Radioactive decay | Definition, Stability belt, Types, Facts | aurayne

RADIOACTIVE DECAY 

In 1896, Prof. Henry Becquerel accidentally discovered radioactivity. He was studying the fluorescence and phosphorescence of compounds irradiated with visible light.  This is when he noticed something interesting.

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He illuminated some pieces of uranium-potassium-sulfate with visible light. Next, he wrapped these pieces in black paper and separated them from a photographic plate with a piece of silver. Left him for several hours. When he developed the photographic plate, he found that there was blackness on the plate.

This meant that something was emitted by the compound that penetrated the silver and black paper and hit the plate.  Subsequent experiments suggest that radioactivity is a nuclear phenomenon that occurs when an unstable nucleus undergoes decay.  This is called Radioactive decay.

Of the 1500 nuclides, less than 260 are stable and others are unstable.

The unstable nuclides achieve stability by emitting alpha particles or beta particles and gamma waves.

The spontaneous emission of alpha particles or beta particles and gamma waves from an unstable nucleus is called radioactive decay.

Radioactivity is a nuclear phenomenon.  The rate of emission of α, β, Y depends only on the concentrations of nuclei.  These reactions remain unaffected by temperature pressures and other physical conditions.

There are three types of radioactive decay in nature:

α-decay – a helium nucleus (42He) is emitted 

β-decay – where electrons or positrons (particles with the same mass as an electron, but with exactly the opposite charge of an electron) are emitted; 

γ-decay – high energy (hundreds  KV or more) photons are emitted.

Which nuclei are unstable — Stability belt 

The nuclei located on the stability belt are stable for Z ≤ 20 stable nuclei that have n / p≈1. Carbon(C), Magnesium(Mg), Phosphorus(P), Calcium(Ca)......

For nuclei Z≥20, the stationary nucleus contains 1 ≤ n / p ≤ 1.6.  (P—P electrostatic repulsion is high, so more neutrons are required). Iron (Fe), Silver (Ag) 

The nucleus above and below the stability belt emits alpha particles, beta minus particles (electrons), beta plus particles (positrons) to react to the stationary belt.  After Z = 83 bismuth no nucleus is stable.  After z = 83, all nuclei are radioactive.

Atoms are radioactive, their nuclei are not on the stability belt. They emit various particles α, β minus, β plus to balance the n / p ratio, so that the stability curve is reached.

A radioactive material is either an α-particle emitter or a β-particle emitter. The Y-ray is emitted with both.

Types of radioactive decay

The three types of radioactive decay, namely alpha, beta, and gamma decay.  We will try to understand how these particles are emitted and what effect it has on the emitting nucleus.

Alpha radioactive decay 

An alpha particle has a helium nucleus 42He. Whenever a nucleus undergoes alpha decay, it turns into a separate nucleus by emitting an alpha particle. For example, when 23892U passes through alpha-decay, it changes to 23490Th.

   23892U —> 23490Th +42He......(1)

Now, 42He has two protons and two neutrons. Therefore, after emission, the mass number of the emitting nucleus decreases by four and the atomic number decreases by two. Therefore, the transformation of AZX nuclei into. A-4Z-2X  nuclei is expressed as,

  AZX→ A-4Z-2X + 42He......(2)

Where AZX is the basic nucleus and.A-4Z-2X  is the daughter nucleus.  It is important to note that the alpha decay of 23892U can occur without an external source of energy.  This is due to the total mass (23490Th and 42He) of the decay products <mass of the original 23892U

Or, the total mass-energy of the decay products is lower than that of the original nuclide. This brings us to the concept of the 'Q value of the process' or 'dissolution energy' which is the difference between the initial and final mass-energy of the decay products. For alpha decay, Q value is expressed as,

   Q = (mX – mY – mHe)c2 ......(3)   

This energy is shared as kinetic energy between the daughter nucleus, A-4Z-2X and the alpha particle, 42He. In addition, alpha decay obeys radioactive laws.

Structure of atomic mass and nucleus-energy and nuclear binding energies.

Beta radioactive decay

Beta decay occurs when a nucleus decays spontaneously by emitting an electron or positron. It is also a spontaneous process, such as alpha decay, with a certain dissolution energy and half-life.  And, it follows radioactive laws. Beta caries can be beta minus or beta plus caries.

In beta minus (β-) decay, an electron is emitted by the nucleus. for example,

           

           3215P → 3216S + e– + v–  ......(4)

Where v-is an antinutrino, a neutral particle with little or no mass. Also, T1/2  = 14.3 days.

In beta plus decay, a positron is emitted by the nucleus.  for example,

   2211Na → 2210Ne + e+ + v ......(5)

Where v is a neutrino, a neutral particle with little or no mass. Also, T1/2 = 2.6 years.  Neutrino and antinutrino are excreted from the nucleus with a positron or electron during the beta decay process. Neutrinos interact very weakly with matter.  Therefore, they were not known for a very long time.

Also, in the beta minus decay, a neutron is converted into a proton within the nucleus:

   n → p + e- + ν-  ......(6)

Also, in beta plus decay, a proton turns into a neutron (inside the nucleus):

   p → n + e+ + ν ......(7)

Therefore, we can see that the mass number (A) of the emitting nuclide does not change.  As shown in equations (6) and (7), either a proton turns into a neutron or vice versa.

Gamma radioactive decay

We know that atoms have energy levels.  Similarly, a nucleus also has an energy level. When a nucleus is in an excited state, it can transition to a low energy state by emitting Electromagnetic Radiation.  In addition, the difference between the energy states in the nucleus is in MeV. Therefore, photons emitted by the nucleus have MeV energy and are called gamma rays.

After alpha or beta emission, most radionuclides leave the daughter's nucleus in an excited state. This child nucleus emits one or several gamma rays and reaches the ground state.  for example,

6027Co undergoes beta decay and changes to 6028Ni.  The daughter nucleus (6028Ni) is in excited state.  This excited nucleus reaches the ground state by emitting two gamma rays with an energy of 1.17 MeV and 1.33 MeV.  The energy level diagram shown below illustrates this process.

| Radioactivity decay | Which nuclei is unstable — Stability belt, Types of Radioactive decay |

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