20 Nuclear Physics

Question 1

Why do majority of α-particles pass undeflected through the foil in Rutherford’s gold foil experiment?

Answer 1

The nucleus is very small compared to the atom, thus the atom is mostly made of empty space

Question 2

Why do a small fraction of α-particles scatter at large angles (>90°) in Rutherford’s gold foil experiment?

Answer 2

Majority of the mass of the atom is concentrated in a very small positively charged region

Question 3

What is a nuclide?

Answer 3

A particular species of nucleus that is specified by its proton number and neutron number

Question 4

What is an isotope?

Answer 4

An isotope is one of two or more atoms with the same atomic number but with different numbers of neutrons

Question 5

Mass-Energy Equivalence Equation

Answer 5

E = mc^2

Question 6

What is the unified atomic mass unit?

Answer 6

The unified atomic mass unit is equivalent to 1/12 of the mass of a carbon-12 atom
u = 1.66*10^-27 kg

Question 7

What is mass defect?

Answer 7

The difference in mass between the mass of an atomic nucleus and the sum of the masses of its constituent particles

Question 8

What is binding energy?

Answer 8

The amount of energy required to separate a nucleus into its constituent nucleons such that the nucleons are infinitely far apart

Question 9

What is the binding energy per nucleon?

Answer 9

The binding energy divided by the number of nucleons in the nucleus
High BE per nucleon means more stable

Question 10

What is count rate?

Answer 10

The measure of the rate of radiation received by a radioactivity detector

Question 11

What is background radiation?

Answer 11

The radiation detected by a radiation counter when no radioactive source is nearby

Question 12

What is an α-particle?

Answer 12

α-particles are He nuclei, with 2 protons and 2 neutrons

Question 13

What is a β-particle?

Answer 13

β-particles are fast-moving electrons

Question 14

What is a γ-particle?

Answer 14

γ-particles are electromagnetic radiation with very high frequencies

Question 15

Order of penetrating power for radioactive decay

Answer 15

γ-particles has the highest penetrating power, α-particles has the lowest penetrating power

Question 16

What is the activity, A, of a radioactive isotope?

Answer 16

The number of nuclear disintegrations per unit time
A = λN
Units: Becquerel, Bq

Question 17

What is the decay constant (λ)?

Answer 17

The probability that a nucleus will decay per unit time
Units: s^-1

Question 18

What is half-life of a radioactive isotope?

Answer 18

The average time taken for the activity of a radioactive isotope to be halved
t(1/2) = ln2 / λ

Question 19

What is the experimental evidence to show that radioactive decay is random?

Answer 19

The count-rate of a sample during radioactive decay experiences fluctuations

Question 20

What is the experimental evidence to show that radioactive decay is spontaneous?

Answer 20

The count-rate of a sample is constant regardless of changes in external conditions