Radioactivity of Lanthanides and Actinides

 

Radioactivity of Lanthanides and Actinides

Radioactivity

Radioactivity is the extra energy, or radiation, emitted by radioactive elements that comes in three different types: alpha, beta, and gamma. Alpha radiation is a stream of alpha particles, which are positively charged. They're fairly large, which means they have a difficult time getting through materials like clothes and paper. Lanthanide and Actinide Series are both referred to as Rare Earth Metals. Both actinides and lanthanides are highly reactive with elements from the halogen group.

Radioactivity of lanthanides

The lanthanide series includes elements 58 to 71, which fill their 4f sublevel progressively. The lanthanide series can be found naturally on Earth. In the lanthanide series only radioactive elements are promethium and samarium. All of the lanthanides have at least one stable isotope except for promethium.

Promethium being radioactive has nothing to do with its chemistry, It may be depend on nuclear structure. The samarium nucleus is more tightly bound so flipping of one Pm’s neutrons to proton results in a lower energy nucleus.

Promethium is not only the radioactive lanthanide it also the only one with no stable isotope. Other lanthanides also have naturally occurring radioactive isotopes. eg: samarium(Sm).

Radioactivity of Actinides

The actinides are elements 89 to 103 and fill their 5f sublevel progressively. Actinides are typical metals and have properties of both the d-block and the f-block elements. None of the actinides have a stable isotope. All actinides are radioactive and some are not found in nature. These elements all have a high diversity in oxidation numbers .The most common and known element is Uranium, which is used as nuclear fuel when its converted into plutonium, through a nuclear reaction. The actinide series is much different. They are all Since actinides are radioactive it releases energy upon radioactive decay; naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth. These are used in nuclear reactors and nuclear weapons. The other actinides are purely synthetic elements.

Plutonium is the most commonly produced actinide, with plutonium 239 being its most abundant isotope. Nuclear reactors also generate other, 'minor' actinides in smaller quantities: such as neptunium 238, americium 241 and 243 as well as curium 244 and 245.

Actinides have much longer half lines than most of the fission products which possess a problem for  long term storage of radioactive waste .As well as the heavy nuclei can emit a- particle, which is absorbed into the body is more dangerous than the b-particle emitted by fission products. Nevertheless, this potential radiotoxicity is not a direct danger. Like arsenic, plutonium and minor actinides must enter our stomachs or our lungs in order to become damaging. Fortunately for us, these elements are both too heavy to remains in the air and are often found in the form of insoluble oxides which are not mobile.

It is possible to go one step further, and either to make actinides disappear by transmuting them into other elements. Another approach is to avoid to let them form in reactors. Thorium-based nuclear reactors have the advantage of no actinide nor plutonium production, a property which makes them appealing.

Radioactive Series

Fig: radioactive series, From Uranium 238 to Lead 206, This diagram maps the journey on a nucleus map of the uranium 238 decay chain. 

The alpha decays cause the number of protons and neutrons to diminish by 2, whereas beta-negative decay diminishes the number of neutrons by 1 and increases the number of protons by 1. The instability caused by the alpha decay is corrected by the eventual beta decay, leading to the stable nucleus of lead 206, with its 82 protons and 124 neutrons.

A certain number of natural radioactive nuclei are still present on Earth, even though their half-lives are particularly short when compared to our planet’s age. These radioisotopes are the descendants of three heavy nuclei with very long half-lives: uranium 235 (with a half-life of 0.7 billion years), uranium 238 (which lives for 4.47 billion years) and thorium 232 (with a half-life of 14.0 billion years).

A nucleus of uranium 238 decays by alpha emission to form a daughter nucleus, thorium 234. This thorium in turn transforms into protactinium 234, and then undergoes beta-negative decay to produce uranium 234. This last isotope changes slowly (with a half-life of 245,000 years) into thorium 230, yet another unstable nucleus.

Applications

1.      Promethium are used in luminous paint, thickness devices.

2.      Thorium is used as nuclear fuel in nuclear reactors alternative to uranium

3.      Uranium is the principal fuel of nuclear reactor.

4.      Plutonium is used in vehicles

5.      Neptunium and its isotopes are used for research studies.