原子裡面有什麼?
『從原子到宇宙』課程第三週
胡維平
國立中正大學化學暨生物化學系
9/29/2011
Ernest Rutherford
1871-1937
1. Discovered the true nature of the radioactive
radiation, a, b, and g rays. Invented isotope
dating.
2. His a particle scattering experiments (1909)
revealed the true nature of the atomic
structure.
3. Rutherford became in 1917 the first person
to deliberately transmute one element into
another, when he converted nitrogen into
oxygen through the nuclear reaction 14N + α
→ 17O + proton.
Nuclear Particles
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3
拉賽福 a 粒子撞擊實驗 (1910)
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James Chadwick
1891-1974
英國
Discovery of neutron in 1932
Deep-Penetrating g-way like radiation
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原子和次原子粒子
• 原子 1-5 Å, Nucleus: 0.00001-0.0001 Å
1Å = 0.00000001 cm
• 構成物質的三種基本粒子:
質子(proton), 中子(neutron), 電子(electron)
• 電荷:
• p = +1, n = 0, e– = –1
• 質量
• p = 1 amu, n = 1 amu, e– = 0.00055 amu
• 6.02×1023 個質子 = 1 公克
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Why are the atomic nuclei stable?
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Radioactive Stability
• Nuclides with 84 or more protons are unstable.
• Light nuclides are stable when Z equals A – Z
(neutron/proton ratio is 1).
• For heavier elements the neutron/proton ratio
required for stability is greater than 1 and increases
with Z.
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10
The Zone of
Stability
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12
Types of Radioactive Decay
• Alpha production ( ):
• Beta production ( ):
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Geiger Counter
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Types of Radioactive Decay
• Gamma ray production ( ):
• Positron production:
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15
Types of Radioactive Decay
• Electron capture:
Inner-orbital electron
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16
Decay Series (Series of Alpha and Beta Decays)
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Nuclear Transformation
• The change of one element into another.
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13
249
98
Al + He 
4
2
30
15
P+ n
263
Cf + 188 O  106
Sg + 4 01 n
Alchemists’ Dream!?
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1
0
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Nuclear Fission and Fusion
•
Fusion – Combining two light nuclei to form a heavier, more
stable nucleus.
•
Fission – Splitting a heavy nucleus into two nuclei with
smaller mass numbers.
1
0
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n+
235
92
U
142
56
19
Ba +
91
36
1
0
Kr + 3 n
Nuclear Fission
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20
Proton Chain Fusion
Energy Released = 25 MeV
C + O2  CO2, DH = 10 eV
Small mass deficit in nuclear reactions translates to large energy release !
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Nuclear Binding Energies
stronger binding,
more mass deficit
more energy released
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Chain Reactions in Nuclear Fission
Critical Mass = 52 kg, 17 cm in diameter
>= critical mass, self-sustained fission
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The “Little Boy”
Mass = 64 kg of 235U
Only 0.6 g of mass was converted to energy
by E = m c2
The mushroom cloud of the atomic
bombing of Nagasaki, Japan on
August 9, 1945 rose some 18
kilometers (11 miles) above the
bomb's hypocenter. ~15 kiloton of
TNT
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Schematic Diagram of a Nuclear Power Plant
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Schematic Diagram
of a Reactor Core
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What particles are really elementary (indivisible)?
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Deep Atomic Structure
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Inner Structure of Nucleons
Proton (+)
Neutron (0)
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Particles of Matter and Messenger
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The Standard Model
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Close-Up View of a Helium Atom
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Particle and Forces in Standard Model
String Theory in 11-D?
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Summary of current knowledge on particles and forces
All elementary particles are either bosons or fermions (depending on their
spin). The spin-statistics theorem identifies the resulting quantum statistics
that differentiates fermions from bosons. According to this methodology:
Particles normally associated with matter are fermions. They have halfinteger spin and are divided into twelve flavours. Particles associated with
fundamental forces are bosons and they have integer spin.
Fermions:
Quarks — up, down, charm, strange, top, bottom
Leptons — electron neutrino, electron, muon neutrino, muon, tau
neutrino, tau
Bosons:
Gauge bosons — gluon, W and Z bosons, photon
Other bosons — Higgs boson, graviton
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Gravitational force
Gravitational force, the weakest of the four forces, is about 10-36
times the strength of the strong nuclear force.The messenger particle
of gravitational force is the graviton. It has not been experimentally
verified, mainly because it is extremely hard to find the smallest
denomination of the weakest force. Recent calculations show that it
will likely be massless.
Gravitational force is always attractive and that's what hold our
universe together.
And somehow scientists are trying to include this in to a grand
unified theory, where they successfully included the other three ..
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Electromagnetism
Its strength is a bit less than strong nuclear force, and unlike gravitational
force, it has both attractive and repulsive nature and is of infinite range-like gravity.
If gravitational force is what responsible for keeping up our universe
together, EM is responsible for keeping up electrons around
nucleus(attraction force between nucleus and electrons).
It is the force that causes the interaction between electrically charged
particles; the areas in which this happens are called EM fields, also
known as B fields in physics classes.
The particle that carry electromagnetism is the photon, a massless
particle that travels at a speed of 299 792 458 m/s or 299 972 km/s .
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The Weak Nuclear Force
The weak nuclear force is one of the less familiar fundamental forces. It
operates only on the extremely short distance scales found in an atomic
nucleus. The weak force is responsible for radioactive decay. In actuality,
it is stronger than electromagnetism, but its messenger particles (W and
Z bosons) are so massive and sluggish that they do not faithfully transmit
its intrinsic strength.
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The Strong Nuclear Force
Like the weak force, its range is limited to subatomic
distances. Guarks which forms the protons and neutrons
stick together through this force. This force is carried by
gluons and is a massless particle, as it glues the quarks
together. Gluons also acts on other gluons and that is why, as
the distance increases the force increases at subatomic level .
Attempts have been going on to unify all these four
fundamental forces to form a grand unified theory, and had
successfully unified the other three, excluding gravity. Hope
they will succeed soon.
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Large Hardon Collider (LHC), Geneva
27 km, $ 4.4 billion
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Compact Muon Solenoid (CMS) Detector at LHC
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Fermilab, Chicago
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