Discovery of Radioactivity Radiation - energy emitted in the
form of electromagnetic waves (i.e. light, microwaves, x-rays,
etc..) 1895 Roentgen discoverer of x-rays - Nobel Prize 1901. video
clipvideo clip Becquerel followed-up on Roentgens work storystory
Marie and Pierre Curie 1899 Rutherford alpha and beta rays
Radioactivity spontaneous emission of particles and energy from
atomic nuclei.
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ELECTROMAGNETIC SPECTRUM LOWER ENERGY HIGHER ENERGY
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Ionizing and Non-ionizing radiation Non-ionizing radiation
(long-wavelength) - Ionizing radiation (shorter wavelength)- Both
transfer energy to matter!
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UV radiation damage
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Isotopes Atoms of the same element that contain different
numbers of neutrons. What chemical symbol do these atoms have? What
is their atomic number? What is the mass number of the atom on the
left?
NOTATION Uranium 238 238 mass number ( p + n ) U 92 atomic
number ( # p )
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Nuclear Radiation It is a form of ionizing radiation that is
caused by changes in the nucleus of an atom. Remember: unstable
nucleus = radioactive atom change in identity of atom as the
nucleus breakdown (radioactive decay). How is this dangerous?
-Unstable nuclei can emit high-speed particles from the nucleus
thus releasing energy (nuclear radiation).
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Stable vs. Unstable isotopes Radioactive Isotopes: unstable
atoms, due to a nucleus with too many or too few neutrons relative
to the number of protons. No amount of neutrons can hold a nucleus
together once it has more that 82 protons. All of the elements with
an atomic number greater than 82 have only unstable isotopes.
Unstable atoms emit energy in the form of radiation when they break
down (decay) Large nucleus (unstable) nucleus + energy Reaction is
EXTREMELY exothermic; called nuclear energy; mass is lost in the
process
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Nuclear RadiationAlpha radiation, low penetrating power 2+ Ex:
Radium-226 Beta Radiation, Moderate penetrating power Ex: carbon-14
Gamma Radiation, Very high penetrating power 0 Cobalt -60
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3 types of nuclear radiation: Alpha & beta particles and
gamma rays Charge of each Gamma rays highest energy similar to
x-rays frequency. UVA, UVB, UVC rays from the sun UVC (100-290 nm
wavelength) UVA (320 -400nm wavelengths)
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ALPHA PARTICLE The same as a helium nucleus 2 protons and 2
neutrons 4 mass of 4 amu He 2 Has a 2+ charge because of 2 protons
LOWEST PENETRATING POWER
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BETA PARTICLE The same characteristics as an electron (not from
an energy levelemitted from the nucleus) 0 essentially no mass e -1
charge of -1 HIGHER PENETRATING POWER
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Gamma Emission gamma emission usually occurs in concert with
other forms of decay that produce nuclei in nuclear excited states
ignoring the alpha decay event, gamma emission looks like
this:
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GAMMA RADIATION Pure electromagnetic energy with high frequency
and short wavelength No mass or charge associated with it MOST
PENETRATING POWER
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Strength of alpha, beta, and gamma radiation
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PENETRATING POWER OF NUCLEAR RADIATION
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Background radiation Background radiation: a constant level of
radioactivity that results from natural sources and from sources
related to human activity. o You cant completely eliminate
background radiation its essentially everywhere: soil, water, food,
rocks, etc o Currently, 500 mrem (millirem) is the established US
background radiation limit for the general public EPA_Cosmic
Radiation ~8% of our annual radiation exposure comes from outer
space. The closer we get to outer space the more we are exposed to
cosmic radiation (such as during flights). Full Body Scanners at
Airports
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Fyis.. BED (Banana Equivalent Dose) The equivalent dose for 365
bananas (one per day for a year) is 3.6 millirems(36 Sv).Sv Bananas
are radioactive enough to regularly cause false alarms on radiation
sensors used to detect possible illegal smuggling of nuclear
material at US ports. Other foods that are above avg. for
radioactivity in food include: potatoes, kidney beans, nuts, and
sunflower seeds.
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Ionizing radiation in you!
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UNITS OF RADIATION DOSAGE GRAY= SI unit that is equivalent to
the dose absorbed: 1 gray = 1 Joule per 1 kilogram of body tissue
SIEVERT: SI unit that is used to express the ability of radiation
to cause ionization in human tissue RAD: abosrbed dose similar to
gray REM: absorbed dose similar to Sievert Copyright by Houghton
Mifflin Company. All rights reserved. 24
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Radiation Doses Causing Death
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Effect of Ionizing Radiation
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Ionizing radiation worksheet Units How much is safe? Look at 3
main factors: 1. Radiation Density (how much per given volume) 2.
Dose (how much total received) 3. Energy associated with that type
of radiation Biological effects of ionizing radiation: Large doses
(but less than 200 rems) can causes changes in DNA or proteins in
the body than can result in mutations leading malfunctioning
proteins that are unable to do their job in the body, to cancer, or
birth defects, etc.. Low level radiation does not produce as unique
effects or obvious mutations attributable to the radiation exposure
that is easy to distinguish from other injuries or illnesses it can
take years for symptoms to even show (making it nearly impossible
in some cases to attribute to radiation damage) Chemotherapy vs.
radiation therapy Radiation Risk from Medical Imaging Cancer and
Radiation
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TRANSMUTATION INVOLVES THE RELEASE OF RADIATION A Radioisotope
emits, or gives off, radiation from its nucleus Each isotope emits
a certain type of radiation; it has a specific decay mode The
radiation can be in the form of particles or rays
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NUCLEAR TRANSMUTATION (natural) Original New Radioisotope
Isotope + Radiation 238 234 4 U Th + He 92 90 2
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A CLOSER LOOK U-238 has alpha decay Total mass before and after
must be equal 238 234 4 U Th + He 92 90 2 Total of atomic numbers
must also balance
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How can you use decay mode information? Can you determine the
new isotope if you know the decay mode? For example, Th-232 is an
alpha emitter. 232 4 Th ? + He 90 2
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STRATEGY *mass numbers must balance 232 = 228 + 4 Th ? + He 90
= 88 + 2 *atomic numbers must balance How do we know what the new
isotope is?
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CHECK THE PERIODIC TABLE! The new isotope has a mass number of
228 and an atomic number of 88. 228 ? 88 each element has a unique
atomic number The new isotope is Radium-228 which is a beta
emitter!
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What happens to Ra-228? 228 0 Ra ? + e 88 -1 (beta particle)
Balance the mass numbers and the atomic numberscareful of that
-1)
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And the result of the decay is mass number stays same 228 Ac
atomic number increases by 1 89 Actinium a new element with a
greater atomic # This is a beta emitter as well! When will it
stop???
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not until a stable isotope is formed! The change from one
radioisotope to another in a specific sequence is called a decay
series We will explore some transmutations that are part of the
uranium-238 decay series... You will be given two radioisotopes and
their decay modes. Determine what the product of each transmutation
will be
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Start off examples are: U-238 is an alpha emitter: 238 234 4 U
Th + He 92 90 2 Th-234 is a beta emitter: 234 234 0 Th Pa + e 90 91
-1
Take your time and think it out 1.Write the symbol of the
radioisotope in the proper notation on the reactant side 2.Write
the notation for the radiation type emitted on the product side
3.Total up the mass numbers on top so the total mass is balanced on
each side 4.Total up the atomic numbers on the bottom so they are
balanced as well 5.Use Periodic Table to identify the element by
its atomic number
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Copyright by Houghton Mifflin Company. All rights
reserved.42
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One very special isotope U-238 Th-234 Pa-234 U-234 Th-230
Ra-226 Rn-222 Po-218 Pb-214 Bi-214 Po-214 Pb-210 Bi-210 Po-210
Pb-206 (stable) Rn-222 is a gas!
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Figure 6.34 Page 626
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Figure 6.35 Page 626
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Figure 6.36 Page 627
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Copyright by Houghton Mifflin Company. All rights reserved.
47
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THIS IS NOT A CHEMICAL CHANGE! Chemical reactions involve atoms
rearranging by breaking and forming bonds involving electrons
TRANSMUTATION involves changes in the nucleus that change the
actual identity of the element These reactions are called NUCLEAR
because they involve the atoms nucleus
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Transmutation Some isotopes are naturally unstable and
spontaneously change to another isotope of a different element This
change from one element to another is called TRANSMUTATION and can
happen 2 ways: 1)by radioactive decay (natural) OR 2) when
particles bombard the nucleus of the atom. (nuclear reactor)
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Figure 19.5: Representation of a fission process. Copyright by
Houghton Mifflin Company. All rights reserved. 52
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are a large fraction of potassium atoms radioactive? are a
large fraction of tellurium atoms radioactive? are a large fraction
of uranium atoms radioactive? no, a tiny fraction is radioactive!
yes, more than 1/2 of tellurium atoms in nature are radioactive.
ALL uranium atoms are radioactive!
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Why is there still uranium on earth? It takes a long time to
decay. (need to consider how long it takes for a radionuclide to
decay)
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HALF LIVES
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Half Lives Half-life - is the time required for one half of
original atoms to decay The half-life is unique to that isotope.
Knowing the half-life of a radioisotope can determine how harmful
or useful that substance can be.
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Half-Life: A Radioactive Clock the time during which half of a
sample of radioactive atoms will decay into their daughter atoms.
after one half-life 50% of the radioisotopic nuclei will have
decayed into their daughter nuclei
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Common Radionuclide Half-Lives
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Common Radionuclide Half-Lives
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Copyright by Houghton Mifflin Company. All rights reserved. 62
Parent IsotopeHalf-Life (yr)Daughter Product Lead-21022Bismuth 210
Carbon-145730Nitrogen-14 Uranium-235704 millionLead-207
Potassium-401.25 billionArgon-40 Uranium-2384.5 billionLead-206
Thorium-23214.0 billionLead-208 Rubidium-8748.8
billionStrontium-87
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Decay Chain of Uranium
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Half-Life: A Radioactive Clock Rutherford says: half-life is a
time during which there is a 50-50 chance a radioactive atom will
undergo nuclear decay If the half life of a radioactive atom is a
small amount of time will it be more of less likely to decay than a
different radioactive atom with a long half life? MORE LIKELY!
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Radiometric Dating
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Radiocarbon Dating Why do living things maintain a constant
concentration of carbon-14? Shouldnt it be consistently decaying in
all material? Where do new sources of 14 C come from?
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Radiocarbon Dating
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Radiometric Dating
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Example Calculations How long will it take for a sample
containing 1 gram of radium 223 to reach a point where it only
contains 0.25 grams of radium 223 if a half- life is 12 days?
Answer: 1 gram 0.5 grams = 12days 0.5 grams 0.25 grams = 12 days 12
days + 12 days = 24 days Copyright by Houghton Mifflin Company. All
rights reserved.70
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Storing High Level Radioactive Waste Store for 10 half lives!
Store in special canisters. Store in special, secured containment
site Copyright by Houghton Mifflin Company. All rights
reserved.71
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Calculations with half-life A particular plant is 50,000 year
old, how many carbon-14 half-lives have occurred? A: 8.7 half-lives
If the plant original had 30o counts of C-14 atoms, roughly how
many radioactive C-14 atoms are left in the plant after 50,000 yrs?
~0.7 counts
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NUCLEAR CHEMISTRY IN MEDICINE Diagnostic & Therapeutic
Uses
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Nuclear Chemistry in Medical Field X-rays CT or CAT scan MRI no
radiation PET scan Radiation Therapy
Fission vs. Fusion Fission: Splitting a heavy nucleus into two
nuclei with smaller mass numbers. = Nuclear transmutation! Fusion:
combining two light nuclei to form a heavier nucleus. Copyright by
Houghton Mifflin Company. All rights reserved.78
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Nuclear Power Plant http://www.nrc.gov/reactors/power.html