Radioactivity Mod:6 Flashcards
Explain Rutherford scattering experiment
A stream of alpha particles from a radioactive source is fired at a very thin gold foil when alpha particles from the source strike a fluorescent screen a tiny visible flash of light is produced
Most of the first charged alpha particles went straight through the foil therefore the atom must mainly be empty. Space
Some alpha particles were deflected through large angles so the centre of the atom must have a large positive charge to repel positive gold ions
Particles were deflected by angles greater than 90° therefore the nucleus must be tiny
Most of the mass must be in the nucleus since the alpha particles with high momentum are deflected by the nucleus
What is the atomic number and what is its symbol?
The atomic number is the number of protons in the nucleus and the the symbol is Z
What is the atomic number and what is its symbol?
The atomic number is the number of protons in the nucleus and the the symbol is Z
What is the nucleon number and what is it symbol?
The nuclear number also called the mass number has the symbol A and it tells you how many protons and neutrons are in the nucleus?
What is an isotope?
Atoms with the same number of protons but different number of neutrons are called isotopes however changing the neutrons does not affect the atoms chemical properties. It only affects the stability of the nucleus.
Explain radioactivity
This is when an isotope is not stable therefore they admit atomic particles and or energy decay will leave behind a more stable nucleus for an individual nucleus. The decay process is spontaneous and random.
Explain how a geiger Muller tube is used to detect radioactive sources 
This is a metal tube filled with argon gas. The tube has a thin wire down the middle and a voltage between the wire and the casing. The tube is good at detecting alpha and beta particles however not so good at detecting gamma particles.
When the radioactivity enters the tube ionises the gas in the tube this produces a pulse of current which is then amplified and passed to the counter
Define count rate
The number of ionisation detected per unit time
What is a radionuclide
An unstable nucleus which emits radioactivity
Define random in terms of radioactivity
Cannot predict when a particular nucleus will decay
Define spontaneous in the terms of radioactivity
It cannot be influenced by external factors such as temperature pressure, chemical reaction, et cetera
Explain the properties of alpha particles
Alpha particles are helium nuclei so have a charge of +2e
They have a relatively high mass and low speed and they interact easily with atoms in a substance
When they collide with atoms, it prevents them from passing through materials therefore alpha particles have a very short range and low penetration
They only travel around 2 to 3 cm in air
They are stopped by skin or a piece of paper
 explain properties of beta particles
Beta particles are electrons so they have charge -e
They have a very low mass and a high speed therefore they interact less easily than other particles with atoms in a substance
They can travel up to 1 m through air and threes some obstacles such as
However, they are stopped by a 3 mm thick layer of aluminium
Explain the properties of gamma radiation
Gamma radiation has no mass and travels at the speed of light therefore gamma rays collide in infrequently with atoms in a substance
Have a greater range and a considerably more penetrating than alpha or beta particle
They can travel long distances through air through pieces of paper and aluminium foil
Several centimetres of lead or several metres of concrete are needed to stop the passage of gamma
Define activity
The rate at which nuclei decay
Define becquerel Bq
A unit of activity equivalent to one emission per second
Define half-life life
 time taken for the activity of a sample to have all the time taken for half the nuclei in a sample to decay
Define decay constant (lamda)
The probability of a nucleus decaying
What 2 particles make up beta radiation
Positrons b+
Electrons b-
Explain the effect of electric and magnetic fields on radiation particles
When two plates of opposite charge are placed either side of a beam of particles, the beta-minus particles are deflected towards the positive plate and the beta-plus particles are deflected towards the neagtive plate. Alpha particles are deflected towards the negative plate however alpha particles are deflected less because of their grater mass.
Beta-minus and beta-plus are mirror images
Gamma particles are not deflected because they are uncharged
What is the background count rate
The count rate without the radioactive source present
What is the background count rate roughly
0.4 counts per second, 20 counts per minute
How do u find the corrected count rate
Substract the background count rate from the measured count rate
What proportion is the nucleus to the atom?
The nucleus is 10,000 of the size of the whole atom
How much bigger are the protons and neutrons than the electron?
They are 2000 times more massive
Explain how the diameter of an atom was found and what is the diameter
By probing atoms using scattering and diffraction methods
The diameter of an atom is 0.1 nm
Roughly what is the diameter of the nucleus?
A few femtometres 10 to the -15
Roughly what is the diameter of the nucleus?
A few femtometres 10 to the -15
What is a molecule?
A number of atoms joined together
How can you measure the size of a nucleus?
By firing particles at it
How do you calculate the density of a nucleus?
Use the formula for volume of this sphere and use the density equation
Which is bigger nuclear density or atomic density and what does this suggest?
Nuclear identity is much higher than the atomic density
This suggests most of an atoms mass is in its nucleus
The nucleus is small compared to the atom
And an atom must contain a lot of empty space
What does the electrostatic force behave as in the nucleus?
It behaves as the repulsive force between the positive charges of the protons
Name some properties of the strong nuclear force
The strong nuclear force holds the nucleus together provided that it is an attractive force that overcome the electrostatic force
It has a short range and it can only hold new together when they are separated by a few femtometres, which is about the sides of a nucleus
They work equally between all nucleons. This means the size of the force is the same whether it is a proton to proton neutron to neutron or a proton neutron.
Very small separations the strong nuclear force is repulsive to avoid crushing the nucleus to a point
Past what nucleon separation length does the strong nuclear force start becoming attractive?
When the nuclear separation is passed 0.5 Sam 2 m
At what nuclear separation does the strong nuclear force stop holding the nucleons together?
When the nucleon separation is 3 fm
What is a nucleon?
A nuclear particle, for example, a proton or a
What is the nuclear number? A
The number of particles in the nucleus
What is a lepton?
A fundamental particle affected by weak electromagnetic forces
What is a quark
Fundamental particle affected by strong electromagnetic forces
What is a hadron
A particle affected by strong electromagnetic charges if charged
What is a? Baryon
A hadron consisting of three quarks or antiquarks
What is a meson
A hadron consisting of a quark/antiquark pair
What is strong nuclear force?
A very short range of attractive forces between hadrons
What is beta decay caused by?
Weak Nuclear forces
What is the half-life of free neutrons?
15 minutes free neutrons are neutrons that are not held in the nucleus
What is the difference between? Hadrons and lepton and what are examples of them.
Hadrons field the strong nuclear force examples are protons and neutrons
Electrons do not fear the strong nuclear force and an example is electrons and neutrinos
What is the charge on the mass of a neutrino?
Neutrino have no mass or charge they only take part and weak interaction such as beta decay
Explain the antiparticle philosophy
For a particle there is a corresponding antiparticle with the opposite charge however it has the same mass for example for a proton there is an ant anti-proton and for an electron there is a positron
What happens when energy is converted into mass?
When energy is converted into mass, there is an equal amount of matter and Anti matter that is produced
For example, if you fired two protons at each other at a high speed you will end up with a lot of energy at the point of impact. This energy might be converted into more particles so if an extra proton is formed then an ant proton will always be formed with it this is called pair production.
Explain the requirements for rpair production
It only happens if one photon has enough energy to produce that much mass
It happens near a nucleus to help conserve momentum
And the minimum amount of energy the food must have is the combined energy of the two particles at rest which are formed this is due to the conservation of energy
It is assumed that the particles have negligible kinetic energy
Which pair production is normally formed and why?
An electron positron pair as they have relatively low mass
What equation do we use to find the energy of the nucleon which produces a pair production
E= 2mc^2
This is because both the particle and antiparticle will have the same rest mass
What is the opposite of pair production?
When a particle meets its antiparticle, this is called annihilation
The mass of the particle and antiparticle gets converted into energy in the form of a pair of photons
What are the different types of quarks and their relative charge?
Up quark (2/3)
Down quark (-1/3)
Strange quark (-1/3)
They are also the Anti quirks which have the opposite charge
What evidence showed that there are quarks
By hitting protons with high energy electrons the way the electrons scattered showed that there were three concentrations of charge inside the proton (quarks)
What combination is a proton and a neutron made up of in terms of quarks
Proton
Uud (2/3 + 2/3 - 1/3=1)
Neutron
Udd ( 2/3 - 1/3 - 1/3 =0)
Give two examples of baryons
Neutrons and protons
 when are mesons produced
When a proton is blasted with enough energy, the energy gets changed into more quarks and antiquarks Which produces a Maison which has two quirks
When calculating the radius of a nucleus using the equation, what should the value of the constant be around?
1.4 fm
Describe the nature and the range of the three forces acting on the protons and neutrons in the nucleus
Gravitational force and attractive force and his long ranged
Strong nuclear force a repulsive force for short distances and attractive for larger distances and a short ranged
Electric static force it is ranged and repulsive force between protons
Density of a uranium nucleus is calculated using the density formula state one assumption made
That the nucleons are packed together with no space
Explain why it is impossible to dislodge the quarks within a proton
Because there is an attractive strong nuclear force between all the quarks
What is the beta minus decay equation?
- -
- N - 1 p + -1e + v
What is the definition of for mass defect
The diff between the combined mass of the separated nucleons and the mass of the nucleus
What is the definition of binding energy
The min energy required to completely separate the nucleus into its constituent nucleons
Define the atomic mass unit
1/12 of the mass of an atom of carbon-12
Why is the mass of the constituent nucleons greater than the mass of the nucleus
Because when you fuse the nucleons together you lose energy in the form of mass
Explain induced fission
A thermal neutron is absorbed by the nucleus of a uranium isotope, an unstable nucleus IS THEN FORMED WHICH QUICKLY disintegrates into several particles which fly off in all directions
What is conserved in nuclear fission reactions
Mass , energy. Momentum, nucleon number
Explain the role of the coolant in the fission reactors
It extracts heat generated in the reactor,
The coolant is pumped into the reactor core and then passed to a heat exchanger where the heat enrgy is passed onto water to create steam
This is to transform the thermal energy into KE which turns turbines and provides electrical energy
Give an example of a coolant in a fission reactor and the dangers of it
C02 and water
Water needs to be pressurised to keep it in liquid form due to the high temps causing it to change state
The coolant becomes radioactive and even if the reactor is shut down the temp still increases due to the radioactive decay of the fission products
How is the Fission reactor kept safe
The core sits inside a steel pressure vessel
Contains high pressure coolant
The reactor is surrounded by concrete to stop neutrons and radiation escaping.
Housed in a building designed to contain radiation
Explain the role of the control rods in the fission reactor
Any more than 1neutron per reaction should be absorbed to avoid disasters
Any less than 1 will stop the reaction
The rods are made of boron and can be raised or lowered into the reactor in order to either speed up or slow down fission
The rods when lowered will absorb excess neutrons to reduce reaction rate
Explain the role of the moderator
Fissio is triggered by the absorption of the slow moving neutrons
However the neutrons prod in the reactions are very fast moving and need to be slowed down
Therfore the neutrons collide elastically with the nuclei of the moderator material , energy is transferred tot= the moderator therfore neutrons slo down after repeated collision the KE of the neutrons falls to the average KE of the moderator hence slowing down
These are known as thermal neutrons
What shld be the properties of the moderator in order to slow down the neutrons
For collisions to transfer energy effeciently the moderator material must have a small nuclei
And must nt absorb too many neutrons
Most moderators are water or graphite.
What happened when there are no control rods in the fission reactors
More fission reactions, more neutrons and ore energy released more output power high temps increases until ex[plosion
There is a lot of helium in the universe and there was also a lot of helium on earth when it was formed billions of years ago however the only small traces of helium are now found in the atmosphere. The Earth use the kinetic theory of gases to explain why only small amounts of helium are found in the atmosphere?
At a certain temperature, all atoms will have the same average kinetic energy
However, the atoms will have a range of speeds and the route mean squared speed of atoms will be less than the escape velocity, however the faster helium atoms will have escaped therefore helium atoms decreasing on earth
Earth was significantly hotter in the past therefore atoms had more kinetic energy and were able to escape with faster velocities
Defined the internal energy of a gas
The sum of the random kinetic and potential energies of all atoms in the system
Define nuclear fission
When a nucleus is broken into 2 smaller nuclei relesing energy
Define nuclear fusion
When 2 smaller nuclei form a larger nucleus releasing enrgy
Name the 2 forces acting in the nucleus of an atom , state what they act upon and their range
Electromagnetic force, acts on protons and has infinite range
Strong nuclear force acts on nucleons and has a short range within nucleus
Explain similarities and differences between fission and fusion reactions
Similarities
Both have a mass defect, therfore the BE produced is greater than the BE of the reactants for both reactions
Both release energy
Difference
Fission breaks a nucleus into 2 smaller nuclei, fusion joins 2 nuclei to form a larger nucleus
Fission releases more enrgy per reaction
What is created in the annihilation of an electron and a positron
2 gamma photons
Explain why nuclear fusion requires high temps
To overcome the repulsion between 2 nuclei of +ve charge
Explain why nuclear reactors use thermal neutrons
Travel more slowly this increases the probability that they will be absorbed by a nucleus allowing a chain reaction
Describe the adv and disadv of using nuclear power for electricity
Adv
No greenhouse gasses prod
Prod large amounts of energy for a small amount of U
Disadv
Prod nuclear waste that needs to be carefully disposed
Target for terrorist attacks/ natural disasters
What other material can be used in nuclear reactions
Plutonium
What is meat by critical mass
The minimum mass of a fissile substance required to maintain a chain reaction
Explain how radioactive waste is disposed
Stored in sealed containers and buried deep underground in land which is geologically stable
Name 3 factors which must be considered when finding a location to dispose nuclear waste
Geological stability
Security from risk of terrorism
Away from water supply
Explain why the total mass of the individual nucleons of a nucleus is different from the mass of the nucleus
There is a mass defect, therefore the mass of the individual nucleons combined is greater than the mass of the nucleus
E equals MC squared where E is binding energy and this is the energy that must be supplied to the nucleus to the nucleus
Suggest why the probability of a fusion reaction at a given temperature is smaller for helium nucleus than a hydrogen nucleus
Helium nucleus has a greater charge as it has more protons therefore it has a greater electrostatic repulsive force therefore there would be a smaller chance of fusion as a greater energy is required for the helium nuclei to be closer together
Describe the process of annihilation
When a passcode meets its antiparticle, the result is annihilation all the mass of the particle and ant particle gets converted into energy in the form of a pair of photons
Fusion usually requires temperatures of 10 to the power of nine Kelvin however sometimes fusion can occur at lower temperature suggest why?
Because some nuclei may be travelling at a higher kinetic energies than the main kinetic energy
State in what form the energy released in fusion and fission reactions are
In the form of kinetic energy
Explain how nuclear fission can provide energy
That is a mass defect, therefore the mass is converted into energy
Suggest a suitable material which can be used as a moderator in a fission reaction and explain its role
Water, The boron nuclei collide elastically with the neutrons causing a transfer of kinetic energy therefore slowing down the fast moving neutrons so that they have a greater chance of causing fission
State where an antiproton might be found
In a particle accelerator
When a proton and an anti-proton meat gamma photons are produced describe these photos as fully as you can for a slow moving proton antiproton collision
Two gamma protons are produced with equal energy travelling in the opposite direction
Why is an electron positron pair produced most of the time during pair production than other pairs?
Because they have relatively low mass, therefore less energy required from the photon
What must be true for pair production to happen?
The minimum amount of energy of the photon must have the combined energy of the two particles at rest
Explain why dealing with waste from vision reactors is particularly important so that it does not come into general public water supply
The waste products of nuclear efficient are radioactive and harmful to humans and the environment. If the nuclear waste contaminates the water supply radioactive isotopes will easily be transferred to organisms and contaminate them.
Explain why a nuclei with a small nuclear number will release energy when it undergoes fusion
Combining small nuclei will increase the average binding energy per nuclear therefore a lot of energy would be released during nuclear fusion
Explain why a greater input power is required for fusion reactors rather than fission reactions
For fusion to happen to nuclei need to get close enough for the attractive strong force to overcome the electric static repulsion between them the higher the temperature in the reactor the greater the speed of the particles and so the closer the nuclei are able to get to each other Therefore it is more likely for a fusion reaction to occur. This means that for higher temperatures a higher power is needed to heat fusion react up
Boron 10 can be produced by either a single beta minus decay from barium 10 or a single beta plasticate from carbon 10 the mass defect of carbon and boron 10 is larger than the mass defect between beryllium 10 and boron 10 therefore which beta particle would have a higher velocity
Ask the most defect is greater between carbon tent and boron 10 more energy is released when carbon 10 decays into boron 10. This means the beta plus particle from the decay would have more kinetic energy and therefore travel at a high velocity. This is because the kinetic energy of the particle is equal to the total energy released minus the beta particle rest energy.
The rest mass of a deutron ( neutron and proton) is less than the sum of the rest masses of the constituent parts. When the duetron is separated It releases energy., compare this with a rocket ship which Deap parts by burning fuel to escape the gravitational pull so that the total of the rocket on the ground is significantly more than the mass of the rocket in space.
The deutron requires an input of energy to separate the proton and neutron. This create a mass defect therefore energy is released. However the rocket uses its internal energy to eject some mass at high-speed in order to gain gravitational potential energy and kinetic energy for the remaining journey of the rocket, however in both, situations energy is conserved considering the earth and the rocket as a single system
Explain why a negatively charged particle is often admitted from the nucleus of an atom even though that nucleus only consist of neutrons and protons
Because this negatively charge particle is caused by the negative radiation which is beta radiation resulting in the decay of neutrons which is when a neutron has into a proton releasing an electron
Why is iron the most stable nuclei?
Because it has the most binding energy per nucleon
When dealing with waste from fission reactors particular cam must be taken so that it does not come into contact with the general public water supply explain why
The waste products of nuclear fission are radioactive and harmful to humans and the environment therefore if the nuclear waste contaminate the water supply radioactive isotopes will be transferred to organisms causing serious harm
Explain why helium release energy when it undergo fusion
Because combining small nuclei will increase the average average binding energy per nuclear this means a lot of energy will be released as energy is conserved.
Explain why a greater input power is required for fusion reactors rather than fission
For fusion, the two nuclei need to get closer enough for the strong, attractive force to overcome the electrostatic proportion between them the higher the temperature in the reactor the greater the speed of the particle and the closer the nuclear are able to get to each other therefore fusion is more likely to occur this means much higher temperatures are required so a higher power is needed to heat the fusion reactors reactors
Boron 10 can be produced by either a single beta minus decay from beryllium 10 or a single beta plasticate from carbon 10 the mass defect between carbon and boron is larger than the mass effect of beryllium 10 and boron 10 which beta particle will have a higher velocity
As carbon and boron have a larger mass defect more energy will be released when carbon 10 the case into boron 10. This means the beta plus particle from the decay would have more kinetic energy and travel at a higher velocity. This is because the kinetic energy of a particle is equal to the total energy released minus the beta particle rest energy.
State some safety precautions when handling radioactive sources
Radioactive sources should be kept in a lead lined box when they are not being used
They should only be picked up using long handled tongues and take care not to point the source at anyone and keep it safe distance from them
Explain an experiment to calculate the half-life of a radioactive source
Using a Geiger tube which is connected to a data log and a computer place this opposite a radioactive source
First remove the radioactive source and calculate the background count by measuring the count on the guy mil tube over an interval of 30 seconds or more do this three times and find the mean then divide the reading on the tube by the interval to get the background count rate
Then place the radioactive source opposite the tube at an appropriate distance and record the radiation in entertainment was of 10 seconds two minutes?
Then plot a graph of count per second overtime and find when the accounts per second halves find the corresponding time and this is the half-life
When does Alpha decay normally happen?
Alpha decay normally happens when the nuclei is too heavy or too massive to be stable therefore needs to lose four nuclear numbers
Explain carbon dating
The radioactive isotope carbon 14 is used in radioactive dating living plants taking carbon dioxide from the atmosphere as part of photosynthesis including the radioactive isotope carbon 14 animals then take this carbon 14 when they eat the plant all living things will contain the same percentage of carbon 14 when they die, the activity of carbon 14 in the plant starts to fall with a half-lifearchaeological finds made from once living material can be tested to find the current amount of carbon 14 in them. This can then be used to calculate how long the material has been dead for or how old it is.
Explain carbon dating
The radioactive isotope carbon 14 is used in radioactive dating living plants taking carbon dioxide from the atmosphere as part of photosynthesis including the radioactive isotope carbon 14 animals then take this carbon 14 when they eat the plant all living things will contain the same percentage of carbon 14 when they die, the activity of carbon 14 in the plant starts to fall with a half-lifearchaeological finds made from once living material can be tested to find the current amount of carbon 14 in them. This can then be used to calculate how long the material has been dead for or how old it is.
What is meant by the decay constant of an isotope?
The probability of decay of a nucleus per unit time
A radioactive substance has 2000 nuclei the decay constant of the isotope of the substance is 0.1 seconds^-1
Given that the changing time is one second estimate the number of nuclei left after two seconds
Number of decay in the first second is 2000 nuclei multiplied by 0.1 meaning 200 nuclei decay so the nuclei left in after the first second is 1800
Therefore the number of decay in the second second is 1800×0.1 so the number of nuclei left after the second second is 1800-180 therefore the answer is 1620
How do you find the half-life of a substance using a graph of ln(A) against T?
Rearrange the formula A=A0 x e^-lt
Using logs, therefore the gradient is minus lambda
Then use this experimental value for lambda to the equation to find T half
Radioactive lead-214 changes to lead-206 series of decays involving alpha and beta minus emissions explain how many alpha and beta particles are admitted during this change
Alpha decay reduces the nuclear number by four and the proton number by two therefore changing the isotopes elements from lead however we want to keep the element as lead therefore as there will be two helium nucleus admitted as two alpha particles are admitted so the nuclear number reduces by 8 and the proton number reduces by 4 to keep the element lead we need to increase the proton number by four therefore there will be four base minus emissions as the beta decay does not change the nuclear number but it increases the proton number
Explain why the method of carbon dating is unreliable if the sample is less than 200 years old and if the sample is more than 60,000 years old
Less than 200 years
The decrease in activity would be too small to measure
More than 60,000 years
Most of the carbon 14 has decayed, therefore not a large enough amount of sample to record
An element can be formed by firing calcium 48 nuclear to a target however large numbers of calcium 48 nuclei need to be fired at the target for the element to be formed. Suggest why?
Positively charged nuclei in the calcium 48 will repel each other due to to the electrostatic force which has a larger range than the strong force which attracts the nucleus is together therefore only a small number of calcium 28 nuclei will have enough energy to get close enough to the target for them to fuse
How can we reduce error within the count rate experiment?
To reduce systematic error, we can calculate the background count radiation and subtracted from each calculated value of
Strontium-90 can be fully absorbed by one centimetre thick aluminium sheet but can pass through a 1 mm thick and aluminium sheet. Explain why this element is appropriate to monitor the thickness of the aluminium foil.
Radiation is only partly absorbed by thin aluminium but however can be fully absorbed by an aluminium past a certain thickness. This means the changes in absorption can be used to monitor thickness.
Give an equation for activity when power and energy is given
A= P/E
