297 research outputs found
Hydrogen flash lamps studied
Parameters of gas pressure, type of gas, tube voltage, and electrode gap are tested on the intensity and shape of a radiation pulse from a hydrogen-filled lamp
Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors
We have constructed a GEANT4-based detailed software model of photon
transport in plastic scintillator blocks and have used it to study the NEMO-3
and SuperNEMO calorimeters employed in experiments designed to search for
neutrinoless double beta decay. We compare our simulations to measurements
using conversion electrons from a calibration source of and show
that the agreement is improved if wavelength-dependent properties of the
calorimeter are taken into account. In this article, we briefly describe our
modeling approach and results of our studies.Comment: 16 pages, 10 figure
A large-scale correlated study of linear optical absorption and low-lying excited states of polyacenes: Pariser-Parr-Pople Hamiltonian
In this paper we present large-scale correlated calculations of linear
optical absorption spectrum of oligo-acenes containing up to seven benzene
rings. For the calculations we used the Pariser-Parr-Pople (P-P-P) Hamiltonian,
along with the configuration interaction (CI) technique at various levels such
as the full CI (FCI), the quadruple CI (QCI) and multi-reference
singles-doubles CI (MRSDCI). The role of Coulomb parameters used in the P-P-P
Hamiltonian was examined by considering standard Ohno parameters, as well as a
screened set of parameters. A detailed analysis of the many-body character of
the important excited states contributing to the linear absorption has also
been performed. The results of our calculations have been compared extensively
with the theoretical work of other authors, as well as with the experiments.Comment: 45 pages, 9 figure
Solid-state-concentration effects on the optical absorption and emission of poly(p-phenylene vinylene)-related materials
We present measurements of the optical absorption and emission properties of poly(p-phenylene vinylene) (PPV)-related materials focusing on the differences between molecules isolated by dispersion in an inert host and concentrated molecular films. Optical absorption spectra, photoluminescence (PL) spectra, PL efficiency, and time-resolved PL spectra of dilute blends of PPV oligomers with 2-5 phenylene-phenyl rings are compared with those of dense oligomer and polymer films. In dilute oligomer-poly(methyl methacrylate) (PMMA) blends with high PL efficiency, the PL decay is exponential, independent of both temperature and oligomer length. This implies that the fundamental radiative lifetime of PPV oligomers is essentially independent of oligomer length. Concentrated spin-cast oligomer films and polymers have a faster and strongly temperature-dependent PL decay that approaches that of the dilute oligomer results at low temperature. The differences in PL decay correspond to changes in PL efficiency. The efficiency of the oligomer-PMMA blend is high and only weakly temperature dependent, whereas that of concentrated films is lower and strongly temperature dependent, decreasing by more than a factor of 3 from 10 to 350 K. The quenching of the PL efficiency in concentrated films is due to migration to extrinsic, impurity related centers as opposed to an intrinsic intermolecular recombination process. The PL spectrum of a dilute oligomer blend redshifts substantially, both as the excitation energy is decreased and as the emission time increases. This spectral redshift is due to disorder-induced site-to-site variation and not to diffusion to lower-energy sites. In contrast, no spectral shift with excitation energy or emission time was observed for dense oligomer films
Development of wavelength shifter coated reflectors for the ArDM argon dark matter detector
To optimise the design of the light readout in the ArDM 1-ton liquid argon
dark matter detector, a range of reflector and WLS coating combinations were
investigated in several small setups, where argon scintillation light was
generated by radioactive sources in gas at normal temperature and pressure and
shifted into the blue region by tetraphenyl butadiene (TPB). Various
thicknesses of TPB were deposited by spraying and vacuum evaporation onto
specular 3M{\small\texttrademark}-foil and diffuse
Tetratex{\small\textregistered} (TTX) substrates. Light yields of each
reflector and TPB coating combination were compared. Reflection coefficients of
TPB coated reflectors were independently measured using a spectroradiometer in
a wavelength range between 200 and 650 nm. WLS coating on the PMT window was
also studied. These measurements were used to define the parameters of the
light reflectors of the ArDM experiment. Fifteen large cm
TTX sheets were coated and assembled in the detector. Measurements in argon gas
are reported providing good evidence of fulfilling the light collection
requirements of the experiment.Comment: 21 pages, 17 figure
SiPMs coated with TPB : coating protocol and characterization for NEXT
Silicon photomultipliers (SiPM) are the photon detectors chosen for the
tracking readout in NEXT, a neutrinoless {\beta}{\beta} decay experiment which
uses a high pressure gaseous xenon time projection chamber (TPC). The
reconstruction of event track and topology in this gaseous detector is a key
handle for background rejection. Among the commercially available sensors that
can be used for tracking, SiPMs offer important advantages, mainly high gain,
ruggedness, cost-effectiveness and radio-purity. Their main drawback, however,
is their non sensitivity in the emission spectrum of the xenon scintillation
(peak at 175 nm). This is overcome by coating these sensors with the organic
wavelength shifter tetraphenyl butadienne (TPB). In this paper we describe the
protocol developed for coating the SiPMs with TPB and the measurements
performed for characterizing the coatings as well as the performance of the
coated sensors in the UV-VUV range.Comment: Submitted to the Journal of Instrumentation on december 26th 201
Volatilised pyrene: A phase 1 study demonstrating a new method of visualising fingermarks with comparisons to iodine fuming
Pyrene is a fluorescent polycyclic aromatic hydrocarbon that can be volatilised under mild conditions. When fumed, pyrene is rapidly absorbed into the sebaceous residues of fingermarks, enabling their fluorescent visualisation upon excitation with ultraviolet radiation. This new means of fluorescent fingermark detection is more sensitive than the non-fluorescent iodine fuming approach for nonporous surfaces. This is demonstrated here in a phase 1 study using split-print comparisons on metal and glass surfaces. Pyrene-treated fingermarks also retain the volatile fluorophore for comparably long time periods relative to iodine fuming (in the order of hours). The phase 1 study comprised four donors, and 80 natural fingermarks that were grouped into two time periods; aged 24 h and 1 week. Iodine fuming was chosen as a reference to showcase the effectiveness of pyrene given it is the most closely-related chemical fuming method in routine use. This study demonstrates that pyrene fuming increases the quantity and quality of fingermark visualisations relative to iodine fuming, and is free of many of the latter method’s drawbacks. Preliminary results shown here also show the effectiveness of pyrene fuming on highly patterned surfaces, and its compatibility with the use of gelatine lifters. Pyrene fuming is thus easy to effect, low-cost, and shows great promise as a new means of visualising fingermarks on non-porous surfaces
Fluorescence Lifetime Standards for Time and Frequency Domain Fluorescence Spectroscopy
- …