Is all radiation harmful? when does it become harmful?

Question

i never really understood radiation. isn't the main definition for it the emission of energy? what makes radiation harmful and if everything causes radiation why is it harmful? whenever someone says radiation, they usually mean something dangerous. i don't really understand. what is the difference between everyday radiation that we experience and the radiation from nuclear bombs? how does radiation become nuclear or how are they related? and how do elements fit into it?

Answer 1

Kuang Eleven did a very good job of defining the different types of radiation.  I just want to take that a step further and explain more specifically why radiation can be harmful.

When we refer to dangerous radiation, we are generally referring to what is known as ionizing radiation; that is, radiation that has enough energy to dislodge electrons from atoms.  This differs from non-ionization radiation which can excite electrons, but not dislodge them to form ions.  Non-ionizing radiation is generally harmless.

Alpha and beta particles are both ionizing.  Neutrons, too, are considered to be indirectly ionizing because they can trigger the other forms of ionizing radiation when they collide with other atoms.  Electromagnetic radiation, however, can be either ionizing or non-ionizing.  Wavelengths of light from the ultraviolet portion of the spectrum and shorter are ionizing.  Some visible light can also be ionizing in certain instances, but generally speaking, it is non-ionizing, along with longer wavelengths.

Ionizing radiation ultimately breaks bonds in the DNA of our cells.  When this happens, there are a few possible outcomes.  In the best case scenario, our cells can repair the damage using repair enzymes.  If the DNA damage is extensive or irreparable, the cell will undergo apoptosis, meaning that it kills itself to prevent problems from arising.  When you get a sunburn from the sun's ionizing ultraviolet radiation, and the skin starts to peel a few days later, this is the result of apoptosis.  In the worst case scenario, the DNA is damaged in an area that contains genes regulating cell growth, and the cell starts dividing uncontrollably; this results in cancer.  When people develop skin cancer from ultraviolet radiation exposure, it is because this kind of damage has occurred.

Humans are, for the most part, built to withstand the radiation from the environment.  The melanin in our skin works to absorb ultraviolet radiation, for example.  However, we aren't built for the immense radiation generated by nuclear bombs.

Additionally, it's important to note that this is just the effect that ionizing radiation has at the DNA level.  Radiation can also generate a lot of heat, resulting in burns.  Thus, while low energy, non-ionizing electromagnetic radiation, such as microwaves or infrared waves, won't cause damage to your DNA, large doses might still cook you from the heat they generate.

Answer 2

There are several types of radiation, alpha, beta, and gamma.

Alpha radiation is created during decay of radioactive particles. It consists of alpha particles, 2 protons and 2 neutrons together. These are relatively heavy, so they cannot penetrate far, bare skin will largely protect against alpha radiation. However, if swallowed or somesuch, they can cause a great deal of damage, as the particles are heavy and impart a lot of energy.

Beta radiation is similar to alpha, but it gives of beta particles, which are either electrons or positrons. These are much smaller, so they cannot do as much damage individually, but they can penetrate much farther than alpha particles, so tend to be more dangerous.

Gamma radiation is emitted through photons, X-rays, visible light, Microwaves, Gamma rays, and Infrared are all examples of gamma radiation.

Nuclear weapons expend about half of their energy in sheer physical blast damage. The next signifigant effect is thermal radiation, letting off a massive burst of light and infrared radiation that sears the area. A relatively small portion of the energy is ionizing radiation, alpha, beta, and high wavelength gamma particles. This causes the surrounding dust and matter to be come radioactive by blowing off electrons. When this dust is blown away from the bomb, it is known as fallout.

Some elements are known as radioactive because they are unstable. After the half-life of the element, half of the mass shot off radiation (alpha and beta) and decayed to something more stable.