radioactivity report
TRANSCRIPT
-
8/6/2019 Radioactivity Report
1/4
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.
Word count
330
-
8/6/2019 Radioactivity Report
2/4
-
8/6/2019 Radioactivity Report
3/4
Open-Book Paper 2008
K t r Ki P 3
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
Word count
382
-
8/6/2019 Radioactivity Report
4/4
Open-Book Paper 2008
K t r Ki P 4
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.
Total word count: 969
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.
Word count:
122