Chapter 26 Nuclear

Question 1

Einstein’s equation of mass energy

Answer 1

E = mc2

Question 2

How does einsteins equation work

Answer 2

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

Question 3

In natural decays of unstable nuclei, particles and ENERGY is released.

How can we work out the energy is released, what conservation thid time?

Answer 3

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

Question 4

What happens when a positron snd electron collide anyways

How to work out energy released for two of no ke but annihilating

Answer 4

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

Question 5

What is PAIR PRODUCTION
Thus what is the minimum energy this photon must have

Answer 5

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

Question 6

What happens in LHC at cern with protons

Answer 6

Protons are collided at very high speeds. From the KE used ti collide, mass is created to make hadrons etc

Always calculate mass difference

Question 7

Why is the mass of separated deuterium atoms GREATER than when it’s just deuterium

Answer 7

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

Question 8

What does mass defect mean
ACCC DEFINITION

What does binding energy mean?
ACC DEFINITION

Answer 8

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

Question 9

How to work out the binding energy of a nucleus then

Answer 9

E = kc 2

Binding energy = mass defect x c 2

Question 10

On the graph , how do we adjust for comparing binding energies between different isoptopes

Answer 10

Different isotopes wil, have different total binding energies, thus they are measured in total binding energy / nucleons

So binding energy per nucleon

Question 11

What does a HIGHER binding energy per nucleon mean in terms of stability

Answer 11

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

Question 12

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

Answer 12

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

Question 13

Why is energy released when nuclei become higher BE nuclei

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What happens in nuclear fission

Hoe does it happen, what is released

Answer 15

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

Question 16

How is energy released in fission

What is this equal to (2 ways)

Answer 16

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

Question 17

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)

Answer 17

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

Question 18

What are all the different components in a nuclear fission reactor

Answer 18

1) fuel rods itself
2) coolant
3) moderator (could be the coolant)
4) control rods

Question 19

Explain all 4 of the main components in a nuclear fission reactor

Answer 19

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

Question 20

How does a moderator work

Answer 20

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

Question 21

What are moderators and coolants typically

Answer 21

Both water, can be the same

And also the control rod is automatically put in

Question 22

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

Answer 22

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

Question 23

What’s the main idea behind fusion how does it work

How is energy released on fusion

Answer 23

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

Question 24

How does fusion actually happen,
what are problems-
and thus what conditions are needed

2) where are these conditions naturally found

Answer 24

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

Question 25

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

Answer 25

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

Question 26

Again (proton proton cycle)

Answer 26

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

Question 27

Why is this the most common reaction in stars and do fusions of HIGHER mass happen?

Answer 27

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

Question 28

How to work out energy of all nuclei in a sample produced potentially

Answer 28

Use molare mass to work out moles

Multiply moles by avagdro

Muktilky avadgaro by each energy