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Observation of scattering and absorption centers in lead fluoride crystals  [PDF]
Patrick Achenbach
Physics , 2006, DOI: 10.1109/23.907578
Abstract: For the first time, lead fluoride is used as a fast and compact material in electromagnetic calorimetry. Excellent optical and mechanical properties of the pure Cherenkov crystals are necessary for the A4 collaboration to perform a measurement of the nucleon's strange form factors. Visible scattering and absorption centers as well as surface damages have been investigated to characterize the quality of more than one thousand crystals. Besides, transmittance measurements have been performed on all crystals to reveal absorption bands produced by intrinsic or impurity related point-structure defects. As a consequence, 89 crystals had to be replaced by the Chinese manufacturer SICCAS.
Contributions of Cherenkov Light to the Signals from Lead Tungstate Crystals  [PDF]
N. Akchurin
Physics , 2007, DOI: 10.1016/j.nima.2007.08.174
Abstract: Results are presented of detailed measurements of the signals generated by high-energy electrons and muons in lead tungstate crystals. A significant fraction of the light produced in these crystals and detected by photomultiplier tubes is the result of the \v{C}erenkov mechanism. This is concluded from the angular dependence of the signals and from their time structure. Depending on the orientation of the crystals and on the particle type, \v{C}erenkov light may account for up to 15% of the total signals.
Scattering Particles in Lead Fluoride Crystals
氟化铅晶体中的散射颗粒

REN Guo-Hao,SHEN Ding-Zhong,WANG Shao-Hua,YIN Zhi-Wen,
任国浩
,沈定中,王绍华,殷之文

无机材料学报 , 1999,
Abstract: Based on the observation with optical microscope and analysis by EDS of electron microprobe and scan electron microscope, the scattering particles existing in lead fluoride crystals were firstly confirmed to be lead metal Their shapes are characterized by gradually evolving from irregrlar shape to diamond shape There is a face which direction is always parallel to the (100) face of PbF 2 crystal It was suggested that the scattering particles are formed from the following process: reduction of lead metal, inclusion of melt, nucleation and solidification along some dection of PbF 2 crystal
A study of high-energy proton induced damage in Cerium Fluoride in comparison with measurements in Lead Tungstate calorimeter crystals  [PDF]
G. Dissertori,P. Lecomte,D. Luckey,F. Nessi-Tedaldi,Th. Otto,F. Pauss,S. Roesler,Ch. Urscheler
Physics , 2010, DOI: 10.1016/j.nima.2010.07.052
Abstract: A Cerium Fluoride crystal produced during early R&D studies for calorimetry at the CERN Large Hadron Collider was exposed to a 24 GeV/c proton fluence Phi_p=(2.78 +- 0.20) x 10EE13 cm-2 and, after one year of measurements tracking its recovery, to a fluence Phi_p=(2.12 +- 0.15) x 10EE14 cm-2. Results on proton-induced damage to the crystal and its spontaneous recovery after both irradiations are presented here, along with some new, complementary data on proton-damage in Lead Tungstate. A comparison with FLUKA Monte Carlo simulation results is performed and a qualitative understanding of high-energy damage mechanism is attempted.
Realtime calibration of the A4 electromagnetic lead fluoride calorimeter  [PDF]
S. Baunack,D. Balaguer Ríos,L. Capozza,J. Diefenbach,R. Frascaria,B. Gl?ser,D. v. Harrach,Y. Imai,R. Kothe,R. Kunne,J. H. Lee,F. E. Maas,M. C. Mora Espí,M. Morlet,S. Ong,E. Schilling,J. van de Wiele,C. Weinrich
Physics , 2011, DOI: 10.1016/j.nima.2011.02.099
Abstract: Sufficient energy resolution is the key issue for the calorimetry in particle and nuclear physics. The calorimeter of the A4 parity violation experiment at MAMI is a segmented calorimeter where the energy of an event is determined by summing the signals of neighbouring channels. In this case the precise matching of the individual modules is crucial to obtain a good energy resolution. We have developped a calibration procedure for our total absorbing electromagnetic calorimeter which consists of 1022 lead fluoride (PbF_2) crystals. This procedure reconstructs the the single-module contributions to the events by solving a linear system of equations, involving the inversion of a 1022 x 1022-matrix. The system has shown its functionality at beam energies between 300 and 1500 MeV and represents a new and fast method to keep the calorimeter permanently in a well-calibrated state.
Determination of shower central position in laterally segmented lead-fluoride electromagnetic calorimeters  [PDF]
M. Mazouz,L. Ghedira,E. Voutier
Physics , 2015,
Abstract: The spatial resolution of laterally segmented electromagnetic calorimeters is studied on the basis of Monte-Carlo simulations worked-out for lead fluoride material. Parametrization of the relative resolution is proposed and optimized in terms of the energy of incoming particles and the elementary size of the calorimeter blocks. A new fit algorithm method is proposed that improves spatial resolution at high energies, and provides guidance for the design optimization of electromagnetic calorimeters.
Studies of an array of PbF2 Cherenkov crystals with large-area SiPM readout  [PDF]
A. T. Fienberg,L. P. Alonzi,A. Anastasi,R. Bjorkquist,D. Cauz,R. Fatemi,C. Ferrari,A. Fioretti,A. Frankenthal,C. Gabbanini,L. K. Gibbons,K. Giovanetti,S. D. Goadhouse,W. P. Gohn,T. P. Gorringe,D. W. Hertzog,M. Iacovacci,P. Kammel,J. Kaspar,B. Kiburg,L. Li,S. Mastroianni,G. Pauletta,D. A. Peterson,D. Pocanic,M. W. Smith,D. A. Sweigart,V. Tishchenko,G. Venanzoni,T. D. Van Wechel,K. B. Wall,P. Winter,K. Yai
Physics , 2014, DOI: 10.1016/j.nima.2015.02.028
Abstract: The electromagnetic calorimeter for the new muon (g-2) experiment at Fermilab will consist of arrays of PbF2 Cherenkov crystals read out by large-area silicon photo-multiplier (SiPM) sensors. We report here on measurements and simulations using 2.0 -- 4.5 GeV electrons with a 28-element prototype array. All data were obtained using fast waveform digitizers to accurately capture signal pulse shapes versus energy, impact position, angle, and crystal wrapping. The SiPMs were gain matched using a laser-based calibration system, which also provided a stabilization procedure that allowed gain correction to a level of 1e-4 per hour. After accounting for longitudinal fluctuation losses, those crystals wrapped in a white, diffusive wrapping exhibited an energy resolution sigma/E of (3.4 +- 0.1) % per sqrt(E/GeV), while those wrapped in a black, absorptive wrapping had (4.6 +- 0.3) % per sqrt(E/GeV). The white-wrapped crystals---having nearly twice the total light collection---display a generally wider and impact-position-dependent pulse shape owing to the dynamics of the light propagation, in comparison to the black-wrapped crystals, which have a narrower pulse shape that is insensitive to impact position.
Luminescence of photochromic centers in calcium fluoride crystals doped with Lu$^{3+}$ ions  [PDF]
Roman Shendrik,Alexandra Myasnikova,Tatiana Sizova,Evgeny Radzhabov
Physics , 2015,
Abstract: We report data on the luminescence spectra associated with photochromic centers in X-ray irradiated calcium fluoride crystals doped with Lu ions. Irradiation in low energy photochromic centers absorption band excites emission, which can be identify with transitions into photochromic centers. Ab initio calculation of absorption spectrum of photochromic center agrees rather well with experimental data.
Spectroscopy of divalent rare earth ions in fluoride crystals  [PDF]
R. Shendrik,A. S. Myasnikova,E. A. Radzhabov,A. I. Nepomnyashchikh
Physics , 2015, DOI: 10.1016/j.jlumin.2015.06.055
Abstract: We have studied the absorption spectra of x-ray irradiation-induced Ce2+ and Pr2+ ions in crystals of alkaline-earth fluorides. We have calculated absorption spectra of divalent praseodymium ions in SrF2 crystals doped with Pr2+ for the first time. The calculated spectra agree rather well with the experimental data. In crystals containing induced Ce2+ ions we have found strong electron-phonon coupling. In BaF2, we do not observe bands corresponded to divalent Ce or Pr ions.
Computer simulations of the mechanism of thickness selection in polymer crystals  [PDF]
Jonathan Doye
Physics , 1999, DOI: 10.1016/S0032-3861(00)00229-9
Abstract: In this paper I describe the computer simulations that I have performed to critically examine the Lauritzen-Hoffman and the Sadler-Gilmer theories of polymer crystallization. In particular, I have computed the free energy profile for nucleation of a new crystalline layer on the growth face to compare with that assumed by the Lauritzen-Hoffman theory, I have analysed the mechanism of thickness selection in a multi-pathway model in which some of the constraints in the Lauritzen-Hoffman theory are relaxed, and I have re-examined the model used by Sadler-Gilmer. These investigations have lead to a mechanism of thickness selection of lamellar polymer crystals that differs from the two theories that I set out to examine.
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