Lesson 1. Biologic effects of radianion.

All organisms are continuously exposed to radiation from either natural or synthetic sources. In the United States, the average dose of radiation an individual receives per year is estimated to be 3.6 milliSieverts (mSv), 80% of which is from natural sources and 20% of which is from man-made sources. The full effects of low-dose natural radiation are not known, but high doses have been shown to be carcinogenic. At very high-dose exposures over a short period of time, immediate and lethal health effects can occur.

Generally, the toxicity caused by radiation is directly related to the quantity of energy deposited into the living organism and the subsequent disruption of metabolic and reproductive pathways. Low-level exposure from accidental contact with radioactive isotopes in laboratory research may lead to relatively minor toxicity. Alternatively, acute sickness and even death may occur after the inappropriate handling of high-level radioactive material such as cobalt-60 from radiographic or radiotherapy machinery. In a terrorism context, a radiation dispersal device (RDD), “dirty bomb,” could result in conventional blast and thermal injuries. If these devices are laced with significant amounts of radioactive material, the additional risk of radiation exposure would exist for both bomb victims and rescue workers. Detonation of nuclear weapons or improvised nuclear devices would lead to catastrophic blast and thermal injuries in addition to far-reaching lethal radiation consequences.

Over the past 50 years, most radiation incidents have had nonlethal consequences. According to the Radiation Accident Registry maintained by the Radiation Emergency Assistance Center/Training Site (REAC/TS) at the Oak Ridge Institute, from 1944-1999, 403 radiation accidents occurred worldwide, with 243 of those occurring in the United States. Of the total, 303 involved radiation devices from sealed sources or x-ray machinery, 81 involved radioisotopes, and 19 involved nuclear reactors. These incidents have led to 120 total deaths: 30 in the United States, 2 in Great Britain, and 32 in the former USSR

Radioactivity

Radioactive decay is the process in which unstable atomic nuclei assume a more stable configuration by emitting particles with kinetic energy (alpha or beta particles) or electromagnetic waves (gamma rays). If a person is exposed to these high-energy particles or electromagnetic waves, energy is deposited into the tissues and can cause injury.

Ionizing versus nonionizing radiation

Radiation can be broken down into 2 categories: ionizing radiation and nonionizing radiation. The term ionizing radiation refers to either high-energy particles or electromagnetic waves that have the ability to deposit enough energy to break chemical bonds and produce an ion pair. Ionization occurs when the process of energy transfer liberates an orbital electron from an atom or molecule producing this ion pair. If living cells receive this energy, cellular function becomes compromised by DNA damage and mutation.

Nonionizing radiation refers to radiation that lacks the energy to liberate orbital electrons. All radiation from the electromagnetic spectrum except x-rays and gamma rays are included in this category. Examples of nonionizing radiation include microwaves, visible light, and infrared light. Because nonionizing radiation is lower energy radiation, injury is usually related to local heat production and is generally less severe. Ionizing radiation is consequently the focus of radiation-induced injury.

Ionizing radiation: electromagnetic radiation

Energy can travel through space in the form of electromagnetic radiation. Electromagnetic radiation is composed of massless waves of oscillating electric and magnetic fields. In a vacuum, these waves move at a constant speed, the speed of light (3 X 10⁸ m/s). All electromagnetic waves propagate with characteristic wavelength and frequency, with the wave's energy being directly proportional to frequency and inversely proportional to wavelength. Within the electromagnetic spectrum, only x-rays and gamma rays have enough energy to produce ion pairs. The remaining waves within the spectrum, such as microwaves and radiowaves, are nonionizing.

Date: 2015-01-12; view: 837