Transcript Norah jones come away with me

PS 101
Kim Cohn
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2
Chapter 14-The Atomic Nucleus
Comments- Norah Jones
Fusion
somewhere
between Jazz,
Country and
Popular.
 Incredible
voice.
 “Come Away
with Me”

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Chapter 14-The Atomic Nucleus
Comments- Today’s Demo
Both balloons were filled with a gas less
dense than air.
 Consequently both balloons will float in
air.
 One balloon was filled with Helium.
 The other was filled with Hydrogen.
 Hydrogen has one proton and one electron.
 Helium has two protons and two electrons.
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Chapter 14-The Atomic Nucleus
4th Grade Standards 1
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Students know how to design and build simple
series and parallel circuits by using components
such as wires, batteries, and bulbs.
Students know how to build a simple compass
and use it to detect magnetic effects, including
Earth's magnetic field.
Students know electric currents produce
magnetic fields and know how to build a simple
electromagnet.
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Chapter 14-The Atomic Nucleus
Alpha, Beta and Gamma Rays
1 – Review
Atoms themselves are made up of three
smaller particles, the electron, the neutron
and the proton.
 The electron is the smallest of the three,
has a charge of –1 and a relative weight of
1.
 The proton and neutron have a relative
weight of about 2000 and a charge of +1
and 0 respectively.
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Chapter 14-The Atomic Nucleus
Alpha, Beta and Gamma Rays
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If the atomic number (number of protons)
is greater than 82 element emits radiation.
 Alpha particles – 2 protons and two
neutrons (he atom) charge +2
 Beta particles – an electron, charge –1
 Gamma rays – “light” whose wavelength
is very short and energy very high.
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Chapter 14-The Atomic Nucleus
Alpha, Beta and Gamma Rays
3
Alpha rays are stopped by paper.
 Beta rays are stopped by aluminum.
 Gamma rays are stopped by lead.
 Unless you ingest a radioactive compound
most radiation damage is caused by
gamma rays.
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Chapter 14-The Atomic Nucleus
Effects of Radiation on Humans
Natural radiation from bricks, stones and
cosmic rays is always present.
 The higher you go the more radiation you
get.
 We tolerate most this radiation.
 Naturally occurring radon (222) heavy gas
is dangerous.
 Coal industry contributes more radiation
than nuclear power.
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Chapter 14-The Atomic Nucleus
Tracers
Can make elements radioactive by
bombarding elements with neutrons and
other particles.
 Can use radioactive elements to trace path
of materials in plants and humans.
 Fertilizer uptake.
 CAT scans.
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Chapter 14-The Atomic Nucleus
Nucleus Revisited
Review- the nucleus of an atom (the total
number of protons and neutrons at the
center of an atom) is surrounded by
electrons.
 Protons and neutrons are composed of
even more elementary particles such as
quarks and leptons.
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Chapter 14-The Atomic Nucleus
Second Demo
Here is a Geiger counter.
 The frequency of the beeps is an indication
of how much radiation is being detected.
 It always beeps.
 Thorium is a pretty good emmitter.
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Chapter 14-The Atomic Nucleus
Isotopes
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The number of protons (atomic number)
determines the element. One proton atoms are
hydrogen, an element with 20 protons is calcium.
The number of neutrons may vary.
Hydrogen (one proton) may have, for example,
no neutrons, one neutron or two neutrons.
The number of neutrons plus the number of
protons determines the atomic mass.
Atoms with the same number of protons but
different numbers of neutrons are isotopes.
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Chapter 14-The Atomic Nucleus
Isotopes - 2
The atomic number of an atom that
contains 32 protons, 30 neutrons and 31
electrons is?
 How many protons and neutrons are there
in U235?
 What is the difference in chemistry
between an atom with one proton and no
neutron to that which contains one proton
and one neutron?
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Chapter 14-The Atomic Nucleus
Half-Life
A radioactive isotope emits particles and
changes. This is called decay.
 The amount of time it takes an original
quantity of a radioactive element to decline
by on half is called the half-life.
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Chapter 14-The Atomic Nucleus
Half-Life 2
If you start with 1.00 gram of element x
that has a half life of 1 day, how much will
be left after three days?
 Which gives a higher count on a radiation
detector, an isotope with a short half life or
one with a long half life?
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Chapter 14-The Atomic Nucleus
Transmutation of Elements.
How many protons and neutrons are there
in U235?
 If U235 emits an alpha particle (review –
this is a particle that consists of 2 neutrons
and 2 protons), what becomes of the
original U235?
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Chapter 14-The Atomic Nucleus
Isotopic Dating
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In the upper atmosphere cosmic rays bombard
nitrogen and transmute it to radioactive carbon.
Plants take up the radioactive carbon.
Animals eat plants until the animals die.
At death the animals no longer eat and the
radioactive carbon decays.
We know the half life of radioactive carbon.
Therefore we can tell when the animal died by
measuring the amount of radioactive carbon.
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Chapter 14-The Atomic Nucleus
Isotopic Dating - 2
The half life of radioactive carbon (carbon
14) is 5730 years.
 If I dig up an animal that has 25% (or ¼)
of the amount of radioactive carbon as a
recently killed animal, when did the animal
I dug up die?
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Chapter 14-The Atomic Nucleus
Nuclear Fission
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Fission means breaking apart.
When uranium 235 is hit by a neutron, it breaks
apart into an atoms of barium 142, and atom of
krypton 91 and three neutrons.
The diagram on page 346 is wrong.
If there is a large enough amount of uranium 235
the neutrons that are produced will continue to
break apart more and more uranium atoms (a
chain reaction).
Illustrate on board.
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Chapter 14-The Atomic Nucleus
Nuclear Fission Reactors
Produce about 20% of power in US.
 Atoms split, produce heat energy, boil
water, turn turbine to make electricity.
 Consist of three parts, nuclear fuel, control
rods to absorb neutrons, water to transfer
heat.
 Biggest problem is disposing of waste.
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Chapter 14-The Atomic Nucleus
Questions
Is there a greater proportion of C14/C12 in
new or old bones?
 Most of the radioactivity we encounter
comes from what source?
 How do astronomers determine what
elements are present in a star?
 Which ray, alpha, beta or gamma, is the
heaviest?
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Chapter 14-The Atomic Nucleus