Nuclear physics

Question 1

Define the decay constant

Answer 1

The probability that one atom will decay per unit time

Question 2

What does N represent

Answer 2

N represents the number of radioactive atoms

Question 3

Define the activity of a sample

Answer 3

The activity of a sample is the number of nuclei that decay per second

Question 4

What is the decay constant

Answer 4

The probability of the decay of any nucleus per unit time

T1/2 = ln2/λ

Question 5

What is the radius of the nucleus

Answer 5

1.4 x 10^-15

Question 6

What does the radius of a nucleus depend on

Answer 6

The radius R of a nucleon number depends on the mass number A.

R = r0A1/3

Question 7

What is r0

Answer 7

r0 is the constant between the radius of a nucleon and the nucleon number

Question 8

Density of the nucleus

Answer 8

Radius = R=R0A^1/3
Volume = 4/3piR^3

Density = mass/volume

Question 9

Define the term atomic mass unit

Answer 9

The atomic mass unit is defined as one twelfth as of the mass of an atom of carbon-12

Question 10

Binding energy

Answer 10

The energy required to completely separate the nucleus into its individual nucleons

Question 11

What is the mass defect of a nucleus

Answer 11

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

Question 12

Nuclear fusion

Answer 12

A process where two nuclei join together to form one larger nucleus due to high temp and pressure that can overcome electrostatic forces

Question 13

What is 1u equivalent to in MeV

Answer 13

1u = 931.3MeV

Question 14

Radius of a nucleus

Answer 14

R = r0A^1/3

Question 15

De broglie wavelength

Answer 15

λ = hc/E (E in J)

Question 16

Electron diffraction first minimum

Answer 16

sinθ = 1.22λ/2R

Question 17

Activity

Answer 17

A = A0e^-λt

Question 18

Number of atoms in a sample

Answer 18

N = n x Na

n = no. of mols
Na = Avogadro

Question 19

Alpha particle that rebounds

Answer 19

Initial Ek = E elec = Charge of nucleus x Charge of alpha/ 4πε0r

Question 20

What is critical mass

Answer 20

The amount of fuel needed for a fission chain reaction to continue at a steady rate on its own

Question 21

Function of the coolant

Answer 21

Coolant is sent around the reactor to remove heat produced by fission. The coolant needs to be a liquid or gas at room temperature and be efficient at transferring heat. Water is often used

Question 22

Function of the Moderator

Answer 22

The moderator slows and absorbs neutrons. A moderator needs to slow down some neutrons so they can cause further fission (high velocity neutrons will just bounce off the U nucleus) The moderator slows neutrons down through elastic collisions.

Water is used because it contains hydrogen which has hydrogen (similar mass to a neutron)

Question 23

Function of the control rods

Answer 23

Limit the number of neutrons in the reactor. They absorb neutrons so that the rate of fission is controlled. Made of a material that absorbs neutrons (Boron)

Question 24

Function of shielding

Answer 24

A thick concrete case surrounds the reactor to stop the radiation escaping

Question 25

Risks and benefits of Nuclear Power

Answer 25

Benefits: There is enough fuel to keep generating energy for centuries
Doesn’t release much greenhouse gas
Very efficient, generates thousands of times more energy per kg than fossil fuels
Energy can be generated constantly unlike other renewables

Risks: Have to be designed and built extremely carefully to avoid the risk of a nuclear disaster.
Waste disposal and making sure it doesn’t endanger people and the environment