Showing papers by "Richard C. Lanza published in 2008"

Observation of the 'head-tail' effect in nuclear recoils of low-energy neutrons

Abstract: Directional detection of dark matter can provide unambiguous observation of dark matter interactions even in the presence of background. This article presents an experimental method to measure the direction tag (“head-tail”) of the dark matter wind by detecting the scintillation light created by the elastic nuclear recoils in the scattering of dark matter particles with the detector material. The technique is demonstrated by tagging the direction of the nuclear recoils created in the scattering of low-energy neutrons with CF 4 in a low-pressure time-projection chamber that is developed by the DMTPC collaboration. The measurement of the decreasing ionization rate along the recoil trajectory provides the direction tag of the incoming neutrons, and proves that the “head-tail” effect can be observed.

A Measurement of Photon Production in Electron Avalanches in CF4

Abstract: This paper presents a measurement of the ratio of photon to electron production and the scintillation spectrum in a popular gas for time projection chambers, carbon tetrafluoride (CF 4 ), over the range of 200–800 nm; the ratio is measured to be 0.34 ± 0.04 . This result is of particular importance for a new generation of dark matter time projection chambers with directional sensitivity which use CF 4 as a fill gas.

Phase-Contrast X-Ray Imaging

Abstract: Phase-contrast imaging is performed by directing radiation from a plurality of pinhole sources through a phase object to be imaged, wherein the phase object includes a first composition that produces a phase shift in the radiation relative to radiation passing through a second composition in the phase object and detecting a phase-contrast image of the radiation after it passes through the phase object. The phase-contrast image is then decoded to generate an image of the phase object in which the first composition is distinguished from the second composition.

High-Resolution $^{125}$ I Small Animal Imaging With a Coded Aperture and a Hybrid Pixel Detector

Abstract: We report on tests of a radionuclide imaging system for in vivo investigations in small animals with low-energy photons as from 125I (27-35 keV). Imaging optics features a high-resolution coded aperture mask and a fine pitch hybrid pixel detector (silicon 300-mum or 700-mum thick, or CdTe 1 mm thick) of the Medipix2 series (55 mum pitch, 256 x 256 pixels). The coded aperture had 480 70-mum holes in 100-mum-thick tungsten. Laboratory tests with a 109Cd 22 keV source and a microfocus X-ray tube (35 kVp, Mo anode) show a system resolution of about 110 mum at magnification m = 2.12 and a sensitivity improvement of 30:1 as compared to a 300-mum pinhole collimator. The field of view also depends on magnification: in the experiments presented, it varied from 6 mm (m = 2.12) to 21 mm (m = 0.66). 125I in vivo mouse thyroid imaging with the 70 mum coded aperture, a 300 mum pinhole and a 100 mum parallel hole collimator was also performed to obtain a qualitative comparison. This low energy, semiconductor-based, compact gamma-ray imaging system can be used as a gamma-ray sub-millimeter resolution imager for energies below about 35 keV and it is the basic imaging unit of a small animal Single Photon Emission Computed Tomography system (MediSPECT) built at University of Napoli Federico II and Istituto Nazionale Fisica Nucleare (INFN), Napoli.

Toward directional detection of Dark Matter with the DM-TPC detector

Abstract: Directional detection can provide unambiguous observation of Dark Matter interactions even in presence of insidious backgrounds. The DM-TPC collaboration is developing a detector with the goal of measuring the direction and sense of nuclear recoils produced in Dark Matter interactions. The detector consists of a Time Projection Chamber with optical readout filled with CF$_4$ gas at low pressure. A collision between a WIMP and a gas molecule results in a nuclear recoil of 1-2 mm. The measurement of the energy loss along the recoil allows us to determine the sense and the direction of the recoil. Results from a prototype detector operated in a low-energy neutron beam clearly demonstrate the suitability of this approach to measure directionality. A cubic meter prototype, which is now being designed, will allow us to set competitive limits on spin-dependent Dark Matter interactions using a directional detector.

Improved measurement of the head-tail effect in nuclear recoils

Abstract: We present new results with a prototype detector that is being developed by the DMTPC collaboration for the measurement of the direction tag (head-tail) of dark matter wind. We use neutrons from a Cf-252 source to create low-momentum nuclear recoils in elastic scattering with the residual gas nuclei. The recoil track is imaged in low-pressure time-projection chamber with optical readout. We measure the ionization rate along the recoil trajectory, which allows us to determine the direction tag of the incoming neutrons.

Systems and methods for multimodal imaging using a volumetric representation of an object

Abstract: The invention relates to imaging systems that include a coded aperture detection system and an optical detection system. The coded aperture detection system is configured to detect radiation emitted by a radionuclide present within an object and to provide a first detector signal from the detected radiation. The optical detection system is configured to detect optical radiation from the object and to provide a second detector signal from the detected optical radiation. The system also includes a processor configured to prepare first image data from the first detector signal, second image data from the second detector signal, and registered data indicative of a spatial relationship in at least one dimension between the first and second image data. The invention also includes methods of using the new systems, e.g., for sentinel lymph node mapping and tissue resection.

Improved measurement of the 'head-tail' effect in nuclear recoils

Abstract: We present new results with a prototype detector that is being developed by the DMTPC collaboration for the measurement of the direction tag ('head-tail') of dark matter wind. We use neutrons from a 252Cf source to create low-momentum nuclear recoils in elastic scattering with the residual gas nuclei. The recoil track is imaged in low-pressure time-projection chamber with optical readout. We measure the ionization rate along the recoil trajectory, which allows us to determine the direction tag of the incoming neutrons.

Erratum to: “Observation of the ‘‘head tail’’ effect in nuclear recoils of low-energy neutrons” [Nucl. Instr. and Meth A 584 (2008) 327 333]

Abstract: Please note that the author list in the originally published version of this paper is not completely correct: Affiliations should read: D. Dujmic,*, H. Tomita, M. Lewandowska, S. Ahlen, P. Fisher, S. Henderson, A. Kaboth, G. Kohse, R. Lanza, J. Monroe, A. Roccaro, G. Sciolla, N. Skvorodnev, R. Vanderspek, H. Wellenstein, R. Yamamoto Physics Department, Boston University, Boston, MA 02215, USA Physics Department, Brandeis University, Waltham, MA 02454, USA Physics Department, Massachusetts Institute of Technology, Cambridge, MA, USA Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139, USA Moreover the Acknowledgement section should read: We acknowledge support by the Advanced Detector Research Program of the US Department of Energy (contract no. 6916448), as well as the Reed Award Program, the Ferry Fund, the Pappalardo Fellowship program, the MIT Kavli Institute for Astrophysics and Space Research, and the Physics Department at the Massachusetts Institute of Technology. The authors apologize for any inconvenience caused.

DM-TPC: a new approach to directional detection of Dark Matter

Abstract: Directional detection can provide unambiguous observation of Dark Matter interactions even in presence of insidious backgrounds. The DM-TPC collaboration is developing a detector with the goal of measuring the direction and sense of nuclear recoils produced in Dark Matter interactions. The detector consists of a Time Projection Chamber with optical readout filled with CF$_4$ gas at low pressure. A collision between a WIMP and a gas molecule results in a nuclear recoil of 1-2 mm. The measurement of the energy loss along the recoil allows us to determine the sense and the direction of the recoil. Results from a prototype detector operated in a low-energy neutron beam clearly demonstrate the suitability of this approach to measure directionality. A full-scale module with an active volume of about one cubic meter is now being designed. This detector, which will be operated underground in 2009, will allow us to set competitive limits on spin-dependent Dark Matter interactions using a directional detector.

Observation of the ‘head-tail’ effect in nuclear recoils of low-energy neutrons

Abstract: We present an experimental method to determine the direction tag ('head-tail') of dark matter wind using a low-pressure time-projection chamber. We demonstrate the method by tagging the direction of the elastic nuclear recoils created in the scattering of low-energy neutrons with CF4 nuclei. The decreasing ionization rate along the recoil trajectory allows us to determine the direction of the incoming neutrons, and proves that the 'head-tail' effect can be measured.

The DMTPC detector

Abstract: Directional detection of Dark Matter allows for unambiguous direct detection of WIMPs as well as discrimination between various Dark Matter models in our galaxy. The DMTPC detector is a low-pressure TPC with optical readout designed for directional direct detection of WIMPs. By using CF4 gas as the active material, the detector also has excellent sensitivity to spin-dependent interactions of Dark Matter on protons.

DMTPC-10L: Direction-Sensitive Dark Matter Detector Prototype

Abstract: The known direction of motion of dark matter particles relative to the Earth may be a key for their unambiguous identification even in the presence of backgrounds. We describe a prototype detector that is able to reconstruct direction vectors of weakly interacting massive particles that may the dominant constituent of the dark matter in our galaxy. The detector uses a low-density gas (CF4) in a 10liter time-projection chamber with mesh-based electrodes and optical and charge readout. Initial results confirm good performance in the reconstruction of direction angle and sense ('head-tail') for low-momentum nuclear recoils.