More Nuclear Physics

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More Nuclear Physics Neutrons and Neutrinos
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More Nuclear Physics Neutrons and Neutrinos
Nucleon particles that can be found in the
nucleus of an atom. There are two types of
nucleons Protons Neutrons
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More Nuclear Physics Neutrons
When investigating the masses of nuclei, it was
determined that nuclei could not contain only
protons. To account for this observation,
Rutherford proposed that there be a particle in
the nucleus that had mass but no charge. He
called this particle the neutron, and imagined
the neutron to be a closely paired proton and
electron. The neutron was eventually discovered
by Chadwick. Common symbol n
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More Nuclear Physics Neutrons
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More Nuclear Physics Neutrinos
Predicted in 1931 by Wolfgang Pauli. Based his
prediction on the fact that energy and momentum
did not appear to be conserved in certain
radioactive decays. He predicted that the
missing energy might be carried off, unseen, by a
neutral particle which was escaping detection. In
1934, Enrico Fermi produced a comprehensive
theory of radioactivity, which included this
hypothetical particle. Fermi called the particle
a neutrino (Italian for little neutral
one). Common symbol ? (Greek letter nu)
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More Nuclear Physics Neutrinos
No particles were detected in the reactions where
energy did not balance. Implication Neutrinos
do NOT interact with matter very easily. As a
result, neutrinos are extraordinarily hard to
detect.
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More Nuclear Physics Neutrinos
First detection occurred in 1956 Utilized
neutrinos (technically antineutrinos) predicted
to be produced by nuclear reactions in the
nuclear reactor at Savannah River, South
Carolina. Reines and Cowan experiment consisted
in using a target made of around 400 liters of a
mixture of water and cadmium chloride. The
anti-neutrino coming from the nuclear reactor
interacts with a proton of the target matter,
giving a positron and a neutron. The positron
annihilates with an electron of the surrounding
material, giving two simultaneous photons and the
neutron slows down until it is eventually
captured by a cadmium nucleus, implying the
emission of photons some 15 microseconds after
those of the positron annihilation. All those
photons are detected and the 15 microseconds
identify the neutrino interaction.
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IMB Irvine-Michigan-Brookhaven detector
underground neutrino detector in salt mine on the
shore of Lake Erie 8,000 ton Water tank USA
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IMB Irvine-Michigan-Brookhaven detector
The United States neutrino detector is 2000 feet
underground in a salt mine near Fairport, Ohio
(slightly east of Cleveland). The detector is the
collaborative effort of the Proton Decay Group of
the University of Michigan, the University of
California (Irvine) and the Brookhaven National
Laboratory. The detector is 10,000 metric tons of
highly purified water. In this pool are 2048
extremely sensitive light-detecting photo
multiplier tubes. These tubes uniformly cover the
walls, floor and ceiling of the totally enclosed
pool of ultra-pure water that measures
approximately 80' x 70' x 70'. A neutrino
travels through water faster than light travels
through water. This gives rise to an optical
shock wave (analogous to a sound wave's sonic
boom) that is perceived as a blue light,
so-called Cerenkov radiation. The array of photo
multiplier tubes senses this light and a
sophisticated computer system quantifies the
amount of light, its location within the tank and
the time that the light flashes occurred.
Physicists then interpret the meaning of the
observed light patterns. The entire complex is
2,000 feet underground so that the mass of the
earth shields the detector from stray cosmic, as
well as earth-born radiation.
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IMB Irvine-Michigan-Brookhaven detector
IMB is an acronym for a neutrino observatory
located under Lake Erie. It is run by a group of
American institutions headed by the University of
California at Irvine, the University of Michigan,
and the Brookhaven National Laboratory (hence the
acronym). IMB consists of a roughly cubical tank
about 20 meters on a side, full of water and
surrounded by 2048 photomultiplier tubes. IMB
detects neutrinos by picking up the Cerenkov
radiation generated when a neutrino collides with
either a proton or an electron (both of which are
plentiful in water). IMB is thus able to estimate
the direction of the neutrino by analyzing the
spatial arrangement of the tubes that detected
radiation. The efficiency of IMB is quite low if
100 trillion neutrinos pass through the detector,
on average only one will be detected.
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IMB Irvine-Michigan-Brookhaven detector
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Beta (ß) Decay
The neutron is not a stable particle. A neutron
will decay into a proton and what was called a
beta particle. The ß particle is now known to be
an electron
n ? p e ?
In this process, an anitneutrino is emitted.
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Beta (ß) Decay
The neutron is not a stable particle. A neutron
will decay into a proton and what was called a
beta particle. The ß particle is now known to be
an electron
n ? p e ?
Gives credibility to Rutherfords hypothesis that
the neutron was, in fact, a tightly bound proton
and electron. This explains the numbers in the
table in slide 4 (previous).
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Electron Capture
A proton can also capture an electron, forming a
neutron while emitting a neutrino.
p e ? n ?
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Radioactive Decay
Atomic Number (Z) Number of protons in the
nucleus. Atomic Mass Number (A) Number of
nucleons in the nucleus. A nucleon can be either
a proton or a neutron. Chemical elements
AZ E
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Beta (ß) Particle Notation
In nuclear processes, the ß particle is
symbolized as
0 1 ß
The electron (ß particle) is NOT a nucleon (A
0) and it is the opposite (electrically) of a
proton (Z -1).
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Radioactive Decay

• ß emission The beta particle is an electron (
  0-1 ?)
• AZ X ?

In beta decay, a neutron in the nucleus decays
into a proton and an electron. The proton stays
in the nucleus because of the strong force, the
electron drifts away from the nucleus.
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Radioactive Decay

• ß emission The beta particle is an electron (
  0-1 ?)
• AZ X ? ?? Y 0-1? photon

In beta decay, a neutron in the nucleus decays
into a proton and an electron. The proton stays
in the nucleus because of the strong force, the
electron drifts away from the nucleus.
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Radioactive Decay

• ß emission The beta particle is an electron (
  0-1 ?)
• AZ X ? AZ1 Y 0-1? photon

In beta decay, a neutron in the nucleus decays
into a proton and an electron. The proton stays
in the nucleus because of the strong force, the
electron drifts away from the nucleus.
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Radioactive Decay

• ß emission The beta particle is an electron (
  0-1 ?)
• AZ X ? AZ1 Y 0-1? photon

In beta decay, a neutron in the nucleus decays
into a proton and an electron. The proton stays
in the nucleus because of the strong force, the
electron drifts away from the nucleus. The
daughter nucleus has moved up one position on the
periodic table.
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Radioactive Decay
ß emission The beta particle is an electron (
0-1 ?) AZ X ? AZ1 Y 0-1? photon
Note if you are monitoring the radiation
provided by a gas of made up of the parent
element, the amount of radiation will be
controlled by the radioactive decay rate.
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Radioactive Decay
Amount of element X
Luminosity
Exponential Decay
Exponential Decay
Time
Time