P6 Quiz

Frage	Antworten
What is an atom? Describe the makeup of it.	An atom is the smallest part of an element which can only be split by a nuclear reactor. Atoms are made up of electrons- which have a mass which is 2000 times smaller than a proton- outside the nucleus. These move at high speeds in orbits and carry a negative charge. Inside the nucleus are bigger particles- protons and neutrons. Protons are positively charged and neutrons are neutral. This means nearly all of the mass of the atom is concentrated in the nucleus. There is always the same number of protons and electrons so an atom is neutral.
What experiment did Rutherford and Marsden carry out?	Fired positive alpha particles at a very thin sheet of gold foil.
What happened? What did this show? How did this contradict the previous model?	Most of the alpha particles passed straight through the foil, the path of a few particles was bent by a small angle, a few particles bounced straight back. From this they concluded that most of the atom is empty space because most of the alpha particles went straight through it. There was a massive positive nucleus because some of the positive alpha particles were repelled by it -showing it was positive- and because when they hit it directly they bounced back- showing it was massive. It had previously thought the positive charge of the atom was spread out.
What holds the nucleus together?	Protons would be expected to repel each other and neutrons can't be held together by electrostatic forces. Therefore it initially appears surprising that the nucleus is held together. However there is a strong nuclear force which holds all the particles in the nucleus together.
What are isotopes?	Different versions of the same elements. Isotopes are atoms with the same number of protons but different numbers of neutrons.
What is a radioactive element?	An element with an unstable nuclei which emits radiation. This changes them to a more stable state. All radioactive elements emit ionising radiation.
What are the two types of ionising radiation? What does it do?	Either high-energy particles or high-energy electromagnetic waves. When they meet an atom it knocks out an outer electron creating a positive ion.
What is background radiation? Name at least three sources.	Low level radiation that is everywhere. Sources include: medical sources; gamma rays from the ground and buildings; cosmic rays; food and drink; nuclear sources; radon gas from the ground.
What speed does decay occur at and what happens when it does decay?	It is random and does not occur at regular intervals. When it does decay it changes into another element.
What are the three types of nuclear radiation? Give the properties of each.	Alpha particles: have a positive charge and are deflected by electric and magnetic fields. Are big and heavy so are good ionisers; their bulk means they can easily knock electrons out of atoms. Beta particles: Have a negative charge and are deflected by electric and magnetic fields (in the opposite direction to alpha particles); are much smaller, faster and lighter so are not as good ionisers as alpha particles. Gamma rays: are short-wavelength electromagnetic waves; have no charge and so are not deflected by electric and magnetic fields; are weak ionisers because they tend to pass through things, but when they do contact an atom they will knock out an electron.
How far will alpha, beta and gamma travel from the source?	Alpha: lose energy quicker as are larger so have more interactions with air molecules. They will stop being detected about 3cm from the source. Beta: detected up to 1m from the source. Gamma: not stopped at all by air although they do spread out and become less intense.
What is needed to stop each type of radiation?	Alpha: can be stopped by a piece of paper and does not penetrate the skin. Beta: stopped by about 3mm of aluminium. Gamma: lots of dense metal. For example thick lead is used when transporting nuclear waste from power stations to reprocessing plants.
What is a practical use of alpha and beta particles?	Can be used to monitor the thickness of paper and metal sheets when they are being manufactured.
What is an alpha particle?	Helium nuclei, meaning they consist of two protons and two neutrons. Alpha particles therefore have a nucleon number, or 'mass number, of 4, and a charge of +2.
What are beta particles?	Beta particles are very fast-moving electrons. They are not orbital electrons from the outer atom- they come from the nucleus. Electrons do not exist in the nucleus, but in some unstable nuclei a neutron changes into a proton and an electron. The electron is then emitted as beta radiation.
What is the symbol for an alpha particle?	Image: 8Cfg57xln1-W-.Zry4HWAA_m (image/jpg)
What is the symbol for the beta particle?	Image: beta1.gif (image/gif)
What else can this sort of notation be useful for?	Showing isotopes. The mass number is the top number, the proton number is the bottom number and the symbol is the particle symbol. It can also be used in decay equations to work out the new element formed.
What does the amount of radiation emitted, or the activity, depend on?	It depends on the number of radioactive nuclei present in a sample.
Explain alpha, beta and gamma decay.	Alpha- produced by many large unstable atoms that decays to a new element and a alpha particle. Beta- Often isotopes form beta particles and a new element. This is because a neutron becomes an electron and a proton. The electron is the beta particle and the changed number of particles causes a new element to be formed. Gamma- does not change anything itself but often accompanies alpha and beta decay. It does not change one element into another.
What do we mean by an unstable nucleus? How does it get out of this state?	We mean that it is in an energetic state. It has excess energy and to become stable it needs to lose some energy. Alpha and beta decay are both ways of changing a large unstable nucleus into a more stable nucleus. However most of the excess energy is got rid of through emmitting photons of gamma radiation
What is the 'half life'?	Although radioactive decay is random when the activity of a mass of radioactive element is measure the same pattern always emerges. No matter how many undecayed atoms you start with, it takes the same amount of time for half of the radioactive element to decay. It then takes the same amount of time for half of the remaining atoms to decay again, and so on. The half life of a radioactive element is the time taken for half of the atoms in a sample to decay.
What is a decay chain?	When the initial element decays into a daughter product that is also a radioactive element, which then decays into another radioactive element. Eventually a stable nucleus will be formed.
How is the rate of decay measured?	The activity of the radioactivity source, i.e. the amount of radiation emitted.
What do the effects of ionising radiation on living cells depend on?	The type of radiation, its intensity, the duration of irradiation and the types of cells.
How does ionising radiation radiation affect living cells? (general, high intensity and low intensity)	High: Can kill living cells causing tissue damage and leading to radiation sickness. Low: Can affect cells' genetic make-up causing mutations. These can then either be repaired or misrepaired. If they are misrepaired they may develop into a cancerous growth. General: when ionising radiation enters the body they knock electrons out of atoms leaving positive ions. These then take part in chemical reactions which is what can cause damage.
What is the most dangerous type of radiation?	It depends. If it is inside the body, alpha radiation causes the most damage. However it dosen't penetrate the skin. Therefore, if the source is outside the body, beta and gamma are more dangerous despite being poorer ionisers. Most gamma rays just pass straight through the body.
What is the sievert (Sv)?	Is a unit of equivalent dose of absorbed radiation. This means that one sievert of alpha, beta or gamma radiation produces the same biological effect.
How can ionisation affect our body indirectly?	If it ionises a water particle it could go on to interfere with the cells DNA. This may be repaired or may go on to behave incorrectly.
What is radiotherapy?	Using ionising radiation to kill cancer cells, if all the cells in the tumour are destroyed, there will be no cancerous cells left to grow out of control. This is called radiotherapy and usually uses gamma radiation. However it can also kill healthy cells around the tumour.
Give two other uses of radiation.	Sterilising medical instruments- this is done by irradiating with gamma radiation which kills all bacteria. Instruments can be sterilised inside their packaging and will remain sterile until the packet is opened. Sterilising food- same process means the food will stay fresh until the packaging is opened. The shelf-life is extended without altering the food itself.
How can we use radiation to detect brain tumours?	By injecting a radioactive tracer. This accumulates in the brain-tumour tissues and a radiographer can detect it from outside using a gamma camera. It has a half life of 6 hours. This allows the tracers to reach the affected part of the body in sufficient quantities to make a picture, but means that it does not last long enough to cause damage. Other tracers an be used to diagnose abnormalities in other parts of the body. Tracers usually emit gamma or beta radiation as they have to exit the body to reach the detector.
What else can radioactive tracers be used for?	To monitor where the waste of factories goes.
What is irradiation?	Exposure to radiation
What is : 1) a hazard 2) a risk	1) anything that may cause harm. 2) The chance, high or low, that somebody could be harmed by the hazard.
What is contamination?	Means something that has come into direct contact with a radioactive material, this then becomes radioactive.
When is radioactive material considered safe? How long does this normally take?	When the level of emitted radiation is the same as the level of background radiation. For products in the chemical industry this usually occurs after five half-lives. In this time the activity will have decayed to about 3% of its original value.
What could be done following fallout from a nuclear explosion?	Huge intervention needed. For example give iodine pills at risk from contamination from radioactive iodine. If the body has enough non-radioactive iodine it will not take up the radioactive iodine.
Give two precautions that can be taken by people working with radioactive isotopes?	Wear film badges to monitor how much radiation they are exposed to. Different thicknesses of plastic allow the medical physicist to determine whether the exposure was to alpha, beta or gamma radiation. Lead screens/ aprons- to sheild from radiation
How can energy be obtained from the nucleus of an atom? What are nuclear fuels?	Nuclear fission- a process in which a heavy nucleus such as uranium is split into two lighter nuclei of almost equal mass. Energy is released when this change happens. Nuclear fusion- a process where two light nuclei such as hydrogen combine to create a larger nucleus. Energy is also released when this change happens. Materials that can be used for either process are called nuclear fuels.
Where does the energy come from in fission and fusion?	It gives off much greater energy than chemical reactions because the energy that holds particles together in the nucleus, called the binding energy, is much greater than the energy that holds electrons in an atom. In both fission and fusion it is some of this binding energy that is released.
How is nuclear fission used to gain energy?	Uranium-235 is used as the nuclear fuel. A neutron is needed to initiate the fission process. It hits the nucleus and is absorbed. The resulting unstable nucleus splits into two other nuclei of almost equal mass. Three neutrons are also produced which can initiate fission in other nuclei. This sets up a chain reaction.
What happens if the chain reaction is not controlled? How is it controlled in a nuclear reactor?	A huge number of neutrons and a lot of energy is produced very quickly. This is what happens in a nuclear bomb. In a nuclear power station the number of available neutrons has to be limited. This is done through control rods which absorb neutrons and are made of materials such as boron. The control rods are raised or lowered to control the fission rate. If all the control rods are lowered into the reactor core all the neutrons are absorbed and the fission process stops.
What is low, intermediate and high level radioactive waste? How is each dealt with?	Low: made up of contaminated paper and clothing. It is not dangerous to handle but must be disposed of with care. It is burned and placed in closed containers before being buried in landfill sites. Intermediate: Consists of chemical sludges and reactor components, as well as contaminated materials from reactor decommissioning. It is more reactive and must be shielded. Waste with a longer half-life is buried deep underground wheras the short half-life is buried in shallow land fill sites. High: such as spent fuel rods. Contains highly radioactive fission products and requires shielding. Some of this waste is mixed with a molten glass and contained in stainless steel drums before careful storage. Spent fuel rods can be reprocessed to produce more fuel, cutting down on waste.
What form is energy released in in a nuclear reactor? What happens to the energy after that?	Kinetic energy of the resultant particles, effectively as heat. The coolant- gas or liquid- flowing around the reactor, absorbs the heat and transfers it, by means of a heat exchanger, to a steam generator. The rest of the process to make electricity is the same as in any other power station, using turbines and generators.
Give an example of nuclear fusion.	The nuclei of Hydrogen-2 and Hydrogen-3 at very high temperature and density can fuse to form helium-4, a neutron and lots of energy. Fusion is the process which produces energy in stars.
Give at least three advantages of fusion.	The by-products are not radioactive; does not release CO2 into the atmosphere; produces more energy than fossil fuels; fuel supplies will last millions of years; small amount of fuel makes this a safe process.
Why is it difficult to produce energy using nuclear fusion?	It requires temperatures of approximately a million degrees; it is difficult to contain hydrogen (which is plasm or ionising gas at these temperatures); magnetic field needed;this means it uses more energy than it generates; research costs high
What equation defines the interchangeability of mass and energy?	E=m(c squared) when E is energy M is mass and C is the speed of light

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