Nuclear Chemistry

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Nuclear Chemistry

• Overview
• Radioactivity
• Alpha, beta, and gamma radiation
• Positron emission and K-capture
• Half-life
• Fission and nuclear weapons
• Nuclear power
• Mass defect
• Fusion
• Radiation and humans benefits and risks

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Nuclear Stability

• Strong nuclear force holds nuclei together,
  neutrons involved
• As Z ? more and more neutrons are needed to
  balance increasing number of protons.
• Neutron to proton ratio

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Red line n/p 1
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Nuclear Stability

• When Z gt 83, i.e. bigger than Bi, inherently
  unstable
• When Z ? 20, i.e. Ca and smaller, usually
  n p or n p1
• e.g. 12C 13C 24Mg 25Mg
• 3. When 20 lt Z lt 84

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Nuclear Stability

• Decay routes
• Too many neutrons beta emission
• Too few neutrons positron or K-capture
• Too big alpha or beta emission

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Radioactive Decay

• Some nuclei are unstable
• Decay to attain stability
• Release nuclear parts
• Decay routes
• Alpha emission
• Beta emission
• Gamma emission
• Positron emission
• K-capture

Historically significant
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Alpha Emission

• Common when Z gt 83
• He nucleus 2 protons 2 neutrons

92 p 146 n
90 p 144 n
2 p 2 n
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Problem 1

• Determine the products and write reactions for
  the alpha decay of the following
• 226Ra
• 212Po

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Beta Emission
6 p 7 p 8 n 7 n
88 p 89 p 142 n 141 n
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Problem 2

• Determine the products and write reactions for
  the beta decay of the following
• 20F
• 231Th

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Gamma Radiation

• Electromagnetic radiation (high energy light)
• Accompanies other forms of decay
• Ionizing radiationmore dangerous than x-rays

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Positron Emission and K-capture

• Either or both occur when too few neutrons.
• Positron positively charged electron, antimatter
  counterpart to an electron
• K-capture Capture inner shell electron, same
  result as positron emission

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Half life

• Way of expressing rates of radioactive decay
• t½ time required for half sample to decay

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Half life

• Shorter half life more radioactive, less stable
  nucleus, shorter life
• Longer half life less radioactive, more stable
  nucleus, longer life
• Half-life activity
• Radio-dating of artifacts

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Problem 3

• 131I has a half life of 8.04 days. If you start
  with a sample of 20.0 mg, how much is left after
  32 days?
• About how long would it take for the sample size
  to dwindle down to lt 1 mg?

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Nuclear FissionBinding energy
fission
fusion
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Nuclear Fission
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Nuclear Fission
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Fission

• Subcritical not enough free neutrons to maintain
  reaction
• Critical just enough free neutrons to maintain
  controlled fission (nuclear power plant)
• Supercritical so many neutrons reaction goes out
  of control (atomic bombs)

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Sustainability
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Nuclear Power

• 235U
• Natural abundance lt 1
• Fuel grade 3
• Weapons grade 7

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Nuclear Weapons

• Supercritical mass uncontrolled chain reaction
• Challenge how to keep reaction controlled before
  bomb is dropped

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Nuclear Power Plant
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Nuclear Power Plant
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Reactor Core
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Nuclear Fusion
fusion
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Nuclear Fusion

• The sun

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Nuclear Fusion

• Fusion does not have waste issues common to
  fission processes.
• Very high activation energy
• Thermonuclear reactions (fission) to produce high
  temperatures required for fusion.
• Hydrogen bomb

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Radiation and Humans Risks

• Calculate your radiation dose
• EPA site
• http//www.epa.gov/radiation/students/calculate.ht
  ml
• Dose effects
• gt 500 rem death
• 100 400 rem sick, likely to survive, risk of
  future cancers or teratogenic events
• 20 100 decrease in wbc count, depressed
  immunity, risk of future cancers
• Smoking (210Pb, 210Po) up to 280 mrem/yr

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Type of radiation

• Penetrating ability
• Alpha dead skin (0.1 cm)
• Beta 1 cm
• Gamma deeply penetrating
• Beneficial Effects disease diagnostics and
  treatment

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Tissue Affected

• External gamma is the most damaging
• Internal Alpha (size)
• Radon gas

t½ 3.8 days
t½ 3.11 min ? emitter
90Sr (?) mimics Ca in the body