# Gamma rays more dangerous?

#### pivoxa15

1. Homework Statement
Why are gamma rays potentially more dangerous than either alpha particles or beta particles?

2. Homework Equations
none

3. The Attempt at a Solution
Is it because gamma rays travel more distance before ionising matter so when a gamma ray is fired at you, it could get well inside your body and damage your internal cells. Whereas alpha and beta particles, even though carry more energy, ionises much more quickly, without travelling far so it may just damage the outer parts of your body which consists of dead cells anyway.

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#### Hootenanny

Staff Emeritus
Gold Member
Gamma rays are more dangerous outside the body for precisely the reasons you state. Alpha particles are 'stopped' if you like by a few cm of air, so unless you are close to an alpha emitter, very few (if any particles are going to reach you). Once in the air, alpha particles can gain electrons and become helium atoms once more. Beta particles have a much higher energy than that of an alpha particle and thus are considered more penetrating. That said, they usually only penetrate a cm or so into tissue so damage is usually limited to skin and eyes; beta particles can be shielded by a thin sheet of metal. Gamma rays on the other hand are EM waves and cannot be 'stopped'; shielding can be used to reduce the intensity of the wave but can never completely negate the radiation. Therefore, gamma rays can pass through your body depositing energy in your tissues are it propagates.

However, inside body tissues, alpha radiation is by far the most dangerous since it is highly energetic and has a strong ability to ionise other atoms. If memory serves correctly (Medical Physicists chip in here) alpha radiation deposited 20 times more energy in body tissues that gamma or beta radiation. So if alpha particles actually reach you (or worse are inside your body close to your vital organs) they are going to deposit large amounts of energy in your tissues; thus causing damage.

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#### pivoxa15

What is 20? What units should be attached. What do you mean by deposit large amounts of energy? You mean they will convert their kinetic energy to kinetic energy in your cells via collision hence damaging your cells.

#### Hootenanny

Staff Emeritus
Gold Member
What is 20? What units should be attached.
Sorry, typo, I should have said 20* times more, I've corrected this in my post. The unit of the measure of absorption in human tissue is the gray.
What do you mean by deposit large amounts of energy? You mean they will convert their kinetic energy to kinetic energy in your cells via collision hence damaging your cells.
Yes, this can cause some cell damage. However, I should have mentioned in my previous post that it is the ionising ability of alpha radiation which causes the more serious effects such as mutations when it interacts with a cells DNA (I also seem to remember from somewhere that alpha radiation causes around 100* times more chromosome damage than gamma or beta). Mutations can cause cancer and/or sterilisation and other effects. Since, the alpha particle has a large charge (twice that of a better particle) and a large mass it interacts with electrons in atoms strong, thus ionising further atoms.

And I do apologise, I'm not making a very strong case for gamma rays to be the more dangerous form of radiation. However, your answer is essentially correct; the key point is that no matter how much shielding you put in place some gamma radiation will still penetrate it (although it will be significantly reduced), you can never completely 'stop' gamma rays since they are EM waves.

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*I'm recalling these figures from (a rather unused) memory, so I wouldn't quote these numbers in your answer without a reference.

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