Radioactivity

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  • Created by: Jan Shah
  • Created on: 11-04-13 12:47
What is radioactivity?
Radioactivity is the spontaneous decay of an unstable nucleus by the emission of ionising radiation. It is the random process which means that it is not predictable and can happen in any way.
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What is an isotope?
An isotope is different forms of an element with the same number of protons but different number of neutrons.
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What are radioisotopes?
They are different forms of an element with the same number of protons and different number of neutrons which are unstable and decay by emitting ionising radiation.
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In a radioactive atom why is the nucleus unstable?
The nucleus is unstable because often there are too many neutrons inside the nucleus and all the protons being positively charged are repelling each other.
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What are the three diferent types of radiation?
Alpha, Beta and Gamma
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What is radiation measured in and what does it mean?
Radiation is measured in Becquerels (Bq). An acitvity of 1 Bq means that 1 nucleus is decaying every second.
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Give two detectors of radiation.
Geiger Muller tube, Photographic film.
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What is backgreound radiation?
Background radiation is produced all around us at a low level. It is produced artificially and naturally and is produced all the time.
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Give three sources and their percentages of naturally produced background radiation.
Radon gas-50%, The ground-14%, Cosmic rays-10%, food and drink and the buildings.
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Give three sources and their percentages of artificially produced background radiation.
Medical-14%, nuclear power and weapons-0.3% and other-0.2%.
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What is alpha radiation?
Alpha radiation is the emission of 2 protons and 2 neutrons from the nucleus of the atom.
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List the properties of alpha radiation.
Alpha is stopper by paper, It travels few centimetres in air, it is strongly ionising (it is good at removing elevtrons from passing materials), it has a positive charge.
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What happens to the nucleus when it emits an alpha particle?
The atomic number decreases by 2 and the mass number decreases by 4.
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Write an alpha decay equation using uranium.
a
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What is a beta particle?
A beta particle is an electron emitted from the nucleus when a neutron truns into a proton and an electron. The proton stays in the nucleus but the electron is emitted as a beta particle.
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List the properties of beta radiation.
It is stopped by a few mm of aluminium, it travels approxiamately 40-50 cm in air, it is ionising but not as strong as alpha, it is negatively charged.
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What happens to the nucleus when it emits a beta particle?
When a nucleus emits a beta particle the atomic number decreases by one and the mass number stays the same.
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Write a beta decay equation using iodine.
a
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What is gamma radiation?
Gamma radiation is the emission of an electromagnetic wave from the nucleus of the atom. The wave carries excess energy away from the nucleus.
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List the properties of Gamma radiation.
It travels an infnite distance in air, it is reduced by thick lead (10cm) or concrete (1m), it has extremely weak ionising power, it has no charge.
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Why can no decay equation be written when gamma radiation is emitted?
When a gamma ray is emitted from the nucleus, the nucleus does not change so no equation can be written.
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What is the half life of a radioactive atom?
A half life is the time it takes for the activity of the radiactive atom to decrease to half its intial value.
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Thorium has a rate which falls from 800cpm (counts per minute) to 100cpm in 72 days. What is the half life?
800=400=200=100 = 3 half lives so 72/3 = 24 days.
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What is radio carbon dating?
Radio carbon dating can be used to date any objects that have lived and exchanged carbon with the atmsphere e.g bones, mummy wrappings any organic matter.
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For an object to be measured by radio carbon dating, why does is need to be at least 500 years old?
It needs to be at least 500 years old because then the decay has barely started so if someone tried to measure it earlier they would have failed since there would be nothing to measure yet.
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Why does any object that is measured by radio carbon dating need to be measured earlier than 50,000 years?
It needs to be measured earlier because otherwise the decay has nearly finished and there would be nothing to measure.
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Why was Rutherfords experiment of the atom carried out in a vacuum?
It was carried out in a vacuum because alpha particles do not travel very far in air and there is no air in a vacuum therefore the alpha particles can travel a lot further.
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After the experiment what conclusions were made of the atom?
Due to the fact that most of the alpha went through it meant that most of the atom was empty space, since some of them were deviated from the path it meant that they came close with soemthing of the same charge so the nucleus is positive.
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After the experiment what conclusions were made of the atom?
Also since some of them were deflected at very large angles it means that the nucleus is small and contains most the mass of the atom.
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What effect does charge have on the path of an alpha particle?
The larger the charge of the nucleus the greater the deflection as there is a larger repulsive force.
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What is nuclear fission?
Nuclear fission is when a neutron hits a Uranium or Plutonium atom which then splits into two daughter nuclei and two neutrons. The nuclei are the fission products.
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Write the equation for nuclear fission.
a
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What is released from the daugther nuclei?
Kinetic energy.
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What is a chain reaction in nuclear fission?
A chain reaction is when a neutron hits a uranium atom which creates two daughter nuclei and two more neutrons. Those neutrons then collide with other uranium atoms to produce the same outcome. This continues until the uranium runs out.
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In a nuclear reactor what do control rods do?
They absorb neutrons which control the rate of fission. If the rate of fission is too high then the control rods would enter the reactor to absorb the neutrons to slow down the rate of fission.
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In a nuclear reactor what does the moderator do?
It absorbs the kinetic energy of the neutrons produced in the fission slowing them down to enable further fission.
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In a nuclear reactor how is electricity produced?
Electricity is produced when the nuclear reator creates heat. Water is pumped into the reactor which turns into steam. The steam then turns the turbine that generates electricity.
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Card 2

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What is an isotope?

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An isotope is different forms of an element with the same number of protons but different number of neutrons.

Card 3

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What are radioisotopes?

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Card 4

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In a radioactive atom why is the nucleus unstable?

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Card 5

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What are the three diferent types of radiation?

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