ch10 nuclear chem

1

Nuclear ChemistryChapter 10

by

Prof. Geronimo J. Fiedalan Jr., MAT

OBJECTIVES

• Define nuclear Chemistry

• Describe stable, unstable, and very

unstable isotopes

• Describe the characteristics of the types

of radiation

• Define half-life

• Give uses of radioisotopes

• Differentiate nuclear fission from

nuclear fusion 2

Nuclear Chemistry

• Nuclear Chemistry

deals with radioactivity,

its origin, nature,

properties and

characteristics as well as

its implication to nature

and the physical world.

3

Nuclear Chemistry

• Radioactivity is the spontaneous

emission of the particles alpha, and beta,

or gamma rays through the disintegration

of atomic nuclei of radioisotopes.

• Radioisotopes are radioactive isotopes.

4

Nuclear Chemistry

• Radioactive decay is the disintegration of

an unstable atomic nucleus by

spontaneous emission of radiation.

5

Nuclear Chemistry

• Radiation is the energy emitted by the

nucleus (of atom) of an infinitesimal size

which travel through space.

– Ionizing radiation

– Non-ionizing radiation

6

Nuclear Chemistry

• Ionizing Radiation

– have sufficient energy to ionize an atom

– α, β, γ

• Non-ionizing Radiation

– The energy radiates (i.e., travels outward in

straight lines in all directions) from its

source.

7

Electromagnetic Radiation

• The Electromagnetic Spectrum

DISCOVERY

OF

RADIOACTIVITY

9

Discovery of Radioactivity• Henri Becquerel (1852 – 1908) found that

uranium crystals had the property of “fogging” a

photographic plate that had been placed near

crystals, which took place even though the

photographic plate was wrapped in black paper.

10

Discovery of Radioactivity• Marie Curie and Pierre Curie discovered other

radioactive elements (Th, Po, Ra) . They also

found that radioactivity of substances was

associated with their elements, not with

compounds.

11

Marie Curie called the

radiation discovered

by Becquerel as

radioactivity.

12

The Nuclear Atom

13

The Rutherford Experiment

14

• Radioactivity was

discovered by Becquerel in

1896.

• Radioactive elements

spontaneously emit alpha

particles (α), beta particles (β)and gamma (γ) rays from their

nuclei.

• By 1907 Rutherford found that

alpha particles emitted by

certain radioactive elements

were helium nuclei ( ).24

2 He

15

Rutherford’s alpha particle scattering experiment.

5.5

Rutherford in 1911 performed experiments that

shot a stream of alpha particles at a gold foil.

16


5.5

Most of the alpha particles passed through the foil

with little or no deflection.

17


5.5

He found that a few were deflected at large angles

and some alpha particles even bounced back.

18


5.5

An electron with a mass of 1/1837 amu could not

have deflected an alpha particle with a mass of 4

amu.

19


5.5

Rutherford knew that like charges repel.

20


5.5

Rutherford concluded that each gold atom

contained a positively charged mass that occupied

a tiny volume. He called this mass the nucleus.

21

If a positive alpha particle approached close

enough to the positive mass it was deflected.

5.5


22

Most of the alpha particles passed through the gold

foil. This led Rutherford to conclude that a gold

atom was mostly empty space.5.5


23

5.5

Deflection and scattering of alpha particles by positive gold nuclei.

Deflection

Scattering

24

Subatomic Particles

of the Atom

What Makes for

Nuclear Stability?

26

Stable and Unstable Nuclides

• Stable

n = 6 p = 6

n = 38 p = 32

27

X12

6

X70

32


• Unstable

n = 2 p = 1

n = 31 p = 28

28

X3

1

X59

28


• Very Unstable

n = 3 p = 5

n = 29 p = 29

29

X8

5

X58

29


1) Atomic nuclei with even number of

protons and neutrons are stable.

(Of the 264 stable isotopes, 157 have

even numbers of both protons and

neutrons. Only 4 have odd numbers of

protons and neutrons.)

30

C12

6


2) Atomic nuclei with even number of

neutron and odd number of proton, odd

number of neutrons and even number of

proton, or odd numbers of both neutrons

and protons are unstable.

31

O17

8


3) “Magic” numbers of either protons

or neutrons.

(Magic numbers are 2, 8, 20, 50, 82,

and 126).

4) An atomic number of 83 or less.

(All isotopes with atomic numbers

greater than 83 are radioactive).

32


5) There should be no more protons than

neutrons in the nucleus, and the ratio of

neutrons to protons should be close to 1

if the atomic number is 20 or below.

33

Types of Radiation

34

Types of Radiation1) Background Radiation is the ever-present

radiation from cosmic rays and from natural

radioactive isotopes in air, water, soil, and

rocks. It causes minimal harm.

2) Ionizing Radiation is a radiation that

produces ions at it passes through matter. It

arises from interaction of radiation by

knocking electrons from atoms and

molecules, converting them into ions.

35

Types of Radiation• Ionizing radiation devastate living cells by

interfering with their normal chemical

processes

– Transformation of water to highly reactive

hydrogen peroxide (H2O2).

– Affects the bone marrow resulting to low

production of RBC leading to anemia, leukemia

and cancer.

– Change in the molecules of heredity (DNA) in

the reproductive cells producing mutations.

36

Types of Radiation

3) Medical Irradiation is obtained from

exposure to X-rays and LASERS for

medical purposes.

- Light Amplification by Stimulated Emission of

Radiation (LASER)

4) Natural Radiation is the type of decay

exhibited by radioactive isotopes.

37

Types of Radiation

5) Artificial Radiation is the type of decay

exhibited by normally non-radioactive

light elements through bombardment.

-nuclear reactions

38

Types of Radiation

Produced by Radioactive

Substances

39

Alpha (α) Particles

• positively charged.

• He nuclei has two

protons and two

neutrons, thus having

a charge of +2.

• result from radioactive

decay of heavy

elements such as

radium and uranium.40

24

2 He


41

He YX 4

2

4A

2Z

A

Z

__U 4

2

238

92

4

2

4A

2Z

A

Z YX

Th234

90

__Po 4

2

212

84Pb208

82


• When an atom emits an alpha particle,

its mass number decreases by 4 and its

atomic number decreases by 2.

• Reason for instability:

– Nucleus is too large

42

Beta (β-) Particles

• Beta particles are negatively

charged.

• Beta particles have a charge

of negative one (1-)

• Beta particles have a very

small mass.

43


• Beta particles are high-speed electrons

produced in the nucleus by the

transformation of a neutron into a proton and

an electron.

– The electron is emitted as a beta particle

and the proton remains in the nucleus.

44

e pn 0

1-

1

1

1

0

retained

in nucleusemitted

0

1-

1

1

1

0 Hn

Beta (β) Particles

45

e YX 0

1-

A

1Z

A

Z

0

1-

234

91

234

90 PaTh

__P 0

-1

32

15 S32

16

__C 0

-1

14

6N14

7

__Zr 0

-1

97

40 Nb97

41


• When an atom emits a beta particle, its

mass number remains the same, but its

atomic number increases by 1.


– Nucleus has too many neutrons

relative to the number of protons.

46

Gamma (γ) Rays

• Gamma rays have no charge

– not affected by an electrostatic

field.

• are not particles, so

– they have no mass.

• are electromagnetic radiation

similar to X-rays.

47

Gamma (γ) Rays

• often emitted along with alpha or beta

particles.

• Originate from unstable atoms releasing

energy to gain stability.

• (*) indicates a slightly lower energy

48

UU *238

92

238

92

Gamma (γ) Rays

m = indicates metastable (unstable)

49

TcTc 99

43

m99

43

Gamma (γ) Rays

• When an atom emits a gamma ray,

there is no change in the atomic number

or mass number.


– Nucleus has excess energy.

50

Other Forms of

Radiation

51

Positron (β+) Emission

• Positron (β+) is a particle equal in mass

but opposite in charge to the electron. It is

represented by .

52

e0

1 e np 0

1

1

0

1

1

Neutrino - an elementary

particle that usually travels

close to the speed of light,

is electrically neutral, and is

able to pass through

ordinary matter almost

unaffected

• After the positron is

emitted, the original

radioactive nucleus

has one fewer proton

and one more

neutron than it has

before.

– Therefore, the mass

number of the

product nucleus is

the same, but its

atomic number has

been reduced by 1.53

When the emitted

positron encounters

an electron, both

particles are

annihilated quickly

resulting to the

production of two

gamma photons.

0

0

0

1

0

1 2 ee

β + β-

Positron (β+) Emission


–Nucleus has too many protons

relative to the number of neutrons

54

__ eF 0

1

18

9

__ K 0

1

38

19Ar38

18

O18

8

Electron Capture (EC)• Electron capture (EC) – is a process in

which a nucleus absorbs an electron from

an inner electron shell, usually the first or

the second. Once inside the nucleus, the

captured electron combines with a proton

to form a neutron.

55

n e p 1

0

0

1

1

1

Electron Capture (EC)

• When an electron from a higher shell

drops to the level vacated by the captured

electron, an X-ray is released.

• Iodine – 125 is used as medicine to

diagnose pancreatic function and intestinal

fat absorption, decays by EC.

56

Te e I 125

52

0

1

125

53

Electron Capture (EC)


– Nucleus has too many protons

relative to the number of neutrons.

57

__ e Ar 0

1

37

18

__ e Fe 0

1

55

26

Cl37

17

Mn55

25

Radioactive Decay and Nuclear ChangeType of

Decay

Decay

Particle

Particle

Mass

Particle

Charge

Change in

Nucleon

Number

Change in

Atomic

Number

Alpha

decay

α 4 2+ Decrease by 4 Decrease by

2

Beta

decay

β 0 1- No change Increase by

1

Gamma

ray

γ 0 0 No change No change

Positron

emission

β+ 0 1+ No change Decrease by

1

Electron

capture

e-

(absorbed)

0 1- No change Decrease by

1

58

Penetrating and

Ionizing Power

of

Radiation

59

Penetrating and Ionizing Power

Penetrating and Ionizing Power– Alpha particles have very low

penetrating power and cannot pass

through skin.

• Can be stopped by skin, Al foil, or paper

– have very high ionizing power

• Cause more damage than X-rays or

gamma radiation

• Not harmful to humans or animals as

long as they do not get into the body.


– Beta particles are less damaging to

tissue than alpha particles but

penetrate farther and so are generally

more harmful.

• Have slight penetrating power but can

be stopped by heavy clothing

62


– Gamma rays, which can easily

penetrate skin, are by far the most

dangerous and harmful form of

radiation.

– causing cellular damage as they travel

through the body.

63

Terms and Unit of

Measurement of Nuclear

Radiation

64

Terms and Units of Measurement of

Nuclear Radiation

The physical unit of radiation is a measure

of the number of nuclear disintegrations

occurring per second in a radioactive source.

• Curie (Ci) - the number of nuclear

disintegrations occurring per second in 1 g of

Ra.

– one Ci = 3.7 x 1010 dps

• Becquerel (Bq): equal to one disintegration or

nuclear transformation per second.

Terms and Unit of Measurement of

Nuclear Radiation

• Roentgen (R): a measure of the energy

delivered by a radiation source.

– A unit of radiation applied to X-rays and

gamma rays only

– the amount of radiation that produces

ions having 2.58 x 10-4 coulomb/kg;

66

Terms and Units of Measurement of

Nuclear Radiation• Radiation absorbed dose (Rad) - total amount

of ionizing radiation absorbed by tissue that

has been radiated; the SI unit is the gray (Gy)

– 1 rad = 100 ergs of energy absorbed/gram of

tissue

– Gray (Gy): one Gy = 1 joule/kilogram (1 J/kg)

• Roentgen-equivalent-man (Rem): a measure of

the effect of the radiation when one roentgen is

absorbed by a person; the SI unit is the sievert

(Sv) where one Sv = 1 J/kg67

Difference Between

Chemical and Nuclear

Reactions

68

Chemical Reactions Nuclear Reactions

Atoms retain their identity Atoms change from one element

to another

Reactions involve only

electrons and usually only

outermost electrons.

Reactions mainly involve protons

and neutrons.

Reactions rates can be

speeded up by raising the

temperature.

Reactions rates are unaffected by

changes in temperature.

Energy absorbed or given

off in reactions is

comparatively small.

Reactions sometimes involve

enormous changes in energy.

Mass is conserved. Huge changes in energy are

accompanied by measurable

changes in mass (E=mc2).69

HALF – LIFE

70

Half - life• Half-life – is the amount of time required for

one-half the radioactive nuclei in a sample to

decay.

– The fraction of the original isotope that

remains after a given number of half-lives

passed is calculated from the relationship

fraction remaining =

where

–n is the number of half - lives

71

n2

1

Half – life

• The amount left after a radioactive atom

underwent decay can be calculated by

– where

• t is the number of half-lives that

passed

72

t

orig2

1AA

Problem 1: Cobalt – 60 has a half-life of 5.25

years. If you have a 400-mg sample of Co-60,

how much remains after 15.75 years?

• Solution:

73

8

1

2

1

2

1remaining Fraction

3n

mg 50A

mg 400A81

Problem 1: Cobalt – 60 has a half-life of 5.25

years. If you have a 400-mg sample of Co-60,

how much remains after 15.75 years?

• Solution:

74

3t

yrs 5.25

yrs 75.15

life-half

years of .not

mg 50A

mg 400

AA

3

21

t

21

orig

Problem 2: Starting with a 2-gram sample of

, how much remains at the end of 48 days? The

half-life of Th-234 is 24 days?

Problem 3. Krypton-81 m is used for lung

ventilation studies. Its half-life is 13 seconds.

How long does it take the activity of this isotope

to reach one-quarter of its original value?

a) 0.5 g b) 26 s

75

Th234

90

Hydrogen-3 (tritium)

Carbon-14

Phosphorus-28

Phosphorus-32

Potass ium-40

Scandium-42

Cobalt-60

Strontium-90

Technetium-99m

Indium-116

Iodine-131

Mercury-197

Radon-205

Radon-222

Uranium-235

Name Half-life Radiation

12.26 y

5730 y

0.28 s

14.3 d

1.28 x 109 y

0.68 s

5.2 y

28.1 y

6.0 h

14 s

8 d

65 h

Polonium-210 138 d

2.8 m

3.8 d

4 x 109 y

Beta

Beta

Positron

Beta

Beta + gamma

Positron

Gamma

Beta

Gamma

Beta

Beta + gamma

Gamma

Alpha

Alpha

Alpha

Alpha

Half-life of Some Common Radioisotopes

Radioisotopes Half-life Uses

Tc-99m 6 hr Imaging of brain, liver, lung, bone

marrow, kidney

Fe-59 45 days Detection of anemia

Ra-226 1600 yr Radiation therapy for cancer

I-131 8 days Thyroid therapy

P-32 14.3 days Detection of skin cancer

Co-60 5.3 yr Radiation cancer therapy

C-11 20.3 min Brain scans

H-3 12.3 yr Determining total body water

Ga-67 78 hr Scan for lung tumors

Cr-51 27.8 days Blood volume determination

Na-24 15 hr Locating obstruction in blood flow

Ir-192 74 days Breast cancer therapy77

USES

of

RADIOISOTOPES

78

Uses of Radioisotopes

1. Tracers

2. Nuclear Medicine

3. Food Irradiation

4. Radioisotopic Dating

5. Warfare

6. Power Generation

79

Tracers• Tracers are radioactive isotopes used to

trace movement or locate the sites of

radioactivity in physical, chemical, and

biological systems.

80

Nuclear Medicine

• Nuclear Medicine involves two distinct

uses of radioisotopes – therapeutic and

diagnostics.

– Therapeutic involves the use of

radiation therapy to treat or cure

diseases.

– Diagnostic involves the use of

radioisotopes to obtain information

about the state of a patient’s health.

81

Nuclear Medicine• Therapeutic

– Iodine-131and Iodine-123 – treatment of

thyroid conditions

– Cobalt-60 and Cobalt-57 – for treatment of

many different types of cancer

– Gold-198 – treatment of pleural and

peritoneal metastases (spreading disease

from original sites).

– X-ray therapy – uses Ra or Co-60. X-rays

can be used for treatment of superficial skin

conditions, deep-seated malignancies and

many different types of cancer.82

Nuclear Medicine

• Diagnostic

– Technetium–99m – used for many

types of scans and measuring blood

volume

– Krypton-79 – for evaluation of

cardiovascular system

– Selenium-75 – for determination and

size of the pancreas

– Mercury-197 – for evaluation of spleen

function and for brain scans.

83

Nuclear Medicine• Diagnostic

– PET (Positron Emission tomography) Scan

– is a technique that uses radioisotopes

to get three dimensional pictures showing

function processes occurring in the

human body.

84

This technique is used

to trace gamma rays

sent forth by positron

producing

radionuclide.


– MRI (Magnetic Resonance Imaging) – is

a noninvasive (nonsurgical) method of

following biochemical reactions in both

cells and entire organs under normal

physical conditions.

85

Nuclear Medicine• MRI (Magnetic Resonance Imaging)

86

MRI doesn’t

involve

ionizing

radiation, as

do X-rays and

CT scans.

MRI takes

advantage of

something you

have plenty of

in your body:

water.


– X-ray - radiation similar to visible light but

of much higher energy and much more

penetrating.

87

Nuclear Medicine

• Radioisotopes have two main uses in

medicine; diagnosis and therapy

Food Irradiation• Food Irradiation consists of exposing food

to some of ionizing radiation, such as gamma

rays or X-rays to kills insects and

microorganisms and also to halt the ripening

of fruits.

89

Co-60 is used for this

purpose. Irradiation

lengthens the shelf life of

food and reduces the need

for preservatives, some of

which have toxic effects.

Radioisotopic Dating• Radioisotopic Dating is used in determining

the age of objects.

– Carbon-14 dating – a technique for

determining the age of artifacts based on the

half-life of C-14. Ex. Shroud of Turin

90


the age of objects.

– Tritium dating (H-3) – is useful for dating items up

to about 100 years old, i.e. beverages, wine.

– Tritium has a half-life of 12.43 years.

91


the age of objects.

– Uranium dating – uses U-238 to determine

the age of the earth and other heavenly

bodies.

92

Warfare • Warfare – involves construction of nuclear

bombs and nuclear weapons.

93

Warfare and Power Generation• Power Generation – involves production of

electricity using nuclear energy from nuclear

fission of radioactive material, i.e., U-235 in

nuclear reactors.

94

Artificial

Transmutation

95

Artificial Transmutation

• Artificial Transmutation is the changing of

one element into another.

• In order to accomplish transmutation, one

must alter the stable nucleus by bombarding

it with

– Alpha particle - Electrons

– Neutrons -Deuterons (Hydrogen-2)

– Protons

– Other particles

96


• The hydrogen nucleus is simply a proton,

hence the alternative symbol for the

proton.

• Answer:

97

H O He N 1

1

17

8

4

2

14

7

H1

1

? Cl n K 36

17

1

0

39

19

He4

2

98

He2 H Li 4

2

1

1

7

3

n __ H Ar 1

0

1

1

40

18

H __ H Cd 1

1

2

1

114

48

n6 __ C U 1

0

12

6

238

92


K40

19

Cd115

48

Cf244

98

H __ n C 1

1

1

0

14

6

n __ Al 1

0

4

2

27

13

C14

6

P30

15


• When chlorine–37 is bombarded with a

neutron, a proton is ejected. What new

element is formed?

99

H S n Cl 1

1

37

16

1

0

37

17

p S n Cl 1

1

37

16

1

0

37

17

Nuclear Reaction

100

Nuclear Reaction

Nuclear Reaction is the process by which

one type of nucleus changes into another.

Types of Nuclear Reaction

1. Nuclear Fission

2. Nuclear Fusion

101

Nuclear Fission• Nuclear Fission – is a process by which

certain heavy nuclei split into lighter nuclei

when they absorb slow moving neutrons.

102

Nuclear Fission

• When uranium-

235 is

bombarded with

neutron, it is

broken into two

smaller

elements.

103

energy n3 Kr Ba U n 1

0

88

36

145

56

235

92

1

0

Nuclear Fission

– The products have less mass than the

starting materials.

– The mass decrease in fission is

converted into energy.

– This form of energy is called atomic

energy.


0

88

36

145

56

235

92

1

0

Nuclear Fission• Nuclear fission is a chain reaction

Chain Reaction is a

self-sustaining

reaction which once

started, steadily

provides energy and

matter needed to

continue the reaction.

Nuclear Fission

• Nuclear reactions do not obey the law of

conservation of mass. They obey the

combined Law of Conservation of Mass and

Energy which states that the amount of

mass that disappears is converted into an

equivalent amount of energy.

• This can be calculated by using Einstein’s

equation E = mc2.

106

Nuclear Fission

• Using Einstein’s equation, E=mc2, we find

107


0

88

36

145

56

235

92

1

0

(kg) 1.0087 234.9934 93.9154 138.9179 3(1.0087)

Total mass of reactants = 236.0021 kg

Total mass of products = 235.8594 kg

Loss in mass = 0.1427 kg

J10 x 28.1E

m/s 10 x 3 kg 1427.0

mcE

16

28

2

Nuclear Fission

• Nuclear reactors use U3O8 (a compound

enriched with scarce fissionable U-235).

• Because the supply of U-235 is limited

breeder reactor has been developed.

• Breeder reactors use neutrons to convert

non-fissionable isotopes such as U-238 or

Th-232 to fissionable isotopes , Pu-239 or

U-233.

108

Nuclear Fission

• Breeder reactors

• Atomic bomb uses Pu-239

109

Pu Np U U n 239

94

239

93

239

92

238

92

1

0

U Pa Th Th n 233

92

233

91

233

90

232

90

1

0

Pu Np U U n 239

94

239

93

239

92

238

92

1

0

Nuclear Fusion• Nuclear Fusion is the process whereby nuclei

of light atoms combine to form a heavier

nucleus with the release of energy.

110

The sun

provides us

with energy

through

nuclear fusion.

Nuclear Fusion in the Sun

• The reaction that takes place in the Sun is

called thermonuclear reactions because

very high temperatures (million of degrees)

are required in order to initiate them. The

fusion of only 1 g of H releases an amount of

energy equivalent to the burning of nearly 20

tons of coal. 111

energy H2 He He He: 3 Step

twice)(occursenergy He H H: 2 Step

energy e H H H: 1 Step

1

1

4

2

3

2

3

2

3

2

1

1

2

1

0

1

2

1

1

1

1

1

PROTECTION FROM

RADIATION

112

Protection from Radiation

• Shielding, distance, and limiting exposure

are the only effective preventive methods

against radiation exposure.

• Exposure to external radiation can be

controlled by increasing distance between the

body and the source of the radiation. The

amount of radiation received varies inversely

as the square of the distance.

113

Problem: A nurse receives an exposure of 20

mrem when standing 3 ft from a radioactive

source. What will be the exposure at a distance

of (a) 6 ft?

114

mrem 5x

2

2

21

22

ft 3

ft 6

xmrem 20

d

d

2 distanceat exposure

1 distanceat osureexp

1 rem = 1 R

rem = amount of

ionizing radiation,

that when absorbed

by human, has an

effect equal to the

absorption of 1 R.

mrem is a smaller

unit.

ch10 nuclear chem

Education

particles alpha

rutherfords alpha particle

nuclear chemistry radiation

positive alpha particle

stream of alpha particles

electromagnetic radiation

unstable nuclides unstable

unstable nuclides stable