Nuclear Chemistry

a.k.a. RadiationAAAAHHHHH NOOOOO!

Duck and cover!

What do you know?

• All nuclear materials remain highly toxic for thousands of years.false -Some radioisotopes have-lives

of seconds or days, while others like plutonium-239 has a half-life of 2.4 x 104 years.

What do you know?

• Man-made radiation is more toxic to humans than naturally occurring radiation even if the dose is the same.false - The body makes no

distinction; it sees radiation as deposited energy regardless of its source.

What do you know?

• The human body has the capability to repair damaged caused by exposure to radiation.true - Many of the DNA lesions induced by

ionizing radiation are similar to identical to those induced as a consequence of normal metabolic activity. DNA repair mechanisms can act to reduce the consequences of this damage. 

What do you know?

• In the US, most cases of cancer in humans are known to be caused by man-made radiation.false - Most cancers have an

unknown cause or etiology.

What do you know?

• I would rather live within a 50 mile radius of a coal-burning plant than a nuclear power plant.false - Actually a coal burning plant

gives off slightly more radioactivity due to the thorium and uranium content in coal. But in both cases the levels are extremely low. 

What do you know?

• One of the chief dangers from nuclear power plants is that they can explode like a nuclear bomb.

false - There's a big difference between a nuclear core and a nuclear bomb. After detonation, the density of uranium (or plutonium) atoms in a bomb is incredibly high, enough for fissions to take place and energy to be released in a hundred millionth of a second! So it flies apart. The density of atoms in a nuclear core is much less, and, even in a meltdown situation would generate heat at a much slower rate than is necessary to fly apart. The act of meltdown actually terminates the explosive process, because when a core "melts down" it spreads out and goes sub-critical.

What do you know?

• It is safer to drive behind a tanker truck carrying gasoline than a truck load of spent nuclear fuel.false - People occasionally die in

gasoline truck accidents, but the DOE and the nuclear industry claim that no one has died or been hurt by a radiation release due to a nuclear waste transportation accident.

What do you know?• On average, people are exposed to

more radiation from nuclear power plants than from radon gas in homes.false - An individual gets about 200

millirems of radiation per year from naturally occurring radon. A normally functioning nuclear power plant exposes a person to about.01 millirem, if the person lives within 50 miles of the plant.

What do you know?

• Since the construction of the first nuclear power plant, man-made radiation in known to have resulted in new species of plants and animals.false - New species don't occur any

more frequently today than before nuclear plants were built.

What do you know?

• The fact that nuclear power plants have elaborate evacuation plans for the surrounding area indicates they are inherently more dangerous than other types of plants.

What do you know?false - Evacuation plans have only been

around since 1980 and are an example of "regulatory ratcheting" by the Nuclear Regulatory Commission. Other countries do not have these plans. Chemical plants do not have evacuation plans even though evacuations in their vicinity are more likely to be necessary than around a nuclear power plant. Most evacuations are due to rail or truck accidents involving toxic chemicals.

The Nucleus

• Remember that the nucleus is comprised of the two nucleons, protons and neutrons.

• The number of protons is the atomic number.• The number of protons and neutrons together

is effectively the mass of the atom.

Isotopes

• Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms.

• There are three naturally occurring isotopes of uranium:Uranium-234Uranium-235Uranium-238

Radioactivity

• It is not uncommon for some nuclides of an element to be unstable, or radioactive.

• We refer to these as radionuclides.

• There are several ways radionuclides can decay into a different nuclide.

Types of Radioactive Decay Alpha Decay

Loss of an -particle (a helium nucleus)

He42

U23892

Th23490 He4

2+

Types of Radioactive Decay Beta Decay

Loss of a -particle (a high energy electron)

0−1 e0

−1or

I13153 Xe131

54 + e0

−1

Types of Radioactive Decay Positron Emission

Loss of a positron (a particle that has the same mass as but opposite charge than an electron)

e01

C116

B115 + e0

1

Types of Radioactive Decay Gamma Emission

Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle)

00

Page 4

• Homework Read Page 5 and answer page 6 in packet.

Stable Nuclei

• There are no stable nuclei with an atomic number greater than 83.

• These nuclei tend to decay by alpha emission.

Radioactive Series

• Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation.

• They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).

Nuclear Fission• How does one tap all that energy?• Nuclear fission is the type of reaction carried

out in nuclear reactors.

Nuclear Fission

• Bombardment of the radioactive nuclide with a neutron starts the process.

• Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons.

• This process continues in what we call a nuclear chain reaction.

Nuclear Fission

• If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out.

• Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: Critical Mass.

Nuclear ReactorsIn nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.

Nuclear Reactors

• The reaction is kept in check by the use of control rods.

• These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.

Nuclear Fusion

• Fusion would be a superior

method of generating power.The good news is that the

products of the reaction are

not radioactive.The bad news is that in order to achieve fusion, the

material must be in the plasma state at several million kelvins.

Tokamak apparati like the one shown at the right show promise for carrying out these reactions.

They use magnetic fields to heat the material.

Nuclear TransformationsNuclear transformations can be induced by accelerating a particle and colliding it with the nuclide.

These particle accelerators are enormous, having circular tracks with radii that are miles long.

Page 8 & Page 10

Nuclear Equations

• Page 16 • Just like a math equation.

• Both sides must equal.

Half Life(no,not middle age)

Read Page 17

The half-life of a radioactive nuclide is the amount of time it takes for half of that nuclide to decay into a stable nuclide.

The half-life of Carbon-14 is 5730 years

•After 5730 years, ½ the mass of an original sample of Carbon-14 remains unchanged.

•After another 5730 years, ¼ (half of the half) of an original sample of Carbon-14 remains unchanged.

•The half-life of a radioactive nuclide cannot be changed.

Regents Question:

As a sample of the radioactive isotope 131I decays, its half-life

(1) decreases

(2) increases

(3) remains the same

How to determine how much of a radioactive isotopes remains unchanged after a period of time.

• Determine how many half-lives have gone by (Time/half-life)

• Halve the mass of the starting material for each half-life period that goes by.How much of a 20.g sample of 131I remains

unchanged after 24 days?The half-life period is 8 days so 24 days is

3 half-lives. Half the mass three times.20.g 10.g 5.0g 2.5g

8 days 8 days 8 days

Regents Question:

Exactly how much time must elapse before 16 grams of potassium-42 decays, leaving 2 grams of the original isotope?

(1)8 x 12.4 hours

(2) 2 x 12.4 hours

(3) 3 x 12.4 hours

(4) 4 x 12.4 hours

16 8 4 2

Page18 . . .

Benefits of Radioactive isotopes

• Tracers – are used to follow the course of chemical (organic) or biological reactions

(C-14)• Medical – isotopes (radioactive), with short

half-lives are quickly eliminated from bodyTechnetium-99: pinpoints brain tumors Iodine-131: diagnosis and treatment of thyroid

disordersRadium and Cobalt-60: treatment of cancer

Benefits of Radioactive isotopes

• Food can be stored longer because radiation kills bacteria, yeast and molds

• Radioactive dating:Geologic dating is based on half-life. Uranium-

238 occurs naturally in rock, it decays to lead-206.

Dating living materials (organisms that were previously alive). The ratio of C-14 to C-12 can determine the age of a sample of wood, bone, animal skin, or fabric.

Benefits of Radioactive isotopes

• Nuclear Power – produce electricity

• Industrial Measurement – a beam of subatomic particles (alpha, beta or gamma) is blocked by a metal of a certain thickness. Measuring the fraction of the beam that is blocked determines the thickness of the metal.

Risks of Radioactive isotopes

• Biological Damage: exposure to radiation can damage cells, or an organism. When sex cells are damaged, offspring may be affected.

• Long term storage: it is not known if storing radioactive isotopes is safe.

• Accidents: cause fuel to escape nuclear reactors (earthquake in Japan).