Nuclear Physics

Question 1

Key observations of Rutherford’s Alpha Scattering Experiment

Answer 1

1) atom is mostly empty
2) nucleus is positively charged
3) mass of atom is concentrated in a very small volume

Question 2

Define atomic mass unit (u)

Answer 2

Atomic mass unit is defined as the 1/12th of the mass of a carbon-12 atom.
u = 1.66 x 10^27 kg

Question 3

Define mass defect

Answer 3

Mass defect is the difference between the total mass of the separate nucleons in a nucleus and the combined mass of the nucleus.

Question 4

Define binding energy

Answer 4

Binding energy is the energy required to separate the nucleons in a nucleus to infinity.
Binding energy is the energy equivalent of the mass defect of a nucleus.

Question 5

Define binding energy per nucleon

Answer 5

Binding energy per nucleon is the average energy per nucleon needed to separate a nucleus into its constituent nucleons to infinity.
( measures the nucleus’s stability )

Question 6

Element of highest binding energy

Answer 6

Fe-56, 8.8 MeV ( one of the most stable nuclei)

Question 7

Define nuclear fission

Answer 7

Fission is the splitting of a heavy nucleus into two lighter nuclei of approximately the same mass.

Question 8

Define nuclear fusion

Answer 8

Nuclear fusion is the process where two light nuclei combine to form a nucleus of greater mass.

Question 9

Factors that are conserved during nuclear reaction

Answer 9

1) total number of nucleon
2) total charge
3) total mass-energy
4) total momentum

Question 10

Define radioactive decay

Answer 10

Radioactive decay is a spontaneous and random process in which an unstable nucleus emits alpha particles, beta particles or gamma radiation to become more stable.

Question 11

Define exponential decrease

Answer 11

An exponential decrease refers to a situation where a quality reduced at a rate proportional to its current value.

Question 12

Define decay constant

Answer 12

Decay constant is the probability per unit time of the decay of a nucleus.

Question 13

Formula to find activity of a radioactive source

Answer 13

A = λ N

Question 14

Define count rate

Answer 14

Count rate is the rate at which emissions from a radioactive source are detected.
Count rate is a fraction of activity of a radioactive source.

Question 15

Define half-life

Answer 15

Half-life is the average time taken for the number of undecayed nuclei to be reduced to half its original value.

Question 16

Alpha decay

Answer 16

Emit alpha particle
mass 4u, charge +2e
strong and efficient ioniser (coz relatively large mass and charge)
penetrating power weak ( stopped by a piece of paper, few centimeter of air)

Question 17

Beta decay

Answer 17

Emit a beta particle(electron) and a neutrino
9.11 x 10^31 kg
-e charge
less efficient/moderate ioniser (smaller mass and charge compared to alpha)
penetrating power moderate ( stopped by few millimetres of aluminium, a metre of air)

Question 18

Gamma decay

Answer 18

emit photon or electromagnetic wave (10^-11 - 10^13 m wavelength)
no rest mass, no charge
weak ionising ability due to lack of charge
strongest penetrating power (stopped by at least 10cm of lead, unlimited air and several metres of concrete)