What is an alpha particle and how does alpha decay change a nucleus?

An alpha particle consists of two protons and two neutrons, resembling a helium-4 nucleus with a two-plus charge. During alpha decay, the parent nuclide emits this alpha particle, reducing the atomic number by two and the mass number by four. For example, polonium-210 converts to lead-206 through alpha decay.

How does beta-minus decay differ from beta-plus decay?

Beta-minus decay converts a neutron into a proton, emitting a high-energy electron and increasing the atomic number by one while keeping the mass number unchanged. Beta-plus decay converts a proton into a neutron, emitting a positron that quickly annihilates with an electron, releasing two 511 keV gamma rays and decreasing the atomic number by one.

What happens during gamma decay and when does it occur?

Gamma decay occurs when an excited daughter nuclide transitions to its nuclear ground state by emitting gamma radiation, a high-energy electromagnetic quantum. The mass number and atomic number remain unchanged during this process. Gamma emission frequently accompanies other decay modes, such as when cobalt-60 beta decay produces excited nickel-60, which then emits two gamma rays.

What is neutron emission and how does it affect the nucleus?

Neutron emission is the ejection of a neutron from the nucleus, occurring either spontaneously or in response to bombardment by gamma rays or particles. During neutron emission, the atomic number remains unchanged while the mass number decreases by one. Beryllium-13 decaying to beryllium-12 exemplifies spontaneous neutron emission.

How does electron capture work and what particles are emitted?

Electron capture occurs when an inner-shell electron combines with a proton in the nucleus, converting it into a neutron. This process decreases the atomic number by one without changing the mass number. The vacancy left by the captured electron is filled by an outer electron, which emits energy typically in the form of X-rays corresponding to the electron transition.

Which radioactive emissions have the greatest penetration power?

Gamma radiation has the greatest penetration power and passes through most materials, while alpha particles, being the most massive nuclear particles, have very low penetration ability. Neutrons and beta particles fall between these extremes and can be blocked effectively by relatively lightweight materials.

What are the fundamental nuclear emissions released during radioactive decay?

Radionuclides emit six fundamental types of nuclear particles and radiation: alpha particles, beta particles, positrons, neutrons, gamma rays, and X-rays. These emissions occur as radionuclides disintegrate to daughter nuclides through various decay processes. Understanding these emissions is essential for studying radioactive decay and radiometric dating applications.

19.2

Types of Radioactivity

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Radionuclides disintegrate to daughter nuclides along with the emission of particles or electromagnetic radiation. The fundamental nuclear emissions include alpha particles, beta particles, positrons, neutrons, gamma rays, and X-rays.

An alpha particle is composed of two protons and two neutrons, resembling the helium-4 nucleus. Each of these particles has a two-plus charge. Alpha decay reduces the atomic number by two and mass number by four, like the conversion of polonium-210 to lead-206.

Beta-minus decay is an emission of high-energy electrons from the nucleus by conversion of a neutron into a proton. The daughter nuclide has an additional proton, and its atomic number is one greater than that of the parent nuclide.

During the process, the number of neutrons decreases by one; however, the number of protons increases by one. Thus, the mass number remains unchanged.

Beta-plus decay is the conversion of a proton to a neutron, emitting a positively charged particle from the nucleus. This particle has the same mass as an electron, making it an antiparticle of the electron, and is called a positron. The emitted positron reduces the atomic number of a daughter nuclide by one.

The positron is short-lived because it quickly collides with an electron, and both particles are annihilated. Their energy is released as two 511 keV gamma rays.

Emission of gamma radiation also occurs when an excited daughter nuclide decays to its nuclear ground state. Thus, beta-minus decay of cobalt-60 produces an excited-state nickel-60, which emits two gamma rays while dropping to the nuclear ground state.

The mass number and atomic number do not change during gamma decay. The emission of gamma radiation occurs in combination with other nuclear decay reactions.

Neutron emission is the ejection of a neutron from the nucleus. It can happen spontaneously, like the decay of beryllium-13 to beryllium-12, or in response to bombardment by gamma rays or particles. The atomic number remains unchanged during this process, whereas the mass number decreases by one.

The conversion of potassium-40 to argon-40 exemplifies the emission of energy due to electron capture. The potassium nucleus captures an inner electron in the atom, and a proton converts to a neutron. An outer electron drops to the inner level to fill the vacancy, characterized by an emission of X-rays with an energy corresponding to the transition.

The penetration power of alpha particles, which are the most massive of the nuclear particles, is very low, whereas gamma radiation passes through most materials. Neutrons and beta particles can be blocked effectively by relatively lightweight materials.