P4 Radioactivity Flashcards
Activity
the number of unstable atoms that decay per second in a radioactive source.
Alpha radiation
alpha particles, each composed of two protons and two neutrons, emitted by unstable nuclei.
Atomic number
the number of protons (which equals the number of electrons) in an atom. It is sometimes called the proton number.
Background radiation
ionising radiation that is around us all the time from a number of sources. Some background radiation is naturally occurring, but some comes from human activities.
Beta radiation
beta particles that are high energy electrons created in, and emitted from, unstable nuclei.
Control rod
a rod that can be lowered into the core of a nuclear reactor, to absorb neutrons and slow down the nuclear chain reaction.
Cosmic rays
charged particles with a high energy that come from stars, neutron stars, black holes and supernovae.
Count rate
Count rate: the number of counts per second detected by a Geiger counter
Decay
when a radioactive isotope emits ionising radiation
Decommission
Dismantle safely
Fuel rod
a rod containing the nuclear fuel for a nuclear reactor.
Gamma radiation
electromagnetic radiation emitted from unstable nuclei in radioactive substances.
Geiger Muller tube
a device that can detect ionising radiation and is used to measure the activity of a radioactive source.
Half life
average time taken for the number of nuclei of the isotope (or mass of the isotope) in a sample to half.
Ionisation
any process that in which atoms become charged.
Irradiated
an object has been exposed to ionising radiation.
Isotope
atoms with the same number of protons and different number of neutrons.
Mass number
the number of protons and neutrons in a nucleus.
Nuclear equation
an equation representing a change in an atomic nucleus due to radioactive decay. The atomic numbers and mass number must balance.
Random
any process that cannot be predicted and can happen at any time is said to be random.
Unstable
an unstable nucleus in an atom is one that will decay and give out ionising radiation.
When is light emitted from an atom?
When an electron falls down an energy level
What happens when an electromagnetic wave is absorbed by an atom?
An electron is promoted to a higher energy level
What is radioactivity?
Caused by nuclear changes. It is harmful and can cause burns or cancer. We are surrounded by it at a low level. Released by nuclear fuels.
What is an alpha particle?
Produced by alpha rays and alpha radiation. +2 charge
How far can alpha particles travel in air?
An inch
What can block alpha particles?
A sheet of paper
How ionising are alpha particles?
Highly
What are alpha particles used for?
Smoke detectors
Treating cancer
Projectiles
What are beta particles?
A fast moving electron emitted by radioactive decay of substances -1 charge
How far can beta particles travel on air?
Several yards
What can beta particles be stopped by?
Thin layer of aluminium or clothing
How ionising are beta particles?
Not as ionising as alpha particles
What are beta particles used for?
Treat cancer
Tracers
Prevent growth of certain tissues
What is a gamma ray?
Penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength of the electromagnetic spectrum. No charge.
How far can gamma rays travel in air?
Hundreds of metres
What can block gamma rays?
Lead
How penetrating are gamma rays?
They have so much penetrating power that they can damage DNA
What can gamma rays be used for?
Sterilise equipment
Tracers
Radio therapy
What is radioactivity?
Where an unstable nucleus changes its composition and emits alpha, beta or gamma radiation
What is an alpha particle?
A helium nucleus
How ionising are gamma rays?
Not very
What are activity and counter rate measured in?
Becquerels (Bq)
What happens in an alpha decay equation?
Loses 4 mass and 2 atomic number every time. Emits gamma radiation as well
What happens in a beta decay equation?
Gains one atomic number + gamma radiation + e- mass number 0, proton number -1
What happens during beta decay?
A neutron splits up into a proton and an electron.
What is the half life?
The time for half the atoms in a sample to decay
What is the equation for activity?
Initial activity x 0.5^number of half lives
What is background radiation?
Comes from natural sources such as rocks and cosmic rays and man made sources such as nuclear accidents. Always around us. May be affected by occupation/ location.
What is radiation dose measured in?
Sieverts
What is nuclear fission?
The splitting of an atomic nucleus
What is induced fission?
Starts with a neutron
What is spontaneous fission?
Happens on its own
What is released in fission?
2 daughter nuclei, 3 neutrons, lots of energy
What is a chain reaction?
Neutrons released cause more fission
How do control rode control nuclear fission?
Absorb neutrons
In the sun what is nuclear fusion?
Hydrogen –> helium + energy
What is fusion in a nuclear reactor?
Heavy hydrogen –> helium + energy
What is fusion in a hydrogen bomb?
Uranium bomb surrounded by hydrogen
What happens in the sun?
2 protons (hydrogen nuclei) fuse making heavy hydrogen nucleus and positron (one proton has changed to a neutron)
Positron - same size as an electron but opposite charge.
Another protons hits heavy hydrogen to make heavier nucleus (a lighter form of helium 3 2) 2 lots of lighter helium collide to make a normal helium nucleus + 2 protons + energy
What happens at short distances? (Nuclear force vs repulsive electrostatic force)
The attractive nuclear force is stronger than the repulsive electrostatic force
What is the main technical difficulty for fusion?
Getting the nuclei close en enough to fuse
Sun fusion facts
75% hydrogen, 25% helium, slowly changing to more helium
Sun is a plasma of bars nuclei with no electrons
Energy given out if colliding nuclei are no bigger than iron
To fuse bigger nuclei, have to put in energy
What happens during nuclear fission in a nuclear reactor?
A neutron collides with a uranium atom, releasing 2 daughter nuclei, 3 neutrons and lots of energy as gamma rays. Some neutrons are absorbed by control rods to keep control.
What is an advantage of nuclear reactors?
Low cost once commissioned
What is a disadvantage of nuclear reactors?
Can cause large scale accidents
What is nuclear fusion?
Hydrogen atoms heated
Fusion reaction
Helium neutron and energy released
Neutron energy heats water
What is irradiation?
When an object is exposed to nuclear radiation
What is contamination?
When atoms of a radioactive material are on or in an object
How can you protect from irradiation and contamination?
Maintaining a distance from the radiation source
Limiting time near the source
Shielding from the radiation
