210Po: An Interesting Nucleus

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210Po An Interesting Nucleus

• The s-process terminator...end point of element
  production the stars...
• Mme. Curie (and some of her mates...) in 1898
• Theres a lot of it about...
• Properties (alpha, energies, gammas?)
• How can/does it harm you?

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Alexander Litvinenko, aged 43 Before and after
effects of radiation poisoning with polonoium
210 . Reported feeling ill on 1 Nov. 2006, died
23 Nov. 2006.
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Alpha-decay of 210Po
Q energy release M(210Po) M(206Pb)
M(4He) c2 5.5 MeV 1 pJ. i.e., around
0.003 of total 210Po mass released kinetic
energy in decay. (rare occasion, 206Pb can be
left in an excited state.803 keV above the
ground state.)
Total energy released shared as KINETIC energy
between 206Pb and 4He. Cons. of linear momentum
means most of the energy (5.3 MeV) goes to 4He.
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lethal dose 50 Mbq actual dose 5 GBq (30 µg)
Production by n-capture on 209Bi
Po-210 Z 84 138 day
ß (100)
5.3 MeV a (100) 2?0 803 keV ?
(0.01)
Bi-209 Z 83 stable
Bi-210 Z 83 5 day
n
Pb-206 Z 82 stable
a (0.0001)
ß
Tl-206 Z 81 4 min
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Not a bad authors list....one for the RAE of
circa 1930 no doubt!
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Map of Europe in 1914 (pre-First World Warnote,
no Poland.
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T1/2140 days
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The Natural Decay Chain for 238U
Qa(210Pb) 5.41 MeV Ea 5.30 MeV E(206Pb)
0.11 MeV T1/2 138 days.
Radium
218At Radium B
210Po Radium F
Radon Emanation
C
218Po Radium A
E
C
D
C
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Figure Wiescher, Regan Aprahamian, Physics
World Feb. 2002, page 33-38
Slow-neutron capture process allows formation of
elements from A56 to A209 (Bi)... terminates
at 209Bi...why?
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S-process makes 209Bi from 208Pbn ? 209Pb
(T1/23.2hr) ? 209Bi Neutron capture on stable
209Bi ? 210Bi (T1/2 5 days) ? 210Po. 210Po ? a
206Pb (stable nucleus, as is 207Pb and 208Pb).
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How much is bad for you ?
From the Daily Telegraph, 4th Dec. 2006, By Ben
Fenton
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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.
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How you estimate the damage?

• Radiation damage measured in Grays
• 1 Gy 1 Joule imparted per kilogram
• Estimates are assessed depending on
• type of radiation (i.e., gammas, betas, alphas)
  
• body tissues/organs affecteddifferent cells
• have different tolerances to radiation damage.

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FromAlpen p426
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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.
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From Alpen p427
The total sum of weighting factors
1.00.....Stomach, colon badly affected by
radiation...uptake in stomach wall leads to
blood and then other organs in body.
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Paddys 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
  7x10-13 J x activity x time exposed

For a 1mCi 210Po source, Power (7x10-13) x
(0.001 x 3.7x 1010) 3x10-5 J / secondEnergy
deposited in 1 hour from 1mCi source (3.6x103
s) x (3x10-5 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?Whole
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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Typical 238U concentrations in crustal rock 1-3
parts per million (see Radioactivity in the
Environment R.L. Kathren, Harwood Academic
publishers.
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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 30mSv (same as 222Rn). (40K 170mSv
  for comparison)
• Annual dose equivalent to epithelial tissue
  lining the lungs from Radon and its daughters
  (e.g., 210Po) 20mSv (double this for cigarette
  smokers).

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How can we tell if someone has 210Po in the
future ?
206Pb first excited state at 803keV 1105
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...
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Summary

• 210Po has an interesting historynamed after
  Poland (which didnt exist at the time).
• It occurs naturally (from the decay of 238U).
• It is responsible for terminating the s-process
  (limiting number of chemical elements).
• You can make it in neutron-capture reactions on
  209Bi.
• Can be detected by alpha- or gamma-ra
  spectroscopy.
• Dont eat or drink it (few mgm are deadly) No
  problem really outside the body.
• Physicist are useful to the public. Numbers
  matter in calming peoples fears.