Chapter 26 Nuclear Flashcards
Einstein’s equation of mass energy
E = mc2
How does einsteins equation work
Any increase in energy (potential and kinetic) results in a resulting increase in mass, and Same for decrease
This happens all the time, but because ofnc2, the increase / decrease in mass so small for us
In natural decays of unstable nuclei, particles and ENERGY is released.
How can we work out the energy is released, what conservation thid time?
CONSERVATION OF MASS ENERGY
- the total mass and energy in a system combined will be conserved
So WORK OUT THE CHANGE IN MASS
= RELATE THAT TO THE INCREASE IN ENERGY
What happens when a positron snd electron collide anyways
How to work out energy released for two of no ke but annihilating
This is ANNHILATION , they collide, mass die spears and energy released
2) Positrons and electrons have same MASS
So chnage in mass = 2 me , and can work out the increase from there
(If they had ke, this would change too
What is PAIR PRODUCTION
Thus what is the minimum energy this photon must have
Here a PHOTOM vanishes and all itd energy turns into TWO PARTICLES, anti and normal
- thus the energy the photon must have must be equal to energy of 2x mass or one particle , to be minimum allowed to happen
What happens in LHC at cern with protons
Protons are collided at very high speeds. From the KE used ti collide, mass is created to make hadrons etc
Always calculate mass difference
Why is the mass of separated deuterium atoms GREATER than when it’s just deuterium
It’s held by string nuclear bonds , and so to break this bond, energy put in
If energy put in by Einstein mass will INCREASE
Thus when separated the mass will be HIGHER
What does mass defect mean
ACCC DEFINITION
What does binding energy mean?
ACC DEFINITION
It’s the difference in mass between COMPLETELY SEPARATED NUCLEONS and the mass of a nucleus when nucleons are BONDED
2) BINDING ENERGY is the energy that related to the MASS DEFECT, the energy put in to CAUSE it in the first placement
- the minimum energy required ti selected a nucleus into its constituent nucleons
How to work out the binding energy of a nucleus then
E = kc 2
Binding energy = mass defect x c 2
On the graph , how do we adjust for comparing binding energies between different isoptopes
Different isotopes wil, have different total binding energies, thus they are measured in total binding energy / nucleons
So binding energy per nucleon
What does a HIGHER binding energy per nucleon mean in terms of stability
It means the nucleons are held more tightly at the nucleus, and thus the atom is MORE STABLE
So more stable = higher binding energy per nuckeon
Explain features of graph binding energy per nucleon against nuclear mass
What is the most stable
1) what is going on with fusion goin up from 0 and fission down from 238
Initially as nuclear mass increases, so does being energy until you get to 56
Similarly as nucleon number decreases from 238, binding energy also increases until 56
= thus iron 56 has the HIGHEST BINDING ENERGY per nucleons, and thus is thr most STABLE isotope ever
2) fusion is the process of smaller mass nuclei combining to produce nuclei if greater A. This will always be of a HIGHER binding energy than the two prior nuclei, as fusion caps at iron 56. This is why arrow points upwards
- here as it goes to a higher binding energy atom than it was before, energy is RELEASED , mass decreases
3) fission is process when big nuclear A goes to smaller daughter nuclear A ti become more stable until iron 56 too
- thus it will always go to two daughters that have HIGHER BE than thr larent. Thus energy is released again
Why is energy released when nuclei become higher BE nuclei
When separated nucleons become the nucleus again, energy is released = ti the binding energy if that nucleus, bevause when it went from nucleus to nucleons, energy put in was binding energy
Thus when going from less binding energy nucleons to higher, energy released is = to the difference of binding energies
So explain again why fusion fission and radialcatice decay all produce energy using the graphs
Why especially alpha radiation had high energy released!
Why fusion more energy than fission
Fission becomes two daughter nuclei of BE greater than parent, as it goes up in the growth. Thus energy released
Fusion become nuckei of greater BE than before, so energy released,
3). RADIATION like alpha decay is bevause the particles produced , new element and alpha, always have greater BE combined than before so energy released. Remember alpha helium has one of highest BE
4) fusion more than fission bevause the increase in BE seems to be much greater than anything else, so the MOST ENERGY IS RELEASED
What happens in nuclear fission
Hoe does it happen, what is released
Isotopes of something like uranium 235 absorb a THERMAL NEUTRON , making it uranium 236 (a more unstable isotope )
- this splits VERY FAST into two other elements , and also 3 fast moving neutrons and energy
How is energy released in fission
What is this equal to (2 ways)
This is because there is a decrease in mass, so energy is released. Energy released = to this in e =mc2
Or an increase in binding energy (goes higher). The energy released is = to the differenc sin binding energy too
How can a potential chain reaction be produced from a fission reactor with a lot of desired uranium 235
Fast or slow neutrons needed?
What would this cause and why are there protection instead)
Each fission reaction produces 3 FAST MOVIJG NEUTRONS. Now only slow moving will induce fission, so imagine if they were slowed down, then it would be a chain reaction, with amount of fissions = 3 ^n, exponential energy growth
Too much energy = bomb. Thus there are barriers in olace
What are all the different components in a nuclear fission reactor
1) fuel rods itself
2) coolant
3) moderator (could be the coolant)
4) control rods
Explain all 4 of the main components in a nuclear fission reactor
1) fuel rods are the source of the reaction, typically uranium 238
2) coolant is a source of liquid like water thst cools down excess thermal energy produced by reactions, don’t want too much
3) moderator is there to SLOW DOWN the 3 FAST neutrons that are produced
4) control rods are made from BORON or cadmium and ABSOROB extra neutrons automatically so thst edponeitsl chain reaction doesn’t take palce
How does a moderator work
Fast neutrons will bounce against fuel almost with no energy loss, but with carbon nuclei or DEUTERIUM, there’s a high chance it transfers significant kinetic energy ti them and SLOW DOWN,
Thus water and CARBIN typical moderators
What are moderators and coolants typically
Both water, can be the same
And also the control rod is automatically put in
what is the most hazardous thing
Why is there a negative environmental impact when dusting fuel like uranium
2) where must it be kept then for disposal why this hard
They regularly absorb a neutron and decay into plutonium 239
This is so stable at 24k years half life and EXTREMELY HAZARDOUS , toxic and radioactive
2) must be buried deep underground, and causes many problems , don’t want to get into water etc
What’s the main idea behind fusion how does it work
How is energy released on fusion
Fusion is the fusing if two small nuclear mass nuckei combining ti make a bigger nuclear mass nuclei, and ENERGY RELEASED IN THE PROCESS
Energy released is = to the change in mass in equation OR the difference in BINDINF ENERGIES OF the two both compared to things after
How does fusion actually happen,
what are problems-
and thus what conditions are needed
2) where are these conditions naturally found
Fusion happens when two nuckei get SO CLOSE together so that’s they can be absorbed together through the STRONG NUCLEAR FORCE
- here as thr nuclei are POSTITIVE, there is a super string repulsion .
- thus high external energy required so thst this can be overcome
2) condtions thus are high tempertaures and pressures , and this is find in cores of our stars
What is the main production route PROTON PROTON / HYDROGEN BURNING CYCLE that most frequently takes place in stars
How is energy released each stage
HOW CAN THE CYCLE REPEAT
1) two protons , hydrogen atoms fuse to make DEUTERIUM, positron + neutrino
(Nuclear mass and charge conserved, so A POSITRON RELEASED + normal NEUTRINO)
- difference in mass and binding energy releases energy, from 0 binding energy to 2.2 MEV
2) deuterium reacts with another proton fully ti make helium 3 nucleus
- releases more energy
3) helium 3 nucleus reacts with another HELIUM 3 NUCKEUS to produce helium 4 2 alpha nucleus, and 2 protons
This releases more energy
NOW THE CYCLE CAN REPEAT WITH THE TWO PROTONS
Again (proton proton cycle)
Proton proton = deuterium, positron and neutrino + energy
Deuterium + proton + 3/2 helium + energy
3/2 helium + 3/2 helium = 4/2 helium + 2 protons and energy
2 protons restart chain
Why is this the most common reaction in stars and do fusions of HIGHER mass happen?
This is EASISEST TO DO, the higher the charge etc and mass it becomes so much harder to fuse
But this does occur in different stages of a stars life, when more harsher condtions are present when density if planet decreases etc and temp goes up agsin, when all hydrogen run out
How to work out energy of all nuclei in a sample produced potentially
Use molare mass to work out moles
Multiply moles by avagdro
Muktilky avadgaro by each energy
