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Nuclear Chemistry Definitions
Nuclear Chemistry

 

Natural Radioactivitythe spontaneous breakdown of atomic nuclei, accompanied by the release of some form of radiation                          
A)     Transmutation: the conversion of one element to another by means of a nuclear change
 
B)     To detect Radioactivity one could use Geiger Counter
 
C)    Types of Radioactive emissions (emanation)
-All differ in mass, size and charge
1)     Alpha Particle:      42a
v     ___positive 2 charge_________
v     ___helium nucleus____________
v     ____mass of 4amu                                   
                         Example: 22688Ra ® 22286Rn +       42He
 
 
2)     Beta Particle:   0-1b
v     __negative charge____________
v     __acts like a high speed electron
v     __no mass______________________
                          Example: 23592® 23593Np +     0-1b
 
 
3)     Gamma Radiation (NOT a Particle) g
v     __no charge____________________
v     __acts like a high speed x-ray but with a lot more energy
v     __no mass______________________
 
4)     Positron Particle:   0+1b
v     __positive 1 charge_________
v     __acts like positive electrons
v     __no mass_____ 
 
Summary of Radioactive emanations:

Particle
Symbol
Mass
Charge
Relative Penetrating Power
alpha
42a
4amu
+2
low
beta
0-1b
0
-1
moderate
gamma
g
0
0
high
positron
0+1b
0
+1
moderate

 ***opposites attract, like charges repel
        
 
 
D)    Half-life: the time it takes for half of the atoms in a given sample of an element to decay       
*Some selected half-lives are found on Table N
*All reactions on Table N are Natural Transmutation
*Formulas for half-life reactions are found on Table T
1)     Fraction Remaining = (1/2)n where n refers to the number of half-lives.
2)     (n) = Number of Half-lives = total time ¸ half-life of isotope
3)     Original Mass = Final Mass x 2n where n refers to the number of half-lives
 
Example: What fraction remains of an original sample of I-131 at the end of 32.28 days?
Half-life of I-131 is 8.07 days. Therefore 4 half-lives have occurred.
(1/2)n = (1/2)4 = 1/16
 
Example: What is the half-life of an element that decays from 100g to 25g in 30 days?
100g®50g®25g = 2 half-lives
Therefore one half-life equals 15 days
 
Example: If we start with 36 g of 42K, how many grams will remain after 37.2 hours?
37.2 hours ¸ 12.4 hours = 3 half-lives
36g®18g®9g®4.5g
 
 
Half-life problems
1.                  If you start with 75 g of P-32, how many grams will be left after 42.9 days?
              42.9 days ¸ 14.3 days = 3 half-lives
              75g®37.5g®18.75g®9.375g
 
 
2.             After 4800 years, there is 2.0 g of Ra-226 remaining. What was the original mass of the sample?
           Original Mass = Final Mass x 2n 
           4800 years ¸ 1600 years = 3 half-lives
          Original Mass = 2.0g x 23 = 16g
 
3.           A 40 gram sample of P-33 decays to 10 grams in 50 days. What is the half-life of P-33?
          40g®20g®10g = 2 half-lives
          Therefore one half life equals 25 days
 
4.         What fraction of C-14 remains of a 1 gram sample after 17,190 years?
           17190 years ¸ 5730 years = 3 half-lives
           Fraction Remaining = (1/2)n = (1/2)3 = 1/8
 
 
Artificial Radioactivity
A)    Artificial Transmutationartificial radioactivity produced by bombarding the nuclei of stable atoms with high energy particles, thereby producing radioactive atoms      
 
B)    Fission Reactions:    the splitting of an atomic nucleus into two smaller nuclei by bombardment of a neutron (Nuclear Bomb). *Nuclear Reactors are fission reactors.
          Example: 23592U + 10n   ® 14256Ba + 19136Kr + 3(10n) + Energy
 
C)    Fusion Reactions:     a nuclear reaction in which two or more light nuclei combine to form a single nucleus. Requires huge amounts of pressure and extremely high temperatures. Produces much more energy than fission. Occurs naturally on the sun. (H-bomb)
    Example: 21H + 21® 42He + Energy
 
Uses of Radioactive Isotopes:
A)    Lab:    to trace chemical reactions 
B)    IndustryRadiating food to preserve by killing bacteria, mold, insect eggs      
C)    Medicine     must have relatively short half-lives and be quickly eliminated from the body.  
1)     I-131 diagnosing and treating Thyroid conditions (half-life 8.07 days)
2)     Co-60 emits large amounts of gamma radiation as it decays, these rays can be aimed at cancerous tumors (half-life 5.26 years)
3)     Ra-226 used in treatment of certain cancers (half-life 1600 years) 
4)     Tc-99 used in diagnosis of brain tumors (half-life 2.13x105 years
D)    Geology: 1)Fossils C-14 to C-12 ratio (while alive they are in equal amounts, once an organism dies C-14 is no longer taken in)
2) Rocks U-238 to Pb-206 ratio (U-238 decays through a series of steps until it forms stable Pb-206. As time passes, the amount of U-238 decreases while the amount of Pb-206 increases).
 
Balancing Nuclear Equations
            Steps for Balancing:
1)     Due to the Law of the Conservation of Matter, whatever is on the left side of the equation must also be on the right side of the equation. 
2)     Add the mass numbers on the left side of the equation, this MUST equal the total mass numbers of the right side of the equation.
3)     Add the atomic numbers on the left side of the equation, this MUST equal the total atomic numbers on the right side of the equation.
 

Example: 3216S + 10® 11H +     3215P



Write Your Questions Below



How can I tell which reactions are natural vs artificial?
September 26, 2011
When you look at the reaction look for the particle type (alpha, gamma, beta, neutron, proton, positron). If it is on the reactant side of the equation, then it is artificial. If it is on the product side of the equation, then it is natural. Also if you look at Refence Table N (NYS Physical Setting/Chemistry Refence Tables) all of the reactions are natural transmutation.
September 26, 2011 -  Replied By Expert

 
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