Chapter 22 Nuclear Reactions. Nuclear Rxns Nuclear reaction-a reaction that involves a change in an...
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Transcript of Chapter 22 Nuclear Reactions. Nuclear Rxns Nuclear reaction-a reaction that involves a change in an...
Chapter 22Nuclear Reactions
Nuclear Rxns Nuclear reaction-a reaction that
involves a change in an atom’s nucleus.
Therefore, an atom of one element changes into an atom of another element.
Nuclear Rxns Nuclide (Nucleus of an atom)
Contains nucleons(protons and neutrons)
Chemical vs. Nuclear Rxns.
Associated with large energy changes
Associated with small energy changes
May involve p, nInvolve only outer electrons
Atoms are often converted into atoms of another element.
Atoms remain unchanged, just rearranges
Occur when nuclei emit particles and/or rays
Occur when bonds are broken and formed
Nuclear RxnsChemical Rxns
Radiation Radiation-The rays and particles
that are emitted by radioactive materials.
Alpha Radiation Alpha radiation-radiation deflected
towards the negatively charged plate and gives off alpha particles
Alpha particles, He or α : 2p, 2n so +2 charge, largest mass (4 amu)
Beta Radiation Beta radiation-radiation deflected
towards the positively charged plate and gives off beta particles (electrons).
Beta particles, β or e: 1e so -1 charge, mass is between alpha and gamma particles
Gamma Radiation Gamma radiation-radiation deflected
towards no plate and gives off gamma rays
Gamma rays, γ : no mass and no charge, usually occupied by α and β
decay.
Nuclear Rxns (1) Ra → Rn + He
α decay
(2) C → N + e β decay
(3) U → Th + He + 2γ γ decay
Types of Radiation (Memorize) Consists Charge Mass Stopped w/ symbol
Alpha
Beta
Gamma
Types of Radiation Positron emission-radioactive decay
that involves the emission of a positron from a nucleus (antimatter)
Positron-particle with the same mass as the electron but opposite charge
• Symbol:
Types of Radiation Electron Capture- nucleus of an
atom draws in a surrounding electron and an X-ray photon is emitted Symbol:
Nuclear Reactions Nuclear Rxn- a rxn that changes the
nucleus
Transmutation-a change in the identity of the nucleus, change in # of protons in nucleus.
Nuclear StabilityMass defect – diff. between mass of an
atom and sum of masses for p, n, e.
Why loss of mass?Caused by conversion of mass to
energy upon formation of nucleus
Nuclear Binding energy – energy released upon formation of nucleus
Nuclear Stability The smaller stable nuclides have a
neutron-proton of 1:1 to the larger nuclides of 1.5:1.
If the nuclei ratio falls above/below the band of stability, the nuclides will undergo decay until they are within the band of stability.
Radioactive decay Radioactive decay-spontaneous
disintegration of an unstable nucleus to a smaller nucleus by giving off nuclear radiation.
Radioactive nuclide- unstable nucleus that will undergo radioactive decay
Nuclear RxnsIdentify the product that balances the
following nuclear rxns.1. 212Po → 4He + ____
2. 230Th → _____ + 4He
3. 238U + 4He → ____ + 1n
4. 27Al + 1n → 24Na + ____
Radioactive decayAlpha Emission
210Po 206Pb + ____Beta Emission
14C 14N + ____Electron Capture (reverse of beta)
106Ag + _____ 106PdPositron emission
11C → 11B + _____
Half-life Half-Life- t1/2 - the time required for half the
atoms of a radioactive element to decay into another element.
Fluorine-21 has a half life,t1/2, of 5 seconds 1000 atoms F-21500 atoms F-21 250 atoms F-21 1(whole amt) ½ left ¼ left 100 g F-21 50 g F-21 25 g F-21
Half-Life ProblemsFormulas:To determine the number of half-lives that past:
#half-lives past = total timet1/2
To determine amount remaining:
Amount remaining = (Initial amt)1 n
2n= # of half lives past
Half-Life Problems1. If the radioactive sample of I-131
was 18.5g, what amt is left after 32 days? (t1/2 = 8 days)
Half-Life Problems2.Iron-59 is used in medicine to
diagnosis blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days?
Half-Life Problems3. If gallium-68 has a half-life of 68.3
minutes, how much of a 10.0 mg sample is left after two half-lives?
Half-Life4. After 15 days only 2 grams remain
of a sample that has a half life of 5 days. How many grams were in the original amount?
5. What is the half life of K-42 if a 750 gram sample decays to 93.75 grams in 24 hours?
6. The half-life of carbon-14 is 5715 years. A sample has only ¼ of its original amount. What is the age of the sample?
Decay Series Decay Series-a series of radioactive
nuclides produced by successive radioactive decay until a stable nuclide is reached
Decay Series QuestionsUse pg. 814 Write the four nuclear equations of
the uranium-238 decay series. What stable nuclide does U-238
finally become? How long is the half life of U-238?
U-238 U-238 is found in small amounts in soil and rock,
particularly, shale and granite.
Rn is one of the daughter nuclide of U-238(parent nuclide) decay.
Rn is a radioactive gas that can be a health hazard trapped in homes from cracks and holes in foundation. It can cause lung cancer and birth defects.
Ra-226, Po-210, Pb-210 are found in cigarettes and the lungs of smokers.
Induced Transmutation Induced Transmutation- bombardment
of stable nuclei with charged and uncharged particles. This process is used to make radioactive
nuclides not found nature, like our newly discovered elements.
Induced Transmutation1. Write a balanced nuclear equation forthe induced transmutation of aluminum-27 into phosphorus-30 by alpha particlebombardment. A neutron is emittedfrom the aluminum atom.
Induced Transmutation2. Write the balanced nuclear equationfor the induced transmutation ofaluminum-27 into sodium-24 byneutron bombardment. An alphaparticle is released in the rxn.
Induced TransmutationWhat element would be formed in the
following nuclear rxn?3. 242Cm + 4He ______ + 1n
Nuclear Radiation Radiation Exposure
Rem-a unit used to measure radiation damage to human tissue like x-rays…
(Complete personal radiation wkst)
Nuclear Radiation Radiation Detection
Geiger Muller counters -measures electrical pulses on gas ionized by radiation
Film badges Scintillation counter
Geiger Counter
Applications of Nuclear Radiation Radiochemical Dating: 14C 0e + 14N
t1/2 = 5715 yrs
Living organisms absorb 14C through food. This C-14 is a constant amt. When the organism dies, there is no new absorption of C-14. The C-14 decays to N-14. By measuring the amount of C-14 the age may be approximated.
Applications of Nuclear Radiation Radioactive Nuclides in Medicine
Radioactive tracers are radioactive atoms incorporated into substances so they can be followed by radiation detectors.
Ex. Tc-99 used to detect bone cancer, I-131 to detect thyroid problems
Applications of Nuclear Radiation Radioactive Nuclides in Agriculture
Radioactive tracers are used to determine effectiveness of fertilizers.
Cobalt-60 is used to irradiate food, to kill bacteria and insects. It is also used to kill cancer cells.
Nuclear Waste1. Produced from nuclear power
plants, nuclear weapons manufacturing, medical research,…
2. Containment on nuclear waste from nuclear power plants is on-site and off-site disposal.
Nuclear Waste*3. Each nuclear reactor has large
pools of water where spent uranium fuel rods can be stored.
4. When the pools are filled, they are sealed in concrete and steel dry casks then moved to permanent storage facilities. There are 77 disposal sites in the US.
Nuclear Fission
Nuclear Fission Nuclear Fission- splitting a larger
nucleus to smaller intermediate nuclides Nuclear Reactors use controlled
fission reactions to produced energy by this rxn:
Parts of Nuclear Reactor Chain rxn-self propagating rxn
Fuel- U-235
Moderator-slows down high speed neutrons to CONTINUE chain rxn; uses water, Be, or C(graphite)
Control Rods -absorbs neutrons, thereby controlling rate of fission rxn; made of Cd
Parts of Nuclear Reactor Coolant-water to remove heat to
turbines to generate electricity Containment structure(shielding)-
structure built around reactor to hold in radiation from escaping in case of an accident; server feet thick concrete.
Recent Nuclear Accidents 1986 Chernobyl power plant in
Soviet Union-Complete meltdown of core
1979 Three Mile Island, USA-partial meltdown
Nuclear Fusion Nuclear Fusion-small nuclei join to
form larger nuclei Ex. sun and stars fusion releases 20X more energy per
gram than fission Uses: hydrogen bomb and in future
fusion power plants
Fusion Reactors Disadvantages of fusion reactors
Huge input of energy needed to start process
A temperature of 200 million K needed to sustain rxn.
Fusion Reactors Advantages of fusion reactors:
Readily available hydrogen from water Nonradioactive products Can stop rxn by dropping temp. Can produce inexhaustible supply of
energy