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Chapter 11 Nuclear Chemistry

Use of 131I in detecting Hyper- or hypo- thyroidism

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Brain images with 123I-labeled compound

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Nuclear Reactions

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© 2003 John Wiley and Sons Publishers

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11.2 The Discovery of Nature of Radioactivity

Radioactivity: The spontaneous emission of radiation from a nucleus.Henry Becquerel, a French physicist, discovered radioactivity in 1896. Henry Becquerel placed a sample of uranium-containing mineral on top of a photographic plate wrapped in black paper. On developing the plate, Becquerel found a silhouette of the mineral on the plate. He concluded some kind of radiation emitted by the mineral passed through the paper and exposed the photographic plate.

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11.3 Stable and Unstable Isotopes A radioactive

isotope has an unstable nucleus and emits radiation to become more stable.

Isotopes of elements may be stable or unstable.

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Alpha Decay

When a radioactive nucleus emits an alpha particle, a new nucleus results.

The mass number of the new nucleus is 4 less than that of the initial nucleus.

The atomic number is decreased by 2.

11.4 Nuclear Decay

Animation

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Equation for Alpha DecayWrite an equation for the alpha decay of Rn-222. 222Rn new nucleus + 4He 86 2

Determine the mass and atomic numbers of the new nucleus.

Mass number: 222 – 4 = 218Atomic number: 86 – 2 = 84Symbol of element 84 = Po

Complete the equation with the new symbol:222Rn 218Po + 4He

86 84 2

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Beta Decay A beta particle Is an electron

emitted from the nucleus.

Forms when a neutron in the nucleus breaks down.1n 0e + 1H0 -1 1

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Potassium - 42 is a beta emitter.42K new nucleus + 0e19 -1

The atomic number of the new nucleus increases by 1.

Mass number : (same) = 42Atomic number: 19 + 1 = 20Symbol of element 20 = Ca

The nuclear equation is42K 42Ca + 0e19 20 -1

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Write the nuclear equation for the beta decay of Co-60.

60Co 27

Learning Check

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Write the nuclear equation for the beta decay of Co-60.

60Co 60Ni + 0e 27 28 1

beta particle

Solution

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Gamma radiation is energy emitted from an unstable nucleus indicated by m.

In a nuclear equation for gamma emission, the mass number and the atomic number are the same.

99mTc 99Tc + 43 43

Gamma Radiation

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Summary of Radiation

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11.6 Radioactive Decay Series

Decay series: A sequential series of nuclear disintigrations (decay) leading from a heavy radioisotope to a nonradioactive product, Fig 11.5.

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Producing Radioactive Isotopes

A nucleus is converted to a radioactive nucleus by bombarding it with a small particle.

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What radioactive isotope is produced when a neutron bombards cobalt-59?

59Co + 1n ???? + 4He 27 0 2

Learning Check

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What radioactive isotope is produced when a neutron bombards cobalt-59?

mass numbers

= 60 = 6059Co + 1n 56Mn + 4H e

27 0 25 2

= 27 = 27atomic numbers

Solution

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11.8 Detecting Radiation

A Geiger counter detects radioactive radiations.

Ions produced by radiation create an electrical current.

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Geiger counter

21Chapter 22 Slide 21

A Geiger counter determines the amount of ionization by detecting an electric current.

A thin window is penetrated by the radiation and causes the ionization of Ar gas.

The ionized gas carried a charge and so current is produced.

The current pulse generated when the radiation enters is amplified and counted.

22Chapter 22 Slide 22

Biological Effects of Radiation

The penetrating power of radiation is a function of its mass: -rays > -particles >> -particles.

When ionizing radiation passes through tissue it removes an electron from water to form H2O+ ions.

The H2O+ ions react with another water molecule to produce H3O+ and a highly reactive •OH radical.

Free radicals generally undergo chain reactions, producing many radicals in the biomolecules.

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Radiation Measurement

The Curie measures the number of atoms that decay in one second. Curie: 1 Ci = 3.7 x 10Curie: 1 Ci = 3.7 x 101010 disintegrationsdisintegrations

The rad (radiation absorbed dose) measures the radiation absorbed by the tissues of the body.

The rem (Roentgen equivalent for man (rem) ) measures the biological damage.

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Calibration of film dosimeters

In calibrating film badges the object is to obtain a series of curves relating radiation exposure to the blackening of the film.

Different typesof film and holder require different conditions of calibration.

Exposure-absorbance curves should be produced for each new batch of films manufactured, and in addition, for each set of films processed, a few badges should be exposed to known doses to check that there has been no change in the exposure-absorbance curve

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Biological Effects of RadiationRadiation absorbed dose (rad)

1 rad = 1 x 10-5 J/g of material

Roentgen equivalent for man (rem)

1 rem = 1 rad x Q Quality Factor-ray = 1

= 1 = 20

Curie: 1 Ci = 3.7 x 10Curie: 1 Ci = 3.7 x 101010

disintegrations/sdisintegrations/s

SI unit is the becquerel: SI unit is the becquerel:

Bq = 1 Bq = 1 disintegrations/sdisintegrations/s

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Units of Radiation Measurement

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Background Radiation

A person is exposed to radiation from naturally occurring radioisotopes and medical X rays.

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Effects of RadiationEffects of Radiation

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Radioactive Decay Rates

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Half-life is the time for the radiation level to decrease (decay) to one-half of the original value.

11.5 Radioactive Half-Life

decay curve

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The decay of a radioactive nucleus over time is shown in the following fig 11.4

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Half-Lives of Some Radioisotopes

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After one half-life, 40 mg of a radioisotope will decay to 20 mg. After two half-lives, 10 mg of radioisotope remain.

40 mg x 1 x 1 = 10 mg 2 2

1 half-life 2 half-lives

Initial40 mg

20 mg10 mg

Half-Life Calculations

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The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours?

1) 32 mg

2) 16 mg

3) 8 mg

Learning Check

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2) 16 mg

Half life = 13 hrs

Number of half lives = 2

Amount remaining = 64 mg x 1 x 1 = 16 mg 2 2

13 hrs 13 hrs

64 mg 32 mg 16 mg

Solution

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Medical Applications

Radioisotopes with short half-lives Are used in nuclear medicine. Have the same chemistry in the body as the

nonradioactive atoms. In the body give off radiation that exposes a

photographic plate (scan), which gives an image of an organ.

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Radioisotopes in Medicine• 1 out of every 3 hospital patients will undergo a nuclear

medicine procedure

• 24Na, t½ = 14.8 hr, emitter, blood-flow tracer

• 131I, t½ = 14.8 hr, emitter, thyroid gland activity

• 123I, t½ = 13.3 hr, ray emitter, brain imaging

• 18F, t½ = 1.8 hr, emitter, positron emission tomography

• 99mTc, t½ = 6 hr, ray emitter, imaging agent

Brain images with 123I-labeled compound

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Some Radioisotopes Used in Nuclear Medicine

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Nuclear Medicine: Nuclear Medicine: ImagingImaging

Thyroid imaging using Tc-99mThyroid imaging using Tc-99m

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Food Food IrradiationIrradiation

•Food can be irradiated with Food can be irradiated with rays from rays from 6060Co or Co or 137137Cs.Cs.•Irradiated milk has a shelf life of 3 mo. Irradiated milk has a shelf life of 3 mo.

without refrigeration.without refrigeration.•USDA has approved irradiation of meats USDA has approved irradiation of meats

and eggs.and eggs.

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Learning Check

Which of the following radioisotopes are most likely to be used in nuclear medicine?

1) 40K half-life 1.3 x 109 years

2) 42K half-life 12 hours

3) 131I half-life 8 days

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Solution

Which of the following radioisotopes are most likely to be used in nuclear medicine?

Radioisotopes with short half-lives are used in nuclear medicine.

2) 42K half-life 12 hours

3) 131I half-life 8 days

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In nuclear fission, a large nucleus is bombarded with a small particle.

The nucleus splits into smaller nuclei, several neutrons and a great amount of energy.

11.11 Nuclear Fission and Nuclear Fusion

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Nuclear Fission

When a neutron bombards U-235, an unstable nucleus of U-236 undergoes fission (splits) to form smaller nuclei such as Kr-91 and Ba-142.

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Chain Reaction

A chain reaction occurs when a critical mass of uranium undergoes fission so rapidly that the release of a large amount of heat and energy results in an atomic explosion.

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Fusion involves the combination of small nuclei to form a larger nucleus.

Nuclear Fusion

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Indicate if each of the following is

1) nuclear fission or 2) nuclear fusion

___ A. A nucleus splits.

___ B. Large amounts of energy are released.

___ C. Small nuclei form larger nuclei.

___ D. Hydrogen nuclei react.

___ E. Several neutrons are released.

Learning Check

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Indicate if each of the following is

1) nuclear fission or 2) nuclear fusion

1 A. A nucleus splits.

1, 2 B. Large amounts of energy are released.

2 C. Small nuclei form larger nuclei.

2 D. Hydrogen nuclei react.

1 E. Several neutrons are released.

Solution

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Chapter Summary Nuclear reaction: reaction that changes an atomic

nucleus, causing the change of one element into another.

Radioactivity: Spontaneous emission of radiation from nucleus of unstable atom.

radiation, radiation, and radiation are the three major types of radiation.

The rate of nuclear reaction is expressed in units of half life (t1/2).

High energy radiation of all type is known as ionizing radiation.

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Chapter Summary Contd. Radiation intensity is expressed in various ways

depending on the radiation properties measured. - The curie (Ci) measures the number of

radioactive disintigrations per second in a sample. - The Roentgen (R) measures the ionizing

ability of radiation; - The rad measures the amount of radiation

energy absorbed per gram of tissue; - The rem measures the amount of tissue

damage caused by radiation.

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Chapter Summary Contd.

Nuclear fission: Splitting of nucleus apart by the bombardment of neutrons to give smaller fragments. Enormous amount of energy is released in the fission process.

Nuclear fusion: Combination of two lighter nuclei to produce a heavier one. Like fusion, fission also releases enormous amount of energy.

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End of Chapter 11