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Alpha decay is a type of radioactive decay where an unstable nucleus ejects an alpha particle. An alpha particle is essentially a helium nucleus, composed of 2 protons and 2 neutrons. This process decreases the atomic number by 2 and the mass number by 4, effectively transforming the original element into a different one.

For instance, when uranium-235 undergoes alpha decay, it transforms into thorium-231.

• The atomic number of uranium is 92, but after losing 2 protons, it becomes 90, which is the atomic number of thorium.
• The mass number reduces from 235 to 231, as the 4 nucleons making up the alpha particle are no longer part of the nucleus.

Alpha decay is common in heavy elements like uranium and plutonium. It is a crucial process since it contributes to the balance of forces within a nucleus by getting rid of some of its excess mass.
In general, not all nuclei can undergo alpha decay. Deuterium, for example, only has 2 nucleons in total, making it impossible to emit an alpha particle.

Positron emission, also known as beta-plus decay, is a unique type of radioactive decay. It involves the conversion of a proton within the nucleus into a neutron. During this transformation, a positron and a neutrino are emitted from the nucleus.

This leads to a decrease in the atomic number by 1, but the mass number remains unchanged.
When aluminium-26 undergoes positron emission, it forms magnesium-26.

• This is because the atomic number drops from 13 (aluminium) to 12 (magnesium).
• The mass number stays at 26, as the overall number of nucleons remains constant.

Positron emission is often seen in isotopes where there is an imbalance of protons to neutrons, typically when there are too many protons.
This decay process helps the atom reach a more stable state by altering its internal composition.

Beta decay is a process that enables unstable nuclei to achieve greater stability. It involves two primary types: beta-minus decay and beta-plus decay. We have already discussed positron emission as beta-plus decay.

In beta-minus decay, a neutron is converted into a proton within the nucleus. During this conversion, an electron (known as a beta particle) and an antineutrino are emitted. Consequently, the atomic number increases by 1, while the mass number remains constant.

• An example of this process is the decay of yttrium-90 to zirconium-90.
• The atomic number of yttrium increases from 39 to 40, transforming it into zirconium.
• The mass number stays at 90 because the total number of nucleons remains the same.

Beta decay is crucial in adjusting the neutron-to-proton ratio in a nucleus, helping it move towards a more stable configuration. This process essentially allows elements to "shift" their identity while retaining their nucleon count, ensuring a balanced and stable nucleus.