Radioactivity nuclear equations and decay chains

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Radioactivity nuclear equations and decay chains

• presentation for May 2, 2007 by
• Dr. Brian Davies, WIU Physics Dept.

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Nuclear notation

• Z atomic number or proton number, is the number
  of protons in the nucleus.
• N neutron number, is the number of neutrons in
  the nucleus.
• A Z N mass number, is the number of
  nucleons in the nucleus.
• In general, the notation is Z X N
• For example, 6 C6 has atomic mass 12.000

A
12
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Periodic table links to isotope data

• The standard periodic table is a useful way to
  organize isotope data
• Lawrence Berkeley Lab interface
  http//ie.lbl.gov/education/isotopes.htm (link)
• Lund University interface (link)
• http//nucleardata.nuclear.lu.se/nucleardata/toi/p
  erchart.htm

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Chart of the nuclides

• All the nuclides may be charted on a single large
  chart, with the neutron number on the horizontal
  axis and the proton number on the vertical axis
  (or vice-versa)
• This has an advantage because it will allow us to
  visualize the decay schemes in a new way.
• Wall-size charts are available.
• Web-based charts are cheaper, and can link to
  massive amounts of data.

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Beta decay on the chart of nuclides

• Carbon-14 decays by negative beta decay to
  nitrogen-14 and an electron (and a neutrino)
• 6C ? 7N -1e n (b- decay)

14
14
0
Z increases by one
Z
N
N decreases by one
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Beta decay on the chart of nuclides

• Negative beta decay creates a daughter nuclide to
  the upper left of the parent
• 6C ? 7N -1e n (b- decay)

14
14
0
Z 7
Z increases by one
Z 6
N 8
N decreases by one
N 7
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Beta-plus decay on the chart of nuclides

• Oxygen-15 decays by positive beta decay to
  nitrogen-15 and a positron (and a neutrino)
• 8O ? 7N 1e n (b decay)

15
15
0
Z decreases by one
Z
N
N increases by one
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Beta-plus decay on the chart of nuclides

• Positive beta decay creates a daughter nuclide to
  the lower right of the parent
• 8O ? 7N 1e n (b decay)

15
15
0
Z 8
Z decreases by one
Z 7
N increases by one
N 7
N 8
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Electron capture (EC)
7
7
0

• 4Be -1e ? 3Li (and an X-ray)
• This process has the same result as b decay,
  except that no beta particle is emitted.

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Alpha decay

• Polonium-210 decays by alpha decay to lead-206
  and an alpha particle
• 84Po ? 82Pb 2He
• The proton number decreases (84 ? 82) and the
  neutron number decreases (126 ? 124).
• Each alpha decay reduces Z by 2 and N by 2.
• The daughter nuclide is diagonally down and to
  the left on the chart of nuclides.
• (link to BNL NUDAT)

210
206
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Decay chains

• Heavy elements may decay by a series of alpha
  decays in a decay chain. Beta decays also occur
  in the chain, and the chain may have branches
  when a nuclide has two modes of decay.
• There are three major decay chains, labelled by
  an important isotope on the chain U-238,
  Th-232, U-235
• All these chains end with a stable isotope of Pb
  (lead).
• Natural ores of uranium and thorium contain all
  of the nuclides on the chain in some equilibrium
  concentration. The waste from processing these
  ores can be quite hazardous due to high activity
  of these nuclides.

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Radioactive decay chain Thorium-232
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Radioactive decay chain Uranium-238
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Radioactive decay chain Uranium-235
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Decay chains for U-238 and Th-232
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Decay chains

• A web site has an animation of these
  (disappeared!)
• Natural ores of the heavy radioactive elements
  will contain these three long-lived isotopes of
  uranium and thorium (U-238, U-235, and Th-232).
  Because the natural ore has been in the ground
  for a long time, the daughter products have
  increased to equilibrium concentrations which
  depend on the half-lives. Each of the products
  in the chain may contribute a similar amount to
  the total activity of the natural ore.

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Qualitative picture of chart of nuclides

• The stable nuclides are in a pattern that runs
  diagonally through the unstable nuclides.
• Nuclides far from the diagonal are less stable
  they have shorter half-lives.
• Nuclides to one side decay by b- decay, on the
  other side they decay by b decay.
• Heavy nuclides decay by alpha decay directly
  toward nuclides closer to the center of
  stability.
• Exotic decays spontaneous fission, p, or n.
• Qualitative picture (link_fr) (link_bnl)
  (uses java controls) http//csnwww.in2p3.fr/amdc/j
  vnubase/jvNubase_en.html (France)
  http//www.nndc.bnl.gov/nudat2/index.jsp (U.S.
  NUDAT site) http//www-nds.iaea.or.at/nudat2/ind
  ex.jsp (European mirror)

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Chart of nuclides with half-lives (note those
with t ½ over 1 hour)
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A table of nuclides with half-lives t ½ over 1
hour is distributed by the Brookhaven National
Laboratory in the U.S., and called Nuclear
Wallet Cards for Radioactive Nuclides, by
Jagdish K. Tuli. This is available as a printed
booklet, a pdf file, and in a form to be loaded
into a PDA (Palm Pilot) for use by emergency
workers in the field. See http//www.nndc.bnl.gov
/wallet/nwccurrent.html This also contains two
lists of isotopes of special interest
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Nuclear Wallet Cards from www.nndc.bnl.gov
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Nuclear Wallet Cards from www.nndc.bnl.gov
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Some more resources for radiation safety CDC
radiation emergencies isotopes, see
http//www.bt.cdc.gov/radiation/isotopes/index.asp
CDC radiation emergencies http//www.bt.cdc.
gov/radiation/index.asp EPA radiation
protection - information - http//www.epa.gov/rad
iation/ EPA link to fact sheets -
http//www.epa.gov/radiation/radionuclides/index.h
tml
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Nuclear technology and its consequences. I
would like to make a few additional remarks about
the nuclear fuel cycle and the basic physics
involved in the production of fission products.
Some of these might show up in the environment,
and will be very consequential if a nuclear
accident or conflict occurs.
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Sources of nuclear contamination

• Mining of uranium ores (and some other special
  cases).
• Processing of uranium ores into uranium, thorium,
  and other naturally-occurring actinides (radium,
  etc.)
• Routine operation of nuclear power plants.
• Spent fuel rods from nuclear power plants.
• Isotopes produced in nuclear reactors by neutron
  activation, used mostly in medical research and
  industrial radiography.
• Accidents in nuclear power plants.
• Nuclear weapons production, use, abuse,
  disposal.

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Mining and processing of uranium ores

• Mining of uranium ores generates tailings with
  lower levels of uranium and its decay products.
  This creates problems similar to some other
  mining operations, except that the contamination
  is radioactive, rather than merely toxic (like
  lead or copper mining).
• Processing of uranium ores into uranium, thorium,
  and other naturally-occurring actinides (radium,
  etc.) can produce concentrated wastes which
  contain relatively long-lived isotopes in
  moderate concentration.
• To understand this issue, look at the decay
  chains and remember that most of the daughters
  will be present if the uranium is extracted, each
  with comparable activity.

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Routine operation of nuclear power plants

• Nuclear power plants operate by the fission of
  uranium (and possibly plutonium) into fission
  products.
• This results in two main types of products
• Fission products, which occur when the U-235 is
  split into two fragments with a range of masses.
  
• Neutrons are generated, some of which participate
  in the fission chain reaction by being absorbed
  by other uranium nuclei. But many neutrons are
  absorbed by other materials in the reactor,
  causing neutron activation of these elements.
  The neutron-activated material can build up huge
  activities (MCi) of long-lived isotopes.
• For detail, I have found some material in an
  older book on nuclear power. (use overhead).

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Spent fuel, medical and industrial isotopes

• Spent fuel rods from fission reactors is, of
  course, a big problem, but unless an accident
  occurs, the material is being contained in ponds
  and will go to storage. Accidents in transport
  are usually not catastrophic.
• Accidents with medical isotopes have been
  notorious and well-publicized, but localized with
  only moderate numbers of casualties.
• (This is my opinion, I believe accidents in
  nuclear power reactors and nuclear weapons issues
  are of much more concern. Some pictures from
  Chernobyl are included on the next slides.)

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Chernobyl nuclear reactor, Ukraine April 26,
1986
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Chernobyl reactor encased in concrete and steel
sarcophagus
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Deserted city with reactors in the background.
The area abandoned is half the size of Colorado.

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4400 people have died so far, about 7 million
have ill health, andover 150,000 abandoned their
homes.