Physics Section 7: Radioactivity and Particles (COMPLETED) (A (Units…
Physics Section 7: Radioactivity and Particles (COMPLETED)
becquerel (Bq) (measure of reactivity)
Structure of an atom
Protons (+) and neutrons are in the nucleus of an element.
Electrons (-) orbit on shells (or orbitals.)
The atomic mass of an element (the number written above an elements symbol) is the number of protons + the number of neutrons.
The atomic number is the number of protons. This will equal the number of electrons in an element.
An isotope of an element is one with the same configuration of protons and electrons but a different amount of neutrons.
The term ionising means they damage cells.
alpha particles, beta particles and gamma rays are all types of radiation.
Radiation is emitted from the nucleus of an atom that is unstable (in a way it is too full and trying to off load.)
Types of radiation
alpha particles are two neutrons and two protons; also known as a helium nucleus. Alpha particles could not penetrate a piece of paper if they tried.
Alpha makes an atom go down 2 on its atomic number and four on its atomic mass: it will change to the element with a the atomic number 2 less than it was.
Beta particles are electrons, they are emitted when a neutron turns into a proton and an electron. It won't penetrate aluminium.
When beta radiation occurs a neutron splits into a proton and a electron, the electron is emitted from the atom, but the proton stays in the nucleus: this changes the atomic number up one, the element becomes that with the next atomic number up. The mass number remains the same as a neutron- mass 1- became a proton- mass 1.
Gamma rays are a type of electromagnetic wave, they are often emitted alongside the other types of radiation. Gamma cannot penetrate lead.
Gamma rays have no specific effect on the atomic or mass number.
Nuclear equations show the atoms atomic number and atomic mass on one side and the radiation (with mass and number) and the new element (with mass and number.)
Radiation imprints on camera film.
A Geiger-Muller detector (or GM counter) beeps in the presence, the more radiation the more frequent the beeps.
There are so many sources of background radiation: different radioactive materials are in the environment.
An example of this is boron in the soil which emits radiation; cosmic rays from space are radioactive too.
The radiation emitted by a radioactive source will decrease over time. Radiation is measured in becquerels.
A half-life is the time it takes for the radiation emitted by a source to decrease by half.
Half-lives are different for different sources of radiation.
a radioactive source is put into a system (like a piping network), it will build up where there is a blockage a be detected, showing where a problem is.
a radioactive source is put into a body and will build up at a blockage so an area of problem can be detected
radiation is used to destroy unwanted cells (cancerous cells.)
aka carbon dating. The amount of radiation from an object is measured, the half life of the carbon is then used to see how old the object is. Archaeologists use this to tell the age of an object.
Radiation can cause mutations in living organisms
radiation can damdge the stucture of a cells DNA, when the cell replicates the changes (mutation) will be passed on; this can be how cancer is caused.
can damage cells and tissue:
atoms can be change by radiation, this prohibits them functioning properly, this can mean cells and so tissue are damaged.
The problems arising in the disposal of radioactive waste
this waste emits radiation that, as shown above, can be dangerous. If the waste is put into water it can poison ecosystems, similarly with land. Radioactive waste tends to be buried under the ground; with the thinking that when it is much less harmful it can be dug up and disposed of.
Gold Foil Experiment
Geiger and Marsden
Alpha radiation was beamed at a sheet of gold foil,
a sheet of zinc sulphide surrounding the foil showed where the alpha particles ended up;
a few went straight through, many were deflected at angles, some were deflected straight back.
The nuclear model of an atom
a central nucleus with positive protons and neutral neutrons surrounded by orbiting negative electrons.
the 'plum pudding' model
a positive sphere contained negative electrons dotted inside.
If this was true the alpha particles would have gone straight through the sheet of gold and all come out the other side.
some were deflected at different angles,
this showed that the positive alpha particles were being repelled by a positive charge and others were going through the space between the charged areas.
The faster they hit it the faster they were repelled. This is where the idea was formed of a nucleus and orbiting electrons.
Uranium-235 has a large nucleus that can be split in two when a neutron is fired at it.
This releases a large amount of energy as the products created move rapidly.
When a neutron is fired at a uranium-235 nucleus, it splits in two. This leaves two 'daughter' nuclei. At the same time, neutrons are emitted.
When split by a neutron, uranium-235 releases neutrons (as well as splitting in half.) These neutrons can then go on to hit other U-235 nuclei which then do the same thing, this will be repeated in a chain reaction.
In nuclear power stations, nuclei are split by having neutrons fired at them, these release other neutrons as well as a large amount of energy.
The energy is used to create electricity, and the radioactive by-products are disposed of.
Control rods can absorb neutrons.
If there are two many neutrons the chain reaction could get out of control, so the control rods are lowered in to the reaction to absorb some neutrons and control the reaction.
The moderator slows neutrons down so that they are at the right speed to split nuclei,
the moderator is usually water.