Nuclear Chemistry Nuclear Chemistry Chemical reaction electrons are transferred

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					                                      Nuclear Chemistry



Chemical reaction: electrons are transferred or shared between atoms

Nuclear Reaction: nucleus of an atom changes

Isotope: atoms of an element with same number of protons but different number of neutrons,
         e.g.126 C, 136 C : isotopes are of same element

Nuclide:
 Atoms of an element with a specific number of protons and neutrons
 Used to describe atomic forms of different elements, e.g. 126C, 168O


Stable nuclide: (nucleus) does not easily undergo change


Unstable nuclide: (nucleus) spontaneously undergo change


Radioactivity: radiation (high energy) spontaneously emitted from unstable nucleus

Radioactive Nuclide: one that will spontaneously emit radioactivity




                    Alpha (, 42He)           Beta (, 0-1e)          Gamma(00)
    Characteristi   Helium Nucleus            electron                High Energy ray
    cs
    Travel dist. in 2-4 cm                    200-300 cm              500 m
    air
    Tissue Dept     0.05 mm                4-5 mm                     >50 cm
    Shielding       Paper, clothing        Heavy      clothing,       Lead, thick concrete
                                           gloves
    Use in          Not very useful as it Used      to    treat       Used in diagnosis and treatment
    Medicine        does    not  penetrate malignancy, e.g. P-        of malignancy, e.g. I-131 use to
                    tissues                32 used to treat           detect iodine uptake by thyroid
                                           leukemia                   I-131 also used to treat
                                                                      hyperthyroidism-
                                                                      Technecium-99 used to detect
                                                                      brain tumors, hemorraging or
                                                                      blood clots


Source of Radiation Exposure:                                                 Fig 11.12

     Constantly exposed to low levels of radiation
     Low levels of exposure: Chromosome damage, if not repairednew abnormal cells produced
     Rapidly dividing cells e.g. bone marrow, lymph nodes, embryonic tissues are most sensitive
     One of first sign of over exposure is drop in red blood cell count
Radioactive Decay
Parent nuclei  Daughter Nuclei + Radiation

Balancing equation: (1) sum of subscripts on both sides equal
                     (2)sum of superscripts on both sides equal
211
      83   Bi             4
                            2          +        207
                                                        Tl
                                                       81


Balance the following equations:
238
       U 
      92
                          4
                           
                           2        + Th
238
       Be 
      92
                           0
                            -1   + B
238
       U 
      92
                          4
                           
                           2        + Th
226
       Ra 
      88
                           4
                            2   +          0
                                              + Rn
                                             0


Half-life (t1/2) : time for ½ of a given quantity of radioactive substance to decay
Radionuclides used in diagnostic medicine have short half-lives; why?

Is the half-life dependent on external conditions such as temperature or pressure?

Nitrogen –13 has a half-life of 10 minutes. If a sample has an activity of 40 Ci and the procedure
requires 30 minutes, what is the remaining activity of the radioisotope?

Time elapsed                            0 min                             10 min   20 min   30 min
Number of t1/2                          0                                 1        23
Remaining                               40Ci                             20Ci    10Ci    5Ci
activity


Iron-59, used in the determination of bone-marrow function, has a half-life of 46 days. If the
laboratory receives a sample of 8.0 g of iron-59, how many grams are still active after 184 days?

The half-life of iodine-131 is 8.0 days. How much of a 0.32 g of I-131 will remain after a period of 24
days?

Nuclear Fusion: two nuclei combine to form a larger one
Process by which the sun generates its energy
3
 1   H +        2
                 H
                 1
                                 135
                                        He
                                       53              +         1
                                                                  n
                                                                  0


Nuclear Fission: large nucleus splits to form two smaller ones and release large amounts of energy
and free neutrons
238
       U +
      92
                     1
                      n
                      0
                                    135
                                       53    I +            97
                                                                  Y + 4 10n
                                                                 39


Controlled nuclear fusion: used in nuclear plants

H.W.
Radioactive Isotopes
A radioactive isotope
•has an unstable nucleus.
•emits radiation to become more stable.
•can be one or more of the isotopes of an element
Nuclear Radiation
Nuclear radiation
•is the radiation emitted by an unstable atom.
•takes the form of alpha particles, neutrons, beta particles, positrons, or gamma rays.




Types of Radiation
Alpha () particle is two protons and two neutrons
                                              0
Beta () particle is a high-energy electron    e
                                              -1

Positron (+) is a positive electron 0e
                                     +1

Gamma ray is high-energy released from a nucleus 


Radiation Protection
Shielding for Radiation Protection




Chapter 9 Nuclear Radiation
Alpha Decay
  When a radioactive nucleus emits an alpha particle, a new
  nucleus forms that has

•a mass number that is 4 less than that of the initial nucleus.
•an atomic number that is decreased by 2.
Balancing Nuclear Equations
Guide to Balancing a Nuclear Equation
Equation for Alpha Decay
Write an equation for the alpha decay of 222Rn.
STEP 1 Write the incomplete equation
                   222
                      Rn            ?s + 4He
                        86                            2

STEP 2     Determine the mass number         222 – 4 = 218
STEP 3     Determine the atomic number        86 – 2 = 84
STEP 4     Determine the symbol of element    84 = Po
STEP 5     Complete the equation
                     222             218
                        Rn               Po + 4He
                        86                84              2



Beta Decay
A beta particle
•is an electron emitted from the nucleus.
•forms when a neutron in the nucleus breaks down.
   1        0
     n        e + 1H
  0         -1           1



Writing An Equation for a Beta Emitter
Example
Solution
           60                                  60
             Co                                  Ni       + 0e
           27                                  28             1

                                                               beta particle
Positron Emission
Gamma  Radiation
Summary of Types of Radiation

Summary of Types of Radiation

Summary of Changes in Mass and Atomic Numbers

Producing Radioactive Isotopes
Radioactive isotopes are produced
•when a stable nucleus is converted to a radioactive nucleus by bombarding it with a small particle.
•in a process called transmutation.
Example
Solution
                                         mass numbers
                    60               =               60
                   59             1                  56                   4
                      Co +          n                   Mn +               He
                   27             0            25                  2

                             27       =                        27
atomic numbers


Chapter 9 Nuclear Radiation
9.3    Radiation Measurement
9.4    Half-Life of a Radioisotope
9.5    Medical Applications Using                     Radioactivity
Radiation Measurement
A Geiger counter
•detects beta and gamma radiation.
•uses ions produced by radiation to create an electrical current.

Radiation Units
Units of radiation include
•Curie
                  - measures activity as the number of atoms that       decay in one second.
•rad (radiation absorbed dose)
                  - measures the radiation absorbed by the tissues      of the body.
•rem (radiation equivalent)
                  - measures the biological damage caused by
        different types of radiation.

Units of Radiation Measurement

Exposure to Radiation
Exposure to radiation
occurs from

•naturally occurring radioisotopes.
•medical and dental procedures.
•air travel, radon, and smoking cigarettes.
Half-Life
         The half-life of a radioisotope is the time for the radiation level to decrease (decay) to one-half of
the original value.




Decay Curve
       A decay curve shows the decay of radioactive atoms and the remaining radioactive sample.




Half-Lives of Some Radioisotopes
Radioisotopes
•that are naturally occurring tend to have long half-lives.
•used in nuclear medicine have short half-lives.
         Half-Lives of Some Radioisotopes
Radioisotope             Half-life
                 14
                    C                     5730      yr
                 40
                    K                     1.3 x 109 yr
                 226
                     Ra                   1600      yr
                 238
                     U                    4.5 x 109 yr
                 51
                   Cr                       28       days
                        131
                           I                     8     days
                        59
                          Fe                    46     days
                        99m
                            Tc                   6.0   hr


Half-Life Calculations
In one half-life, 40 mg of a radioisotope decays to 20 mg.
After two half-lives, 10 mg of radioisotope remain.

                       40 mg x 1 x 1 = 10 mg
                               2   2


Example
The half life of 123I is 13 hr. How much of a 64 mg sample of 123I is left after 26 hours?
        1) 32 mg
        2) 16 mg
        3) 8 mg

Solution 2) 16 mg
STEP 1 Given 64 g; 26 hr; 13 hr/half-life
STEP 2 Plan     26 hours           Number of half-lives
STEP 3 Equalities 1 half-life = 13 hr
STEP 4 Set Up Problem
        Number of half-lives = 26 hr x 1 half-life = 2 half-lives
                                          13 hr
        64 mg         32 mg  16 mg


Solution
Medical Applications
   Radioisotopes with short half-lives are used in nuclear medicine because
•they have the same chemistry in the body as the nonradioactive atoms.
•in the organs of the body, they give off radiation that exposes a photographic plate (scan) giving an
image of an organ.

Some Radioisotopes Used in Nuclear Medicine
Example
       Which of the following radioisotopes are most likely to be used in nuclear medicine?
                40
           1)     K half-life 1.3 x 109 years
                42
           2)     K half-life 12 hours
                131
           3)       I half-life 8 days

Solution
           Which of the following radioisotopes are most likely to be used in nuclear medicine?

           Radioisotopes with short half-lives are used in nuclear medicine.
                42
           2)        K half-life 12 hours
                131
           3)        I half-life 8 days


Chapter 9 Nuclear Radiation

9.6
Nuclear Fission and Fusion
Nuclear Fission
Nuclear Fission
When a neutron bombards 235U,
   • an unstable nucleus of 236U undergoes fission (splits).
   • smaller nuclei are produced such as Kr-91 and Ba-142.
   • neutrons are released to bombard more 235U.

                                                                                                  Energy




         1          235            236                91            142               1
             n +          U       “        U”              Kr +           Ba + 3 n +
         0          92                92             36             56            0




When a neutron bombards 235U,

•an unstable nucleus of 236U undergoes fission (splits).
•smaller nuclei are produced such as Kr-91 and Ba-142.
•neutrons are released to bombard more 235U.
    1              235
        n +             U         “236U”                   91
                                                             Kr + 142Ba + 3 1n +
    0              92                 92              36                 56               0




Nuclear Fission Diagram




1
 n + 235U                     “236U”                  91
                                                           Kr + 142Ba + 3 1n + energy
0             92                  92                  36                 56                   0




Example
  Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction.

1             235                           137
 n +                U                            Te + ?X + 2 1n + energy
0             92                                52              ?             0




Solution

1             235                 137
 n +                U                 Te + 97Zr + 2 1n + energy
0             92                      52              40                 0




Chain Reaction
  A chain reaction occurs
•when a critical mass of uranium undergoes fission.
•releasing a large amount of heat and energy that
 produces an atomic explosion.
Nuclear Power Plants
In nuclear power plants,
•fission is used to produce energy.
•control rods in the reactor absorb neutrons to slow and control the chain reactions of fission.
Nuclear Fusion
Fusion
•occurs at extremely high temperatures (100 000 000°C).
•combines small nuclei into larger nuclei.
•releases large amounts of energy.
•occurs continuously in the sun and stars.




Example
Indicate if each of the following describes
1) nuclear fission          or 2) nuclear fusion.

___ A.   a nucleus splits.
___ B.   large amounts of energy are released.
___ C.   small nuclei form larger nuclei.
___ D.   hydrogen nuclei react.
___ E.   several neutrons are released.

Solution
Indicate if each of the following is
1) nuclear fission          or 2) nuclear fusion.

 1     A.   a nucleus splits.
1, 2   B.   large amounts of energy are released.
 2     C.   small nuclei form larger nuclei.
 2     D.   hydrogen nuclei react.
 1     E.   several neutrons are released.

				
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