# 22.3 RADIOACTIVITY When atomic nuclei are unstable, they naturally transform into more stable configurations by emitting particles or energy. This process is called **radioactivity**. It was first discovered by Henri Becquerel and extensively studied by Marie Curie. Radioactivity has significant applications in medicine and energy production, though it requires careful handling due to associated health hazards. --- ## Discovery of Radioactivity - **Henri Becquerel** first discovered natural radioactivity. - **Marie Curie** extensively studied radioactivity, detecting it in uranium and thorium. She used an electrometer to measure conductivity, observing that air around radioactive samples became conductive. --- ## Definition of Radioactivity Radioactivity is the natural emission of radiations from unstable atomic nuclei. It is the phenomenon by which unstable atomic nuclei spontaneously decay into other nuclei, emitting radiation in the process. Radioactivity occurs because certain nuclei have an unstable balance of protons and neutrons. The instability arises from the nuclear force not being sufficient to maintain a stable configuration. For more detail on why some nuclei are unstable, refer to . --- ## Spontaneous Nuclear Decay Spontaneous nuclear decay is the natural process by which an unstable atomic nucleus breaks down into a more stable configuration by emitting radiation. It is spontaneous and occurs without any external influence or trigger (such as temperature or pressure changes). This process can lead to the formation of a new element known as the **daughter nucleus**. The spontaneous nature of this decay is a fundamental characteristic of radioactivity. --- ## Significance and Applications Spontaneous nuclear decay is a natural process occurring in many elements. It has many practical applications in fields such as: - Energy production - Medicine (Radiotherapy and Tracers) - Materials sciences (Carbon dating and sterilization) However, radioactivity can pose significant health hazards if not properly managed due to its ionizing nature. --- ## Main Types of Radioactive Decay The three main types of radioactive decay are: 1. **Alpha decay ($\alpha$):** Emission of a helium nucleus ($^4_2He$). These particles have high ionizing power but low penetration. 2. **Beta decay ($\beta$):** Emission of an electron or positron. This occurs when a neutron converts to a proton (or vice versa) within the nucleus. 3. **Gamma decay ($\gamma$):** Emission of high-energy photons. This usually follows alpha or beta decay when the nucleus is in an excited state. Other radiations and particles, such as X-rays and neutrons, can also be produced in nuclear processes. For more on the nature of these emissions, see .