Radioactivity

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Radioactivity
Particles And Nuclear Equations
Mr. Shields Regents Chemistry U02 L02
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Radioactive Emissions

• There are several types of particles that can be
  expelled from a nucleus undergoing nuclear decay

Alpha, Beta Gamma were First identified By
Rutherford
(see Table O)
3
Penetrating abilities

• Particles emitted during radioactive decay have
• specific penetrating power into various
  materials.
• This provides an Indication of how much
• material or SHIELDING would be needed to
• stop the particle

The greater the penetrating power the greater
the health risk !
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Particle Penetrating Power

• Alpha particles are easy to stop, gamma rays are
  hard to stop.                                   
                                                    
                                                    
   

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N to P Ratio
Remember the Neutron to Proton Ratio?
Natural radioactivity is an attempt to correct a
bad Neutron to Proton ratio Its an attempt to
get back into the band of stability
Or to get below Atomic number 83 a nucleus may
shed nuclear mass
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Alpha Emission

• Notice that this equation is BALANCED. Why?
• Mass and Atomic number on one side of the
  equation
• equals Mass and Atomic number on the other side

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Alpha Emission

• Why would emitting an alpha particle from U-238
• increase nuclear stability?

• Atomic mass is decreased by 4 (shedding mass)
• Atomic number is decreased by 2 (decreases
  Atomic )

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Beta Emission
Notice that the atomic number increases by 1 But
the mass stays the same
Hey! How do we get an electron out of the nucleus?

• Neutrons can decay to a
• Proton and a beta particle.
• The proton remains in the nucleus
• and the beta particle is expelled.

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Beta Emission
C n/p ratio 8/6 1.33 N n/p ratio 7/7 1.00

• Favored by Nuclides above the Band of Stability
• N/P ratio is too high
• Beta emission Decreases the N/P ratio
• neutron decays into a proton

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Positron Emission
The positron is the opposite of an beta particle
(electron)
Hey! So how do we get a positron out of the
nucleus?

• Like the Neutron, Protons can decay .
• However, Proton decay into a positron
• And a neutron.
• The neutron remains in the nucleus
• and the positron is expelled.

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Positron Emission
O n/p ratio 7/8 0.88 N n/p ratio 8/7 1.14

• Favored by Nuclides below the Band of Stability
• N/P ratio is too Low
• Positron emission Increases the N/P ratio
• Proton decays into a neutron

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The last decay mode doesnt actually involve a
particle.
Gamma radiation is actually a part of the high
energy end of the EM Spectrum.
Increasing Energy
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Gamma Radiation
In nuclear decay processes, gamma radiation is a
way For an excited, or metastable, nucleus to
get rid of excess energy. It occurs typically as
part of an alpha or beta decay process in which
the nucleus is left in a high energy state.
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Nuclear Equations

• Describes the decay process.
• Has a reactant side (left) and a product side
  (right)
• starting isotope
• ending isotope and emitted particle.
• An ? separates the two sides of the equation
• Several isotopes and their decay mode can be
  found in Table N.

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Nuclear Equations

• Must Demonstrate the law of conservation of mass
• The SUM of the Atomic numbers and Mass numbers on
  each side of the arrow must be the same

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Determining Unknowns in Nuclear Equations

• Write the equation for the decay of Thorium-232
• Use Table N to find the decay mode
• Write the initial equation

?
We need to figure out what X is
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Alpha decay, thorium-232

• 232Th ? 4He X

228
90
2
Conservation of Mass Number The sum of the mass
numbers on the left side must equal the sum of
the mass numbers on the right side.
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Decay Equations

• 232Th ? 4He 228X

88
90
2
Conservation of Atomic Number The sum of the
atomic numbers on the left side must equal the
sum of the atomic numbers on the right side.
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? Decay of Am-241

• 241Am ? 4He X X has to be?

2
95
So X is Np-237
X has to be?
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Problems

• Write the nuclear equation for the natural decay
  of Co-60. (Hint Table N)