Stability of Nucleus

The nucleus is the central part of an atom that contains protons and neutrons. Protons have a positive charge, and neutrons have no charge. The number of protons in the nucleus of an atom can be positive or negative, but every nucleus in each atom has the same number of nucleons. The nucleus is stable, and it’s just about impossible for it to change into another element isotope or change its state. The stability of the nucleus depends on protons and neutrons. Protons in the nucleus of an atom are attracted by the negative charges of electrons surrounding it. 

The Nucleus

In physics, a nucleus is defined as a positively charged part of an atom that contains protons and neutrons. While the electrons orbit around that nucleus, the protons are kept close to the neutrons by the nuclear force.

The stability of the nucleus is tried to attain by fission and fusion.

Isotopes

An isotope atom of the same element with a different number of neutrons in its nucleus. For example, hydrogen has three isotopes: 1H (protium), 2H (deuterium), and 3H (tritium).

Stability of Nucleus

Molecules are unstable. So the stability of the nucleus also differs in every molecule. They can’t exist by themselves. If a molecule has more than one atom, the molecule is stable and will not decompose. The stability of a nucleus is defined by the number of protons it contains. It is structurally stable because the size of its atomic volume stays the same, and when it enters a new state (i.e., fission), it tends to stay at this state:

This fact explains why a single nucleon cannot change its energy level without leaving a trace, thanks to Einstein’s principle of conservation of energy. Also, the mass defect for any nucleus is constant, and values ​​are given by these laws that describe the mass-energy relationship.

Nuclear Fission

A nucleus has relative stability of the nucleus, compared to another nucleus. Some “stable” nuclei are unstable, and some “unstable” ones are relatively stable. The most common isotope of a fissionable element is U-235. The mass number is 235, and its atomic number is 92. It takes one neutron to knock out one proton, so one atom of U-235 will fission into two lighter atoms of uranium-236 or U-236.

It takes one neutron to knock out one proton, so one atom of U-235 will fission into two lighter atoms of uranium-236 or U-236. The mass of the fragments (the two uranium atoms) is less than the mass of the original atom – that means energy is released!

Nuclear Fusion

Unlike nuclear fission, nuclear fusion doesn’t release any energy. It takes a lot of energy to initiate fusion. You need to provide enough energy to overcome the electromagnetic force that holds protons together in a nucleus. This enormous energy can come only from the movement of particles, photons.

When you start a fusion reaction, you need to heat the nuclei fast enough so that they can overcome their electromagnetic forces and become ions. When two nuclei merge into ions and release more energy than was needed to pry them apart, the reaction is “in equilibrium.”

Nuclear fission happens at temperatures above 100 million degrees Celsius. The temperature inside stars is about 15 million degrees Celsius. So stars use nuclear fusion to generate energy.

The Sun is a star, and it uses nuclear fusion to produce heat and light. That produces enough gravity to compress the atoms until they fuse in the Sun’s centre and release enormous energy.

Stability Curve of Nucleus

When a nucleus has too many neutrons, it is unstable. If one extra neutron is added to a nucleus, the nuclear force will not be strong enough to keep it from decaying.

Since every nucleon affects the stability of a nucleus, the curve could be drawn in different ways depending on which type of reaction we are interested in:

If the curve is plotted by comparing nuclei with different numbers of neutrons, they will have the same vertical scale. Still, different horizontal half-lives of nuclei give the normal curve nuclei with different numbers of neutrons.

The “Stability curve” is a plot of the half-lives of several isotopes. A new nucleus is added at each plot point, and its half-life is measured. The curve shows how long these nuclei will last if many are added (squares); it also shows how long they have already lasted (diamonds). The curve is drawn so that diamonds for non-radioactive nuclei extend only as far as the square for the isotope with the longest half-life.

The curve tells us that, before a nucleus has gone through one time period of being changed, it will have undergone at least two changes since there are about two or more possible outcomes for any change.

Conclusion

Proton-proton and neutron-neutron reactions are much more stable than other types of reactions. If a nucleus reacts with another nucleus, the reaction will always be the same. If two nuclei collide and one is knocked out, that proton or neutron will always go back into a nucleus with the same number of protons or neutrons.

In fission and fusion reactions, the nuclear forces are much stronger. These stronger forces require temperatures much higher than those required for the fission and fusion of ordinary matter. The mass of the fragments is less than the mass of the original atom.