SOLUTIONS - PHY583 - Test 3 - AS2315M

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UITM - Faculty of Applied Science
PHY583 – Test 3 – AS2315M – 18.12.12
Answer all questions
1.
a)
Describe the sequence of events in the fission of 235U.

235
 nucleus captures a thermal (slow-moving) neutron.
 This capture results in the formation of ∗, & the access energy of this nucleus
causes it to undergo violent oscillation.

 ∗
 becomes highly distorted, & repulsive force between protons in the two halves of
the dumbbell shape tends to increase the distortion.
 The nucleus splits into 2 fragments, emitting several neutrons in the process.
b)
235
92
94
can fission when bombarded with a neutron by forming 140
54 and 38 . In
this fission neutrons are also released. Find the number of neutrons released in
this event.
235
92
+ 10 →
140
54
+
94
38
+  10
2 neutrons are released in the above fission so that the nucleon numbers are
conserved.
c)
State the advantages and some anticipated problems of fusion generated power
over fission-generated power.
Advantages of fusion generated power



The low cost & abundance of fuel (deuterium),
The impossibility of runaway accidents
A lesser radiation hazard than with fission
Some anticipated problems:
 The unestablished feasibility of fusion reactors,
 The very high proposed plant costs,
 The scarcity of lithium,
 The limited supply of helium needed to cool the superconducting magnets used to
produce strong confining fields (this problem may be reduced by the development of
high-temperature superconductors)
1
2.
a)
Describe the two categories of radiation damage in biological systems.
Somatic damage is the damage associated with any body cell except the reproductive
cells. At high dose rate this can lead to cancer or seriously alter the characteristics of
specific organisms.
Genetic damage affects only reproductive cells. Damage to the genes in reproductive cells
can lead to defective offspring.
b)
Briefly explain the following radiation detectors,
i) the cloud chamber and
A cloud chamber:
 Contains a vapour that has been supercooled to just below its usual condensation
point.
 An energetic particle passing through the chamber ionizes the vapour along its path.
 These ions serve as centres for condensation of the supercooled vapour.
 The tract can be seen with the naked eye & can be photographed.
 A magnetic field can be applied to determine the charges of the particles as well as
their momentum & energy.
ii) Geiger counter.
 The most common form of ion chamber.
 It can be considered as the prototype of all counters that use the ionization of the
medium as the basic detection process.
 makes use of the electron-pairs generated by the passage of radiation through a gas to
produce an electrical signal.
3.
a)
Describe the four fundamental forces of nature and the field particle that
mediates each.
Strong force




A force that holds nucleus together
Short-ranged  1 fm
The strongest of the four forces
Field particles are gluons
Electromagnetic force




Force between charges that holds atoms and molecules together
Infinite range
Obeys inverse-square law
Field particles are photons
2
Weak force
 Involved in many decays of nuclear particles which require a change of a quark from
one flavor to the onother
 accounts for the  decay of nuclei & the decay of heavier quarks & leptons.
 Range  1018 m
 Its strength is 106 times that of the strong force.
 Scientists now believe that the weak & electromagnetic forces are two manifestations
of a unified force called the electroweak force.
 Field particles: W, Zo particles
Gravitational force
 Attractive force between two masses
 Infinite range
 The weakest of the four forces  1043 times that of a strong force.
 Obeys inverse-square law
 Although this force holds the planets, stars & galaxies together, its effect on
elementary particle is negligible.
 Fields particles are gravitons but this particle is not yet discovered.
b)
List all the fundamental particles known today.
Leptons: electron, electron-neutrino, muon, muon-neutrino, tau, tau-neutrino
Force field carriers: gluons, photons, W+, W, and Z-boson
Quarks: up, down,strange, charmed, bottom, top
Newly discovered: Higgs boson
c)
Describe thefollowing classification of particles:
i) Hadrons
 Particles that interact through the strong force.
 Two classes of hadrons: mesons (spin 0 or 1) & baryons (spin odd half-integer values
1 3 5
, , ,..)
2 2 2
 Composite particles composed of more elemental units called quarks.
ii) Mesons





A type of hadron made up of a quark and an antiquark.
All have spin 0 or 1,
Their masses between that of the electron & proton.
All mesons are known to decay finally into electrons, positrons, neutrinos & photons.
Eg. Pion and Kaon
iii) Baryons
 Another type of hadrons, made up of 3 quarks.
1 3 5
 Their spins are always odd half-integer values (2 , 2 , 2 , ).
3
 Have masses equal to greater than the proton
 E.g. Protons & neutrons
 With the exception of the proton, all baryons decay in such a way that the end
products include a proton.
4.
a)
State the fundamental interactions responsible for the following decays and
provide the reasoning for your answer.
i) Delta plus (+) decays into a pion (+) and a neutron (n) with half-life of about
1024 s.
∆ + → + + n
Strong force because the half-life is < 1020 s.
ii) The neutral kaon (K0) decays into two pions (+ and ) with half-life of about
1010 s.
 0 → + + −
Weak force because the half-life is  1010 s.
b)
Explain the three conservation laws applied only in particle physics.
Conservation of baryon number
 Whenever a nuclear reaction or decay occurs, the sum of the baryon numbers before
the process must equal the sum of baryon numbers after the process.
 An equivalent statement: the net number of baryons remains constant in any process.
 To apply conservation of baryon number, assign baryon number B = +1 for all baryons,
B = 1 for all antibaryons, & B = 0 for all other particles.
Conservation of lepton number
 Three conservation laws involving lepton numbers, one for each variety of lepton:
 The law of conservation of electron-lepton numbers (lepton flavour conservation)
states that the sum of the electron-lepton numbers before a reaction or decay must
equal the sum of the electron-lepton numbers after the reaction or decay. [similar
statement for muon-lepton & tau-lepton]
 The electron & the electron neutrino are assigned a positive lepton number, Le = +1.
 The antileptons e+ & ̅ e are assigned a negative lepton number, Le = 1.
 All others (the muon & tau families) have Le = 0.
Conservation of strangeness
 The law of conservation of strangeness states that whenever a nuclear reaction or
decay occurs, the sum of the strangeness before the process must equal the sum of the
strangeness numbers after the process.
4
 The slow decay of strange particles can be explained by assuming that the strong &
electromagnetic interactions obey the law of conservation of strangeness but the weak
interaction does not.
c)
Briefly explain what is meant by Quantum Chromodynamics.
 Quantum Chromodynamics (QCD) is the general theory of how quarks interact with
each other.
 In QCD the color charge carried by each quark is responsible for the strong force
between the quarks.
 Basic color charge interaction: like colors repel, opposite colors attract
d)
State 3 areas of research and development carried out by Nuclear Malaysia.






Medical Technology
Waste, Water & Environment
Agro Technology
Industrial Technology
Radiation Technology
Nuclear Reactor Technology
Any 3
5
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