Radioactivity
Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. Because the nucleus experiences the intense conflict between the two strongest forces in nature, it should not be surprising that there are many nuclear isotopes which are unstable and emit some kind of radiation. The most common types of radiation are called alpha, beta, and gamma radiation, but there are several other varieties of radioactive decay.

Radioactive decay rates are normally stated in terms of their half-lives, and the half-life of a given nuclear species is related to its radiation risk. The different types of radioactivity lead to different decay paths which transmute the nuclei into other chemical elements. Examining the amounts of the decay products makes possible radioactive dating.

Radiation from nuclear sources is distributed equally in all directions, obeying the inverse square law.

The nuclei of most atoms are very stable. They are put together in such away that they never change. However some nuclei are unstable and emit radiation to gain stability. These nuclei are said to be radioactive. The reasons for instability vary. Some nuclei have a neutron-to-proton ratio that is too high or too low. Some nuclei are in an exited state while other are just to heavy for stability. To remedy instability, nuclei decay. Since the conditions of instability differ the ways nuclei decay also differ. The most common ways are:
α - particle emission
β - particle emission
γ - ray emission

α, β, and γ stand for alpha, beta, and gamma, the first three letters of the Greek alphabet.

Alpha (γ) particles (42He) are nuclei of fast-moving helium atoms. They are easily absorbed by thin sheets of paper a few centimeters of air.
Beta (β) particles (0-1β) are fast-moving electrons. They can penetrate a few millimeters of aluminum or about 100 centimeters of air. The mass of an electron is so small that compared to other nucleons, it is 0. With no protons to balance the electron, it has a charge of -1.
Gamma rays (ɣ) are electromagnetic radiations of high frequencies. They have an indeterminate range in matter. On the average, they can penetrate long distances through air or several centimeters through lead. When an alpha or an beta particle is emitted by a nucleus. The atom becomes a new element.

In a sample of radioactive material, the unstable nuclei do not all decay at the same time. Instead, decay is a random event. However, since most radioactive samples contain literally billions of radioactive nuclei, the average rate of decay is "smooth." The amount of time it takes half of the unstable nuclei of a sample to decay into more stable nuclei is called the half-life. Each kind of radioactive element has a unique half-life. The half-life can serve as a "fingerprint" for identifying a radioactive material. A typical radiation intensity-vs.-time curve. From this you can see that although the half-time for a given radioactive material is a specific amount of time, a radioactive sample theoretically never completely decays. "Half" is always left. Some half-lives are only small fractions of a second; others are hundreds to billions of years.

Writing Nuclear Equations

1. When a nucleus emits an ɑ particle, the mass number decreases by 4 and the atomic number decrease by 2.

Example: (32290Th) -----> (22888Ra) (42α)

2. When a nucleus emits an β particle in the mass number does not change however the atomic number increase by 1.

Example: (22888Ra) -----> (22889Ac) (0-1β)

3. When a nucleus emits a gamma rays both the atomic number and the mass number remain unchanged.

Example: (11349In) -----> (11349In) (00γ), m = metasble

4. When a nucleus absorbs a neutron the mass number increases by one and atomic number remain unchanged.

Example: (23892U) (10N) -----> (23992U)