Chapter 22. Nuclear Chemistry
Recommended Post : 【Chemistry】 Chemistry Index
1. Overview
3. Application 1. Nuclear Power Generation
4. Application 2. Nuclear Weapons
a. Types of Radioactive Elements and Particle Accelerators
b. Interaction of Radioactive Isotopes and Particles
1. Overview
⑴ Structure of an Atom
① Atom: Nucleus + Electrons
② Atomic Nucleus: Protons + Neutrons
③ Protons: Up Quarks × 2, Down Quarks × 1
④ Neutrons: Up Quarks × 1, Down Quarks × 2
⑤ Electrons: Leptons × 1
⑵ Atomic Mass Unit (amu)
① 1 u = 1.6605 × 10^-27 kg
② 12 u: Mass of one carbon atom
③ 12 g: Mass of Avogadro’s number (NA) of carbon atoms
④ Proton: 1.0073 u
⑤ Neutron: 1.0087 u
⑥ Electron: 0.0005 u, 1/1840 of proton mass
2. Nuclear Reactions
⑴ Nuclear Fission Reactions
① Nuclear Fission: Division of one nucleus into different nuclei
○ (Distinguishing Concept) Nuclear Decay: Emission or transformation of nucleus components
② Einstein’s Mass-Energy Equivalence Principle predicts released energy
○ Sum of masses of nuclei before fission > Sum of masses of nuclei after fission
○ (Note) In nuclear fusion reactions, sum of masses of nuclei before fusion > Sum of masses of nuclei after fusion
③ Reasons for Nuclear Fission and Decay
○ Light elements stable when Neutrons: Protons = 1:1
○ Heavy elements stable when Neutrons: Protons = 1.5:1
Figure. 1. Proton-Neutron Graph
④ Types of Nuclear Fission Reactions
Figure. 2. Types of Nuclear Fission Reactions [Footnote: 6]
○ One radionuclide can undergo multiple reactions with certain probabilities
○ Type 1: Beta Decay
○ Also known as β- decay
○ β particle typically refers to β- electron; it can sometimes include positrons (β+) and electrons
○ Type 2: Positron Emission
○ Also known as β+ decay
○ Positron: Antiparticle of electron
○ When electrons and positrons combine, they produce light and mutually annihilate
○ Type 3: Electron Capture (EC)
○ Capture of K shell electron in EC leads to X-rays, gamma rays, Auger electrons
○ Auger electron: Emitted due to EC or Compton effect, low energy
○ Type 4: Alpha Decay
○ Type 5: Gamma Decay
○ No change in atomic nucleus composition
○ Only energy state changes
○ Penetration of Radiation
○ Alpha particles: Cannot pass through paper
○ Beta particles: Can pass through paper but not aluminum
○ Gamma and X-rays: Can pass through paper and aluminum but not lead
○ (Note) Electromagnetic waves (gamma and X-rays) are more penetrating than particle waves
⑵ Nuclear Fusion Reactions
① Overview
○ Definition: Small atomic nuclei fusing to form larger nuclei
○ Energy released as predicted by Einstein’s Mass-Energy Equivalence Principle
○ Sum of masses of nuclei before fusion > Sum of masses of nuclei after fusion
○ (Note) In nuclear fission reactions, sum of masses of nuclei before fission > Sum of masses of nuclei after fission
② Example 1: Nuclear Fusion Reactions in Main Sequence Stars
○ Hydrogen nuclei in the core of main sequence stars fuse to form helium nuclei
○ Energy loss due to mass defect becomes source of solar energy
③ Example 2: Nuclear Fusion in Tokamak: Also Known as Artificial Sun
○ Nuclear Fusion Reaction Equation
○ Fusion Reactor
Figure. 3. Fusion Reactor
⑶ Binding Energy per Nucleon: Theory explaining trends in nuclear fission and fusion
① Binding energy decreases as atoms become larger and atomic number increases
② Trends in Nuclear Fission and Fusion: Generally, elements undergoing fusion only fuse, while elements undergoing fission only undergo fission
Figure. 4. Mass Number-Binding Energy Graph
③ Reason for Iron as Final Stellar Element: Fusion dominates up to iron
⑷ Nuclear Reaction Kinetics
① Reaction Rate Equation: First-order reaction
② Integrated Rate Equation
③ Half-Life: Remains constant
④ Continuous Reactions
3. Application 1. Nuclear Power Generation
⑴ Definition: Power generation using nuclear fission
① Nuclear Power Generation
○ Uses 2-5% uranium fuel
○ Slow chain reaction
○ Generates heat sufficient to boil water at around 310°C
② (Note) Atomic Bombs
○ Over 90% composed of highly enriched uranium-235
○ Rapid chain reaction
⑵ Uranium Nuclear Fission Process
Figure. 5. Uranium Nuclear Fission Process
(ㄱ) represents a neutron
① Law of Conservation of Charge
② Law of Conservation of Energy
③ Law of Conservation of Mass does not apply after fission: Released energy is due to mass defect
⑶ Necessary Conditions for Nuclear Fission
① Critical Mass: Sufficient amount of uranium required for sustained fission
② Chain Reaction: Reaction must occur continuously
③ Moderator: Slows down neutron speed for effective uranium absorption
④ Control Rod: Absorbs neutrons released in nuclear reactions
⑷ Types
① Boiling Water Reactor (BWR)
○ Moderator: Material for chain reaction
○ Coolant: Material to maintain reactor temperature
② Pressurized Water Reactor (PWR)
③ Graphite-Moderated Water-Cooled Reactor (RBMK)
○ Uses carbon dioxide (coolant) and graphite (moderator)
○ Allows fuel replacement without reactor shutdown
④ Fast Breeder Reactor (FBR)
○ Uses water (coolant) and sodium (moderator)
○ Utilizes natural uranium, fire risk
⑸ Light Water and Heavy Water
① Light Water: Regular water
② Heavy Water: Water made of deuterium, tritium
③ Price: Heavy Water > Light Water
④ Moderator Efficiency: Heavy Water > Light Water
⑤ Plutonium Accessibility: Heavy Water > Light Water
⑹ Uranium Enrichment
① Fuel for Nuclear Power Generation: Uranium-235
② Natural Uranium Composition: Uranium-235 (0.3%), Uranium-238 (99.7%)
③ Reason for Enrichment: Requires 2-5% uranium for chain reactions
④ Enrichment Methods: Gas Diffusion, Centrifugation, Nozzle Method, Ion Exchange
4. Application 2. Nuclear Weapons
⑴ Type 1: Nuclear Fission Weapon : Also known as Atomic Bomb
⑵ 1-1. Uranium Nuclear Weapon
① Natural Uranium
○ U-238 : Most common isotope
○ U-235 : 0.7% of natural uranium. Used as fuel for uranium nuclear weapons.
○ U-234 : 0.005%
② Principles
Figure 6. Principles of Uranium Nuclear Weapons
○ Utilizes the nuclear fission process of uranium atomic nuclei : Refer to Figure 5.
○ Step 1: Neutron chain reactions do not occur if the density of uranium is not sufficiently high.
○ Step 2: Two uranium masses with subcritical mass collide like bullets to reach supercritical mass.
○ Step 3: Chain reaction and atomic explosion.
③ Example 1: Hiroshima Atomic Bomb (Date: 1945.08.06, Codename: Little Boy)
○ Contains 50 kg of U-235 : Energy equivalent to 15,000 tons of TNT
⑶ 1-2. Plutonium Nuclear Weapons
① Principles
○ Step 1: Pu-239 generated from common uranium U-238.
○ Step 2: Pu-239 placed in a special device like a spherical core (plutonium pit).
○ Step 3: Pu-239 reaches supercritical mass due to density increase.
○ Step 4: Chain reaction and atomic explosion.
② Example 1: Nagasaki Atomic Bomb (Date: 1945.08.09, Codename: Fat Man) : Second plutonium nuclear weapon.
③ Example 2: Gadget : First plutonium nuclear weapon.
④ Example 3: North Korean Nuclear Weapons
⑷ Type 2: Fusion Weapons : Also known as hydrogen bombs or thermonuclear bombs.
① Fission weapons have an upper limit of about 500 kilotons TNT in power.
② Fusion weapons can produce powers up to about 50 megatons TNT.
③ Principles : Liquid deuterium and tritium are used.
④ Example 1: Ivy Mike
⑸ Current Status of Nuclear Weapons
① Russia : 6,600
② United States : 6,450
③ France : 300
④ China : 290 (Estimated)
⑤ United Kingdom : 215
⑥ Pakistan : 130-140 (Estimated)
⑦ India : 120-130 (Estimated)
⑧ Israel : 80 (Estimated)
⑨ North Korea : 10-20 (Estimated)
5. Appendix: Radiation
⑴ Radioactivity
① Definition : The property of atomic nuclei emitting radiation while trying to become stable nuclei, the ability to emit radiation.
② SI Unit : Bq (Becquerel)
○ 1 dps : The ability to decay in 1 second.
○ 1 Bq = 1 disintegration per second = 1 dps
③ Conventional Unit : Ci (Curie)
○ 1 Ci = 3.7 × 10^10 Bq
○ 1 Bq = 2.7 × 10^-11 Ci
○ 1 Ci is equivalent to the radioactivity of 1g of 226Ra.
⑵ Radiation
① Definition : Light energy emitted through nuclear reactions.
② Radiation Dose : Amount of radiation, typically indicating absorbed dose.
③ Dose Rate : Amount of radiation per unit time.
③ Radiation = Artificial Radiation + Natural Radiation
④ Artificial Radiation : Used artificially.
⑤ Natural Radiation : Exists naturally. Classified into terrestrial and cosmic radiation.
○ Global average exposure : Annual dose of 2.4 mSv per person.
○ South Korea : Annual dose of about 3.1 mSv.
⑶ Absorbed Dose (X)
① Amount of radiation absorbed in the air
② SI unit : C/kg
○ Amount of γ(X)-rays that produce 1 ion per 1 C in 1 kg of air
③ Conventional unit : R (roentgen)
○ 1 R = 2.58 × 10-4 C/kg
⑷ Absorbed Dose (D)
① Amount of radiation absorbed per unit mass by the exposed substance
② SI unit : Gy, cGy (gray)
○ 1 Gy = 1 J/kg
③ Conventional unit : rad (rad)
○ 1 Gy = 100 rad
⑸ Equivalent Dose or Dose Equivalent (H)
① Measure of radiation exposure’s impact on human health
○ Equivalent Dose = Absorbed Dose × Radiation Weighting Factor
○ Radiation Weighting Factor
○ X, γ, β = 1
○ Neutrons = 5 ~ 20
○ Nuclear fission and creation = 20
② SI unit : Sv, mSv (sievert)
③ Conventional unit : rem (rem)
○ 1 Sv = 100 rem
⑹ Effective Dose (E)
① Amount of radiation absorbed by different human tissues
○ Effective Dose = Equivalent Dose × Tissue Weighting Factor
○ Tissue Weighting Factor
○ Reproductive organs = 0.2
○ Bone marrow, stomach, lungs = 0.12
○ Bladder, breasts, liver, esophagus, thyroid = 0.05
○ Bones, skin = 0.01
② SI unit : Sv
③ Conventional unit : rem
⑺ Radiation-Related Phenomena
① Cloud Chamber Experiment : Observation of radiation trajectories using adiabatic expansion
Figure. 7. Wilson’s Cloud Chamber Experiment
○ (a) : View of adiabatic expansion with vapor in a box containing air
○ (b) : View of condensed vapor along radiation tracks in the expanded box (a) as radiation passes
② Auger Effect
○ 1st. Inner electrons of specific atom emit after external radiation
○ 2nd. Electrons relatively outer to the atom fill the vacancy
○ 3rd. X-rays are emitted
③ Bystander Effect
○ Phenomenon of non-irradiated cells undergoing death
○ Believed to be caused by signaling from irradiated cells
⑻ Radiation Risk
① Relationship between Exposure Dose and Acute Effects (Source: ICRP 103)
○ Exposure Dose ≤ 0.1 Gy : Almost no clinical symptoms
○ Exposure Dose = 0.5 Gy : Hematopoietic function impairment
○ Exposure Dose = 1-2 Gy : 10% mortality
○ Exposure Dose = 4 Gy : 50% mortality within 60 days
○ Exposure Dose = 5-7 Gy : 90% mortality
Input : 2019.03.16 17:06