physics topic 4

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what did John Dalton do for the model of the atom?
he proposed that matter was made up of tiny spheres that couldn't be broken up, but that each element was made up of a different type of these spheres (atoms)
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what did J J Thompson do for the model of the atom?
he discovered particles called electrons, that could be removed from atoms, and suggested that atoms were tiny spheres of positive charge with tiny negative electrons stuck in them (the plum pudding model)
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what was the alpha particle scattering experiment?
scientists in Rutherford's lab fired a beam of alpha particles at thin gold foil
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what happened in the alpha particle scattering experiment?
most of the particles went straight through, but some were deflected more than was expected or were deflected totally, which lead scientists to conclude that most of the mass of the atom was concentrated at the centre in a tiny nucleus
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what nuclear model resulted from the alpha particle scattering experiment?
a positively charged nucleus surrounded by a cloud of negative electrons
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what did Niels Bohr do for the model of the atom?
he said that electrons orbiting the nucleus do so at certain distances called energy levels, and his theoretical calculations agreed with experimental data
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what did James Chadwick do for the model of the atom?
he proved the existence of the neutron, which explained the imbalance between the atomic and mass numbers
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what is the radius of an atom?
1 x 10 -10
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what is the size of the nucleus?
1/10,000
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why do atoms have no overall charge?
the number of electrons equals the number of protons, and as protons and electrons have equal but opposite charges, they cancel eachother out
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how can electrons move within an atom?
if they gain energy by absorbing EM radiation, they move to a higher energy level, and if they release EM radiation, they move to a lower energy level
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what is the atomic number?
the number of protons (and electrons) in an atom
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what is the mass number?
the number of protons and neutrons in its nucleus
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what are isotopes?
atoms with the same number of protons but a different number of neutrons
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what is radioactive decay?
unstable isotopes decaying into other elements and giving out radiation as they try to become more stable
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what do substances release when they decay?
alpha, beta or gamma radiation, or neutrons
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what is ionising radiation?
radiation that knocks electrons off atoms, creating positive ions
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what is alpha radiation?
when an alpha particle (2 neutrons and 2 protons) is emitted from the nucleus
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how far does alpha radiation penetrate?
they don't penetrate far into materials, only travelling a few cm in air ad being absorbed by a sheet of paper
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how ionising is alpha radiation?
strongly ionising due to their size
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what is alpha radiation used for?
used in smoke decectors as it ionises air particles, causing a current to flow, but if there is smoke in air, it binds to the ions, meaning that the current stops and the alarm sounds
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what is beta radiation?
when a beta particle (a fast-moving electron) is released by the nucleus
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how far does beta radiation penetrate?
they penetrate moderately far, having a range in air of a few metres and being absorbed by a sheet of aluminium (5mm)
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how ionising is beta radiation?
moderately ionising
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what is beta radiation used for?
used to test the thickness of sheets of metal, as the particles aren't immediately absorbed by the material, so slight variations in the thickness affect the amount of radiation passing through the sheet
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what is gamma radiation?
when gamma rays (waves of EM radiation) are released by the nucleus
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how far does gamma radiation penetrate?
they penetrate far into materials, travelling a long distance through air, but being absorbed by thick sheets of lead or concrete
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how ionising is gamma radiation?
weakly ionising as they will tend to pass through rather than collide with atoms
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what is the form of nuclear equations?
atom before decay -> atom after decay + radiation emitted
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what happens during alpha decay?
its atomic number reduces by 2, its mass number reduces by 4, which decreases the charge of the nucleus
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what happens during beta decay?
a neutron in the nucleus turns into a proton, increasing the number of protons by 1, which increases the positive charge of the nucleus, but doesn't affect its mass
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what happens during gamma decay?
gamma rays are a way of getting rid of excess energy from a nucleus, so there's no change in the atomic mass or atomic number of the atom
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how can radiation be measured?
using a Geiger-Muller tube and counter, which records the count-rate
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what can't you predict about radioactivity?
which nucleus in a sample will decay next, or when any one of them will decay
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what is meant by a source's activity?
the rate at which a source decays, measured in becquerels
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what is half-life?
the time taken for the number of radioactive nuclei in an isotope to halve
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what does a short half-life mean?
the activity falls quickly, as the nuclei are very unstable and decay rapidly, which can be dangerous as they emit a high amount of radiation at the start, but quickly become safe
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what does a long half-life mean?
the activity falls slowly, as most of the nuclei don't decay for a long time, which can be dangerous as nearby areas are exposed to radiation for a long time
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what does backround radiation come from?
radioactivity of naturally occurring unstable isotopes all around us, radiation from space (cosmic rays from the sun), radiation due to human activity (eg. fallout from nuclear explosions)
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what does radiation dose tell you?
the risk of harm to body tissue due to exposure to radiation, measured in sieverts
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what affects your radiation dose?
where you live, if you have a job that involves radiation, if you've had to have x-rays taken
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what does it mean if an object is irradiated?
they're exposed to it, but doesn't mean that they're now radioactive
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how can irradiation by a radioactive source be reduced?
keeping them in lead-lined boxes, standing behind barriers, being in a different room, using remote-controlled alarms
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what does it mean if an object is contaminated?
unwanted radioactive atoms getting onto or into an object, which might then decay, which could cause you harm, especially if they get inside your body
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how can contamination by a radioactive source be reduced?
use gloves and tongs when handling to stop it getting onto skin or under nails, or wear protective suits to stop breathing in particles
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which type of radiation is the most dangerous outside the body?
beta and gamma radiation, as they can penetrate the body and get to delicate organs
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which type of radiation is the most dangerous inside the body?
alpha radiation, as they do all their damage in a very localised area
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how can radiation be used in medical tracers?
radioactive isotopes can be injected into people and their progress around the body can be followed using an external detector, the results of which a computer converts into a display, showing where the strongest reading is coming from
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what is an example of this?
iodine-123, which is absorbed by the thyroid gland, and gives out radiation which can be detected to indicate whether the thyroid gland is taking in iodine as it should
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what type of radiation should be used to do this?
usually gamma emitters, so that the radiation passes out of the body without causing much ionisation, and should have a short half-life so that radioactivity quickly disappears from the body
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how is gamma radiation used to treat cancer?
gamma rays are directed directly and at just the right dosage to kill cancer cells, without damaging too many normal cells, or radiation emitting implants can be put next to or inside cells
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what are the side effects of this?
quite a lot of damage is done to normal cells, which makes the patient feel very ill, but is worth it if it successfully kills the cancer
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what are the risks to using radiation?
radiation can enter cells, ionising atoms and molecules within them, which can lead to tissue damage
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what do lower doses of radiation do?
cause minor damage without killing the cells, which can give rise to mutant cells which divide uncontrollably (cancer)
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what do higher doses of radiation do?
kill cells completely, which can cause radiation sickness if a lot of cells get blasted at once
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what is nuclear fission?
a type of nuclear reaction that's used to release energy from large and unstable atoms, by splitting them into smaller atoms
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what does the atom release when it splits?
2 new lighter eleents that are about the same size and have the same amount of kinetic energy, aswell as 2 or 3 neutrons
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what is a chain reaction?
if any of the neutrons released are moving slowly enough to be absorbed by another nucleus, they can cause more fission to occur
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what do uncontrolled chain reactions lead to?
lots of energy being released as an explosion, which is how nuclear weapons work
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what happens to the energy not transferred to kinetic energy?
it's carried away by gamma rays
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what can the products of nuclear fission be used for?
to heat water, making steam to turn turbines and generators
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what is nuclear fusion?
2 nuclei colliding at high speed and joining to create a larger, heavier nucleus
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what is released during nuclear fusion?
lots of energy (more than fission)
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why can't fusion be used to generate energy for us to use?
the temperatures and pressures needed for fusion are so high that fusion reactors are very difficult and expensive to build
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Other cards in this set

Card 2

Front

what did J J Thompson do for the model of the atom?

Back

he discovered particles called electrons, that could be removed from atoms, and suggested that atoms were tiny spheres of positive charge with tiny negative electrons stuck in them (the plum pudding model)

Card 3

Front

what was the alpha particle scattering experiment?

Back

Preview of the front of card 3

Card 4

Front

what happened in the alpha particle scattering experiment?

Back

Preview of the front of card 4

Card 5

Front

what nuclear model resulted from the alpha particle scattering experiment?

Back

Preview of the front of card 5
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