Radioactivity | Definition, Discovery, Types, Applications

Definition of Radioactivity

As its name implies, radioactivity is the act of emitting radiation spontaneously. And this is done by an atomic nucleus that. Because for some reason, is unstable; it “wants” to give up some energy to shift to a more stable configuration.


During the first half of the twentieth century, much of modern physics was devoted to exploring why this happens, with the result that nuclear decay was fairly well understood by 1960.

Too many neutrons in a nucleus lead it to emit a negative beta particle, which changes one of the neutrons into a proton. And too many protons in a nucleus lead it to emit a positron (positively charged electron), changing a proton into a neutron.

Much energy leads a nucleus to emit a gamma-ray, which discards great energy without changing any of the particles in the Nucleus. Because too much mass leads a nucleus to emit an alpha particle, discarding four heavy particles (two protons and two neutrons).

Units of Radioactivity

units of radioactivity

Curie and Rutherford are the units of radioactivity.

1C = 3.7 × 104 Rd is the relationship between Curie and Rutherford.


Henry Becquerel discovered radioactivity by accident. A Uranium compound was placed in a drawer containing photographic plates wrapped in black paper. When the plates were examined later, it was found that they were exposed! However, his exposure gave rise to the concept of Radioactive decay.

Types of radioactivity

 Radioactivity can be seen in such forms:

Gamma Decay (Photons having high energy are emitted)

gamma decay

Gamma decay is the emission of electromagnetic radiation of an extremely high frequency; i.e. very high energy, giving out excess energy in order to stabilize the unstable Nucleus. You must be quite familiar with the various energy levels in an atom.

The Nucleus has its own energy levels. Gamma decay is the Nucleus’s way of dropping from a higher energy level to a lower energy level through the emission of high energy photons. Because the energy level transition energies in the atom are in the order of MeV.

Therefore, the gamma-ray emitted is also of very high energy of the order of MeV, just like x-rays. The gamma rays emitted can be differentiated from x-rays only by the fact that gamma rays come from the Nucleus. Due to their high energy, they are extremely penetrating and thereby dangerous to biological life forms.

Beta Decay (Emission consists of Electrons)

beta decay

Beta Decay is a type of radioactive decay in which a proton is transformed into a neutron or vice versa inside the Nucleus of the radioactive sample.

Processes like beta decay and alpha decay allow the Nucleus of the radioactive sample to get as close as possible to the optimum neutron/ proton ratio. While doing so, the Nucleus emits a beta particle which can either be an electron or positron.

Remember that there either a proton can turn to a neutron or neutron to a proton. Electron and the positron are generated to obey the law of conservation of charge. Beta decay occurs via the weak interaction.

Alpha Decay (Emission consists of Helium nucleus)

alpha decay

Alpha decay is a type of radioactive disintegration in which some unstable atomic nuclei dissipate excess energy by spontaneously ejecting an alpha particle.

Because alpha particles have two positive charges and a mass of four units. And their emission from nuclei produces daughter nuclei having a positive nuclear charge or atomic number two units less than their parents and a mass of four units less.

Thus polonium-210 (mass number 210 and atomic number 84, i.e., a nucleus with 84 protons) decays by alpha emission to lead-206 (atomic number 82).

Applications of Radioactivity

applications of radioactivity

In medicine

Radioisotopes have found extensive use in diagnosis and therapy, and this has given rise to a rapidly growing field called nuclear medicine. These radioactive isotopes have proven particularly effective as tracers in certain diagnostic procedures. As radioisotopes are identical chemically with stable isotopes of the same element, they can take the place of the latter in physiological processes. 

Though many radioisotopes are used as tracers, iodine-131, phosphorus-32, and technetium-99m are among the most important. Physicians employ iodine-131 to determine cardiac output, plasma volume, and fat metabolism and particularly to measure the activity of the thyroid gland where this isotope accumulates.

Phosphorus-32 is useful in the identification of malignant tumours because cancerous cells tend to accumulate phosphates more than normal cells do. Technetium-99m, used with radiographic scanning devices, is valuable for studying the anatomic structure of organs.

In Industry

Foremost among industrial applications is power generation based on the release of the fission energy of uranium (see nuclear fission; nuclear reactor: Nuclear fission reactors).

Other applications include the use of radioisotopes to measure (and control) the thickness or density of metal and plastic sheets, to stimulate the cross-linking of polymers, to induce mutations in plants in order to develop hardier species and to preserve certain kinds of foods by killing microorganisms that cause spoilage.

In tracer applications, radioactive isotopes are employed. For example, to measure the effectiveness of motor oils on the wearability of alloys for piston rings and cylinder walls in automobile engines. 

In Science

Research in the Earth sciences has benefited greatly from the use of radiometric dating techniques. Which are based on the principle that a particular radioisotope (radioactive parent) in geologic material decays at a constant known rate to daughter isotopes.

Using such techniques, investigators have been able to determine the ages of various rocks and rock formations and thereby quantify the geologic time scale. 

A special application of this type of radioactivity age method, carbon-14 dating, has proved especially useful to physical anthropologists and archaeologists.

It has helped them better determine the chronological sequence of past events by enabling them to date fossils and artifacts from 500 to 50,000 years old more accurately.

The Harmful Effects of Radiation

harmful radiation

1. If radiation collides with molecules in the air or in your body, it throws out the electrons. By throwing out electrons, you produce charged particles called ions. This means it is the radiation responsible for ionizing molecules.

2. If this happens in our body, the cells may die or undergo a change called a mutation. The result is called radiation sickness. A large dose of radiation will cause death!

3. Small doses of radiation over a long period of time can cause the cells to multiply. However, these cells are mutated. Sometime later, cancer may occur.

4. Background Radiation: We are surrounded by background radiation all of the time. Because, background radiation comes from the soil, rocks, the air, water, plants, building materials and food. Some radiation is due to cosmic rays from outer space. However, fortunately, our body can withstand low-level radiation without ill effects because it can repair any damage.

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