radioactivity what you don’t see...... can hurt you!
TRANSCRIPT
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Radioactivity
What you don’t see ...... can hurt you!.
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IsotopesAtomic Mass
Atomic Number
Neutrons
Protons Electrons
Carbon-
12 12
6
6
6
6
Carbon-
13 13
6
7
6
6
Carbon-
14 14
6
8
6
6
- =
- =
- =
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The extra neutron causes The extra neutron causes 235235UU to produce the to produce the unstable unstable 236236U.U. Thus causing a chain reaction that Thus causing a chain reaction that eventually leads to a big eventually leads to a big BOOM!!!BOOM!!!
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The The splittingsplitting of a nucleus of a nucleus
accompanied by the release accompanied by the release
of of neutrons neutrons and a large and a large
amount of amount of energy energy
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The process of The process of combiningcombining nucleinuclei
to produce a nucleus of to produce a nucleus of greater massgreater mass
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Approx. Approx. 200,000200,000 Japanese Japanese deaths (mostly Civilians)deaths (mostly Civilians)
Only Only 22 nuclear weapons have nuclear weapons have ever been used in war.ever been used in war.
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Nuclear Reaction any change that involves nucleus
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Radioactivity 1896 - Antoine Henri Becquerel
accidently discovered uranium ores emit invisible rays.
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his 2 students, Marie Curie and Pierre Curie, isolated several radioactive elements.
Marie Curie named the process by which uranium gives off rays of radioactivity – radioactive decay
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The Atomic Nucleus
Made of nucleons..+ proton & neutral - neutron.
held by“strong nuclear force.”
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STRONG NUCLEAR FORCE = force
that holds the nucleus togetherAs size of nucleus increases, a stronger
force needed to hold nucleus
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Radioisotope – unstable isotope which undergoes radioactive decay
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Type of Decay
Particle emitted
Change in mass #
Change in atomic #
alpha decay
42He decreases
4decreases
by 2
beta decay 0-1β no change increases
by 1
positron emission
01β no change decreases
by 1
electron capture
x-ray photon
no change decreases by 1
gamma emission
00γ no change no change
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Radioactive Decay
Nucleus unstable when too many
Protons & undergoes Radioactive decay
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Band of Stability As long as the ratio of neutrons to
protons is between 1.0 and 1.5, the atom will be stable.
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How can these radiation be stopped?
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Alpha Radiation Radium - 226 decays into radon -222
and alpha particles.
88Ra226 --> 86Rn222 + 24
24 = 2e4
Alpha particles - helium nuclei
Use “Radioisotope, Radio Activity &Radioactive
Decay” to describe the above Nuclear Reaction The Radioisotope, Radium 226, undergoes
radioactive decay to form Radon. The type of radioactivity emitted is Alpha radiation
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Beta Radiation
38Sr90 --> 39Y90 + -
- = -1e0
Beta particles - high speed e-
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Electron Capture nucleus catches one close electron which
combines with a proton to form a neutron.
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Beta Radiation
38Sr90 --> 39Y90 + -
High speed e- from nucleus?
How is mass the same for Y90 but the charge is greater!
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Beta Radiation
38Sr90 --> 39Y90 + -
Consider neutron decay...
0n1 --> ? + -
0n1 --> 1p1 + -
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* Isotopes chemically alike as protons & electrons determine chemical properties
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Gamma Radiation
Iron - 60 decays to Co-60 & gamma particles.
26Fe60 --> 27Co60 + +
0 = electromagnetic rad.
high energy photons.
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Where is Radiation in our Life Carbon – 14 dating Nuclear Waste X-rays Radiation therapy for cancer
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How they discovered Isotopes:
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Hydrogen
–Hydrogen has 3 isotopes • Hydrogen-1 = “Protium” 1
1H
• Hydrogen-2 = “Deuterium” 21H
• Hydrogen-3 = “Tritium” 31H
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Nuclear Fusion
Nuclear fusion - 2 small nuclei COMBINE
larger element.Fusion releases more energy than fission because only @ very high temp 40,000,000oC
fusion of hydrogen into helium
keeps the sun burning.
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Fusion Fusion is how the sun continually
produces energy.
4 11H + 2 0
-1β 42He + a lot of energy
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Fusion
Fusion – the combining of atomic nuclei
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Fission
Fission – the splitting of a large nucleus
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Fission (cont.)
Fission is what nuclear power plants use for energy.
U – 235 + a neutron =
a chain reaction of
neutrons and energy
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The Thorium Decay Series
90Th232 --> 24 + 88Ra228
88Ra228 --> -+ 89Ac228
89Ac228 --> - + 90Th228
90Th228 --> 24 + 88Ra224
88Ra224 --> 24 + 86Rn220
86Rn220 --> 24+ 84Po216
Pg 97& 97 b
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The Thorium Decay Series
86Rn220 --> 24 + 84Po216
84Po216 --> 24 + 82Pb212
82Pb212 --> -+ 83Bi212 or
83Bi212 --> 24 + 81Tl208
81Tl208 --> -+ 82Pb208
82Pb208 is stable
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ChernobylHurt
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Half-life Pg 96& 97a
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If you have 100 g of Uranium,
How many half lives are
needed to reach ~ 3% of the original radioactivity.
100 g 50 g 1st ½ life
25 g 2nd ½ life
12.5 g 3rd 4th ½ life life
6.25 g
3.125 g 5th ½ life
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Half – Life Problems:
1) If I have 50g of Pb-208 and it has decayed during 2 half-lives, how much is remaining?
2) If I have 25g of U-235 and it has a half-life of one day, how much will be left after a week?
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Critical Mass & The Enola Gay
Nuclear Activities
Directions: Each student will hold 3, 6 or 9 ping pong balls. Divide the room into two sections. Throw one ping pong ball. The rule is that when a student is hit by one ping pong ball, three must be released randomly.
1. What happened? Why?
Directions: Now put the entire class within a 3 meter radius and try again.
2. What happened? Why?
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Transmutationconversion of an atom of one
element to another
can induce by striking nuclei with high velocity charged particles
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44
Neutron-Proton Ratio and Nuclear Stability
Example nuclides with magic numbers of nucleons includes:
nucleus magicdoubly a Pb
nucleus magicsingly a Sn
nucleus magicdoubly a Ca
nucleus magicdoubly a Ca
nucleus magicdoubly a O
nucleus magicdoubly a He
12620882
70120
50
284820
204020
816
8
242
These proton and neutron numbers are called “Magic Numbers.”Magic numbers are:
2 8 20 28 50 82 126
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Half-life
time needed for 1/2 of the particles to decay.
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1. 86Rn217 He + ____
3. 234 U He + Y + ____
Ba-140 beta
56Ba-140 57La140 -1 b o +
2134
2 84
gamma
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Radiation Practice
1) *U – 235 + → U – 235
2) Ag – 107 + → In – 111
3) N – 12 + → O -12
4) Fe – 57 + → Ni - 61
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7. Show the equation for the fission of Th-232 with one fission product being Mo-96 plus the release of 2 neutrons
23290 Th Mo +
96 10
10 n + n
Pg 108
If I had 20g of U-235 & it decayed over 3 half-lives, how much would I have left?
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1) If I have 10g of U-235 and it has decayed over 7 half-lives, how much U-235 will I have remaining?
2) If I have 40g of Pb-208 and it has a half life of 15 seconds, how much will remain after 1 minute?
3) If I have 20g of Pt- 144 remaining after it decayed for a week. Given that it has a half-life of a day, how much did I have originally?
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Fusion vs. Fission
There are two processes that make use of the enormous amount of energy in a nucleus:
Fusion
and
Fission
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Ionizing Radiation
Ionizing radiation = radiation with enough energy to knock an electron off an atom and create an ion.
X-rays and gamma rays will ionize almost any molecule or atom
Radiation is harmful, but when used carefully it can be used in medical and scientific procedures.
-
--
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X-Rays in Medicine
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Transuranium Elements - are all elements with an atomic number of 93 or greater–all radioactive
–all man-made (SYNTHETIC)
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Leptons Up quarks
Charm quarks
e+νe 1 ud
3|Vud|2
cd
3|Vcd|2
μ+νμ 1 us
3|Vus|2
cs
3|Vcs|2
τ+ντ 1 ub
3|Vub|2
cb
3|Vcb|2
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58
Nuclear Stability and Binding Energy
Example 26-1: Calculate the mass deficiency for 39K. The actual mass of 39K is 39.32197 amu per atom.
amu 32307.39
amu 0104.0 amu 1740.20 amu 1387.19
amu 0.000545819 amu 1.008720 amu 1.0073 19
electrons and neutrons, protons, of masses of sum
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Fission & Fusion Demos
Directions: Blow up a balloon. Pinch and twist in the center. Nuclear Fission!
Directions: Put 2 drops of water on the overhead projector. Nuclear Fusion!
Questions:1. Why do Doctors use radioactive isotopes which have
short half lives?
2. What happens to the nucleus during Nuclear Fission?
3. How many half-lives does Radon need to live out to get rid of about 87.5% of the radioactivity?
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