Transcript Intro to Nuclear Chemistry Chemistry Mrs. Coyle

Intro to Nuclear Chemistry
Chemistry
Mrs. Coyle
http://www.chem.orst.edu/graduate/pics/Reactor.jpg
How does a nuclear reactor work?
http://www.lanl.gov/science/1663/images/reactor.jpg
How does a small mass contained
in this bomb cause……
• Nuclear
Bomb of
1945
known as
“fat man”
http://www.travisairmuseum.org/assets/images/fatman.jpg
…this huge nuclear explosion?
http://library.thinkquest.org/06aug/01200/Graphics/705px-Nuclear_fireball.jpg
Is there radon in your basement?
http://a.abcnews.com/images/Blotter/abc_1radon_ad_070625_ssh.jpg
Notation
Nucleons
• Protons and Neutrons
• The nucleons are bound together by the
strong force.
Isotopes
• Atoms of a given element with:
same #protons
but
different # neutrons
H
H
http://education.jlab.org/glossary/isotope.html
H
Isotopes of Carbon
Radioactive Isotopes
• Isotopes of certain unstable elements that
spontaneously emit particles and energy
from the nucleus.
• Henri Beckerel 1896 accidentally observed
radioactivity of uranium salts that were
fogging photographic film.
• His associates were Marie and Pierre
Curie.
Marie Curie: born 1867, in Poland
as Maria Sklodowska
• Lived in France
• 1898 discovered the
elements polonium and
radium.
http://www.radiochemistry.org/nuclearmedicine/pioneers/images/mariecurie.jpg
Marie Curie a Pioneer of
Radioactivity
• Winner of 1903
Nobel Prize for
Physics with Henri
Becquerel and her
husband, Pierre
Curie.
• Winner of the sole
1911 Nobel Prize
for Chemistry.
3 Main Types of Radioactive Decay
• Alpha
a
• Beta
b
• Gamma g
Alpha Decay
Emission of alpha particles a :
•
•
•
•
•
helium nuclei
two protons and two neutrons
charge +2e
can travel a few inches through air
can be stopped by a sheet of
paper, clothing.
Alpha Decay
Uranium
Thorium
Alpha Decay
http://education.jlab.org/glossary/alphadecay.gif
Beta Decay
• Beta particles b: electrons ejected from the
nucleus when neutrons decay
( n -> p+ +b- )
• Beta particles have the same charge and
mass as "normal" electrons.
Beta Decay
• Beta particles b: electrons ejected from the
nucleus when neutrons decay
n -> p+ +b• Beta particles have the same charge and
mass as "normal" electrons.
• Can be stopped by aluminum foil or a
block of wood.
Beta Decay
Beta Decay
Thorium
Protactinium
Gamma Decay
• Gamma radiation g : electromagnetic
energy that is released.
• Gamma rays are electromagnetic waves.
• They have no mass.
• Gamma radiation has no charge.
– Most Penetrating, can be stopped by 1m thick
concrete or a several cm thick sheet of lead.
Examples of Radioactive Decay
Alpha Decay
Po 
Pb + He
Beta Decay p
n
+
n 
p
+ e
C 
N
+ e
Gamma Decay
Ni 
Ni
+ g
(excited nucleus)
e
Which is more penetrating? Why?
Part II
•Nuclear Stability
•Half-Life
Nuclear Stability
• Depends on the neutron to proton ratio.
Band of Stability
Number of Neutrons, (N)
Number of Protons (Z)
What happens to an unstable
nucleus?
• They will undergo decay
• The type of decay depends on the reason
for the instability
What type of decay will happen if
the nucleus contains too many
neutrons?
• Beta Decay
Example:
14
6
C 
14
N
7
+
0
e
-1
In N-14 the ratio of neutrons to protons is 1:1
• Nuclei with atomic number > 83 are
radioactive
Radioactive Half-Life (t1/2 ):
• The time for half of the radioactive nuclei
in a given sample to undergo decay.
Common Radioactive Isotopes
Isotope
Half-Life
Radiation
Emitted
Carbon-14
5,730 years
b, g
Radon-222
3.8 days
a
Uranium-235
7.0 x 108 years
a, g
Uranium-238
4.46 x 109 years
a
Radioactive Half-Life
• After one half life there is 1/2 of original
sample left.
• After two half-lives, there will be
1/2 of the 1/2 = 1/4 the original sample.
Graph of Amount of Remaining
Nuclei vs Time
A=Aoe-lt
A
Example
You have 100 g of radioactive C-14. The
half-life of C-14 is 5730 years.
• How many grams are left after one halflife? Answer:50 g
• How many grams are left after two halflives?
Problem
A sample of 3x107 Radon atoms are trapped
in a basement that is sealed. The half-life of
Radon is 3.83 days. How many radon atoms
are left after 31 days?
answer:1.2x105 atoms