Alpha (?) Decay

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Topic 4
Alpha (?) Decay
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Written and produced by Michael A. Thompson,
Professor Nuclear Medicine Technology
Program University of Alabama at Birmingham ?
Board of Trustees, University of Alabama, 1999
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Alpha (?? ) particle emission occurs from those
unstable nuclei having too many protons and too
many neutrons
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What is an alpha particle?
2 p 2 n
? Particle
A helium nucleus consisting of

• 2 protons, and

• 2 neutrons

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Properties of Alpha Particles
Mass 8000 me
Charge 2 (i.e., 2 x 1.6 x 10-19 coul)
SI high LET high
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Specific Ionization (SI)
The number of ion pairs (IP) created per unit
path length traveled
Units IP/?
Linear Energy Transfer (LET)
The quantity of energy lost per unit of
pathlength traveled
Units keV/?
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Properties of Alpha Particles (cont)
Energy monoenergetic (single-energy)
Range in Air 1 cm/MeV
Penetrating Power very low (travels only
mm to ?m in matter
depending upon its energy)
Best Shielding air, paper, cardboard
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Alpha Particle Paths Are Characterized by
Straight-Line Paths With High Ionization Along
the Path and a Burst of Ionzation at the End of
its Path
ions
Range
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Alpha Decay Equation (Pure ? emission)
A-4
A
4
2
X
Y

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Z-2
Z
(parent) (daughter) (? particle)
Example
241
237
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Am
Np

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95
93
2
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Method of Alpha Particle Interaction in Matter
Alpha particles lose their energy through
electrical interactions with shell electrons
When all its energy is lost, the alpha particle
picks up two electrons and becomes a neutral
helium atom.
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