Radioactive Elements Chapter 4.5

Review: Radioactive decay  the atomic nuclei of unstable isotopes release fast-moving particles and energy

alpha particles beta particles gamma rays 3major forms of radiation produced during the radioactive decay of an unstable nucleus.  alpha particles beta particles gamma rays

Alpha Decay two protons and two neutrons  break off from the nucleus (alpha particle) 2 p+ and 2 n (He)

Beta Decay a neutron inside the nucleus changes into an electron and a proton The fast moving electron (beta particle) leaves The proton stays in the nucleus Overall the mass stays the same (one neutron turned into one proton, each weight 1 amu) a different element is formed (e.g. Carbon-14 becomes Nitrogen-14)

Gamma Radiation/Gamma Rays (ENERGY) Almost always produced with alpha and beta decay high-energy waves has no charge and does not cause a change in either the atomic mass or the atomic number.

Penetration of Radiation Particles Though very small and very fast moving, radiation particles can be stopped when they collide with other atoms Alpha particles are least penetrating – can be stopped by paper Gamma particles are most penetrating, need several cm of lead or ~1 m of concrete to stop them

Types of Radiation Produced by Radioactive Decay Gives Off New Nucleus Characteristics Alpha Decay 2 protons and 2 neutrons  (Alpha Particle) Positive charge New element – 2 less protons, 2 less neutrons Weighs 4 amu less Fast; Blocked by paper Can damage skin Beta Decay One fast moving electron (Beta Particle) Negative charge New element – 1 less neutron, 1 more proton Weighs the same Faster/More penetrating; Pass through paper, blocked by aluminum sheet Can travel into human body Gamma Radiation High Energy Waves Given off with alpha and beta decay no charge No change to atomic mass or number Most penetrating; Need thick lead or ~1 meter of concrete to stop Can pass right through a body

Some Uses of Radiation A radioactive isotope “signals” where it is by emitting radiation that can be detected.  Tracers are radioactive isotopes that can be followed through the steps of a chemical reaction or industrial process.  Used by biologists to learn about plants Used to find weaknesses in metals, such as pipes and cracks in structures Used in medicine to diagnose problems and treat cancer

What do I need to know about radioactivity for the test? Henry Becquerel discovered Radioactive decay Radioactive decay – unstable nucleus releases: fast moving particles (alpha and beta particles) and energy (gamma radiation) 3. Alpha rays can be blocked by paper. Beta Rays blocked by an aluminum sheet. 4. Tracers – are radioactive isotopes that can be used by doctors to detect medical problems