Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: paul.fr on 24/03/2007 21:54:52
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How Many x-rays would you have to have over a year/life time to be exposed to unsafe levels of radiation?
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The total allowable radiation for people who work with radiation is 5 rem (Roentgen Equivalent Man) or 5000 mrem per year in the US. This number is based on risk estimates from data when radiation was not as well regulated for medical usage and from survivors of atomic bombs. If anything this is probably an estimate on the safe side (and actually radiation workers usually get way less than this- the average nuclear worker gets about 300 mrem above background.) This is total (which means whole body exposure, inside and out) and total is very different than local exposure. But let's start with 5 rem (5000 mrem) as the most you'd want to get- so how many x-rays can you have?
First you should subtract out the background radiation. The average American gets about 350 mrem (sorry, I only have data from the US).
That leaves you with 4650 mrem to go. Let's assume you spread these out over the course of the whole year (there is a difference between acute dosage and dosage spread out over time).
The following are all estimates- it of course depends on how "thick" you are:
So suppose you need chest x-rays. The chest is thicker and harder to get through than the extremities, so it requires a pretty hefty dose compared to say an arm x-ray. The dosage equivalent you get from a Chest x-ray is about 8 mrem- so you could get 580 chest x-rays every year before you get to your 5 rem.
If you had to have skull or neck x-rays, that causes a bit higher effective dose, 20 mrem, so you could only have 230 of those per year.
Lumbar x-rays are even a bit higher at 130 mrem, so you could only check your back out 35 times /year.
A whole-body CT scan is pretty high at 1,100 mrem so if you could find an insurance program willing to pay for it, you could only have 4 of those.
But there are other sources of radiation too- so say you want to fly across the pond- I think it's an 8-10 hour flight or so? That's 5 mrem, so you could only do that 930 times /year. Or you shouldn't spend more than 9300 hours in the air (unless someone invents time travel that'd be tough anyway).
Sit too close to the TV? Besides exploding penguins there are other problems. . . sitting 1 inch away from the TV for 2 hours will give you 1 mrem dose. Again, you couldn't sit that close all year and go over your 5,000 mrem safety target.
But remember, this is all statistical analysis, based on average populations. There are a lot of other factors involved- for example, our genetic background will make a difference in how likely we are to get cancer from radiation exposure. Therefore, we should minimize our exposure whenever possible (quit taking those x-rays for fun). It is really a risk- benefit type of decision- every time you get an x-ray you are increasing the risk - but sometimes, considering how small the risk increase is, that is worth it.
Colleen
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wow, thanks Colleen
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You're welcome!
Every year I have to take a radiation safety test and one question is "what is the total effective dose equivalent for people who work with radiation?" I always get it wrong because 5 rem seems incredibly high (for what I work with). So every year when I get that wrong I look up what would I have to do to get that dose- so I knew I could find the answer.
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so, how much radiation are "we" exposed to from our pc screens.....would it be the same as a tv?
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Here's another way of looking at it:
Procedure Effective Dose (mrem) = # of Cigarettes Smoked = Highway Miles Driven
Chest Radiograph 3.2 9 23
Skull Exam 15 44 104
Barium Enema 54 148 357
Bone Scan 440 1300 3200
from Idaho State University Physics Dept:
http://www.physics.isu.edu/radinf/risk.htm
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All the data I can find now for PC screens is pretty old. . .
So I'm going to assume it is the same as a TV screen- the point is that if you are sitting more than 2 inches away from the screen, you are probably fine (dosage goes down quickly with distance). However, this is only from the front of the screen, there are some arguments that it is worse from the back and side.
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....if you are sitting more than 2 inches away from the screen, you are probably fine (dosage goes down quickly with distance....
inverse square law? or inverse of inverse square! oh it's too early to think....
thank you any way, Colleen. [:)]
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Hi everybody!
I read that CAT scans expose you to much higher doses of radiation than simple and single x-ray 'pictures' [:o].
Do you have any data about this?
ikod
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"so, how much radiation are "we" exposed to from our pc screens?" is an interesting question. Many PC screens these days are LCD types and, unlike the old CRTs they have no prospect of genertaing Xrays (even the old ones were pretty well screened with lead glass). Of course, Xrays are not the onlt sort of radiation; there's naturaly occurring radioactive material to consider too. I think that 4 elements contribute the bulk of this. Carbon (13C produced by cosmic ray interactions with nitrogen high in the atmosphere and responsible for radiocarbon dateing) Uranium, Thorium, and Potassium. There's probably some potassium in the glass parts of this PC display but there's no reason to expect thorium or uranium. While there will be carbon it will have been derived from oil so any 13C will have decayed away while the prehistoric plants got converted to oil.
Overall the only source of radiation is from the potassium and there's not a lot of that.
On the other hand, I contain quite a lot of potassium and also a lot of carbon, some of which is 13C.
Overall I my pc monitor is probably exposed to more radiation from me than I am from it.
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I'll try my layman's concept and hope that a professional will correct me where I'm wrong. So, according to me:
Being exposed to radiation is a bit like having a picnic on a firing range. The bullets that don't hit you don't hurt you. With X rays, or high energy radiation in general, exposure recommendations have to do with the statistical likelihood of having one of the photons disrupt something important. And since we can't avoid them altogether, we accept a certain level of radiation as being within a natural range.
How'd I do?
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All about radiation Poisoning....which is NOT nice !! http://en.wikipedia.org/wiki/Radiation_poisoning
Great thread Paul with great posts !
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The problem I see here is that much of this is about whole body exposure. From what I had believed, the biggest problem with radiation is the damage to bone marrow (not saying there is no risk elsewhere, but the risk to different parts of the body would be different, and damage to stem cells would probably be more damaging than damage to highly differentiated cells). Am I wrong with this?
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All about radiation Poisoning....which is NOT nice !! http://en.wikipedia.org/wiki/Radiation_poisoning
Great thread Paul with great posts !
are you saying my other threads were not great! or just general comment about by attire? [;D]
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All about radiation Poisoning....which is NOT nice !! http://en.wikipedia.org/wiki/Radiation_poisoning
Great thread Paul with great posts !
are you saying my other threads were not great! or just general comment about by attire? [;D]
That's right....all your other threads are crap !!... [;D]
*it has been a long night...I'm allowed the absence of social graces*
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*it has been a long night...I'm allowed the absence of social graces*
I thought the nights were getting shorter [:)]
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All about radiation Poisoning....which is NOT nice !! http://en.wikipedia.org/wiki/Radiation_poisoning
Great thread Paul with great posts !
are you saying my other threads were not great! or just general comment about by attire? [;D]
That's right....all your other threads are crap !!... [;D]
*it has been a long night...I'm allowed the absence of social graces*
oh, just checking...
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All about radiation Poisoning....which is NOT nice !! http://en.wikipedia.org/wiki/Radiation_poisoning
Great thread Paul with great posts !
are you saying my other threads were not great! or just general comment about by attire? [;D]
That's right....all your other threads are crap !!... [;D]
*it has been a long night...I'm allowed the absence of social graces*
oh, just checking...
oops...sorry Paul...hope I didn't offend.
My apologies if I did !
..same to you George....sorry If I upset you recently.
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All about radiation Poisoning....which is NOT nice !! http://en.wikipedia.org/wiki/Radiation_poisoning
Great thread Paul with great posts !
are you saying my other threads were not great! or just general comment about by attire? [;D]
That's right....all your other threads are crap !!... [;D]
*it has been a long night...I'm allowed the absence of social graces*
oh, just checking...
oops...sorry Paul...hope I didn't offend.
My apologies if I did !
..same to you George....sorry If I upset you recently.
no problem...i note i did not get any flowers though!
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The problem I see here is that much of this is about whole body exposure. From what I had believed, the biggest problem with radiation is the damage to bone marrow (not saying there is no risk elsewhere, but the risk to different parts of the body would be different, and damage to stem cells would probably be more damaging than damage to highly differentiated cells). Am I wrong with this?
You're exactly right, George.
Highly replicating cells are in the bone marrow (Haematopoietic stem cells), in the gut and respiratory tract.
For years I've been asking myself (do you say that?) whether blood stem cells hide in the bone to be partially protected from radiation by calcium molecules...
Ikod
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You might want to look into a therory called hormesis. It's a bit contraversial but it says that low level exposure is beneficial because it stimulates the body's defense mechanisms.
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Hi B.Chemist,
I think I am just fine with the 'background noise' of natural radiation, radon, cosmic radiations and UltraViolet rays to get older and crappier!
By the way, did you read that in Chernobyl there were 59 dead people in the end?
Not to mean that it wasn't an horrible disaster, but I thought that thousands had succumbed.
Talking of correct information!
ikod
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Yes, I saw that and I think it was mainly the firefighters who died as a result of trying to solve a problem that they hadn't caused and knowing that it might kill them. It seems only fair to me to point out that while the Soviet Union had some really bad polictics it had some truly fine people.
BTW, I seem to recall that some recent research on "conan the bacterium"
http://en.wikipedia.org/wiki/Deinococcus_radiodurans
has cast doubts on the model of radiation damage too.