Saturday, March 26, 2016

Ionizing Radiation for Dummies

Not actually Erin.
& is used with permission.
PREVIOUSLY: Hard vs. Soft Radiation for Dummies

Weeks ago, I gave a brief overview of radioactivity and why the ionizing radiation it emits is bad. This week is a more in-depth explanation about how ionizing radiation works and how to protect against it.

What It Is
Put simply, ionizing radiation is anything which is strong enough to knock an electron out of an atom's orbit, thus ionizing that atom.

Why This Is Bad
As Chaplain Tim has explained, atoms prefer to exist in a neutral state where the number of positively charged particles in the nucleus (protons) equals the number of negatively charged particles in the orbit (electrons). When neutral atoms gain or lose electrons, they become ions and possess an electrical charge. Since having a charge is the opposite of having a neutral state, these atoms will seek to balance themselves by forming chemical bonds with other atoms While these chemical reactions are fine in nature, they become a problem when the atoms so affected are the ones inside your body.

Remember that you are made of cells, and your cells are programmed by your DNA, and that your DNA (like everything else) is made of atoms. If parts of your DNA atoms are given an electrical charge, they will bond with other atoms to return to a neutral state, which means that your DNA changes. This is bad on a variety of levels, as it can result in such things as cells growing at an accelerated rate (cancer), or parts of your body not working the way they should (leukemia), or your body attacking itself (autoimmune diseases).

Of course, this very nature is why radiation is often used to kill cancers: if you can precisely aim the radiation at the cancer cells, you can destroy their DNA using the same method that turned the cells cancerous in the first place.

Types and How to Protect Against Them
There are several kinds of ionizing radiation.
  • Alpha Radiation: A helium nucleus (2 protons, 2 neutrons, no electrons) that is emitted from a larger atom as a result of nuclear decay. 
    • Since it lacks electrons it will try to acquire them from other atoms, either by forming bonds or by stripping lone electrons from the highest levels of their shells. 
    • Alpha radiation is stopped by something as simple as a piece of paper or your skin, although it can be very dangerous if inhaled or ingested.
  • Beta Radiation: A lone electron expelled from an atom as a result of nuclear decay. Because it has much smaller mass, it moves faster and penetrates further than alpha radiation. 
    • This electron will try to occupy an empty orbital position within an electron shell, ionizing that atom. 
    • Beta radiation is stopped by aluminum foil or thick clothing.
  • Gamma and X-ray Radiation: Unlike alpha and beta, gamma radiation is an energy wave.* The main difference between the two is that gamma radiation comes from the nucleus of the atom and x-ray radiation comes from the electron cloud. 
    • The energy from these rays will knock electrons from their orbits, which will leave their atoms positively charged. 
    • Both forms of this radiation are stopped by dense materials like iron or lead; the denser the material, the thinner it needs to be.
  • Neutron Radiation: A lone neutron expelled from a nucleus as the result of atomic decay. 
    • This is technically not ionizing radiation because it doesn't affect the electrical charge of an atom it interacts with. Instead, what happens is much nastier: when the free neutron becomes absorbed by another atom's nucleus, it changes that atom's mass, often turning it into a radioactive isotope. 
    • All it takes is two free neutrons to be absorbed by a stable carbon atom to turn it into radioactive carbon-14... and 18.5% of your body is carbon. In other words, neutron radiation can turn your body into a radioactive element. 
    • Neutron radiation is absorbed by concrete, gravel, and water, and the more of it the better. 
  • Delta and Epsilon Radiation: These are secondary and tertiary forms of radiation that are a result of gamma rays or x-rays knocking electrons free. These are relatively insignificant, because if you are shielded against the previous three forms of ionizing radiation, you will also be protected against these.

Shielding against x-ray, gamma and neutron radiation isn't an easy fix like with alpha and beta particles. The amount of material needed to reduce a certain intensity of radiation by half is known as the half-value layer, and therefore the greater the intensity the greater the thickness. I did some quick and dirty calculations in my previous blog post and came up with values of 10 feet of water and 12.5 inches concrete or 18 inches packed dirt being sufficient to protect against most such radiation bursts, but I do not guarantee these numbers. If anyone is more inclined to number-crunching, please be my guest; you might find this page to be of use.

What's This About Electron Energy Levels?
This is complex but I'll try to give you the simplified version; perhaps Chaplain Tim will go into more detail later.

Electrons orbit atomic nuclei in in levels (and sublevels, but those are too complex to explain here). These levels form the electron shell (or cloud) around the atoms, and each level has a maximum number of electrons it can accommodate. The larger the atom, the more electrons it has, and these occupy levels starting nearest the nucleus and extend outward. Only the outer level of electrons can be affected by anything, as the outermost level protects the others.

An electron level that is at full capacity is stable and non-reactive; the noble gases are non-reactive because their upper levels are complete. However, a level that is incomplete is always looking to complete it, either by capturing other electrons (often through ionic bonding with other atoms, such as how hydrogen bonds with two oxygen atoms) or by giving up single electrons that exist in the highest level. In the latter case, once the lone electron disappears, that energy level essentially 'disappears' and the atom now has a stable electron shell.

* Technically, both gamma and x-rays are high-energy photons, and because of the double-slit experiment photons are simultaneously particles AND waves. This is known as wave-particle duality, No, I don't know how this is; like much of quantum physics, it simply is and you either accept it or you go mad.

In fact, it's now theorized  that all subatomic particles are waves to some extent. Electrons definitely have some characteristics of particles and some of waves, and at least one researcher believes that atoms are waves -- essentially, waves of matter.

TL;DR quantum mechanics is confusing. It's not truly important whether or not ionizing radiation is a particle or a wave, as it's bad for you regardless.

NEXT: Preventing Radiation Sickness for Dummies

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