Nuclear Chemistry: Principles, Applications, and Impacts

Nuclear Chemistry

Introduction to Nuclear Chemistry

Nuclear chemistry is the study of the chemical and physical properties of elements as influenced by changes in the structure of the atomic nucleus. This field explores the processes of radioactive decay, nuclear reactions, and the applications and consequences of nuclear phenomena in medicine, energy, and the environment.

Background Radiation and Radiation Exposure

Sources of Radiation

• Background radiation accounts for approximately three-fourths of all radiation exposure, originating from natural sources such as cosmic rays, rocks, and soil.

• The remaining exposure is primarily from medical irradiation (e.g., X-rays, CT scans).

Radiation Damage to Cells

Ionizing Radiation and Cellular Effects

• Ionizing radiation removes electrons from molecules, forming ions and free radicals that can disrupt cellular processes.

• Fastest-growing cells (e.g., white blood cells, bone marrow) are most affected.

• Radiation can damage DNA, leading to mutations and potentially cancer.

Nuclear Equations and Types of Radiation

Balancing Nuclear Equations

Nuclear equations must conserve both the atomic number (protons) and the mass number (protons + neutrons). The sum of atomic and mass numbers on both sides of the equation must be equal.

Alpha Decay

• Alpha decay emits an alpha particle (α), which is a helium-4 nucleus (4He).

• The parent nucleus loses 2 protons and 2 neutrons.

Beta Decay

• Beta decay emits a beta particle (β), which is an electron (0e-1).

• A neutron in the nucleus converts to a proton, increasing the atomic number by 1.

Positron Emission

• A positron (β+) is emitted, which is the antimatter counterpart of the electron.

• A proton in the nucleus converts to a neutron, decreasing the atomic number by 1.

Electron Capture

• The nucleus absorbs an inner-shell electron, which combines with a proton to form a neutron.

• The atomic number decreases by 1.

Types of Radiation: Properties and Penetrating Power

Radiation	Mass (u)	Charge	Identity	Velocity	Penetrating Power
Alpha (α)	4	2+	He2+	0.1c	Very low
Beta (β)	0.00055	1−	e−	<0.9c	Moderate
Gamma (γ)	0	0	High-energy photon	c	Extremely high

Penetrating Power of Radiation

• Alpha particles are stopped by paper or skin.

• Beta particles penetrate skin but are stopped by aluminum foil.

• Gamma rays require thick lead or concrete for shielding.

Comparing Chemical and Nuclear Reactions

Chemical Reactions	Nuclear Reactions
Atoms retain their identity	Atoms usually change identity (element changes)
Involve electrons (mainly outermost)	Involve protons and neutrons
Rates affected by temperature	Rates unaffected by temperature
Small energy changes	Large energy changes
Mass conserved	Measurable mass changes (E = mc2)

Symbols for Subatomic Particles

Particle	Symbol	Nuclear Symbol
Proton	p	11H or p
Neutron	n	10n
Electron	e− or β−	0−1e
Positron	e+ or β+	0+1e
Alpha particle	α	42He
Gamma ray	γ	γ

Half-Life and Radioactive Decay

Definition and Calculation

• The half-life is the time required for half of a radioactive sample to decay.

• The fraction remaining after n half-lives: $\text{Fraction remaining} = \frac{1}{2^n}$

Radioisotopic Dating

Principles and Applications

• Radioisotopic dating uses the known half-lives of isotopes to determine the age of materials.

• Carbon-14 dating is used for organic materials up to about 50,000 years old.

• Other isotopes (e.g., potassium-40, uranium-238) are used for dating rocks and the Earth's crust.

Artificial Transmutation

Artificial transmutation is the process of bombarding stable nuclei with particles (e.g., alpha particles, neutrons) to create new elements or isotopes. This is a key method for producing radioactive isotopes for research and medicine.

Uses of Radioisotopes

Tracers and Medical Applications

• Radioisotopes are used as tracers to detect leaks, study wear in machinery, and track nutrient uptake in plants.

• In medicine, radioisotopes are used for both diagnosis (e.g., imaging, blood volume determination) and therapy (e.g., cancer treatment).

Isotope	Half-life	Medical Use
11C	20.39 min	Brain scans
60Co	5.271 y	Radiation cancer therapy
131I	8.040 d	Thyroid diagnoses and therapy
99mTc	6.0 h	Imaging of organs
3H (Tritium)	12.26 y	Determining total body water
... (see full table in source)

Protection from Radiation

• Distance: Radiation intensity decreases with distance from the source.

• Shielding: Materials such as lead are used to block or reduce radiation exposure.

Energy from the Nucleus

Mass-Energy Equivalence

• Einstein's equation: $E = mc^2$ (where E = energy, m = mass, c = speed of light).

• When nucleons combine to form a nucleus, some mass is converted to binding energy.

Nuclear Fission and Chain Reactions

Nuclear Fission

• Fission is the splitting of a large nucleus into smaller nuclei, releasing energy and neutrons.

• Fission can lead to a chain reaction if released neutrons induce further fission events.

The Manhattan Project and Atomic Bombs

• The Manhattan Project (1939) was a U.S. effort to develop nuclear weapons during World War II.

• Key goals: sustain fission, enrich uranium, produce plutonium-239, and construct atomic bombs.

Radioactive Fallout

• Nuclear explosions produce harmful isotopes such as strontium-90 (accumulates in bone) and iodine-131 (concentrates in the thyroid).

• These isotopes pose long-term health risks due to their chemical similarity to essential elements.

Nuclear Power Plants

• Civilian nuclear power plants use controlled fission of uranium-235 to generate heat, which is converted to electricity.

• Fuel is less enriched than weapons-grade uranium.

Thermonuclear Reactions (Fusion)

• Nuclear fusion is the process of combining small nuclei to form larger ones, releasing vast amounts of energy.

• Fusion is the primary energy source of the sun and stars.