Radioactive Decay

Quick Review Atom made of 3 subatomic particles Protons (positive, inside nucleus) Protons (positive, inside nucleus) Electrons (negative, outside nucleus) Electrons (negative, outside nucleus) Neutrons (neutral, inside nucleus) Neutrons (neutral, inside nucleus) Can determine the number of each by using the Periodic Table of Elements

Periodic Table & Subatomic Particles Atomic Number = number of protons = number of electrons Atomic Weight/Atomic Mass Mean (weighted average) of all the isotopes of an element Approx. weight of the sum of the protons & neutrons in an atom of the element Number of Neutrons = mass # - atomic # = 23 – 11 = 12

Isotopes Atoms of the same element (same number of protons) but different numbers of neutrons Carbon-12 (98.8% of all carbon) 6 neutrons Carbon-12 (98.8% of all carbon) 6 neutrons Carbon-13 (1.1% of all carbon) 7 neutrons Carbon-13 (1.1% of all carbon) 7 neutrons Carbon-14 (less than 0.1%) 8 neutrons Carbon-14 (less than 0.1%) 8 neutrons

Isotopes Calculate Atomic Weight (approx) 98.8% of carbon= x 12 = x 12 = % of carbon= x 13 = x 13 = % of carbon= x 14 = x 14 =

Radioactivity Certain isotopes are RADIOACTIVE, or spontaneously release particles and energy because of an unstable nucleus Alpha decay Alpha decay 3 types of Beta decay 3 types of Beta decay Gamma decay Gamma decay *type of decay depends on energy in the nucleus and the number of protons & neutrons present

Alpha Decay, α 238 U  α Th

Beta Decay, β 3 types of Beta Decay Beta minus, β - (electron emission) Beta minus, β - (electron emission) neutron converted into a proton & electron is emitted Beta plus, β + (positron emission) Beta plus, β + (positron emission) “Antimatter” electron (same mass, 1+ charge) energy is used to convert a proton into a neutron, a positron (e+) & a neutrino (neutral charge, mass of electron) Electron capture (or K-capture) Electron capture (or K-capture) β + decay and inner most electron from the atom is captured during process

Example of Beta Minus Decay C-14 (6p, 8n) decays to produce N-14 (7 p, 7n) and a beta particle (β - ) 14 C  14 N + β - *daughter nucleus (nitrogen-14) has 1 more proton and 1 less neutron than parent nucleus (carbon-14) *daughter nucleus (nitrogen-14) has 1 more proton and 1 less neutron than parent nucleus (carbon-14)

Gamma Decay Nucleus is at too high of energy state; releases gamma particle and lowers energy state Often occurs in conjunction with other types of decay

Half-Life The time it takes for ½ of a radioactive sample to decay g ½ 50.0 g ¼ 25.0 g 1/ g 1/ g