FISIÓN Y FUSIÓN

Fission and Fusion: The Foundations of Nuclear Reactions

Introduction to Fission

• In the 1930s, physicists and chemists aimed to create elements beyond uranium by bombarding heavy nuclei with particles, specifically neutrons due to their lack of electric charge.

• Enrico Fermi initiated experiments in 1934 by bombarding uranium nuclei with neutrons, leading to discoveries by Otto Hahn and Fritz Strassmann in 1938 that produced barium-56 among other elements.

• Lise Meitner and Otto Frisch explained that when a neutron hits uranium-238, it transforms into uranium-239, which then undergoes fission into two lighter nuclei of approximately equal size.

Mechanism of Fission

• The fission process occurs when the excitation energy is sufficient to deform the nucleus critically, increasing repulsion between the resulting halves.

• Uranium-235 is particularly fissile when bombarded with slow neutrons; Fermi used paraffin or water blocks to slow down these neutrons effectively.

• Each fission event produces an average of 2.5 additional neutrons, leading to a chain reaction where each neutron can induce further fissions.

Chain Reactions and Their Control

• In 1942, Fermi achieved the first controlled self-sustaining chain reaction, laying the groundwork for nuclear reactors. Uncontrolled reactions lead to atomic bombs.

Introduction to Fusion

Basics of Fusion

• Fusion is the reverse process of fission where two light nuclei combine to form a heavier nucleus, releasing energy as a result.

• Arthur Eddington proposed in 1920 that stars produce energy through thermonuclear reactions using hydrogen fusion into helium via a proton-proton cycle.

Stellar Fusion Processes

• Two hydrogen nuclei fuse into deuterium; this deuterium can then react with another hydrogen nucleus producing helium-3. Helium can also be formed from helium-three reactions under high temperatures.

Conditions for Fusion

• A minimum temperature of about 10 million Kelvin is required for these fusion reactions; our sun reaches around 14 million Kelvin while hotter stars exceed this threshold enabling different fusion processes like carbon-nitrogen cycle (CNO).

Challenges in Achieving Controlled Fusion

Energy Production Potential

• The immense energy released during stellar fusion suggests potential for harnessing similar processes on Earth; however, achieving necessary conditions poses significant challenges due to nuclear repulsion forces requiring extremely high temperatures.

Historical Context

• The hydrogen bomb developed in the late 1940s utilized uncontrolled fusion triggered by fission. Since the 1950s efforts have been made towards controlled fusion reactors as they promise less radioactive waste and greater energy output compared to current fission reactors.

Current Research Directions