Absolute light yield measurements on SrF2_{2} and BaF2_{2} doped with rare earth ions

Results of absolute light output measurements on strontium and barium fluoride doped with PrF$_3$ and CeF$_3$ are presented and compared with scintillators having well-known light output (NaI-Tl, CsI-Tl, BGO). For pure SrF$_2$ crystal we obtain a value of about 28600 photons/MeV.Comment: 5 pages, 2 figure

Luminescence of cadmium fluoride doped with rare-earth ions

Absorption, excitation and emission spectra of cadmium fluoride crystals doped with rare-earth ions were investigated. In contrast to alkaline-earth fluorides the absorption spectra due to 4f - 5d transitions of Ce$^{3+}$, Pr$^{3+}$ and Tb$^{3+}$ ions are broadened. No 5d-4f emissions were observed. These prove that 5d(e$_g$) levels of rare earth ions lie in conduction band of CdF$_2$ crystal. Emission spectra of Tb$^{3+}$ show the group of 4f-4f $^5$D$_4$-$^7$F$_j$ lines in contrast to other alkaline-earth fluorides where emission due to $^5$D$_3$-$^7$F$_j$ transitions is also observed. The absence of the emission is due to position of $^5$D$_3$ level within condution band. Among the all measured crystals doped with impurity ions (Pr, Nd, Eu, Ho, Tb, Tm, Yb, Ga, In or Mn), the CdF$_2$ doped with Pr$^{3+}$, Tb$^{3+}$, or Mn$^{2+}$ ions have the highest light outputs under x-ray excitation.Comment: presented on conference SCINT201

Comparison of Ce3+^{3+} and Pr3+^{3+} activators in alkaline-earth fluoride crystals

The emission spectra of Ce$^{3+}$ or Pr$^{3+}$ doped CaF$_2$, SrF$_2$, BaF$_2$ excited by vacuum ultraviolet photons or by x-ray as well as excitation and absorption spectra in vacuum ultraviolet region (6-13 eV) were studied. The transfer of exciton energy is the main channel for Ce$^{3+}$ excitation in alkaline-earth fluorides. Three different stages of energy transfer were observed. Pr$^{3+}$ excited by two processes, slow f-f luminescence excited by excitons, fast d-f luminescence excited by some fast process.Comment: 4 pages, 8 figure

Forty-fifth anniversary of the Nambu-Jona-Lasinio model

A short review of the development of the Nambu-Jona-Lasinio (NJL) model is given. The SU(2)x SU(2) and U(3)x U(3) local quark NJL models are considered. The mechanisms of spontaneous breaking of chiral symmetry and vector dominance are shown. The local NJL model allows us to describe the mass spectrum and main strong and electroweak decays of the four ground-state nonets of pseudoscalar, scalar, vector and axial-vector mesons. Applications of this model to the description of mesons in hot and dense medium are discussed. It is shown that for solving problems connected with the description of the meson radial excitations and quark confinement it is necessary to consider a nonlocal extension of the NJL model. The main attention is attracted to the description of the methods used in different versions of the NJL model. Physical results for low-energy hadron physics obtained in these models can be found in the cited works.Comment: 19 pages, 2 figure

Anomalous europium luminescence in LaF3

Optical spectra (absorption, emission, excitation, decay) and dielectric relaxation were measured for divalent europium (and partially for ytterbium) in lanthanum fluoride crystals. Absorption of Eu$^{2+}$ contains not only asymmetric weakly structured band at 245 nm but also long-wavelength bands at 330, 380 nm. Broadband Eu$^{2+}$ emission at 600 nm appeared below 80 K, having decay time 2.2 $\mu$s at 7.5 K. Emission at 600 nm is attributed to so-called anomalous luminescence. Bulk conductivity is directly proportional to absorption coefficient of Eu$^{2+}$ bands. Dielectric relaxation peak of LaF$_3$-EuF$_3$ is attributed to rotation of dipoles Eu$^{2+}$-anion vacancy. The long-wavelength absorption bands at 330, 380 nm are assigned to transitions from 4f$^7$ Eu$^{2+}$ ground state to states of neighbouring fluorine vacancy.Comment: presented on LUMDETR2015 conference, submitted to Radiation Measurement

Charged pion polarizability in the nonlocal quark model of Nambu-Jona-Lasinio type

The polarizability of a charged pion is estimated in the framework of the nonlocal chiral quark model of the Nambu--Jona-Lasinio type. Nonlocality is described by quark form factors of the Gaussian type. It is shown that the polarizability in this model is very sensitive to the form of nonlocality and choice of the model parameters.Comment: 5 pages, 2 figure

Vacuum ultraviolet 5d1^14f9^9-4f10^{10} emission of Ho3+^{3+} ions in alkaline-earth fluorides

Time-resolved emission, excitation as well as emission decay curves of CaF$_2$, SrF$_2$, BaF$_2$ doped with HoF$_3$ were investigated. Most intensive emission bands near 168 nm, having long decay time, belong to spin-forbidden transitions from 5d$^1$4f$^9$ high spin (HS) states to ground $^5$I$_8$ states of Ho$^{3+}$ ions. Weak spin allowed 5d$^1$4f$^9$(LS)-4f$^{10}$ emission band at 158 nm was observed only in CaF$_2$-Ho crystals. Spin allowed and spin-forbidden excitation bands were observed in all crystals near 166 and 155 nm respectively. Fast component of spin-forbidden emissions due to multiphonon relaxation to low-lying 4f$^{10}$ Ho$^{3+}$ level was observed for all crystals.Comment: 4 pages, 7 figure

Mott dissociation of pions and kaons in hot, dense quark matter

We describe the Mott dissociation of pions and kaons within a Beth-Uhlenbeck approach based on the PNJL model, which allows for a unified description of bound, resonant and scattering states. Within this model we evaluate the temperature and chemical potential dependent modification of the phase shifts both in the pseudoscalar and scalar isovector meson channels for $N_f=2+1$ quark flavors. We show that the character change of the pseudoscalar bound states to resonances in the continuum at the Mott transition temperature is signaled by a jump of the phase shift at the threshold from $\pi$ to zero, in accordance with the Levinson theorem. In particular, we demonstrate the importance of accounting for the scattering continuum states, which ensures that the total phase shift in each of the meson channels vanishes at high energies, thus eliminating mesonic correlations from the thermodynamics at high temperatures. In this way, we prove that the present approach provides a unified description of the transition from a meson gas to a quark-gluon plasma. We discuss the occurrence of an anomalous mode for mesons composed of quarks with unequal masses which is particularly pronounced for $K^+$ and $\kappa^+$ states at finite densities a a possible mechanism to explain the "horn" effect for the $K^+/\pi^+$ ratio in heavy-ion collisions.Comment: 11 pages, 9 figures, discussion of K+/pi+ and references adde

The Pauli Form Factor of Quark and Nontrivial Topological Structure of the QCD

We calculate the electromagnetic Pauli form factor of quark induced by the nontrivial topological fluctuations of QCD vacuum called instantons. It is shown that such contribution is significant. We discuss the possible implications of our result in the photon-hadron reactions and in the dynamics of quark-photon interactions in the dense/hot quark matter.Comment: 5 pages, 4 figures,conclusion extended and references adde

The meson-exchange induced light--by--light contribution to (g−2)μ(g-2)_\mu within the nonlocal chiral quark model

The current status of the muon anomalous magnetic moment (AMM) problem is briefly presented. The corrections to the muon AMM coming from the effects of hadronic light-by-light (LbL) scattering due to light quark-antiquark exchange in pseudoscalar and scalar channels are estimated within the nonlocal chiral quark model (N$\chi$QM). Within this approach the full kinematic dependence on the photon and meson virtualities are taken into account. As a result, the meson exchange contributions to the muon AMM calculated within N$\chi$QM are, in general, smaller than the contributions obtained within other models. The contribution from the scalar channel is positive and small, but stabilizes the combined with pseudoscalar channel result with respect to variation of the model parameters.Comment: 6 pages, 3 figures. Talk at Light Cone 2012 Conference, 8-13 July 2012, Cracow, Polan