Radioactive Isotopes and Decay

• Chemical reactions disturb the atom's outer electrons, while nuclear reactions affect the nucleus, irrespective of the atom's chemical environment.

Radioactive Decay

• Occurs when a nucleus spontaneously disintegrates and gives off radiation.
• Emission can include electrons, nuclear particles, smaller nuclei, and electromagnetic radiation.
• Antoine Henri Becquerel discovered radioactivity in 1896 from uranium minerals.
• Radiation splits into alpha (α), beta (β), and gamma (γ) rays in electric and magnetic fields.
• Alpha rays have a positive charge, consist of helium-4 nuclei (two protons and two neutrons).
• Beta rays have a negative charge and are high-speed electrons.
• Gamma rays, like X-rays, are electromagnetic radiation unaffected by electric and magnetic fields, with shorter wavelengths (about 1 pm).
• Uranium-238 emits alpha rays and decays into thorium-234.

Nuclear Equations

• Nuclear reactions can be expressed with equations similar to chemical reactions, using nuclide symbols.
• ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He exemplifies alpha-particle emission.
• The subscript represents charge, and the superscript indicates the total number of protons and neutrons.
• During a nuclear reaction, the total charge and total number of nucleons are conserved.

Additional Particles

• Proton: ¹₁H or ¹₁p
• Neutron: ¹₀n
• Electron: ⁰₋₁e or ⁰₋₁β
• Positron: ⁰₁e or ⁰₁β
• Gamma photon: ⁰₀γ
• Beta emission is the decay of a nucleus through electron emission (⁰₋₁e, ⁰₋₁β).
• A positron shares the electron's mass but has a positive charge.
• Positron-electron collisions result in annihilation and release two gamma photons: ⁰₁e + ⁰₋₁e → 2⁰₀γ
• A gamma photon refers to electromagnetic radiation with short wavelengths (around 1 pm) and high energy.

Nuclear Equation Example

• Radium-226 undergoes alpha decay to form radon-222: ²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He.
• The sum of subscripts and superscripts must be equal on both sides of the equation
• Potassium-40 decays into calcium-40 via beta emission.

Nuclear Stability

• Nuclear force, a strong attraction between nucleons, holds stable nuclei together, effective only at short distances (about 10⁻¹⁵ m).
• Magic numbers relate to when nuclei with certain numbers of protons or neutrons appears to be very stable.
• Magic numbers of protons are 2, 8, 20, 28, 50, and 82, with neutron magic numbers being identical, with the addition of 126.
• Pairing of protons and neutrons also affects the nuclear model, which explains these magic numbers and exceptionally stable nuclei.
• There are more stable isotopes with even numbers of both protons and neutrons than isotopes with odd numbers.
• The band of stability represents the region where stable nuclides lie when plotted by number of protons vs number of neutrons.
• Nuclides to the left tend to decay by beta emission, whereas those to the right usually decay by positron emission or electron capture.
• For nuclides with Z <= 20, the ratio of neutrons to protons is about 1.0 to 1.1, but as Z increases, this ratio approaches 1.5.
• No nuclides are stable with atomic numbers greater than 83, except all elements with Z <= 83 have one or more stable nuclides save technetium (Z = 43) and promethium (Z = 61).

Types of Decay

• There are generally six types of decay, with the first five listed in Table 20.2. 1. Alpha emission (α) - Radiation: ⁴₂He - Equivalent Process: -2 Atomic Number, -4 Mass Number - Z > 83 2. Beta emission (β) - Radiation: ⁰₋₁e - Eqivalent Process: ¹₀n → ¹₁p + ⁰₋₁e - +1 Atomic Number, 0 Mass Number - N/Z too large 3. Positron emission (β⁺) - Radiation: ⁰₁e - Equivalent Process: ¹₁p → ¹₀n + ⁰₁e - -1 Atomic Number, 0 Mass Number - N/Z too small 4. Electron capture (EC) - Radiation: x-rays - Equivalent Process: ¹₁p + ⁰₁e → ¹₀n - -1 Atomic number, 0 Mass number - N/Z too small 5. Gamma emission (γ) - Radiation: ⁰₀γ - Equivalent Process: - - 0 Atomic Number, 0 Mass Number - Excited

• Nuclides to its left have a neutron-to-proton ratio (N/Z) which is higher than needed; these decay via beta emission.

• Beta emission reduces the ratio, turning a neutron into a proton.

• Nuclides on the right lack a high enough neutron count, and decay through positron emission or electron capture.

• Both convert a proton to a neutron, increasing the neutron-to-proton ratio, which creates a stable nuclide.

• Alpha emission, also known as alpha particle emissions, happens with unstable nucleus such as Radium-226.

• Emitting leads to an atomic number dropping by two and the mass number dropping by four

Beta Emission

• This involves the emission of a high-speed electron from an unstable nucleus
• It is equivalent to converting a neutron to proton ¹₀n → ¹₁p + ⁰₋₁e
• Radioactive decay happens with carbon-14 turning into nitrogen-14

Positron Emission

• Results from emission from an unstable nucleus, essentially converting a proton to a neutron ¹₁p → ¹₀n + ⁰₁e
• The same occurs in the radioactive decay of technetium-95

Electron Capture

• Refers to the decay of an unstable nucleus by capturing an electron from inside the atom for an inner orbital ¹₁p + ⁰₋₁e → ¹₀n
• Potassium-40 undergoes decay by electron capture

Gamma Emission

• Refers to excited nucleus when emitting a gamma photon, that contains its energy levels
• Excited states decay after radioactive decay
• Metastable nuclei, has a lasting nucleus in its excited state for at least one nanosecond (1 × 10⁻⁹ s).
• It decays through gamma emission, such as metastable technetium-99

Spontaneous Fission

• Refers to the spontaneous decay of an unstable nucleus, usually with heavy nuclei above mass number 89.
• They tend to split into lighter nuclei while in decay.

Radioactive Decay Example

• Considering isotopes like carbon-12 and carbon-13 are stable where other carbon isotopes tend to be radioactive.
• Isotopes with a smaller mass number decay by positron emission.
• Carbon-11 undergoes positron emission into boron-11
• Heavier isotopes tend to decay by beta emission, turning into produce nitrogen-14
• Positron emission and electron capture are decaying processes that varies upon the relative rates of the two processes
• Electron capture grows with the decaying nuclide's atomic number and becomes significant within heavier elements.

Predicting Radioactive Decay

• Stable nuclides are predicted using type of radioactive decay
• Nuclides of an N/Z ratio(neutron/proton) higher emit a beta particle
• Nuclides with an N/Z ratio lower emit a positron emission or electron capture
• Comparing mass numbers rather than their N/Z ratios

Radioactive Decay Series

• All nuclides with atomic numbers over 83 and above are radioactive and decay through alpha emission
• Emitting an alpha particle reduces its nucleus's atomic number and gains its stability
• Natural radioactive give rise to a radioactive series, starting with uranium-238
• There are three series found to occur in nature, eventually reaching a stable nuclide that results in lead

Nuclear Bombardment

• A nucleus decays on its on, emitting alpha or beta particle via radioactive decay
• Bombarding a nucleus by another or nuclear particle is known as nuclear bombardment.
• Rutherford discovered methods to change nucleus and discover new elements on his own

Transmutation

• Changing one element to another, Rutherford discovered alpha particles collide with nitrogen nuclei and eject protons.
• Experiments that was made with the ejection of a proton supported all nuclei contains protons, and the possibilities of creating newer elements.
• Beryllium gets bombarded by alpa particles, emits radiation which is called neutrons

Abbreviated Notation

• Nuclear bombardment reactions gets a simplified notation
• ¹⁴N + ⁴₂He → ¹⁷₈O + ¹₁H
• ¹⁴N(α, p)¹⁷₈O
• Write the original number in the nuclide symbol, the projectile particle in parenthesis before the symbol, and symbol and the ejected particle
• Symbols of particles:
• Neutron: n
• Proton: p
• Deuteron, ²₁H: d
• Alpha, ⁴₂He: α

Trans-uranium Elements

• Elements that has atomic numbers greater than uranium (Z = 92) is known as trans-uranium elements
• They are discovered by McMillan and P. H. Abelson, by bombarding uranium-238 with neutrons
• Which gave uranium-239 via the capture of a neutron, and decayed by beta emission to neptunium-239.
• Plutonium (Z = 94) was discovered by bombarding hydrogen-2 atoms at a uranium target to create neptunium-238
• Plutonium-239 is also used in nuclear weapons

Applications of Nuclear Radiations

• It creates elements that exists in nature, especially for trans uranium elements
• Nuclide decay rates that provides a clock of for dating back the era
• Dating wood that contains carbon via carbon dating, has a halflife of 5730 years
• Analysing radioactive tracers in chemical analysts
• Nuclear chemistry can be used to analyse elements with neutron activation
• Radioistopes treats cancer
• Assists with diagnosing diseases

Explore nuclear reactions, radioactive isotopes, and processes like alpha and beta decay. Learn about the differences between X-rays and gamma rays. Understand charge and mass number conservation in nuclear equations.