P2.5 What happens when radioactive substances decay, uses and dangers Flashcards
Describe the relative size of the nucleus compared to the rest of the atom
nucleus is tiny, but it makes up most of the mass of the atom.
rest of the atom is mostly empty space
What are the relative masses in an atom?
proton- 1
neutron- 1
electron- very small
What are the relative electric charges in an atom?
proton- +1
neutron- 0 (no charge)
electron- -1
In an atom, the number of electrons is equal to the number of….
protons
What overall charge does an atom have?
no charge
as the number on electrons is equal to the number of protons
When are ions formed?
if an atom loses or gains electrons
What do atoms of the same element always have the same number of?
protons
What is an isotope?
different atomic forms of the same element, which have the same number of protons but a different number of neutrons
What does the atomic number show?
the total number of protons in an atom
What does the mass number show?
The total number of protons and neutrons in an atom
What are radioactive substances?
substances that give out radiation from the nuclei of their atoms all the time whatever happens to them
Radioactive decay is a ………. process
random
Where does background radiation come from?
air, food, building materials, rocks
radiation from space- cosmic rays (mostly come from the sun)
man-made sources- fall out from nuclear weapons, nuclear accidents, dumped nuclear waste
Describe the structure of alpha particles
2 neutrons and 2 protons, the same as a helium nucleus
Describe the structure of beta particles
an electron
Describe the structure of gamma radiation
electromagnetic waves
What are some properties of alpha particles?
big and heavy so relatively slow moving
therefore do not penetrate very far into materials- stopped quickly even travelling through air
Because of their size they are strongly ionising
What does it mean if a particle was ‘ionising’?
the particle bashes into lots of atoms and knock electrons off them before they slow down. This creates lots of ions
What are some properties of beta particles?
Move quite fast and are quite small
penetrate moderately into materials
have a long range in air
moderately ionising
What are some properties of Gamma rays?
opposite of alpha particles
penetrate far into materials with out being stopped
pass straight through air
means they are weakly ionising as they tend to pass through rather than colliding with atoms
have no mass or charge
What are alpha particles stopped by?
paper
What are beta particles stopped by?
aluminium
What are gamma particles stopped by?
thick lead
What is the charge of an alpha particle?
positive
2 protons, 2 neutrons
What is the charge of a beta particle?
negative
it is an electron
Describe what happens when alpha, beta and gamma radiations travel through a magnetic field?
both alpha and beta are deflected in opposite directions because of their opposite charge.
Alpha particles have a larger charge than beta particles so feel a greater force in magnetic and electric fields. BUT they are deflected less because they have a much greater mass.
Gamma radiation is an EM wave and has no charge so does not get deflected at all.
Describe the basic structure of an atom
a small central nucleus composed of protons and neutrons surrounded by electrons
What does the extent of the harmful effects of radiation depend on?
how much exposure you have from the radiation
the energy and penetration of the radiation, since some types are more hazardous than others
What type(s) of radiation are most dangerous outside the body? WHY?
beta and gamma
as they can penetrate far into materials so can damage delicate organs.
Alpha is less dangerous as it can not penetrate into the skin
What type(s) of radiation are most dangerous inside the body?
Alpha
as alpha sources do their damage in a very localised area.
Beta and gamma are less dangerous inside the body because they mostly pass straight out without doing much damage.
Describe how radiation is dangerous
alpha, beta and gamma radiation can enter living cells and collide with molecules.
These collisions are called ionisation and they damage or destroy the molecules
This can cause cancer
What measures can be taken to reduce the exposure to nuclear radiations?
in experiments, use radioactive sources for as short time as possible so exposure is kept to a minimum
handle with tongs- never allow skin contact
hold the source at arms length- decrease the amount of radiation that hits you, especially for alpha particles as they do not travel far in air
Store radioactive sources in a lead box as lead absorbs all 3 types of radiation- also wear lead aprons and stand behind lead screens
What is a use of alpha radiation?
Smoke Detectors
weak source of alpha radiation is placed in the detector, close to 2 electrodes
The source causes ionisation, and a current flows between the 2 electrodes
If there is a fire then smoke will absorb the radiation so the current stops and the alarm sounds
Describe a use of beta and gamma radiation in tracers in medicine
certain radioactive isotopes can be injected into people and their progress around the body can be followed using and external detector
A computer shows where the strongest reading is coming from - eg used to indicate if the thyroid gland is taking in iodine as it should
must be gamma or beta emitters (not alpha) so that radiation passes out of the body.
THEY SHOULD HAVE A SHORT HALF LIFE so that the radioactivity inside the patient quickly disappears- less ionisation
Describe how gamma rays are used to treat cancer
high doses of gamma will kill living cells so can be used to kill cancerous cells
gamma rays have to be directed carefully and at just the right dosage to kill the cancer cells without damaging too many normal cells
Describe how gamma rays can be used in the sterilisation of food and surgical instruments
Food can be exposed to a high dose of gamma rays which will kill all microbes- keep food fresh for longer
food is not radioactive afterwards
medical instruments can be sterilised in the same way
Advantage over boiling is that is does not involve high temperatures- cheaper, food is not damaged
What is the half-life of a radioactive isotope?
the average time it takes for the number of nuclei in a radioactive isotope sample to halve,
or
the time it takes for the count rate from a sample containing the isotope to fall to half its initial level
Describe the plum pudding model
They used to believe that atoms were spheres of positive charge with tiny electrons stuck in them
Who proved the plum pudding theory wrong?
Rutherford and Marsden
What were the results of Rutherford’s and Marsden’s experiment and how did this prove the plum pudding model wrong?
1) Most alpha particles passed straight through the gold foil
- suggests most of the atom is empty space
2) Some alpha particles passed through but were deflected by varying amounts - Suggests an atom has a positive centre (alpha particles deflected as are positive)
3) Some alpha particles cam straight back- Suggests the positive centre is very dense
Describe Rutherford’s and Marsden’s experiment and what did they expect to happen?
fired a beam of alpha particles at thin gold foil
expected the particles would be slightly deflected by the electrons in the plum pudding model (thought overall charge of an atom is positive)
What does it mean if a radioactive sample has a short half life?
radioactivity falls quickly, because lots of the nuclei decay quickly
What does it mean if a radioactive substance has a long half life?
radioactivity falls slowly because most of the nuclei don’t decay for a long time.
Which 2 types of radiation can pass through a sheet of card?
beta and gamma
Which type of radiation has the greatest range in air?
gamma
If a radioactive source is stored in a freezer, why does the radiation emitted from the source not decrease?
As nothing you do to a radioactive substance changes the rate of decay
Suggest why a person may receive a higher than average dose of radiation from background sources
- frequent flying
- living at high altitude
- having more than the average number of x rays
- working in a nuclear power station
Name some manmade sources of background radiation
nuclear power stations
nuclear weapons
nuclear accidents
Why are readings of background radiation in a room always different?
as radioactive decay is a random process
How many protons and how many neutrons are there in an alpha particle?
2 protons
2 neutrons
How do you balance an equation in which a substance emits a beta particle?
0
+1
How do you balance an equation in which a substance emits an alpha particle?
- 4
- 2
When a substance decays and releases a beta particle, why does the atomic number of that substance increase by one?
Because for every beta particle emitted, a neutron turns to a proton in the nucleus
Inside what part of a power station is an isotope produced by radioactive decay produced?
reactor
How do you know beta radiation was emitted?
atomic number increases by 1
because a neutron becomes a proton
mass number does not change
Explain the risk to a patient of using a radioactive substance as a medical tracer
radiation causes ionisation
that may then harm healthy cells (cause cancer)
suggest why doctors use radioactive substances for medical diagnosis even though there is a risk
benefit is greater than the risk
