Physically, what does it mean when people or objects are contaminated with radiation? Is it because they actually carrying heavy metal particles?
[Physics] How does “contamination” through (radioactive) radiation work
radiation
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The dose that kills a tumor is deliberately aimed at that tumor. If, instead of using a collimated beam, you put a person in a wide beam for radio "therapy", you would be treating their entire body as a tumor and kill them.
The dose in RT is computed locally - "this" part of the body (these grams of tissue) absorbed (were exposed to) "this many" Joules of ionizing radiation .
You can't simply average local dose over the entire body - although blood perfusing the irradiated area will carry some damaged cells to other parts of the body, the majority of the tissue / cells in the body get a dose below the damage threshold - and the body is pretty good at repairing itself.
Note however that some organs are much more sensitive than others - there are tables of acceptable maximum dose (or 'dose sensitivity') that show that organs involved in reproduction (gonads) and blood production (bone marrow), and organs with a low ability to self-heal (spinal cord, brain, eyes) or that are acutely vital (heart), should be spared as much as possible during RT.
Having said that, RT does carry a risk - but when a patient is already diagnosed with cancer it is better to take away as much of the "known bad" tissue and take the risk of creating the potential of other mutated cells, rather than leave the cancer alone. At least that is the judgment that oncologists make on a per case basis when they refer for RT.
I will look up some references...
When you put the pot on the stove, the heat from the stove is somehow getting to the pot, which gets hot.
- The pot and the stove are obviously in contact with each other. Therefore conduction plays a role here. If you have an old pot, with a warped bottom, it will heat up slower, because the contact surface between pot and stove is smaller.
- When you hold your hand over the stove (not touching it), you can feel the heat. The air above the stove is heated and because it is a gas, moves upward. This is convection. The bottom of the pot and the surface of the stove are not 100% flat. That's why there will be little pockets of air underneath the pot, even if you place it on the stove.
- If you heat up the stove as much as you can, it will glow red. This is a visible sign of radiation. I'd assume that even if not visibly glowing, the stove radiates heat, too. In those areas where the stove and the bottom of the pot are not in contact, radiation transports heat from the stove to the heat.
As you can see, all 3 kinds of heat transfer are involved. Conduction certainly does the most part, which is why you want to have pots with flat bottoms, to make best contact with the stove.
Best Answer
There are two distinct ways for previously non-radioactive material to become radioactive.
Contamination refers to any behavior where existing radioactive material sticks to or is incorporated in an previously non-radioactive object or body (this can include a tract of land). This requires you to go to where there is mobile radioactive material or for that material to come to you.
This is the more common way.
Activation refers to materials in a body getting transmuted by exposure to radiation. Most kinds of ionizing radiation can cause activation under the right circumstance, but it is usually a very slow process. Rare outside of labs and nuclear power facilities.
In the case of a nuclear power facility accident the scary issue is almost entirely contamination where the containment is lost material from the core (and nearby activated structural material, but mostly the core) which get carried into the wider environment by the action of water and steam. Chernobyl was special because the antique design of the reactor allow a significant conventional explosion to launch portions of the core out of the building directly.