P2 - radioactivity Flashcards
Explain the Rutherford scattering experiment
A stream of alpha particles from a radioactive source where fired at very thin gold foil. When it hits a flash of light is produced that can be seen on the fluorescent screen surrounding the area so scattering at any angle can be seen
What are the conclusions from the Rutherford experiment and what do they show?
The Rutherford scattering shows that atoms must have a small positively charged nucleus that contains most of the atoms mass.
This is because the atom must have mostly empty space for most the alpha particles to just pass through.
Must have large positively charged nucleus as some of the positively charged alpha particles where deflected
Most the mass must be in the middle as the alpha particles are striking something that is bigger than themselves to be deflected back. Alpha particles have high momentum
How can you measure nuclear radius using the closest approach method?
what equation do you use?
By using the Rutherford scattering experiment ,when an alpha particle bounces back, the closet distance it got to the nucleus and stopped is distance R.
initial kinetic energy = electric potential energy so use the eletric potebital energy equationa dn re arrange for r
How can you measure nuclear radius using electron diffraction?
Use sin thearte = 1.22landa/2Radius
What’s the radius of a typical nucleus?
10^-15 metres
What is radioactive decay?
If an atomic nuclei is unstable, it will ‘break down’ to become more stable by releasing energy and or particles. Induvial radioactive decay is random an cannot be predicted
What is released in alpha decay?
what is released in beta minus decay?
what is released in beta plus decay?
what is released in gamma decay?
2 protons and 2 neutrons
electron
positron
short wavelength, high frequency electromagnetic wave
what stops the types of radiation?
paper stops alpha or few centineters of air,
3mn of aluminon stops beta,
several cm of lead or concrte stops gamma
what stops beta plus decay?
beta plus almost immediately get annihilated with electrons so they effectively have no range
what does I, K, x stand for in the inverse square law equation?
I stands for intensity
K stands for constant of proportionality
X stands for distance from source, m^2
What does A, landa, N mean in the decay rate equation?
Wat does N0 stand for?
A is the activity, Bq (1 bequell sis 1 decay per second)
Landa is the decay constant
N is the number of unstable nuclei in sample
The initial number of nuclei
what does Na and little n mean?
little n is the number of moles in a sample,
Na is the Avogadro’s constant
What is half life?
The half life of an isotope is the average time it takes for the number of unstable nuclei to halve.
How do you find the half life from a graph?
Look at the initial nuclei, go to half that value, draw a line across and down, this is ur half life
How does nuclear stability work in a nucleus?
the nucleus has the influence of the strong nuclear force holding it together and the electromagnetic force pushing the protons apart.
When is a nucleus unstable?
If it has too many neutrons
Too few neutrons
too many nucleons altogether so its too heavy
too much energy
When does alpha decay (emission) occur, what’s released?
Alpha emissions only happen in very heavy atoms. When an alpha is emitted the nucleon number decreases by 4 and the proton number decreases by 2
when does beta minus and plus decay occur (emission), what’s released?
Beta minus decay is the emission of an electron from the nucleus along with an antineutrino. Beta minus decay happens in isotopes that are neutron rich.
As a neutron changes to a proton in beta negative decay the proton number increases by one and nucleon number stays the same
Beta plus decay happens in isotopes that are proton rich. A proton gets changed into a neutron so the proton number decreases by 1 and the nucleon number stays the same. A neutrino and positron (beta plus particle) is emitted
When does gamma decay/emission occur?
After alpha or beta decay the nucleus often has excess energy as its an excited state. This energy is lost by emitting a gamma ray.
Another way is from electron capture , this is when a nucleus absorbs one of its own orbiting electrons which causes a proton to change into a neutron. A neutrino is also released. causes the nucleus to be unstable and release gamma radiation
In a NUCLEAR reaction what are the conservation rules?
In every nuclear reaction, momentum, charge, nucleon number and lepton number must be conserved.
what is the mass defect?
The difference between the mass of the nucleons and the mass of a nucleus.
So mass defect = mass of nucleons - mass of nucleus
What is binding energy?
How do you calculate the binding energy when given the mass defect?
The energy needed to separate all of the nucleons in a nucleus and its equivalent to the mass defect.
Change the mass defect into KG then find its energy equivalent using the E = mc squared equation. Then this gives you the answer in joules so find it now in Ev
How do you covert from J to eV?
J divided by the charge of an electron
How do you find the average binding energy per nucleon?
average binding energy = Binding energy/ nucleon number
What does higher average binding energy mean?
more stable nucleus
What is nuclear fission?
Large nuclei are unstable and some can randomly split into two smaller nuclei, this is called nuclear fission. This process is spontaneous if it happens itself and induced if we encourage it
How can fission be induced?
fission can be induced by making a neutron enter a nucleus causing it to be very unstable. (low energy thermal neutrons)
What is nuclear fusion?
Two light nuclei can combine to create a larger nucleus, this is called nuclear fusion. A lot of energy is released as the new nucleus has a lot more binding energy per nucleon
why do the nuclei need a lot of energy to get to the nucleus/
as all nuclei are positively charged, there will be an electrostatic force of repulsion between them, and nuclei need to get close enough for the attractive force of the strong force
What does energetically favourable mean?
where on the graph does fusion and fission become energetically favourable?
When does energy get released?
How do you find the energy released?
That the fusion or fission will give out energy.
Fusion to the left, fission to the right of 56 fe (iron)
Because energy is only released when the average binding energy per nucleon decrease’s
The change in binding energy
What si the fuel rods purpose in a nuclear reactor?
They provide as fuel for fission reactions, these fission reactions produce more neutrons which will induce other nuclei to fission (chain reaction), The neutrons have to be slowed down to be captured and are thermal neutrons.
what is the moderator’s job in a nuclear reactor?
Fuel rods need to be placed down in a moderator to slow down and absorb neutrons, keeps the fission going at a steady rate. As the moderator slows down neutrons through elastic collisions where kinetic energy is conserved.
The mass of the particles need to be similar too that of the neutron so water is used as helium is close, (more efficient collisions)
What’s the control rods purpose in the nuclear reactor?
The control rods control the number of neutrons in a reactor as the critical mass needs to be maintained for continues fission. The fuel rods absorb neutrons.
what is the job of the coolant in nuclear reactions?
the coolant is sent around the reactor to remove heat produced by fission, efficient at transferring heat, the heat is then used to make steam for powering turbines
What is reactor shielding?
The nuclear reactor is surrounded by a thick concrete case, which acts as shielding. This prevents radiation escaping and reaching the people working in the power station
What is the emergency shutdown process of a reactor?
The reactor can be shutdown if the control rods are fully lowered into the reactor.
How is fission waste products stored and handled?
unused uranium fuel rods only emit alpha radiation which is easy to contain.
However used fuel rods are more dangerous as they are unstable and radioactive and emit betta and gamma radiation. As its initially very hot it goes into cooling ponds and then when cooled is handled with sufficiently
what is the atomic mass unit?
1/12 the mass of a atom of carbon
