Nuclear Magnetic Resonance
Superconductivity I -- electrical and magnetic properties
of superconductors
Superconductivity II -- tunnel functions & Mr. SQUID
Superfluidity
X-ray Diffraction
Nuclear Radiation Physics
Nuclear Magnetic Resonance
In general "resonance" in a physical system involves the absorption of
energy from an external source at a "natural" frequency of the system.
In an NMR experiment the resonant frequency is determined by the energy
states of the magnetic moment of the nucleus in an applied magnetic field
and the energy is absorbed from an electromagnetic wave. By sending
pulses of radio frequency electromagnetic radiation into your sample, you
can get the nuclear spins to play some very interesting tricks.
In addition to the physics of the phenomema, you will learn something about
tuned LC circuits and impedance matching, about how to produce an inhomogeneous
magnetic field and to measure it. Having picked up a black box for measuring
magnetic fields, you may well decide that you should find out how it works and
do a "mini-experiment" on how magnetic fields are measured. In the end you may
relate what you have learned to Magnetic Resonance Imaging (MRI) which is used
universally as a medical diagnostic tool.
Superconductivity I
When someone says "superconductor" the first thing you think of is a substance
with zero electrical resistance. In this first experiment, you will fabricate
you own superconducting thin film samples, and watch the resistance drop suddenly
to zero as they become superconducting at low temperature. Superconductors
also have very interesting magnetic properties. A superconductor tries
to expell all magnetic field from its interior. You will study how superconductivy
is destroyed by a sufficiently large magnetic field or electric current.
Superconductivity II
Once you have done the preceeding set of experiments, you can move on to
more advanced topics. Now you can fabricate you own NIS (normal metal
-- insulator -- superconductor) or maybe even SIS tunnel junctions.
The latter exhibit the famous Josephson effect, whereby an electrical current
flows across the junction without any voltage drop. When you make
a circuit with 2 such junctions, you get a "SQUID", i.e. a Superconducting
QUantum Interference Device. We won't make our own SQUID's, but we
will use a commercial SQUID made from high-Tc superconductors, which it
operates at liquid nitrogen temperature.
Superfluidity Nuclear Radiation Physics
Helium gas becomes a liquid at about 4.2 K. If you cool it to still lower
temperatures, there is a phase transition at about 2.2K to a new liquid
state called a superfluid. Below 2.2K the real liquid is
a mixture of normal and superfluid. In this
regime many properties of the two components are different. You will learn
to handle liquid helium; to learn about the different properties; to determine
which properties we can measure and to do such measurements. In particular:
X-ray Diffraction
You all know about the optical diffraction (interference) grating and roughly
how it works. In fact, any periodic structure will produce an interference pattern
when it is irradiated by an electromagnetic (or deBroglie) wave whose wavelength
is approximately equal to the spacing, d, of the periodic structure. Starting
with a system in which both d and the wavelength are about 3 cm, you will learn
how both the geometrical and physical properties are important in the interaction.
You will then proceed to the case where both d and the wavelength are about 10-8
cm and finally if we are lucky, take some data on a real crystal using a "state
of the art" x-ray system and do a careful analysis of the crystal structure of
the crystal. We may consider the connection between what you have learned and
the medical diagnostic tool, the CAT scan.
This is a set of experiments in which you will learn some of the experimental
techniques which are used in Nuclear Physics to study the energy spectrum, absorption
and the lifetime of the nuclear decay process. These include:
Here too we may study some aspect of the biological effects (good and
bad) of nuclear radiation.