A.J.J. Bos

High sensitivity thermoluminescence dosimetry

Abstract This paper reviews the physics of the phenomenon of thermoluminescence (TL) related to dosimetric applications. Basic concepts are given using the simple model of one trap–one recombination centre. General characteristics of thermoluminescence dosimetry (TLD) materials are reviewed. Two high sensitivity TL materials are discussed in detail namely LiF:Mg, Cu, P and α-Al 2 O 3 :C. What is understood and what knowledge is still lacking of the TL mechanism in both materials is indicated. Field measurements show that in spite of incomplete understanding of the TL mechanism, both materials can be used to measure very low doses in a reliable way.

Optical dating of young coastal dunes on a decadal time scale

We explore the use of quartz optically stimulated luminescence (OSL) dating for reconstructing coastal evolution on a time scale of decades to a few hundred years. Samples are taken from the accretionary south-west coast of Texel, a barrier island just offshore of the northern Netherlands. The ages of dune ridges are known from historical sources; an excellent chronology with a decadal accuracy exists for the past 260 years. OSL ages of less than 10 years on the youngest samples indicate that the OSL signal of the quartz grains is very well zeroed prior to deposition and burial. OSL ages of five samples from a 250-year-old dune ridge are indistinguishable, and the OSL ages on 17 out of 20 samples are in excellent agreement with the well-known independent age controls. Our results highlight the potential of OSL dating for high-resolution reconstruction of coastal evolution over the past few centuries.

Afterglow and thermoluminescence properties of Lu2SiO5:Ce scintillation crystals

The afterglow and thermoluminescence (TL) properties of several Ce3+ doped Lu2SiO5 crystals are reported. Both properties are caused by the presence of charge traps in the crystals. At least six different glow peaks are observed in the TL glow curve. Each is related to a specific charge trap. The parameters for these charge traps, such as the trap depth and the frequency factor, were obtained from first-order kinetics peak analysis of the TL glow curve. A charge trap with a depth of 1.0 eV is responsible for the afterglow observed at room temperature. Ce3+ ions appear to be the luminescence centres in the recombination process of the trapped charge carriers. It will be shown that optical excitation in the 5d levels of Ce3+ produces trap filling. The possible nature of the charge traps will be discussed.

Control of electron transfer between Ce3+ and Cr3+ in the Y3Al5−xGaxO12 host via conduction band engineering

Among inorganic compounds doped with lanthanide or transition metal ions for persistent phosphors, the transfer process of the localized electron in the dopant cations to the conduction band (CB) is crucial. In Y3Al5−XGaxO12:Ce3+–Cr3+, we found that the electron produced by photoionization of the Ce3+ ion by UV and blue excitation transfers to the Cr3+ ion through the CB. The electron trapped by Cr3+ is thermally released at different temperatures from 400 K to 150 K in the YAGG host with different Ga content because we managed to decrease the energy gap between the CB and the electron trap by increasing the Ga content. The persistent luminescence mechanism has been explained by constructing the vacuum referred binding energy (VRBE) diagram comprising the Ce3+, Cr2+, valence band (VB) and conduction band (CB) level energies in the YAGG host with different Ga/Al ratios.

CeBr

CeBr3 crystals have been studied to assess their utility as potential gamma ray spectrometers for future ESA planetary missions. Pulse height spectra, scintillation time profiles, X-ray excited emission spectra, and photoluminescence spectra have been recorded as a function of temperature between 78 and 600 K. In addition, the influence of exposing CeBr3 to various doses of gamma rays from a strong 60Co source on its scintillation performance has been investigated.

_{3}

The effects of the cooling rate alpha and heating rate beta on trapping parameters and thermoluminescent (TL) glow peak intensities in LiF:Mg, Ti(TLD-100) crystals have been studied by glow curve fitting from room temperature to 500 K. It is found that under the investigated circumstances (1 K min-1 FOM>0.2%). Glow peak intensities (peak area) for peaks 2,3,4 and 5 increase with both increasing cooling rate and heating rate in accordance with earlier investigations. However, the activation energies for most peaks vary strikingly with both cooling rate and heating rate: for peak 2 from 1.12 to 1.38 eV, for peak 3 from 1.06 to 1.43 eV, for peak 4 from 1.55 to 1.87 eV and for peak 5 from 1.73 to 2.08 eV. A qualitative explanation has been given in terms of clustering and precipitation of the defects responsible for TL during the annealing and readout stage.

Scintillator Development for Possible Use in Space Missions

A study has been made on the incorporation of some trace elements and minerals into human hair by measuring their distributions across hair diameters. For this study the Particle Induced X-ray Emission (PIXE) technique using the proton microbeam of the Vrije Universiteit of Amsterdam has been applied. Results of measurements on single hair strands at different positions in the root and outside the skin provide evidence that the elements not only can enter the cortex via the matrix but also via the hair root sheaths. Moreover, there are indications that the distribution of an endogenous element is not always homogeneously spread over a cross section of the hair. Endogenous Fe and Pb seem to be peaked on the periphery of the hair by natural means, while the elements S,Zn and Cu of the samples measured are found to be distributed homogeneously across the hair diameter. The consequences for hair analysis in use for monitoring the trace elements status of an individual are discussed.

Effects of cooling and heating rate on trapping parameters in LiF:Mg, Ti crystals

Abstract Monochromated synchrotron radiation (SXRF), 17.5 keV photons from an X-ray tube (XRF) with Mo anode and 3 MeV protons (PIXE) were used to excite X-ray spectra from thin samples of standard reference materials. Relative detection limits derived from these X-ray spectra were calculated to compare the different excitation modes. XRF shows the highest detection limits, while protons and synchrotron radiation monochromated to 16.5 keV are comparable. Much lower detection limits (down to 0.1 ppm) are experimentally shown with synchrotron radiation monochromated to 9.1 keV. Results are in agreement with theoretical predictions. The advantage of the polarization of the synchrotron radiation has been discussed theoretically and shown experimentally.

Incorporation routes of elements into human hair; implications for hair analysis used for monitoring

In this work we study the persistent luminescence properties of europium-doped alkaline earth silicon oxynitrides (CaSi2O2N2, SrSi2O2N2 and BaSi2O2N2). All compounds show afterglow emission, with an emission spectrum which is similar to the steady state photoluminescence. The afterglow decay time for BaSi2O2N2:Eu and SrSi2O2N2:Eu is about 50 and 100 minutes respectively, while for CaSi2O2N2:Eu the afterglow intensity is very low. Although the persistent luminescence can be induced by ultraviolet light (250-300 nm) in all three phosphors, only for BaSi2O2N2:Eu low energy radiation (350-500 nm) allows filling of the traps responsible for the afterglow.

Experimental comparison of synchrotron radiation with other modes of excitation of X rays for trace element analysis

Abstract The scintillation properties of three Lu 2 SiO 5 : Ce 3+ crystals are presented. The crystals show different light yields and afterglow intensities. The afterglow decay time is related to specific glow peaks in the thermoluminescence glow curve which in turn are related to charge traps. A study of these thermoluminescence properties is presented.