yr2-Nuclear (radioacivity)

Radioactive decay

when an unstable nucleus becomes stable

Neutron rich nucleus

too many neutrons

What decay does a neutron rich nucleus experience?

Beta minus

n → p + e^- + anti electron neutrino

Proton rich nucleus

Too many protons in the nucleus

Proton rich decay?

Beta plus decay

p → n + e⁺ + electron neutrino

Heavy nucleus

too many neutrons and protons

Heavy nucleus decay/?

Alpha / helium emission

Nucleus with too much energy emits….

Gamma radiation

Have we discovered the heaviest elements?

snf keeps nucleus together , electrostatic force of repulsion between protons.

snf uses the pion which has limited range so over a large range it is non existent, electrostatic force uses a photon has endless range so it will always exist.

the larger the nucleus, the shorter the distance the snf can cover so the nucleus cant stay together and will decay.

Number of protons varying with the number of neutrons

Between 0-20 protons the rate at which the neutrons and protons increase is almost identical

Between 20-80 protons, the rate of increase of the neutrons is faster than the increase of protons

Why does the rate of neutrons increase faster than the rate of protons?

An increase of protons would increase the electrostatic force of repulsion between the protons in the nucleus. By increasing the number of neutrons, there is natural increase in the snf which keeps the nucleus together rather than apart.

Why is decay random?

Each unstable nuclei has an equal chance of decaying

Half life?

The average time taken for the number of unstable nuclei to fall by half of its current amount

Current number of unstable nuclei formula?

N = N_o / 2ⁿ 

where N_o is the original number of nuclei and n is the number of half lives that have passed

Activity?

number of decays per second

Bq

Activity formula?

the rate in change of the number of unstable nuclei over a change in time

what relationship does activity posses?

exponential

current number of unstable nuclei with a constant lambda?

N = N_o e^{-lambda x t}

what else follows the N= N_o e^{-lambda x t} format?

Activity

Mass

Intensity

Count rate

Half life formula?

t_1/2 = ln(2)/lambda

What is lambda?

the decay constant

what does the decay constant mean?

how probable a given unstable nuclei will decay

what does it mean for half life if lambda is really large ?

half life will be very small

Intensity?

total energy per unit area

I = nhf / 4 pi r²

what law does intensity follow?

inverse square law

I = k / r²

What is 1u equal to?

1u = 931.5 MeV

Binding energy?

The total energy required to separate a nucleus into protons and neutrons

Binding energy equation?

E =C² m

Mass defect ?

The difference in the mass between the separate protons and neutrons and its nucleus

Binding energy of a free neutron?

Zero!

Binding energy per nucleon vs atomic mass graph?

Starting at 1MeV, our gradient is steep, hence the change in binding energy per nucleon is large as we approach Iron.

After Iron our gradient is gently sloping hence we have a smaller change in binding energy per nucleon

Why does fusion produce more energy than fission ?

Because it has 7.7MeV with less elements before iron compared to the 0.9MeV with more elements afterwards

Why do we want fission?

Greater binding energy

Breaking down to reduce the number of protons and neutrons

Product B energy > reactant B energy

Why do we want fusion?

Releases more energy than fission from a small initial mass

Abundant fuel supply - readily available and better than finite resources

Does not cause pollution

Less radioactive waste produced compared to fission

Higher power output

Closest approach?

Allows us to find the radius of a given nucleus

True radius formula?

R = r (A)^1/3

r = radius of a proton or neutron

A = atomic mass of element

Radius of a nucleus approximation?

1×10^-15

HEED?

High energy electron diffraction

HEED Radius approximation?

Rsintheta =0.61lambda

What does our sintheta stand for ?

Angle at the first minimum

Lambda in HEED?

Wavelength of the electrons being used

Benefits of HEED?

Electrons are leptons and do not experience the SNF unlike alpha particles so it would not interact with nucleons in a nucleus

Law of the closest approach method ?

We cannot accelerate our alpha particle further as the range for SNF is 0.5-3 fm , hence the particle would become a part of the element used in the experiment

Same thing goes for using an isotope of the element , introducing more nuclei introduces more SNF, possibly attracting the alpha took much and causing them to merge

What is nuclear fission?

When a nucleus splits to form two daughter nuclei, neutrons and energy

Control rods?

Rods found in nuclear reactors to absorb neutrons and control the rate of reaction

The lower the rods, the more neutrons that are absorbed hence the rate of fission decreases

The moderator?

A material that absorbs energy from fast moving neutrons to slow them down to speeds that can be absorbed by thermal neutrons to induce fission

Fuel rods?

Contains a fissile material where each rod has less than the critical mass so that fission reactions do not become uncontrollable

Coolant?

Carries away the thermal energy produced by fission reactions to generate steam and turn generators

What is the critical mass?

The smallest amount of mass required in a fission reactor to create a chain reaction

What is nuclear fusion?

The joining of two smaller nuclei to form a larger nucleus and to release energy

Rutherford scattering

The discovery of a positively charged nucleus by firing alpha particles at a thin sheet of gold

What happened to most alpha particles?

They passed straight through

Hence the atom is mostly empty space

What happened to some alpha particles?

They were deflected by a large angle

Suggesting that the centre of the atom is very positively charged

What happened to few alpha particles?

They were deflected by more than 90 degrees

Suggesting that the centre of the atom is very dense but small