Radioactivity Fundamentals

Radioactivity Objectives

• Learn types of radioactive decay
• Learn how to write nuclear equations for radioactive decay
• Understand how one element can be changed to another by particle bombardment
• Understand the concept of half-life

Review of Atomic Terms

• Nucleons: particles in an atom's nucleus (neutrons and protons)
• Atomic Number (Z): number of protons in the nucleus
• Mass Number (A): sum of protons and neutrons
• Isotopes: atoms with identical atomic numbers but different mass numbers
• Nuclide: each unique atom or the nuclei of a specific isotope

Why Study Nuclear Reactions?

• Central to nuclear energy development
• Used in cancer treatment and medical imaging (PET)
• Used in chemistry to investigate reaction mechanisms
• Used in archaeology to date ancient objects
• Part of military strategies of many nations

Radioactive Decay

• Radioactive nucleus: a nucleus that spontaneously changes and emits energy
• Spontaneous process: occurs by itself with no outside energy required.
• Isotopes undergo radioactive decay naturally, releasing particles and energy.
• This is a random process without outside influence

Radioactive Decay (Continued)

• Radioactivity: the spontaneous decomposition of a nucleus creating a different nucleus and producing one or more particles.
• Nuclear Equation: shows the radioactive decomposition of an element. An example is shown: 14C → 14N + −0e1
• Nuclear Forces: the strong nuclear force holds neutrons and protons together to create a nucleus. It counters electromagnetic repulsion. Weak nuclear force operates within nucleons and produces some types of radioactivity.

Discovery of Radioactivity

• Antoine Henri Becquerel (1852-1908): noticed fogging of photographic plates by uranium crystals
• Pierre Curie (1859-1906) and Marie Curie (1867-1934): further studied uranium and discovered polonium and radium. Marie won two Nobel Prizes but died from radiation exposure.
• Ernest Rutherford (1871-1937): His understanding of atomic structure helped us understand the nucleus. He defined many modern terms for radioactivity.

Alpha Decay

• Alpha particle production (alpha decay): alpha particle = helium-4 nucleus. Blocked by paper, deflected by electric and magnetic fields.
• Net effect: loss of 4 in mass number and loss of 2 in atomic number. Examples shown: 222Ra → 4He + 218Rn and 230Th → 4He + 226 Ra
• Nuclear reactions obey two rules:
  1. Sum of mass number is the same on both sides of the reaction
  2. Sum of atomic number is the same on both sides of the reaction

Beta Decay

• Beta-particle production (beta decay): Beta particle = electron.
• Penetrates paper but not aluminum. Deflected oppositely by electric and magnetic fields.
• Less massive than alpha particle. Travels with speed less than 90% of the speed of light. Produced by a decaying free neutron.
• Examples shown: 234Th → 234Pa + −0e−1 and 131I → −0e−1 + 131Xe
• Net effect: neutron changes to a proton.

Gamma Decay

• Gamma ray release (gamma decay): Gamma ray = high energy photon.
• Travels at the speed of light. Can penetrate almost anything but blocked by lead.
• Undeflected by electromagnetic fields. Present in almost all nuclear reactions
• Examples shown: 238U → 42He+234Th+20y

Positron Production

• Positron production: Positron = particle with same mass as an electron but positive charge, an antimatter version of an electron.
• Produced when nuclei has more protons than neutrons
• Example shown: 22Na → 1e + 22Ne
• Net effect: proton changes to a neutron

Conservation of Mass and Charge Number in Nuclear Reactions

• Both mass and charge numbers are conserved in nuclear reactions
• Sum of mass numbers and charge numbers of reactants equal to the sum of mass numbers and the charge numbers of products

Decay Series

• Decay series: the series of radioactive decay from a parent nucleus to a stable daughter nucleus.
• Starts with Uranium-238 (238U) and ends with Lead-206 (206Pb). Each nuclide is radioactive in this series except for 206Pb. Each step shows the successive transformations using arrows.

Nuclear Transformations

• Nuclear transformation or transmutation: forced change of one element to another
• Bombard elements with particles
• Example shown: 14N + 4He → 17O + 1H and 27Al + 42He → 3015P

Practice Problems

• Write and balance the following equation: 13153I → e−1 +...?
• Write and balance the following equation: 5927Co + 1n0 →...?

Detection of Radioactivity

• Geiger-Muller counter: instrument that measures radioactive decay by registering ions and electrons created by a radioactive particle passing through a gas-filled chamber.

Half-Life

• Half-life: time needed for half of the original radioactive sample to decay
• Table shows half-lives for some radium nuclides.

Decay of a Radioactive Element

• Half of the parent radioactive atoms decay after one half-life. Half of the remainder decay after another half-life. The proportion of parent atoms remaining decreases exponentially.

This quiz explores the essential concepts of radioactivity, including types of radioactive decay, nuclear equations, and the significance of half-life. Understanding these topics is crucial for applications in nuclear energy, medicine, and archaeology. Test your knowledge on these pivotal aspects of nuclear science!