Radioactive Decay

The nucleus of the atom decays, and in the process, the nucleus transforms into another element, or into an isotope or isomer of the same element. In radioactive decay, the nucleus always emits some kind of particle(s). It is the high-energy emission of these particles that we call radiation. There are many different types of radioactive decay:

• Alpha decay results in the emission of an alpha particle (two neutrons and two protons)
• Beta decay results in the emission of a beta particle (an electron or a positron)
• Neutron decay results in the emission of a neutron
• Proton decay results in the emission of a proton
• Gamma decay results in the emission of a gamma particle (a photon)
• Neutrino decay results in the emission of a neutrino or antineutrino

In some cases, a combination of the above emissions takes place. For example in double beta decay, a single nucleus emits two electrons and two antineutrinos in the same event.

No shielding material truly absorbs electromagnetic radiation, it attenuates it. The attenuation is by a certain amount for a certain standard thickness. The standard thickness is called the half thickness and is used to quantify shielding effectiveness for a given type of electromagnetic radiation. One half thickness attenuates the power of the given type of radiation by 50% or in decibel units -3dB. Thus the power of the radiation after a given number of half thicknesses of a given shield is:

1. 50% or -3dB
2. 25% or -6dB
3. 12.5% or -9dB
4. 6.25% or -12dB
5. 3.125% or -15dB
6. 1.5625% or -18dB
7. 0.78125% or -21dB
8. 0.390625% or -24dB
9. 0.1953125% or -27dB
10. 0.097655625 or -30dB
11. etc.

As you can see no thickness of shield material can completely attenuate electromagnetic radiation to nothing, also the higher the frequency of electromagnetic radiation the longer the half thickness is so for x-rays and gamma rays it takes very large thicknesses to get any useful attenuation.

For particle radiation the situation is completely different, the radiation can sometimes be absorbed and sometimes can't:

1. alpha particles are 100% absorbed by a single sheet of paper or the first layer of living tissue they encounter
2. most beta particles are 100% absorbed by a single sheet of thin metal foil (e.g. aluminum foil)
3. neutrons penetrate most matter as if it was not there, unless it contains certain elements (e.g. boron, cadmium, uranium) that have high neutron capture crosssections in which case the neutron flux is attenuated much like electromagnetic radiation as described above
4. neutrinos penetrate all matter as if it was not there
5. etc.

Gamma decay is primarily "energy only", in that it is the emanation of photons that represent energy. However, and this is important to understand, gamma does not exist by itself - gamma is a secondary reaction to a primary reaction that involves a change to the nucleus - a change that is usually represented by alpha or beta decay.

So, with the exception of the few metastable forms of radionuclides, gamma still, ultimately, is preceded by particle emission. (Even in the metastable forms, the gamma is preceded by particle emission - its just that the event is delayed enough to "count it" as a separate event.)

The answer to this question varies dramatically depending on the TYPE of radiation involved, as there are many; as well as how the "large amounts of radiation" are received.

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First there are two different main types of radiation, and within each type there are different subtypes, each having differing effects in overdose:

1. Electromagnetic radiation - e.g. radio, TV, microwave, infrared, light, ultraviolet, x-ray, gamma ray.
2. Particulate radiation - e.g. alpha, beta, gamma, neutron, cosmic ray, heavy ion.

Note: The gamma ray listed as electromagnetic radiation and gamma listed under particulate radiation are the same radiation, but at that very high energy per photon particle quantum mechanics makes it impossible to clearly say it is either an electromagnetic wave or a particle.

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The effects of overdose exposure of each of the above listed types of radiation are:

• radio - very difficult to impossible to overdose
• TV - very difficult to impossible to overdose
• microwave - you get cooked inside, this is called "deep tissue burns" and can be instantly fatal in some cases
• infrared - thermal skin burns
• light - very difficult to impossible to overdose, except directly to the eyes which produces temporary blindness
• ultraviolet - sunburn, exposure to the eye will cause permanent blindness
• x-ray - radiation sickness/poisoning
• alpha (external exposure) - intact skin shields 100% of alpha particle radiation, impossible to overdose
• alpha (internal exposure) - cancer
• beta - beta burns, on skin resembles a very very bad sunburn (but may be in small dots around the points of contact with beta emitting fallout grains), internally it is usually fatal as it causes massive tissue death
• gamma - radiation sickness/poisoning
• neutron - radiation sickness/poisoning, also will make you radioactive (no other type of radiation will do this)
• cosmic ray - on the surface of earth the atmosphere is such a good shield that it is impossible to overdose, but in space radiation sickness/poisoning are possible
• heavy ion - tends to be shielded effectively by skin, but at high enough energies will cause radiation sickness/poisoning

The symptoms of radiation sickness/poisoning are nausea, vomiting, diarrhea, hair loss, etc. but in extremely high overdose it kills the nervous system causing very sudden death. The insidious thing about radiation sickness/poisoning is that just as the patient begins to appear to improve, the immune system fails and massive infections set in, which kill many.