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Search Results: 1 - 10 of 297461 matches for " J. Martoff "
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The measurement of scintillation emission spectra by a coincident photon counting technique
J E McMillan,C J Martoff
Physics , 2006,
Abstract: In the evaluation of novel scintillators, it is important to ensure that the spectrum of the light emitted by the scintillator is well matched to the response of the photomultiplier. In attempting to measure this spectrum using radioactive sources, it is found that so few photons are emitted per scintillation event that conventional spectroscopic techniques cannot easily be used. A simple photon counting technique is presented, using two photomultipliers operated in coincidence, the one viewing the scintillator directly, while the other views it through a monochromator. This system allows the spectrum to be measured without using specially cooled photomultipliers, intense radioactive sources or particle beams.
On the Mechanism of Townsend Avalanche for Negative Molecular Ions
M. P. Dion,C. J. Martoff,M. Hosack
Physics , 2009, DOI: 10.1016/j.astropartphys.2010.02.002
Abstract: Time projection chambers drifting negative ions (NITPC) instead of electrons have several advantages. A NITPC can operate at very high reduced drift fields without diffusion runaway, and the readout digitization sampling rate requirement is considerably relaxed due to the low drift speed of negative ions. The initiation of Townsend avalanches to allow gas gain in these devices has not been understood until now. It is shown here that the avalanche in low pressure CS$_2$ vapor is most likely initiated by collisional detachment of the electron from the negative molecular ion. In mixtures of Nitromethane vapor with CO$_2$ the mechanism appears to be more complex.
Measurement of Carbon Disulfide Anion Diffusion in a TPC
Tohru Ohnuki,Daniel P. Snowden-Ifft,C. J. Martoff
Physics , 2000, DOI: 10.1016/S0168-9002(01)00222-4
Abstract: A Negative Ion Time Projection Chamber was used to measure the field dependence of lateral and longitudinal diffusion for CS$_2$ anions drifting in mixtures of CS$_2$ and Ar at 40 Torr. Ion drift velocities and limits on the capture distance for electrons as a function of field and gas mixture are also reported.
Near threshold electroproduction of the omega meson at Q2 ~ 0.5 GeV2
P. Ambrozewicz,J. Mitchell,J. Dunne,P. Markowitz,C. J. Martoff,J. Reinhold,B. Zeidman
Physics , 2004, DOI: 10.1103/PhysRevC.70.035203
Abstract: Electroproduction of the omega meson was investigated in the p(e,e'p)omega reaction. The measurement was performed at a 4-momentum transfer Q2 ~ 0.5 GeV2. Angular distributions of the virtual photon-proton center-of-momentum cross sections have been extracted over the full angular range. These distributions exhibit a strong enhancement over t-channel parity exchange processes in the backward direction. According to a newly developed electroproduction model, this enhancement provides significant evidence of resonance formation in the gamma* p -> omega p reaction channel.
A benign, low Z electron capture agent for negative ion TPCs
C. J. Martoff,M. P. Dion,M. Hosack,D. Barton,J. K. Black
Physics , 2009, DOI: 10.1016/j.nima.2008.09.042
Abstract: We have identified nitromethane (CH$_3$NO$_2$) as an effective electron capture agent for negative ion TPCs (NITPCs). We present drift velocity and longitudinal diffusion measurements for negative ion gas mixtures using nitromethane as the capture agent. Not only is nitromethane substantially more benign than the only other identified capture agent, CS$_2$, but its low atomic number will enable the use of the NITPC as a photoelectric X{}-ray polarimeter in the 1{}-10 keV band.
Low Pressure Negative Ion Drift Chamber for Dark Matter Search
D. P. Snowden-Ifft,C. J. Martoff,J. M. Burwell
Physics , 1999, DOI: 10.1103/PhysRevD.61.101301
Abstract: Weakly Interacting Massive Particles (WIMPs) are an attractive candidate for the dark matter thought to make up the bulk of the mass of our universe. We explore here the possibility of using a low pressure negative ion drift chamber to search for WIMPs. The innovation of drifting ions, instead of electrons, allows the design of a detector with exceptional sensitivity to, background rejection from, and signature of WIMPs.
Negative Ion Drift and Diffusion in a TPC near 1 Bar
C. J. Martoff,R. Ayad,M. Katz-Hyman,G. Bonvicini,A. Schreiner
Physics , 2004, DOI: 10.1016/j.nima.2005.08.103
Abstract: Drift velocity and longitudinal diffusion measurements are reported for a Negative Ion TPC (NITPC) operating with Helium + carbon disulfide gas mixtures at total pressures from 160 to 700 torr. Longitudinal diffusion at the thermal-limit was observed for drift fields up to at least 700 V/cm in all gas mixtures tested. The results are of particular interest in connection with mechanical simplification of Dark Matter searches such as DRIFT, and for high energy physics experiments in which a low-Z, low density, gaseous tracking detector with no appreciable Lorentz drift is needed for operation in very high magnetic fields.
GEM Operation in Negative Ion Drift Gas Mixtures
J. Miyamoto,I. Shipsey,C. J. Martoff,M. Katz-Hyman,R. Ayad,G. Bonvicini,A. Schreiner
Physics , 2003, DOI: 10.1016/j.nima.2004.02.018
Abstract: The first operation of GEM gas gain elements in negative ion gas mixtures is reported. Gains up to several thousand were obtained from single-stage GEMs in carbon disulfide vapor at low pressure, and in mixtures of carbon disulfide with Argon and Helium, some near 1 bar total pressure.
Gaseous Dark Matter Detectors
Gabriella Sciolla,C. Jeff Martoff
Physics , 2009, DOI: 10.1088/1367-2630/11/10/105018
Abstract: Dark Matter detectors with directional sensitivity have the potential of yielding an unambiguous positive observation of WIMPs as well as discriminating between galactic Dark Matter halo models. In this article, we introduce the motivation for directional detectors, discuss the experimental techniques that make directional detection possible, and review the status of the experimental effort in this field.
The DRIFT Project: Searching for WIMPS with a Directional Detector
M. J. Lehner,K. Griest,C. J. Martoff,G. E. Masek,T. Ohnuki,D. Snowden-Ifft,N. J. C. Spooner
Physics , 1999,
Abstract: A low pressure time projection chamber for the detection of WIMPs is discussed. Discrimination against Compton electron background in such a device should be very good, and directional information about the recoil atoms would be obtainable. If a full 3-D reconstruction of the recoil tracks can be achieved, Monte Carlo studies indicate that a WIMP signal could be identified with high confidence from as few as 30 detected WIMP-nucleus scattering events.
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