Chapter 4Nuclear Chemistry and Radiation

What is RADIATION? A form of energy that is emitted from atoms

Radiation exists all around you.Several Factors can affect your exposure to radiation:1) Where you live2) Health3) Lifestyle

The ability of radiation to cause harm is measured in rem.The average U.S. citizen is exposed to approximately 0.360 rem per year. (360 millirem)

Lethal doses of radiation begin at 500 rem. Exposure to radiation damages the cells in our body.

If sufficient numbers of cells are killed, the organs in our body will stop functioning properly. The victim will show signs of radiation sickness that may include nausea, vomiting, inflammation of exposed areas and skin burns.

If only a few cells are killed, our body can replace the dead cells and there will be no visible sign of ill effects.

• Sometimes, the cells are damaged rather than killed by radiation. This may lead to abnormal cells that exhibit a rapid growth rate or what is commonly known as cancer.

• The signs and symptoms of abnormal cell growth may

not be apparent until many years later.

The use of radiation IS important is our daily lives.1) Food is irradiated to kill bacteria and prolong shelf life.

2) Radiation is used in medical diagnostics and therapy. “tracer” - radioactive substances whose location can

be identified by the radiation they emit.

barium swallow

3 Major Forms of Radioactivity:

1. Alpha Particles –

positively charged particles (+2)

nuclei of Helium atoms,

2. Beta Particles – negatively charged particles (-1)

electrons ejected from an atom,

3. Gamma Rays – neutrally charged waves (0)

high energy non-visible light,

42He

01e

00

How is Radioactivity produced?

The nucleus of an atom is held together by the strong nuclear force.

If this force is reduced, the nucleus can fall apart; or decay.

The stability of a nucleus is determined by: 1.) size of nucleus (small nuclei are more stable) 2.) number of neutrons compared to protons

( a 1:1 ratio is most stable)

If a nucleus is unstable, it will undergo radioactive decay.

Examples:

vs.

vs.

4020Ca

13756Ba

126C

146C

NUCLEAR DECAY can cause transmutation – changing one element into another.

1. Alpha Decay

Decay equation:

2. Beta Decay

Decay equation:

3. Gamma Decay (does not result in transmutation)

Decay equation:

Radioactive Decay Song

Rate of Nuclear DecayHALF-LIFE : the amount of time it takes for a radioactive

sample to decay to exactly ½ its original amount.

Half-life can be measured in years, days, minutes, seconds, milliseconds, etc….

Isotopes that decay quickly are more radioactive than those that decay slowly.

Practice Problems:1. The half-life of an isotope is 5 seconds. How long will it

take a 200 gram sample to decay to 12.5 grams?

Time

Amount

2. The half-life of an isotope is 3 days. How many grams of a 1,000 gram sample will be left after 9 days?

Time

Amount

3. If a 300 gram sample of an isotope decays to 75 grams in 10 minutes, what is the half-life of the isotope?

Time

Amount

Isotopic Dating Measures the Age of a Material

Carbon – 14 datingHow does it work?

1. All living things contain carbon. A small portion of the carbon is radioactive.

2. When you die, the carbon starts to decay.

3. Knowing that carbon decays at a particular rate, scientists can count backwards to find out when

the living thing died.

Power of the Nucleus1. Fission - splitting a nucleus to form smaller atoms

+ + + 3

In the example shown, a neutron bombards the nucleus of Uranium. The nucleus breaks apart forming two daughters, Sr and Xe. In addition, 3 neutrons are knocked away from the nucleus.

10n

23592U

14354 Xe

9038Sr

10n

Fission reactions produce an incredible amount of heat and light .

Fission is the reaction that powers nuclear energy and the atomic bomb.

Practice:

+ + ______ + 4

+ ______ + + 6

10n

15463Eu

24797Bk

10n

13053 I

24494Pu

10n

10n

When nuclear fission takes place, a small amount of mass is lost from the protons and neutrons that make up the nuclei of atoms.

The amount of mass lost is called the mass defect.

The “missing” mass has been converted into huge amounts of energy.

E = mc2

Because the speed of light is so BIG, even small amounts of lost mass results in a huge output of energy.

2. Fusion - combining nuclei to form a larger atom.

+ +

In the example shown, two isotopes of Hydrogen bombard each other so that nuclei fuse (stick together). The result is a heavier isotope, Helium; and a neutron is knocked away from the nucleus.

31H

21H

42He

10n

Fusion reactions produce an incredible amount of heat and light. Fusion is the reaction that powers the sun.

Practice:

+ ______ +

+ _____ +

3115P

105B

10n

94Be

2713Al

10n