NUCLEAR CHEMISTRY

Nuclear Chemistry Radioactivity is the emission of subatomic particles or high- energy electromagnetic radiation by the nuclei of certain atoms. These atoms are considered radioactive. Alpha Decay: occurs when an unstable nucleus emits an alpha particle which is a helium atom – 2 protons, 2 neutrons.

Nuclear Chemistry Beta Decay: an unstable nucleus emits an electron. A neutron changes into a proton and an electron and the electron is emitted. It is known as a “beta β particle”. Can penetrate skin - MODERATE PENETRATING POWER.

Nuclear Chemistry Positron Emission: unstable nucleus emits a positron which is equivalent to an electron except it has a (+) charge. A proton converts to a neutron. MODERATE PENETRATING POWER.

Nuclear Chemistry Electron Capture: electron combines with a proton to form a neutron. Mass does not change because electron is very light – but atomic number decreases by 1.

Nuclear Chemistry Gamma Ray Emission: the emission of electromagnetic energy. Very high energy EM radiation – HIGH PENETRATING POWER.

Nuclear Chemistry Neutron Emission: unstable nucleus emits a neutron. Have no charge and a mass of 1 – HIGH PENETRATING POWER.

Nuclear Chemistry X-Ray Emission: same mechanism as gamma ray emission. However, X-rays do not have the same magnitude of frequency or energy as gamma rays. Can penetrate skin.

Nuclear Chemistry What is a half life, t1/2? The # of nuclei that disintegrate per second depends only on the # of radioactive nuclei in the sample. Half life is the amount of time a radioactive, unstable substance takes to change or “decay” to 50% of the original mass of sample. EXAMPLE: the half life of lead-210 is 25 years. In a sample starting with 50 micrograms of lead-210, how much is left after 100 years? EXAMPLE: How much time will the same mass of above substance take to decrease to a mass of 5.0 micrograms? EXAMPLE: 99% of a radioisotope disintegrates in 36.0 hours. What is the half-life of the isotope? EXAMPLE: Br-82 has a t1/2 of 35.7 hours. How many mg of Br-82 will remain if 2.30mg of substance decays for exactly one week?

Nuclear Chemistry Based on the above data, what is the approximate half life of cobalt-57?