7. Radioactivity And Particles Flashcards
(16 cards)
understand that a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei
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.
What is the role played by the control rods and moderator when the fission process is used as an energy source to generate electricity?
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.
understand that the fission of U-235 produces two daughter nuclei and a small number of neutrons
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.
What is ‘fission’?
An atom contains protons and neutrons in its central nucleus. In fission, the nucleus splits, either through radioactive decay or because it has had a neutron fired at it.
Two daughter nuclei are formed which then go on to split again
describe Rutherford’s nuclear model of the atom and how it accounts for the results of Geiger and Marsden’s experiment.
What are the factors which affect the deflection of alpha particles by a nucleus?
Rutherford’s nuclear atom: a central nucleus with positive protons and neutral neutrons surrounded by orbiting negative electrons. ( how we view it today)
Before the Geiger Marsden experiment, the ‘plum pudding’ model of an atom was believed: 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.
What actually happened was that 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.
Charge and speed affect the deflection of alpha particles by a nucleus.
describe the results of Geiger and Marsden’s experiments with gold foil and
alpha particles
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.
describe the uses of radioactivity in…
medical and non-medical tracers
Radiotherapy
radioactive dating of archaeological specimens and rocks
Tracers- 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.
Medical tracers- a radioactive source is put into a body and will build up at a blockage so an area of problem can be detected.
Radiotherapy- radiation is used to destroy unwanted cells (cancerous cells.)
Radioactive dating- 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.
Describe the dangers of ionising radiations and describe how the associated risks can be reduced
Ionising radiation can break molecules into smaller fragments. These charged particles are called ions. Ions can then take part in other chemical reactions in the living cells. As a result, ionising radiation damages substances and materials, including those in the cells of living things. The ions themselves can take part in chemical reactions, spreading the damage. This may result in the living cells dying or becoming cancerous. Radiation can also affect DNA, causing mutations.
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.
Radiation 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.
What does the term ‘half-life’ mean?
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.
What is radiation measured in?
Complete: ‘Over time, the radiation emitted by a radioactive source will … (Increase/Stay the same/Decrease)
The radiation emitted by a radioactive source will decrease over time.
Radiation is measured in becquerels.
What are some sources of background radiation?
Buildings
The ground (the majority of background radiation comes from radon gas in the ground)
Food and drink
Cosmic rays
Medical sources
How can ionising radiations be detected?
Radiation imprints on camera film.
A Geiger-Muller detector (or GM counter) beeps in the presence of radiation, the more radiation the more frequent the beeps.
describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the three main types of radiation
Alpha
Beta
Gamma
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.
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 have no specific effect on the atomic or mass number.
describe…
alpha particles
beta particles
gamma rays
Which materials block them (the particles/rays cannot pass through)?
alpha particles are two neutrons and two protons; also known as a helium nucleus.
Alpha particles cannot penetrate a piece of paper.
Beta particles are electrons, they are emitted when a neutron turns into a proton and an electron. Beta particles can’t penetrate aluminium.
Gamma rays are a type of electromagnetic wave, they are often emitted alongside the other types of radiation.
Gamma cannot penetrate lead.
What are the 3 types of radiation?
What does the term ‘ionising’ mean?
Where is the radiation emitted from(in an atom)?
alpha particles, beta particles and gamma rays are all types of radiation.
The term ionising means they damage cells.
Radiation is emitted from the nucleus of an atom that is unstable (in a way it is too full and trying to off load.)
Define:
Atomic number
Atomic mass
Isotope
The atomic mass of an element 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.
Isotopes are two or more atoms with the same number of protons but a different amount of neutrons.
Carbon-12 and Carbon-14 are examples of isotopes.
