Nuclear_Physics_1_Complete_Flashcards

Question 1

What are the approximate sizes of atoms and nuclei?

Answer 1

Atoms: ~0.1 nm or 10^-10 m; Nuclei: ~1–10 fm or 10^-15 m.

Question 2

Define isotopes, isotones, and isobars.

Answer 2

Isotopes: same Z, different A; Isotones: same N, different Z; Isobars: same A, different Z.

Question 3

Why was mass spectrometry important for identifying isotopes?

Answer 3

It showed that atoms of the same element can have different masses, revealing the existence of isotopes.

Question 4

If a particle has orbital angular momentum l = 1 and spin s = 3/2, what total angular momentum values j are possible?

Answer 4

j = 1/2, 3/2, 5/2; with 2j+1 quantum states each: 2, 4, and 6 respectively.

Question 5

Why does the integer spin of nitrogen-14 rule out the neutron being a proton-electron bound state?

Answer 5

A p + e− system would yield half-integer spin, but 14N has integer spin, so neutrons must be fundamental.

Question 6

What are the main photon interactions with matter?

Answer 6

Photoelectric effect, Compton scattering, and pair production.

Question 7

How do photons and charged particles differ in their interactions with matter?

Answer 7

Photons interact probabilistically and can travel long distances; charged particles lose energy continuously via ionisation.

Question 8

What does the Bethe equation describe?

Answer 8

The mean energy loss per unit distance (stopping power) of charged particles due to ionisation and excitation.

Question 9

What is a Bragg peak?

Answer 9

It’s the peak in energy deposition by charged particles just before stopping, used in proton therapy.

Question 10

Write the exponential decay law for radioactive nuclei.

Answer 10

N(t) = N_0 e^(-λt), where λ is the decay constant.

Question 11

How are half-life and mean life related to the decay constant?

Answer 11

Half-life: t_1/2 = ln2 / λ; Mean life: τ = 1 / λ.

Question 12

What types of nuclear decay release energy?

Answer 12

Alpha, beta (β−, β+), gamma decay—all release energy (Q > 0).

Question 13

What are key properties of the nucleon–nucleon (NN) interaction?

Answer 13

Short range (~1–2 fm), strongly attractive with repulsive core, spin-dependent, charge-independent.

Question 14

What is the Yukawa potential and what does it explain?

Answer 14

V(r) = -g^2 e^(-μr)/r; describes nuclear force as pion exchange.

Question 15

Why is there no bound diproton or dineutron?

Answer 15

Only the triplet (spin-1) np state is bound; nn and pp singlet states are unbound due to spin dependence.

Question 16

What is the binding energy of a nucleus?

Answer 16

Energy required to separate a nucleus into its constituent protons and neutrons.

Question 17

What does the semi-empirical mass formula (SEMF) include?

Answer 17

Volume, surface, Coulomb, asymmetry, and pairing terms.

Question 18

What causes the valley of stability?

Answer 18

Balance between Coulomb repulsion and nuclear attraction; heavier nuclei require more neutrons (N > Z).

Question 19

What is a nuclear reaction Q-value?

Answer 19

Q = (mass_initial − mass_final) × c^2; it’s the net energy released or absorbed.

Question 20

Define nuclear cross-section.

Answer 20

Effective area representing the probability of a reaction occurring, measured in barns (1 b = 10^-28 m²).

Question 21

What is a compound nucleus?

Answer 21

An intermediate excited state formed when an incident particle is absorbed by the target nucleus.

Question 22

Describe the fission of uranium-235.

Answer 22

235U + n → two fission products + ~3n + ~200 MeV energy.

Question 23

What is the neutron multiplication factor k?

Answer 23

k = neutrons in generation n+1 / neutrons in generation n; determines criticality of a reactor.

Question 24

What is the Lawson criterion?

Answer 24

nTτ > constant; condition for net energy gain in fusion (plasma confinement).

Question 25

What are absorbed dose and equivalent dose?

Answer 25

Absorbed dose: energy deposited per mass (Gy); Equivalent dose: dose × radiation weighting factor (Sv).

Question 26

Why are α particles dangerous internally but not externally?

Answer 26

They have high LET and cause severe damage if inhaled or ingested, but cannot penetrate skin.

Question 27

What does the Rutherford scattering formula describe?

Answer 27

Elastic scattering of charged particles via Coulomb interaction; scales as 1/sin⁴(θ/2).

Question 28

What is a form factor in nuclear physics?

Answer 28

Fourier transform of the nuclear charge density; modifies scattering cross-section.

Question 29

How does nuclear radius scale with mass number A?

Answer 29

R ≈ R₀ A^{1/3}, where R₀ ≈ 1.2 fm.

Question 30

What is the purpose of the shell model in nuclear physics?

Answer 30

To explain nuclear stability and predict spin/parity using nucleon energy levels.

Question 31

What is the spin–orbit interaction's role in the shell model?

Answer 31

It splits levels with same l but different j, explaining magic numbers.

Question 32

How many nucleons can fit into a j level?

Answer 32

2j + 1 nucleons.

Question 33

What is alpha decay?

Answer 33

Emission of a helium-4 nucleus (α particle) from a heavy nucleus.

Question 34

What is the Gamow factor?

Answer 34

Exponent in the tunnelling probability for alpha decay through the Coulomb barrier.

Question 35

What does the Geiger–Nuttall law state?

Answer 35

log10(t_1/2) ∝ Z / √Q; empirical relation between half-life and Q-value of alpha decay.

Question 36

What is Mott scattering?

Answer 36

An extension of Rutherford scattering that includes the effects of electron spin; describes elastic scattering of electrons off nuclei.

Question 37

How is momentum transfer q² related to scattering angle in elastic scattering?

Answer 37

q² = 4p² sin²(θ/2), where p is the momentum of the incoming particle.

Question 38

What is the form factor of a uniform charge sphere?

Answer 38

F(q) = 3[sin(qR) - qR cos(qR)] / (qR)³; it describes the charge distribution's effect on scattering.

Question 39

How does the form factor change with nuclear size?

Answer 39

Larger nuclei lead to faster oscillations and earlier zero crossings in the form factor.

Question 40

What is the Woods–Saxon potential?

Answer 40

A realistic potential used in the shell model: V(r) = -V₀ / [1 + exp((r - R)/a)] with finite depth and surface smoothing.

Question 41

What is spectroscopic notation in nuclear physics?

Answer 41

Notation (nlj)^x where n is radial node, l is orbital angular momentum, j is total angular momentum, and x is number of nucleons.

Question 42

How do you determine nuclear spin and parity from the shell model?

Answer 42

The spin and parity are determined by the last unpaired nucleon; parity = (-1)^l.

Question 43

How does the Coulomb barrier affect alpha decay?

Answer 43

The α particle must tunnel through the Coulomb barrier; height and width of the barrier determine tunnelling probability.

Question 44

What is the transmission coefficient in quantum tunnelling?

Answer 44

T ≈ exp(-2G), where G is the Gamow factor representing the integral over the classically forbidden region.

Question 45

How does barrier height and width influence alpha decay rate?

Answer 45

Higher and wider barriers decrease tunnelling probability, increasing the half-life.

Question 46

What is beta decay and how does its energy spectrum look?

Answer 46

Beta decay emits an electron or positron and a neutrino, resulting in a continuous energy spectrum for the emitted beta particle.

Question 47

What is electron capture and when does it occur?

Answer 47

A process where a proton-rich nucleus absorbs an inner orbital electron, converting a proton into a neutron and emitting a neutrino.

Question 48

What is the difference in Q-value conditions for β⁺ decay vs electron capture?

Answer 48

β⁺ decay requires Q > 1.022 MeV to produce a positron; electron capture only needs Q > 0.