Nuclear

Band of Stability

Nu

mb

er o

f n

eutr

on

s

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

Stable nuclides

Naturally occurring radioactive nuclides

Other known nuclides

Number of protons10 20 30 40 50 60 70 80 90 100 110

n = p

120

100

80

60

40

20

0

Neu

tro

ns

(A-Z

)

0 20 40 60 80 100 120Protons (Z)

Nuclear Decay

• Why nuclides decay…– need stable ratio of neutrons to protons

He Th U 42

23490

23892

e Xe I 0-1

13154

13153

e Ar K 01

3818

3819

Pd e Ag 10646

0-1

10647 DECAY SERIES TRANSPARENCYCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

P = N

e-captureor

e+ emission

stable nuclei

120

100

80

60

40

20

0N

eutr

on

s (A

-Z)

P = N

0 20 40 60 80 100 120Protons (Z)

stable nuclei

e-captureor

e+ emission

120

100

80

60

40

20

0

Neu

tro

ns

(A-Z

)

P = N

0 20 40 60 80 100 120Protons (Z)

stable nuclei

• Why nuclides decay…– need stable ratio of neutrons to protons

Nuclear DecayNuclear Decay

Discovery of the Neutron

James Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted.

n10

+He42

+Be94 C12

6

Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764

Types of Radiation

Type Symbol Charge Mass (amu)

Alpha particle2+ 4.015062

Beta particle1- 0.0005486

Positron 1+ 0.0005486

Gamma ray0 0

01

01

He42

Alpha, Beta, Gamma Rays

Lead block

Radioactivesubstance

Electrically chargedplates

Photographicplate

rays

rays

rays

(negative charge)

(positive charge)

(no charge)

(+)

(-)

Aligningslot

(detecting screen)

Alpha, Beta, Positron Emission

Examples of Nuclear Decay Processes

emission(alpha)

emission(beta)

emission(positron)

Th He U 23490

42

23892

Ra He Th 22688

42

23090

Rn He Ra 22286

42

22688

Al Mg 2713

01-

2712 e

Cl S 3517

01-

3516 e

Ca K 4020

01-

4019 e

N O 147

01

148 e

S Cl 3216

01

3217 e

N O 147

01

148 e

Although beta emission involves electrons, those electrons come from the nucleus. Within the nucleus, a neutron decays into a proton and an electron. The electron is emitted, leaving behind a proton to

replace the neutron, thus transforming the element. (A neutrino is also produced and emitted in the process.)

Herron, Frank, Sarquis, Sarquis, Schrader, Kulka, Chemistry, Heath Publishing,1996, page 275

Nuclear Decay

• Alpha Emission

He Th U 42

23490

23892

parentnuclide

daughternuclide

alphaparticle

Numbers must balance!!

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Nuclear Decay

• Beta Emission

e Xe I 0-1

13154

13153

electron• Positron Emission

e Ar K 01

3818

3819

positronCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Nuclear Decay

• Electron Capture

Pd e Ag 10646

0-1

10647

electron• Gamma Emission

– Usually follows other types of decay.

• Transmutation – One element becomes another.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Half-Lives of Isotopes

Isotope Half-Live Radiation emitted

Half-Lives and Radiation of Some Naturally Occurring Radioisotopes

Carbon-14 5.73 x 103 years

Potassium-40 1.25 x 109 years

Thorium-234 24.1 days

Radon-222 3.8 days

Radium-226 1.6 x 103 years

Thorium-230 7.54 x 104 years

Uranium-235 7.0 x 108 years

Uranium-238 4.46 x 109 years

Half-Life Plot

Timberlake, Chemistry 7th Edition, page 104

Am

ount

of

odin

e-13

1 (g

)

20

15

10

5

0

40 48 560 8

1 half-life

16

2 half-lives

24

3 half-lives

32

4 half-lives etc…

Time (days)

Half-life of iodine-131 is 8 days

Half-LifeHalf-life (t½)

– Time required for half the atoms of a radioactive nuclide to decay.

– Shorter half-life = less stable.1/1

1/2

1/4

1/8

1/160R

atio

of

Rem

ain

ing

Po

tass

ium

-40

Ato

ms

to O

rig

inal

Po

tass

ium

-40

Ato

ms

0 1 half-life1.3

1 half-lives2.6

3 half-lives3.9

1 half-lives5.2

Time (billions of yearsTime (billions of years))

Newly formed rockPotassium

Argon

Calcium

Half-LifeHalf-life (t½)

– Time required for half the atoms of a radioactive nuclide to decay.

– Shorter half-life = less stable.

1/1

1/2

1/4

1/8

1/16

0

Rat

io o

f R

emai

nin

g P

ota

ssiu

m-4

0 A

tom

sto

Ori

gin

al P

ota

ssiu

m-4

0 A

tom

s

0 1 half-life1.3

1 half-lives2.6

3 half-lives3.9

1 half-lives5.2

Time (billions of yearsTime (billions of years))

Newly formed rock

Potassium

Argon

Calcium

Nuclear Fusion

Sun

+ +

Fourhydrogen

nuclei(protons)

Two betaparticles

(electrons)

Oneheliumnucleus

He e2 H4 4

2

0

1-

1

1 + Energy

Conservation of Mass…mass is converted into energy

Hydrogen (H2) H = 1.008 amuHelium (He) He = 4.004 amu

FUSIONFUSION

2 H2 1 He + ENERGY

1.008 amux 44.0032 amu = 4.004 amu + 0.028 amu

This relationship was discovered by Albert EinsteinE = mcE = mc22

Energy= (mass) (speed of light)2

Mass Defect

• Difference between the mass of an atom and the mass of its individual particles.

4.00260 amu 4.03298 amu

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

The Energy of FusionThe fusion reaction releases an enormous amount of energy relative to themass of the nuclei that are joined in the reaction. Such an enormous amountof energy is released because some of the mass of the original nuclei is con-verted to energy. The amount of energy that is released by this conversioncan be calculated using Einstein's relativity equation E = mc2.

Suppose that, at some point in the future, controlled nuclear fusion becomes possible. You are a scientist experimenting with fusion and you want to determine the energy yield in joules produced by the fusion of one mole of deuterium (H-2) with one mole of tritium (H-3), as shown in the following equation:

n He H H 10

42

31

21

n He H H 10

42

31

21

First, you must calculate the mass that is "lost" in the fusion reaction. Theatomic masses of the reactants and products are as follows: deuterium (2.01345 amu), tritium (3.01550 amu), helium-4 (4.00150 amu), and a neutron (1.00867 amu).

2.01345 amu 3.01550 amu 4.00150 amu 1.00867 amu

5.01017 amu5.02895 amu

Mass defect:

5.02895 amu 5.01017 amu

-0.01878 amu