Radioactivity Report

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Open-Book Paper 2008

Katarzyna Kiebala Page 1

Figure 1a: -decay of Plutonium nucleus

239Pu

235U +

Mass number 239 = 235 + 4

Atomic number 94 = 92 + 2

Number of neutrons 145 = 143 + 2

In -decay the number of all nuclides must be

balanced. Plutonium decays to form an Uranium

isotope and an -particle.

Figure 1b: -decay of

14

Carbon nucleus

14C

14N+

Mass number 14 14

Atomic number 6 7

Number of neutrons 8 7

Here a neutron in Carbon nucleus is converted

to a proton forming and new element Nitrogen

and a -particle is emitted.

Chemistry report: Radioactive decay, nuclear fission and nuclear fusion

When an atomic nucleus is unstable it loses energy to obtain stability. It emits radiation in the form

of particles or electromagnetic waves. This process is called a radioactive decay and has several

forms such as - and -decay and nuclear fission.

The difference between these lies in the types of particles which are emitted when decay occurs.

During -decay, an atomic nucleus of an element with the higher mass number,particularly such that

is heavier than209

Bi , ejects two protons and two neutrons in the form of an -particle (4He nucleus)

forming another more stable element e.g. Plutonium nucleus undergoes -decay to form Uranium

nucleus and -particle, shown in Fig.1a (ref1.)In comparison, in -decay a neutron in the nucleus of

an atom is converted into a proton an electron, which is then released as a -particle. This is shown

in Fig.1b, where14

Cnucleus forms a stable14

N nucleus and emits an electron known as -particle

(ref.2&1).

Both - and -decay are forms of natural radioactive decay and occur in natural Earths conditions

and do not need to be initiated by an external factor, in contrast to nuclear fission reaction which

needs to be initiated with a bombarding neutron, which causes the nucleus of an atom to oscillate

and become unstable. This triggers a division (fission) of nucleus into two new lighter nuclei of

approximately equal mass and one or more neutrons, which trigger further fission

reactions(Fig.2)(ref.2.1&3). Fission reaction does not occur naturally, but when it is under control it

can be used to generate energy. (ref.3)The main difference between fission and natural radioactive

decay is that fission reaction approximately evenly distributes mass and energy of the decay

products to achieve nuclear stability, whereas in natural decay the mass number of a radioactive

element changes slightly producing harmful radiation. It is significant that fission reaction is

commonly occurring on heavy nuclides in comparison to natural forms of decaywhich are present

among a wide range of unstable elements.

Figure 2a: Possible fission reaction of Uranium-235

n +

U

Kr +

Ba+3

n

This example of fission reaction of235

U can be also represented as the liquid drop model of the nucleus

shown in fig.2b.

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Both fission and fusion aree

amples of nuclear reactions which allow generation ofenergy. Fission

reaction ischaracteristic for its occurrence on heavy, neutron-rich atoms and has to be initiated with

hitting neutron, which disturbs thestability of the nucleuscausing the nucleus to split apart and

form two new nuclei and emitting several neutrons. An e

amplecould be the fission of Uranium

isotope which produces new elements and emits three neutrons which trigger further fissions.

Splitting of atoms generatesenormous amounts of thermal energy. The generator, where fissionoccurs needs to becooled down to avoid eventual risk ofe

plosion and this is achieved by installing

pipes running with cool substancessuch as molten sodium or CO2 gas, which warms up they go

around the reactor. This heats the water and formed steam is used to generateelectricity.

In comparison, fusion reaction ischaracteristic for itsspecificconditions, which are;verye

tremely

high temperature and pressure. Nuclear fusion is the pioneer reaction of all nuclear reaction since it

is responsible for synthesis of majority ofelements in the universe, starting with thosesimplest

ones, moving on to heavier ones. Itsspecificconditions allow a wide range of fusion products to be

formed. If fusion could becontrolled on Earth, it would giveenormous amounts ofelectricity.

However, controlling fusion is difficult compared to controlling fission, because it re

uirese

treme

temperature and pressureessential for maintenance of plasma ionised gases. On the other sidefusion generates at least 10 times moreenergy than it re

uires, what makes it better moreefficient

process than nuclear fission.

In terms ofcontrol of both fission and fusion the re

uirements arevaried due to thesignificant

difference in thecourse of reactions, re

uirements and the products formed. Table1compares the

control procedures during both reactions:

The main advantages of using fission to generateelectricity is that its relativelycheap and doesnt

re uire new, developed technologies as opposed to nuclear fusion, which isstill worked on since it is

very difficult to imitatestellar conditions on Earth. However fission reactions involvevery dangerous

radioactiveelements what can cause problems ifeventual break down of a reactor occurs. This

method of generating electricity is unsafe and disposal of products is a major problem. It stands a

Type of controlNuclear reaction

Nuclear Fission Nuclear Fusion

Locus of the reaction Takes place in a nuclearreactor.

Doughnut-shaped type ofvessel.

Rate of reaction control

Uranium-238 used to absorb

e

cess neutrons- rate of

reaction isslowed.

Helium products are pumped

out to prevent disturbance of

reaction.

Graphite moderator slows

down neutrons to condition

further fission.

High temperatures and

pressures are re

uired to

enableefficiency and rate of

reactions.

Control rods are used to vary

the rate of reaction by

increasing or decreasing

absorbance ofe

cess neutrons.

Electromagnetism and carbon

coating ofvessels are used to

avoid heat loss and improve

theefficiency.

Table1: Thecontrol of fission and fusion reaction in electricity generating

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threat to theenvironment. On the other hand nuclear fusion is a safe processsince it usessmall

amounts of fuel and its main advantage is that it is highlyefficient and produces incredibly high

amounts ofenergy. Though a disadvantage of fusion is that the research and construction are

e

pensive, the Earths natural energysources are limited and theres a hope in nuclear

fusion.(ref2.1&2.2)

At the moment scientists face problems developing fusion power stationssuch as research on such

largescale is highlye

pensive and appropriate materials for some of thevessel elements arestill to

be discovered, since those used today arecausing problemse.g. Carbon coating of thevessel erodes

and products are impurities which disturb fusion of plasma.

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Bibli

gr

p

Reference 1: Radiochemistry, David J. alcome-Lawes, published 1979 by the AC ILLAN

PRESS LTD

, ISBN0-333-26124-0, Chapters;1.2-1.3

Reference 2.1: Article1: Lise eitner, Radiochemist, physicist and co-discoverer of nuclear

fission

Reference 2.2: Article2: Fusion, Powering the future?

Reference 3: Particle Physics, Christopher Bishop, published 2002 by John urray LTD, ISBN

0-71958589-9, Chapter 2: Fission and fusion

Reference 4: Astronomy: A Physical Perspective,

arc L. Kutner, published 2003 by PRESS

SYNDICATE OF UNIVERSITY OF CA BRIDGE, ISBN 0-521-52927-1, Chapter 9.2: Nuclear

physics and 9.3: Nuclear energy for stars.

Reference 5: AS Physics for AQA, COLLINS ADVANCED ODULAR SCIENCES, Franc Ciccotti

and Dave Kelly, published 2000 by HarperCollins Publishers LTD, ISBN 0-00-327755-0,

Chapter 3: TheFundamental particles.

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122

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