By Ojjas Sharma, Sophomore Year, Himachal Pradesh, India
Radioactivity is a very interesting phenomenon, which has transformed the power resources to the highest degree! After reading this blog, your misconceptions about radioactivity will be cleared, and your basics concepts will be polished!
Some History: Radioactivity was discovered in 1896 by A.H. Becquerel
Radioactivity is a process by which an unstable atomic nucleus loses energy by radiation. An unstable atomic nucleus here means atomic nucleus whose internal and external forces are not balanced. This basically happens either due to excess number of protons or neutrons.
Only certain combinations of neutrons and protons are stable in an atomic nucleus. Stability of an atomic nucleus can be defined as a balance between strong nuclear force and electromagnetic force.
Neutrons hold protons together with help of strong nuclear force, whereas to protons repel each other due to electromagnetic force since they possess same charge. Strong nuclear force is able to overcome this electromagnetic force only at very small distance, like that between neutrons and protons. Also, the electromagnetic force and strong nuclear force are balanced out.
Therefore, number of neutrons needs to be increased with an increase in Z.
Let’s suppose that number of protons is increased, whereas the number of neutrons isn’t sufficient against the number of protons. Such an atomic nucleus is called unstable nucleus.
There can be two cases in this nucleus:
- Strong nuclear force is very large as compared to Electromagnetic force, arising due to large number of neutrons, as compared to number of protons.
- Electromagnetic repulsion dominates strong nuclear force, due to a very large number of protons as compared to number of neutrons.
- We know that atoms of elements try to be stable. In case of non radioactive atoms, they lose their valence electrons or gain them in their valence shell to obtain a stable configuration, but in case of unstable nuclei, they release energy in form of radiation and become stable.
Radioactive decay, as the name suggests, is a random process in which the nucleus of an atom decays i.e. disintegrates. This basically includes emission of a particle like alpha, beta particles or photons. Although time of decay of particles cannot be predicted for individual atoms, it
can be predicted for a group of atoms, which is particularly expressed as decay constant, the overall decay rate for the atoms.
The Law of Radioactive Decay suggests that the number of nuclei which will undergo radioactive decay will be directly proportional to the total number of nuclei in that sample.
You might be thinking what actually is this decay? Well decay, often called Exponential Decay, is the process in which an object’s current quantity decreases over a period of time. The decrease rate is proportional to the current value of object and inversely proportional to the time taken.
ΔN÷ΔT = -JN Eq(1)
Here, N is the quantity of object as calculated during beginning of reaction and T is time.
The above equation represents an exponential decay, which undergoes integration to be solved.
N(t) = N(o)e^-JT
Here, N(t) denotes quantity of that object which undergoes decay, N(o) represents quantity of object at the beginning, e is the Euler’s number ( here 2.718 ) and T is the time. J is the decay constant.
By Eq (1), you may deduce that it is roughly the rate at which an object’s quantity decreases per unit time.
Hence forth, larger decay constants eventually mean that the objects will disappear really quickly.
For instance, Higgs Boson, has a really large decay constant, and it lasts only for 1.56 X 10²² seconds approximately!
Poor Higgs Boson, it can’t even celebrate its birthday….. ☺
Coming back to topic, you should must know about the types of radioactive decay, and all types of them release energy in a large quantity.
Types of radioactive decay that have been observed are:
1) Alpha decay: In this type of decay, the unstable nucleus loses 2 neutrons and protons. Hence, Z decreases by 2, leading to formation of a new element! Also, the ratio of protons to neutrons decreases, although by same factor, but allows more stable ratio of protons to neutrons.
2) Beta – decay : In this type of decay, a neutron converts to a proton, leading to release of Electron and an Antineutrino. This reduces number of neutrons and increases number of protons, by a factor of 1 each, providing more stable proton to neutron ratio
3) Beta + decay : In this type of decay, proton converts to neutron, and a positron and neutrino is released. This decreases the number of protons
4) Gamma decay : This takes place after the former decays, or sometimes after latter decays too! Basically, the nucleus is left in a really excited state. Lower state nucleus is achieved by emitting a photon of gamma ray, having energy usually more than 100 keV.
5) Neutron Emission : This primarily occurs with nuclei beyond the nuclear drip line. In this decay, a neutron slowly and slowly decays away, as a part of neutron emission. This decay occurs in nuclei which is rich in neutrons. Neutrons therefore decay in such cases, and it is only possible because neutrons in a nucleus have comparatively more energy as compared to a nucleus and neutron(s)
6) Electron capture : This might not seem the best way of decay, but the mechanism behind this is quite interesting. A free
electron is pulled by the nucleus and causes a proton to convert to proton, simultaneously releasing a neutrino and guess what : gamma ray
7) The Lazy Method : Lazy method, as I’d like to call it, is a decay in which a nucleus heavier than an alpha particle is released….quite nice and quick way to get rid of unstable nuclei!
All elements in the 7th period are radioactive in nature!
Radioactive elements are of an immense importance since they serve as a really important source for energy. They should be judiciously used since they are non-renewable and rare.
hARTS magazine 