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210 Po: An Interesting Nucleus The s-process ‘terminator’...end point of the stars... Mme. Curie (and some of her mates...) in 1898 There’s a lot of it.

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Presentation on theme: "210 Po: An Interesting Nucleus The s-process ‘terminator’...end point of the stars... Mme. Curie (and some of her mates...) in 1898 There’s a lot of it."— Presentation transcript:

1 210 Po: An Interesting Nucleus The s-process ‘terminator’...end point of the stars... Mme. Curie (and some of her mates...) in 1898 There’s a lot of it about... Properties (alpha, energies, gammas?) How can/does it harm you?

2 Alexander Litvinenko, aged 43 : Before and after effects of radiation poisoning with ‘polonoium – 210’. Reported feeling ill on 1 Nov. 2006, died 23 Nov

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4 Alpha-decay of 210 Po 4 He (Z=2) (N=2) 206 Pb (Z=82) (N=124) 210 Po (Z=84) (N=126) Q = energy release = [ M( 210 Po) – { M( 206 Pb) + M( 4 He)} ] c 2 ~ 5.5 MeV ~1 pJ. i.e., around 0.003% of total 210 Po mass released kinetic energy in decay. (rare occasion, 206 Pb can be left in an excited state….803 keV above the ground state.) Total energy released shared as KINETIC energy between 206 Pb and 4 He. Cons. of linear momentum means most of the energy (5.3 MeV) goes to 4 He.

5 Po-210 Z = day Bi-209 Z = 83 stable Bi-210 Z = 83 5 day Pb-206 Z = 82 stable Tl-206 Z = 81 4 min n α (0.0001%) 5.3 MeV α (100%) 2 +  keV γ (0.01%) β β (100%) lethal dose ~50 Mbq actual dose ~5 GBq (30 μg) Production by n-capture on 209 Bi

6 Not a bad authors list....one for the RAE of circa 1930 no doubt!

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9 Map of Europe in 1914 (pre-First World War…note, no Poland.

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11 T 1/2 =140 days

12 Q  210 Pb) = 5.41 MeV E  = 5.30 MeV E( 206 Pb) = 0.11 MeV T1/2 = 138 days. ‘ 218 Po =Radium A’ ‘ 218 At =Radium B’ C D E 210 Po =Radium ‘F’ Radon =‘Emanation’ ‘Radium’ C’ C’’ The Natural Decay Chain for 238 U

13 Figure Wiescher, Regan & Aprahamian, Physics World Feb. 2002, page Slow-neutron capture process allows formation of elements from A~56 to A=209 (Bi)... terminates at 209 Bi...why?

14 S-process makes 209 Bi from 208 Pb+n → 209 Pb (T 1/2 =3.2hr) → 209 Bi Neutron capture on stable 209 Bi → 210 Bi (T 1/2 =5 days) → 210 Po. 210 Po →  Pb (stable nucleus, as is 207 Pb and 208 Pb).

15 Po-210 Z = day Bi-209 Z = 83 stable Bi-210 Z = 83 5 day Pb-206 Z = 82 stable Tl-206 Z = 81 4 min n α (0.0001%) 5.3 MeV α (100%) 2 +  keV γ (0.01%) β β (100%) lethal dose ~50 Mbq actual dose ~5 GBq (30 μg) Production by n-capture on 209 Bi

16 ….. Now the AWE files show how small that risk really is because they record the only known secondary contamination with the element. The Establishment, Britain's most closely-guarded nuclear weapons site in Aldermaston, Berks, was the only place at which polonium-210, the substance which killed Alexander Litvinenko, was regularly handled in Britain because it was used in the 1950s as a trigger for early atom bombs. Only on two occasions did the metal, potentially lethal if swallowed or inhaled in large quantities, cause a health scare at the AWE, according to the files, unearthed at the National Archives in Kew. On the first occasion, in 1953, a worker in the polonium department was found to have high levels of alpha radiation in his routine urine test. From the Daily Telegraph, 4 th Dec. 2006, By Ben Fenton How much is ‘bad’ for you ?

17 The second, much more serious incident occurred in 1955, when 15 workers in the section where polonium was processed were exposed when a load of waste material was spilled over a table. The material was gathered up into a large paper bag, but then the worst happened. "While collecting the waste into the bag, it was accidentally compressed and a puff of air came up into the faces of two men," the report said. "Because it was known that the waste was grossly contaminated, it seems reasonable to assume that the doses were received by inhalation." This level of direct exposure by inhalation must be many times greater than any passenger would be likely to receive from sitting on a plane, according to Dr Paddy Regan, a reader in nuclear physics at the University of Surrey. "They effectively breathed this in directly from a powerful source and the dose they got would have been several orders of magnitude greater than anyone could have got from simply sitting on a plane," he said. And the top secret files show that the peak level of radiation detected in the two men was 0.6 microcuries in one and 0.2 microcuries in the second. A lethal dose for ingestion or inhalation by a human being would be between 500 and 5,000 microcuries, according to calculations by Dr Regan and his colleagues. Although they are not named, there is no suggestion in the file that either man suffered any kind of health setback from their exposure. In 1957, the fire and explosion at the nuclear reactor at Windscale (now called Sellafield), Cumbria, released 240 curies of polonium into the atmosphere, enough to kill thousands of people if ingested, but rendered harmless by being diffusion in the atmosphere.

18 How you estimate the damage? Radiation damage measured in units of ‘Grays’ 1 Gy = 1 Joule imparted per kilogram Estimates are ‘assessed’ depending on –type of radiation (i.e., gammas, betas, alphas…) –Body tissues/organs affected…different cells have different tolerances to radiation damage.

19 FromAlpen p426

20 SRIM output for 5.3 MeV alphas on skin (1000 histories)..typical range ~0.04mm No problem outside the body...alphas stop in dead layers of the skin.

21 From Alpen p427 The total sum of weighting factors = Stomach, colon badly affected by radiation...uptake in stomach wall leads to blood and then other organs in body.

22 ICRP Recommended Annual Dose Limits Note these recommended limits EXCLUDE any medical or natural background radiation doses.

23 Paddy’s ‘back of the envelope’ Calculation.... Need to calculate the energy emitted per second at 1mCi for 210 Po and assume 'lethal' value (assume 0.1 Gray = 0.1 J/Kg deposited as a lethal 'whole body dose’ for human over entire body) Total alpha energy emitted by 210 Po = E_a ~ 7*E-13 J x activity x time exposed For a 1mCi 210 Po source, Power =(7*E-13) x (0.001 x 3.7*E10) =3x10 -5 J / second Energy deposited in 1 hour from 1mCi source ~ (3.6E3 s) x (3E-5 J/s) ~ 0.1 J/hour → (neglecting excretion) ~ 1 Joule in 10 hours. Clearly would be worse if you get this in the lungs where none would be excreted out...but assuming just the guts etc.... Mass of intestinal tract/stomach etc. ~5 kg perhaps? Lethal dose in 5 hours of ingestion for 1 mCi source if swallowed? Who body exposure/dose for 100kg man after ~ 5 days for 1mCi source. Conclusion...1mCi would be enough....5mCi to be sure...but must be ingested.

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25 Typical 238 U concentrations in crustal rock ~1-3 parts per million (see ‘Radioactivity in the Environment’ R.L. Kathren, Harwood Academic publishers.

26 Some 210 Po Numbers..(taken from ‘Radioactivity in the Environment’ R.L. Kathren, Harwood) Estimated annual internal ‘whole body’ dose equivalent from natural 210 Po radioactivity in the USA = 30  Sv (same as 222 Rn). ( 40 K =170  Sv for comparison) Annual dose equivalent to epithelial tissue lining the lungs from Radon and its daughters (e.g., 210 Po) ~20  Sv (double this for cigarette smokers).

27 206 Pb first excited state at 803keV 1:10 5 possible way to tell... 1mCi = 3.7 x 10 7 decays per second ~ 400 gammas per second.... Enough for a signal in a whole body counter ? Biological half-life for 210 Po ~50-60 days, only if you are alive to ‘excrete it’ (collects in the Kidneys).....look for activity in the (dried) urine... How can we tell if someone has 210 Po in the future ?

28 Summary 210 Po has an interesting history…named after Poland (which didn’t exist at the time). It occurs naturally (from the decay of 238 U). It is responsible for ‘terminating the s-process (limiting number of chemical elements). You can make it in neutron-capture reactions on 209 Bi. Can be detected by alpha- or gamma-ra spectroscopy. Don’t eat or drink it (few  gm are deadly): No problem really outside the body. Physicist are useful to the public. Numbers matter in calming peoples fears….


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