Radioactivity * Flashcards
What is the number of protons equal to?
the number of electrons
What is the atomic number?
the number of protons
What is the mass number?
the number of protons and neutrons
Which number is at the top of the element on the periodic table and which is on the bottom?
mass number (bigger number) is at the top and the atomic number is at the bottom
What was Rutherfords gold foil experiment?
he fired a beam of alpha particles at a sheet of gold foil
What were the three conclusions of the gold foil experiment?
1) most particles passed through - shows that most of an atom is empty space
2) a few particles rebounded - shows that an atom contains a tiny, dense nucleus
3) some particles passed through but were deflected in a different direction - shows that the positive alpha particles were repelled by the positive charge of the nucleus
What is alpha decay?
when an alpha particle is emitted from the nucleus of an atom
What is an alpha particle?
2 protons and 2 neutrons
What charge and mass do alpha particles have?
+2 charge and a mass of 4
What happens to the element when an alpha particle is emitted?
the element changes - the mass number decreases by 4 and the atomic number decreases by 2
What are the ionising and penetrating powers of alpha decay?
its highly ionising but weakly penetrating
What are alpha particles stopped by?
a sheet of paper
What is beta minus decay?
when a neutron turns into a proton, and a beta minus particle is released by the nucleus
What is a beta minus particle?
an electron
What happens to the element when a beta minus particle is emitted?
the element changes - the mass number stays the same but the atomic number goes up by 1
What are the ionising and penetrating powers of beta minus decay?
medium ionising power and medium penetrating power
What are beta minus patricles stopped by?
a few mm of aluminium
What is beta plus decay?
when a proton changes into a neutron and a beta plus particle is released by the nucleus
What is a beta plus particle?
a positron
What happens to the element when a beta plus particle is released?
the element changes - the mass number stays the same and the atomic number decreases by 1
What is gamma decay?
when a gamma ray is emitted by the nucleus to get rid of energy to become more stable
What is a gamma ray?
an electromagnetic wave that has no mass or charge
What happens to the element when a gamma ray has been emitted?
it stays the same - gamma rays have no mass and no charge
What are the ionising and penetrating powers of gamma rays?
its weakly ionising and highly penetrating
What is gamma radiation stopped by?
thick lead or concrete
What is neutron emission?
when the nucleus emits a neutron
What happens to the element when a neutron is emitted?
the element changes - the mass number decreases by 1 and the atomic number stays the same
What happens to the nucleus after a neutron has been emitted?
the nucleus because a different isotope of the element
What is background radiation?
low level ionising radiation that is present at all times
What is activity?
the number of nuclei that decay per second
What is activity measured in?
Bequerels (Bq)
How do you calculate activity?
activity = counts / time
Give three sources of background radiation
- nuclear power and weapons
- medical sources
- food and drink
What is ionising radiation?
radiation that has enough energy to knock electrons off of atoms
What is ionisation?
the gaining or losing of an electron
How is background radiation measured?
using a geiger-muller counter
How is background radiation detected?
using a geiger-muller tube or photographic film
What is half life?
the time taken for half the unstable nuclei in a sample of a radioactive isotope to decay
Give four uses of ionising radiation
smoke alarms, radiotherapy, PET scans, medical tracers
Which kind of radiation is used in smoke alarms?
alpha
Which kind of radiation is used in radiotherapy?
ionising radiation - usually gamma or alpha
Which kind of radiation is used in PET scans?
beta plus
Which kind of radiation is used in medical tracers?
gamma
What are the dangers of very low radiation?
can enter living cells and cause ionisation which can lead to tissue damage
What are the dangers of low radiation?
damages cells without killing them which can cause mutations leading to cancerous cells which divide forming a tumour
What are the dangers of high radiation?
kills cells completely causing radiation sickness which causes vomiting, tiredness and hair loss
What is irradiation?
radiation from a source that reaches your body (including background radiation)
Give two precautions people working with radioactivity can take
- staying out of range
- protective clothing
What is contamination?
radioactive substances or atoms that get into your body (this can happen if you touch a source)
Why is contamination so dangerous?
these atoms will continue to decay producing ionising radiation, even when the source is removed
What precautions can be taken to avoid contamination? (3)
- gloves and tongs used when handling radioactive sources
- protective suits to prevent contamination through breathing particles or getting any on the clothes or skin
- radioactive sources used in medicine need to have appropriate half lives to reduce damage to the patients body
What is nuclear fission?
a process in which energy is released from the nucleus of atoms as they are split
The process of nuclear fission:
Fill the gaps:
- a _______ is fired at a uranium235 ______
- the ______ absorbs the ______, turning it into Uranium236 and making it more _______
- the ______ splits in half into two daughter nuclei - _______ and ______
- ______ is produced and 2 or 3 ______ are released from the ______
- a neutron is fired at a uranium235 nucleus
- the nucleus absorbs the neutron, turning it into Uranium236 and making it more unstable
- the nucleus splits in half into two daughter nuclei - Krypton and Barium
- energy is produced and 2 or 3 neutrons are released from the nucleus
What is a chain reaction in nuclear fission?
a process where the products from nuclear fission causes further nuclei to split
this can get out of control because each splitting of a nucleus causes more nuclei to split
What does the control rod do inside a nuclear reactor?
its placed between the fuel rods and is raised and lowered into the reactor to control the chain reaction - the control rods absorb the excess neutrons
usually made of boron
What does the moderator do inside a nuclear reactor?
it slows down the neutrons which allows more reactions to take place
usually made of graphite
What does the fuel rod do inside a nuclear reactor?
its made of uranium nuclei and captures slow moving thermal neutrons
What does the shielding do inside a nuclear reactor?
it prevents the radioactive substances from getting out
What is nuclear fusion?
the process of joining two nuclei to form a nucleus
What happens in nuclear fusion?
two hydrogen atoms (one lighter and one heavier) are combined to form helium, which produces energy
What conditions are needed for nuclear fusion?
extremely high pressures and temperatures - because the positively charged nuclei need to be very close to fuse so a lot of energy is needed to overcome the strong force of electrostatic repulsion
How does nuclear fusion produce energy?
some of the mass of the lighter nuclei before fusion is converted into energy during fusion
How is the energy released in nuclear fusion?
by radiation
Where does nuclear fusion naturally occur?
in the sun
What is a pro of nuclear fission and nuclear fusion
pro of nuclear fission - more energy is produced than is needed
pro of nuclear fusion - lots of hydrogen is available from water
What are the practical issues of nuclear fusion?
a lot of energy is needed to achieve the high pressures and temperatures - this is expensive too
Give two pros and cons of nuclear power (fission)
pros :
- reliable alternative to fossil fuels - doesn’t produce CO2
- huge amounts of energy can be generated
cons :
- risk of radioactive leaks and explosions from power stations
- waste products have a very long half life and may not be disposed of safely
