Lecture 2: Basic Nuclear Physics

Question 1

Name four coolant element examples:

Answer 1

H20, CO2, Na, Pb

Question 2

Name two moderator element examples:

Answer 2

H20, C

Question 3

Name three fuel element examples:

Answer 3

U, Pu, Th

Question 4

Name five waste element examples

Answer 4

U, Pu, Np, Am, Cm

Question 5

What is the atomic number?

Answer 5

Number of protons

Question 6

What is the neutron number?

Answer 6

Number of neutrons

Question 7

What is the atomic mass and how is it calculated?

Answer 7

Total mass (protons + neutrons)

Question 8

What is the conversion from amu to kg?

Answer 8

1.66 x 10^-27

Question 9

What is the mass (in amu) of a proton?

Answer 9

1.0073

Question 10

What is the mass (in amu) of a neutron?

Answer 10

1.0087

Question 11

What is the mass (in amu) of an electron?

Answer 11

0.0005

Question 12

Define a mole:

Answer 12

Unit for measuring large quantities of very small entities

Question 13

How many entities make one mol and what is it known as?

Answer 13

6.023 x 10^26 per kmol (Avogadro’s constant)

Question 14

What electrical unit is used for nuclear applications?

Answer 14

Electron Volt

Question 15

What is the definition and unit for Power?

Answer 15

Rate of doing work (J/s or W)

Question 16

Define an isotope:

Answer 16

A form of the same element with an equal number of protons but different number of neutrons in their nuclei.

Question 17

Why are isotopes useful as a nuclear fuel?

Answer 17

Unstable > Energetically favourable to change form > Radioactive decay

Question 18

Define alpha decay:

Answer 18

Ejection of a helium nucleus known as a alpha particle

Question 19

Define beta decay:

Answer 19

Neutron > Proton + Electron (emitted)

Question 20

Define gamma decay:

Answer 20

Emission of a gamma (high energy photon)

Question 21

What can stop alpha, beta, and gamma emissions?

Answer 21

Paper
Metal sheet
Lead or thick concrete

Question 22

What is the rate of decay dependent on?

Answer 22

Number of present isotopes

Question 23

Define half-life:

Answer 23

Time taken for radioactivity of an isotope to halve.

Question 24

Why are short half-lives dangerous?

Answer 24

Heavy / fatal dose in a short time.

Question 25

What is the purpose of neutrons in a nucleus?

Answer 25

Attract nucleons due to very short range of nuclear forces, acting as a glue.

Question 26

True or false: More neutrons are needed to ‘glue’ protons together for higher atomic masses.

Answer 26

True

Question 27

Define a mass defect:

Answer 27

Difference between the mass of an atom and its constituent particles.

Question 28

What is the mass defect equal to?

Answer 28

Binding energy of a nucleus.

Question 29

How does the mass defect relate to fission and fusion?

Answer 29

Explains release of energy per nucleon (E=mc^2)

Question 30

What does the binding energy per nucleon inform about fission and fusion?

Answer 30

Nuclei inherently want to exist in highest energy state, therefore fission can occur spontaneously whereas fission must overcome repulsive forces.

Question 31

How is sufficient activation energy provided to initiate fission?

Answer 31

Neutron collision with nucleus causes unstability.

Question 32

How is heat generated by fission?

Answer 32

KE of fragments lead to collisions of with atomic lattice of the fuel

Question 33

Name two interaction mechanisms between neutrons and nuclei:

Answer 33

Elastic scattering and absorption

Question 34

Define Elastic Scattering:

Answer 34

Neutrons are deflected with some loss of KE. They bounce off nucleus without joining, therefore nucleus absorbs energy.

Question 35

Define Absorption:

Answer 35

Neutron absorbed by target nucleus, thus gaining KE and binding energy. Becomes unstable so followed by energy release mechanism.

Question 36

Name five energy release mechanisms and their short codes:

Answer 36

Emission of gamma radiation (n, gamma)
Emission of charged particle (n, p) or (n, alpha)
Emission of several neutrons (n, 2n)
Fission (n, f)
Inelastic scattering (n, n’gamma)

Question 37

Define inelastic scattering:

Answer 37

KE of incoming neutron is retained then excess energy release in the form of a gamma.

Question 38

What is neutron capture?

Answer 38

Any absorption that does not result in fission

Question 39

Define cross-section, sigma:

Answer 39

The probability of a neutron interacting with surrounding matter.

Question 40

Why are moderators so critical?

Answer 40

To reduce the incident neutron energy to match the nucleus discrete energy levels in order to increase the probability of capture and fission.

Question 41

What is neutron moderation?

Answer 41

Slowing down neutrons to lower energy to improve the probability of fission occurring.

Question 42

How is moderation achieved?

Answer 42

Scattering

Question 43

Are lighter or heavier nuclei better at performing moderation and why?

Answer 43

Lighter as they transfer momentum better from the neutron (KE transferred from neutron to nuclei)

Question 44

What is the energy of a thermal neutron?

Answer 44

0.023 eV

Question 45

What is a thermal neutron?

Answer 45

A neutron readily able to cause fission

Question 46

What is the energy of a fast neutron?

Answer 46

2 MeV

Question 47

What are the two fundamental forces between nuclear particles?

Answer 47

Strong nuclear force (attractive)
Electromagnetic force (repulsive)

Question 48

What are the relative ranges of the two nuclear forces?

Answer 48

Strong nuclear force (attractive):
Very short, within the nucleus.

Electromagnetic force (repulsive)
Infinite range, diminishes with distance.