Transcript What particle is formed when polonium

Nuclear Chemistry
Chapter 25
Nuclear Radiation
Section 25.1
Nuclear Reactions
1. Occur when nuclei emit particles and/or
rays.
2. Atoms are often converted into atoms of
another element.
3. May involve protons, neutrons, and
electrons
4. Associated with large energy changes.
5. Reaction rate is not normally affected
by temperature, pressure, or catalysts.
Wilhelm Roentgen
• 1845-1923
1895:
 When electrons
bombarded surface of
certain materials,
invisible rays were
emitted
Henri Becquerel
• 1852-1908
 studied minerals that
when exposed to
sunlight, emit light
 phosphorescence
 discovered uranium salts
(pitchblende)
Marie Curie
• 1867-1934
Marie & Pierre Curie
 isolated components
emitting rays
 identifed Po & Ra
MORE HISTORY
Rutherford (1871-1937)
 identified alpha,
beta, and gamma
radiation
PROPERTIES OF RADIATION
1.
2.
3.
Alpha ()
4 He, helium nuclei

2

Blocked by paper; 6.64 x 10-24 kg

Slow moving due to mass and charge!
Beta ()
0  or 0 e, electrons

-1
-1

Blocked by metal foil; 9.11 x 10-28 kg

Fast moving

Emitted from a neutron of an unstable nucleus

Insignificant mass compared with mass of nucleus

Greater penetrating power than alpha particles
Gamma ()
0  , photons

0

Not completely blocked by lead or concrete; 0 kg

High energy electromagnetic radiation

Almost always accompanies alpha and beta radiation
Radioactive Decay
Section 25.2
NUCLEAR STABILITY
• Correlated with atom’s neutron-toproton ratio.
• < 20 atomic number most stable
BETA DECAY
• Instability of isotope due to too many
neutrons relative to its number of
protons.
ALPHA DECAY
• All nuclei with more than 83 protons
decay spontaneously
POSITRON EMISSION
• Positron is a particle with the same mass
as an electron but the opposite charge
• 01 or 01e
• During emission, a proton in the nucleus
is converted to a neutron and a positron
•
1
1p
-->
1
0n
+ 01
ELECTRON CAPTURE
• Nucleus of an atom draws in a
surrounding electron (from lowest energy
level)
• Captured electron combines with a
proton to form a neutron
•
1
1p
+ 0-1e -->
1
0n
PROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
PROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
210 Po
84
-->
mass
atomic #Po
PROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
210 Po
84
-->
4 He
2
+
PROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
210 Po
84
-->
4 He
2
+
206
How did I get 20682 ?
82
?
PROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
210 Po
84
-->
4 He
2
+
206
82
?
How did I get 20682 ? The numbers must
add up the same on both sides of the
equation (top #’s =, and bottom #’s =)
PROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
210 Po
84
-->
4 He
2
+
206
82
?
How do you determine the element?
By atomic number!
PROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
210 Po
84
-->
4 He
2
+
206
82
Pb
How do you determine the element?
By atomic number!
PROBLEM
What would the decay process of iodine131 into xenon-131 look like?
PROBLEM
What would the decay process of iodine131 into xenon-131 look like?
131 I
53
-->
131 Xe
54
+ ?
PROBLEM
What would the decay process of iodine131 into xenon-131 look like?
131 I
53
-->
131 Xe
54
+
0
-1?
What type of radiation: 0-1?
PROBLEM
What would the decay process of iodine131 into xenon-131 look like?
131 I
53
-->
131 Xe
54
+
0
-1
What type of radiation: 0-1? Beta!
RADIOACTIVE SERIES
• A series of nuclear reactions that begins
with an unstable nucleus and results in
the formation of a stable nucleus.
TRANSMUTATION
Section 25.3
TRANSMUTATION
• Conversion of an atom of one element to
an atom of another element
• In all but gamma emission nuclear
reactions
INDUCED TRANSMUTATION
• Striking nuclei with high-velocity
charged particles
• Must be moving at high speeds to
overcome electrostatic repulsion of target
atom’s nucleus
• Use particle accelerators (“atom
smashers”
TRANSURANIUM ELEMENTS
• Elements immediately following uranium
in the periodic table
• Atomic number of 93 or greater
• Developed in the laboratory by induced
transmutation
• Radioactive
PROBLEM
Write a balanced nuclear equation for the
induced transmutation of
aluminum-27 into phosphorus-30 by
alpha particle bombardment. A neutron
is emitted from the aluminum atom in the
reaction.
PROBLEM
Write a balanced nuclear equation for the induced
transmutation of aluminum-27 into phosphorus-30 by
alpha particle bombardment. A neutron is emitted
from the aluminum atom in the reaction.
Write all symbols on proper sides of the
equation. Make certain numbers add up!
PROBLEM
Write a balanced nuclear equation for the induced
transmutation of aluminum-27 into phosphorus-30
by alpha particle bombardment. A neutron is
emitted from the aluminum atom in the reaction.
Write all symbols on proper sides of the
equation. Make certain numbers add
up!
27 Al
13
+
4
2He --->
1
0n +
30
15P
PROBLEM
Write a balanced nuclear equation for the induced
transmutation of aluminum-27 into phosphorus-30
by alpha particle bombardment. A neutron is
emitted from the aluminum atom in the reaction.
27 Al
13
+
4
2He --->
1
0n +
30
15P
How did I know the symbol for a neutron?
A neutron has mass but no nuclear charge!
HALF-LIFE
• Time required for one-half of a
radioisotope’s nuclei to decay into its
products.
• Exponential decay!
• Strontium-90 has a half-life of 29 years.
• So, if you had 10 g of this, in 29 years you
would have 5 grams left.
HALF-LIFE
Amount remaining = (initial amount)(1/2)n
n
is equal to the number of half lives that has
passed
OR
Amount remaining = (initial amount)(1/2)T/t 1/2
T is equal to the elapsed time and t 1/2 is the
duration of the half-life
PROBLEM
Iron-59 is used in medicine to diagnose
blood circulation disorders. The half-life
of iron-59 is 44.5 days. How much of a
2.000 mg sample will remain after 133.5
days?
PROBLEM
Iron-59 is used in medicine to diagnose blood circulation
disorders. The half-life of iron-59 is 44.5 days. How
much of a 2.000 mg sample will remain after 133.5
days?
Amount remaining = (initial amount)(1/2)n
X = 2.000 (1/2)133.5/44.5
PROBLEM
Iron-59 is used in medicine to diagnose blood circulation
disorders. The half-life of iron-59 is 44.5 days. How
much of a 2,000 mg sample will remain after 133.5
days?
Amount remaining = (initial amount)(1/2)n
X = 2.000 (1/2)133.5/44.5
Amount remaining = 0.2500 mg
RADIOCHEMICAL DATING
• Process of determining an age of an object by
measuring the amount of a certain radioisotope
remaining in that object
• Uranium
• Half-life of 4.5 c 109 years
• Meteorites; have estimated age of solar system at 4.6
x 109 years
• Carbon dating
• 146C ---> 147N + 0-1
• Half-life of 5730 years
• Limited to accurately dating objects up to 24,000
years of age
Fission and Fusion of Atomic
Nuclei
Section 25.4
∆E = ∆ mc2
• I lied! (kind of…)
• For most practical situations, mass is
conserved, but…
• Energy and mass can be converted into each
other!
• It has been determined that the mass of the
nucleus is always less than the sum of the
masses of the individual protons and neutrons
that comprise it. (CALLED MASS DEFECT)
• The missing mass provides tremendous energy
required to bind the nucleus together.
NUCLEAR FISSION
• Heavier atoms (mass # > 60) tend to
fragment into smaller atoms to increase
their stability
• This is accompanied by a very large
release of energy
NUCLEAR POWER PLANTS
• Use fission to generate power
• UO2 encased in corrosion-resistant fuel rods
• Enriched to contain 3% uranium-235 (meets
critical mass to sustain the chain reaction)
• Control rods of cadmium or boron absorb
neutrons released during the reaction,
controlling the fission process
• Water circulates throughout the core to carry
off the heat generated
• This is used to power stream driven turbines
which produce electrical power
• Dense concrete structure encloses the reactor
NUCLEAR POWER PLANTS
• Drawbacks
• Hazardous radioactive fuels and fission products
• Limited supply of uranium-235
• Where to store spent fuel rods?
• Require 20 half-lives to decay to safe levels
Amount of spent fuel for a lifetime/person
would equal the size of a basketball
NUCLEAR FUSION
• Binding together two light (mass # < 60) and
less stable nuclei
• Capable of releasing very large amounts of
energy
• The sun!
• Requires temperatures of 40,000,000 K!
• Can achieve this by atomic explosion (not safe!)
• Don’t have materials capable of withstanding
these high temperatures
ATOMIC BOMB
• Utilizes principles of fission
(uncontrolled!)
• Equal to effect of 20,000 tons of TNT
HYDROGEN BOMB
• Never used in warfare
• Explosive force 1000 X greater than
atomic bomb
 Fission reaction triggers a fusion reaction
of hydrogen isotopes (deuterium and
tritium)
 Equal to 15 million tons of TNT
IONIZING RADIATION
• Radiation energetic enough to ionize
matter with which it collides
• Detected by:
• Geiger counter
• Metal tube filled with a gas; gets ionized; creates
an electrical current
• Scintillation counter
• Radiation energizes a phosphorcoated surface
that releases bright flashes
USES OF RADIATION
• Neutron activation analysis
• Determine quality of silicon wafers used in
computers
• Radiotracers
• Trace biological pathways
• PET
• Imagery used in medical diagnoses
• Radiation to kill cancer cells
• Irradiation of meats, fruits…