Topic 11 - Nuclear Radiation Flashcards
What does an atom do if its unstable
it breaks down to become more stable
What is instability caused by?
- too many neutrons
- no enough neutrons
- too much energy in the nucleus
Structure of Alpha
helium nucleus (2 protons, 2 neutrons)
Structure of Beta
Made of single electron (no mass)
Structure of Gamma
short wavelength, high frequency electromagnetic wave
Range of alpha in air
between 2cm-10cm (loses energy due to interactions)
Range of Beta in air
a few metres (17m)
Range of Gamma in air
Very long/ infinite (no charge/mass)
Penetration of alpha
weak (absorbed by paper)
Penetration of Beta
absorbed by 3mm of aluminium
Penetration of Gamma
absorbed by metres of lead
Ionising ability of alpha
strong
Ionising ability of beta
weakly
Ionising ability of gamma
very weakly
speed of alpha
slow
speed of beta
fast
speed of gamma
speed of light
is alpha affected by B-fields
yes
is beta affected by B-fields
yes
is gamma affected by B-fields
no
uses of alpha
smoke detectors, cancer treatment, poisin
uses of beta
tracers, monitoring material thickness
uses of gamma
cancer treatment, sterilising equipment
what emits background radiation?
rocks, cosmic radiation, living things, manmade radiation, air
How to account for background radiation
record it before you do the experiment and subtract it from the totals
method of detecting radiation
- photographic film
- leaf electroscope
- cloud/bubble chambers
- Geiger Muller tube
Geiger Muller Tube
when any type of radiation enters the tube it produces ions in the gas, enabling the tube to conduct and complete the circuit. This creates a voltage pulse which is outputted, amplified and counted.
Photographic Film
where the film has been exposed to radiation it darkens
Leaf electroscope
a radioactive source ionises the air discharging the electroscope
Cloud/Bubble Chambers
a radioactive source ionises and condenses the alcohol leaving a trail
Ionisation
radiation is very energetic and knocks electrons off molecules
Why is alpha the most ionising
its heavy and slow moving with the strongest charge meaning it interacts strongly with matter
Dangers of ionising radiation
- release lots of energy and cause burning
- changes the chemistry of cells causing radiation sickness or hair loss
- cells may be genetically changed causing cancer
Inverse square law for gamma radiation
- gamma rays always spread out away from the source.
- the intensity of gamma follows an invers square
When does an inverse square apply for alpha and beta
in a vacuum so that no interaction can occur
how is a nucleus held together
strong nuclear force
why would a nucleus not hold together without the strong nuclear force?
its made up of many positive charges which would all repel by the electrostatic force of repulsion
stable nuclei
electrostatic and strong nuclear forces are balanced
unstable nuclei
electrostatic forces and strong nuclear forces are not balanced. they try to become more stable by emitting alpha, beta or gamma
daughter nucleus
when a parent nucleus attempts to become more stable it emits alpha or beta particle its left with a different number of protons and neutrons
parent nucleus
the original unstable nucleus
alpha decay
produced when a large unstable nucleus decays
Beta decay
produced when a neutron changes to a proton also produces a neutrino
How do we a neutrino is produced in beta decay?
The beta particles are emitted with a range of energies that can only be explained if another particle was emitted
neutrino with beta - decay
electron antineutrino
neutrino produced with beta + decay
electron neutrino
When does beta + decay happen
for nuclides below the stability line
When does beta - decay happen
for nuclides above the stability line
Gamma decay
the release of energy from a nucleus which leaves the structure of the nucleus otherwise unchanged
When does gamma often occur
after alpha/beta emission because the nuclei is left in an excited state
Electron capture
when an unstable nucleus captures an orbital electron from one of its lowest energy levels. A proton then changes to a neutron and a neutrino is emitted.
When doe electron capture happen?
for nuclides below the stability line
Why can you no predict nuclear decay
it spontaneous and random
How can you try and measure decay
calculate the probability of decay. Every type of isotope decays a different rate but particular isotopes decay at the same rate.
decay constant, λ
the probability that an individual nucleus will decay within a unit of time
activity, A
the number of nuclei that decay in a unit of time
activity/ decay constant equation
A = λN
half life, Τ
the average time is takes for the number of undecayed nuclei to half
decay constant and half life equation
λ = ln2/Τ
finding the half life from an exponential decay graph
read the time when N is half the original value
how do carbon dating work
all living things take in carbon-14 and when they die this stops. Over time carbon-14 decays and so the amount of carbon-14 in an ancient specimen can be used to date bones
How to age rocks
measure how much uranium-235 has changed to lead-206
mass defect
the difference in mass
Einsteins equation
E = mc^2
How is extra mass explained
the total amount of mass and energy is conserved E = mc^2
binding energy
The energy needed to separate a nucleus into individual protons and neutrons
What makes a nucleus more stable
if it has a higher binding energy per nulceon
What does the daughter nucleus always have
a higher binding energy per nucleon than its parent
1 atomic mass unit, u
1.66x10-27kg
Nuclear Fission
A slow moving neutron is fired at a heavy nucleus which absorbs it and making it unstable. This causes it to split into daughter nuclei and excess neutrons.
How does nuclear fission work
the strong nuclear force only acts over a short distance so when a neutron is absorbed it displaces particles possibly allowing the electrostatic force to overcome strong nuclear force
chain reaction
when the neutrons released from one reaction go on to cause another reaction
Nuclear fusion
when smaller nuclei combine to produce larger nuclei and release energy in the process.
Why is Fusion better than Fission
- power output per kilogram is greater
- raw materials are cheap and easily available
- no radioactive waste is produced (if there is some it has a very short halflife)
How does fusion occur in stars?
- proton fuses with proton, forming He-2
- one proton decays to a neutron, leaving H-2
- another proton fuses with H-2, forming He-3
- two He-3 nuclei fuse resulting in He-4 and a left over proton which are returned to the process
Where does fission occur on the binding energy curve
To the right of iron
Where does fusion occur on the binding energy curve
to the left of iron
Advantages of fusion over fission
- power output per kilogram is greater
- raw materials are cheap and easily available (water)
- no radioactive waste (if there is any it has avery short half life)
What are control rods made of in nuclear power stations?
boron (very stable)
Random process of decay
don’t know when or or which nucleus will decay next. In a given time interval each nucleus has a fixed probability of decay.
In smoke detectors when does a stream of alpha particles cause a charge to flow.
The alpha particles ionise the air and the ions/electrons move in the uniform electric field between the plates.
Spontaneous decay
can’t be influenced by external factors
Kinetic energy in nuclear fusion method
- KEa + KEb = Q
- conservation of momentum MaVa = MbVb
- rearrange Va = MbVb/Ma
- find value of Mb/Ma (using relative masses)
- find Ea/Eb
- Use this proportion and Q to calculate KEa
The total number of free neutrons immediately after a fission reaction…
increases
The mass of the fission fragments is…
less than the mass of the nucleus before fission
What is required for fission to occur
Must absorb neutrons
What is true for both fusion and fission
Binding energy per nucleon increases
radioactive atom
has an unstable nucleus with emits alpha, beta or gamma radiation
fusion conditions (natural)
- extremely high temperatures to overcome electrostatic repulsion
- high density for sufficient collision rate
fusion conditions (reactor)
- extremely high temperatures to overcome electrostatic repulsion
- Strong magnetic fields to keep plasma from reactor wall
- high density/ enough fuel
why does fusion release energy
- binding energy per nucleon increases as the number of nucleons increases
- if binding energy per nucleon increases energy is released
why does fission release energy
- binding energy per nucleon increases as the number of nucleons decreases
- if binding energy per nucleon increases energy is released
why does fission require high temperature?
high temperature to provide enough energy to overcome the electrostatic repulsive force between
nuclei
why does fusion require high density?
high density to give big enough collision rate to maintain reaction
binding energy
The energy equivalent to the mass deficit when nucleons bind together to form an atomic nucleus
Alternative unit for activity/ what this means
s^-1. You can use it as a time, e.g. P = E/t you could use activity as time
