Radioactive DecayRadioactive Decay

Quick ReviewQuick Review

Atom made of 3 subatomic particlesAtom 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 Can determine the number of each by using the Periodic Table of Elementsusing the Periodic Table of Elements

Periodic Table & Subatomic Periodic Table & Subatomic ParticlesParticles

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

IsotopesIsotopes

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

IsotopesIsotopes

Calculate Atomic Weight (approx)Calculate Atomic Weight (approx)

98.8% of carbon=1298.8% of carbon=12 0.988 x 12 = 11.8560.988 x 12 = 11.856

1.1% of carbon=131.1% of carbon=13

0.011 x 13 = 0.1430.011 x 13 = 0.143

0.1% of carbon=140.1% of carbon=14 0.001 x 14 = 0.001 x 14 = 0.0140.014

12.01312.013

RadioactivityRadioactivity

Certain isotopes are RADIOACTIVE, or Certain isotopes are RADIOACTIVE, or spontaneously release particles and spontaneously release particles and energy because of an unstable nucleusenergy because of an unstable nucleus Alpha decayAlpha decay 3 types of Beta decay3 types of Beta decay Gamma decayGamma decay

*type of decay depends on energy in the *type of decay depends on energy in the nucleus and the number of protons & nucleus and the number of protons & neutrons presentneutrons present

Alpha Decay, Alpha Decay, αα

238U α + 234Th

Beta Decay, Beta Decay, ββ3 types of Beta Decay3 types of Beta Decay Beta minus, Beta minus, ββ- - (electron emission)(electron emission)

neutron converted into a proton & electron is neutron converted into a proton & electron is emittedemitted

Beta plus, Beta plus, ββ+ + (positron emission)(positron emission)““Antimatter” electron (same mass, 1+ charge)Antimatter” electron (same mass, 1+ charge)energy is used to convert a proton into a neutron, a energy is used to convert a proton into a neutron, a positron (e+) & a neutrino (neutral charge, mass of positron (e+) & a neutrino (neutral charge, mass of electron)electron)

Electron capture (or K-capture)Electron capture (or K-capture)ββ+ + decay and inner most electron from the atom is decay and inner most electron from the atom is captured during processcaptured during process

Example of Beta Minus DecayExample of Beta Minus Decay

C-14 (6p, 8n) decays to produce N-14 (7 p, C-14 (6p, 8n) decays to produce N-14 (7 p, 7n) and a beta particle (7n) and a beta particle (ββ--))1414C C 1414N + N + ββ--

*daughter nucleus (nitrogen-14) has 1 more *daughter nucleus (nitrogen-14) has 1 more proton and 1 less neutron than parent proton and 1 less neutron than parent nucleus (carbon-14)nucleus (carbon-14)

Gamma DecayGamma DecayNucleus is at too high of energy state; releases gamma particle and lowers energy state

Often occurs in conjunction with other types of decay

Half-LifeHalf-Life

The time it takes for ½ of a radioactive sample to decayThe time it takes for ½ of a radioactive sample to decay11 100.0 g100.0 g

½½ 50.0 g 50.0 g

¼¼ 25.0 g 25.0 g

1/81/8 12.5 g 12.5 g

1/161/16 6.25 g 6.25 g