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:

isotope	abundance %
ruthenium-96	5.54
ruthenium-98	1.87
ruthenium-99	12.76
ruthenium-100	12.60
ruthenium-101	17.06
ruthenium-102	31.55
ruthenium-104	18.62

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:

106	Ru	→	0	e	+	106	Rh
44			-1			45

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

A_Bq = activity in becquerels = 200 x 10⁹ Bq (averaged)
mass = ? grams
atomic weight = 106 g/mol (from the Periodic Table)
N_A = 6 x 10²³ mol^-1 (Avogadro's number)
t_½ =  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

Titanium Gold Alloy

Titanium is the metal used to replace hip and knee joints because it is strong, resistant to wear, and, is nontoxic.

Before titanium was used to replace hips and knees, stainless steel was used.
The density of stainless steel used to make replacement hips and knees is about 7.8 g cm³. The density of titanium metal is 4.506 g cm³, about half the density of stainless steel. This means that a replacement joint made out of titanium will weigh less than the same replacement joint made out of stainless steel.
Titanium is also strong. The strength of the material used to replace hip and knee joints is important because you do not want your new joint to bend or break or under strain.

Titanium has a melting point of 1670°C and a boiling point of 3287°C, which means it remains solid over the range of temperatures humans are exposed to. This is important because you want your new hip or knee replacement to remain a solid!
Naturally occurring titanium is made up of a number of isotopes, all of which are stable so they do not undergo nuclear decay. This is important because it means that there is no loss of titanium mass due to radioactive decay, and there is no fear of damage to cells from the emission of radiation.

isotope	atomic mass	abundance
46Ti	45.953	8.25
47Ti	46.952	7.44
48Ti	47.948	73.72
49Ti	48.948	5.41
50Ti	49.945	5.18

Titanium metal will react with water, halogens and dilute hydrochloric acid, but only if the temperature is elevated well above body temperature. Similarly, titanium metal will react with oxygen in a combustion reaction at elevated temperatures. Titanium metal does not appear to react with bases at all. Therefore, titanium is unlikely to react with substances found in the human body.

Researchers at Rice University have found that alloying titanium with gold can produce an even better material to use for replacement hips and knees. Mixing titanium and gold in the ratio of 3:1 at high temperature produces an alloy that is 3 times harder than steel and 4 times harder than the pure titanium commonly in use for hip and knee replacements. The atoms of titanium and gold in this alloy are packed in a cubic arrangement, an arrangement that is usually associated hardness. The structure of this alloy is shown below:

This titanium gold alloy has been found to be even more biocompatible that pure titanium.
The researchers intend to undertake further studies to investigate whether using chemical dopants might improve the alloy's hardness even further.

Reference:
Rice University. "Titanium and gold equals new gold standard for artificial joints: Titanium-gold alloy that is 4 times harder than most steels." ScienceDaily. ScienceDaily, 20 July 2016. 

Further Reading
Metals and Non-metals 
Density
Isotopes
Relative Atomic Mass
Alloys

Suggested Study Questions

1. Titanium and gold are both metallic metallic elements.
   • What are the physical properties common to most metallic elements?
   • What are the chemical properties common to most metallic elements?
2. Draw up a table of the physical properties of titanium.
3. A typical knee replacement made out of titanium has a mass of 560 g.
   • Calculate the volume of the titanium knee replacement.
   • Calculate the mass of the same knee replacement if it were made out of stainless steel
4. Define the term isotope.
5. Determine the number of protons in the nucleus of an atom of each of the isotopes of titanium listed in the article above.
6. Determine the number of neutrons in the nucleus of an atom of each of the isotopes of titanium lists in the article above.
7. Which is the most abundant isotope of titanium? Explain your answer.
8. Use the data in the article above to calculate the relative atomic mass of naturally occurring titanium.
9. Given the atomic radius of titanium is  176 pm (1.76 x 10^-10 m) and the atomic radius of gold is 174 pm (1.74 x 10^-10 m), do you think the alloy of titanium and gold discussed in the article above is an interstitial alloy or a substitutional alloy? Explain your answer.
10. Consider the structure of the titanium gold alloy shown in the diagram in the article above.
    • The blue balls represent which atoms of which element?
    • The red balls represent which atoms of which element?

Atomic Weights to Change

The atomic weights of 10 elements are to be changed in order to more accurately reflect how these elements are found in nature. These 10 elements are:

• hydrogen
• lithium
• boron
• carbon
• nitrogen
• oxygen
• silicon
• sulfur
• chlorine
• thallium

The atomic weights of these 10 elements will now be expressed as intervals, having upper and lower bounds.
For example, sulfur is commonly known to have a standard atomic weight of 32.065. However, its actual atomic weight can be anywhere between 32.059 and 32.076, depending on where the element is found. In sports doping investigations, performance-enhancing testosterone can be identified in the human body because the atomic weight of carbon in natural human testosterone is higher than that in pharmaceutical testosterone.

Elements with only one stable isotope do not exhibit variations in their atomic weights. For example, the standard atomic weights for fluorine, aluminum, sodium and gold are constant, and their values are known to better than six decimal places.

IUPAC will feature the change in the standard atomic weights table as part of associated International Year of Chemistry activities in 2011.

Reference
Michael E. Wieser, Tyler B. Coplen. Atomic weights of the elements 2009 (IUPAC Technical Report). Pure and Applied Chemistry, 2010; 1 DOI: 10.1351/PAC-REP-10-09-14

Further Reading
http://www.ausetute.com.au/isotopes.html
http://www.ausetute.com.au/atomicmass.html

Study Questions

1. What is meant by the term isotope?
2. How is atomic weight calculated?
3. If naturally occurring hydrogen contains 99.99% hydrogen-1 and 0.01% deuterium, what is the atomic weight of naturally occurring hydrogen?
4. If you took an air sample from a planet on which there was 100 times more deuterium than on earth, what would you expect the atomic weight of hydrogen to be then?
5. Why is tritium not included in the calculation of the atomic weight of hydrogen?
   
6. Why would the atomic weight of an element with only one stable isotope be more consistent than the atomic weight of an element with two or more stable isotopes?
7. Why are unstable isotope abundances not used when calculating the atomic mass of a naturally occurring element?
8. Why would the atomic weight of carbon in natural human testosterone be higher than that in pharmaceutical testosterone?