how do nuclei change during these reactions

Everly

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18-03-2025

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How Do Nuclei Change During Nuclear Reactions?

Nuclear reactions involve changes in the composition of atomic nuclei. Understanding these changes is fundamental to comprehending nuclear physics, energy production, and radioactive decay. This article will explore the various ways nuclei transform during different types of reactions.

Types of Nuclear Reactions and Nuclear Changes

Nuclear reactions fundamentally alter the number of protons and/or neutrons within an atomic nucleus. This contrasts with chemical reactions, which only rearrange electrons. The key changes we'll explore are:

1. Radioactive Decay: This spontaneous process alters the nucleus to achieve greater stability. Several types exist:

• Alpha Decay (α-decay): The nucleus emits an alpha particle (two protons and two neutrons), effectively reducing its atomic number by 2 and its mass number by 4. For example, Uranium-238 decaying to Thorium-234.

• Beta Decay (β-decay): This involves a neutron transforming into a proton (or vice versa), emitting a beta particle (an electron or positron) and an antineutrino (or neutrino). Beta-minus decay increases the atomic number by 1 while leaving the mass number unchanged. Beta-plus decay decreases the atomic number by 1, again with no change in mass number. Carbon-14's decay to Nitrogen-14 is a classic example of beta-minus decay.

• Gamma Decay (γ-decay): This process doesn't change the number of protons or neutrons. Instead, the nucleus releases a gamma ray (high-energy photon) to transition to a lower energy state. It often follows alpha or beta decay, as the nucleus may be left in an excited state after these primary decays.

2. Nuclear Fission: A heavy nucleus splits into two or more lighter nuclei, releasing a significant amount of energy. This process often involves neutron bombardment initiating the splitting. For example, Uranium-235 undergoing fission to produce Krypton-92 and Barium-141, along with several neutrons. The resulting nuclei have significantly lower mass numbers and different atomic numbers than the original nucleus.

3. Nuclear Fusion: Two light nuclei combine to form a heavier nucleus, also releasing substantial energy. This is the process powering the sun and other stars. Deuterium (Hydrogen-2) and Tritium (Hydrogen-3) fusing to form Helium-4 and a neutron is a common example. The resulting nucleus has a higher mass number and potentially a different atomic number than the original nuclei.

4. Neutron Capture: A nucleus absorbs a neutron, increasing its mass number by 1 without altering its atomic number. This often leads to an unstable nucleus, which may then undergo radioactive decay.

Conservation Laws in Nuclear Reactions

Several conservation laws govern nuclear reactions:

• Conservation of Mass-Energy: The total mass-energy of the system remains constant (E=mc²). Mass can be converted to energy and vice versa.

• Conservation of Charge: The total electric charge remains constant.

• Conservation of Nucleon Number: The total number of nucleons (protons and neutrons) remains constant.

• Conservation of Momentum: The total momentum of the system remains constant.

Illustrative Examples:

Example 1: Alpha Decay of Polonium-212:

Polonium-212 (⁸⁴Po²¹²) undergoes alpha decay to become Lead-208 (⁸²Pb²⁰⁸) and an alpha particle (₂He⁴). The atomic number decreases by 2 (84-2=82), and the mass number decreases by 4 (212-4=208).

Example 2: Beta-Minus Decay of Carbon-14:

Carbon-14 (₆C¹⁴) undergoes beta-minus decay to become Nitrogen-14 (₇N¹⁴) and a beta particle (₋₁e⁰). The atomic number increases by 1 (6+1=7), but the mass number remains unchanged (14).

Conclusion

Nuclear reactions are powerful processes that fundamentally alter the structure of atomic nuclei. Understanding the types of reactions (decay, fission, fusion, neutron capture) and the associated changes in proton and neutron numbers is crucial for comprehending various phenomena, from radioactive decay to nuclear energy production. The conservation laws governing these reactions ensure that certain quantities remain constant throughout the transformation.