Radiation Q&A

Page - April 9, 2011


Dose = total amount of radioactivity absorbed by the body over a certain period.
Measuring units:
− microSievert (µSv)
− milliSievert (1 mSv = 1000 uSv)
− Sievert (1 Sv = 1000 mSv).

Dose rate = the amount of radioactivity absorbed per hour, expressed in
− microSievert per hour (µSv/h)
− milliSievert per hour (mSv/h =1000 µSv/h)

1. What is nuclear radiation?

There are several types of radiation: heat, light, microwave and nuclear. Nuclear radiation can occur in different forms (see question 5 below). The common characteristic of all types of nuclear radiation is that it is so energetic that it can destroy molecules. Heat and sunlight are unable to do such damage.

2. Why is nuclear radiation dangerous?

Radiation (from here, we will use the word ‘radiation’, to mean nuclear radiation) can destroy molecules, including the molecules in our bodies. When DNA-molecules in our cells are destroyed, this creates a risk of developing cancer. Radiation is therefore called carcinogenic: it causes cancer. The specific problem with radiation, compared to other carcinogenic substances (i.e. chemical etc.) is that there is no 'safe dose' below which there is no effect (see question 9).

3. What is the origin of radiation?

Radioactive substances emit radiation. These substances are made of non-stable atoms that disintegrate into stable atoms. During disintegration the atom emits energy in the form of radiation. This process is also called radioactive decay.

4. What is radioactivity?

The radioactivity of a substance is the indicator for the amount of disintegrations of atoms in the substance. When there is a lot of radioactivity in a substance, the substance is called very radioactive, and there can be two reasons for this:
1.The substance has many radioactive atoms within it
2.The radioactive atoms in this substance decay very quickly.
A combination of both makes for the most radioactive substances.

5. What kind of radioactive atoms exist?

Three categories of radioactive atoms exist: gamma-emitting atoms, beta-emitting atoms, and alpha-emitting atoms, resulting in three types of radiation: gamma, beta and alpha radiation. Most radioactive atoms send out a combination of these three types of radiation, with one type being the most dominant.

6. What is the difference between gamma, beta and alpha radiation?

Gamma radiation is a 'wave', just like light, but with more energy. Beta radiation consists of small particles (electrons) travelling at an incredible speed. Alpha radiation consists of big particles (two protons and two neutrons altogether), also travelling with incredible speed.

More important is the difference in 'destructive power'. Alpha radiation has the most 'destructive power' and gamma radiation the least. Fortunately, radiation with the greatest 'destructive power' does not travel far, because it loses energy rapidly. Alpha particles, for instance, do not penetrate through skin, or even through a piece of paper.

7. What is radiation dose and how is it influenced by different radiation-types?

The radiation dose is the amount of energy that the radiation gives to the body. The dose is the indicator of the risk, thus a high dose is a high risk. A radiation dose is received when radiation travels through the body and hits cells and organs. This explains why alpha-emitting atoms are not dangerous outside of the body; the radiation coming from them doesn't even enter the body. However, if, for instance, a plutonium atom is taken up in an organ , the alpha-radiation it gives off in the form of large particles will create significant damage in the body. The radiation can have an impact on everything it encounters (such as DNA or cell membranes) and therefore result in a relatively high dose.

Gamma radiation travels right through your body, but the chances of it 'hitting' something are quite small and therefore does not deliver such high doses. However all gamma- emitting atoms, whether inside or outside of the body, add to the radiation risk.

8. What is radioactive contamination?

Something/somebody becomes contaminated when radioactive elements (particles varying in size, but sometimes as small as a few atoms) are present on it (external contamination) or in it (internal contamination). Remember that radioactive elements behave like all elements: they can end up anywhere: dust, food, furniture, humans etc. Like normal 'dirt' most of the contamination is washable, after which the person/material is called decontaminated. Internal contamination is a bigger problem: both because the risk from alpha-emitting atoms is present and because it’s more difficult to remove.

9. What is a safe dose-limit?        

As stated in the beginning: there is no safe dose of radiation. Next to the need for keeping the radiation dose as low as possible, internationally accepted limits are set for doses that occur in addition to background or natural radiation.  For members of the public  this is set at 1 milliSievert per year. For nuclear workers, it is 20 milliSievert per year. To compare, the global average for natural radiation doses is 2.4 milliSievert per year.