Science Park HS -- Honors Chemistry The ABC's (or Alpha, Beta, Gamma) of Radioactivity

Science Park HS -- Honors Chemistry

The ABC's (or Alpha, Beta, The ABC's (or Alpha, Beta, Gamma) of RadioactivityGamma) of Radioactivity


AgendaAgenda

Definition of Radioactivity and emissionsDiscussion of the three most important

types of emissionsWhat do we mean by half-life?Where is Radioactivity encountered?Is Radioactivity dangerous?


ExpectationsExpectations

SWBAT state what radioactivity is, where these rays come from, what each ray is made of and state why they are dangerous.

SWBAT identify 4 pioneer scientists who made important contributions to understanding radioactivity

SWABT to explain the meaning of “half-life”. Student will be asked to find any sources of

Radioactivity in his/her environment


Early Pioneers in RadioactivityEarly Pioneers in Radioactivity

Roentgen:

Discoverer of X-rays 1895

Becquerel:

Discoverer of Radioactivity

1896

The Curies:

Discoverers of Radium and

Polonium 1900-1908

Rutherford:

Discoverer Alpha and Beta

rays 1897


What do we mean by What do we mean by Radioactivity?Radioactivity?

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.

There are numerous types of radioactive decay. The general idea:

An unstable nucleus releases energy to become more stable


Some Key Definitions Before We Some Key Definitions Before We Move onMove on

Z = The Atomic Number. It’s the Number of Protons in the nucleus of an Atom.

Nucleus: It’s where the Protons and Neutrons are located in an Atom.

Protons: Positively Charged Particles in the Nucleus of the atom. Mass = (approx) 1 AMU

Neutrons: Neutrally charged particles in the nucleus of an atom Mass = (approx) 1 AMU

Mass Number of an atom: Number of Protons + Number of Neutrons in the nucleus of an atom.


The Nuclear Stability BeltThe Nuclear Stability Belt


Kinds of RadioactivityKinds of Radioactivity

The three main decays are Alpha, Beta and Gamma


Three Common Types of Three Common Types of Radioactive EmissionsRadioactive Emissions

Alpha

Beta

Gamma

An alpha particle is identical to that of a helium nucleus.

It contains two protons and two neutrons.

Alpha Decay

XA

ZY

A - 4

Z - 2+ He

4

2

Alpha Decay

unstable atom

more stable atom

alpha particle

Alpha Decay

Ra226

88

Rn222

86

He4

2

XA

ZY

A - 4

Z - 2+ He

4

2

Ra226

88Rn

222

86+ He

4

2

Alpha Decay

Rn222

86He

4

2+Po

218

84He

4

2

Rn222

86+Y

A

ZHe

4

2

Alpha Decay

He4

2U

234

92+Th

230

90He

4

2

X A

Z+Th

230

90He

4

2

Alpha Decay

Th 230

90+Y

A

ZHe

4

2

Alpha Decay

He4

2+Ra

226

88He

4

2Th

230

90

X A

Z+Pb

214

82He

4

2

Alpha Decay

He4

2+Pb

214

82He

4

2Po

218

84

Beta Decay

A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.

Beta decay occurs when a neutron changes into a proton and an electron.

Beta Decay

As a result of beta decay, the nucleus has one less neutron, but one extra proton.

The atomic number, Z, increases by 1 and the mass number, A, stays the same.

Beta Decay

Po218

84

0

-1

At218

85

XA

ZY

A

Z + 1+

0

-1

Beta Decay

Po218

84Rn

218

85+

0

-1

Th234

90Y

A

Z+

0

-1

Beta Decay

Th234

90Pa

234

91+

0

-1

X A

ZPb

210

82+

0

-1

Beta Decay

Tl210

81Pb

210

82+

0

-1

Bi210

83Y

A

Z+

0

-1

Beta Decay

Bi210

83Po

210

84+

0

-1

X A

ZBi

214

83+

0

-1

Beta Decay

Pb214

82Bi

214

83+

0

-1


Three Common Types of Three Common Types of Radioactive Emissions - Radioactive Emissions -

PenetrabilityPenetrability

Alpha particles may be completely stopped by a sheet of paper, beta particles by aluminum shielding. Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead.


Another Contribution from Rutherford:Another Contribution from Rutherford: Half-life of Radioactive Atoms Half-life of Radioactive Atoms

The half-life of a radioactive substance, is the time required for one half of it to decay.


Sources of RadioactivitySources of Radioactivity

Primordial - from before the creation of the Earth

Cosmogenic - formed as a result of cosmic ray interactions

Human produced - enhanced or formed due to human actions (minor amounts compared to natural)


Where are the Sources of Where are the Sources of Radioactivity?Radioactivity?

Naturally Occurring Sources:

– Radon from the decay of Uranium and Thorium

– Potassium -40 – found in minerals and in plants

– Carbon 14 – Found in Plants and Animal tissue Manmade Sources:

– Medical use of Radioactive Isotopes

– Certain Consumer products –(eg Smoke detectors)

– Fallout from nuclear testing

– Emissions from Nuclear Power plants


Radioactivity – Is it a Health Radioactivity – Is it a Health Problem?Problem?

The Alpha, Beta and Gamma particles all add energy to the body’s tissues. The effect is called the Ionizing Energy. It can alter DNA.

Even though Alpha particles are not very penetrative if the decaying atom is already in the body (inhalation, ingestion) they can cause trouble.

The Time, Distance and Shielding principle


Radiation Exposure to AmericansRadiation Exposure to Americans


Summary/QuestionsSummary/Questions

Name three of the science pioneers in the study of Radioactivity.?

Why does a nucleus decay? Order these emissions from least to greatest penetrability:

Gamma, Alpha, Beta. What is the greatest source of exposure to radioactivity in

our everyday lives? If I tell you that that the half-life of Fellmanium-250 is

10 days, how much would be left after 30 days if I started with 1600 atoms?


Where to Get More InformationWhere to Get More Information

http://www.physics.isu.edu/radinf/natural.htm

EPA (Environmental Protection Agency)Dept of Energy

Documents

Science Park HS -- Honors Chemistry The ABC's (or Alpha, Beta, Gamma) of Radioactivity