Saturday, November 25, 2017

Ruthenium-106 Cloud

In October 2017 the German Federal Office for Radiation Protection detected a radioactive cloud containing ruthenium-106 wafting over Europe. They identified the Southern Ural Mountains in Russia or Kazakhstan as the most likely source of the cloud. In November 2017 Roshydromet, the authority responsible for monitoring radiation in Russia, finally admitted that it had found extremely high levels of ruthenium-106 at two monitoring stations in this region in late September and early October.

Ruthenium is a transition metal element with the chemical symbol Ru and an atomic number of 44.
 Naturally occurring ruthenium has 7 stable isotopes: 96Ru, 98Ru, 99Ru, 100Ru, 101Ru, 102Ru, and, 104Ru. The abundance of each isotope in naturally occurring ruthenium is given in the table below:

isotopeabundance %
ruthenium-965.54
ruthenium-981.87
ruthenium-9912.76
ruthenium-10012.60
ruthenium-10117.06
ruthenium-10231.55
ruthenium-10418.62

In addition to these naturally occurring stable isotopes, about 30 unstable, or radioactive, isotopes have also been identified. The most stable of these radioisotopes is ruthenium-106 which has a half-life of  359 73.days. It decays by emitting a beta particle to produce rhodium-106:
106Ru0e+ 106Rh
44-145

Ruthenium-106 is produced in a nuclear reactor as a product of the nuclear fission of uranium-235. Ruthenium-106 can be extracted from spent nuclear fuel and then it can be used in medicine to treat eye tumors.

The radioactive cloud wafting across Europe is most likely to be due to a spill of ruthenium-106 rather than a nuclear reactor accident since this would have released other radioisotopes which would have been detected in the cloud. France's nuclear safety agency has estimated the amount of radiation released at the source as between 100 and 300 billion becquerels.
A becquerel (Bq) is the SI unit for measuring radioactivity. It is equivalent to the radioactive decay of 1 nucleus in 1 second.
We can use this to estimate the mass of ruthenium-106 spilled:
ABq =       mass      
atomic weight
x NA x ln(2)
t½

ABq = activity in becquerels = 200 x 109 Bq (averaged)
mass = ? grams
atomic weight = 106 g/mol (from the Periodic Table)
NA = 6 x 1023 mol-1 (Avogadro's number)
t½ =  373.59 days = 373.59 days x 24 hours/day x 60 minutes/hour x 60 seconds/minute = 3.22 x 107 seconds
200 x 109 =       mass      
106
x 6 x 1023 x 0.6931
3.22 x 107
200 x 109 =       mass      
106
x 6 x 1023 x 2.15 x 10-8
200 x 109 =       mass      
106
x 1.29 x 1016
mass = 200 x 109 x 106
1.29 x 1016
mass = 1.64 x 10-3 g

If the source of this ruthenium-106 was an accident involving spent fuel rods, then we can calculate the mass of spent fuel involved since 1.9 kg of ruthenium-106 can be extracted from 1 ton (or 1000 kg) of used fuel.
1.9 kg = 1.9 kg x 1000 g/kg  =  1900 g
1900 g of ruthenium-106 can be extracted from 1000 kg (1 000 000 g) of spent nuclear fuel.
1 g of ruthenium-106 can be extracted from 1 000 000 g/1900 g =  526 g of spent fuel
1.64 x 10-3 g ruthenium-106 would be produced from 1.64 x 10-3 x 526  = 0.86 g of spent fuel

A typical nuclear power plant produces 20 tons (2 x 107 g) of  used nuclear fuel per year, about 0.6 grams per second!

Reference:
http://www.smh.com.au/world/with-a-radiation-cloud-comes-a-mystery-from-russia-20171123-gzrvtf.html 

Further Reading:
Isotopes 
Atomic Number (number of protons) 
Mass Number (number of nucleons) 
Calculating Relative Atomic Mass (atomic weight)
Nuclear Half-life 


Suggested Study Questions
  1.  What does the term "isotope" mean?
  2.  Give the atomic number of each of the following species:
    • ruthenium-96
    • ruthenium-98
    • ruthenium-100
    • ruthenium-102
    • ruthenium-104
    • ruthenium-106
  3. Give the mass number (or nuclear number) of each of the following species:
    • ruthenium-96
    • ruthenium-98
    • ruthenium-100
    • ruthenium-102
    • ruthenium-104
    • ruthenium-106
  4. Determine the number of protons in the nucleus of an atom of each of the following:
    • ruthenium-96
    • ruthenium-98
    • ruthenium-100
    • ruthenium-102
    • ruthenium-104
    • ruthenium-106
  5. Determine the number of neutrons in the nucleus of an atom of each of the following:
    • ruthenium-96
    • ruthenium-98
    • ruthenium-100
    • ruthenium-102
    • ruthenium-104
    • ruthenium-106
  6. Use the information in the article to calculate the relative atomic mass (atomic weight) of ruthenium.
  7. Explain what is meant by the term "unstable isotope".
  8. Explain what is meant by the term "beta decay".
  9. A number of unstable isotopes of ruthenium undergo beta decay. Write balanced nuclear decay equations for the beta decay of the following ruthenium isotopes:
    • ruthenium-103
    • ruthenium-105
    • ruthenium-106
    • ruthenium-107
    • ruthenium-108
    • ruthenium-109
  10. Explain what is meant by nuclear "half-life"?
  11. Ruthenium-106 has a half-life of of  359 73.days. Calculate the percentage of ruthenium-106 remaining after:
    • 359.73 days
    • 719.46 days
    • 1079.19 days
    • 3597.3 days
  12. If the mass of ruthenium-106 in the cloud over Europe is currently 1.64 x 10-3 g, calculate the mass of ruthenium-106 remaining in the cloud after:
    • 1 year
    • 2 years
    • 10 years

No comments:

Post a Comment