**PUBLICATIONS**
** **

**The following is a list of some of
our recently published papers in the field of thermoluminescence. **

**You can click on the links to view and DOWNLOAD the PDF files.**

**Please send all Comments, Suggestions and Corrections to vpagonis@mcdaniel.edu**

**The nonmonotonic dose
dependence of optically stimulated luminescence in Al _{2}O_{3} :C:
Analytical and numerical simulation results**

**R. Chen, V. Pagonis and J. L. Lawless**

**JOURNAL OF APPLIED PHYSICS 99, 033511,2006**

*Abstract *

**Nonmonotonic dose dependence of optically
stimulated luminescence _OSL_ has been reported in a number of materials
including Al2O3 :C which is one of the main dosimetric materials. In a recent work,
the nonmonotonic effect has been shown to result, under certain circumstances,
from the competition either during excitation or during readout between
trapping states or recombination centers. In the present work, we report on a
study of the effect in a more concrete framework of two trapping states and two
kinds of recombination centers involved in the luminescence processes in Al2O3 :C.
Using sets of trapping parameters, based on available experimental data,
previously utilized to explain the nonmonotonic dose dependence of
thermoluminescence including nonzero initial occupancies of recombination
centers _F+ centers_, the OSL along with the occupancies of the relevant traps
and centers are simulated numerically. The connection between these different resulting
quantities is discussed, giving a better insight as to the ranges of the
increase and decrease of the integral OSL as a function of dose, as well as the
constant equilibrium value occurring at high doses.**

**Evaluation of
activation energies in the semi-localized transition model of
thermoluminescence**

**V Pagonis**

**J. Phys. D: Appl. Phys. 38 (2005) 2179–2186**

*Abstract *

**Recently a semi-localized transition (SLT) kinetic
model was developed for thermoluminescence (TL), which is believed to be
applicable to important dosimetric materials like LiF : Mg,Ti. This model
contains characteristics of both a localized transition model and a single trap
model and is characterized by two distinct activation energy levels. This paper
describes the simulation of several standard methods of analysis for the TL
peaks calculated using the SLT model in an effort to extract the two activation
energy parameters of the model. The methods of analysis are applied to both
possible types of transitions within the model, namely the direct recombination
of the hole–electron pairs as well as the delocalized transitions involving the
conduction band. In the former case of direct recombination, the methods
of analysis give consistent results for
the activation energy E. In the latter case of transitions involving the
conduction band, it was found that extra caution must be exercised when
applying standard methods of analysis to the SLT model because of the
possibility of strongly overlapping TL peaks. Specifically the peak shape
methods consistently fail to yield the correct value of E, while careful
application of the fractional glow, thermal cleaning and variable heating rate
methods can yield the correct energy values when no retrapping is present
within the localized energy levels. A possible explanation is given for the
previously reported failure of the peak shape methods to yield the correct
activation energies within the SLT model. The heating rate methods of analysis
consistently yield the correct activation energies E with an accuracy of
a few per cent.**

**A model for
non-monotonic dose dependence of thermoluminescence**

**J L Lawless, R Chen, D Lo and V Pagonis**

**J. Phys.: Condens. Matter 17 (2005) 737–753**

*Abstract *

**In the applications of
thermoluminescence (TL) in dosimetry and archaeological and geological dating,
a desirable dose dependence of TL intensity is a monotonically increasing
function, preferably linear. It is well known that in many dosimetric
materials, nonlinear dependence is observed. This may include a superlinear
dependence at low doses and/or sublinear dose dependence at higher doses, where
the TL intensity approaches saturation. In quite a number of materials,
non-monotonic dose dependence has been observed, namely, the TL intensity
reached a maximum value at a certain dose and decreased at higher doses. This
effect is sometimes ascribed to ‘radiation damage’ in the literature. In the
present work we show, both quasi-analytically and by using numerical
simulation, that such dose dependence may result from a simple energy level
scheme of at least one kind of trapping state and two kinds of recombination
centers. One does not necessarily have to assume a destruction of trapping
states or recombination centers at high doses. Instead, the main concept
involved is that of competition which takes place both at the excitation stage
and the readout stage during the heating of the sample. This may explain the
fact that the phenomenon in question, although very often ignored, is rather
common. Cases are identified in which competition during excitation dominates,
and others in which competition during read-out dominate**

**SIMULATION
OF THE EXPERIMENTAL PRE-DOSE TECHNIQUE FOR RETROSPECTIVE DOSIMETRY IN QUARTZ**

**Vasilis Pagonis and Hezekiah Carty**

**Radiation Protection Dosimetry (2004), Vol. 109, No. 3, pp. 225±234**

*Abstract *

**The pre-dose technique of thermoluminescence for quartz
has been used extensively for retrospective dosimetry of quartz and other
natural materials. A recently published model that is a modification of the
well-known Zimmerman theory is used here to simulate the complete sequence of
experimental steps taken during the additive dose version of the pre-dose
technique. The results of simulation show how the method can reproduce
accurately the accumulated dose or paleodose received by the sample. The
solution of the kinetic differential equations elucidates the various electron
and hole processes taking place during the experimental pre-dose procedure and
shows clearly the mechanism of hole transfer from the reservoir to the
luminescence centre caused by heating to the activation temperature. The
numerical results show that the pre-dose technique can reproduce the paleodose
with an accuracy of _1±5%, even when the paleodose is varied over more than an
order of magnitude. New quantitative results are presented for the effect of
the test dose and of the calibration beta dose, b, on the accuracy of the
pre-dose technique. The conclusions drawn from the simple model for quartz can
be used to make improvements to more general quartz models.**

**Applicability of the
Zimmerman predose model in the** **thermoluminescence of predosed and annealed synthetic quartz samples**

**Vasilis Pagonis, George Kitis, Reuven Chen**

**Radiation Measurements, 37, (2003), 267-274. **

*Abstract *

**The "110 ^{ o}C"
thermoluminescence (TL) peak of unfired synthetic quartz is known to exhibit a
highly superlinear growth**

**Cooling rate effects
on the thermoluminescence glow curves of **

**G. Kitis, V. Pagonis, and C. Drupieski**

**Phys. stat. sol. (a) 198, No. 2, 312– 321 (2003)**

*Abstract*

**Samples of quartz annealed at high temperatures are
known to exhibit thermoluminescence (TL) properties which depend on the rate of
cooling of the samples to room temperature. Powder samples of **

**Modelling thermal
activation characteristics of the sensitization of thermoluminescence in quartz**

**Reuven Chen and Vasilis Pagonis**

**J. Phys. D: Appl. Phys. 36 (2003) 1–6****
**

*Abstract*

**The sensitization of the «110°C thermoluminescence
peak in quartz, also termed the ‘pre-dose’ effect, was previously explained
using an energy level model including two electron trapping states and two hole
centers. The experimental procedure includes a stage of high temperature
activation following a relatively large irradiation of the sample. The response
to a** **small test-dose was found to depend on this activation temperature.
With different quartz samples, different behaviors of the thermal activation
characteristics (TACs) were found. In typical TACs, the sensitivity reached a
maximum at 500°C, followed by a rather sharp decline in some samples;** **in
others a maximum was reached at 350°C followed by a slight decline** **towards
a plateau level. In this work, we show that these behaviors can rather easily
be explained within the framework of the two traps–two centers model. This is
done by numerical solution of the relevant sets of differential equations
governing the different stages of the experimental procedure. The different
kinds of dependence were simulated with different sets of trapping** **parameters.
A better insight into the processes taking place is reached,** **which may have
implications in the application of pre-dose dating of archaeological quartz
samples and in retrospective dosimetry.**

**SEARCH FOR COMMON
CHARACTERISTICS IN THE GLOW CURVES OF QUARTZ OF VARIOUS ORIGINS**

** V. Pagonis, E. Tatsis, G. Kitis
and C. Drupieski**

**Radiation Protection Dosimetry (2002), Vol. 100, Nos. 1-4, pp. 373-376**

*Abstract *

**The thermoluminescence glow curves of quartz of
various origins were measurd under two different conditions, (1) unannealed
samples and (2) samples annealed at 500 ^{o}C and 900 ^{o}C.
The different glow curves were analyzed using first order kinetics and glow
curve deconvolution analysis (GCD). The comparison of the glow curves obtained
was mainly concentrated in studying the sensitivities of the glow peaks as a
function of the annealing temperature, and in obtaining the kinetic parameters
of the glow peak at 110 ^{o}C. Furthermore, in four samples the
detailed comparison was extended to the trapping parameters of all existing
glow peaks. It was found that despite their different origin and the different
shapes of the glow curves, there are several basic characteristics which are
common to all samples studied.**

**DETAILED KINETIC
STUDY OF THE THERMOLUMINESCENCE GLOW CURVE OF SYNTHETIC QUARTZ**

**G. Kitis, V. Pagonis, H. Carty and E. Tatsis**

**Radiation Protection Dosimetry (2002), Vol. 100, Nos. 1-4, pp. 225-228**

*Abstract *

**A detailed kinetic analysis has been performed of
the thermoluminescence glow curve of high purity synthetic quartz. The kinetic
parameters of the glow peak at 110 ^{o}C were evaluated for doses ranging
from 0.1 Gy to 100 Gy using glow curve deconvolution (GCD) methods, initial
rise, variable heating rate and phosphorescence decay methods. All the methods
gave results that agree within the experimental errors.**

**An improved
experimental procedure of separating a composite thermoluminescence glow curve
into its components **

**by V. Pagonis and C. Shannon **

**Radiation Measurements, 32, 805-812 (2000). **

*Abstract*

**We present an improved experimental procedure of
separating a composite thermoluminescence glow curve into its components.
Careful monitoring of the isothermal cleaning process using the initial rise
method ensures the complete thermal removal of TL peaks. Digital subtraction of
two experimental TL glow curves yields individual experimental TL glow peaks.
Several standard methods (initial rise and whole glow curve) are used to obtain
the energy values and frequency factors of the traps. The method has been used
successfully to analyze the well-known composite TL glow curve of the
dosimetric material LiF (TLD-100). The limitations of the method are
illustrated by analyzing the highly complex TL glow curve of a UV irradiated
synthetic calcite consisting of at least 6 TL peaks. Although the method works
best for TL glow curves described by first order kinetics, it should also be
applicable to more general kinetics. **

**FIT OF **

**by V. Pagonis and G. Kitis**

**Radiation Protection Dosimetry, 93, No.3, 225-229 (2001). **

*Abstract*

**A new Thermoluminescence glow-curve deconvolution
(GCD) function is introduced that accurately describes second order
thermoluminescence (TL) curves. The logistic asymmetric (LA) statistical
probability function is used with the function variables being the maximum peak
intensity, the temperature at the maximum peak intensity and the LA width
parameter a2. An analytical expression is derived from which the activation
energy E can be calculated a sa function of Tm and the LA width parameter a _{2}
with an accuracy of 2% or better. The accuracy of the fit was tested for values
of E between 0.7 and 2.5 eV, for s values between 10^{5} and 10^{25}
s^{-1}, and for trap occupation numbers n_{o}/N between 1 and
10^{6}. The goodness of fit of the LA function is described by the
Figure of Merit (FOM) which is found to be of the order of 10^{-2}. **

**FIT OF **

**by V. Pagonis, S.M. Mian and G. Kitis**

**Radiation Protection Dosimetry, 93, 11-17 (2001). **

*Abstract*

**A new Thermoluminescence glow-curve deconvolution
(GCD) function is introduced that accurately describes first order
thermoluminescence (TL) curves. The GCD functions are found to be accurate for
first order TL peaks with a wide variety of the values of the TL kinetic
parameters E and s. The 3-parameter Weibull probability function is used with
the function variables being the maximum peak intensity (I****m), the temperature of the maximum peak
intensity (T****m) and the Weibull
width parameter b. An analytical expression is derived from which the activation
energy E can be calculated as a function of T****m and the Weibull width parameter b. The accuracy of the Weibull
fit was tested using the ten reference glow-curves of the GLOCANIN
intercomparison program and the Weibull distribution was found to be highly
effective in describing both single and complex TL glow curves. The goodness of
fit of the Weibull function is described by the Figure of Merit (FOM) which is
found to be of comparable accuracy to the best FOM values of the GLOCANIN
program. The FOM values are also comparable to the FOM values obtained using
the recently published GCD functions of Kitis et al [3]. It is found that the
TL kinetic analysis of complex first-order TL glow curves can be performed with
high accuracy and speed by using commercially available statistical packages.**