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Unstable Isotopes

An unstable nucleus leads to unstable isotopes and make them radioactive. There are other more stable nuclei and has less or no radioactivity. There is definitely very strong repulsive force acting among the packed protons inside the atom’s nucleus and has an effect on the nuclear stability. 

Apart from this the uncharged relative neutron numbers present inside the nucleus also plays a big role. In comparison to stable and non-radioactive isotopes the unstable isotopes are large in numbers as there is always a chance of instability getting formed inside a nucleus of an atom. In this article we will discuss about stability of nucleus and all the salient features of unstable isotopes.


What are Unstable Isotopes?

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The stability of any nucleus is basically a characteristic of the number of protons and neutrons. Apparently the mass numbers of any stable isotope are always found to be twice as large as atomic number or may be even higher. It also appears that greater number of protons in the nuclei requires greater number of neutrons to make it stable.

In chemistry an isotope is a different form of an element which will have different neutron number and thus has a different mass number as well. But the chemical properties and other related characteristics remain same as that of the element. As far types of isotopes are concerned, there are three types in all. One which is found in nature, stable and not radioactive, the second type is the one which is naturally radioactive and not stable, while the third type is produced artificially by bombarding atoms with neutrons which are again unstable and radioactive.

The atomic weight given for any element is the average of all the atomic weights for each of the available isotopes in exact proportion to their abundance or prevalence within the element. If any of these average values result in fraction then the value is rounded off and marked to closest whole number.

Unstable Isotopes Definition

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Any element having excess of neutrons in the nucleus as compared to the stable form of atom tends to be unstable in nature. These elements tend to be radioactive and undergo radioactive decay by emitting energy which could be measured by a detector. The rate of decay of any such radioactive unstable isotope could be represented by its half-life characteristics which are nothing but the period required for half of the radioactive material present in original form to undergo decay radioactively.

Whenever we observe an element showing short half-lives we need to understand that these are due to high rates of decay while any element showing long half-lives could be the result of low or very low rates of decay. The nuclei of radioisotopes do not undergo decay all at once. The decay rather goes slowly and radiate off energy in each of the sequence of such decay until the stable form of atom is formed.

Why are Radioactive Isotopes Unstable?

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In general, in stable atomic forms the protons having same charge repel each other but the greater binding energy of atom stabilizes the repulsion force and help it remain stable. The instability of radioactive isotopes is mainly due to excess of neutrons present in nucleus which helps in overcoming the atoms binding energy making it unstable. 

For any stable atoms with same number of protons and neutrons the atomic stability is maintained properly and in some cases one or two extra neutrons are accommodated as well but when the number of neutrons in an atom is in excess, the forces of repulsion by protons breach the critical point and the atom becomes unstable. In order to maintain and restore the stability of the nucleus, the atom tends to release neutron during decay process.

Examples of Unstable Isotopes

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The examples of naturally occurring stable and radioactive or unstable isotopes are mentioned below:

Naturally occurring stable isotopes  Radioactive unstable isotopes  
Carbon 12  Carbon 14 
Calcium 40
Calcium 43
Calcium 46
Calcium 48
Vanadium 51 Vanadium 50 
Germanium 70
Germanium 72
Germanium 74
Germanium 76 
Selenium 74
Selenium 76
Selenium 78
Selenium 80
Selenium 82 
Krypton 80
Krypton 82
Krypton 84
Krypton 86
Krypton 78
Rubidium 85
Rubidium 87 
Platinum 192
Platinum 194
Platinum 196
Platinum 198
Platinum 190
  Uranium 234

Most of the radioisotopes are used in the field of medicine, aptly put under nuclear medicine which basically provides the specific organ based information and it’s functioning. Apart from nuclear medicine the radioisotopes or unstable forms of isotopes are used in diagnostic fields where these are used as tracers in medicinal fields to understand the physiological processes. 

Other uses are in the field of radiotherapy, biochemical process and radio pharma where these unstable forms of isotopes are used for killing or destruction of damaged or malignant cells.
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