K. W. Krämer

Scintillation properties of RbGd/sub 2/Br/sub 7/:Ce. Advantages and limitations

The scintillation properties of RbGd/sub 2/Br/sub 7/ crystals, doped with Ce/sup 3+/ concentrations of 0.02, 0.11, 0.88, 2.05, 4.1, and 9.8%, are studied under X-ray and /spl gamma/-quanta excitations. For the RbGd/sub 2/Br/sub 7/ sample doped with 9.8% Ce, the authors measured a light yield of 56000/spl plusmn/6000 photons per MeV of absorbed /spl gamma/-ray energy with a main decay time of 43/spl plusmn/1 ns, using a Hamamatsu R1791 photomultiplier (PMT), a /sup 137/Cs radioactive source, and a shaping time of 10 /spl mu/s. A time resolution of 790/spl plusmn/10 ps was measured for the RbGd/sub 2/Br/sub 7/:9.8% Ce compound, using BaF/sub 2/ as second scintillator, two XP2020Q PMTs, a /sup 22/Na source, and an energy threshold set at E/spl ges/511 keV. With the R1791 PMT, an energy resolution of 4.1% (FWHM over peak position) for the 662-keV full absorption peak has been observed for two crystals of 7/spl times/4/spl times/2 mm/sup 3/ and 15/spl times/5/spl times/1 mm/sup 3/ with 4.1 and 9.8% Ce content, respectively. Moreover, the nonproportional responses of three RbGd/sub 2/Br/sub 7/:Ce compounds with different concentrations (0.11, 2.05, and 9.8%) were studied revealing an almost-constant light output response from 17.4 keV to 1 MeV. These properties are compared to three other well-known scintillators: NaI:Tl, CsI:Tl, and Lu/sub 2/SiO/sub 5/:Ce.

New thermal neutron scintillators: Cs/sub 2/LiYCl/sub 6/:Ce/sup 3+/ and Cs/sub 2/LiYBr/sub 6/:Ce/sup 3+/

The thermal neutron detection properties of Cs/sub 2/LiYCl/sub 6/:0.1%Ce/sup 3+/ and Cs/sub 2/LiYBr/sub 6/:1%Ce/sup 3+/ single crystals are presented. The compounds show high scintillation photon yields of 70 000 and 88 200 photons emitted per absorbed thermal neutron, respectively. Events caused by primary electrons with energy below 2.9 and 3.4 MeV, respectively, can be separated from neutron-induced events by pulse-height discrimination. For Cs/sub 2/LiYCl/sub 6/:0.1Ce/sup 3+/, due to the presence of a 4-ns fast core-valence luminescence, thermal neutrons and gamma rays can also be discriminated by means of the shape of the scintillation pulse. The main part of the scintillation pulse in Cs/sub 2/LiYCl/sub 6/:0.1%Ce/sup 3+/ is relatively slow, however, Cs/sub 2/LiYBr/sub 6/:1%Ce/sup 3+/ has a relatively intense component with /spl tau/=85;ns decay time.

Scintillation properties of LuI/sub 3/:Ce/sup 3+/-high light yield scintillators

The scintillation properties of LuI/sub 3/:Ce/sup 3+/(pure, 0.5%, 2%, and 5% Ce/sup 3+/), a new member of the generation of Ce/sup 3+/ doped lanthanide trihalide scintillators, are presented. This material has a calculated density of 5.6 g/cm/sup 3/ and an atomic number Z/sub eff/ of 60.2. Under optical and X-ray excitation, Ce/sup 3+/ emission is observed to peak at 472 and 535 nm. A high light yield of 76 000 photons per MeV (ph/MeV) was measured for LuI/sub 3/:2% Ce/sup 3+/. LuI/sub 3/:Ce/sup 3+/ has a nonexponential decay time. The contribution of short decay components (within 50 ns) to the total light yield is around 50%. An energy resolution (full-width half maximum over peak position) for the 662 keV full energy peak of 4.7/spl plusmn/0.5% was observed for LuI/sub 3/:0.5% Ce/sup 3+/.

Lanthanide 4f-level location in lanthanide doped and cerium-lanthanide codoped NaLaF4 by photo- and thermoluminescence

Photo- and thermoluminescence (TL) spectra of NaLaF4:Ln3+ (Ln = Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm) and NaLaF4:Ce3+, Ln3+ (Ln = Nd,Sm,Ho,Er,Tm) are presented and used together with the empirical Dorenbos model in order to establish the 4f energy level positions of all tri- and divalent lanthanide ions doped in NaLaF4. The information will be presented in the form of an energy level diagram. It is shown that in addition to this diagram only two assumptions, viz., the presence of two host related electron traps and the presence of Vk-centers, are necessary for explaining the lanthanide-specific TL glow curves of both Ln mono- and Ce–Ln codoped NaLaF4.

Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder

We measure by inelastic neutron scattering the spin excitation spectra as a function of applied magnetic field in the quantum spin-ladder material (C5H12N)2CuBr4. Discrete magnon modes at low fields in the quantum disordered phase and at high fields in the saturated phase contrast sharply with a spinon continuum at intermediate fields characteristic of the Luttinger-liquid phase. By tuning the magnetic field, we drive the fractionalization of magnons into spinons and, in this deconfined regime, observe both commensurate and incommensurate continua.

High-light-output scintillator for photodiode readout: LuI3:Ce3+

In this paper, we investigated the scintillation properties of LuI3:Ce3+. Radioluminescence, light output, energy resolution, and ?-scintillation decay are reported. We find an extremely high light output of 98?000±10?000?photons/MeV. LuI3:Ce3+ also gives a very high electron-hole (e-h) pair response when it is coupled with an avalanche photodiode (APD) (92?000±9000?e?h?pairs?MeV). With an APD, a best energy resolution (full width at half maximum over the peak position) of 3.3%±0.3% for 662?keV ? quanta is observed. A combination of an extremely high light output and a good energy resolution makes LuI3:Ce3+ an ideal scintillator for radiation sensor applications. Some drawbacks due to the hygroscopicity and the difficult growth of LuI3:Ce3+ crystals are also discussed.

Development of elpasolite and monoclinic thermal neutron scintillators

Scintillation properties of Ce doped Cs/sub 2/LiYBr/sub 6/, Rb/sub 2/LiScBr/sub 6/, Rb/sub 2/LiYBr/sub 6/, Rb/sub 2/LiLaBr/sub 6/, Rb/sub 2/LiYI/sub 6/ elpasolite, and Li/sub 3/YBr/sub 6/ monoclinic inorganic thermal-neutron scintillator crystals were investigated. Light yields and decay times were studied. Cs/sub 2/LiYBr/sub 6/:Ce and Rb/sub 2/LiYBr/sub 6/:Ce show a high light yield of /spl ges/64,000 photons per thermal neutron. More details will be presented and advantages and disadvantages of these new scintillator materials will be discussed.

Li-Based Thermal Neutron Scintillator Research;

We investigated gamma- and neutron-scintillation properties of A₂LiLnX₆:Ce³⁺ (A=Cs, Rb, K, Na, Li; Ln=La, Y, Lu, Sc; X=Br, I) with the aim to develop new scintillators with high neutron detection efficiencies. Among the investigated thermal neutron scintillators, Rb₂LiYBr₆:Ce³⁺ shows an excellent neutron peak resolution of 3.6%. This is the best neutron peak resolution ever reported. Together with the large alpha/beta ratio of 0.74, Rb₂LiYBr₆:Ce³⁺ offers the possibility of excellent neutron/gamma discrimination. The highest thermal neutron scintillation light yield of 83,000 photons/neutron is also reported for Rb₂LiYBr₆:Ce³⁺.

{\hbox {Rb}}_{2}{\hbox {LiYBr}}_{6}:{\hbox {Ce}}^{3+}

Here, we report the scintillation properties of LaBr3?xIx:5%Ce3+ with four different compositions of x, i.e., x = 0.75, 1.5, 2, and 2.25. Radioluminescence spectra reveal a shift of the emission wavelength with the LaBr3 to LaI3 ratio. LaBr1.5I1.5:5%Ce3+ shows the highest scintillation light yield of 58?000?photons/MeV, whereas LaBr0.75I2.25:5%Ce3+ shows the fastest scintillation decay time of 12 ns under 662 keV ?-ray excitation. This decay time is faster than that of 16 ns in LaBr3:Ce3+. The temperature dependence of radioluminescence spectra is presented. The structures and lattice parameters of the materials were determined from powder x-ray diffraction.

and Other Elpasolites

Scintillation and luminescence characteristics of Rb2LiYBr6 doped with 0.1%, 0.5%, 1%, and 5%?Ce3+ are presented. Under optical and x-ray excitation, Ce3+ doublet emission is observed at 385 and 420 nm. Rb2LiYBr6:0.5%?Ce3+ shows very high thermal neutron scintillation light output of 83?000 photons/neutron. An excellent neutron peak resolution of 3.6% (full width at half maximum over peak position) is observed for the 4.8 MeV neutron-reaction products energy response in Rb2LiYBr6:0.1%?Ce3+. This peak shows up at 3.6 MeV ?-equivalent energy and therefore it gives an ?/? ratio of 0.74. The combination of a large fraction of neutron absorption in natural i?(62%), a sharp neutron response peak, high light yield, and large ?/? ratio makes Rb2LiYBr6:Ce3+ an efficient scintillator for thermal neutron detection.