Bellwork- Half-life

A patient is administered 20 mgof iodine-131.How much of the isotope willremain in the body after 40 daysif the half- life for iodine-131 is 8days?

Fission and Fusion of Atomic NucleiThe sun is not actuallyburning. If the energygiven off by the sun werethe product of acombustion reaction, thesun would have burnedout approximately 2000years after it was formed,long before today. Youwill learn how energy isproduced in the sun.

When the nuclei of certainisotopes are bombarded withneutrons, they undergo fission,the splitting of a nucleus intosmaller fragments.

This often produces moreneutrons.

25.3

In a chain reaction, some of theneutrons produced react withother fissionable atoms,producing more neutrons whichreact with still more fissionableatoms.

25.3

Nuclear Fission

25.3A Nuclear Power Plant uses fission to produce energy

Neutron Moderation

Neutron moderation slowsdown neutrons so the reactorfuel (uranium-235 or plutonium-239)can capture them to continuethe chain reaction.

25.3

Neutron absorption is a processthat decreases the number ofslow-moving neutrons.

Control rods, made of a material such acadmium, are used to absorb neutrons.

25.3

Used fuel rods are kept under water inholding tanks.

Water cools the spent rods, and alsoacts as a radiation shield to reduce theradiation levels.

Fusion occurs when nuclei combineto produce a nucleus of greater mass.

In solar fusion, hydrogen nuclei(protons) fuse to make helium nucleiand two positrons.

Fusion reactions, in which smallnuclei combine, release much moreenergy than fission reactions, inwhich large nuclei split.

25.3

The use of controlled fusion as anenergy source on Earth is appealing.

•The potential fuels are inexpensiveand readily available.

•There is no radioactive wasteproduct

25.3

•The problems with fusion lie inachieving the high temperaturesnecessary to start the reactionand in containing the reactiononce it has started.

25.3

25.3 Section Quiz.

1. One of the control mechanisms for asustainable nuclear chain reactor involvesslowing down the released neutrons so theymay be captured by other nuclei. This is doneusing

a. moderators.

b. shielding.

c. absorbers.

d. control rods.

25.3 Section Quiz.

2. Spent fuel rods are stored in

a. lead-lined containers.

b. deep pools of water.

c. thick concrete bunkers.

d. cadmium or graphite containers.

25.3 Section Quiz.

3. Choose the correct words for the spaces. Insolar fusion, _______ nuclei fuse to form_______ nuclei.

a. helium, hydrogen

b. hydrogen-1, hydrogen-2

c. hydrogen, helium

d. hydrogen-1, hydrogen-3