Search

The New Small Wheel (NSW) is an upgrade for the ATLAS detector to provide enhanced triggering and reconstruction of muons in the forward region. The large LV power demands of the NSW necessitate a point-of-load architecture with on-detector power conversion. The radiation load and magnetic field of this environment, while significant, are nevertheless still in the range where commercial-off-the-shelf power devices may suffice. We present studies on the radiation-hardness and magnetic-field tolerance of several candidate buck converters and linear regulators. Device survival and performance are characterized when exposed to gamma radiation, neutrons, protons and magnetic fields.

Radiation hardness is one of the fundamental parameters characterizing a scintillator. The reason is that ionizing radiation often induces the formation of color centers in the irradiated material. These centers are related to lattice defects and may absorb light in the visible range. Possible overlap of the induced absorption spectrum with the emission spectrum of the scintillator can reduce the number of photons emitted by the scintillator, influencing negatively the energy resolution of the detector. In this paper, the irradiation (/sup 60/Co) induced absorption of Ce/sup 3+/ (Tb/sup 3+/) phosphate scintillating glasses is reported in the dose range 1-10 Gy. Irradiation tests were performed in the "Calliope" irradiation plant, placed in the Research Centre ENEA-Casaccia in the same dosimetric point (3.7 Gy/h), and the irradiation-induced damage was investigated by transmission measurements. Results are discussed by taking into account the possible dependence of radiation hardness on the composition of glass matrix.

A novel pair of transition metal ions Cu+, Mn2+ is co-doped in borosilicate glasses. Both copper and manganese ions exist in lower valence states (Cu+, Mn2+) in the as-prepared glasses. Around 5-time enhanced Mn2+ emission under the UV excitation is observed, which, as demonstrated by excitation spectra and emission decay curves, is due to an energy transfer from Cu+ ions resulting in greatly increased absorption of Mn2+ ions in the UV region, and relaxation on doubly-forbidden transition of Mn2+ leading to the much shortened Mn2+ emission lifetime from millisecond to microsecond level. Besides, a composite white emission is generated by combining the blue-green part from Cu+ ions with the green-red part from Mn2+ ions and it can be effectively tuned from cold to warm by adjusting host glass composition and altering excitation wavelength. Relevant mechanisms are discussed.

Several types of organic scintillator were exposed to a 60 Co γ-ray source at a dose rate of 1.838 x 10 −2 Gy/s in order to study the radiation damage in the range 10 3 -4 x 10 4 Gy of absorbed dose, both in air and in nitrogen environment. The effect of radiation damage was measured by the change in optical transmission and light output before and after the irradiation of each sample. A different degree of damage, related to the type of scintillator and to the radiation environment, was observed.

Optical characterization of scintillating phosphate and silicates glasses is presented including absorption, emission spectra and decay kinetics. A new concept of energy transfer sensitization is developed, based on nearly resonant energy migration through a rare earth ion subsystem (Gd 3+ ions at sufficiently high concentration) in the glass matrix, followed by a single-step transfer towards the emission centers created by Ce 3+ or Tb 3+ doping. While Ce 3+ doping in phosphates results in emission spectra in the near UV-violet, the Tb 3+ doping in silicates gives a four-band spectrum with a dominating one at 545 nm. Intense UV irradiation produces a reduction of emission intensity in phosphate glasses.

Avalanche photodiodes have been chosen as photon sensors for the electromagnetic calorimeter of the CMS experiment at the LHC. These sensors should operate in the 4 T magnetic field of the experiment. Because of the high neutron radiation in the detector extensive studies have been done by the CMS collaboration on the APD neutron radiation damage. The characteristics of these devices after irradiation have been analyzed, with particular attention to the quantum efficiency and the dark current. The recovery of the radiation-induced dark current has been studied carefully at room temperature and at slightly lower and higher temperatures. The temperature dependence of the annealing has been evaluated.

Prototypes of DC/DC power and Point of Load (PoL) converters were designed and built with the aim of satisfying the foreseen working parameters of the High Luminosity (HL) LHC experiments, using both Silicon (Si) MOSFETs and/or more recent devices substantiated of better power performance, like Silicon Carbide (SiC) and Gallium Nitride (GaN) transistors. Optimization of their design, based on the comparison between the simulated and measured thermal, electrical and mechanical performance, is in progress, and many improvements with respect to the previous versions are under implementation. We discuss in this paper the results of the last modifications. In addition, many tens of discrete component samples, chosen among the devices commercially available in the three different technologies (Si, SiC and GaN), were electrically characterized and tested under γ-rays, neutron, proton and heavy ion radiation, also using a combined run method. We have also planned to test some commercial DC/DCs under the extreme conditions of radiation and magnetic field expected in the upgrades of the LHC experiments. Here we show the first results on few samples. © 2014 IOP Publishing Ltd and Sissa Medialab srl.

A very good radiation resistance of lead tungstate crystals is mandatory for their use in the high-precision electromagnetic calorimeter of the CMS experiment at LHC. Since the beginning of 1996 we have organised systematic investigations of the parameters influencing the radiation hardness of this crystal. Two classes of parameters have been particularly studied, the first one related to the control of the stoichiometry and structure-associated defects, the second one connected with the suppression and the charge compensation of existing defects with different kinds of doping ions. This paper reports about the second part of this study and complements a first paper where the role of the stoichiometry was already discussed. Results of tests are given on a significant statistical sample of full size crystals (23 cm) which show a considerable improvement in the optical properties and the radiation resistance of appropriately doped crystals.

In the framework of its search for new heavy, fast and radiation hard scintillators for calorimetry at future colliders, the Crystal Clear Collaboration performed a systematic investigation of the properties and of the scintillation and radiation damage mechanisms of CeF 3 monocrystals. Many samples of various dimensions up to 3 × 3 × 28 cm 3 were produced by industry and characterised in the laboratories by different methods such as: optical transmission, light yield and decay time measurements, excitation and emission spectra, gamma and neutron irradiations. The results of these measurements are discussed. The measured light yield is compared to the theoretical expectations. Tests in high energy electron beams on a crystal matrix were also performed. The suitability of CeF 3 for calorimetry at high rate machines is confirmed. Production and economical considerations are discussed.

A systematic investigation of the properties of cerium fluoride monocrystals has been performed by the “Crystal Clear” collaboration in view of a p

Single crystals of PbWO 4 have been studied in connection with their application for high energy physics experiments. A comprehensive characterization of PbWO 4 by means of transmission, thermoluminescence and emission spectra measurements will be described. Annealing procedures in the air and vacuum atmospheres at high temperatures were used to study induced changes in the transmission. The gamma radiation induced changes in the absorption spectra of several PbWO 4 crystals of different origin, and intentionally doped will be illustrated.

Hydrogenated amorphous silicon films 0.45 and 1.12 μm thick, grown by RF glow discharge plasma PECVD on Corning-7059 glass, were irradiated by a 60Co source (activity 2.8 × 1015 Bq) in the dose range 10–450 kGy at different dose rates. The dark current of the samples, under 100 V applied voltage, was measured before, during and after gamma irradiation. When the irradiation starts, the dark current increases up to a level linearly dependent on the dose rate. When the irradiation is switched off, the dark current returns close to the initial value in a few days. Such behaviour suggests a possible application of hydrogenated amorphous silicon films in dosimetry and as gamma ray sensors. Moreover, the film optical constants were computed from the transmittance spectra measured in the range 500–2500 nm, before and after irradiation. After irradiation, the film optical absorption is slightly increased and the energy gap is substantially unchanged.

The features of the passive radiation damage (transmission loss) are reviewed for well known CsI(Tl), CeF3 and PbWO4 scintillators and the underlying physical mechanisms are discussed as well. Moreover, promising new material systems for scintillation detectors are briefly described.

The effect of several stable trivalentions (Lu, Y and Gd) and pentavalent Nb5+ on the radiation resistance and thermoluminescence characteristics of PbWO4 is investigated. While rather uniform behaviour is observed for all the trivalent ions, apparently different mechanisms apply in the case of the Nb doping. This fact could be explained by different effect of the dopants on the oxygen sublattice, namely on the concentration of oxygen vacancies. Electron centers based on oxygen vacancy(ies) participate in thermoluminescence processes round 200 K.

Transmittance and luminescence measurements of Bi-doped and Nb-doped PbWO4 crystals after vacuum annealing were performed. Annealing effect on the optical and scintillation properties of the crystals was detected at various annealing temperatures. The gamma radiation damage is presented at different absorbed doses to investigate radiation resistance after annealing.

(a) ENEA-INN/TEC, Via Anguillarese 301, S.Maria di Galeria, 00060 Roma, Italy (b) Institute of Physics, Cukrovarnicka 10, 16200 Prague, Czech Republic (c) INFN, Dept. of Physics, University of Roma 1, P. le A. Moro 2, Roma, Italy (d) SIT, Shonan Institute of Technology, Fujisawa 251, Japan (e) CRYTUR Preciosa a.s., Palackeho 175, 51119 Turnov, Czech Republic (f) KEK, National Laboratory for High Energy Physics, Tsukuba 305, Japan (g) INFM and Dept. of Physics, University of Milano, Via Celoria 16, 20133 Milano, Italy (h) Furukawa Co., Yoshima, Iwaki 970-11, Japan

A set of undoped, Ce/sup 3+/-doped and Si/sup 4+/-codoped Y/sub 3/Al/sub 5/O/sub 12/ [yttrium aluminum garnet (YAG)] crystals were grown by the Czochralski method and submitted to /spl gamma/ irradiation in the dose range 1-236 Gy at RT, to investigate the possibility to reinforce crystal radiation hardness by Si/sup 4+/ doping. The absorption coefficients induced by the irradiation were calculated and analyzed. Crystals also underwent light yield (LY) and scintillation decay measurements using the /sup 241/Am and /sup 22/Na radioactive sources in 1 /spl mu/s time gate. The induced absorption at 550 nm (at the Ce/sup 3+/ luminescence peak) decreases with Ce concentration and further decrease is obtained in the Si/sup 4+/-codoped samples. LY values are independent on the Ce/sup 3+/ concentration within 0.12% - 0.3% and on the moderate Si/sup 4+/ codoping as well.