Physics 2.5

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  • Created by: Laura
  • Created on: 13-01-13 10:15

What is the structue of an atom?

The structure of an atom is a center nucleus, made up of neutrons and protons, surrounded by shells of electrons. In the first shell there can be up to 2 electrons, in the second and third up to eight electrons, and above this up to 18. Also in an atom the number of protons will be equal to the number of electrons.

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What are the relative masses in an atom?

Proton = 1

Neutron = 1

Electron = Almost 0

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What are the relative charges in an atom?

Proton = +1

Neutron = 0

Electron = -1

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What's the difference between atoms and ions?

Atoms are neutral because they have equal numbers of protons and electrons, so equal numbers of positive and negative charges. Ions are atoms which have lost or gained electrons and so have a charge. If an atom loses electons it will have more protons so a positive charge, and if an atom gains electrons it will have more electrons than protons so a negative charge.

The difference between atoms and ions is that atoms are neutral and ions have a charge.

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What is an isotope?

An isotope is a version of the original element which has the same number of protons and electrons but different a different number of neutrons, so a different mass number.

For example the element carbon has 6 protons and 6 neutrons so an atomic number of 6 and a mass number of 12. An isotpe of carbon is carbon-14 which has 6 protons but 8 neutrons, meaning that it has the same atomic number of 6 as the element carbon, but it has a different mass number of 14 rather than 12 as it has 2 more neutrons than the element carbon.

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How do you find the mass number in a diagram?

The mass number of an atom is the number of protons add the number of neutrons, so when looking at a diagram you only need to look at the nucleus, as this is where you get the protons and neutrons. Then you simply add up the number of protons and neutrons you see to get the mass number. If the drawing is not clear then you can work out the number of protons by counting the number of electrons in the shells as the number of protons and electrons in an atom is always the same.

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What is radioactive material?

Radioactive material is a material where the nuclei in the particles is unstable and and may start to decay, causing it to admit radiation.

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What is an alpha particle?

An alpha particle is two protons and two neutrons (the same as a helium nucleus).

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What is a beta particle?

A high energy (fast moving) electron.

However it is not an electron lost from the shell, it is an electron from the nucleus which is formed when a neutron splits into a proton and electron.

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What is gamma radiation?

A high energy (high frequency) electromagnetic wave.

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Can you change a substances radioactivity?


Nothing can be done at all.

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What is background radiation?

Some radioactive detectors register radiation even when there are no radioactive substances near by because of background radiation. Background radiation is what is says in the name, radiation in the background and doesn't pose any immediate danger.

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Where does background radiation come from?

Natural Sources:

  • Radon gas rom the ground
  • Buildings and the ground
  • Food and drink
  • Cosmic rays

Artificial Sources:

  • Medical procedures/waste/processes
  • Nuclear power and weapons testing
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What causes a higher exposiure to BGR?

BGR = Background Radiation

Where you live can cause a higher exposiure to background radiation. For example living in cornwall can cause a higher exposiure because there is lots of granite and granite releases radon.

What activities you do can cause a higher exposiure too. For example long haul flights increase your exposiure to cosmic radiation because there is less atmosphere to absorb the radiation and the aluminium body of a plane doesn't protect you from the radiation.

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What are the nuclear equations?

The nuclear equations are equations to show the decay of a single alpha and beta atom.

They are similar to chemical reaction equations as they have to start and something and become something else but no material can be lost, so the equations must be balanced.

However they differ because they produce either alpha or beta radiation.

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What is the nuclear equation for alpha decay?

[219/86]Rn -> [215/84]Po + [4/2]a (

This is an equation for alpha decay because the original atom loses two protons and two neutrons, which go to make the alpha radiation (two protons and two neutrons) and a new atom.

To make sure this equation is balanced as you take a mass of 4 (from the two neutrons and two protons) away from the original atom, the mass number of the atom you create must be 4 less. As you take away 2 from the atomic number (from the two protons) you need to take 2 from the atomic number of the atom you create.

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What is the nuclear equation for beta decay?


This is an equation for beta decay because the mass number of the new atom stays the same (as the neutron which is lost becomes a proton and electron and the proton has the same mass as the neutron), the atomic number of the new atom increases by one (because the new proton adds 1 more positive charge), and finally the equation produces beta radiation which is the high energy electron.

To balance this equation you have to keep the mass number the same for both the decaying atom and the new one as the neutron lost becomes a proton so no mass is lost. For the atomic number in the produced atom it increases by 1 because the new proton adds a charge of +1, this is balanced out by the -1 charge of the electon.

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What is the ionising power of radiation?

The power of radiation to break molecules into ions.

Relatively alpha radiation is the most ionising, then beta radiation and finally gamma radiation is the least ionising.

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What is the penetration of radiation?

The penetration of radiation is how easily the radiation can be stopped or absorbed by a substance.

Alpha is the least penetrating and can be stopped by paper or skin. Then it is beta which can be stopped by aluminium. Finally gamma is the most penetrating and can be stopped by lead or many metres of concrete.

alpha radiation cannot pass through humans, beta is stopped by aluminium, gamma by lead  (

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What does the range of radiation mean?

The range of radiation is how far the radiation can travel before it loses its power and is completely absobed.

In air alpha has the lowest range of only a few centimetres, then it is beta which can travel a few metres. Finally gamma has the highest range in air of a couple hundred metres.

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Can radiation be deflected?

Yes, alpha and beta radiation can be deflected by electric and magnetic fields, but gamma radiation can't. This is because alpha and beta radiation has a charge so is attracted to either the positive oor negative, but gamma radiation is neutral so isn't deflected.

As alpha radiation has two protons it has a positive charge of two. This means that in electric and magnetic fields it is attracted to the negative side. Beta radiation is a high energy electron so it has a negative charge of one. This means that in electric and magnetic fields it is attracted to the positive side.

The mass and charge of the radiation effects how much the radiation will be deflected in electric and magnetic fields. This is because the heavier the mass the higher energy will be needed to deflect the radiation, so as alpha radiation has a mass of 4 and beta radiation a mass of almost 0, beta radiation will be deflected more as it is ighter. The charge of the radiation also effects how much the radiation will be deflected (as well as which way the radiation will be deflected) as the higher the charge of the radiation the more it will be deflected.

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What are the uses of radiation?

In Medicine:

  • Sterilizing medical instruments (as the ionising power of radiation destroys any molecules on the instruments)
  • Killing cancer cells (as the ionising power of radiation if concentrated on the cancerous cells can destroy them)
  • In chemical tracers to help with medical diagnosis (radioactive chemicals can be put into the body to release radiation and as the chemical concentrates on the diseased part of the body radiation detectors can find where the diseased part of the body is as this is where the radiation will be coming from. Beta or gamma radiation is used for this as its too penetrating to be absorbed into the cells in the body and do more damage)


  • Monitering the thickness of materials (radiation can be passed through a material and if too little is detected on the other side it is too thick, if too much radiation is detected then the material is too thin)
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What are the dangers of radiation?

Radiation is dangerous because of its ionising power which, absorbed by living cells, can damage them, if the DNA is effected then cause the cell to become cancerous or high levels of radiation can kill the cells completely.

Inside of the body alpha radiation is the most dangerous because it is absorbed by the cells causing them damage, whereas beta and gamma radiation will penetrate through the cells and out of the body without causeing too much damage.

Outiside of the body gamma and beta radiation are the most dangerous as they can penetrate through the skin and be absorbed (so do damage to) thw cells within. Whereas alpha radiation can't penetrate the skin so does not do damage to the cells within.

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What is half-life and count-rate?

The half-life of the radioactive isotope is how long it takes for half the nuclei of a piece of radioactive material to decay. This is measured by the count rate, which is the number of counts for radioactive emissions for a given period of time. For the same particular isotope the half life always stays the same because as the count rate decreases by half after each half life, the length of the half life stays the same.

The half life does not depend on the initial number of nuclei as more nuclei will have a faster emission and fewer nuclei will have a slower emission, so the half life will not change. It also doesn’t depend on the initial count rate because a higher count rate will be faster to reduce, and a lower count rate will be slower so the half life stays the same.

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Physics 2.5

  • Radiation
  • Uses Of Radiation
  • Dangers Of Radiation
  • Atomic Structure


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