What happens when the U-235 nucleus is “hit” with a neutron? There are a number of things that happen here. Describe all of them in as much detail as you can. Use the pause button when needed.
The correct answer and explanation is:
When a uranium-235 (U-235) nucleus is hit by a neutron, a complex nuclear reaction called fission occurs. This process involves several key steps and outcomes:
First, the neutron is absorbed by the U-235 nucleus, creating an unstable uranium-236 (U-236) nucleus. This new nucleus is highly unstable because it contains too much energy and an imbalance of nuclear forces. Due to this instability, the U-236 nucleus quickly deforms and splits apart into two smaller nuclei, called fission fragments.
The splitting releases a large amount of energy primarily as kinetic energy of the fragments. The two fission fragments are usually different isotopes of lighter elements, commonly around mass numbers 90 to 140, but the exact products vary randomly with each fission event.
Along with the fission fragments, the process releases additional neutrons. Typically, 2 or 3 free neutrons are emitted per fission event. These neutrons can then go on to collide with other U-235 nuclei, causing a chain reaction if enough fissile material is present.
In addition to neutrons and fission fragments, the fission reaction emits gamma radiation. Gamma rays are high-energy photons released from the excited fission fragments as they settle into more stable states.
The energy released in the fission process originates from the conversion of mass into energy according to Einstein’s equation E=mc². The combined mass of the fission fragments and emitted neutrons is slightly less than the original U-235 nucleus plus the absorbed neutron, and this mass difference is converted into energy.
The entire fission event happens extremely quickly, in less than a trillionth of a second. The chain reaction enabled by the free neutrons can be controlled in nuclear reactors or uncontrolled in nuclear weapons.
In summary, when U-235 absorbs a neutron, it becomes unstable U-236, which rapidly splits into two smaller nuclei, releases energy, emits multiple neutrons, and produces gamma radiation. This process underpins nuclear energy production and atomic weapons.