Everything Science Grade 11

CHAPTER 4. ATOMICNUCLEI 4.8

DEFINITION: Nuclear fission

The splitting of an atomic nucleus into smaller nuclei

Below is a diagram showing the nuclear fissionof Uranium-235. An atom of Uranium-235 isbom-
barded with a neutronto initiate the fission process. This neutron isabsorbed by Uranium-235, to
become Uranium-236.Uranium-236 is highly unstable and breaks down into a number of lighter ele-
ments, releasing energyin the process. Free neutrons are also producedduring this process, andthese
are then available to bombard other fissionableelements. This processis known as a fission chain
reaction, and occurs when onenuclear reaction starts off another, which then also starts off another
one so that there is a rapid increase in the number of nuclear reactions that are taking place.

neutron

U-235 U-236

Neutron is absorbed by

the nucleus of the U-23 5

atom to form U-236

Massive release of en-

ergy during nuclear fis-

sion

U-236 splits into lighter

elements called fission

products and free neu-

trons

The elements and num-

ber of neutrons produced

in the process, is ran-

dom.

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See simulation: VPidw at http://www.everythingscience.co.za)

The Atomic bomb - an abuse of nuclear fis-

sion

ESBAQ

A nuclear chain reactioncan happen very quickly, releasing vast amountsof energy in the process. In
1939, it was discoveredthat uranium could undergo nuclear fission. Infact, it was uranium that was
used in the first atomicbomb. The bomb contained large amounts of uranium-235, enough tostart
a runaway nuclear fission chain reaction. Because the process was uncontrolled, the energy fromthe
fission reactions was released in a matter of seconds, resulting in the massive explosion of that first
bomb. Since then, moreatomic bombs have been detonated, causing massive destruction and loss of
life.

Activity: Nuclear weapons testing - an ongoing issue

Read the article below which has been adapted from one that appearedin ’The Globe’ in

Washington on 10th October 2006, and then answer the questions that follow.

US officials and arms control specialists warnedyesterday that North Korea’s test of

a small nuclear device could start an arms race in the region and threaten the land-

mark global treaty designed nearly four decades ago to halt the spreadof nuclear

weapons. US officials expressed concern that North Korea’s neighbours, including