P2 topic 11

Physics topic 3- about radiation

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  • Created by: Roseanna
  • Created on: 22-02-12 17:18

Types of radiation

There are three types of radiation. Alpha, Beta, and Gamma.

Alpha particles are helium nuclei. These are big, heavy and slow. They have a positive charge, as they contain two neutrons, and two protons. They are strongly ionising, as they are large, they bash into lots of atoms and knock electrons off them. Alpha radiation can be stopped by skin or paper, as they are not very absorbant.

Beta particles are quite small and fast. They have a negative charge, as they are electrons. They are moderately ionising, and penetrating, as they can be stopped by thin aluminium.

They are the opposite of alpha particles. They don't ionise, as they don't collide with atoms.They are very fast. They pentrate a long way into materials, as they can only be stopped by thick lead or concrete.

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How did Marie Curie die?

Marie Curie was born in Poland in 1867 and moved to Paris to study chemistry. She discovered two unknown elements, which she named polonium and radium. She won the Noble physics prize with her husband in 1903, and then again for chemistry in 1911.

Radium, now discovered, was a new 'wonder element', used for many different things. The exposure to radiation, was incredably, damaging, and many people became ill and died, and they didn't know why.

Marie Curie developed cancer in 1934 due to prolonged exposure to radiation. She died later.

Radiation can cause mutation to cells if it gets into the body. When you handle radioactive sources, you should use tongs and not point it at anybody. You should keep it in lead lined cases to stop alpha and beta radiation and weaken  gamma radiation with.

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Background Radiation

Background radiation comes from space, as cosmic rays, mainly from the sun. The Earth's magnetic field deflects most of these, and the ozone layer absorbs the majority of the rest. Natually occuring isotopes are found in food, air, building materials, and even the rocks under our feet. Radiation from human activity, such as dumped nuclear waste represents a tiny proportion of the total background radiation.

The level of background radiation depends on where you are. At high altitudes, you have more exposure to cosmic rays, which means commercial pilots have a higher risk of getting some types of cancer. Underground in mines exposes you to rocks.

The radon concentration in peoples houses vary depending on what type of rock the house is built on. High doses of radon gas can give you lung cancer. The higher the concetration, the higher the risk. There's a lot of debate over the risk of lower doses. Good ventilation systems are now installed in houses built in high radon areas.

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Half-life

The radioactivity of a sample always decreases over time.

Half life= The time taken for half of the radioactive atoms now present to decay.

A short half life means tthe activity falls of quickly, and visa versa.

You may be asked to work out half life in an exam, or read a graph of some results

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Uses of radiation

High doses of gamma rays can be directed carefully and at just the right doses to kill off cancer cells without damaging healthy cells. However, some damage is done to the healthy cells around the cancer, which can make the patient feel ill for a while.

Food and surgical instruments are sterilised using gamma rays. Things like fresh apples or plastic instruments can be sterilised without boiling, which often damages them. The food is not radioactive afterwards, so it's safe to eat.

A weak source of alpha radiation is placed in the decector, close to two electrodes. The source causes ionisation, and a current flows. If there is a fire then the smoke absorbs the radiation and the current stops, so the alarm sounds.

Certain radioactive isotopes and be injected into people and their progress around the body can be followed using an external dectector. Iodine-131 is absorbed by the thyroid to see wheather the thyroid gland is working. Isotopes taken into the body must be Gamma or Beta, and not Alpha, because otherwise they can't get out again. They should also have a very short half life, so they radioactivity inside the patient dissapears.

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Radioactive dating

Scientists can work out the age of fossils, rocks and archaeological specimens. By measuring the amount of a radioactive isotope left in a sample, and knowing it's half life, you can work out how long it's been around.

Carbon-14 makes up about one ten millionth of the carbon in the air. The same proportion is also found in living things. When the die, the C-14 is trapped inside, and it gradually decays with a half life of 5730 years.

However, this may not be totally accurate, as it relys on three things.

1. The level of C-14 in the atmosphere has always been constant
2. All living things take in the same proportion of carbon as C-14
3. Substances haven't be contaminated by a more recent source of carbon after they died.

Nobody can be 100% sure about all these things, so measuring error can affect the accuracy of results.

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Handling radioactivity safely

Lower doses of radiation tend to cause minor damage without killing the cell, which can give rise to mutant cells with divide uncontrollably. Higher doses kill cells completely, which causes radiation sickness if a lot of body cells are affected.

The extent of the harmful effects depend on two things.
1. How much exposure you have to the radiation
2. The energy and penetration of the radiation, since some types are more hazardous than others.

Outside the body, gamma and beta sources are the most dangerous. This is because they can get inside the delcate organs, whereas alpha particles cannot pentrate the skin.

Inside the body, alpha particles do their damage in avery localised area. However, beta and gamma radiation sources can pass straight out without doing much damage.

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Atomic structure

A nucleus contains protons and neutrons. Most of the mass of the atom is contained in the nucleus, but it takes up virtually no space. The electrons fly outside, which are negativly charged and even smaller.

The bigger number is the mass number, the number of protons and neutrons added together. The other number is the atomic number, which is number of protons.

Isotopes have the same number of protons but a different number of electrons. This means they have the same atomic number but a different mass number.

Most elements tend to have different isotopes, but only one or two stable ones. Unstable nuclei will decay and in the process give out radiation. This process is entirely random, and there is nothing you can do to make a decay happen.

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