Nuclear Chemistry

College Chemistry

Isotope Notation

the number of protons

Atomic Mass

Atomic Number

protons + neutrons

Strong Nuclear Force

The strong nuclear force is usually strong enough to keep all of the + protons and neutral neutrons together in the nucleus.

When the strong nuclear force isn’t strong enough, the nucleus loses pieces (radioactivity) or breaks apart into 2 or more different atoms (fission).

Nuclear Reactions

When the nucleus of an atom is unstable, it will spontaneously decay and the nucleus will emit particles.

A change like this in the nucleus of an atom is called a nuclear reaction.

Radiation vs. Radioactivity

What is the difference between radiation and radioactivity?

Radiation: general term for any type of energy that radiates outward in all directions (example: light or heat)

Radioactivity: occurs with the breakdown (decay) of certain unstable atomic nuclei

Alpha Decay An alpha particle is a helium atom:

ThHeU

ThU234

9042

23892

23490

23892

During alpha decay: Two protons are lost Two neutrons are lost

Alpha Decay Example

Americium-241 is used in smoke detectors, where it emits an alpha particle that ionizes the oxygen and nitrogen in the air. Smoke interrupts the flow of ions and sets off an alarm. Write the alpha decay reaction for Am-241.

He+ Np Am 42

23793

24195

Beta Decay A neutron inside the nucleus of the atom changes

into an electron and a proton. The proton stays inside the nucleus and the

electron is emitted.

LaBa 14057

14056

During beta decay: One neutron is lost One proton is added

LaeBa 14057

01

14056

Practice Problem

Complete the following reactions AND identify whether it is alpha or beta decay:a.

b.

____01

210___

ePb

____42

230___ HeTh

Nuclear Reactions Particle Mass Charge NotationAlpha

(helium)4 N/A

Beta (Electron)

0 -1

Proton 1 1

Neutron 1 0

Positron 0 1

1

0 e

1

1 p

0

1 ne0

1+

He42

Gamma Rays

Gamma () rays: high energy electromagnetic radiation (higher than X rays!) and the most dangerous type of radioactive emission. The following decay of cobalt-60 is used in cancer treatment:

Note: gamma rays are accompanied by beta emission

e+ Ni Co -01-

6028

6027

Nuclear Reaction Example

Beryllium-9 plus an alpha particle produces another element and a neutron. Write the nuclear reaction.

Positron Emission

Positron emission: A positron is a particle with the same size and mass as an electron, but with a positive charge.

___ + ___ Po20784

Bi+ e Po 20783

01+

20784

Electron Capture

Electron capture: An electron is captured to turn a proton into a neutron

Lie+ Be 73

-01-

74

Animation:http://www2.wwnorton.com/college/chemistry/gilbert/tutorials/ch2.htm

______ + Be74

Half Life

Half Life: the time it takes for half a sample of unstable radioisotopes to decay

Elements take very different amounts of time to decay to half of the original sample:

Parent Isotope Half-Life Daughter Isotope

Carbon-14 5730 yrs. Nitrogen-14

Potassium-40 1.26 billion yrs. Argon-40

Thorium-230 75,000 yrs. Radium-226

Uranium-235 700,000 million yrs. Lead-207

Uranium-238 4.5 billion yrs. Lead-206

Half Life Example

Half-life Calculations

Radioactive decay rate is proportional to the number of radioactive nuclei (N) in a sample. Thus: Rate = kN (k is called the decay constant)

Using a little calculus, you can turn this into:

ktN

N

0

ln

If you assume ½ sample remains we can rearrange the above equation to:

Where: N = # left after a time interval and N0 = # nuclei at time = zero

2/1

693.0

tk

kt

693.02/1 OR

FYI: 0.693 = ln 2

OR ktNN 0lnln

Radioactive Dating

Radiocarbon dating is useful only for dating formerly living things

While an organism is alive it takes in carbon -- most of it as carbon-12 but a small % is carbon-14 (a radioactive form of carbon).

Carbon-14 is formed in the atmosphere by the following process (helped along by cosmic rays)

p+ Cn + N 11

146

10

147

Radioactive Dating As soon as the organism dies, it stops taking in carbon.

The amount of carbon 12 stays the same over time, but the amount of carbon 14 decreases as it decays.

Carbon-14 has a half life of 5715 years. It decays by the following process:

-01-

147

146 e+ N C

Geologists and archeologists can use the ratio of carbon-12 to carbon-14 to determine how old an object is

Nuclear Power in MN

Source: http://www.xcelenergy.com

Nuclear Power in MN

Source: http://www.eia.gov/state/?sid=mn#tabs-1

Nuclear Power in MN

Source: www.xcelenergy.com

Prairie Island Nuclear Generating Plant

Monticello Nuclear Generating Plant

Nuclear Power

Source: XCel Energy web site (http://www.xcelenergy.com)

2005 Xcel Energy-owned Generating Facilities

Unit Type Number of

Generating Facilities Number of

Generating Units Generating Capacity

(MW)

Coal 17 35 8,207

Natural Gas 26 61 4,913

Nuclear 2 3 1,617

Hydro 28 83 508

Oil 9 24 460

Refuse-derived Fuel 3 6 67

Wind 1 37 27*

*Xcel Energy purchased 1,296 megawatts of wind power in 2006.

2006 Xcel Energy-owned Generating Facilities

Nuclear PowerUranium

Mines/Milling Sites in the USA

Image from http://www.nrc.gov/info-finder/materials/uranium/

http://www.wise-uranium.org/umaps.html

Nuclear PowerOperating Nuclear Reactors in the USA Image from http://www.nrc.gov/info-finder/reactor/

Nuclear power is produced in reactors. These include various components principally, nuclear fuel, moderators, coolants, steam generators, turbines, condensers, cooling towers and of course a containment structure.

Typical pressurized water reactor

Chapter 2. Nuclear Energy Production

Nuclear plant containment building

Nuclear plant fuel pool

New nuclear plants incorporate multiple safety layers.

Uranium provides the energy source for nuclear reactors. 1 ton of uranium has the equivalent energy of 20,000 tons of coal!

Typical fuel pellet

Fuel assembly in a representative boiling water reactor (about 4.3 meters [14 feet]) tall and each weighing about 317.5 kilograms (700 pounds). NFI type 9x9 Fuel.

Commercial spent fuel storage

Above-ground fuel storage containers

Note: The blue glow is called Cerenkov radiation. It only happens when highly radioactive fuel rods are immersed in water. They cause the water molecules to get excited and emit blue light when they drop back to their normal state.

Spent fuel pool storage at reactors

http://en.wikipedia.org/wiki/File:Nuclear_waste_locations_USA.jpg

Permanent Storage Facility?

The proposed Yucca Mountain Nuclear Waste Repository near Las Vegas, Nevada