Describe the processes by which individual nuclei decay.

• Some processes by which nuclei decay emit subatomic particles with unique properties.
• An alpha particle, or helium nucleus, consists of two neutrons and two protons and is symbolized by α or He²⁺. (In Physics 2, only He-4 nuclei will be considered.)
• Neutrinos and antineutrinos are subatomic particles that have no electrical charge, have negligible mass, and are symbolized by ν and ν, respectively.
• Neutrinos and antineutrinos only interact with matter via the weak force and the gravitational force, which results in very little interaction with normal matter.
• Positrons, or antielectrons, are subatomic particles that have an electric charge opposite that of an electron, have the same mass as an electron, and are symbolized by e⁺ or β⁺.
• Nuclei can undergo radioactive decay via alpha decay, beta-minus decay (β^-), beta-plus decay (β⁺), and gamma decay (γ).
• In all nuclear decays, nucleon number (the number of neutrons and protons), lepton number (the number of electrons and neutrinos), and charge are conserved.
• Alpha decay occurs when a nucleus ejects an alpha particle.
• Beta-minus decay occurs when a neutron changes to a proton by emitting an electron and antineutrino.
• Beta-plus decay occurs when a proton changes to a neutron by emitting a positron and neutrino.
• Gamma decay occurs after a nucleus has undergone alpha or beta decay and the excited nucleus decays to a lower energy state by emitting a photon.
• The type of decay exhibited by a given nucleus is determined by the isotope of the element.

AP Physics 2 does not expect students to memorize the processes by which specific isotopes decay or the half-lives of specific isotopes. Neutron emission and electron capture are not included in the AP Physics 2 curriculum framework. Additionally, types of neutrinos, the characteristics that distinguish neutrinos and antineutrinos, and an explanation or application of the weak force are not within the scope of this course.

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