Radioactivity Flashcards
How does a radioactive substance become more stable?
It contains unstable nuclei that become more stable by emitting radiation
What is in every atom?
Protons & neutrons
What are the three main types of radiation?
Alpha
Beta
Gamma
How specific is radioactive decay?
Completely random, we can’t predict or influence when it will happen
Where does background radiation come from?
It comes from the environment, space or from devices such as X Ray machines
What is radon gas?
Product of the day of uranium found in certain areas
What is an isotopes
Element where the atoms have the same number of protons but different number of neutrons - same atomic number and different masses.
What did Rutherford do?
He carried out alpha radiation scattering experiments to prove that :
an atom has a small positively charged central nucleus where most of the atom is located
What is used to detect radioactivity?
A Geiger counter
Why was the plum pudding model rejected?
It couldn’t explain why some alpha particles were scattered through large angles
Why was the apparatus in a vacuum chamber?
To prevent air molecules from absorbing the alpha particulars
Why was the nuclear model excepted?
It could explain why the alpha particles are scattered and why some are scattered through large angles.
What is a radioactive substance?
A substance that gives out radiation from the nuclei of their atoms, no matter what is done to them
What is a beta particle?
A high speed electron with a negative charge
What is an alpha particle?
A helium nucleus
with 2 protons and 2 neutrons
Positive charge
What is alpha decay?
the nucleus
loses 2 protons and 2 neutrons
the mass number decreases by 4
atomic number increases by 2
What is beta decay?
In beta decay a neutron changed into a proton and an electron which is emitted
The mass number dosent change
The atomic number increases by 1
What is gamma radiation? & gamma decay?
Electromagnetic radiation and in gamma decay the nucleus loses energy
What is alpha radiation stopped by?
Paper
What is the range of alpha radiation?
A few cm
What is alpha radiation deflected by?
Magnetic fields
What stops beta radiation?
Thin metal
What is the range of beta radiation?
About a metre
What is beta radiation deflected by?
Electric and magnetic fields in the opposite direction to alpha radiation
What stops gamma radiation? & what is its range?
Thick lead
Unlimited range in air
What affect do magnetic and electric fields have on gamma radiation
No affect
What is the activity of a radioactive source?
The number of nuclei that decay per second
What is ionisation? & what affect does it have on a living fell?
The process by which atoms become charged because they lose electrons.
Ionisation in a living cell can damage or kill it.
What is the half life of a radioactive isotope?
The average time it takes for the number of unstable nuclei in the isotope to halve
What is count rate? What is it measured by?
The number of counts per second or minute and is measured using a Geiger counter
What 2 factors determine the purpose of a radioactive isotope?
- half life
- type of radiation it emits
What emitters are used in smoke alarms?
Alpha emitters
How do smoke alarms use certain emitters?
They use alpha emitters because the alpha particles ionise the air in a gap in the circuit so the current an cross the gap.
If the smoke particles get in the way, the current across the gap drops and the alarm sounds
What emitters are used in automatic thickness monitoring? what factor should be considered with the isotope?
- have a long half life
- beta emitter usually
what emitters are used for radioactive tracers?
Beta or gamma emitters that last long enough to monitor but not too long
What is nuclear fission?
The splitting of a nucleus into 2 approximately equal fragments
energy is realised
and then releasing 2 or 3 neutrons
What do you need for radioactive dating of a sample?
You need a radioactive isotope that
- is present in the sample
- has a half life about the same age as the sample
Eg.
uranium for igneous rocks
Carbon-14 for organic material
What is nuclear FUSION?
The process of
- forcing 2 nuclei close enough together at high speed
- SO they form a single larger nucleus
What is released when two light nuclei are fused together? What happens to do with the Suns core?
energy
nuclear fusion in the Suns core releases energy
What is an advantage of fusion l?
- fuel is readily available because it’s in sea water
- the reaction product which is helium, is a non-radioactive gas
When does nuclear fission occur?
- when a neutron
- hits a uranium-235 nucleus or
- plutonium-239 nucleus
- the nucleus splits
What is a chain reaction?
A chain reaction occurs when each fission even cause further fission events
How is a chain reaction in a nuclear reactor controlled?
- In a nucleus reactor control rods absorb neutrons
- to ensure that on average only one neutron per fission
- chain reactions slow down because there are fewer neutrons
Why is it difficult to make a nuclear fusion reactor?
- The plasma needs to be at a very high temperature
- before nuclear fusion can take place
- this is to ensure that the nuclei have enough energy have enough energy to overcome the force of repulsion
Why is the plasma contained in a magnetic field?
- the plasma is contained by a magnetic field so it DOSENT touch the reactor wall because if it did it would go cold and fusion would stop
What happens when two protons ( hydrogen nuclei) fuse?
They form a heavy hydrogen nucleus (deuterium)
What is radiation dose?
How much radiation each person gets in a year from a particular source
List sources of background radiation? & highlight the one that is man made?
- cosmic rays
- food & drink
- medical
- air travel
- ground and buildings
- natural radioactivity in the air
- nuclear weapons testing
- nuclear power
What does the effect on living cells or radiation of radioactive substances depend on?
- the type and amount of radiation received
- whether the source of the radiation is inside or outside the body
- how long the living cells are exposed to the radiation
Where is alpha the most dangerous?
Inside rather than outside
Where must nuclear waste be stored? & what must be done first?
- In safe and secure conditions for many years
- the unused uranium and plutonium should be removed from it
How can alpha beta and gamma radiation be separated?
A magnetic or electric field can be used
Why is alpha beta and gamma radiation dangerous?
They ionise substances they pass through - this can damage or kill the cell
What type of radiation is
A uncharged
B charged
C negatively charged
A gamma rays
B alpha
C BETA
What is beta radiation
Beta particles that are high energy elections created in and emitted from unstable nuclei
What makes gamma decay different from alpha and beta decay?
Gamma decay is an electromagnetic wave whilst in alpha and beta decay a charged particle is emitted from the nucleus
What type of particles do neutron-heavy nuclei emit? & neutron-light nuclei emit?
Heavy - Negative beta particles
Light - Positive beta particles
What do the heaviest elements emit?
Alpha particles
What does any sufficiently energetic nuclei emit?
Gamma rays
What is gamma particles charge and why?
They have no charge because they are electromagnetic waves
How heavy are alpha beta and gamma rays?
alpha - very heavy
Beta - x7300 lighter than alpha
Gamma - no mass
What is radon gas?
Gas created by the radioactive decay of uranium in the earths crust
One other substance that can be used as fuel in a nuclear reactor?
plutonium (239)
Describe how the energy from nuclear fuels generates electricity?
1 energy used to heat water
2 produces high pressure steam
3 the steam drives a turbine
4 which then turns a generator
What factors could lead to a greater risk of radioactive poisoning?
- working in a nuclear power station
- having more x rays than normal
- living in a place of high radon concentration eg Cornwall
- living at altitude
What does the plum pudding model represent?
The positively charged matter in the atom evenly spread about (as in a pudding)
Electrons buried inside (like plums within it)
What does fission mean?
To split
What do control rods do?
’ soak up ‘ excess neutrons
Why does fusion only occur at very high temperatures and pressures?
They have to be pushed together with a force large enough to overcome the force of repulsion
Which two types of radiation will pass through a sheet of card?
Beta
Gamma
Which two types of radiation would be deflected by an electric field?
Alpha
Beta
Which type of radiation has the greatest range in air?
Gamma radiation
What did scientists think the pudding part of an atom was?
Positively charged matter that was evenly spaced out
Where does most of the helium gas on earth come from?
Alpha decay of radioactive elements of rocks in the earths crust
Do gamma particles have charge?
No mass
What is the difference between alpha&beta decay and gamma decay?
In gamma decay an electromagnetic wave is emitted instead of a charged particle
How did Rutherford prove the nucleus?
From the measurements from alpha scattering experiment
Why did Rutherford experiment take place in a vacuum?
To prevent air molecules from absorbing alpha particles I
How did Rutherford prove the nucleus?
From the measurements from alpha scattering experiment
Why did Rutherford experiment take place in a vacuum?
To prevent air molecules from absorbing alpha particles I
What happens in gamma decay?
The nucleus loses energy
How can you separate radiations of alpha and beta?
Using a magnetic field or an electric field
What happens when gamma radiation comes in to contact with a field?
It’s unaffected
What direction is beta deflected by an electric or magnetic field?
In the opposite direction to alpha
What is ionisation?
The process by which atoms become charged because they lose electrons
What is the activity of a radioactive source?
Number of nuclei that decay per second
How does an alarm work?
An alpha particle ionises he air in a gap in the circuit so the current can cross the gap
If smoke particles get in the way the current across the gap drops and the alarm sounds
What type of radiation is used for radioactive tracing and why?
Beta or gamma because they last long enough to monitor
When does a fission occur?
When fissions cause further fission events
What do control rods do in a nuclear reactor?
They absorb surplus fission neutrons to ensure that only one neutron goes onto produce further fission
Why is the reactor core made of steel?
Thick steal to withstand high temperature and pressure
Why is water used in a pressurised water reactor?
The water acts as a moderator
I slow down the fission neutrons
What is waters alternate use in a PWR?
Acts as a coolant
It’s molecules gain kinetic energy from the neutrons and fuel rods
It gives up energy via a heat exchanger
Sources of background radiation?
Food Drink Cosmic rays Medical Air travel Nuclear power /weapons
What radioactive isotope emits naturally through the ground?
Radom gas - alpha
Why is a very high temperature used in a fusion reactor?
To ensure the nuclei have enough energy to overcome the force of repulsion
How is the plasma heated in fusion?
A very large electric current
What colour is a proton?
Black
What colour is a neutron?
White
What does nuclear fission release?
Energy (electromagnetic radiation as gamma rays)
2 or 3 neutrons at high speed
2 aprox equal fragments of nucleus
These release kinetic energy
What causes further fission?
Fission neutrons may cause further fission resulting in a chain reaction
Why is one fission neutron (aprox) released from each fission of two or three?
To ensure energy is released at a steady rate
What causes further fission?
Fission neutrons may cause further fission resulting in a chain reaction
Why is one fission neutron (aprox) released from each fission of two or three?
To ensure energy is released at a steady rate
How does the energy of fission provide energy?
Energy used to heat water
Produces high pressure steam
Steam drives turbine
Which turns a generator
How is fission energy made useful?
Energy used to heat water
Produced high pressure steam
Steam drives turbine
Turbine turns a generator
What does water do in a nuclear reactor?
Coolant
Moderator - slows the fission neutrons as they collide with water molecules
Chain reaction stops
What is in a nuclear reactor?
Control rods
Fuel rods
High pressure water
Describe the reactor core in a nuclear reactor?
Thick steel to withstand high temp and pressure
Thick concrete walls to absorb radiation that escaped from steel
What do the control rods do in a nuclear reactor?
Absorb surplus neutrons
Keeps chain reaction Under control
The lower the rods the fewer neutrons chain reaction slows down stops
When does fission happen?
Occurs when a slow moving neutron hits the nucleus of uranium -235 or plutonium -239
And the nucleus splits
And two or three neutrons released
How does fission release energy?
Radiation energy
Kinetic energy from the 2/3 neutrons released and fragmented nuclei
What is the problem with fusion reactors?
Very high temperature needed before the plasma of light nuclei fuse
because two nuclei will repeal as they have the same positive charge
Why is a magnetic field needed in a fission reactor?
So it dosent touch the reactor walls
If it did it would go cold and the fission would stop
Fusion in the sun?
Two protons of hydrogen fuse to form heavy hydrogen ( 2-1)
Two heavy hydrogen nuclei collide to form 4-2 (helium)
Energy released at each stage is carried as kinetic energy
What is an ion?
An atom that had lost or gained electrons
Why is it important that the doctor used an isotope with a short half life rather than a long half life?
Short half life the level of radiation in the body decreases rapidly
To a safe level
Why do towns need to stay connected to national grid even with own electricity supply?
Electricity demand may be greater than supply
No case it fails
In the nuclear model, what is most of the atom?
Empty space
Natural sources of radiation?
Rocks
Cosmic rays from so we
Artificial sources of radiation?
Fallout from nuclear weapons tests
Nuclear accidents
Definition of radioactive substance?
Some substances give out radiation from the nuclei or their atoms all the time
Describe the basic structure of an atom?
A small centeral nucleus composed of protons and neutrons
Surrounded by electrons
Describe the difference in alpha and beta particles when deflected?
Alpha deflected LESS
And in the opposite direction to Beta
What do most nuclear reactors use?
Uranium 235
What has to first happen for fission to offer?
Uranium or plutonium nucleus must first absorb a neutron
What happens to a nucleus undergoing fission?
The nucleus splits into two smaller nuclei and two or three neutrons and energy is released
How do planets form?
Smaller masses may also form and be attracted to a larger made to become planets
Why was Rutherford nuclear model quickly accepted?
It agreed with the measurements made in experiments
It predicted the existence of the neutron
It explains radioactivity in terms of changes that happen to an unstable nucleus
Describe the plum pudding model?
Positively charged matter evenly spread out and electrons buried inside
What happens during nuclear fission
NUCLEI split
Where are isotopes produced in a nuclear power station?
NUCLEAR REACTOR
How does water act as a coolant?
Molecules gain kinetic energy from the neutrons and the fuel rods
Water pumped into core
Then it goes into sealed pipes to and from s heatb exchanger
