First-principles calculations of electronic structures and optical, phononic, and thermodynamic properties of monoclinic α-spodumene

A first-principles investigation of structural properties, electronic structures and optical properties of β- and γ-LiAl(SiO3)2

The electron absorption-, photoluminescence- and electron paramagnetic-resonance spectra of Mn3+ in red beryl from Wah Wah Mountains (Utah USA) and of pink- and purple vesuvianite from Jeffrey Mine (Asbestos, Canada) were measured at room- and low temperatures. The crystal field stabilization energies are equal to 130.9 kJ/mol for the red beryl, and 151.5–158.0 and 168.0 kJ/mol for for the pink- and the purple vesuvianite, respectively. The red photoluminescence of Mn3+ was not intensive either at room- or at low temperatures. The high Mn content in the crystals caused the emergence of an additional emission band and short photoluminescence-decay lifetimes. The latter are only 183 μs for beryl and 17 μs for vesuvianite.

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The absorption- and luminescence spectra of Mn 3+ in beryl and vesuvianite

In this work, synthetic polycrystals of calcium silicate (CaSiO3) are prepared. The objective is to expand the current knowledge of low cost and easy production thermoluminescent detectors for doses of gamma radiation, thermal neutrons and accelerated ions beam, as well as, the possible applications in nuclear medicine or monitoring actual radiotherapy treatment. For that reason, calcium silicate doped with Boron, Cadmium, Dysprosium, and Europium were produced keeping in mind gamma and neutron detection. For the production of synthetic calcium silicate polycrystals, the devitrification method was used. In this process, two polytypes of undoped CaSiO3 were identified, αand βpolytypes. α-CaSiO3 is a very sensitive gamma radiation detector with main prominent thermoluminescence (TL) peak occurring at about 250270 ◦C and a low-temperature peak at 120 ◦C, using 4 ◦C/s heating rate. The TL response of α-CaSiO3 is linear for dose < 10 Gy and then has a supralinear behavior up to about 7 kGy and saturating beyond. The TL behavior changes very little by doping with B, Cd, and Dy while Eu doping brings changes. Additionally, β-CaSiO3 polycrystal exhibits three TL peaks at 124 ◦C, 250 ◦C, and 306 ◦C. All peaks at 124, 250 and 306 ◦C for β-CaSiO3 have a linear behavior in the dose range from cGy to 1 Gy. After that, the TL responses are supralinear up to about 3 kGy and then they are saturated. Synthetic polycrystals of CaSiO3 (doped or not) were also irradiated with neutrons from a nuclear research reactor. This thermal neutron reacts with Ca, Si and O through (n, γ) process, all or part of the gamma emitted in this reaction is absorbed by the sample and is responsible for the induction of TL. The total energy emitted by the (n, γ) reaction on the sample of CaSiO3 was calculated analytically. Furthermore, Monte Carlo simulations using the MCNP5 radiation transport code was carried out at the Nuclear Engineering Center in IPEN to calculate the deposited dose on CaSiO3 by the neutron interaction finding doses ranging from 42 Gy to 21 kGy. CaSiO3 TL

Production of synthetic polycrystals of CaSiO3 and their study as new detectors of gamma radiation, thermal neutrons and accelerated ions.

Comparative study of the thermoluminescence properties of natural metamorphic quartz belonging to Turkey and Spain

Synthetic spodumene polycrystals as a TL dosimetric material

Thermoluminescence, electron paramagnetic resonance and optical absorption properties of rhodonite, a natural silicate mineral, have been investigated and compared to those of synthetic crystal, pure and doped. The TL peaks grow linearly for radiation dose up to 4 kGy, and then saturate. In all the synthetic samples, 140 and 340°C TL peaks are observed; the difference occurs in their relative intensities, but only 340°C peak grows strongly for high doses. Al2O3 and Al2O3 + CaO-doped synthetic samples presented several decades intenser TL compared to that of synthetic samples doped with other impurities. A heating rate of 4°C/s has been used in all the TL readings. The EPR spectrum of natural rhodonite mineral has only one huge signal around g = 2.0 with width extending from 1,000 to 6,000 G. This is due to Mn dipolar interaction, a fact proved by numerical calculation based on Van Vleck dipolar broadening expression. The optical absorption spectrum is rich in absorption bands in near-UV, visible and near-IR intervals. Several bands in the region from 540 to 340 nm are interpreted as being due to Mn3+ in distorted octahedral environment. A broad and intense band around 1,040 nm is due to Fe2+. It decays under heating up to 900°C. At this temperature it is reduced by 80% of its original intensity. The pink, natural rhodonite, heated in air starts becoming black at approximately 600°C.

José Roberto Braz Paião

Papers

Synthetic spodumene polycrystals as a TL dosimetric material

Thermoluminescence, electron paramagnetic resonance and optical absorption in natural and synthetic rhodonite crystals