Date

Talk

Thursday
April 2

Will Williams

Smith College

"Trace Analysis, Cold Atom Physics and Smith College"

Abstract: Atom Trap Trace Analysis (ATTA), a MOT-based atom counting method developed in the late 1990s by Zheng-Tian Lu at Argonne National Laboratory, can be used to analyze three noble gas radioisotopes (⁸¹Kr, ⁸⁵Kr, ³⁹Ar) covering a wide range of geological ages and has many important applications including monitoring nuclear proliferation with atmospheric ⁸⁵Kr, monitoring ocean currents with ³⁹Ar (climate change), ultra-pure noble gas detectors with ⁸⁵Kr (dark matter), dating underground water with ⁸¹Kr (replenishment rates for underground aquifers), and measuring the age of ice core samples with ⁸¹Kr (climate history). The isotopic abundances are extremely low, in the range of 10^-16 – 10^-11. Yet, ATTA can trap and unmistakably detect these rare isotopes one atom at a time. The system at Argonne National Laboratory is currently limited by the excitation efficiency of the RF discharge that produces the metastable atoms needed for laser cooling and trapping.

The Smith College Atomic Physics Laboratory plans to build the next version of ATTA by replacing the RF discharge with a photon excitation scheme that employs a two-photon transition at 215 nm. The optical source is a frequency quadrupled Ti-Sapphire laser coupled to a power-build-up optical cavity. The predicted metastable transfer efficiency is 0.9, far larger than current methods that use a discharge source with an efficiency of 10^-3. The ATTA built at Smith College will be at least 1000 times more sensitive than the current best version of ATTA. This highly effective apparatus will be the only ATTA in the world sensitive enough to measure the age of ice core samples and the only United States based ATTA dedicated to monitoring nuclear proliferation.This talk will cover how atomic physics is used to perform trace analysis, the current state of the field, and plans for the future at Smith College.

Thursday
April 9

Thursday
April 16

Available

Thursday
April 23

Available

Thursday
April 30

Peter Sorensen

Lawrence Berkely National Laboratory

"Can atomic scale physics solve a riddle which spans particle physics and cosmology?"

Abstract: Many different astrophysical observations suggest that about 25% of the mass of the universe takes the form of a non-baryonic, non-luminous material, aka dark matter. The most simple and successful model of modern cosmology, lambda-CDM, is supported by these observations. At the same time, particle physics has long expected there to be a new symmetry of nature (supersymmetry) at the weak scale. Simple arguments have long suggested that the new particles predicted by this symmetry could be the dark matter, in the form of Weakly Interacting Massive Particles (WIMPs). I will discuss efforts to directly detect these WIMPs using a liquid xenon particle detector which is located at the bottom of a former gold mine in South Dakota.

Thursday
May 7

No Colloquium due to Steinmetz

Thursday
May 14

Available

Thursday
May 21

Sean Marshall

Cornell University

"Radar and Infrared Observations of Near-Earth Asteroids"

Abstract: Near-Earth asteroids have attracted an increasing level of interest in recent years for a variety of reasons, from scientific curiosity to future exploration to concerns about potential impactors. I will discuss my research on using radar and infrared observations to characterize the physical properties of near-Earth asteroids. With radar observations, a powerful series of coherent radio waves is transmitted toward an asteroid, and the echoes that reflect off the asteroid are received some time later. Careful analysis of echoes received over the course of an asteroid's rotation makes it possible to determine the asteroid's size, shape, and spin state. Thermal modeling based on the asteroid's shape from radar observations, combined with optical and infrared measurements, can provide information on its albedo (reflectivity), thermal inertia, and other properties.

Thursday
May 28

SPS Inductions

Thursday
June 4

Corey Stambaugh

NIST

"Towards the redefinition and dissemination of the kilogram"

Abstract: The National Institute of Standards and Technology is tasked with providing standard weights and measures to the United States. To that end they work with international groups to define the International System of Units (SI) the world uses. Of the seven base SI units only the unit of mass, the kilogram, is still defined by a physical artifact. However, this is changing.  The expectation is by 2018 the kilogram will be defined based on a fixed value of the Planck constant. In this talk, I will give a brief background of the SI and the kilogram. I will then describe how the kilogram will be redefined using the Watt balance. Finally, I will explain the unique approach we are developing at NIST for direct vacuum-to-air mass comparisons.

Schedule for Fall 2015