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Nuclear_L2 & Atomic Bombs

Properties of a b g, geiger counter, half life, decay series, dosage, effect on humans
by

Emma van Leeuwen

on 18 February 2016

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Transcript of Nuclear_L2 & Atomic Bombs

Properties of Alpha, Beta and Gamma
Radiation
Nuclear physics
Alpha particle
3 types of natural radiation:
Alpha, Beta and Gamma
Radiation
come from the
nucleus
-> dangerous, but detectable
2 protons and 2 neutrons
Beta particle
Neutron decays into a proton, electron and anti-neutrino
Gamma rays
Shielding
Incorrect ratio for size of particles
Incorrect ratio of mass of particles
Unable to demonstrate the speed of the alpha and beta particles, and that of gamma rays
Unable to demonstrate the ionising property of the alpha and beta particles
Limitations
Parent
Daughter
In any nuclear reaction
atomic and mass
numbers are

conserved
Electron
Too many neutrons in nucleus!
Too many protons
Proton decays into a neutron,
positron
and a neutrino
Beta positive decay
8
EM radiation from nucleus
Writing Formulas
In any nuclear reaction
atomic and mass numbers are conserved
NB: If no. of protons changes element changes
-> deflected by magnetic field
-> deflected by magnetic fields
(Helium nucleus)
No charge, no mass
Travel at speed of light (3x10 m/s)

Half life = time required for half of the remaining sample to decay

Cannot determine when a specific atom will decay

Each nucleus has a 50/50 chance of decaying during each half life
Carbon dating
C-14 levels are maintained in the body & plants when alive
When dead, use amount left to date
NB: Can't use on dinosours - C14 too short hl for that
date the rocks they're surrounded by
Use for upto 60,000 year old things
Artificial Irradiance/transmutaion
Create artificial radioactive decays by smashing protons/neutrons into nuclei
Also used to create new elements
Dangers & Dosage
How dangerous?
1) What kind of radiation?
2) How close are you?
3) Do you have protection?
4) What's its half life?
5) Time of exposure?
Measuring radiation
Absorbed dose (Gy)
=
energy absorbed (J)
mass of tissue (kg)
Dose equivalent (Sv)=
Absorbed dose x Quality factor
Decay Series
Rutherford (1919)
Alpha particle
Beta particle
Gamma rays
Penetration
Types of decay
3 main types of "natural'' nuclear decay:
alpha, beta and gamma
Other nuclear decays ( incl. artificial) include:
neutrons, protons, positrons, anti-protons
Rip electrons off atoms
Slow with each ionisation
Can crash into electrons and bounce off atoms
Slow with each collision
Can excite nuclei to ionise electrons
But low chance as atom mostly empty space
High energy EMR
Alpha particles 20
Neutrons (>10keV) 10
Beta particles 1
Gamma rays 1
X-rays 1
Radiation Quality factor
Medical Physics
that's what a technetium cow looks like from the inside!
in the middle, there would be (this is a dummy...) the Mo-99 mother, fixed into a rod. as it decays, free Tc-99m builds up in the chamber. by putting an evacuated glass on the top, the sterile saline solution (bottom, empty now) gets sucked through the generator and eluates the technetium. the whole thing is shielded by lead, as the (radio-) activity is within the giga-becquerel range (billions of decays every second).
Radiotherapy
Irradiate
inject
inhale
Measuring Radiation
Radioactivity:
amount of ionising radiation released
units: Curie (Ci) or becquerel (Bq)
Exposure:
Amount of radiation traveling thru the air
units: Roentgen (R) or coulomb/kg (C/kg)
Absorbed dose:
Amount of radiation absorbed by a person
units: radiation absorbed dose (rad), gray (Gy)
Dose equivalent:
Combines radiation absorbed with the medical effect of that type of radiation -> best indicator of danger
units: roentgen equivalent man (rem), sievert (Sv)
Medical tracer isotope must be...
Short half life means radioisotope made on-site by 'Radioactive cow'
Mother long hl, daughter short
drain daughter = 'milking the cow'
Ionizing radiation works by damaging the
DNA of exposed tissue leading to cellular death
Radiation Therapy
& Ionisation
How far it gets without hitting something
How easily it removes electrons
(How to stop it)
http://phet.colorado.edu/en/simulation/radioactive-dating-game
Carbon dating
C-14 levels are maintained in animals & plants when alive
When dead it decays -> use amount left to date
Works on things up to 60,000 years old
http://www.onlinemathlearning.com/nuclear-energy.html
Videos
http://www.uraweb.org/reports/skoog.pdf
Kinda crap activities
Ionisation + penetration power
Recap
alpha:
He
4
2
mass no. down 4
atomic no. down 2
238
92
U
Th +
234
90
->
?
?
2
234
90
Th
Pa + + v
234
?
->
?
0
-1
-
252
98
?
Cm +
?
?
->
He
4
?
Beta decay of 212-Lead
Alpha decay of 232-Thorium
Examples:
Half-life equation applies for:
number of atoms
mass
activity (1 Bq = 1 decay/s)
It is not affected by any change in physical or chemical conditions
How much is too much?
Absorbed dose
=
energy absorbed
mass
_
_
_
_
_
_
_
Absorbed dose:
amount of radiation received
Dose equivalent:
takes type of radiation into account - best indication of danger
Approx quality factors:

gamma, xrays
beta
slow neutrons
fast neutrons
alpha
1
1
3
10
10 to 20
Chem:
13.6 eV
Hydrogen ion and free electron
Phys:
28,300,000 eV
+
+
free protons and neutrons
ionisation
fission
or bring them together
(fusion)
-> 28 MeV released!
A nucleus weighs less than the sum of its parts!!
Energy
released
when nucleons combined (mass lost)
or
Energy
needed
to separate nucleons
(mass added)
Mass Defect
Mass number vs Binding Energy per nucleon
Energy released by fission
Energy released by fusion
DS: Energy from the nucleus
Fe most stable
more binding energy/nucleon <-> less mass/nucleon
Deuterium (H-2) has 1.115 MeV of BE per nucleon. What energy is released when it is fused?
What amount of energy is released as 239-Pu is fissionerised (?) into 144-Pm and 92-Zr?

Find total binding energy of all atoms:
get E/nucleon from graph
x by mass number

Find difference in energy before and after
Ereleased = sum(Eproducts) - sum(Ereactants)

Method
Examples
Pu-239 (BE 8.7 MeV per nucleon) is broken into Pm-144 (9.5 MeV per nucleon) and Zr-92 (10.1 MeV per nucleon). What amount of energy is released for one fission event?
s
U-235 decays into Pb-82 after a long series of alpha and beta decays. Write the single decay equation for this decay chain.
Example
WS: effect of radiation on the body
Alexander Litvinenko 1962-2006
Polonium -210
Sasha died Nov 23rd 2006
"I want the world to see what they did to me"
7th Oct 2006
+ E
+ E
Mass energy equivalence
Break up (fission) to get E
Put together (fusion) to get E
Thermonuclear fusion in stars
Nuclear fission
strong force wins
critical deformation
Electrostatic force wins
Chain reaction
Natural Uranium ore
Only 1 part in 140 is U-235
Cattenom Nuclear Power Plant
France
Applications:
1) Nuclear power
2) Nuclear weapons
Critical mass
Need large volume-to-surface-area ratio....
sustained chain reaction :)
maybe, maybe not
...or neutrons escape
no chance.
Bomb designs
subcritical + subcritical =
Possible decays of Uranium-235:
Shock wave
nuclear radiation
Nuclear winter
EMP
thermal radiation
Radioactive fallout
Effects of nuclear bombs
Fusion
http://www.zamandayolculuk.com/cetinbal/HTMLdosya1/atomicnucleus.htm
good site
Main departments of the Manhattan Project
exponential increase
Gun-type assembly method
Implosion assembly method
UNSHIELDED ELECTRONICS
+ E
Break up (fission) to get E
+ E
Put together (fusion) to get E
Nuclear fission
Blue: X-ray (4-6 keV),
Green: X-ray (0.3-1.4 keV)
Yellow: Optical; The optical image reveals 10,000 degrees Celsius gas where the supernova shock wave is slamming into the densest regions of surrounding gas.
Red: Infrared

Thermonuclear fusion in stars
Nuclear fusion reactors?
H-bomb
Implosion type fission bomb...
... temp raises beginning fusion reaction
What makes this so hard to achieve?
Electrostatic repulsion!
=> Need to create temperatures of
millions
of degrees Celsius.
So nuclei need to be moving v. fast...
But how to create high enough temp on Earth?????
Ionising
: can knock into other atoms & dislodge e
2+ Charge
Ejecting speed: ~0.1c
Electron (& anti-neutrino) ejected from
nucleus

NOT electron cloud
-1 Charge
Ejecting speed: ~0.9c
Helium nucleus
* Alpha emitter
* Half life: 138 days
* if ingested 50 ng is enough kill
-> ionise atoms
-
-> break molecular bonds
Mass defect
= 4.03188 - 4.0017
=0.03018 amu
Where did the missing mass go??!!
Binding Energy
E = mc
2
Building the Elements
What makes this so hard to achieve?
Electrostatic repulsion!
=> Need to create temperatures of
millions
of degrees Celsius...
So nuclei need to be moving v. fast...
Building the Elements
Stars only can fuse up to Iron
Less and less energy is released when heavy elements are fused...
... but elements heavier than iron require an INPUT of energy to be fused,
...So Stars have to fuse them faster...
So even the largest stars must loose against gravity in the end....
Elements >Fe are created in Supernova:
239-Pu
~8.7
144-Pm
92-Zr
~10.1
~9.5
239-Pu
~8.7
144-Pm
92-Zr
~10.1
~9.5
Can find BE/nucleon from graph:
How can we break up the nucleus?
Why doesn't Uranium ore explode?
U235 is Fissile, U238 is not
Amount of U235 is increased via "enrichment" processes
Stars fight gravity with nuclear fusion
- the death of a massive star
3-4% Enrichment (reactor grade)
>90% Enrichment (weapons grade)
http://phet.colorado.edu/en/simulation/nuclear-fission
10 x hotter than Sun's core
U235
H2 and H3
http://www.nuclearsecrecy.com/nukemap/
http://phet.colorado.edu/en/simulation/nuclear-fission
Stars can fuse elements up to Fe
Full transcript