Why do radioactive elements decay

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Many atoms of the elements of high atomic number have the property of spontaneously transforming themselves into another atomic nucleus without any external influence. Radiation is emitted in the process. This is called radioactivity.

H. Becquerel discovered this property in 1890 when he noticed that pitchblende, a uranium mineral, emits radiation that is invisible to humans and can blacken photographic plates. In the following years, several elements that are radioactive were discovered. It was found that certain rays can be deflected (in different directions) in a magnetic field, while others cannot.

There are three types of radioactive radiation:
Tab. 1
Types of radioactive radiation
Type of radiationdescriptionchargeRange
αHelium nuclei+2A few centimeters in the air; cannot penetrate a sheet of paper.
βElectrons-1Several meters in the air; However, they are shielded by metal, plastic and wooden panels (from a few millimeters).
γelectromagnetic waves0Virtually no attenuation in air, thick lead plates required for shielding.

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The cause of the radioactive radiation are processes in the atomic nucleus. Very large atomic nuclei (e.g. all isotopes of the elements from polonium) are unstable. They are subject to radioactive decay. On the one hand, the atomic nuclei are converted into a lighter nucleus by emitting a helium nucleus (α radiation). On the other hand, when an electron is emitted (β radiation), a neutron can be converted into a proton and another element of the same mass is created. Often γ-radiation is still released during both processes.