Radioactivity and Nuclear Physics

Beta rays are much lighter energy particles. The beta particles are energetic electrons given off by the nucleus of unstable isotopes to restore energy balance. They leave the nucleus at a speed of 270,000 kilometres per second.

Nuclear transmutation is the conversion of one chemical element or isotope into another. This occurs either through nuclear reactions (in which an outside particle reacts with a nucleus), or through radioactive decay (where no outside particle is needed).

A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g. 235U) or the fusion of light isotopes (e.g. 2H and 3H.)

The rem is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of thousandths of a rem, or mrem. To determine equivalent dose (rem), you multiply absorbed dose (rad) by a quality factor (Q) that is unique to the type of incident radiation. For gamma rays and beta particles, 1 rad of exposure results in 1 rem of dose.

By utilizing the radioactive properties of Americium-241, smoke from a fire can be detected at a very early stage so it is used in smoke detectors. This early warning capability has saved many lives.

The roentgen is a unit used to measure a quantity called exposure. The roentgen measures the energy produced by gamma radiation in a cubic centimeter of air. This can only be used to describe an amount of gamma and X-rays, and only in air. One roentgen is equal to depositing in dry air enough energy to cause 2.58E-4 coulombs per kg. It is a measure of the ionizations of the molecules in a mass of air.

Beta decay occurs when the neutron to proton ratio is too great in the nucleus and causes instability. In basic beta decay, a neutron is turned into a proton and an electron. The electron is then emitted. e.g.hydrogen-3.

The final type of beta decay is known as electron capture and also occurs when the neutron to proton ratio in the nucleus is too small. The nucleus captures an electron which basically turns a proton into a neutron. E.g. beryllium-7.

Hydrogen-3 is also known as tritium. Gaseous tritium source exit signs are 'EXIT' sign boards, used to indicate emergency exit. They are the most widely used exit signs nowadays. Tritium exit signs are better compared to other traditional or hard-wire exit signs, because they do not require electricity. They work on the principle of radio-luminescence.

The alpha particle is a type of ionizing radiation. With its partners the gamma particles and beta particles, alpha particles are one of the most prevalent forms of radiation. An alpha particle is essentially a helium nucleus, which consists of two neutrons and two protons, without electrons, giving it a net positive charge. Due to its relatively high mass, alpha particles are the most destructive form of ionizing radiation.

The uranium decay-series contains several radioactive isotopes.U-238 decays by alpha emission into thorium Th-234. Th-234 decays by 2 alpha & 3 beta emission changes into Ra-220.

In a disease called Polycythemia vera, an excess of red blood cells is produced in the bone marrow. Phosphorus-32 is used to control this excess.

Yttrium-90 is used for treatment of cancer, particularly non-Hodgkin's lymphoma, and its more widespread use is envisaged, including for arthritis treatment. Lu-177 and Y-90 are becoming the main RNT agents.

A new field is Targeted Alpha Therapy (TAT) or alpha radioimmunotherapy, especially for the control of dispersed cancers. The short range of very energetic alpha emissions in tissue means that a large fraction of that radiative energy goes into the targeted cancer cells, once a carrier such as a monoclonal antibody has taken the alpha-emitting radionuclide to exactly the right place. TAT using lead-212 is said to show promise for treating pancreatic, ovarian and melanoma cancers.

Gamma rays are high-energy photons with a very short wavelength (0.0005 to 0.1 nm). The emission of gamma radiation results from an energy change within the atomic nucleus. Gamma emission changes neither the atomic number nor the atomic mass so it will remain unaffected by the electric field.