Nuclear ChemistryNuclear Chemistry

Chapter 25

Nuclear RadiationNuclear Radiation

Section 25.1

Nuclear ReactionsNuclear 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 RoentgenWilhelm Roentgen

• 1845-1923

1895: When electrons

bombarded surface of certain materials, invisible rays were emitted

Henri BecquerelHenri Becquerel

• 1852-1908

studied minerals that when exposed to sunlight, emit light

phosphorescence discovered uranium salts

(pitchblende)

Marie CurieMarie Curie

• 1867-1934

Marie & Pierre Curie isolated components

emitting rays identifed Po & Ra

MORE HISTORYMORE HISTORY

Rutherford (1871-1937) identified alpha,

beta, and gamma radiation

PROPERTIES OF RADIATIONPROPERTIES OF RADIATION

1. Alpha () 4

2He, helium nuclei Blocked by paper; 6.64 x 10-24 kg Slow moving due to mass and charge!

2. Beta () 0

-1 or 0-1e, electrons

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

3. Gamma () 0

0 , photons Not completely blocked by lead or concrete; 0 kg High energy electromagnetic radiation Almost always accompanies alpha and beta radiation

Radioactive DecayRadioactive Decay

Section 25.2

NUCLEAR STABILITYNUCLEAR STABILITY

• Correlated with atom’s neutron-to-proton ratio.

• < 20 atomic number most stable

BETA DECAYBETA DECAY

• Instability of isotope due to too many neutrons relative to its number of protons.

ALPHA DECAYALPHA DECAY

• All nuclei with more than 83 protons decay spontaneously

POSITRON EMISSIONPOSITRON EMISSION

• Positron is a particle with the same mass as an electron but the opposite charge

• 01 or 0

1e

• During emission, a proton in the nucleus is converted to a neutron and a positron• 1

1p --> 10n + 0

1

ELECTRON CAPTUREELECTRON 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

PROBLEMPROBLEM

What particle is formed when

polonium-210 undergoes alpha decay?

PROBLEMPROBLEM

What particle is formed when

polonium-210 undergoes alpha decay?

21084Po --> mass

atomic #Po

PROBLEMPROBLEM

What particle is formed when

polonium-210 undergoes alpha decay?

21084Po --> 4

2He +

PROBLEMPROBLEM

What particle is formed when

polonium-210 undergoes alpha decay?

21084Po --> 4

2He + 20682 ?

How did I get 20682 ?

PROBLEMPROBLEM

What particle is formed when

polonium-210 undergoes alpha decay?

21084Po --> 4

2He + 20682 ?

How did I get 20682 ? The numbers must

add up the same on both sides of the equation (top #’s =, and bottom #’s =)

PROBLEMPROBLEM

What particle is formed when

polonium-210 undergoes alpha decay?

21084Po --> 4

2He + 20682 ?

How do you determine the element?

By atomic number!

PROBLEMPROBLEM

What particle is formed when

polonium-210 undergoes alpha decay?

21084Po --> 4

2He + 20682 Pb

How do you determine the element?

By atomic number!

PROBLEMPROBLEM

What would the decay process of iodine-131 into xenon-131 look like?

PROBLEMPROBLEM

What would the decay process of iodine-131 into xenon-131 look like?

13153I --> 131

54Xe + ?

PROBLEMPROBLEM

What would the decay process of iodine-131 into xenon-131 look like?

13153I --> 131

54Xe + 0-1?

What type of radiation: 0-1?

PROBLEMPROBLEM

What would the decay process of iodine-131 into xenon-131 look like?

13153I --> 131

54Xe + 0-1

What type of radiation: 0-1? Beta!

RADIOACTIVE SERIESRADIOACTIVE SERIES

• A series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus.

TRANSMUTATIONTRANSMUTATION

Section 25.3

TRANSMUTATIONTRANSMUTATION

• Conversion of an atom of one element to an atom of another element

• In all but gamma emission nuclear reactions

INDUCED TRANSMUTATIONINDUCED 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 ELEMENTSTRANSURANIUM ELEMENTS

• Elements immediately following uranium in the periodic table

• Atomic number of 93 or greater

• Developed in the laboratory by induced transmutation

• Radioactive

PROBLEMPROBLEM

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.

PROBLEMPROBLEM

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!

PROBLEMPROBLEM

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!

2713Al + 4

2He ---> 10n + 30

15P

PROBLEMPROBLEM

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.

2713Al + 4

2He ---> 10n + 30

15P

How did I know the symbol for a neutron?A neutron has mass but no nuclear charge!

HALF-LIFEHALF-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-LIFEHALF-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

PROBLEMPROBLEM

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?

PROBLEMPROBLEM

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

PROBLEMPROBLEM

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 DATINGRADIOCHEMICAL 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• 14

6C ---> 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

Fission and Fusion of Atomic Nuclei

Section 25.4

∆E = ∆ mc2∆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 FISSIONNUCLEAR 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 PLANTSNUCLEAR 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 PLANTSNUCLEAR 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 FUSIONNUCLEAR 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 BOMBATOMIC BOMB

• Utilizes principles of fission (uncontrolled!)

• Equal to effect of 20,000 tons of TNT

HYDROGEN BOMBHYDROGEN 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 RADIATIONIONIZING 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 RADIATIONUSES 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…