25.1. The Nucleus http://www.ck12.org
25.1 The Nucleus
Objectives
The student will:
- Know the particles making up the atomic nucleus.
- Understand binding energy.
- Understand the strong nuclear force.
- Understand “mass defect.”
- Solve problems involving binding energy.
- Understand the three forms of radioactivity.
- Solve problems involving alpha decay.
Vocabulary
- alpha decay: Occurs when anαparticle (a helium nucleus^42 He) is ejected from the nucleus of a parent atom.
- atomic mass numberA: The total number of all nucleons in the nucleus.
- atomic number Z:The number of protons in the nucleus.
- beta decay:Occurs when a neutron within the nucleus changes into a proton by emitting an electron.
- binding energy: The energy equivalent of the mass difference(∆m), also known as the mass deficit.
- daughter nucleus: Nucleus formed by decay.
- deuterium: An isotope of hydrogen composed of one proton, one neutron, and one electron.
- gamma decay:When a nucleon falls to a lower energy level in the nucleus, a high-energy electromagnetic
pulse, called a gamma ray(γ)is emitted. - isotopes: The different masses of nuclei of an element.
- neutron: Electrically neutral particles.
- parent nucleus:Original nucleus of a radioactive atom.
- proton:Particle with a positive charge.
- transmutation: A process by which unstable nuclei can be transformed into entirely different ones. The
transmutation process occurs when a particle is captured by the nucleus and through different nuclear decay or
disintegration processes.
Introduction
The three common types of radioactivity were termed alpha(α)decay, beta(β)decay and gamma(γ)decay by
Ernest Rutherford.
- Alpha decayis easily absorbed, stopped by a sheet of paper. It was found to be heavy, with a positive charge.
- Beta decayis roughly 100 times more penetrating, stopped by a few millimeters of aluminum. It is very
light-weight with a negative charge.