J.S. Nagpal

Some studies of thermoluminescent MgF2 phosphors

Abstract Optical grade MgF 2 , fused in nitrogen atmosphere with individual dopants Mn, Dy, Tm and Tb (0.1% by wt), has been studied. After γ-ray irradiations phosphors exhibit 10 TL glow peaks between RT and 400°C around 80, 115, 137, 165, 190, 225, 265, 290, 315 and 360°C. Their response to u.v. and γ-rays, their PTTL, TL emission spectra, photoluminescence spectra and absorption spectra are reported. Rare earth ions in a triply ionized state replace Mg 2+ in MgF 2 and take part in TL emission, whereas Mn is in a doubly ionized state in the doped phosphor. High temperature treatment in air enhances the high temperature peaks in MgF 2 :Tb, while the contribution from lower temperature peaks becomes negligible. MgF 2 phosphors show γ-induced sensitization. For a post-annealing for 1 h at 300°C and a test exposure of 10 R at RT, the sensitization factor is 2.2 for MgF 2 : Mn (pre-exposed to 10 3 R) and 25 for MgF 2 : Tb (pre-exposed to 5 × 10 4 R).

Effect of temperature during UV and gamma irradiations of TL phosphor CaSO4:Dy

Abstract Temperature is an important parameter in thermoluminescence studies. Irradiation at enhanced temperatures reduces the γ response of TL phosphor CaSO 4 :Dy. However, in the presence of fluorescent lights, the γ response of the phosphor is enhanced by ≅20% for temperatures around 60–100°C. If the phosphor temperature during UV exposure is kept high, the integrated TL output continues to increase until it reaches 18 times at 160°C as compared to that produced by UV exposure at room temperature.

Thermoluminescence of rare earth doped BaSO4 phosphors and its applications

Abstract Thermoluminescence of synthetic BaSO 4 samples individually doped with Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy and Tm has been studied after γ- and microwave irradiations. BaSO 4 : Eu has the highest response for γ-radiation while BaSO 4 : Tb exhibits highest reduction in its γ-induced TL after exposure to microwave radiation (2425 ± 25 MHz ). The reduction depends on the microwave radiant exposure and is independent of the irradiance level in the range 25−200 mW · cm −2 and hence can be useful for microwave dosimetry.

Gamma ray induced sensitization in CaSO4: Dy and competing trap model

Abstract Gamma ray induced sensitization in CaSO4 :Dy has been compared for different temperatures during irradiation (25° 120° and 250°C). Enhanced sensitization at elevated temperatures seems to support the competing trap model for supralinearity and sensitization in CaSO4 :Dy.

Ultraviolet dosimetry using thermoluminescent phosphors-rate dependence

Abstract Intrinsic thermoluminescence response of various TL phosphors to ultraviolet radiation is found to be highly exposure rate dependent. The explanation lies in the nature of exciton assisted process in TL materials. TL phosphors should be employed for UV dosimetry with due caution.

Photoluminescence and absorption spectra of various common TL phosphors—Interpretation of TL mechanisms

Abstract Photoluminescence and absorption spectra of TL phosphors TLD-100, CaF 2 :Dy, CaSO 4 :Dy (0.05% wt ),CaSO 4 :Tm (0.05% wt ) and Mg 2 SiO 4 :Tb have been measured. The absorption spectra are typical of RE 2+ in rare earth doped irradiated phosphors. On heating RE 2+ → RE 3+ and emission from the excited states of RE 3+ is observed.

A preliminary study of thermoluminescent phosphors as dosemeters for microwave radiation

Reports experiments on a number of phosphors using BaSO4, MgF2 and CaSO4 as matrices together with a variety of different activators. None of the phosphors studied comes anywhere near to meeting the requirements of an ideal personal microwave radiation dosimeter. Some could be employed for microwave radiant exposure measurements but with severe limitations.

Monitoring of environmental radiation levels using TL photon counting system with CaSO4:Dy phosphor

Abstract With CaSO4:Dy (0.5 mol %) encapsulated in glass capillaries, each containing 15 mg of the TL phosphor, it is possible to measure gamma radiation exposures up to a lower limit of 2.6 × 10−8 C/kg employing the thermoluminescent photon counting technique. Bare glass capillaries, without any additional energy compensating filter, having enhanced response due to the contribution from low energy components of the background gamma radiation, can be usefully employed to monitor environmental gamma radiation levels and even day-to-day variations in the background. The energy weighted correction factor for CaSO4:Dy is derived from the background gamma spectrum measurements with a 3″ × 3″ NaI(T1) scintillator. At two locations of Trombay, the radiation level was measured to be 2.86 × 10−9 C kg·h.

Thermoluminescence of magnesium oxide and its trapping kinetics

MgO (Norton), on u.v. and γ irradiation, exhibits TL glow peaks around 88, 150, 172, 195 and 250°C (heating rate 55°C min−1). TL emission is observed around 340, 390, 445, 705 nm can be attributed to the impurities Fe3+ and Cr3+, which act as luminescence centers. ESR studies rule out any participation of Mn2+ ions. The glow peak around 88°C has E = 1.055 eV, s = 4.3 × 1013 s−1 and has order of kinetics b = 1.7.

X-ray excited optical luminescence studies of rare earth activated thermoluminescent phosphors

Abstract XEOL spectra of CaSO 4 :Dy, MgF 2 :Dy, and CaO:Dy are typical of Dy 3+ and similar to that of TL emission spectra. However, the studies fail to reveal the charge conversion state of the RE ion on irradiation. Minor differences, as regards the intensity ratio of various lines are observed depending upon the host matrix and the radiation history.