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Alkali-Free Ce-Doped and Co-Doped Fluorophosphate Glasses for Future HEP Experiments
Chen Hua, Alfred Margaryanb, Ashot Margaryanb, Fan Yanga,c, Liyuan Zhanga, and Ren-Yuan Zhua
California Institute of Technology,1200 E California Blvd, Pasadena, CA 91125, USA
AFO Research Inc., 676 W Wilson Ave #A, Glendale CA 91203, USA
Nankai University, 94 South Weijin Road, Tianjin, China, 300071
Abstract We report current status of alkali-free cerium-doped and co-doped fluorophosphate glasses as a potential inorganic scintillator for future HEP experiments. Optical and scintillation properties, such as emission, transmittance, light output, decay time and their degradation after γ-ray irradiations, are measured for glass samples produced at AFO Research Inc. Further developments are needed for this potential cost-effective glass scintillator to be used for the HHCAL detector concept. Because of its relatively lower fabrication cost as compared to inorganic crystals scintillating glasses have a potential to be used in future HEP experiment where a large volume of scintillators are needed. One example is the Homogeneous Hadronic Calorimeter (HHCAL) detector concept featured with unprecedented jet mass resolution by measuring both scintillation and Cherenkov light, where up to 100 m3 scintillators are required. With a density of 4.6 g/cm3 and a nuclear interaction length of 26.4 cm, alkali-free cerium-doped and co-doped fluorophosphate glass is a potential material for the HHCAL detector concept. We report optical and scintillation properties of fluorophosphate glass scintillators produced by AFO Research Inc. Fig. (a) shows ten glass samples of 10×10×10 mm3 with cerium doping levels ranged between 0.5 and 5 wt% and various co-doping. Fig. (b) and (c) show the excitation, emission and transmittance spectra for four glass samples. Also shown in Fig. (c) are the numerical values of the emission weighted longitudinal transmittance (EWLT) and the cutoff wavelength. Their cut-off wavelength is at ~340 nm excellent for Cherenkov light. Their emission is peaked at 367 nm, indicating no self-absorption.
(a) (b) (c)
Fig. (d) and (e) show the pulse height spectra (PHS) excited by 22Na γ-rays and 241Am α-rays respectively for four glass samples, and compared to a PWO sample of the same size. Their light output (LO) and FWHM energy resolution (E.R.) are also shown in the figures. While the γ-ray peaks are not well distinguished because of their low effective Z value, the α-ray peaks are clearly observed. The LO of samples 1 and 4 is higher than 2 and 3, and is also higher than PWO. Fig. (f) shows decay kinetics of their scintillation light. All four samples have a decay time of about 40 ns originated from the cerium dopant. An ytterbium co-doped sample shows an additional faster decay component with a decay time of 12 ns.
(d) (e) (f)
Fig. (g) and (h) show the transmittance spectra and the α-exited PHS respectively for four glass samples before and after irradiation with ionization doses of 10 and 100 krad. Corresponding values of EWLT, cut-off wavelength, LO and E.R. are also shown. Fig. (i) summarizes the normalized values of EWLT (top) and LO in 200 ns gate (bottom) as a function of the integrated dose. While samples 1 and 4 are more radiation hard than 2 and 3, significant radiation damage is observed in all samples. The result shows that these glasses may be used in a radiation environment up to 10 krad.
(g) (h) (i)
R&D will continue to improve optical and scintillation quality and radiation hardness for fluorophosphate glass scintillators. If successful, this material may find a broad applications beyond HEP experiments. One particular application for future HEP experiments is a HHCAL in a future lepton collider, where radiation environment is not as severe as hadron colliders, provided that this material can be mass produced at a cost much lower than commercial available inorganic scintillators.
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