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Transcript of Nuclear Chemistry
What is Radioactivity?
Certain isotopes of elements have an unstable ratio of
neutrons to protons.
An unstable nucleus is radioactive and will spontaneously emit particles and energy.
All isotopes above atomic number 82 are radioactive.("no known stable isotopes")
The major particles emitted by radioactive isotopes (radioisotopes) are shown on Table O:
Reactions that involve transmutations (changes in the nucleus).
Transmutations may be natural or artificial.
Transmutations result in the conversion of one element into another.
Nuclear Particle Charges
Alpha Particle = +2
Beta Particle = -1
Neutron = 0
Gamma Radiation = 0 (just energy)
Positron = +1
Proton = +1
Penetration Power of Particles
Alpha < Beta < Gamma
Alpha particles have the least and gamma the most penetrating power.
Gamma radiation is high energy and causes mutations to DNA in cells.
Nuclear Emissions in an Electric Field
Beta Particles (neg. charge)
Gamma Rays, Neutrons (no charge)
Alpha Particles, Positrons, Protons (Pos. charge)
Gamma Radiation Pool
Nucleus emits an alpha particle.
Nucleus emits a beta particle.
Nucleus emits a positron particle.
"Bombard the nucleus" with high energy particles (alpha, neutrons) to cause a transmutation to occur.
Recognizing Artificial Transmutations
Artificial transmutations will have an extra particle as a reactant. (on the left side of arrow)
A heavy uranium-235 nucleus is split into lighter nuclei to release energy
In fission reactions, mass is converted to energy.
Controlled Fission (Nuclear Power Plant)
How is nuclear power generated?
Bottom # in symbol on Table O is charge.
Uncontrolled Fission Reactions
Nuclear Bombs are uncontrolled fission (all energy released at once)
Fusion reactions involve the combining of lighter
atoms into heavier nuclei.
The Sun provides energy to earth by fusion.
Why Not Use Fusion?
Fusion reactions are the most energetic reactions known.
Require temps in millions of degrees.
Cold fusion is an attempt to get fusion to occur at a lower temp.
Beneficial Uses of Radioactivity
Medical Procedures (X-Rays)
Radioactive Dating of Materials (Half-Life)
Irradiation of Food to kill bacteria.
Smoke Detectors (Am-241)
Generation of Power
Common Uses of Radioisotopes
: Thyroid Disorders
: Brain Tumors
: Radioactive Dating of once living material (fossils)
: Radioactive Dating of geologic structures (rocks)
: Fuel for Power Plants
Radioisotopes used in medical procedures should have a short half life and should be quickly/easily eliminated from body
Risks Associated with Radioactivity and Nuclear Power
Damage to DNA (Mutations) leading to cancers and illness.
Waste Products of fission remain radioactive for a long time.
Finding safe storage and disposal of the wastes
Moderator: Slow down neutrons (graphite or water)
Control Rods: Absorb excess neutrons (cadmium or boron)- Prevent chain reaction
Fuel Rods: U-235 (Uranium)- Undergoes fission reaction to produce energy
The amount of time it takes for 1/2 the mass of a radioisotope to decay.
How long does it take for a 200 gram sample of K-42 to decay to 25 grams?
Half Life of K-42 (Table N): 12.36 hours
(12.36 hrs/half life)(3 Half Life Periods)=
It requires 3 half life periods for 200g to break down to 25g.
200g -> 100g -> 50g -> 25g
Half life does not change under any conditions, it is a characteristic value of a radioisotope
How old is a fossil that contains 1/16 the original mass of C-14?
Half Life of C-14 from Table N: 5715 years
1/16th = 4 Half Life Periods passed
(1HL = 1/2 , 2 HL = 1/4, 3 HL = 1/8,
4 HL = 1/16, 5 HL = 1/32, 6 HL = 1/64)
(4 Half Lifes)(5715 years)=
If 6.25 grams of a sample of N-16 remain unchanged after 35.7 seconds, what was the original mass of the sample?
Half Life of N-16 (Table N): 7.13 sec
Time/Half Life = # Half Lifes
35.7 sec/7.13 sec = 5 Half Lifes
6.25g -> 12.5g -> 25 g -> 50g -> 100g -> 200g
200g in original sample
If an 80 gram sample of a radioisotope decays to 5 grams in 100 days, what is the half life of the radioisotope?
80g -> 40g -> 20g -> 10g -> 5g
It requires 4 Half Life periods to decay from 80g to 5g
100 days / 4 Half Lifes =
25 days per half life
How many grams of a 400 gram sample of Co-60 remain unchanged after 15.8 years?
Half Life of Co-60: 5.271 years
Total Time / Half Life = # Half Lifes
15.8 years / 5.271 years = 3 Half Lifes
50 grams will remain
Table N list Half Life Values for each radiois-otope
Table N Shows the type of Decay radioisotopes go through
Risk of potential meltdown
Photographic Film (X-Rays)
Shut it Mia!