Basic Nuclear Chemistry

Line vs. Continuous Spectra

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Continuous Spectrum

all colors (wavelengths)

are present

prism separates different wavelengths

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photographic plate

Line Spectrum

7.3

Important Information: Line location Line intensity

Nuclear Atom

electron (e-) 9.10939 x 10-28 g

charge = -1 proton(p+)

1.672623 x 10-24 g

charge = +1 neutron (no)

1.674929 x 10-24 g

no charge

A 19

X F

Z 9

Isotopic Symbol

element symbol

atomic number Z = # protons

mass number A = Z + #neutrons

Isotopes

12 13 14

C C C 6 6 6

These are isotopes of carbon (same Z, different A).

Only 14C is radioactive (unstable).

The Stable Isotopes

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614C→ 7

14N + −10β

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3 24He→ 6

12C

Nuclear Reactions Fusion - joining of 2 or more nuclei

Fission - splitting of a nucleus

radioactive decay - emission of particles and/or radiation from the nucleus

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92235U → 38

90Sr + 54143Xe + 2 0

1n

1p11H1or

proton1n0

neutron0e-1

0 -1or

electron (beta-)

0e+10+1or

positron (beta+)4He2

42or

particle

Particles Involved in Nuclear Rxns

…and (gamma) radiation (not a particle)

n/p too large

n/p too small

beta decay

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01n → 1

1p + −10β

positron emission

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11p→ 0

1n + +10β

electron capture

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11p + −1

0e− → 01n

Geiger Counter

decay unshielded cpm, cardboard cpm, aluminum cpm, leadnuclide type counts per minute (% of unshielded) (% of unshielded) (% of unshielded)

210Po 928 3 (0 .3% ) 0 (0% ) 0 (0% )

90 Sr 2971 2196 (74 % ) 1517 (51 % ) 0 (0% )

60 Co 886 883 (100 % ) 901 (100 % ) 567 (64% )

22 Na ? 349 145 (42% ) 117 (33% ) 87 (25% )

Radioactive Decay and Shielding (Problem #6)

Balancing Nuclear Equations

1. Conserve mass number (A)

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

235 + 1 = 138 + 96 + 2x1

2. Conserve atomic number (Z)

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

92 + 0 = 55 + 37 + 2x0

Problem #7: 212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.

4He2 =

212 = 4 + A; A = 208

84 = 2 + Z; Z = 82

212Po 4He + 208Pb84 2 82

212Po 4He + AX84 2 Z

Radioisotopes in Medicine

1/3 of all hospital patients undergo nuclear medicine procedures.

Brain images with 123I-labeled compound

24Na, t1/2 = 14.8 hr, emitter, blood-flow tracer

131I, t1/2 = 8 hr, emitter, thyroid gland activity

123I, t1/2 = 13.3 hr, ray emitter, brain imaging

18F, t1/2 = 1.8 hr, emitter, positron emission tomography

99mTc, t1/2 = 6 hr, ray emitter, imaging agent

Half Lives of Medical Isotopes

t1/2 = time for half the nuclide to decay

These nuclides are chosen because they have short half lives. Why?