Self-absorption in SrI2:2%Eu2+ between 78K and 600K

Self-absorption of the Eu2+ emission is an important aspect in SrI2:Eu that affects its scintillation performance. To calculate the probability of self-absorption, we measured the light yield and the decay time of 1–15 mm thick SrI2:2%Eu samples at temperatures between 78 K and 600 K. The obtained properties of SrI2:2%Eu crystals were then compared to those of SrI2:5%Eu. The decay times of SrI2:5%Eu crystals were the same or somewhat longer compared to those of twice as thickSrI2:2%Eu crystals. Accordingly, doubling the thickness has the same effect on the probability of self-absorption as doubling the Eu concentration

Optical and scintillation properties of CsBa2I5:Eu2+

The scintillation and luminescence properties of pure CsBa2I5 and CsBa2I5 doped with 0.5% Eu and 5% Eu were studied between 78 K and 600 K. Single crystals were grown by the vertical Bridgman method from the melt. CsBa2I5:5% Eu showed a light yield of 80,000 photons/MeV, an energy resolution of 2.3% for the 662 key full absorption peak, and an excellent proportional response. Two broad emission bands centered at 400 nm and 600 nm were observed in the radioluminescence spectrum of pure CsBa2I5. The Eu2+ 5d-4f emission band was observed at 430 nm. The radiative lifetime of the Eu2+ excited state was determined as 350 ns. With increasing temperature and Eu concentration the Eu2+ emission shifts to longer wavelengths and its decay time lengthens as a result of self-absorption of the Eu2+ emission. Multiple thermoluminescence glow peaks and a sharp decrease of the light yield at temperatures below 200 K were observed and related to the presence of the charge carrier traps in CsBa2I5:Eu

Optical properties and defect structure of Sr2+ co-doped LaBr3:5%Ce scintillation crystals

Sr2+ co-doped LaBr3:5%Ce scintillators show a record low energy resolution of 2% at 662 keV and a considerably better proportional response compared to standard LaBr3:5%Ce. This paper reports on the optical properties and time response of Sr co-doped LaBr3:5%Ce. Multiple excitation and emission bands were observed in X-ray and optically excited luminescence measurements. Those bands are ascribed to three different Ce3+ sites. The first is the unperturbed site with the same luminescence properties as those of standard LaBr3:Ce. The other two are perturbed sites with red-shifted 4f-5d1 Ce3+ excitation and emission bands, longer Ce3+ decay times, and smaller Stokes shifts. The lowering of the lowest 5d level of Ce3+ was ascribed to larger crystal field interactions at the perturbed sites. Two types of point defects in the LaBr3 matrix were proposed to explain the observed results. No Ce4+ ions were detected in Sr co-doped LaBr3:5%Ce by diffuse reflectance measurements

STED properties of Ce^3+, Tb^3+, and Eu^3+ doped inorganic scintillators

Scintillator-based X-ray imaging is a powerful technique for noninvasive real-space microscopic structural investigation such as synchrotron-based computed tomography. The resolution of an optical image formed by scintillation emission is fundamentally diffraction limited. To overcome this limit, stimulated scintillation emission depletion (SSED) X-ray imaging, based on stimulated emission depletion (STED) microscopy, has been recently developed. This technique imposes new requirements on the scintillator material: efficient de-excitation by the STED-laser and negligible STED-laser excited luminescence. In this work, luminescence depletion was measured in several commonly-used Ce3+, Tb3+, and Eu3+ - doped scintillators using various STED lasers. The depletion of Tb3+ and Eu3+ via 4f-4f transitions was more efficient (Ps = 8…19 mW) than Ce3+ depletion via 5d-4f transitions (Ps = 43…45 mW). Main origins of STED-laser excited luminescence were one- and two-photon excitation, and scintillator impurities. LSO:Tb scintillator and a 628 nm cw STED-laser is the most promising combination for SSED satisfying the above-mentioned requirements

Stimulated scintillation emission depletion X-ray imaging

ISSN:1094-408

Improved scintillation proportionality and energy resolution of LaBr3LaBr_3:Ce at 80 K

Using highly monochromatic synchrotron X-rays in the energy range from 10.5 keV to 100 keV the temperature dependence of nonproportionality and energy resolution of LaBr3 scintillators doped with 5% Ce3+ were studied at 80K, 295K, and 450K. Improvement of the proportionality and better energy resolution was observed on lowering the temperature. This effect suggests that the already outstanding energy resolution of LaBr3:Ce can be improved even further. It also may provide new clues to better understand the processes that cause nonproportionality of inorganic scintillator response.Comment: 5 pages, 2 figures submitted for publication at Nucl. Instr. Meth.

Higgs Boson Mass and New Physics

We discuss the lower Higgs boson mass bounds which come from the absolute stability of the Standard Model (SM) vacuum and from the Higgs inflation, as well as the prediction of the Higgs boson mass coming from the asymptotic safety of the SM. We account for the three-loop renormalization group evolution of the couplings of the SM and for a part of the two-loop corrections that involve the QCD coupling alpha(s) to the initial conditions for their running. This is one step beyond the current state-of-the-art procedure ("one-loop matching-two-loop running"). This results in a reduction of the theoretical uncertainties in the Higgs boson mass bounds and predictions, associated with the SM physics, to 1-2GeV. We find that with the account of existing experimental uncertainties in the mass of the top quark and alpha(s) (taken at the 2 sigma level) the bound reads M-H >= M-min (equality corresponds to the asymptotic-safety prediction), where M-min = (129 +/- 6) GeV. We argue that the discovery of the SM Higgs boson in this range would be in agreement with the hypothesis of the absence of new energy scales between the Fermi and Planck scales, whereas the coincidence of M-H with M-min would suggest that the electroweak scale is determined by Planck physics. In order to clarify the relation between the Fermi and Planck scales a construction of an electron-positron or muon collider with a center-of-mass energy similar to (200 + 200 GeV) (Higgs and t-quark factory) would be needed

A facility to search for hidden particles at the CERN SPS: the SHiP physics case.

The standard model of elementary particle physics has provided a consistent description of Nature's fundamental constituents and their interactions. Its predictions have been tested and confirmed by numerous experiments. The Large Hadron Collider's runs at 7 and 8 TeV culminated in the discovery of a Higgs boson-like particle with the mass of about 126 GeV—the last critical standard model component [1–5]. Thus for the first time we are in the situation when all the particles, needed to explain the results of all previous accelerator experiments have been found. At the same time, no significant deviations from the standard model were found in direct or in indirect searches for new physics (see e.g. the summary of the recent search results in [6–25] and most up-to-date information at [26–29]). For this particular value of the Higgs mass it is possible that the standard model remains mathematically consistent and valid as an effective field theory up to a very high energy scale, possibly all the way to the scale of quantum gravity, the Planck scale [30–32]