CHM 111 Lecture Notes - Lecture 18: Critical Mass, Marie Currie, Beta Particle
CHM 111: Tuesday, April 17th
Day 18 Notes
Chemistry in Modern Society
What is Radioactivity
• Spontaneous disintegration/decay of unstable nucleus; emits radiation
• Discovered by accident (1896)
• Further Research by Marie Curie
o Radioactive emission results in the change of on element to another
• Types of Radiation
o Electromagnetic Radiation: refers to all of the different types of light (UV, visible,
IR, microwave, x-ray, gamma)
▪ X-ray radiation OR x-ray light
o Nucleus Radiation: refers to the radiation emitted by a nucleus
Types of Radioactive Decay
Writing Nucleus Equation
• The decay process is represented by a balanced nuclear equation.
o Both the total charge and the total mass must be balanced
CHM 111: Tuesday, April 17th
Day 18 Notes
Fission vs. Nuclear Decay
• Fission
o Radioactive nucleus is hit with a neutron and splits apart
o Large amounts of energy are produced (E=mc2)
o Only certain radioactive isotopes undergo fission
o Critical mass is required for chain reaction
o Process is instantaneous
• Nuclear Decay
o Spontaneous Event
o Energy is released
o All Nuclei, N=84 and higher, undergo decay to become more stable
o Decay time measured by half life
Nuclear Reactor
• A device in which nuclear chain reactions are initiated, controlled, and sustained at a
steady rate
CHM 111: Tuesday, April 17th
Day 18 Notes
Nuclear Waste
• High-level radioactive waste (HLW)
o Requires permanent isolation from biosphere
• Spent Nuclear Fuel (SNF)
o 3% of waste, 95% of radioactivity
o Each plant produced 27 tons per year
o Threat to national security, Why?
▪ Most of these fission products can be used in nuclear weapons
• Low-Level Radioactive waste (LLW)
o Waste with less radioactive materials (less hazardous)
▪ More of this than SNF
o Excludes spent fuel
o Contaminated materials, tools, etc.
HLM Storage
• Short term (at plant)
• Requires continual maintenance
• Two Types
o Deep Water Storage Pools
▪ Water cools fuel and absorbs alpha/beta radiation
o Dry Casket Storage
Document Summary
Ir, microwave, x-ray, gamma: x-ray radiation or x-ray light, nucleus radiation: refers to the radiation emitted by a nucleus. Writing nucleus equation: the decay process is represented by a balanced nuclear equation, both the total charge and the total mass must be balanced. Nuclear reactor: a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate. Hlm storage: short term (at plant, requires continual maintenance, two types, deep water storage pools, water cools fuel and absorbs alpha/beta radiation, dry casket storage. Day 18 notes: spent fuel stored in a leak-tight steel cylinder. How long does it take: half life (t1/2): time required for the level of radioactivity to fall to one half its initial value. Day 18 notes: this does not depend on the initial amount. 12. 5% radioactivity remain: 3 x 12. 3 = 37 years.