12.8    Radioactive Terminology

AL:  Action Level- if a drinking water system exceeds the action level in more than 10% of the homes tested, the water system must treat the water delivered to its customers.  Unfortunately, the same protection is not extended to wildlife. 

ACTIVITY:  rate of radiation release in the number of particles per second.  The greater the activity the more radioactive is the material.  The standard unit is the Becquerel, defined as one emission (disintegration) per second.  Also, see Curie, below.

ACTIVATION PRODUCTS:  those materials that have become radioactive because of the radiation in a reactor, like nickel-59, carbon-14, and cobalt-60.

ALPHA RADIATION:  a particle composed of two protons and two neutrons, ejected when a nucleus reduces it’s mass and transforms itself into a different element.  Slow-moving alpha particles cannot penetrate paper or skin, but are very dangerous when substances emitting them are ingested or inhaled. (See Figure in Appendix 12.9, Figure 12.9)

BACKGROUND RADIATION:  refers to the radiation we receive from our everyday lives, and is usually associated with radiation from natural sources.  Typical background radiation doses range from 100 to 200 millirem per year depending upon geographic location and lifestyle.

BETA RADIATION:  an electron emitted when a neutron becomes a proton, moving at nearly the speed of light.  Beta particles can penetrate paper or several millimeters of skin, and like alpha particles, are very dangerous when substances emitting them are ingested or inhaled.

CRITICAL MASS:  the mass (amount) and configuration (shape) of a given fissionable element needed to spontaneously undergo nuclear fission and sustain a nuclear chain reaction.  Thus, a critical mass is the amount needed to make a bomb, even a “dirty bomb.”

CURIE:  an older and still widely used unit of activity, which is equal to 37 billion emissions per second. A picocurie, used widely in water analysis as picocuries per liter or pCi/L, is 10^-12 curies.

DECAY:  when a substance on its own releases radiation, and in the process becomes a difference substance.  After one substance has decayed to another, it could still be radioactive.  Anything that is radioactive is in a process of decay (radioactive decay). 

DOSE:  is a measure of how much radiation is absorbed by a person and the health effects.  A common unit used in relation to biological exposure is the rem.   The standard unit of dose is the sievert, which is 100 rem, and a typical chest X-ray is a dose of 10 millirems (0.100 rem) or 1 millisievert.    A dose of one rem is a large dose for a single exposure.

GAMMA RADIATION:  a short, intense burst of electromagnetic energy, emitted by an unstable nucleus.  With high energy and no electrical charge, gamma rays have great penetrating power.  Not even a thick piece of lead or concrete will stop all of them, and they pass easily into the human body, damaging tissue in the process.

GEIGER COUNTER:  a device for measuring radiation.

FISSION PRODUCTS:  these are the highly radioactive fragments that result from splitting the atom.  They tend to have half-lives of less than 1,000 years.

HALF-LIFE:    refers to the time required for half of the radioactive substance to decay away.  If the half-life is large then the activity is small.

IONIZING RADIATION:  any of a type of radiation that can induce ionization; knock electrons off of atoms.  Ionizing radiation is the most harmful kind of radiation.

ISOTOPES:  nuclei of the same element but differing in the number of neutrons; for example uranium-238 (U-238) and U-235 are the same element but vary in mass.  Isotopes have almost exactly the same chemical properties, and the body is unable to distinguish between isotopes.

KILOTON, MEGATON:  1,000 and 1,000,000 tons of TNT equivalent.  These terms are typically used to refer to the explosive force of nuclear weapons.

LIFETIME HA: Health Advisory- the concentration of a contaminant that is not expected to cause adverse health affects for a lifetime of exposure. The lifetime HA is based on a 154 lb adult drinking two liters of water per day.

MCL:  Maximum Contaminant Level- the highest level of a contaminant allowed in drinking water at one time.  MCLs are health-based and are legally enforceable.

NUCLEAR TEST VERSUS DETONATION:  Detonation is defined by the Department of Energy as:  “A single nuclear device explosion; one or more comprise a test.”  In at least one test, five nuclear weapons were detonated at the same time.  At the Nevada Test Site, 1021 bombs were exploded, or detonated.  100 were above ground, before 1963.  828 tests were conducted below ground, which involved exploding, or detonating, 921 nuclear bombs.

NUCLEAR FISSION:  the splitting of an atom fragments (fission products).  Any atom that is capable of fission is know as fissile.  Fission products are highly radioactive, and always result from nuclear fission.

NUCLEAR PROLIFERATION:  refers to human actives that increase the amount of radioactive materials that are used to make nuclear weapons; mostly plutonium-239 and uranium-235.

PLUTONIUM:  a radionuclide that is almost entirely human-made and has become the substance of choice for making nuclear weapons.  It is also one of the most toxic materials known, and has a half life of about 24,000 years.  Plutonium is also in radioactive waste from nuclear power reactors.

RADIONUCLIDE:  any atom (nucleus, actually) that is unstable, meaning it will decay, and hence is radioactive.

RADIATION:  most generally refers to energetic particles.  Sunlight is a form of radiation, and so is the heat from a campfire.  When a substance is in the process of radioactive decay, it will give off radiation.  Five general types of radiation are given off from the decay process:  gamma, x-rays, neutrons, beta particles, and alpha particles.  Any of these can be harmful.

SPENT NUCLEAR FUEL (SNF):  this is the nuclear waste from a reactor. After nuclear fuel has been in the reactor for about four years, it is considered, “spent,” hence spent nuclear fuel.  It is very radioactive due to “fission products”.

SUBCRITICAL TEST:  an experiment that uses high explosives and some amount of plutonium (typically) that will simulate the conditions in a nuclear weapons test, but leads just to the point of the nuclear explosion (nuclear chain reaction) without triggering the chain reaction.  Thus, the mass of plutonium is below criticality, hence subcritical.

TRANSPORTATION CASK:  a “dumbell shaped” container, used for transporting the waste from reactors.

TRANSMUTATION:  is the general changing of one atom (nucleus) into another.  All decay is transmutation, but not all transmutation is decay; for example, nuclear fission in a power reactor is transmutation, but not decay.  Plutonium is formed from uranium in a reactor, so the uranium is transmuted into plutonium.

TRANSURANIC:  any element (type of atom) larger (in the number of protons, atomic number) than uranium; plutonium is an example of a transuranic element.

WASTE CASK OR CANISTER:   the containers to be used to hold nuclear waste in a long term repository (dump).

WEAPONS COMPLEX:  all the facilities in the US that are involved in the production of nuclear weapons.  These facilities are run by the Department of Defense and the Department of Energy, and now the National Nuclear Safety Administration (NNSA).

X-RAYS:  a form of cosmic radiation or man-made, produced by firing electrons at a heavy metal target.  X-rays are somewhat less penetrating than gamma rays, though their effects are similar.