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Description
Flashcards by finn squires, updated more than 1 year ago
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Created by finn squires
over 6 years ago
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| Question | Answer |
| Why did the nuclear model of the atom replace the plum pudding model? | Thompson suggested atoms where spheres of positive charge with tiny negative electrons stuck in them (plum pudding). Rutherford fired lots of alpha particles at a thin sheet of god foil. From the plum pudding model they expected the particles to pass straight through. Most passed through, some deflected more and some deflected straight back proving the plum pudding model was wrong. There must have been a concentrated mass at the centre of it which was positive as it was repelling the positive alpha particles. Also most of the atom was empty space as most passed through. Bohr then refined the model (energy levels) Chadwick again (neutrons). |
| What is the relative charge and mass of a proton, neutron and electron? | Number of protons = number of electrons (no overall charge). |
| What is an isotope? | Isotopes of an element are atoms with the same number of protons but a different number of neutrons. There are a few stable isotopes for each element however the unstable isotopes decay into other elements and give out radiation (to try and become stable). This is radioactive decay. |
| What happens during radioactive decay? | Radioactive substances spit out one or more types of ionising radiation (alpha, beta, gamma). They also can release neutrons when they decay. Ionising radiation knocks electrons off atoms, creating positive ions. The ionising power is how easily it can knock off electrons. |
| What is alpha radiation? | Alpha radiation is when an alpha particle is emitted from the nucleus. Its two neutrons and two protons (like He). Short penetration distance (few cm in air, a sheet of paper can absorb it) Strongly ionising due to size. |
| How are alpha radiation used in smoke detectors? | Air is ionised causing current to flow, smoke binds to ions stopping current and triggering an alarm. |
| What is beta radiation? | A beta particle is a fast moving electron released by the nucleus. For every beta particle emitted, a neutron is turned into a proton. Medium penetration distance (few metres in air, 5mm aluminium can stop it). Moderately ionising. |
| How are beta emitters to test thickness of metal? | Slight variations in the amount of radiation passing through can determine how thick a sheet of metal is. Doesn't get immediately absorbed like alpha, doesn't pass straight through like gamma. |
| What is gamma radiation? | Gamma rays are waves of electromagnetic radiation (EM) radiation released by a nucleus. Far penetration distance (far into materials, long distance in air, absorbed by thick lead or metres of concrete). Weakly ionising as they pass through rather than collide with atoms, eventually they hit and cause damage. |
| In a nuclear equation to show radioactive decay what has to balance? | Mass and atomic number has to balance. Atom before decay ---> atom after decay + radiation emitted. |
| What is a nuclear equation for alpha decay? | Alpha particles are like a helium nucleus so when one is emitted the atomic number reduces by 2 and the atomic mass reduces by 4 and the charge of the nucleus decreases. |
| What is a nuclear equation for beta decay? | The number of protons increases by one, so charge is positively increased, lost a neutron and gained a proton so mass doesn't change. |
| What is a nuclear equation for gamma rays? | Gamma rays are getting rid of excess energy from the nucleus, no change to the atom. |
| What is a half-life? | The time taken for the number of radioactive nuclei in an isotope to halve. Can be used to find the rate at which a source decays. Its measured in becquerels Bq (1 Bq is 1 decay per second). |
| How dangerous is an isotope with a short half-life? | Activity falls quickly as its very unstable. Very dangerous as high amount of radiation the radiation they emit at the start but then quickly become safe. |
| How dangerous is an isotope with a long half-life? | Falls more slowly but more nuclei don't decay for a long time. Small amount of radiation for a long time. Dangerous to nearby object exposed for millions of years. |
| How would you calculate the half-life from a graph? | Initial activity/2 then find this time, the difference in this time is the half-life. |
| What is background radiation? | Background radiation is low-level radiation around us all the time. The main sources are: naturally occurring unstable isotopes (air, food,buildings,rocks,etc) space - cosmic rays from sun human activities- nuclear explosions |
| What is irradiation? | Exposure to radiation. Not radioactive. Lead lined boxes reduce irradiation. |
| Outside the body what sources are harmful? | Beta and gamma sources are the most dangerous outside the body as they can penetrate and get to vital organs. Alpha is less dangerous as it is usually blocked by air. High levels of irradiation can be dangerous for all of them. |
| Inside the body what sources are harmful? | Alpha is the most dangerous as they do all damage in a localised area. So contamination is the greater concern. Beta are less damaging as it damages over a wider area and some passes out of the body. Gamma is least dangerous inside the body as it just passes straight out and has lowest ionising power. |
| What are the main uses of radiation? | Gamma is used in medical tracers - short half-life so quickly disappears and can locate if organs aren't functioning. Radiotherapy killing cancer (gamma) - directed to kill cancer cells. Beta emitting implants are also used. However healthy cells also killed. Can lead to tissue damage. Lower dose = increased mutation = increased cancer. Higher dose = kills all cells = increase in radiation sickness. |
| What is nuclear fission? | Usually triggered by a nucleus absorbing a neutron. The large unstable nucleus then splits into two lighter elements and two/three neutrons are also released. If those neutrons are moving slow enough they can be absorbed by other nucleus causing a chain reaction. The energy produced by fission can be used to power turbines etc. Control rods can be lowered into the nuclear reactors to control how quickly the chain reaction occurs (energy produced). Uncontrolled chain reactions can cause explosions. |
| What is nuclear fusion? | Two light nuclei collide at high speed and fuse together to create a larger, heavier nucleus. The heavier has less mass than both the nuclei as some mass is converted to energy and released as radiation. Fusion releases a lot of energy (more than fission for an amount). Temperature and pressure so high in reactors making them really expensive and hard to build. |
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