H.C. Kim

Characteristics of hybrid plastic scintillators for slow neutron measurements

In this paper, we report the characteristics and the performance of the hybrid plastic scintillators for slow neutron measurements. The 10B-doped and Gd-layered scintillators were manufactured and tested for slow and fast neutrons, and gamma rays. The slow neutrons were provided by an energy moderation of the fast neutrons emitted from a 0.5 Ci 252Cf source. The energy of the slow neutrons ranged from 10 to 600 meV with a peak at 75 meV. Neutron response functions for the hybrid plastic scintillators were measured with the calibrated slow neutron flux. Furthermore, the pulse-shape analysis was performed to differentiate the slow neutrons from the gamma rays. For the 10B-doped scintillators, the difference lying in the tail-to-total charge ratio distribution of the pulses was conductive to estimate the fraction of the gamma rays in the neutron data. However, for the Gd-layered scintillators, the difference was insignificant.

Magic polarization for optical trapping of atoms without stark-induced dephasing

We demonstrate that the differential ac-Stark shift of a Zeeman-sensitive ground hyperfine transition in an optical trap can be eliminated by using properly polarized trapping light. We use the vector polarizability of an alkali-metal atom to produce a polarization-dependent ac-Stark shift that resembles a Zeeman shift. We study a transition from the |2S1/2,F=2,mF=-2> to the |2S1/2,F=1,mF=-1> state of 7Li to observe 0.59±0.02  Hz linewidth with interrogation time of 2 s and 0.82±0.06  s coherence time of a superposition state. Implications of the narrow linewidth and the long coherence time for precision spectroscopy and quantum information processing using atoms in an optical lattice are discussed.

THE CMS RPC SYSTEM OVERVIEW

The Muon System of the CMS experiment at CERN employees three different detector technologies—Drift Tube Chambers (DT) in the barrel part, Cathode Strip Chambers (CSC) in the endcaps and Resistive Plate Chambers (RPC) both in the barrel and the endcaps. TDs and CSCs serve as precise muon trajectory measurement devices. The RPCs are responsible for the bunch crossing identification and for a fast muon transverse momentum measurement. The total number of RPCs is 480 in the barrel and 756 in the endcaps, covering an area of about 3500 square meters. A brief overview of the system will be presented as well as some recent results about the system stability and performance.