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Ch 21 Nuclear

Chemistry: the Risks

and Benefits

Laser fusion PET scans

Chapter Outline

▪ 21.1 Changing the Identities of Atoms (including

Ch 2, Sec 2.6)

▪ 21.2 Fusion and the Quest for Clean Energy

▪ 21.3 The Belt of Stability

▪ 21.4 Rates of Radioactive Decay

▪ 21.5 Nuclear Fission

▪ 21.6 Measuring Radioactivity

▪ 21.7 Biological Effects of Radioactivity

▪ 21.8 Medical Applications of Radionuclides

▪ 21.9 Radiometric Dating

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Nuclear Chemistry

▪ Nuclear Chemistry: The field of chemistry

that studies nuclear reactions

▪ Nuclear Reaction: Process that alters the

number of neutrons and protons in the

nucleus of an atom

E = mc2

Review: Symbols for Isotopes

Isotopes of an element have the same atomic number Z, but

differ in the number of neutrons in the nucleus. The mass A

is equal to the number of protons + neutrons

XAZ

Mass Number

Atomic NumberElement Symbol

C C C6 6 6

12 13 14

protons =

neutrons =

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Ch 2, Sec. 2.6 - Subatomic Particles

Involved in Radioactive Decay

-particle = helium nucleus

- particle = electron

-ray = high energy,

massless photon

+ particle = positron

https://www.quora.com/What-are-subatomic-particles-What-are-some-examples-of-it

Symbols for Subatomic Particles

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Balancing Nuclear Equations (Sec. 2.7)

The total number of protons and neutrons has to be the same

on both sides -

Nuclear Binding Energies

▪ The stability of a nucleus is proportional to its binding energy (E)

▪ Mass defect (m): Difference between the mass of the stable nucleus and the masses of the individual particles that comprise it

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Mass Defect: He nucleus (p. 63)

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Chapter Outline

▪ 21.1 Changing the Identities of Atoms (including Ch

2, Sec 2.6)

▪ 21.2 Fusion and the Quest for Clean Energy

▪ 21.3 The Belt of Stability

▪ 21.4 Rates of Radioactive Decay

▪ 21.5 Nuclear Fission

▪ 21.6 Measuring Radioactivity

▪ 21.7 Biological Effects of Radioactivity

▪ 21.8 Medical Applications of Radionuclides

▪ 21.9 Radiometric Dating

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Nuclear Stability - Some General

Observations1. All isotopes with Z > 83 are radioactive. In addition, all isotopes of

technetium (Tc, Z = 43) and promethium (Pm, Z = 61) are radioactive.

2. Nuclei with "magic numbers" are more stable:

o # protons or #neutrons = 2, 8, 20, 50, 82, or 126

o similar to filled shells of inert gases: 2, 10, 18, 36, 54, and 86 (there

is a quantum mechanics of the nucleus)

3. Nuclei with even number of protons and/or neutrons generally more

stable:

Nuclear Stability - All That Positive

Charge in Such a Little Space!

Density of the nucleus:

What holds the nucleus together?

Nuclear stability depends on the neutron/proton ratio - as

the atomic number goes up, the ratio increases

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n/p too large

n/p too small

"Belt of

Stability"

beta emission

1n 1p + 00 1 -1

positron emission

or electron capture

1p 1n + 01 0 +1

1p + 0e 1n 1 0-1

n/p = 1

# n

eu

tro

ns

# protons

"Belt of Stability" Examples

1. If n/p above, then -emission

2. If n/p below, then positron-emission or electron capture

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Number of protons

Num

be

r o

f n

eu

tro

ns

0 5 10 15 20

5

10

15

20

0

Nuclides with Z > 83 undergo -decay

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Radioactive Decay Series

Ma

ss N

um

be

r

(A =

n +

p)

Atomic Number (Z)

Summary Chart

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Chapter Outline

▪ 21.1 Changing the Identities of Atoms (including Ch

2, Sec 2.6)

▪ 21.2 Fusion and the Quest for Clean Energy

▪ 21.3 The Belt of Stability

▪ 21.4 Rates of Radioactive Decay

▪ 21.5 Nuclear Fission

▪ 21.6 Measuring Radioactivity

▪ 21.7 Biological Effects of Radioactivity

▪ 21.8 Medical Applications of Radionuclides

▪ 21.9 Radiometric Dating

Radiometric Dating

[N]t = [N]0exp(-k1t) ln[N]t = ln[N]0 – k1t

[N]

ln [

N]

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Radiocarbon Dating

14N + 1n 14C + 1p7 160

14C 14N + 06 7 -1

t½ = 5730 years

Radiocarbon Dating

▪ Assume rate of generation of 14C in the atmosphere

constant over the last 50,000 yr (not always true!).

▪14C incorporated into food chain by 14CO2 absorption by

plants.

▪14C constant in a plant or animal while it's alive, but 14C

starts decaying upon death.

▪ Fresh organic matter has a decay rate of 13.56 dis min-1

per g carbon

▪ Age range: 500 – 50,000 ± 40 yr

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Requires corrections:1. variations in cosmic ray intensity over geologic time

2. fluctuations in the earth’s magnetic field (deflects cosmic wind)

3. sunspot activity

4. Changes in organic activity on earth’s surface

5. Injection of large amounts of CO2 into the atmosphere (burning of

fossil fuels)

6. detonation of nuclear devices

http://astronomy.neatherd.org/Sunspots.htm http://www.nmm.ac.uk/gcse-astronomy/sun-and-moon/solar-weather/http://en.wikipedia.org/wiki/Mushroom_cloud

Accuracy of Radiocarbon Dating

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Accuracy of Radiocarbon Dating

http://en.wikipedia.org/wiki/Dendrochronology

http://web.utk.edu/~grissino

Dendrochronology:great link:

http://www.ltrr.arizona.edu/dendrochronology.html

Corrections to Radiocarbon Dating

14N + 1n 14C + 1p7 160

measured

actual