Chapter 4 Section Chapter 4 Section 4.44.4Nuclear Reactions: Nuclear Reactions: Decay Decay

Radiation and RadioactivityRadiation and Radioactivity• RadioactivityRadioactivity was discovered by was discovered by

Henri Becquerel in 1896.Henri Becquerel in 1896.• It is the spontaneous emission of It is the spontaneous emission of

particles or energy by unstable particles or energy by unstable atomic nuclei.atomic nuclei.

• The emitted particles are called The emitted particles are called radiationradiation, and the change in , and the change in nucleus that results is called nucleus that results is called radioactive decayradioactive decay..

RadiationRadiation• There are three types of There are three types of

radiation we will discuss, alpha radiation we will discuss, alpha ((), beta (), beta () and gamma () and gamma () ) particles.particles.

• Alpha particles have the least Alpha particles have the least amount of energy, while gamma amount of energy, while gamma particles have the most.particles have the most.

1) Alpha Decay1) Alpha Decay• Alpha decay occurs when Alpha decay occurs when

unstable isotopes try to stabilize unstable isotopes try to stabilize by emitting an by emitting an alpha particlealpha particle..

• An alpha particle is made of two An alpha particle is made of two protons and two neutrons, and protons and two neutrons, and its symbol is its symbol is or He. or He.

• Ra Ra

4422

4422

2362368888 He + RnHe + Rn44

22232232

8686

2) Beta Decay2) Beta Decay• There are three types of beta There are three types of beta

decay; decay; beta emission, positron beta emission, positron emission and electron captureemission and electron capture..

• A A beta particlebeta particle is the same thing is the same thing as an electron with a symbol of as an electron with a symbol of or e or e--..

• Beta emission looks likeBeta emission looks like• C C e e-- + N + N

00--11

00--11

00--11

114466

114477

Electron Capture and PositronElectron Capture and Positron• Electron captureElectron capture occurs when occurs when

instead of emitting an electron, instead of emitting an electron, one is pulled into the nucleus.one is pulled into the nucleus.

• Au + eAu + e-- Pt Pt

• A A positronpositron is an odd particle; it is is an odd particle; it is an electron with a positive an electron with a positive charge!charge!

• Sb Sb e e-- + Sn + Sn

1951957979

1951957878

00--11

1161165151

00+1+1

1161165050

3) Gamma Radiation3) Gamma Radiation• Frequently Frequently or or decay produces decay produces

energy, which is released as energy, which is released as gamma rays (gamma rays ().).

• In most cases, it is only given off In most cases, it is only given off when other types of radiation when other types of radiation occur, and since it has no occur, and since it has no particles, its symbol is just particles, its symbol is just ..

Why does radioactive decay Why does radioactive decay occur?occur?• All stable isotopes of an atom lay All stable isotopes of an atom lay

inside what is called the band of inside what is called the band of stability.stability.

• This is a ratio of protons to This is a ratio of protons to neutrons that is inherently neutrons that is inherently stable.stable.

• Atoms not in this band will Atoms not in this band will undergo radioactive decay to do undergo radioactive decay to do so.so.

Predicting how an isotope will Predicting how an isotope will decay:decay:

• An isotope is just too big:An isotope is just too big:– decaydecay

• An isotope has too many An isotope has too many neutrons:neutrons:– decaydecay

• An isotope has too few neutrons:An isotope has too few neutrons:– ee-- capture, positron emission capture, positron emission

Write the Nuclear Reaction Write the Nuclear Reaction for:for:• The The decay of Americum-245 decay of Americum-245• The The decay of Thorium-236 decay of Thorium-236• The electron capture of Iodine-The electron capture of Iodine-

125125• The positron emission of The positron emission of

Potassium-40Potassium-40