Why does the size of a radioactive sample matter?

[localrob]

We are taught that the three basic types of radioactive particles are alpha, beta, and gamma. I know there are other particles, but for now I'm just focusing on these.
Alpha particles don't penetrate skin, beta particles do and can cause burns, and gamma rays are very powerful.
But my chem book also says that the source of the radiation also determines how dangerous it is. But I don't understand why. Isn't an alpha particle and alpha particle no matter where it came from?
Also, why is it safe to handle radioactive isotopes that are shooting our gamma rays?
Flinn Scientific sells radioactive sources of Po-210, Sr-90, and Co-60
http://www.flinnsci.com/store/Scripts/prodView.asp?idProduct=17227
How is it that they are "safe" even though it's a gamma ray?

 

[fatra2]

Hi there,

You are right about the three types of decays (as a first approach). For the rest of you comment, there are some specifications to be added. First, you must know the difference between these three types of radiation: alpha is the emission of a He2 nucleus, beta is the emission of electrons, and gamma is an electromagnetic radiation.

Now, if you are only talking about external radiation (radiation coming from outside our body), then the gamma radiation has the most penetration "power". From a radioactive source (of the type you mentioned) standing nearby, most alpha particles will be absorb in the slab of air, which beta particles will be stopped in the first layers of skin, which into very high intensity can cause some degree of burning.

Of course, and that goes for the three types of decay, the penetration "power" will depend greatly on the particles' energy. Therefore, the more energy the particles have, the further they will penetrate. Therefore, it is also true to say that the energy of the decay will set the level of "danger" of exposition.

Hope this helps you a bit more. Cheers

 

[AJ Bentley]

why is it safe to handle radioactive isotopes that are shooting our gamma rays?

It isn't.

'Safe' is one of those words that the public uses with abandon where science treads carefully.
Is it safe to eat arsenic? What about salt? is that safe to eat? King John famously died from eating Lampreys.

A small radioactive source of any type of radiation might be considered safe if it's weak enough - granite is radioactive but people make houses out of it in some areas.

The radioactive sources used in smoke detectors are deemed 'safe' but it you collected a bunch of them together you could literally be storing up trouble.

Then again, it depends what you do with the material. Alpha rays are stopped by air so they are usually safe(ish) - but if you ingest one, inside your body it would be very dangerous.
Since Alpha particle sources are very often found as a powder, they can be very risky to handle
On the other hand, gamma ray emitters are often metals and easier to handle safely.

Gamma ray sources are often sold stored in lead containers, where they are 'safe' until you take them out. Provided you handle them carefully with proper precautions they stay safe.

 

[localrob]

Thanks for the replies.
I am only talking about external radiation. Aside from inhaling dust, I doubt anyone would eat a sample. But this does bring up the question of food absorption. Maybe I'll make a new thread for that.

A small radioactive source of any type of radiation might be considered safe if it's weak enough

Why does the size of the sample matter? Is it that a larger sample would be shooting out more gamma rays than a smaller one? Or when you say weak are you referring to the type of decay.

gamma ray emitters are often metals and easier to handle safely.

Easier to handle safely because they aren't powders and less likely to be ingested?
But the gamma ray danger is still there right?

 

[fatra2]

Hi there,

Why does the size of the sample matter? Is it that a larger sample would be shooting out more gamma rays than a smaller one? Or when you say weak are you referring to the type of decay.

The size of the sample means its activity (Bq). It has nothing to do with the actual physical size of the sample, and not the type of radiation emitted.

Once again, for the gamma emitters, you should not see it as solid/liquid/gas form, but as penetrating "power". To protect the worker from intense gamma radiation, the source are often put into cask, seal tight and with great shielding. These casks make it easier to handle the sources inside, rather than water completely contaminated with tritium.

By the way, you really have to understand that the danger of radiation is not into the type of decay, but into the activity and the energy. The more radiation you are confronted to, the greater the danger.

Cheers