What is Radiation?

Radiation is energy transmitted in the form of high speed particles and electromagnetic waves. We are familiar with electromagnetic radiation in the form of visible light, radio and television waves, microwaves and so on. The nuclear industry is engaged in practices which expose people and the environment to far more powerful kinds of radiation: gamma radiation and alpha, beta and neutron particles.

You can't see these kinds of radiation. You can't smell them, taste them or even feel them unless the doses are high enough to burn your skin or burn out your nervous system. But any dose can do you damage.

While the health effects of sudden high doses of radiation are well documented, the effects of continual exposure to low level radiation are far more subtle, complex and insidious. In "No Immediate Danger, Prognosis for a Radioactive Earth," Dr. Rosalie Bertell writes:

Alpha Radiation
A positively charged particle emitted by certain radioactive material consisting of two neutrons and two protons, the nucleus of a helium atom. A dangerous carcinogen when inhaled or ingested. Alpha radiation can penetrate the body to just below the dead skin, but is blocked by clothing or even a sheet of paper. When released inside our bodies from material we breathe or swallow, alpha rays are able to transfer their energy at short range to damage body cells.

Beta Radiation
A beta particle is a single high-energy electron moving at high speed and carrying a negative charge. They can travel about one metre through air and can penetrate the skin, to reach internal tissue. Can cause skin burns and, when ingested, cancer. Beta rays are especially dangerous when emitted inside the body.

Gamma Radiation
Gamma rays are electromagnetic waves or photons emitted from the nucleus (center) of an atom. They have no electrical charge and penetrate deeply into the body, or pass through it, creating ions as they collide with atoms along their path. Gamma rays are similar to X-Rays, but are much more powerful.

Neutron Radiation
Neutrons are the neutral particles that are normally contained in the nucleus of all atoms. Neutron radiation occurs when the nucleus of a heavy element like uranium decays into a lighter element and emits a neutron. In a nuclear reactor core or atom bomb, enough neutrons are released to split more uranium atoms, releasing more neutrons and creating a critical mass: a self sustaining reaction. In a nuclear weapon, the reaction is uncontrolled and leads to a massive explosion and burst of neutron radiation. In a nuclear reactor, the critical mass is 'moderated' or slowed, generating tremendous heat without actually exploding. Neutron radiation is perhaps the most dangerous for living creatures.

 

The nature of atoms
All matter is made up of atoms: tiny bubbles of force so small they can scarcely be imagined. These entities seem to exist as pointlike knots of condensed energy (the nucleus) surrounded by a shimmering cloud of electrons.

The nucleus itself is normally composed of two kinds of particle: positively charged protons and uncharged neutrons. For an atom to be considered electrically neutral (that is, have no charge), it must have one negatively charged electron in the cloud to balance each positively charged proton in the nucleus. The number of neutrons, while affecting the mass of the atom, has no influence on electric charge.

Hydrogen, the simplest kind of atom, normally has no neutrons at all: it is simply a single proton coupled to one whirling electron. Carbon, a more complex element, contains six protons, six electrons, and between six and eight neutrons.

It's a common misconception that matter and energy are two different things, but in the early years of this century, Albert Einstein introduced the notion that an atom is a tightly concentrated, meta-stable bundle of energy arising from the universal field (a concept that might seem familiar to ancient cosmologies). According to the theory, this energy can be liberated under certain circumstances: when an atom is split, for example, or when it fused with other particles to make a heavier element.

Atomic and Mass Numbers
Each element is commonly referred to as having an atomic number and a mass number. The atomic number is simply the number of protons in the nucleus, and the mass number is the combined total of protons and neutrons.

Elements are sometimes written in the following format: ₂₃₈U or Uranium-238. The 238 is the mass number of the element.

Knowing that uranium has an atomic number of 92, you can calculate that it must also have 146 neutrons by subtracting 92 from 238 - at the scale of atoms, this makes it a monster.

Isotopes
The variability in the number of neutrons packed into the core of the atom is what gives rise to the phenomenon of isotopes. Most naturally occuring elements are mixtures of several isotopes, and many of these are stable under normal conditions. Uranium, with 92 protons, has three flavours: _234U, _235U and _238U. While all isotopes of an element are chemically identical to each other, the isotopes have differing physical properties - this is one of the reasons uranium is subject to exotic (and dangerous) refinement and enrichment processes.

Half Lives and Radioactive Decay
Uranium-238, the most prevalent isotope in uranium ore, has a half-life of about 4.5 billion years; that is, half the atoms in any sample will decay in that amount of time. Uranium-238 decays by alpha emission into thorium-234, which itself decays by beta emission to protactinium-234, which decays by beta emission to uranium-234, and so on. The various decay products, (sometimes referred to as "progeny" or "daughters") form a series starting at uranium-238.

After several more alpha and beta decays, the series ends with the stable isotope lead-206. The property of uranium important for nuclear weapons and nuclear power is its ability to fission, or split into two lighter fragments when bombarded with neutrons releasing energy in the process. Of the naturally-occurring uranium isotopes, only uranium-235 can sustain a chain reaction -- a reaction in which each fission produces enough neutrons to trigger another, so that the fission process is maintained without any external source of neutrons. In contrast, uranium-238 cannot sustain a chain reaction, but it can be converted to plutonium-239, which can.

Plutonium-239, virtually nonexistent in nature, was used in the first atomic bomb tested July 16, 1945 and the one dropped on Nagasaki on August 9, 1945.