210 Po: An Interesting Nucleus
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Transcript of 210 Po: An Interesting Nucleus
210Po: An Interesting Nucleus
• The s-process ‘terminator’...end point of the stars...
• Mme. Curie (and some of her mates...) in 1898
• There a lot of it about...
• Properties (alpha, energies, gammas?)
• How can/does it harm you?
Figure Wiescher, Regan & Aprahamian, Physics WorldFeb. 2002, page 33-38
Slow-neutron capture processallows formation of elementsfrom A~56 to A=209 (Bi)...
terminates at 209Bi...why?
S-process makes 209Bi from 208Pb+n → 209Pb (T1/2=3.2hr) → 209Bi
Neutron capture on stable 209Bi → 210Bi (T1/2 =5 days) → 210Po.
210Po → + 206Pb (stable nucleus, as is 207Pb and 208Pb).
Po-210Z = 84138 day
Bi-209Z = 83stable
Bi-210Z = 835 day
Pb-206Z = 82stable
Tl-206Z = 814 min
n
α (0.0001%)
5.3 MeV α (100%)2+0+ 803 keV γ (0.01%)
β
β (100%)
lethal dose ~50 Mbqactual dose ~5 GBq (30 μg)
Production by n-capture on 209Bi
Not a bad authors list....one for the RAE of circa 1930 no doubt!
T1/2=140 days
Q210Pb) = 5.41 MeVE = 5.30 MeV E(206Pb) = 0.11 MeVT1/2 = 138 days.
‘218Po =Radium A’
‘218At =Radium B’
C
D
E
210Po=Radium ‘F’ Radon
=‘Emanation’
‘Radium’
C’
C’’
The Natural Decay Chain for 238U
…..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, 4th Dec. 2006,By Ben Fenton
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.
FromAlpen p426
From Alpen p427
The total sum of weighting factors = 1.00.....Stomach, colonbadly affected by radiation...uptake in stomach wall leads to blood and then other organs in body.
ICRP Recommended Annual Dose Limits
Body Part Occupational General Public
Whole body(HE)
20mSv 1mSv
Eye lens (HT) 150mSv 15mSv
Skin (HT) 500mSv 50mSv
Hands & Feet(HT)
500mSv ---------
Note these recommended limits EXCLUDE any medical or naturalbackground radiation doses.
Paddy’s ‘back of the envelope’ Calculation....
• Need to calculate the energy emitted per second at 1mCi for 210Po andassume '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 210Po = E_a ~ 7*E-13 J x activity x time exposed
• For a 1mCi 210Po 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 beexcreted 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.
Typical 238U concentrations in crustal rock ~1-3 parts per million (see ‘Radioactivity in the Environment’ R.L. Kathren, Harwood Academic publishers.
Some 210Po Numbers..(taken from ‘Radioactivity in the Environment’ R.L. Kathren, Harwood)
• Estimated annual internal ‘whole body’ dose equivalent from natural 210Po radioactivity in the USA = 30Sv (same as 222Rn). (40K =170Sv for comparison)
• Annual dose equivalent to epithelial tissue lining the lungs from Radon and its daughters (e.g., 210Po) ~20Sv (double this for cigarette smokers).
SRIM output for 5.3 MeV alphas on skin (1000 histories)..typical range ~0.04mm
No problem outside the body...alphas stop indead layers of the skin.
206Pb first excited state at 803keV 1:105 possible way to tell...
1mCi = 3.7 x 107 decays per second ~ 400 gammas per second....
enough for a signal in a whole body counter ?
Biological half-life for 210Po ~50-60 days, only if you are alive to ‘excrete it’ (collects in the Kidneys).....look for activity in the (dried) urine...