Lecture 1

Question 1

What is the atomic number (Z)?

Answer 1

The number of protons in the nucleus.

Question 2

What is the mass number (A)?

Answer 2

The sum of protons and neutrons in the nucleus (A = Z + N).

Question 3

Define isotopes.

Answer 3

Two or more forms of the same element with different numbers of neutrons.

Question 4

What are isobars?

Answer 4

Nuclei with the same mass number but different atomic numbers.

Question 5

What are isotones?

Answer 5

Nuclei with the same number of neutrons but different atomic numbers.

Question 6

Define isomers.

Answer 6

Nuclei with the same Z and A, existing in one or more excited states.

Question 7

What is the nucleus density approximately?

Answer 7

200,000 ton/mm³.

Question 8

What is mass defect?

Answer 8

The difference in mass that results in the release of energy during nuclear binding.

Question 9

What is nuclear binding energy (Eb)?

Answer 9

The energy required to disassemble a nucleus into its individual protons and neutrons.

Question 10

True or False: The structure of some nuclei is unstable.

Answer 10

True.

Question 11

What are magic numbers in nuclear chemistry?

Answer 11

Certain numbers of nucleons that result in high stability of nuclei: 2, 8, 20, 28, 50, 82, 126.

Question 12

What is radioactive decay?

Answer 12

A spontaneous nuclear transformation unaffected by pressure, temperature, or chemical form.

Question 13

What is half-life (t1/2)?

Answer 13

The time required for half of the radioactive atoms in a sample to undergo decay.

Question 14

List the modes of radioactive decay.

Answer 14

• Alpha-decay (α-particles)
• Beta-decay (β-particles)
• Gamma-decay (γ-rays)
• Internal conversion
• Spontaneous fission

Question 15

What is alpha decay?

Answer 15

The emission of helium nuclei from a heavy nucleus.

Question 16

What is beta decay?

Answer 16

The emission of either negatrons (electrons) or positrons.

Question 17

What is gamma decay?

Answer 17

The emission of electromagnetic radiation from a nucleus.

Question 18

What is the role of conservation laws in radioactive decay?

Answer 18

Energy, momentum, charge, mass number, and angular momentum must all be conserved.

Question 19

What is the charge and mass of an alpha particle?

Answer 19

Charge: +2; Mass: 4 u.

Question 20

What are the characteristics of beta particles?

Answer 20

Charge: -1 or +1; Mass: mass of electron; lower ionization power than alpha particles.

Question 21

What is the neutrino theory?

Answer 21

A theory that suggests beta decay involves the emission of a neutrino to conserve energy and momentum.

Question 22

Fill in the blank: The first medical X-ray was taken by _______.

Answer 22

[Wilhelm Röentgen]

Question 23

Who discovered polonium?

Answer 23

Marie Curie and Pierre Curie.

Question 24

What are radionuclides used for?

Answer 24

Applications in medicine, industry, and scientific research.

Question 25

What is the significance of the stability line in nuclear chemistry?

Answer 25

It indicates the ratio of neutrons to protons for stable nuclei.

Question 26

What is the decay energy in radioactive decay?

Answer 26

The energy difference between the original nuclide and the product nuclide.

Question 27

What is the equation for energy decay in a nuclear reaction?

Answer 27

p → n + β+ ## Footnote This represents a proton decaying into a neutron and a positron.

Question 28

What processes can remove excitation energy from a daughter nucleus after α or β decay?

Answer 28

* γ-ray emission * Internal conversion process

Question 29

Define gamma-ray emission.

Answer 29

Gamma-rays are electromagnetic radiation that produce very low density ionization.

Question 30

How quickly does γ-ray emission typically occur after α or β decay?

Answer 30

Within 10^-12 seconds.

Question 31

What are isomers in the context of nuclear decay?

Answer 31

Longer-lived exited nuclei that remain in a higher energy state for a measurable length of time.

Question 32

What happens during the internal conversion process?

Answer 32

Excitation energy is transferred directly to the orbital electron, which escapes from the atom.

Question 33

What is a conversion electron?

Answer 33

An ejected electron from an inner orbital during the internal conversion process.

Question 34

What is the conversion coefficient?

Answer 34

The ratio between the number of conversion electrons and the number of γ-rays emitted.

Question 35

Radioactive decay is a spontaneous nuclear transformation that is unaffected by what factors?

Answer 35

* Pressure * Temperature * Chemical form

Question 36

True or False: Radioactive decay is a random process.

Answer 36

True

Question 37

What does radioactivity measure?

Answer 37

The number of disintegrations per second in a given sample.

Question 38

What is the significance of atomic numbers greater than 92 in nature?

Answer 38

All isotopes of these elements have lifetimes shorter than the age of the earth.

Question 39

Fill in the blank: The number of radioactive nuclei remaining can be calculated from the equation N = N0/2^n, where n is the number of _______.

Answer 39

half-lives

Question 40

What is considered a useful lifetime for a radioactive species?

Answer 40

10 half-lives (210)

Question 41

How is the number of α-particles emitted from a sample calculated?

Answer 41

∆N = N0 λ t

Question 42

What is the formula to calculate the half-life (t1/2) from the decay constant (λ)?

Answer 42

t1/2 = ln 2 / λ

Question 43

What is secular equilibrium in radioactive decay?

Answer 43

When the rate of decay of daughter equals the rate of decay of parent.

Question 44

Give an example of a case of secular equilibrium.

Answer 44

137Cs (t1/2 30y) and 137mBa (t1/2 22.6min).

Question 45

What is transient equilibrium?

Answer 45

When the observation time is greater than 6 half-lives of the daughter.

Question 46

What are the four processes of gamma-ray absorption?

Answer 46

* Coherent scattering * Photoelectric effect * Compton effect * Pair production

Question 47

What occurs during coherent scattering?

Answer 47

The γ-ray is absorbed and re-emitted with unchanged energy in a different direction.

Question 48

What happens during the photoelectric effect?

Answer 48

The energy of γ-rays is absorbed completely by atomic electrons, resulting in ionization.

Question 49

How is the energy of the emitted photoelectron (Ee) determined?

Answer 49

Ee = Eγ - Ebe

Question 50

What is the Compton effect?

Answer 50

γ-rays interact with electrons, giving part of their energy to eject the electron.

Question 51

What is pair production?

Answer 51

The process where a γ-ray converts its energy into a particle-antiparticle pair.

Question 52

How do α-particles primarily lose their energy?

Answer 52

By ionization and excitation.

Question 53

What is the typical energy range for α-particles?

Answer 53

Between 4 and 9 MeV.

Question 54

What is the primary mechanism for β-particles losing energy?

Answer 54

* Ionization * Excitation * Bremsstrahlung * Positron annihilation * Cerenkov radiation

Question 55

What unique process occurs with positron interactions?

Answer 55

Positron annihilation, resulting in the emission of two γ-rays.

Question 56

What is Cerenkov radiation?

Answer 56

Electromagnetic radiation emitted when a particle moves faster than the speed of light in a medium.

Question 57

What is the Compton effect?

Answer 57

The interaction of γ-rays of intermediate energy with an electron, resulting in the electron being excited and ejected while the γ-ray is deflected with lower energy. ## Footnote The energy of the scattered γ-ray is given by the equation E' γ=E γ - Ee, where Ee is the kinetic energy of the Compton electron.

Question 58

How does the probability of Compton scattering change with target Z and Eγ?

Answer 58

Increases with target Z and decreases with Eγ. ## Footnote Target Z refers to the atomic number of the material interacting with the radiation.

Question 59

What is pair production?

Answer 59

The interaction of γ-rays with an absorber in the Coulomb field of the nucleus, resulting in the conversion of γ-ray energy into a negatron and a positron. ## Footnote This process produces a pair of electrons, one positive and one negative, and is the inverse of positron annihilation.

Question 60

What is the minimum γ-ray energy required for pair production?

Answer 60

1.022 MeV. ## Footnote This value corresponds to the combined rest mass energy of a positron and an electron.

Question 61

What happens to the probability of pair production as γ-ray energy increases?

Answer 61

The probability of pair production increases. ## Footnote This means that higher energy γ-rays are more likely to result in the production of electron-positron pairs.