CHAPTER 28
Nuclear Chemistry
CHAPTER 28
Nuclear Chemistry
Radioactive Decay
Radioactive Decay
A. Nuclear StabilityA. Nuclear Stability
Nuclide = atom of an isotope
A. Nuclear StabilityA. Nuclear Stability
Nuclear stability – stable nuclei always have at least as many neutrons as protons.
A. Nuclear StabiityA. Nuclear Stabiity
For an odd/even or even/odd nucleus, if the mass number is different by more than 1 amu from the rounded atomic mass, the nuclide is unstable.
Ex: N177
A. Nuclear StabilityA. Nuclear Stability
For an even/even nucleus, if the mass number is different by more than 3 amu from the rounded atomic mass, the nuclide is unstable.
Ex: O208
A. Nuclear StabilityA. Nuclear Stability
For odd/odd nuclei, only four stable isotopes are found in nature:
H21 Li6
3 B105 N14
7
He42
B. Nuclear DecayB. Nuclear Decay
Alpha particle () helium nucleus paper2+
Beta particle (-) electron e0
-11-
leadPositron (+)
positron e01
1+
Gamma () high-energy photon 0
concrete
B. Nuclear DecayB. Nuclear Decay
Alpha Emission
He Th U 42
23490
23892
parentnuclide
daughternuclide
alphaparticle
Top and bottom numbers must balance!!
B. Nuclear DecayB. Nuclear Decay
Beta Emission
e Xe I 0-1
13154
13153
electronPositron Emission
e Ar K 01
3818
3819
positron
B. Nuclear DecayB. Nuclear DecayElectron Capture
Pd e Ag 10646
0-1
10647
electronGamma Emission
Usually follows other types of decay.
Transmutation Atom of one element changes into an
atom of another element.
B. Nuclear DecayB. Nuclear Decay
Why nuclides decay… need stable ratio of neutrons to protons
He Th U 42
23490
23892
e Xe I 0-1
13154
13153
e Ar K 01
3818
3819
Pd e Ag 10646
0-1
10647
DECAY SERIES TRANSPARENCY
C. Half-lifeC. Half-life
Half-life (t½) Time required for half the atoms of a
radioactive nuclide to decay. Shorter half-life = less stable.
D. Radiocarbon DatingD. Radiocarbon Dating
Carbon-14 is in all living things through the carbon cycle.
Amount of carbon-14 stays constant until organism dies, then it begins to decay.
N C 147
0-1
146
D. Radiocarbon DatingD. Radiocarbon Dating
Amount of carbon-14 can be expressed as either a percentage or as a decimal number.
Example: amount of carbon-14 in a dead tree could be expressed as 38% or 0.38 of the original amount.
N C 147
0-1
146
D. Radiocarbon DatingD. Radiocarbon Dating
Half-life of carbon-14 : 5730 years
E. FissionE. Fission
Occurs when isotopes are bombarded with neutrons and split the nucleus into smaller fragments, accompanied by the release of neutrons and a large amount of energy. (Each atom can capture 1 neutron.)
E. FissionE. Fission
Chain reaction – occurs when atomic nuclei that have split release energetic neutrons that split more nuclei.
E. FissionE. Fission
Two steps in controlling fission: Neutron moderation – water or carbon
slows down the neutrons Neutron absorption – decreases the
number of slow neutrons through the use of control rods made of neutron-absorbing materials (usually cadmium)
F. FusionF. Fusion
Occurs when two light nuclei combine to produce a nucleus of heavier mass, accompanied by the release of a large amount of energy.
F. FusionF. Fusion
Occurs in all starsHigh temperatures are necessary to
initiate fusion (no cold fusion yet)Possible future energy sourceHydrogen bomb is a fusion reaction
(fusion of two deuterium nuclei).
G. Methods of DetectionG. Methods of Detection
Geiger Counters (primarily beta)Scintillation counter – coated screen
detects radiation particles. Film badge – several layers of
photographic film encased in a holder. Detects beta and gamma.
H. Radioisotopes in Medicine
H. Radioisotopes in Medicine
X-rays: Useful in imaging soft-tissue organs.
Tracers: Iodine-131 is used to check for thyroid problems
Radiation treatment: Some cobalt isotopes are used as radiation sources to treat cancer.
