Who Discovered the Radioactivity

Henri Becquerel earned the 1903 Nobel Prize in Physics for discovering radioactivity in 1896. Ernest Rutherford classified radiation into three types, alpha (α), beta (β), and gamma (γ), according to how they were deflected in a magnetic field.

Types of Radiation: Alpha, Beta, and Gamma Rays. Physicists classify radiation into three types. Alpha and beta radiation is actually particles. Gamma radiation is high energy electromagnetic waves.

Alpha Radiation

Alpha, or α, radiation consists of particles rather than rays. Alpha particles are helium nuclei, containing two protons and two neutrons. By particle physics standards, alpha particles have a relatively large mass and nuclear cross section. Nuclear physicists use the cross section to measure how likely a particle is to interact with matter.

The large cross section makes alpha radiation both fairly safe and fairly lethal. Because alpha particles easily interact with matter, they are easily absorbed. These particles therefore have a short range and little penetrating power. Paper or ordinary indoor clothing can block most alpha particles. Hence it is quite easy to shield radioactive alpha sources.

If however one were to eat or drink a source of alpha radiation, the emitted alpha particles would interact inside the body. A sufficiently large dose would be lethal despite the short range. Food or water contaminated with radioactive isotopes that undergo alpha decay can be dangerous.

An example of a radioactive decay process emitting alpha radiation is the decay of uranium into thorium. Uranium 238 is an isotope of uranium with 92 protons and 146 neutrons in the nucleus. When uranium 238 undergoes alpha decay, it emits a helium nucleus leaving 90 protons and 144 neutrons in the nucleus. The nucleus thus decays from uranium into thorium.

Beta Radiation

Like alpha radiation, beta, or β, radiation consists of particles rather than rays. Beta particles are either electrons or positrons, which are the antimatter particles corresponding to electrons.

Beta radiation has a little more range and penetrating power than alpha radiation. A sheet of aluminum a few millimeters thick is, however, enough to block most beta particles. As for alpha radiation, beta radiation is most dangerous when one eats or drinks a beta decay source.

In beta decay one of the neutrons in the atomic nucleus splits into a proton and an electron. The nucleus emits the electron or beta particle as well as an antineutrino produced in the reaction. The product (called daughter by physicists) nucleus has one more proton, and one less neutron, than the original nucleus. Hence it decays into a different element.

In a similar process, called inverse beta decay, a proton emits a positron and a neutrino as it decays into a neutron. The daughter nucleus has one less proton and one more neutron than the original.

The decay of the radioactive isotope carbon 14, used in carbon dating, provides a good example of beta decay. A carbon 14 nucleus has 6 protons and 8 neutrons. After the beta decay it becomes nitrogen 14 with 7 protons and 7 neutrons. During the decay, the nucleus emits an electron and an antineutrino.

Gamma Radiation

Like light, radio waves, and X-rays, gamma, or γ, rays are a type of electromagnetic wave. With the highest energy on the electromagnetic spectrum, gamma rays have much more penetrating power than either alpha or beta radiation and can pass through concrete walls. It takes several centimeters of lead to block gamma rays. The high energy and penetrating power make gamma radiation dangerous.

Gamma decay occurs when a radioactive nucleus is in a higher than normal energy level. The nucleus emits a gamma ray as it drops to its normal energy level.

Radiation can be dangerous, but it is not completely bad. There are also important lifesaving medical uses of radiation.

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