Posts Tagged ‘Radiation’
So I wrote about ionizing radiation dose a couple of weeks ago. But it wasn’t until today that I found a good, visual rendering of the equivalences between radiation doses from different activities. Randall Munroe, the delightful mind behind XKCD, has made a chart of common radiation doses, standards, and equivalences. It’s definitely worth a look.
Now that we have a basic idea of what ionizing radiation is, let’s talk about what it does to you. Today we will focus on acute radiation syndrome (also known as radiation sickness and radiation poisoning). This is the sort of thing that occurs due to short-term, high-dose exposure to ionizing radiation, such as that from nuclear weapon discharge or nuclear industrial accidents. We’ll take a look at the long term effects and generation of neoplasms in a future post.
The precise nature of radiation syndrome varies by dose, radiation type, tissue exposed, and duration of exposure. These factors are all rolled together in an SI unit called the Sievert (Sv), which is known as the dose equivalent. The measure of dose is known as the Gray (Gy), but that raw information doesn’t tell us much about biological effect. So the Gray is transformed as a function of quality factor Q which is the ratio between the effects of gamma radiation and the effects of your radiation type of interest (e.g. Q[gamma]=1, Q[alpha]=20). There is a further factor called N which relates the effects of radiation based on differences in species and tissue, for simplicity’s sake N[human]=1. The final product of this calculation is the dose equivalents in Sv, which gives us useful info on biological effect. The units of Gy and Sv are J/kg and because time is an important factor we usually see Gy and Sv expressed over seconds, hours, or days. Both the Gy and Sy deal with pretty large amounts of radiation, so it is much more likely to see quantities expressed in milli or micro versions (for instance at one point the ongoing Fukushima I accident peaked at 400 mSv/hour).
Certain types of (particle based) ionizing radiation are of greater or less concern depending on the location of their source. For instance, alpha and beta-particles have low penetrance. They can cause surface skin burns, but generally can’t penetrate far enough to cause excessive internal damage. However, an internal source of alpha or beta-particles is a more dire circumstance because just as they do not have the penetrance to enter the body, they cannot leave. This is why contamination of food, water, and dust is such a concern. High penetrance radiation, like neutron radiation or (photon based) gamma-rays is less affected by location of source.
The symptoms of radiation syndrome begin at 1 Sv and at about 8 Sv they become invariably fatal. Not all symptoms present at once, and it can take up to four weeks for the full effects of minor radiation poisoning to be seen. Usually the time between exposure and onset decreases as the Sv increase (with there being very little delay at the 8 Sv level). The immediate symptoms include: nausea and vomiting, diarrhea, headache, and fever. These occur within ten minutes to six hours after exposure. In the next one to four weeks (or sooner in the case of extremely high doses) the victim may suffer: fatigue, hair loss, bloody vomit and stools, infections, poor wound healing, low blood pressure, dizziness, and disorientation. Usually there is also some level of skin redness, peeling, ulceration, and possibly necrosis.
All of these symptoms result from a disturbance in cellular chemistry. As we discussed last time, ionizing radiation generates ions (particularly reactive ions known as free radicals). The cell is an impressive machine dedicated to controlling multiple ongoing, complex chemical reactions. So we can see why the spontaneous introduction of new reactants would be bad, and why a high concentration of them at one time would be very bad. Essentially cells will be faced with a critical failure of their functions and this will lead to massive cell death. And this is not going to be the pretty, well-controlled cell death either (no, that isn’t facetious, remind me to tell you about the pathways of cell death sometime). In most cases the immediate cause of death is opportunistic infection due to a failure of the immune system caused by the destruction of large amounts of bone marrow; however, in extreme cases the victim just basically falls apart at a cellular level.
As mentioned, these are only the acute affects of radiation exposure, even if you survive these, there are still the long-term consequences of cell damage to look forward to.
This is what is at stake in Japan. This is what a whole host of brave rescue workers are risking to try to keep everyone else safe. Show a little compassion and (if you can) a little support.
Sources & Further Reading
With an eye towards discussing the effects of ionizing radiation on humans, particularly with respect to cancer, I thought it would be best to write up a quick and dirty reference post on what exactly ionizing radiation is. This is a good example of my continuing struggle to find an appropriate voice for this blog. I never really know what I can safely assume my readers know. So, let’s (hopefully) review:
Ionizing radiation consists of particles or photons capable of inducing detachment of electrons from their atoms resulting in free electrons and a corresponding positive ion. There are five broad types of ionizing radiation: alpha-particles, beta-particles, neutron radiation, gamma rays, and X-rays.
- alpha-particles: result from radioactive decay, and consist of two protons and two neutrons. They are directly ionizing.
- beta-particles: result from radioactive decay, and consist of either an electron or positron. They are directly ionizing.
- neutron radiation: results from nuclear fission, and is simply a free neutron. They are indirectly ionizing as they have no charge themselves, but can collide with and excite charged particles that then directly ionize.
- gamma rays: are high frequency photons emitted to right the energy of a decayed atomic nucleus. They are also indirectly ionizing as they are chargeless wave-packets that when absorbed can cause electron expulsion which then ionizes directly.
- X-rays: kind of overlap with gamma rays. They are high frequency photons. The only major difference is their origin.
The ionizing capability is dependent on the energy of the individual unit (particle or photon) interacting with the atom (this is why high frequency electromagnetic waves are ionizing and low frequency are not). Thus, high energy, low concentration radiation can still have an ionizing effect.
As we will discuss next time, it is generally the chemical characteristics of the resulting ions that cause damage in cell physiology and DNA.