Nuclear Chemistry

Antoine Henri Becquerel (1896):
- Discovered U salts emitted rays that fogged photographic plates.
- U metal was found to be a stronger emitter.
Marie and Pierre Curie:
- Isolated Polonium (Po) and Radium (Ra) which exhibited similar behavior.
- Marie Curie termed the phenomenon radioactivity.
Joseph John Thomson and Ernest Rutherford:
- Investigated radiation and discovered two types: alpha (α) and beta (β) particles.
Henri Becquerel's & Villard’s Contributions:
- Villard discovered gamma (γ) radiation.

Table of radiation types includes:
- Alpha particle (α): Symbol = He²⁺, Charge = +2, Mass = 6.65 x 10⁻²⁴g, Penetrating power ≈ 0.03 mm
- Beta particle (β): Symbol = e⁻, Charge = -1, Mass = 9.11 x 10⁻²⁸g, Penetrating power ≈ 2 mm
- Gamma radiation (γ): Symbol = γ, Charge = 0, Mass = 0, Penetrating power ≈ 100 mm
- Note: Mass ratios suggest mα ≈ 10,000 mβ

Rutherford & Soddy (1902): Defined radioactivity as the transformation of a radioactive isotope into a different element via decay.
Example:
- Decay of Radium-226 ( $^{226}{88}Ra$ ) to Radon-222 ( $^{222}{86}Rn$ ) + α particle ( $^{4}_{2}He$ ).

Alpha Emission:
- ^{234}{92}U ightarrow ^{230}{90}Th + He
Beta Emission:
- ^{90}{38}Sr ightarrow ^{90}{39}Y + e^{-1}
Mechanism behind beta decay involves:
- Neutron ( $n$ ) transforms into a proton ( $p$ ) and an electron ( $e^{-1}$ ).

A decay product (daughter isotope) often proves unstable leading to a radioactive decay series:
- Number of neutrons can be calculated as: $N = A - Z$ , where A is the mass number and Z is the atomic number.

Positron Emission: A positron is a positive electron ( $e^+$ ) which interacts destructively with matter.
- Example: ^{43}{21}Sc ightarrow ^{43}{20}Ca + e^+
Electron Capture (EC): Occurs when an inner-shell electron is captured by the nucleus.
- Example: ^{7}{4}Be + e^{-1} ightarrow ^{7}{3}Li

Stability Criteria:
- Generally, for lighter elements, $N ext{ (neutrons)} \neq Z ext{ (protons)}$ .
- Odd atomic numbers lead to less stability.
- Heavy elements such as bismuth (Bi) have no stable isotopes.

Elements with Z < 83 typically decay to reach stability (e.g., via β- decay).
Heavier isotopes (>83) primarily undergo alpha decay to achieve stability.
Isotopes which are too light or too heavy can often decay via beta (+) emission or electron capture to balance the neutron/proton ratio.

Binding energy reflects the energy necessary to maintain nucleon cohesion within a nucleus.
- Calculated using Einstein’s theory: $E = mc^2$ .
- Example: Determine binding energy for Carbon-12 (12C) by comparing individual nucleon masses to total nucleus mass:
- For Carbon-12, $ext{Binding Energy } (E_b) = ext{mass of nucleons} - ext{mass of nucleus}$

Radioactive decay follows first-order kinetics: $ext{ln }[X]t = -kt + ext{ln }[X]0$ .
Half-life: $t_{1/2} = \frac{0.693}{k}$ .
Example: For 239Pu with a half-life of 24,400 years, the amount remaining can be calculated over several half-lives.

Food Irradiation: Uses gamma rays to sterilize and increase shelf life without making food radioactive.
Medical Imaging: Radioactive tracers like 99mTc provide imaging information while minimizing biological damage.
Therapeutic Applications: Radiation therapy targets rapidly dividing cancer cells, exploiting their higher susceptibility to radiation than normal cells.

Nuclear Reactors:
- Utilize controlled fission reactions to generate energy; controlled by materials such as cadmium and boron.
- Difference between reactor-grade and weapons-grade uranium (>90% U-235 for bombs).
Pros & Cons:
- Clean energy with little CO2 emission versus concerns about radioactive waste and safety.
Future challenges include difficulties with nuclear fusion as a clean power source, requiring significant energy inputs and complex containment.

Radioactivity presents vast applications across multiple fields including energy generation and medicine, though safety and waste management remain areas for ongoing concern and development.