life of 210Po

we gat activity as, (dN/dt) = ( ln2 2.867 1015 ) / ( 138 24 3600 ) = 1.667 108 Bq

( Bq :- Becquerel is unit of radioactivity that equals 1 disintegration per second )

Each disintegration of 210Po emits 5.3 MeV particle

hence particle energy E released every second by 1 mass of 210Po is given by

E = 1.667 108 5.3 1.602 10-13 J = 1.415 10-4 J

Let us assume Arafat's body mass is around 70 kg

Required time t to get internal dose 0.25 J / kg or   0.25 70 = 17.5 J , is calculated as follows

t = 17.5 / 1.415 10-4 = 12.367 104 s = [13.109 104 / 3600 ] = 36.41 hours

Above analysis shows that intake of 1 mass of 210Po in Arafat's body would have given the fatal internal dose (D50) in 36 hours or in one and half day.