radioactive decay.ppt

8/10/2019 Radioactive Decay.ppt

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Nuclear

Reactions

Alpha, Beta, and Gamma Decay


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The Atom

The atom consists of two parts:

1. The nucleus which contains:

2. Orbiting electrons.

protons

neutrons


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All matter is made up of elements (e.g. carbon,

hydrogen, etc.).

The smallest part of an element is called an atom.

Atom of different elements contain different numbers of

protons.

The mass of an atom is almost entirely due to the

number of protons and neutrons.

The Atom


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X

A

Z

Mass number

Atomic number

Element symbol

= number of protons + number of neutrons

= number of protons


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XA

Z

A = number of protons + number of neutrons

Z = number of protons

AZ= number of neutrons

Number of neutrons = Mass Number Atomic Number


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U23592

U23892

There are many types of uranium:

A

Z

Number of protonsNumber of neutrons

A

Z

Number of protonsNumber of neutrons


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U23592

U23892

There are many types of uranium:

Isotopes of any particular element contain the same

number of protons, but different numbers of neutrons.

A 235

Z 92

Number of protons 92Number of neutrons 143

A 238

Z 92

Number of protons 92Number of neutrons 146


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Most of the isotopes which occur naturally are stable.

A few naturally occurring isotopes and all of the man-

made isotopes are unstable.

Unstable isotopes can become stable by releasing

different types of particles.

This process is called radioactive decay and the

elements which undergo this process are called

radioisotopes/radionuclides.


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Radioactive decay results in the emission of either:

an alpha particle (a),

a beta particle (b),

or a gamma ray(g).

Radioactive Decay


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

It contains two protons and two neutrons.

Alpha Decay


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X

A

Z Y

A - 4

Z - 2 + He

4

2

Alpha Decay

unstable atom

more stable atom

alpha particle


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Alpha Decay

Ra226

88

Rn22286

He42


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XA

ZY

A - 4

Z - 2+ He

4

2

Ra226

88 Rn222

86 + He4

2

Alpha Decay


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Rn

222

86 He

4

2+Po

218

84 He

4

2

Rn222

86+Y

A

ZHe

4

2

Alpha Decay


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He

4

2U

234

92 +Th

230

90 He

4

2

XA

Z+Th

230

90He

4

2

Alpha Decay


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Th230

90+Y

A

ZHe

4

2

Alpha Decay

He

4

2+Ra

226

88 He

4

2Th

230

90


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XA

Z+Pb

214

82He

4

2

Alpha Decay

He

4

2+Pb

214

82 He

4

2Po

218

84


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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 aproton and an electron.


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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.


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Beta Decay

Po218

84

b0-1

At21885


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XA

ZY

A

Z + 1+ b

0

-1

Beta Decay

Po218

84 At218

85 + b0

-1


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Th234

90Y

A

Z+ b

0

-1

Beta Decay

Th234

90 Pa234

91 + b0

-1


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XA

ZPb

210

82+ b

0

-1

Beta Decay

Tl210

81 Pb210

82 + b0

-1


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Bi210

83Y

A

Z+ b

0

-1

Beta Decay

Bi210

83 Po210

84 + b0

-1


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XA

ZBi

214

83+ b

0

-1

Beta Decay

Pb214

82 Bi214

83 + b0

-1


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Gamma Decay

Gamma rays are not charged particles like a and bparticles.

Gamma rays are electromagnetic radiation with high

frequency.

When atoms decay by emitting aor bparticles to form a

new atom, the nuclei of the new atom formed may still

have too much energy to be completely stable.

This excess energy is emitted as gamma rays (gamma ray

photons have energies of ~ 1 x 10-12J).

radioactive decay.ppt

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