- NP: Nuclear / Particle
- AMO: Atomic / Molecular / Optics
- CM: Condensed Matter
Nuclear / Particle Physics Cycle:
Particle physics Engineering
drawing of the new setup that is being built: (drawing)
This
experiment was built in Fall 2005, mostly by the Fall 2005 class, the Hertzog
research group, and the NPL techs. Sorry, we took it all down so you
can start again "clean" this semester. It will be great fun.
Here we provide a snapshot of what we are doing
The experiment provides basics training in the use and setup of common detectors
in nuclear and particle physics, such as photomultipliers (we have 28 in the
setup); coincidence counting and NIM electronic use, and fast data acquisition
through CAMAC and an interface to a modern DAQ program. Analysis is
required to extract the physics and the tools are the very ones we use in
modern research projects. The physics that can be addressed with the
setup includes the muon lifetime (which gives the Fermi constant, a measure
of the strength of the weak interaction), the rate of negative muon capture
on some materials, and the magnetic moment of the muon (using an external
field and precessing the polarized positive muons that stop in our setup).
Muons are stopped in a stack of plastic scintillators and lead (or other material) sheets. They are generated when high energy particles bombard the earth's atmosphere. These high energy particles are primarily protons and are produced by processes which are not yet well understood. Energies in excess of 10^20 eV have been detected. Few of these particles reach the earth's surface. Most are converted to mesons which quickly decay to mu mesons which, because they interact weakly with matter, arrive at the surface where we can detect them. Muons, like electrons, are leptons and are spin-1/2 particles with either positive or negative charge. Their rest mass is 106.66 MeV, about 200 times that of the electron. These particles are unstable, decaying into an electron (or positron) and two neutrinos. The lifetime is 2.197 microsecond in free space. Because the incoming muons are highly relativistic, their lifetime is effectively infinite until they are stopped in our detector. Once they are stopped, the negative muons can interact with the positive nuclei of the carbon atoms or the lead absorber sheets or the aluminum plates, decaying by a different path. The accepted ratio of positive muon to negative muon is 1.225: 1.
Nuclear Decay and Attenuation of Radiation: (PDF ) When an atomic nucleus decays, one or more of the three forms of radioactivity is released. This release of radioactivity is also known as nuclear radiation. Radiation measurements are important in medicine, industry and research. Primarily there are three kinds of radiation measurements - gamma rays, alpha particles and beta particles. Due to their distinct properties, each of them could be measured by appropriate detectors. This experiment explores the properties of gas-filled detectors, also known as Geiger-Muller tube, and solid-state detectors. You will measure how far an alpha particles travel in air or its range using a solid state detector and a PC-controlled multichannel analyzer. In addition to measure the range of alpha particles, beta particles, and gamma radiation in matter, you will observe the spectra of radioactive species using a cooled solid state detector and the multichannel analyzer. Since you will be using various radioisotopes, you will learn the basics of radiation safety and understand the radiation monitoring devices provided in the lab. Before you begin this experiment, familiarize the radiation safety manual on the web at http://www.ehs.uiuc.edu/~rad/ .
Atomic
/ Molecular / Optics Cycle:
Most of these experiments
are all new:
Optical Pumping of Rubidium Gas
I am quoting directly from the TeachSpin cite here. Please see their wonderful website for more information on this experiment and on the Pulsed NMR (below)
Optical Pumping of Rubidium GasTWO !! New Optics Labs built by Nick Peters from the Paul Kwiat Quantum Information research group (link)
Optical Pumping is a widely used and powerful technique for exploring atomic energy states, atomic transitions, and atomic collisions using electromagnetism in the form of light, radio frequency, and uniform constant magnetic fields. TeachSpin’s OP1-A explores the atomic physics of both isotopes of natural rubidium.
The rubidium atom is an ideal model system for students to study.
Its energy states, in an externally applied uniform magnetic field, can be understood using a semi-classical model. This model describes the coupling of a single electronic orbital and spin angular momentum with the nuclear spin angular momentum and of the coupled system to the external field. The experimental determination of these atomic energy states can be compared to the theoretical predictions of the Briet-Rabi equation. The two isotopes of rubidium, Rb85 and Rb87, with different nuclear magnetic moments, make the experimental data even richer. The apparatus allows the student to explore a wealth of atomic physics, including temperature dependent cross-sections for photon absorption, zero magnetic field transitions, spin-spin collision processes, field inversion measurements, Rabi oscillation of the atomic magnetic moment, optical pumping times, and other atomic physics experiments. It is only a small exaggeration to claim these experiments constitute an atomic physics course.
Quantum Information: “Berry’s phase” in a Sagnac interferometer
A Sagnac interferometer is a loop where a clockwise and counter-clockwise path interfere. Because these paths overlap in space, the interferometer is very stable. We will use a Sagnac to study Berry’s phase—if the polarization state of light is cycled through a closed path on the Poincaré sphere (whose surface represents all possible pure polarization states, i.e., linear, circular, etc.), the photons will acquire an additional phase that depends only on the net solid-angle subtended by the path of the polarization trajectory on the sphere
“Quantum Erasers” in a Michelson interferometer
In this experiment, you will study several unintuitive consequences of quantum mechanics, by constructing an interferometer of the type used in the famous Michelson-Morley experiment. The Michelson interferometer can be tuned so that there is complete destructive interference in one output port and complete constructive interference in the other output port. If one uses wave plates to prepare a path-dependent polarization for the photon, the quality of the interference will degrade. The “which-path” information provided by different polarizations in each arm makes the underlying physical processes distinguishable. Remarkably, a polarizer can be used at the output of the interferometer to “erase” the which-path information and recover the interference fringes.
(an older experiment, used occasionally, but quite nice) Electron
Paramagnetic Rsonance (EPR)
EPR of various materials, ferromagnetic resonance: (PDF ) Electron paramagnetic resonance is a branch of spectroscopy in which electromagnetic radiation of microwave frequency is absorbed by atoms in molecules or solids, possessing electrons with unpaired spins. We can therefore study with the EPR technique: atoms or ions with incomplete inner shells, e.g. transition metal atoms, rare earth atoms and actinides; atoms, molecules and lattice defects with odd numbers of electrons, e.g. free sodium atoms, organic free radicals; and, metals. This selection is contrasted by the atoms suitable for NMR (Nuclear Magnetic Resonance or Magnetic Resonance Imaging) spectroscopy, where diamagnetic behavior is required. The purpose of this experiment is to become familiar with the technique of electron paramagnetic resonance and to measure the g-factor and the hyperfine splitting constant for the ion V2+ in a MgO crystal.
Condensed
Matter Cycle:
Two New experiments
being prepared for Fall 2006 (designed by Eugene Kolla)
Ferroelectrics and ferroelectric phase transition.
In this experiment we are going to study the dielectric susceptibility as a function of temperature, frequency, time (aging effects) and electrical field of several classical and some disordered ferroelectrics. Among the regular materials we plan to investigate BaTiO3 (barium titanate) and KH2PO4 (KDP). Some complex oxides with perovskite crystalline structure (e.g. PbMg1/3Nb2/3O3-PbTiO3) could also be available for measurements as examples of the disordered ferroelectrics.
We can also measure the pyroelectric current in parallel with susceptibility and from this data the polarization can be calculated. The next what we plan (not done yet) to add is the setup for study of the hysteresis loops of the ferroelectric materials.
The vacuum film deposition.
The is the a small vacuum deposition setup with a residual pressure in the chamber could be close to 10-6 torr. The deposition system is equipped with two thermal evaporators, temperature sensor and will be also equipped with a crystal monitor for measurement of the thickness of the film. The list of materials which can be used for film preparation is rather long and the typical metals are Al, Au, Cu, Pb, Sn, In. This setup will be used for preparation of the electrodes for dielectric samples and also for fabrication of the films for conductivity and superconductivity investigations. This equipment can be also used to make optical mirrors of high quality.
Second sound in liquid helium (PDF ) 
The superfluid experiment is a measurement of a wave phenomenon, known as second sound, that is unique to the superfluid. The superfluid we used in this experiment is liquid helium. One of the superfluid properties of liquid helium is that its viscosity is zero that it will climb up the walls of the containers. Another property is that its velocity of sound in the liquid changes when it phases into superfluid state from normal state. Second sound is that velocity of sound in superfluid helium that you will measure in this experiment. The technique used is just that of a standing wave in a closed pipe, although in this case the wave is launched by a heater and received by a thermometer. The goal of the experiment is to observe standing second-sound resonances and to use them to study the temperature dependence of the second-sound velocity as the temperature approaches the normal-superfluid transition, known as the lambda point at a temperature of 2.17 K.
SQUID
The second cryogenic experiment is based on Super-conducting Quantum
Interference Device also known as SQUID. SQUID is the most sensitive
detector of magnetic fields. For example, SQUIDs are used in detecting
the magnetic fields of human brains in medical research, and, in detecting
changes in earth magentic fields in geophysical exploration. This experiment
relies on a device manufactured by Conductus, Inc. using the high temperature
superconductor YBa2Cu3O7. This material is superconducting below 93
K, making it possible to observe the critical current and the ac Josephson
effect at liquid nitrogen temperatures of 77 K. By making use of the
ac Josephson effect (Shapiro steps) an accurate measurement of the
fundamental constant h/e can be obtained.
Scanning Probe Microscope
(PDF ) Today, in order to view the surface of a material at atomic scale, various scanning probe microscopy techniques are used in industry and research. For example, in scanning tunneling microscpy (STM), a metallic tip is held close to ten millionth of a meter and moves across a section of the surface. The resulting image of the surface reveals the atomic structure of the material. The key to the STM is the quantum tunneling current. between the tip and the surface. In actual operation, it is a few nanoampere (billionth of an ampere). By measuring the changes in the current, one can map out the surface topology. STM was invented by G. Binning and H. Rohrer in 1982. Another SPM technique is called Atomic Force Microscopy (AFM). In AFM, a tip or cantilever is brought within interatomic separations of a surface. The tip and the surface are then at repulsive potentials. When the tip is moved along the surface, it bounces up and down along the contour of the surface. By measuring the displacement of the tip, the surface topology can be mapped out at atomic resolution. In this laboratory, you will primarily use STM to study the surface structure of graphite, gold and other materials. If time permits, one can study the surface properties using the AFM.
I am quoting directly from the TeachSpin site here. Please see their wonderful website for more information on this experiment and on the Optical Pumping (listed above)
Pulsed nuclear magnetic resonance has been a powerful tool for physics, chemistry and biological research since its discovery by Erwin Hahn in 1950. Hahn's observation and explanation of the spin echo revolutionized magnetic resonance.
This revolution has been accelerated in the past 15 years by the commercial development of high-field superconducting magnets, high-frequency pulsed spectrometers and computers which automate these systems. Such apparati can be found in the chemistry departments of every major research university as well as in many physics and biology departments.
Magnetic Resonance Imaging (MRI) utilizes the basic principles of pulsed NMR to create cross-section images of the human body. This new technology has revolutionized radiology. With all these research and medical applications of pulsed NMR, it is surprising that no commercial apparatus has been developed for teaching the basic principles of this unique and important spectropy.
