Radioactivity — KCSE Chemistry

Radioactivity involves the decay of unstable nuclei, leading to the emission of particles. There are two common types of decay: alpha decay and beta decay.

1. Alpha Decay: In this process, an alpha particle (2 protons and 2 neutrons) is emitted. The atomic number decreases by 2, and the mass number decreases by 4.

   • Example:
     • Nuclear equation: ( _{88}^{226}Ra \rightarrow _{86}^{222}Rn + _{2}^{4}He )
     • Here, the atomic number changes from 88 to 86, and the mass number changes from 226 to 222.

2. Beta Decay: A neutron is transformed into a proton, emitting a beta particle (an electron). The atomic number increases by 1, while the mass number remains unchanged.

   • Example:
     • Nuclear equation: ( _{6}^{14}C \rightarrow _{7}^{14}N + _{-1}^{0}e )
     • Here, the atomic number changes from 6 to 7, while the mass number remains 14.

Understanding these changes helps in predicting the behavior of radioactive substances.

Half-life is defined as the time required for half of the radioactive nuclei in a sample to decay. This concept is crucial in understanding radioactive decay processes. Each radioactive isotope has a unique half-life, which can range from fractions of a second to billions of years.

To perform calculations involving half-life, use the formula:

N = N₀ (1/2)^(t/T₁/₂)

Where:

• N = remaining quantity of the substance
• N₀ = initial quantity of the substance
• t = total time elapsed
• T₁/₂ = half-life of the substance

For example, if you start with 80 grams of a radioactive substance with a half-life of 3 years, after 6 years (which is 2 half-lives), the calculation would be:

N = 80g (1/2)^(6/3) = 80g (1/2)² = 80g (1/4) = 20g

Thus, 20 grams of the substance would remain after 6 years.

Radioactivity is the process by which unstable atomic nuclei lose energy by emitting radiation. This can occur in three main forms: alpha particles, beta particles, and gamma rays.

• Alpha particles consist of 2 protons and 2 neutrons; they have low penetration power and can be stopped by paper.
• Beta particles are high-energy, high-speed electrons or positrons; they penetrate further than alpha particles but can be stopped by a few millimeters of aluminum.
• Gamma rays are electromagnetic waves with high energy; they have the greatest penetration power and require thick lead or concrete to be blocked.

Radioactive decay is characterized by the half-life, which is the time taken for half the nuclei in a sample to decay. This property is crucial in applications such as carbon dating and medical treatments. Understanding these concepts is essential for grasping the implications of radioactivity in both nature and technology.