Lecture 52 bio Fermi

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Lecture 52 bio Fermi
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Enrico Fermi
Developed theory of beta decay 1938 Nobel Prize
in physics Harassed politically for Jewish wife
went to US Built first controlled Nuclear
fission chain reaction in 1942 Worked on atomic
bomb at Los Alamos
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Check homework
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Check homework

• Read pages 642 647
• Do problems 1-11 on page 647

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Return papers
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Hand back quiz and grade the quizzes
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Nuclear the science of the change of the nucleus
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Bacquerel put the mysterious mineral on top of
the plate and it effected the film even though
the film case was not opened

• Bacquerel was too busy with his study of
  fluorescence so he gave the research of the
  mysterious minerals to his assistant Mrs Curie

Mrs Curie called the phenonemena radioactivity
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Through studies it was learned that this
radioactivity was caused by the nucleus of an
atom that shoots out alpha particles, beta
particles and gamma rays
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We know the nucleus made up of

• Electrons mass of 0 negative charge
• Protons mass of 1 positive charge
• Neutrons mass of 1 neutral charge

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As we have said in the past

• The number of protons dictates what something is
• 7 protons
• 9 protons

The number of neutrons may make it heavier or the
number of electrons will give it a particular
charge but the number of protons dictates what it
is
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If we could add protons, one by one,
experimentally to an atom we would proceed to
form one element to the next.

• The mass of the elements do not however increase
  in mass quite so nicely.
• The strange and sometimes unpredictable
  increases in mass of elements are due to the
  number of neutrons that are present in the
  nucleus.

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To designate the weight of an element when
writing the complete name of an element you write
the atomic symbol

• atomic number as a subscript and the mass number
  as the superscript

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• How many neutrons
• How many protons
• If it is neutral
• How many electrons

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• How many neutrons
• How many protons
• How many electrons

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Not all atoms of the same element have the same
mass.

• all forms of Lithium have 3 protons, however
  some lithium have 3 neutrons and some have 4
  neutrons.

If there is more than one mass number for a
particular element the elements are considered
isotopes.
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You name a element specifically by stating the
element and then the mass

• Carbon 13 has a mass of 13
• Neon 23 has a mass of 23
• polonium 218
• Plutonium 240
• radium 226

How many protons how many neutrons
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While there are 110 or so elements there are 1500
isotopes of those 110 elements

• Carbon has two isotopes.
• Carbon 12 6 protons and 6 neutrons
• carbon 13 6 protons and 7
  neutrons
• Nitrogen has two isotopes
• Nitrogen 14 7 protons and 7
  neutrons
• Nitrogen 15 7 protons and 8
  neutrons

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The general name for the nucleus of an atom is
called the Nuclide

• Nucleus means center
• Nuclide means center of atom

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Most of the isotopes are stable meaning they do
not have a tendency to alter themselves to be in
a more stable state.

• Other isotopes are unstable. These unstable
  isotopes to need to change to become stable. In
  order to be more stable the isotope will lose or
  in some way eject part of the nuclide and in
  doing so decrease the number of protons or
  neutrons. By decreasing the number of protons
  the element itself changes.

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When the number of protons change and the atomic
number changes then the element changes and this
is called a transmutation. Nuclei that
undergo transmutation are said to be radioactive
or undergoing radioactive decay.
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For a unstable nucleus to become stable the
element must obtain the correct proton to neutron
balance. If that balance does not exist the
nucleus will eject a particle until the stability
is obtained.
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It is kind of like when you eat too much and need
to barf you hurl until you feel better

• An unstable atom will barf until it is stable
  but what cookies, what chunks does it hurl????

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Atoms spew typically one of four things

• 1) alpha radiation the nucleus of a helium
  atom it has a 2 charge has a weight of 4 and
  contains 2 protons 2 neutrons
• 2) beta radiation
• a) e or an electron has a 1 charge, no mass
  and contains 1 electron.
• b) positron a positive electron with a charge
  of 1 no mass
•  3) gamma radiation, no mass no charge is like
  light and high power radio waves
• 4) Neutron loss or neutron capture no charge
  change but mass will alter by a unit of one
•  

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Dont mix up electron stability and the loss and
or gain of electrons where cations or anions are
created and nuclear radiation .. These are two
different issues
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One more thing about alpha beta and gamma
radiation. There is ionizing and no ionizing

• Ionizing radiation is radiation that puts a
  charge on what it hits. Most ionizing radiation
  is high power gamma radiation.

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Radioactive Decay 

• Nuclear decay is a exothermic reaction, it is the
  process where a atom goes from a unstable state
  into a more stable state
• And it becomes stable by spewing out radioactive
  puke

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In nuclear decay the initial nucleus is called
the parent nucleus. And the new nucleus is
called the daughter nucleus.  
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One kind of nuclear decay is when an alpha
particle is ejected. Remember that an alpha
particle is 2 protons and 2 electrons with a 2
charge and is written 
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What would happen to an atom that underwent alpha
particle decay

• It would lose how many protons?
• It would lose how many neutrons?
• It would lose how much in overall mass?

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To show radioactive decay of thorium by alpha
particle decay in an equation type format you show
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• 1)     Write an equation to represent the decay
  of radium 226 by alpha emission
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• 2)     Write an equation to represent the decay
  of plutonium 240 by alpha emission

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• 3) The decay products from a nuclear reaction are
  an alpha particle and polonium 218. What is the
  parent nuclide in this reaction?

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So a alpha particle will stabilize a nucleus
that has too many protons.
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What if instead of losing an alpha particle a
beta particle is radiated out of the nucleus?????
A beta particle is an electron A particle that
has a mass of 0 and a charge of -1
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So where does the beta particle (electron) come
from. Are they stuck in-between the neutrons
and protons of the nucleus like lone socks stuck
between shirts in the laundry only to fall out
when you least expect them
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No..

• Like some kind of perverted worm the electron is
  spewed from the inside of a neutron
• does the neutron lose any mass when it spits the
  electron out???????

The neutron stays the same mass but because the
neutron kicks out a negative charge it is no
longer neutral.
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The neutron mutates into a proton

• If the neutron becomes a proton then the element
  changes into a new element

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How would you write the chemical equation for the
beta emission of Neon 23
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What if instead of losing an alpha particle a
beta particle is radiated out of the nucleus?????

• If a beta particle radiates does the nucleus lose
  any mass????

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Sometimes an electron falls inside
Electron capture where an electron goes inside a
nucleus and changes a proton into a
neutron Neutron capture where a neutron is
absorbed
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Gamma and the tent example
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? 10n ? 14256Ba 9136Kr 3 10n
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We now see that some atoms have nucleuses that
not only have enough neutrons to neutralize the
protons, they have soooo many that the nucleolus
is actually unstable
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These unstable nucleases will spew out parts of
the oversized nucleus to obtain the proper
neutron to proton ratio and become more stable .

• This occurs via the gain or loss of alpha
  particle beta particle neutron or gamma ray

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This atomic ejection process is called
radioactive decay

• If the decay causes the atom to change from one
  element to another (loss or gain of a proton)
  then it is termed
• Transmutation.

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So what is this ratio of protons to neutrons that
will allow a nucleus to be stable????

• 1 to first 30 it is 1 to 1
• for 30 to 60 it is 1 to 1.5
• and for 60 to 83 it is 1 to 2

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Graphing this you get a band of stability

• If you deviate from this band of stability the
  nucleus will be unstable.

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This band of stability illustrates the proper
proton to neutron ratio to allow nuclear
stability.
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radioactive
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These large atoms with over 83 protons are in a
constant state of imbalance and shed part of the
atomic mass from the inside of the nucleus in
order to become stable. This breaking off and
expulsion of particles form the nucleus is called
radioactive decay.
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A more radical form of decay is when instead of
simply ejecting an alpha or beta particle the
atom fractures in half.
This is called nuclear fission
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Here U235 captures a single neutron and then
undergoes fission into two daughters and two
additional neutrons
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The result of fission is typically radioactive
unbalanced daughter nuclei
Radioactive fallout Radioactive waste
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We have discussed nuclear decay and
transmutationand now nuclear fission
(to split)

• Another nuclear reaction involves the actual
  coming together of atomic particles. This
  process is called fusion.

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Fusion is where a new atom is formed from the
addition of individual nuclei

• Do you think there is a greater chance for two
  large parent nuclide will fuse to make a stable
  daughter nucleus
• or
• do you think small parent nuclei will fuse?????

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Small nuclei fuse

• The small nuclei are hydrogen atoms of a special
  kind

Heavy hydrogen
Isotopes of hydrogen
Hydrogen Deuterium tritium
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Small heavy hydrogen parent nuclei will fuse
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11H 31H ? ?

• 23892U 42He ? ? 10n

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Radioactive decay involves the progressive
radiation of alpha or beta particles in order
that a nucleus becomes more stable.
Fission involves the incredible splitting of an
atoms usually because of the capture of a
particle resulting in INCREDIBLE fragmentation
Fusion is the union and then the rearrangement of
small atoms
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Nuclear Energy

• On the left is an animation that represents
  fission.
• On the right is an animation that represents
  fusion.
• Notice the difference in the two.

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In either case Dont forget that every time an
nucleus moves to a more stable energy state by
either fusion fission or nuclear decay, energy is
given off as gamma ray radiation
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GAMMA RAY RADATION

• Is energy that is released in packets
• These packets of energy have no mass and no
  charge.
• Gamma ray radiation at lower energy levels is
  seen as light or radio waves.

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Gamma ray radiation can be the most powerful
radiation and can ionize anything it comes in
contact with.

• Gamma Ray radiation can blow through 100 feet of
  concrete while alpha particle are stopped by
  tissue paper and beta are stopped by 1 or 2 mm of
  glass

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We can see the Geiger counter identifying the
presence of gamma ray radiation

• Alpha particles are not powerful enough to get
  through the glass

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Show Geiger counter
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How a Geiger counter works

• Remember that electricity (electron) can only
  move if it can jump from one positive charge to
  another positive charge

If there are no ions around then electricity can
not move
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No current can pass
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Current can pass
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how a Geiger counter works
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So realizing that radioactive elements decay,
when will Uranium kick out the alpha particle and
undergo decay
In one second in one year in one billion years?
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We dont know when but we know on the average how
long it takes for half the material to undergo
decay

• We know that the rate of decay is not altered by
  the size of the sample, the temperature of the
  sample or the pressure of the sample

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By knowing on average how often a radioactive
material undergoes decay and Because of the
incredible consistency with which radioactivity
occurs, the rate of decay and thus the amount of
energy released by a radioactive element can be
quantitatively expressed