Physics of 21st Century

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Physics of 21st Century

• Moskov Amarian
• Department of Physics
• Old Dominion University

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Introduction

• In this lecture we discuss some aspects of
  nuclear
• physics
• Research in nuclear physics is an integral part
  of the search for knowledge and understanding of
  the world in which we live. All matter is
  composed of a hierarchy of building blocks.
• Living creatures, as well as our inanimate
  surroundings, are made of molecules, which are in
  turn made of atoms, whose mass resides almost
  entirely in the nuclei.
• The nuclei are composed of protons and neutrons,
  which ultimately consist of quarks and gluons.

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• The science of nuclear physics concerns itself
  with the properties of nuclear matter.
• Such matter constitutes the massive centers of
  the atoms that account for 99.9 percent of the
  world we see about us.
• Nuclear matter is within the proton and neutron
  building blocks of these nuclei, and appears in
  bulk form in neutron stars and in the matter that
  arose in the Big Bang.
• Nuclear physicists study the structure and
  properties of such matter in its various forms,
  from the soup of quarks and gluons present at the
  birth of our universe to the nuclear reactions in
  our Sun that make life possible on Earth.

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Rutherford experiment

• From angular distribution of rescattered ?
  -particles Rutherford concluded existence of
  positively charged core of atom then called
  nucleus
• The size of the nucleus was much smaller(10-14m)
  than size of the atom (10-10m)

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Angular distribution of scattered ?-particles
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Models of Atom
Rutherford model of atom
Thomson model of atom
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Nuclear Stability
Proton unstable
Stable nuclei
Neutron unstable
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?-decay
During beta-minus decay, a neutron in an atom's
nucleus turns into a proton, an electron and an
antineutrino. The electron and antineutrino fly
away from the nucleus, which now has one more
proton than it started with. Since an atom gains
a proton during beta-minus decay, it changes from
one element to another. For example, after
undergoing beta-minus decay, an atom of carbon
(with 6 protons) becomes an atom of nitrogen
(with 7 protons).
Homework Explain ? decay
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Homework ?-decay
Full equations
Solve the following
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Binding energy per nucleon
EB(Z,N) ZMpNMn - M(Z,N)

• Nuclei with the largest binding energy per
  nucleon are the most stable.
• The largest binding energy per nucleon is 8.7
  MeV, for mass number A 60.
• Beyond bismuth, A 209, nuclei are unstable.

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Fusion and Fission Reactions
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Fusion Reactions
To obtain a fusion reaction, we must bring two
nuclei sufficiently close together for them to
repel each other, as they are both charged
positively.
A certain amount of energy is therefore vital to
cross this barrier and arrive in the zone,
extremely close to the nucleus, where there are
the nuclear forces capable of getting the better
of electrostatic repulsion. The probability of
crossing this barrier may be quantified by the "
effective cross section". The variation against
interaction energy expressed in keV of effective
cross sections of several fusion reactions is
shown on the graph .
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Fission Chain Reaction
At each step energy is released !
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Abundances of elements
Solar system abundances of the elements. Note
that the 14 ratio of helium to hydrogen (by
weight) is what the Big Bang theory would
predict. But other, heaver elements must come
from other processes.
Abundances of the elements in Earth. Comparison
with the figure above shows that Earth has lost
most of its primordial hydrogen and helium.
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Nuclear fusion chain in the Sun
The energy radiated from solar surface is
produced in the interior of the Sun by fusion of
light nuclei to heavier, more strongly bound
nuclei.
Homework Calculate the released energy.
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Nuclear Fission
Homework Calculate the released energy
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Electricity from Nuclear Fission
Nuclear power plants account In a nuclear
reactor, enriched Uranium, which is Uranium-238
with a high concentration of Uranium-235,
undergoes a process known as Induced Nuclear
Fission. Nuclear Fission occurs when an atom of
a fissionable material is struck by a neutron and
splits into two lighter atoms, releasing a
massive amount of heat and gamma radiation. The
heat is used to boil water, producing steam used
to turn a generator.
17 percent of the worlds power.
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Power Plants
This is the Byron nuclear power plant in
Illinois with two reactors, one capable of
producing 1,194 Megawatts and the other 1,162
Megawatts. The cooling towers in the background
are not releasing smoke. The fog coming out is
merely condensed water vapor from cooling the
return steam from the turbines. This steam is not
coming out of the nuclear reactor.
There are several heat exchangers in between the
reactor water and the cooling water. Once cooled,
the water is circulated back through the reactor
to be heater to steam again.
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The Sun Shines
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Stars Shine
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and its all nuclear physics
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and its all nuclear physics

• 1905 Einstein finds Emc2
• 1920 Aston measures mass defect of helium (!
  4ps)
• 1920 Nuclear Astrophysics is born with Sir
  Arthur Eddington remarks in his presidential
  address to the British Association for the
  Advancement of Science

Certain physical investigations in the past year
make it probable to my mind that some portion of
sub-atomic energy is actually set free in the
stars If only five percent of a stars mass
consists initially of hydrogen atoms which are
gradually being combined to form more complex
elements, the total heat liberated will more than
suffice for our demands, and we need look no
further for the source of a stars energy
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The p-p chains - ppI
As a star forms density and temperature (heat
source ?) increase in its center
Fusion of hydrogen (1H) is the first long term
nuclear energy source that can ignite. Why ?
With only hydrogen available (for example in a
first generation star right after its
formation) the ppI chain is the only possible
sequence of reactions. (all other reaction
sequences require the presence of catalyst nuclei)
3- or 4-body reactions are too unlikely chain
has to proceed by steps of 2-body reactions
or decays.
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The ppI chain
Step 1
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To summarize the ppI chain
On chart of nuclides
3He
4He
2
1H
2H
1
1
2
Or as a chain of reactions
bottle neck
(p,g)
(3He,2p)
(p,e)
1H
d
3He
4He
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Sidebar A chain of reactions after a bottle
neck
Steady Flow
For simplicity consider chain of proton captures
(p,g)
(p,g)
(p,g)
(p,g)
1
2
3
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Slowbottleneck
Assumptions

• Y1 const as depletion is very slow because of
  bottle neck
• Capture rates constant (Yp const because of
  large reservoir, conditions constant as well)

Abundance of nucleus 2 evolves according to
production
destruction
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For our assumptions Y1const and Yp const, Y2
will then, after some timereach an equilibrium
value regardless of its initial abundance
In equilibrium
and
(this is equilibrium is called steady flow)
Same for Y3 (after some longer time)
and
with result for Y2
and so on
So in steady flow
or
steady flow abundance
destruction rate
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Timescale to achieve steady flow equilibrium
for lconst
has the solution
with
equilibrium abundance
initial abundance
so independently of the initial abundance, the
equilibrium is approached on a exponential
timescale equal to the lifetime of the nucleus.
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Back to the ppI chain
bottle neck
(p,g)
(3He,2p)
(p,e)
1H
d
3He
4He
large reservoir(Ypconst ok for some time)
d steady flow abundance ?
S3.8e-22 keV barn
S2.5e-4 keV barn
therefore, equilibrium d-abundance extremely
small (of the order of 4e-18 in the sun)
equilibrium reached within lifetime of d in the
sun
NApd1e-2 cm3/s/mole
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For our assumptions Y1const and Yp const, Y2
will then, after some timereach an equilibrium
value regardless of its initial abundance
In equilibrium
and
(this is equilibrium is called steady flow)
Same for Y3 (after some longer time)
and
with result for Y2
and so on
So in steady flow
or
steady flow abundance
destruction rate
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Timescale to achieve steady flow equilibrium
for lconst
has the solution
with
equilibrium abundance
initial abundance
so independently of the initial abundance, the
equilibrium is approached on a exponential
timescale equal to the lifetime of the nucleus.
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3He equilibrium abundance
(p,g)
(3He,2p)
(p,e)
1H
d
3He
4He
different because two identical particles
fusetherefore destruction rate l3He3He
obviously NOT constant
but depends strongly on Y3He itself
But equations can be solved again (see Clayton)
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3He has a much higher equilibrium abundance than
d
- therefore 3He3He possible
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Hydrogen burning with catalysts

• ppII chain
• ppIII chain
• CNO cycle

1. ppII and ppIII
once 4He has been produced it can serve as
catalyst of the ppII and ppIII chainsto
synthesize more 4He
out
in
(e-,n)
(p,4He)
(4He,g)
3He
7Be
7Li
4He
ppII (sun 14)
(b)
(p,g)
decay
8B
8Be
24He
ppIII (sun 0.02)
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(Rolfs and Rodney)
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Electron capture decay of 7Be
Why electron capture
QEC862 keV
only possible decay mode
QbQEC-1022 -160 keV
Earth
Capture of bound K-electron
T1/277 days
Ionized fraction Capture of continuum electrons
Sun
depends on density and temperature
T1/2120 days
Not completely ionized fraction capture of bound
K-electron
(21 correction in sun)
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Summary pp-chains
ppI
ppI ppII ppIII
7Be
8Be
6Li
7Li
Why do additional pp chains matter ?
3He
4He
pp dominates timescale
2
1H
2H
1
1
2
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CNO cycle
Ne(10)
F(9)
O(8)
N(7)
C(6)
3
4
5
6
7
8
9
neutron number
All initial abundances within a cycle serve as
catalysts and accumulate at largest t
Extended cycles introduce outside material into
CN cycle (Oxygen, )
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Competition between the p-pchain and the CNO
Cycle
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Summary pp-chains
ppI
ppI ppII ppIII
7Be
8Be
6Li
7Li
Why do additional pp chains matter ?
3He
4He
pp dominates timescale
2
1H
2H
1
1
2
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CNO cycle
Ne(10)
F(9)
O(8)
N(7)
C(6)
3
4
5
6
7
8
9
neutron number
All initial abundances within a cycle serve as
catalysts and accumulate at largest t
Extended cycles introduce outside material into
CN cycle (Oxygen, )
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Competition between the p-pchain and the CNO
Cycle
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Neutrino emission
0.27 MeV
E0.39,0.86 MeV
6.74 MeV
ppIII loss 28
ppII loss 4
ppI loss 2
note /Q0.27/26.73 1
Total loss 2.3
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2 neutrino energies from 7Be electron capture ?
7Be e- ? 7Li ne
En
En
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Continuous fluxes in /cm2/s/MeV Discrete fluxes
in /cm2/s
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Neutrino Astronomy
Photons emitted from sun are not the photons
created by nuclear reactions (heat is
transported by absorption and emission of photons
plus convection to the surface over
timescales of 10 Mio years)
But neutrinos escape !
Every second, 10 Bio solar neutrinos pass through
your thumbnail !
But hard to detect (they pass through 1e33 g
solar material largely undisturbed !)
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First experimental detection of solar neutrinos
1964 John Bahcall and Ray Davis have the idea to
detect solar neutrinos using the reaction

• 1967 Homestake experiment starts taking data

• 100,000 Gallons of cleaning fluid in a tank 4850
  feet underground
• 37Ar extracted chemically every few months
  (single atoms !) and decay counted in counting
  station (35 days half-life)
• event rate 1 neutrino capture per day !

• 1968 First results only 34 of predicted
  neutrino flux !

solar neutrino problem is born - for next 20
years no other detector !
Neutrino production in solar core T25
nuclear energy source of sun directly and
unambiguously confirmed
solar models precise enough so that deficit
points to serious problem
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Neutrino Astronomy
Photons emitted from sun are not the photons
created by nuclear reactions (heat is
transported by absorption and emission of photons
plus convection to the surface over
timescales of 10 Mio years)
But neutrinos escape !
Every second, 10 Bio solar neutrinos pass through
your thumbnail !
But hard to detect (they pass through 1e33 g
solar material largely undisturbed !)
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First experimental detection of solar neutrinos
1964 John Bahcall and Ray Davis have the idea to
detect solar neutrinos using the reaction

• 1967 Homestake experiment starts taking data

• 100,000 Gallons of cleaning fluid in a tank 4850
  feet underground
• 37Ar extracted chemically every few months
  (single atoms !) and decay counted in counting
  station (35 days half-life)
• event rate 1 neutrino capture per day !

• 1968 First results only 34 of predicted
  neutrino flux !

solar neutrino problem is born - for next 20
years no other detector !
Neutrino production in solar core T25
nuclear energy source of sun directly and
unambiguously confirmed
solar models precise enough so that deficit
points to serious problem
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Are the neutrinos really coming from the sun ?
Water Cerenkov detector
high energy (compared to rest mass) - produces
cerenkov radiation when traveling in water (can
get direction)
nx
nx
neutral current (NC)
Z
e-
e-
Super-KamiokandeDetector
ne
ne
chargedcurrent (CC)
W-
e-
e-
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Astronomy Picture of the Day June 5, 1998
Neutrino image of the sun by Super-Kamiokande
next step in neutrino astronomy