130 research outputs found
Development of a triple GEM UV-photon detector operated in pure CF4 for the PHENIX experiment
Results obtained with a triple GEM detector operated in pure CF4 with and
without a reflective CsI photocathode are presented. The detector operates in a
stable mode at gains up to 10^4. A deviation from exponential growth starts to
develop when the total charge exceeds ~ 4 10^6 e leading to gain saturation
when the total charge is ~ 2 10^7 e and making the structure relatively robust
against discharges. No aging effects are observed in the GEM foils after a
total accumulated charge of ~ 10 mC/cm^2 at the anode. The ion back-flow
current to the reflective photocathode is comparable to the electron current to
the anode. However, no significant degradation of the CsI photocathode is
observed for a total ion back-flow charge of ~ 7 mC/cm^2.Comment: 14 pages, 11 figures, Submitted to NIM
Novel Single Photon Detectors for UV Imaging
There are several applications which require high position resolution UV
imaging. For these applications we have developed and successfully tested a new
version of a 2D UV single photon imaging detector based on a microgap RPC. The
main features of such a detectors is the high position resolution - 30 micron
in digital form and the high quantum efficiency (1-8% in the spectral interval
of 220-140 nm). Additionally, they are spark- protected and can operate without
any feedback problems at high gains, close to a streamer mode. In attempts to
extend the sensitivity of RPCs to longer wavelengths we have successfully
tested the operation of the first sealed parallel-plate gaseous detectors with
CsTe photocathodes. Finally, the comparison with other types of photosensitive
detectors is given and possible fields of applications are identified.Comment: Presented at the 5th International Workshop on RICH detectors Playa
del Carmen, Mexico, November 200
Geiger Mode APD performance in a cryogenic two-phase Ar avalanche detector based on THGEMs
Characteristic properties of a Geiger Mode APD (G-APD) in a THGEM-based
cryogenic two-phase Ar avalanche detector were studied in view of potential
applications in rare-event experiments. G-APD signal amplitude and noise
characteristics at cryogenic temperatures turned out to be superior to those at
room temperature. The effective detection of avalanche scintillations from
THGEM-multiplier holes in two-phase Ar has been demonstrated using a G-APD
without wavelength shifter. At an avalanche gain of 60, the avalanche
scintillation yield measured by the G-APD was as high as 0.9 photoelectrons per
avalanche electron, extrapolated to 4pi acceptance.Comment: 4 pages, 8 figures. Presented at Vienna Conference on Instrumentation
(Feb 15-20, 2010, Vienna, Austria). Submitted to the Proceeding
On Bootstrap Percolation in Living Neural Networks
Recent experimental studies of living neural networks reveal that their
global activation induced by electrical stimulation can be explained using the
concept of bootstrap percolation on a directed random network. The experiment
consists in activating externally an initial random fraction of the neurons and
observe the process of firing until its equilibrium. The final portion of
neurons that are active depends in a non linear way on the initial fraction.
The main result of this paper is a theorem which enables us to find the
asymptotic of final proportion of the fired neurons in the case of random
directed graphs with given node degrees as the model for interacting network.
This gives a rigorous mathematical proof of a phenomena observed by physicists
in neural networks
On the low-temperature performances of THGEM and THGEM/G-APD multipliers in gaseous and two-phase Xe
The performances of THGEM multipliers in two-phase Xe avalanche mode are
presented for the first time. Additional results on THGEM operation in gaseous
Xe at cryogenic temperatures are provided. Stable operation of a double-THGEM
multiplier was demonstrated in two-phase Xe with gains reaching 600. These are
compared to existing data, summarized here for two-phase Ar, Kr and Xe
avalanche detectors incorporating GEM and THGEM multipliers. The optical
readout of THGEMs with Geiger-mode Avalanche Photodiodes (G-APDs) has been
investigated in gaseous Xe at cryogenic temperature; avalanche scintillations
were recorded in the Near Infrared (NIR) at wavelengths of up to 950 nm. At
avalanche charge gain of 350, the double-THGEM/G-APD multiplier yielded 0.07
photoelectrons per initial ionization electron, corresponding to an avalanche
scintillation yield of 0.7 NIR photons per avalanche electron over 4pi. The
results are compared with those of two-phase Ar avalanche detectors. The
advantages, limitations and possible applications are discussed.Comment: 22 pages, 14 figures. Revised Figs. 10,11 and Table 1. To be
published in JINS
Detectors for Energy-Resolved Fast Neutron Imaging
Two detectors for energy-resolved fast-neutron imaging in pulsed broad-energy
neutron beams are presented. The first one is a neutron-counting detector based
on a solid neutron converter coupled to a gaseous electron multiplier (GEM).
The second is an integrating imaging technique, based on a scintillator for
neutron conversion and an optical imaging system with fast framing capability
- …