Chapter 19a Radioactivity and Nuclear Energy. Chapter 19 Table of Contents 2 19.1Radioactive Decay 19.2 Nuclear Transformations 19.3 Detection of Radioactivity

Chapter 19a

Radioactivity and Nuclear Energy

Chapter 19

Table of Contents

2

19.1Radioactive Decay

19.2 Nuclear Transformations

19.3 Detection of Radioactivity and the Concept of Half-life

19.4Dating by Radioactivity

19.5Medical Applications of Radioactivity

Section 19.1

Radioactive Decay

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3

Review

• nucleons – particles found in the nucleus of an atom neutrons protons

• atomic number (Z) – number of protons in the nucleus • mass number (A) – sum of the number of protons and

neutrons • isotopes – atoms with identical atomic numbers but

different mass numbers • nuclide – each unique atom XAZ

Section 19.1

Radioactive Decay

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4

Radioactive Decay

• radioactive – nucleus which spontaneously decomposes forming a different nucleus and producing one or more particles

• nuclear equation – shows the radioactive decomposition of an element

Paper Wood Lead

Section 19.1

Radioactive Decay

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5

Various Types of Radioactive Processes

Section 19.1

Radioactive Decay

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Copyright © Cengage Learning. All rights reserved 6

Types of Radioactive Decay – Alpha Particle Production

• Alpha particle – helium nucleus Examples

• Net effect is loss of 4 in mass number and loss of 2 in atomic number. Mainly occurs in elements of atomic number 80 or higher.

Section 19.1

Radioactive Decay

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Types of Radioactive Decay – Beta Particle Production

• Beta particle – electron Examples

• Net effect is to change a neutron to a proton.

Section 19.1

Radioactive Decay

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Types of Radioactive Decay – Gamma Ray Release

• Gamma ray – high energy photon Example

• Net effect is no change in mass number or atomic number.

Section 19.1

Radioactive Decay

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Types of Radioactive Decay – Positron Production

• Positron – particle with same mass as an electron but with a positive charge Example

• Net effect is to change a proton to a neutron.

Section 19.1

Radioactive Decay

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Types of Radioactive Decay – Electron Capture

• Process in which one of the inner-orbital electrons is captured by the nucleus to change a proton into a neutron. Example

Section 19.1

Radioactive Decay

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Decay Series

• Occurs until a stable nuclide is formed.

Section 19.1

Radioactive Decay

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Concept Check

Which of the following produces a particle?

electron capture

positron

alpha particle

beta particle

68 0 6831 1 30a) Ga + e Zn

62 0 6229 1 28b) Cu e + Ni

212 4 20887 2 85c) Fr He + At

129 0 12951 1 52d) Sb e + Te

Section 19.2

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Nuclear Transformations


• Change of one element to another • Bombard elements with particles

Examples

Section 19.2

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Transuranium Elements

• Elements with atomic numbers greater than 92 which have been synthesized. Called Transmutation.

Section 19.2

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Concept Check

If the bombardment of with alpha particles leads to the emission of a neutron, which nuclide is formed in this nuclear transformation process?

243

95 Am

247

97

247

96

248

96

246

97

a) Bk

b) Cm

c) Cm

d) Bk

24395Am + 4

2He 24697Bk + 1

0n

Section 19.3

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Detection of Radioactivity and the Concept of Half-life

16

Geiger–Mϋller Counter

• Instrument which measures radioactive decay by registering the ions and electrons produced as a radioactive particle passes through a gas-filled chamber.

Section 19.3

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17

Scintillation Counter

• Instrument which measures the rate of radioactive decay by sensing flashes of light that the radiation produces in the detector.

Section 19.3

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18

Discovery of Po and Ra

Marie Skłodowska Curie (1867-1934)Marie, and her husband Pierre, analyzed a ton of Uranium ore. After removing the uranium the radioactivity increased. This led to the discovery of Polonium, more radioactive than uranium, named after here home country of Poland. After removing the Polonium the radioactivity increased again. This led to the discovery of a small amount in their hand of Radium, so radioactive that it glowed in the dark.(1943 Marie Currie Movie 2hrs)

Section 19.3

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19

Half-life

• Time required for half of the original sample of radioactive nuclides to decay.

Section 19.3

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Concept Check

Strontium-90 is a by-product of nuclear fission and a contaminant associated with the testing of nuclear weapons. It is of particular concern to humans because it tends to become concentrated in bones, substituting for calcium (similar ionic radius and both 2+ ionic charge). The half-life of is 29 years. If milk contaminated with is ingested, after 58 years what percentage of the replacing Ca in bones would remain to continue emitting beta particles?

a) 100%b) 75%c) 50%d) 25%

Sr9038 Sr90

38

Sr9038

Section 19.4

Dating by Radioactivity

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Radiocarbon Dating (Carbon-14 Dating)

• Originated in 1940s by Willard Libby

Based on the radioactivity of carbon-14

• Used to date wood and artifacts

Section 19.4

Dating by Radioactivity

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22

Potassium Argon Dating

The ratio of remaining K and Ar gas formed can indicate the age of solidified lava rock. Calibration is impossible.

Section 19.5

Medical Applications of Radioactivity

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Radiotracers• Radioactive nuclides that can be introduced into

organisms and traced for diagnostic purposes.

Section 19.5


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• Radon

– A rare noble gas which has also been implicated as a possible cause of lung cancer.

– Accumulates in houses from particular kinds of soils or rock strata.

15-

Section 19.5


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Predicted Indoor Radon Levels

15-

red zones-greater than 4 pCi/L orange zones-between 2 and 4 pCi/Lyellow zones-less than 2 pCi/L

Santa Barbara/ Ventura Countieshighest levels

Section 19.5


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Preventing Radon in Homes

Section 19.5


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27

Chapter 19b

Radioactivity and Nuclear Energy

W

Section 19.5


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28

19.6Nuclear Energy

19.7Nuclear Fission

19.8Nuclear Reactors

19.9Nuclear Fusion

19.10Effects of Radiation

Predicted Indoor Radon Levels

Section 19.6

Nuclear Energy

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• Two types of nuclear processes can produce energy.

Combining two light nuclei to form a heavier nucleus - fusion

Splitting a heavy nucleus into two nuclei with smaller mass numbers - fission

Iron has the most stable nucleus

Section 19.7

Nuclear Fission

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• Releases 2.1 1013 J/mol of uranium-235

• Each fission produces 3 neutrons.

Section 19.7

Nuclear Fission

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• Chain reaction – self sustaining fission process caused by the production of neutrons that proceed to split other nuclei

• Critical mass – mass of fissionable material required to produce a chain reaction http://youtu.be/9gERUtbtkRc

Section 19.7

Nuclear Fission

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A Schematic Diagram of a Nuclear Power Plant

Section 19.7

Nuclear Fission

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Nuclear energy generates about 21 percent of the electricity produced in the United States. Questions of safety, costs, and nuclear waste disposal have halted construction of nuclear reactors in the United States.

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

Section 19.7

Nuclear Fission

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Nuclear Power plants locations throughout the world.

Section 19.7

Nuclear Fission

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Disposal of Radioactive Waste

Where can you dispose of radioactive waste where it will be safe? In the ground as shown to the right? Into space? Into the Sun?

Section 19.7

Nuclear Fission

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The first chain reaction was demonstrated by the Italian physicist Enrico Fermi in Chicago in 1942.

Enrico Fermi (1901-1954)

As he brought together the critical mass, the atomic pile began to heat up. By inserting control rods he was able to control the nuclear reaction.

Section 19.7

Nuclear Fission

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PlutoniumWhen nonfissionable U-238 captures a fast neutron, it eventually forms the fissionable nuclide of plutonium, Pu-239, which can support a chain reaction. Plutonium is a transuranium element, meaning that it has an atomic number greater than the 92 of uranium. The fissionable plutonium produced in a uranium-fueled reactor can be used as a fuel or in nuclear weapons.

Little Boy Fatman

Section 19.7

Nuclear Fission

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Nuclear BombsTrinity Bomb Test

First nuclear bomb

http://www.metacafe.com/watch/400824/

trinity_nuclear_weapon_test/

Section 19.7

Nuclear Fission

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Nuclear Bombs

Hiroshima bomb- Little BoyEquivalent to 12-15 kilotons of TNT 70,000 killed immediately and 70,000 died afterward. Half from blast, a third radiation and rest

from radioactivity

Hiroshima before the bomb. Hiroshima after the bomb.

Section 19.7

Nuclear Fission

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Hiroshima after the blast.

Imprint of sitting person from gamma ray incineration.

The sky turned pink from gamma rays and about 15 seconds later the shock wave hit.

Section 19.7

Nuclear Fission

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Nagasaki-Fatman bomb

Equivalent to 20-22 kilotons of TNT. About 20,000 killed immediately and another 20,000 died afterward. A military target that contained a weapons factory.

Section 19.7

Nuclear Fission

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• Process of combining 2 light nuclei • Produces more energy per mole than fission • Powers the stars and sun

Nuclear Fusion

Section 19.7

Nuclear Fission

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• Requires extremely high temperatures• Currently not technically possible for us to use

as an energy source

Nuclear Fusion

Section 19.7

Nuclear Fission

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Nuclear fusion produces tremendous quantities of energy and has the potential of becoming the ultimate source of energy on earth.

Nuclear Fusion

Section 19.7

Nuclear Fission

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Biological Effects of Radiation

Depend on:

1. Energy of the radiation

2. Penetrating ability of the radiation

3. Ionizing ability of the radiation

4. Chemical properties of the radiation source

Section 19.7

Nuclear Fission

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Effects of Short–Term Exposures to Radiation

Section 19.7

Nuclear Fission

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Typical Radiation Exposures for a Person Living in the U.S.

Documents

Chapter 19a Radioactivity and Nuclear Energy. Chapter 19 Table of Contents 2 19.1Radioactive Decay 19.2 Nuclear Transformations 19.3 Detection of Radioactivity