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A radioactive isotope, or radioisotope, is an atom with an unstable nucleus that releases energy by emitting radiation. This instability often results from an imbalance in the number of protons and neutrons within the nucleus. These isotopes strive for stability, which they achieve by undergoing radioactive decay.
In the process of radioactive decay, the isotope typically transforms into a different element or a different state of the same element. One of the common types of decay is alpha decay, where the isotope releases an alpha particle.
Little by little, this helps the isotope reach a more stable nuclear configuration. Radioactive isotopes are naturally occurring or artificially created and are important in fields such as medicine, archaeology, and energy production.

The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. It gives the atom's total weight in atomic mass units (amu). For example, in the uranium isotope mentioned, the mass number is 238.
It's important to note that the mass number is not the same as the atomic mass, which may consider isotopic distributions and their relative abundances.

• The mass number is always a whole number.
• It changes only when the number of protons or neutrons in the atom's nucleus changes, as seen in reactions like alpha decay.

Learning the mass number helps us understand the identity and stability of isotopes, as seen when uranium undergoes alpha decay, reducing its mass number.

The atomic number is a unique identifier for elements, representing the number of protons in the nucleus of an atom. For uranium, the atomic number is 92.
The atomic number determines an element's identity and its position on the periodic table. This number is pivotal as it also equals the number of electrons in a neutral atom.
When an atom emits an alpha particle during decay, the atomic number decreases by two, as two protons leave the nucleus.

• The change in atomic number results in the atom transforming into a different element.
• In the exercise, uranium with an atomic number of 92 becomes thorium with an atomic number of 90.

Knowing the atomic number is crucial for predicting the outcome of nuclear reactions and understanding elemental properties.

A nuclear reaction involves changes in an atom’s nucleus, often resulting in the production of a different element. This is distinct from chemical reactions, which involve electron exchanges.
During a nuclear reaction, like an alpha decay, the composition of the nucleus changes, either by releasing particles or by accepting other particles.
Nuclear reactions can be spontaneous or induced, with applications ranging from energy production to medical treatments. In alpha decay, the reaction can be summarized as follows:

• An unstable radioactive isotope emits an alpha particle.
• The isotope's mass number decreases by 4 units, and its atomic number decreases by 2 units.
• The original isotope of uranium transforms into a different element, thorium, in this specific alpha decay process.

Understanding nuclear reactions provides insight into fundamental atomic behavior and helps us harness nuclear energy safely and efficiently.