February 2007
Number 345
Chemical in the news — Polonium-210
Lew Brubacher
Chemistry Department, University of Waterloo
Waterloo ON N2L 3G1
The poisoning death of Alexander Litvinenko in
November has put polonium-210 in the news. A
recent article1 in the Los Angeles Times contains
much interesting background. A few facts,
gleaned from that article and other sources,
follow. You can find a lot more by googling on the
internet; but what you see must be assessed
carefully — see activity #3 below.
∙
In 1898 Marie Curie extracted polonium from
pitchblende, a uranium ore. For isolating
polonium and radium, she won the 1911
Nobel Prize in Chemistry.2
∙
The half-life of 210Po is 138.39 days.3
∙
A tonne of uranium ore contains about 0.1 mg
of polonium and about 50 mg of radium.3
∙
Today polonium is prepared in nuclear
reactors by bombarding 209
83 Bi with neutrons
according to
209
83 Bi
+
1
0n
→
210
83 Bi
→
210
84 Po
+
0 3
-1e .
∙
About 100 g of 210Po is produced annually,
mostly in Russia.1
∙
210Po
decays to lead by releasing an alpha
particle of such high energy (5.3 MeV per
disintegration or about 140 W/g) that a
capsule containing 0.5 g of the metal will
reach a temperature of 500oC.3
INSIDE:
•
•
•
•
•
•
∙
Metallic 210Po is difficult to control. When a
nucleus disintegrates, the energy released
tends to blast out small chunks of the metal,
perhaps a few hundred atoms in size, into the
air, where it can be breathed if it’s not
contained.1
∙
The first death from polonium poisoning was
in 1927. The victim was exposed while
preparing polonium sources in the lab of Marie
Curie’s daughter, Irène Joliot-Curie.1
∙
During the Manhattan Project, out of concern
for the safety of persons working with polonium,
some ethically dubious experiments on terminal cancer patients produced the first solid
information about the health effects of 210Po.1
∙
In Litvinenko’s case, John Emsley, Cambridge
University, says a dose of white powder smaller
than a grain of salt could have been dropped
into his drink without affecting the taste.1
∙
As that dose travelled through Litvinenko’s
gastrointestinal tract, the highly energetic
alpha particles released would have destroyed
cells lining the tract. As they sloughed off
there would have been nausea, pain and
internal bleeding.1 Absorption of some of the
polonium into the blood stream would have
dispersed the poison throughout the body.
continued on page 6
Why camels can go weeks without water, page 4
Blueprint making with UV (ultraviolet) changing dye, pages 5-6
Applications Matter. Part 6 – Teaching and support strategies, pages 8-10
Methanol poisoning, pages 11-12
An odoriferous crostic, pages 14-15
Chemical explorations: Super slurp, page 16
•
Once the design template is removed from the paper/tshirt yellow solution that has gotten behind the
template will gradually turn blue as it is exposed to
small doses of UV light coming through the windows.
Rinsing the paper/t-shirt as described in the references
will remove as much unexposed dye as possible so
that the entire surface does not end up blue.
I made 100 mL of the “developing solution” according to the
directions below. I had twenty-five students create a design on
a piece of 8x10 poster board and this was not quite enough. I
had to make an extra 100 mL. Other references used slightly
different amounts of each chemical but I found this recipe to
work well.
I found this in a few locations on the internet and have to give
big credit to Paul Groves at www.chemmybear.com and Kathy
Kitzman at Mercy High School Farmington Hills, MI (who is also
referenced at this website). I first found it at chemmybear.com
with pictures of the students doing the activity along with recipes
for the solutions. Kathy Kitzman was very helpful with
alternative recipes for the developing solution that I have used in
my classroom. I also received much needed advice from other
teachers who are a part of SEMTCO (South Eastern Michigan
Chemistry Teachers’ Organization). A version of this activity
can also be found in the Journal of Chemical Education,
September 1999 as a JCE Classroom insert. More clarification
of the chemical reactions can also be found in the same issue.1
Recipe page
I made solution A and solution B separately and did not combine
them until one hour prior to the activity. (The UV light source is
needed to catalyze the reaction but I did not want the reaction to
happen any earlier than necessary.)
To make 2 L of developing solution:
Solution A: 240 g of ferric ammonium citrate in 1.0 L of solution
Solution B: 120 g of potassium ferricyanide in 1.0 L of solution
To make 100 mL of developing solution:
Solution A: 12 g of ferric ammonium citrate in 50 mL of solution
Solution B: 6 g of potassium ferricyanide in 50 mL of solution
References
1. G. Lawrence and S. Fishelson, Journal of Chemical
Education, September 1999, Volume 76, page 1199-1200,
1216A-1216B
2. www.chemmybear.com
∎
Chemical in the news (continued from page 1)
∙
210Po
∙
On a mass basis, 210Po is about a million times as toxic as
HCN. See student activity #3 below.
∙
210Po
must be ingested in order to kill. It can be handled
safely if it is in a container since a barrier as thin as a sheet
of paper or plastic will not allow the alpha particles to pass.1
has been used as a heat source to power thermoelectric generators; as a neutron source by alloying it with
bismuth, which absorbs the alpha particle and emits a
neutron; and as a static eliminator (alloyed with gold, for
example, for safety) in textile mills.4
Possible student activities
1. Write the nuclear equation for the decay of
with the emission of an alpha particle.
210
84 Po
to lead,
2. Consult the Chemical Rubber Company Handbook of
Chemistry and Physics to find out whether this isotope of
lead is stable, and if so, what percent it represents of pure
lead.
3. The 1982-83 edition of the CRC Handbook (reference 3
below) says that 210Po is 2.5 x 1011 more poisonous than
HCN on a mass basis — nearly a trillion-fold (1012). This
seems to be wrong. Other sources state that the factor is
only one million (106). What does your edition of the CRC
Handbook say? By googling the internet, can you find other
sources that compare the lethal doses of 210Po and HCN?
What do they say? Which value should you trust, and why?
4. What is the rate constant for the decay of 210Po, given a
half-life of 138.39 days?
5. The integrated rate law for nuclear decay is N = N e-kt,
0
where N is the number of atoms remaining at time t, and N0
is the number to start with. In one gram of polonium atoms,
how many atoms decay in the first second?
6. 1 MeV (million electron volts) is equivalent to 1.6 x 10-13 J.
How much energy is released in one second from one gram
of pure 210Po (see question 5), given that each decay releases 5.3 MeV? Does this agree with the statement above
that 210Po releases energy at the rate of about 140 W/g?
(Remember that 1 watt (W) equals 1 joule per second.)
Questions 3, 5 and 6 are fairly challenging. Answers will be
provided next month.
References
1. Los Angeles Times, “Polonium-210’s quiet trail of death”,
January 1, 2007. (Find it by googling on ‘latimes polonium’)
2. nobelprize.org/nobel_prizes/chemistry/laureates/1911/index.html
3. CRC Handbook, 63rd edition, 1982-83, Chemical Rubber
Company, pages B31-32.
4. Wikipedia Encyclopedia,
http://en.wikipedia.org/wiki/Polonium. ∎
6 Chem 13 News/February 2007