unit 08 nuclear structure
TRANSCRIPT
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Unit 08
Nuclear Structure
• Nuclear Structure
• Radiation
Unit 08 – Nuclear Structure – Slide 1
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The Plan
Unit 08 – Nuclear Structure – Slide 2
Nuclear Structure
Nuclear Decays
Measuring Radiation
Nuclear Power Plants
Major Nuclear Power Accidents
New Possibilities for Nuclear Power
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Definitions
Unit 08 – Nuclear Structure – Slide 3
~10-15m
Size of atom ~ 10-10m (100,000 times bigger)
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Definitions
Unit 08 – Nuclear Structure – Slide 5
Element – determine by number of
protons (or electrons)
Every uranium atom as 92 protons
Atomic Number (Z) – number of
protons
Z = 92 for uranium
Nucleon – all the things inside a
nucleus, the protons and neutrons
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Definitions
Unit 08 – Nuclear Structure – Slide 6
Mass Number (A) - number of protons
plus neutrons
Isotope – a sub-set of an element with a
specific number of neutrons
uranium 235
-143 neutrons and 92 protons
uranium 238
- 146 neutrons and 92 protons
U235
92
U238
92
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Periodic Table
Unit 08 – Nuclear Structure – Slide 7
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Oxygen
Unit 08 – Nuclear Structure – Slide 8
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Like charges repel
Unit 08 – Nuclear Structure – Slide 9
p+p+
Need the strong force
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Unit 08 – Nuclear Structure – Slide 10
p+p+
n
n
Add some neutral particles as “glue”
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Like Goldilocks…..
Unit 08 – Nuclear Structure – Slide 11
• Too many protons? – too much repulsion
and it flies apart.
• Too many total nucleons? – too big for
strong binding to work
• Too many neutrons? – neutron turns into
a proton and it flies apart.
Make up of nucleus has to be “just right”….
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Stable Nuclei
Ends here??
Unit 08 – Nuclear Structure – Slide 12
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Binding Energy
Unit 08 – Nuclear Structure – Slide 13
The amount of
energy needed
to break into
pieces
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Alpha Decay
Unit 08 – Nuclear Structure – Slide 14
Heavy nuclei can spit out an alpha
particle.
How do unstable nuclei change the
proton-neutron ratio?
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Beta Decay
Unit 08 – Nuclear Structure – Slide 15
Lighter nuclei change a neutron into a proton
spitting out an electron (“beta particle”)
How do unstable nuclei change the
proton-neutron ratio?
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Gamma Decay
Unit 08 – Nuclear Structure – Slide 16
The nuclei gets rid of the excess
energy by spiting out a high energy
electro-magneti can spit out an alpha
particle.
Some times the nucleus just has too
much energy.
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How do you make radioactive material?
Unit 08 – Nuclear Structure – Slide 17
U235
92n
1
0
Sr94
38+ +Xe140
54U236 *
92
n1
0+ n
1
0+
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Nuclear Decays
Unit 08 – Nuclear Structure – Slide 18
Nuclear Decays• One or more particles emitted from nucleus • May or may not turn into different element• e.g.
Th227
90 Ra223
88He
4
2
Different than fission!
Notice the numbers have to add up
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Three Types (Different Effects!)
Unit 08 – Nuclear Structure – Slide 19
• Alpha – Helium nucleus emitted
• Why He emitted?
Th227
90Ra
223
88He
4
2+
Binding Energy
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Decay Types – Beta
Unit 08 – Nuclear Structure – Slide 20
• Beta – electron or positron emitted
• Why neutrino?
C14
6N
14
7e
-
+ + n
Na22
11Ne
22
10e
+
+ + n
Energy of
emitted
positrons
Required for energy
conservation
Massless?
neutron turns into
proton
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Decay Types – Gamma
Unit 08 – Nuclear Structure – Slide 21
• Gamma – photon emitted from the nucleus
• Gamma rays from nucleus • very short wavelength• 0.1 to 10MeV (as opposed to ~20eV from
atomic decay)
• No change in charge
Co60 *
27g+Co
60
27
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Longer wavesHigher frequency
Enough
energy to
damage
cells
Gamma Rays
Unit 08 – Nuclear Structure – Slide 22
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How does it decay?
Unit 08 – Nuclear Structure – Slide 23
Y94
39
140
55Cs
Sr94
38
Zr94
4018.8m1.2m
140
54Xe
1.3s
140
57La
1.0m
140
56Ba
12.7d
140
58Ce
1.6d
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How does it decay?
Unit 08 – Nuclear Structure – Slide 24
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Decay Chain
Unit 08 – Nuclear Structure – Slide 25
alpha
beta
Unstable thorium 232
Stable lead 208
Series of
decays,
not just one.
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Summary
Unit 08 – Nuclear Structure – Slide 26
• Alpha (He nucleus) • Most deadly• Easiest to block
• Beta (electron or positron)
• Gamma (photon from nucleus • Least deadly • Toughest to block
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Example 8.1: Decay products
Unit 08 – Nuclear Structure – Slide 27
27Si -> 27Al + ??
What type of decay is shown
below and what are the
unshown decay particles?
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Example 8.1 (con’t)
Unit 08 – Nuclear Structure – Slide 28
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Example 8.1: Decay products
Unit 08 – Nuclear Structure – Slide 29
27Si -> 27Al14 13
+ e+ + n
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Question
Unit 08 – Nuclear Structure – Slide 30
What is the missing daughter particle in the alpha decay below?
Po210
84 He4
2+?
A)
B)
C)
Pb206
82
Pb210
82
Po206
84
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Question
Unit 08 – Nuclear Structure – Slide 31
What is the missing daughter particle in the beta decay below?
In116
49e-+?
A)
B)
C)
Cd116
48
Cd115
48
Sn116
50
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Question
Unit 08 – Nuclear Structure – Slide 32
In what type of radioactive decay are the mass numbers of the parent and daughter nuclei the same?
A. AlphaB. BetaC. GammaD. Both Alpha and BetaE. Both Beta and Gamma
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Measuring Radioactivity
Unit 08 – Nuclear Structure – Slide 33
Different ways to measure radioactivity depending on need and/or available equipment.
Can be very confusing. In general:
1) Activity – Just count decay (Curie)
2) Energy deposited in some material (Rad)
3) Energy deposited in human body (REM)
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Activity
Unit 08 – Nuclear Structure – Slide 34
• Just count number of decays per second.
•
• Simplest equipment (e.g. Geiger counter)
• Units • Becquerel (bq) 1 decay/sec• Curie (Cu) 3.7X1010 decay/sec (1g of Ra)
DN
DtR =
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Example 11.1 Activity
Unit 08 – Nuclear Structure – Slide 35
A Geiger counter is held 6cm from a radioactive sample and gives a reading of 3200 counts of a period of 2 minutes. Assuming the Geiger counter covers 1/8 of the total area, what is the activity of the sample?
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Measuring Radiation – Absorbed Dose
Unit 08 – Nuclear Structure – Slide 36
Rad (Radiation Absorbed Dose) – amount of radiation that deposits
100 erg/gram of materialor
0.01 J/kg of material
• Depends on the material absorbing radiation
• Internationally being replaced by Gray (Gy)
• 1Rad = 0.01Gy
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Example 11.4 – Effect on Human
A beam of protons is directed at a 0.015kg cancer tumor. The particles have an energy of 5MeV each. If 1.6X1010 particles emitted every second, what is the absorbed dose delivered to the tumor in 25 seconds?
Unit 08 – Nuclear Structure – Slide 37
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Absorbed Dose in Humans
Unit 08 – Nuclear Structure – Slide 38
Roentgen Equivalent Man (rem) – takes into account amount of harm done to human body
• More deadly radiation has higher “Relative Biological Effectiveness (RBE)” or “Q factor”
• International units are Siverts (Sv)
• 100 Rem = 1 Sv
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Absorbed Dose in Humans
• X-rays have Q = 1 (by definition)
• medium energy neutrons Q=2.5 (1rad of neutrons 2.5 more harmful to humans than 1rad of x-rays.)
• Alpha particles Q=20!!! (very deadly but easy to stop)
Unit 08 – Nuclear Structure – Slide 39
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Example 11.4 – Effect on Human
A beam of protons is directed at a 0.015kg cancer tumor. The particles have an energy of 5MeV and a relative biological equivalent of Q=4. If 1.6X1010 particles emitted every second, what is the biologically equivalent dose delivered to the tumor in 25 seconds?
Unit 08 – Nuclear Structure – Slide 40
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Example 8.7 – Radiation Effects
A 0.5kg biological sample receives of dose of 456 rad from neutrons with an RBE of 6.2.
a) How much energy is absorbed by the sample?
b) What is the effective dosage in REM?
Unit 08 – Nuclear Structure – Slide 41
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Effect on Human
Unit 08 – Nuclear Structure – Slide 42
There is 1.6 X 10-19 Joules (J) in one electron-volt (eV). How many Joules are in 5.6MeV?
A) 1.6 X 10-19JB) 1.6 X 10-13JC) 9X10-19JD) 9X10-13 JE) 18X 10-13J
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Effect on Human
Unit 08 – Nuclear Structure – Slide 43
A beam of protons is directed at a 0.01kg cancer tumor. The particles have an energy of 9x10-13
Joules each. If 1.2X1010 particles emitted every second, what is the absorbed dose delivered to the tumor in 20 seconds?
A) 9X10-13 J/kg = 9X10-13GrayB) 8.2 GrayC) 12.4 GrayD) 21.6 GrayE) 80.2 Gray
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Allowed Human Dose
• Average annual dose • 0.62rem (~50% natural, 50% medical)
• Nuclear Regulatory Commission (NRC) Limit for general public • 0.1rem/year (1mSv) above background
• Nuclear Regulatory Commission (NRC) Limit for rad workers• 5rem/year (50mSv) above background
• Any “external source” e.g. power plant• 0.02rem/year
Unit 08 – Nuclear Structure – Slide 44
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Dose Effects on Humans
• Low does limits somewhat controversial
• Based on high dose cancer rates• 50rem – blood count change• 320rem – LD50/60 with no medical• 800rem - mortality
• Linear No Threshold Model (LNT)
• “2 bottles of aspirin will kill you, so 2 aspirin kills you a little” ??
Unit 08 – Nuclear Structure – Slide 45
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Most conservative always best?
What is more harmful to the people 15 miles from the Fukushima power plant:
Having to evacuate their home orRadiation from plant? (~0.0001rem/hr)
Unit 08 – Nuclear Structure – Slide 46
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Summary
Activity – Just counting • Curies • Becquales
Absorbed Dose - Energy Deposited • Roentgens• Rad• Gray
Biological Equivalent Dose – Damage to Humans • Sv• rem
Unit 08 – Nuclear Structure – Slide 47
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Half Life
T1/2 – Average amount of time it
takes for half the sample to decay
Also average amount of time it
takes for the decay rate to drop to
half
Unit 08 – Nuclear Structure – Slide 48
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Example 11.4
Unit 08 – Nuclear Structure – Slide 49
Barium-122 has a half-life of 2
minutes. A fresh sample weighing 80 g
was obtained. If it takes 10 minutes to
set up an experiment using barium-
122, how much barium-122 will be left
when the experiment begins?
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Example 11.5
Unit 08 – Nuclear Structure – Slide 50
Carbon-14 has a half-life of 5730 years and is
used to date archaeological objects.
A fresh charcoal made from a tree contains
carbon-14 which will give a radioactive count of
13.60 disintegrations per minute per gram of
carbon. Prehistoric cave paintings were found in
Spain. A piece of charcoal found in the ancient
cave in Altamira, Spain gave 1.70 disintegrations
per minute per gram of carbon. From this
information, determine the age of the cave
paintings.
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Question
Unit 08 – Nuclear Structure – Slide 51
Iodine-131 is used to destroy thyroid tissue in
the treatment of an overactive thyroid. The
half-life of iodine-131 is 8 days. If a hospital
receives a shipment of 200 g of iodine-131,
how much I-131 would remain after 32 days?
A. 100 g
B. 50 g
C. 25 g
D. 12.5 g
E. 6.2 g
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Question
Unit 08 – Nuclear Structure – Slide 52
The half life of radon is 3.82
days. How long does it take for
60% of a 10kg sample of radon
222 to decay?
A.~1 day
B.~2.5 days
C.~5 days
D.~8 days
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Question
You have 10 kg each of a radioactive
sample A with a half-life of 100 years, and
another sample B with a half-life of 1000
years. Which sample has the higher
activity?
A.sample A
B.sample B
C.both the same
D.impossible to tell
Unit 08 – Nuclear Structure – Slide 53