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Energy and mementum conservation in nuclear and particle physics Gil Refael.
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Energy and mementum conservation in nuclear and particle physics Gil Refael
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Transcript of Energy and mementum conservation in nuclear and particle physics Gil Refael.
Energy and mementum conservation in
nuclear and particle physics
Gil Refael
Conservation laws:
1 2
'' 22112211 vmvmvmvm
Momentum conservation:
222
211
222
211 '
2
1'
2
1
2
1
2
1vmvmvmvm
Energy conservation:
(Elastic collision)
Conservation laws:
1 2
'' 22112211 vmvmvmvm
Momentum conservation:
222
211
222
211 '
2
1'
2
1
2
1
2
1vmvmvmvm
Energy conservation:
(Elastic collision)
Conservation laws:
1 2
')( 212211 vmmvmvm
Momentum conservation:
ndeformatioheatingEvmmvmvm 221
222
211 ')(
2
1
2
1
2
1
Energy conservation:
(inelastic collision)
21
‘Explosion type’ collision
1 2
02211 vmvm
Momentum conservation:
storedEvmvm 222
211 2
1
2
1
Energy conservation:
Radioactivity
Radioactivity and Elementary particles
Uranium (238):
Very crowded!
92 protons +
146 neutrons
+
+
+
+
+
+
+
+++
++
+
+
+
+
+
+
+
++
++
+
+ +
Radioactive “alpha” decay
Thorium
Alpha particle=Helium nuclei
eNp mmm 1840
Uranium Decay
+
+
+
+
+
+
++
++
+
0 vmvm ThTh
Momentum conservation:
storedThTh Evmvm 22
2
1
2
1
Energy conservation:
What is ?storedE Clue: Some mass disappears in the transition!
eUTh mmmm 8
8 electron masses missing!
+ +
2cME ngmissistored
c=speed of light=300,000,000 m/s
Uranium (238)
Alpha (4)
Thorium (234)
(half time: 4.46 billion years)
Another example: Plutonium
+
+
+
+
+
+
++
++
+
What is ?storedE
ePuU mmmm 11
+ +
2cME ngmissistored
c=speed of light=300,000,000 m/s
Plutonium (239)
Alpha (4)
Uranium (235)
(half time: 24,100 years)
What is the recoil speed?
Uses of Uranium and Plutonium
Uranium (235):
• Fuel for nuclear reactors.
Uranium (238):
• Fuel for nuclear reactors. • Plutonium (239) production.
Plutonium (239):
• Fuel for nuclear reactors.• Nuclear weapons…
Elementary particles: Neutron decay
Just like Uranium, the neutron itself (outside a nucleaus) is also unstable:
N
eN mm 1839
+
eN mm 1836e
ee mm
eNeP mmmm 2
22 2 cmcME engmissistored
Expect: electrons have the same energy in the end of the process.
But:
0 PPee vmvm
222 22
1
2
1cmvmvm eeePP
Every experiment gave a different result!
Neutron decay
Just like Uranium, the neutron itself (outside a nucleaus) is also unstable:
N +e
eN mm 1839
eN mm 1836
ee mm
What about momentum and energy conservation ?!?
Answer: There must be another particle!
Neutrino
Very light particle, that can go unscatteredThrough the entire galaxy!
How was this measured?
Bubble chambers
X
MagneticField
X
X
Liquid Hydrogen on the verge of becoming gas.
Particles leave trail of bubbles!
How was this measured?
Bubble chambers
+
X
MagneticField
X
X
XX
X
e
rqBmvp
Radius proportional to momentum
Proton (+1)
Neutron (0)
Aurora Borealis – aka, Northern Lights
© Jack Finch—Science Photo Library/Photo Researchers, Inc.
Fairbanks, Alaska:
Aurora Borealis – aka, Northern Lights
Kangerlussuaq, Greenland’s west coast:
(www.greenlandholiday.com)
Aurora Borealis – aka, Northern Lights
+
Proton (+1)
Fast particlesfrom the sun:
The particle hunters
How to produce new particles like the neutrino?
Make very energetic collisions between them!
This happen in particle accelerators:
Electrons are accelerated up to near the speed of light!
Monster accelerators
Fermilab in Chicago:
Monster accelerators
Cern in Geneva:
Elementary particles – Quarks and Leptons
So far: • Protons (+1)• Neutrons (0)• Electrons (-1)
But also: Neutrinos.
+
N
e
Proton itself consists of quarks:
+up
upd
up
d
- “up” quark (charge: +2/3)
- “down” quark (charge: -1/3)
Neutron:
Nup
dd
More quarks: (!)
To discover new quarks and other elementary particles:
Need energy of:
eeLHC mmE 000,000,1010~ 7 !!!
Right now searching for:
The Higgs
“The particle that gives all particles their masses…”
