Atomic structure and radiation

Atoms and Radiation

• Atoms are very small, with a radius of about 1 × 10⁻¹⁰ meters.
• An atom's basic structure includes a positively charged nucleus with protons and neutrons, surrounded by negatively charged electrons.
• A nucleus has a radius less than 1/10,000 of the radius of an atom.
• Almost all of an atom's mass is in the nucleus.
• Electrons are arranged at different distances (energy levels) from the nucleus.
• Electron arrangements change by absorbing electromagnetic radiation (move further, higher energy) or emitting it (move closer, lower energy).
• New evidence may lead to changes or replacements of scientific models.
• Before electron discovery, atoms were thought to be indivisible, tiny spheres.
• The discovery of the electron led to the plum pudding atomic model.
• The plum pudding model suggested that the atom is a positive charge ball with embedded negative electrons.
• Alpha particle scattering experiments led to the conclusion that an atom's mass is concentrated in a charged nucleus.
• The nuclear model replaced the plum pudding model.
• Niels Bohr adapted the nuclear model, suggesting electrons orbit the nucleus at specific distances.
• Bohr's theoretical calculations agreed with experimental observations.
• Later experiments showed that the positive charge of a nucleus can be subdivided into smaller particles, each with the same amount of positive charge, called protons.
• James Chadwick's work showed the existence of neutrons in the nucleus, about 20 years after the nucleus became scientifically accepted.

Changes in the Nucleus

• In an atom, the number of electrons equals the number of protons, making the atom electrically neutral.
• All atoms of a specific element have the same number of protons.
• An element's atomic number is the number of protons in an atom of that element.
• An atom's mass number is the total number of protons and neutrons.
• Atoms of the same element with different numbers of neutrons are isotopes of that element.
• Atoms become positive ions if they lose one or more outer electrons.

Nuclear Decay Equations

• Nuclear equations represent radioactive decay.
• An alpha particle is represented as ⁴₂He.
• A beta particle is represented as ⁰₋₁e.
• Emission of radiation may change the mass and/or charge of the nucleus.
• Alpha decay causes a decrease in both the mass and charge of the nucleus. An example is Radon (²¹⁹₈₆Rn) decaying into Polonium (²¹⁵₈₄Po) and an alpha particle (⁴₂He).
• Beta decay does not cause the mass to change but causes the charge of the nucleus to increase. An example is Carbon (¹⁴₆C) decaying into Nitrogen (¹⁴₇N) while emitting a beta particle (⁰₋₁e).
• Gamma ray emission does not cause the mass or charge of the nucleus to change.
• A gamma ray (γ) is electromagnetic radiation from the nucleus.
• A neutron is represented as (n).

Alpha, Beta, and Gamma Radiation

• Knowledge of alpha, beta, and gamma radiation is limited to their penetration through materials, their range in air, and ionizing power.

Activity and Half-Life

• Some atomic nuclei are unstable and emit radiation to become more stable, this random process is called radioactive decay.
• Activity is the rate at which unstable nuclei decay, measured in becquerels (Bq).
• Count-rate is the number of decays recorded each second using a detector, like a Geiger-Muller tube.
• Nuclear radiation emitted includes:
• Alpha particles (α): two neutrons and two protons (helium nucleus).
• Beta particles (β): high-speed electrons from the nucleus when a neutron turns into a proton.
• Gamma rays (γ): electromagnetic radiation from the nucleus.
• Neutrons (n).
• Half-life is the time it takes for the number of nuclei of a radioactive isotope in a sample to halve, or the count rate to halve.

Contamination and Irradiation

• Radioactive contamination refers to the unwanted presence of materials containing radioactive atoms on other materials.
• The hazard from contamination is due to the decay of the contaminating atoms, where the type of radiation emitted affects the hazard level.
• Irradiation is the process of exposing an object to nuclear radiation, without making the object radioactive.

Nuclear Issue Hazards

• Compare the hazards associated with contamination and irradiation.
• Suitable precautions must be taken to protect against any hazard that the radioactive source used in the process of irradiation may present.
• It is important for the findings of studies into the effects of radiation on humans to be published and shared with other scientists so that the findings can be checked by peer review.