Chapter 26 - Nuclear Physics

Question 1

Einstein’s Mass-Energy Equation

Answer 1

E = mc^2

Question 2

Interpretations of Einstein’s Mass-Energy Equation

Answer 2

Mass being a form of energy or energy having mass

Question 3

Rest Mass

Answer 3

The mass of an object when it isn’t moving

Question 4

Total kinetic energy released from a reaction

Answer 4

Use E=mc^2 by finding m as the difference in mass of the reactants and the products
This works the same for the Ek of particles causing a collision

Question 5

Binding Energy (ΔE)

Answer 5

The work that must be done to separate a nucleus into its constituent neutrons and protons

Question 6

Mass Defect (Δm)

Answer 6

The difference between the mass of the separated nucleons and the mass of the nucleus

Question 7

Finding the mass defect

Answer 7

Find the mass of the protons and neutrons and subtract the actual mass

Question 8

Binding energy per nucleon

Answer 8

The average work done per nucleon to remove all of the nucleons from a nucleus

Binding energy/number of nucleons

Question 9

Nuclear Fission

Answer 9

The process of splitting a large nuclei into smaller nuclei

Question 10

Induced Fission

Answer 10

The parent nucleus absorbs a neutron, causing it to split

Question 11

Spontaneous Fission

Answer 11

The parent nucleus splits but it isn’t caused by any external factors

Question 12

Thermal Neutrons

Answer 12

The slow neutrons absorbed by U-235 with mean kinetic energy similar to the thermal energy of the particle in the reactor

Question 13

Fission equations

Answer 13

U(235,92) absorbs a neutron to become U(236,92)

U(236,92) decays into Ba(141,56), Kr(92,36) + 3 fast neutrons for example

Question 14

PWR Reactor

Answer 14

A steel case contains uranium fuel rods, interspersed with control rods
Water is used as a moderator and coolant, it is heated by the fast electrons released and reduces their kinetic energy so it can be further absorbed
The water is pumped through a pressuriser to transfer steam to the turbines
Cold water from the turbines is pumped into the steel core

Question 15

Fuel rods

Answer 15

Made of enriched uranium, 97% U-238 and 3% U-235

Question 16

Control rods

Answer 16

Made from a material that readily absorbs neutrons (boron or cadmium)
They control the rate of reaction by being raised and lowered into the reactor core
If they are lowered further, they absorb more neutrons and the rate is slowed

Question 17

Moderator

Answer 17

Slows down fast neutrons released by the fission
Cheap, available and doesn’t absorb neutrons
Neutrons slowed down to energies close to the moderator particles
Mean kinetic energy 3kT/2

Question 18

Fission safety features

Answer 18

A steel vessel around the reactor core withstands pressure and temperature, absorbs gamma and beta
All encased in concrete to absorb gamma and neutrons
Reactors have a shut down system to lower the control rods completely
Remote handling devices raise and lower the fuel rods, more radioactive after use

Question 19

Fission environmental concerns

Answer 19

Neutrons of intermediate kinetic energy are absorbed by U-238, this decays into Pu-239, with a half-life of 24000 years and is toxic

Question 20

High-level waste storage

Answer 20

e.g. fuel rods/ radioactive sources
Fuel rods removed by remote control and stored underwater for at least a year to cool
Unused uranium and plutonium is removed and stored in containers
Excess waste is left in deep containers for centuries

Question 21

Intermediate-level waste storage

Answer 21

e.g. radioactive materials with low activity and containers of radioactive material
Stored in steel drums encased in concrete

Question 22

Low-level waste storage

Answer 22

e.g. lab equipment

Buried underground in metal casing

Question 23

Nuclear fusion

Answer 23

Bringing two smaller nuclei to around 10^-15m, the strong nuclear force becomes attractive and joins them

Needs high temperatures and pressures

Question 24

Hydrogen burning cycle

Answer 24

2 protons form deuterium, a positron and a neutrino
deuterium and a proton form He-3
2 He-3 nuclei fuse to He-4 and 2 protons

Question 25

Fusion on Earth

Answer 25

We don’t have the same pressures as the Sun so we need a 10x higher temperature, magnets must be used to control the plasma