297 research outputs found
A prototype for SONTRAC, a scintillating plastic fiber tracking detector for neutron imaging and spectroscopy
We report on tests of a prototype detector system designed to perform imaging and spectroscopy on 20 to 250 MeV neutrons. Although developed for the study of high-energy solar flare processes, the detection techniques employed for SONTRAC, the SOlar Neutron TRACking experiment, can be applied to measurements in a variety of disciplines including atmospheric physics, radiation therapy and nuclear materials monitoring. The SONTRAC instrument measures the energy and direction ofneutrons by detecting double neutron-proton scatters and recording images of the ionization tracks of the recoil protons in a densely packed bundle of scintillating plastic fibers stacked in orthogonal layers. By tracking the recoil protons from individual neutrons, the kinematics of the scatter are determined. This directional information results in a high signal to noise measurement. SONTRAC is also capable of detecting and measuring high-energy gamma rays \u3e20 MeV as a “solid-state spark chamber”. The self-triggering and track imaging features of a prototype for tracking in two dimensions are demonstrated in calibrations with cosmic-ray muons, 14 to ~65 MeV neutrons and ~20 MeV protons
Testing Lorentz Invariance with GRB021206
Since the discovery of the cosmological origin of GRBs there has been growing
interest in using these transient events to probe the quantum gravity energy
scale in the range 10^16--10^19 GeV, up to the Planck mass scale. This energy
scale can manifest itself through a measurable modification in the
electromagnetic radiation dispersion relation for high energy photons
originating from cosmological distances. We have used data from the gamma-ray
burst (GRB) of 6 December 2002 (GRB021206) to place an upper bound on the
energy dispersion of the speed of light. The limit on the first-order quantum
gravity effects derived from this single GRB indicate that the energy scale is
in excess of 1.8x10^17 GeV. We discuss a program to further constrain the
energy scale by systematically studying such GRBs.Comment: 10 pages, 3 figures, accepted for publication in ApJ
Personalforschung als Ad-hoc-Aktionismus. Der Personalmanagement-Professionalisierungs-Index der DGFP
SPI Measurements of Galactic 26Al
The precision measurement of the 1809 keV gamma-ray line from Galactic
Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge
detector camera. We aim for determination of the detailed shape of this
gamma-ray line, and its variation for different source regions along the plane
of the Galaxy. Data from the first part of the core program observations of the
first mission year have been inspected. A clear detection of the \Al line at
about 5--7 significance demonstrates that SPI will deepen \Al studies.
The line intensity is consistent with expectations from previous experiments,
and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more
consistent with RHESSI's recent value. Only preliminary statements can be made
at this time, however, due to the multi-component background underlying the
signal at \about 40 times higher intensity than the signal from Galactic
Al.Comment: 5 pages, 8 figures; accepted for publication in A&A (special INTEGRAL
volume
Electrical coupling of neuro-ommatidial photoreceptor cells in the blowfly
A new method of microstimulation of the blowfly eye using corneal neutralization was applied to the 6 peripheral photoreceptor cells (R1-R6) connected to one neuro-ommatidium (and thus looking into the same direction), whilst the receptor potential of a dark-adapted photoreceptor cell was recorded by means of an intracellular microelectrode. Stimulation of the photoreceptor cells not impaled elicited responses in the recorded cell of about 20% of the response elicited when stimulating the recorded cell. This is probably caused by gap junctions recently found between the axon terminals of these cells. Stimulation of all 6 cells together yielded responses that were larger and longer than those obtained with stimulation of just the recorded cell, and intensity-response curves that deviated more strongly from linearity. Evidence is presented that the resistance of the axon terminal of the photoreceptor cells quickly drops in response to a light flash, depending on the light intensity. Incorporating the cable properties of the cell body and the axon, the resistance of the gap junctions, and the (adapting) terminal resistance, a theoretical model is presented that explains the measurements well. Finally, it is argued that the gap junctions between the photoreceptor cells may effectively uncouple the synaptic responses of the cells by counteracting the influence of field potentials.
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