Dosimetric characteristics of ultraviolet and x-ray-irradiated KBr:Eu21
thermoluminescence crystals
R. Meléndreza) and R. Pérez-Salasa)
Programa de Posgrado en Fı́sica de Materiales, Centro de Investigación, Cientı́fica y de Educación
Superior de Ensenada, Apartado Postal 2681, Ensenada, Baja California, 22800 Mexico
R. Aceves, T. M. Piters, and M. Barboza-Flores
Centro de Investigación en Fı́sica, Universidad de Sonora, Apartado Postal 5-088, Hermosillo, Sonora,
83190 Mexico
~Received 12 February 1996; accepted for publication 12 June 1996!
Thermoluminescence ~TL! characteristics of KBr:Eu21 ~150 ppm! previously exposed to ultraviolet
~UV! light ~200–300 nm! and x-ray radiation at room temperature have been determined. The TL
glow curve of UV-irradiated samples is composed of six peaks located at 337, 384, 402, 435, 475,
and 510 K. The TL glow curves of x-irradiated samples show mainly a TL peak around 384 K. The
TL intensities of UV-irradiated ~402 and 510 K glow peaks! and x-irradiated specimens present a
linear dependence as a function of radiation dose as well as fading stability 300 s after irradiation.
These results further enhance the possibilities of using europium-doped materials in nonionizing
~actinic region! and ionizing radiation detection and dosimetry applications. © 1996 American
Institute of Physics. @S0003-6951~96!04334-3#
It is well known that europium-doped alkali halide single
crystals possess good thermoluminescence ~TL! dosimetric
properties for a broad range of radiation energies, from 200
to 300 nm ultraviolet light1 to high energy ionizing
radiation.2–4 A recent investigation has suggested that the
defects responsible for the TL glow peaks for nonionizing
UV radiation are the same as those for ionizing ~x, a , b , and
g! radiation, despite the observed difference in glow curve
shapes.5,6 The interest in these materials has recently been
increased because of the many practical and novel applications. For instance, Eu21 -doped KBr and KCl have been
examined for their application in nonionizing ~actinometric
region! and ionizing radiation dosimetry, using the TL and
optically stimulated luminescence ~OSL! properties. In fact,
the OSL behavior of these phosphors has brought up the idea
to use them as UV radiation detectors and dosimeters, and
more recently as optical storage memory devices.7,8
NaCl:Eu21 and KBr:Eu21 detectors are highly sensitive materials for thermoluminescence dosimetry ~TLD!, the first
has been successfully tested for x, a, b, g, and UV radiation3
and the second shows good TLD characteristics after g-ray
exposure.4
In the present letter we further examine the TLD properties of KBr:Eu21 under UV and x-ray radiation, and the
TL glow curves of samples irradiated with UV light and x
rays are compared. Also, the integrated thermoluminescence
as a function of radiation dose and the TL fading at room
temperature are studied in order to assess the dosimetric performance for UV and x-ray radiation.
The KBr:Eu21 ~200 ppm! crystal samples were 332
30.5 mm3 in size and grown by the Czochralski method
following the procedure previously described.9 The crystals
were subjected to a quenching procedure, consisting of annealing the sample at 773 K for 1 h followed by fast cooling
a!
Permanent address: Centro de Investigación en Fı́sica, Universidad de Sonora, Apartado Postal 5-088, Hermosillo, Sonora 83190, México.
through contact with a large piece of copper. This procedure
prevents the aggregation of Eu21 -vacancy (I – V) dipoles.
The UV irradiation was performed with a 1000 W Oriel
Hg–Xe high-pressure arc lamp monochromated with a 0.25
m focal length Kratos monochromator. We estimate the flux
rate to be about 0.01 mW/cm2 s. A Tel-X-Ometer system
model 580M ~Tel-Atomic!, operating at 20 kV and 80 mA
with an estimated exposure rate of 80 mR/s ~;0.7 mGy/s, air
equivalent!, was used for x irradiations. All irradiations were
done at room temperature and care was taken to avoid exposure of the samples to environmental light. Thermoluminescence measurements were performed under a N2 atmosphere
with a Harshaw 4000 TLD system with a linear heating rate
of 5 K s21 .
A characteristic thermoluminescence glow curve of a
quenched KBr:Eu21 sample irradiated 180 s with 240 nm
UV light is shown in Fig. 1 ~upper part!. The peaks shown in
Fig. 1 ~dotted lines! were obtained by a computer fitting
using a first order kinetic model. They are located at 337,
384, 402, 435, 475, and 510 K; numbered from 1 to 6 for
identification purposes. The lower part of Fig. 1 shows the
TL glow curve of an x-irradiated specimen along with the
TL glow curve of a sample irradiated with 202 nm light. The
x-irradiated crystal shows mainly one TL peak located
around 384 K. An examination of the glow curves of the
UV- and x-irradiated samples indicates that in both cases the
same TL glow peaks are present, occurring, however, with
different peak intensities. The resemblance between the glow
curves of the UV- and x-irradiated KBr:Eu21 is stronger for
high-energy ~200 nm! than for low-energy ~240 nm! UV
light, as can be seen in Fig. 1. These observations are in
agreement with recent TL experiments performed on
europium-doped KCl.10 The same TL glow curve structure
observed in x-irradiated KBr:Eu21 crystals, composed of a
strong peak at 384 K and a much weaker one at 473 K, has
been observed in g-irradiated samples.4 Therefore, one may
conclude based on these results that peak 2 ~384 K! is the
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Appl. Phys. Lett. 69 (8), 19 August 1996
0003-6951/96/69(8)/1068/3/$10.00
© 1996 American Institute of Physics
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FIG. 3. Integrated thermoluminescence intensity as a function of irradiation
time of a KBr:Eu21 crystal previously irradiated with 240 nm light. Each
curve corresponds to a TL glow peak numbered accordingly in Fig. 1.
one with higher sensitivity to ionizing radiation, and peaks 3,
4, 5, and 6 are more sensitive for nonionizing radiation.
Thermoluminescence fading of KBr:Eu21 at room temperature was investigated for all six TL peaks shown in Fig.
1 ~UV irradiation!. The fading for a sample quenched from
773 K to room temperature irradiated with 240 nm light is
shown in Fig. 2. Peak 1 ~337 K! fades away very rapidly
during the first few seconds, decaying 60% in the first 50 s,
all other peaks reach a stable plateau at around 300 s. Figure
3 displays for each peak the integrated TL as a function of
240 nm UV light radiation dose. From Figs. 1 and 2 one may
conclude that peaks 3 and 6 could be more suitable for UVdosimetry due to their high TL intensity and stability. The
characteristic fading of an x-irradiated KBr:Eu21 is shown in
Fig. 4; signal stability is reached around 300 s, and decaying
about 50% in the first 100 s. The integrated TL as a function
of radiation dose is shown in the inset of Fig. 4. As in UVirradiated samples, the TL intensity follows a good linear
relation for the used radiation dose range. The TL measurements are characterized with 5%–10% reproducibility factor.
The TL emission spectrum is composed of a broadband
peaked at 420 nm, corresponding to the Eu21 emission being
observed in europium-doped alkali halides crystals.1 An interesting feature, advantageous to dosimetric application in
the actinometric region, is the fact that the TL excitation
spectrum of KBr:Eu21 covers a broad 200–300 nm range
with higher TL efficiency for 190 and 230 nm.
It is important to stress the fact that the present TL results are characteristic of freshly quenched samples, where
the Eu21 impurity is mainly in the form of I – V dipoles.
Therefore, one may expect a radically different TL behavior
for different annealing temperatures, mainly due to the diversity of Eu21 precipitated or aggregated phases that could be
formed in the host crystals.11 In fact, we have performed the
same type of TL study in samples subjected to different annealing temperatures, finding that some of the TL glow
peaks were strongly reduced in intensity when compared to
FIG. 2. Thermoluminescence fading of KBr:Eu21 previously irradiated with
240 nm light. Each curve corresponds to a TL glow peak numbered accordingly in Fig. 1.
FIG. 4. Thermoluminescence fading of KBr:Eu21 previously irradiated with
x rays. The inset displays the dose response of the integrated TL as a function of irradiation time.
FIG. 1. Thermoluminescence glow curves of UV- and x-irradiated samples
of KBr:Eu21 . The measured TL glow curve ~dots! shown in the upper part
belongs to a crystal irradiated with 2V40 nm light. The solid line is the result
of a computer fitting using six first order kinetic glow peaks ~broken lines!.
The lower part shows the TL glow curve of a sample exposed to 220 nm
light along with an x-irradiated specimen.
Appl. Phys. Lett., Vol. 69, No. 8, 19 August 1996
Meléndrez et al.
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the present results, meaning a strong dependence of the TL
glow curve structure on the aggregated phase; a detail investigation on this matter is in progress. In conclusion, the
KBr:Eu21 phosphor possesses fairly good TL properties
making it suitable for dosimetric application for nonionizing
radiation as well as for x and g radiation.
The authors are thankful to Professor H. Riveros and R.
Guerrero ~IFUNAM, México! for growing the crystals. We
acknowledge the technical assistance of Jesús Morán and M.
Atondo Encinas. This work is supported in part by
CONACyT ~México, Grants Nos. D1520-E9201 and
4138-E; Fellowships Nos. 84683 and 85628!, DGICSA-SEP
~México!, FOMES ~Universidad de Sonora, México!, and
the Third World Academy of Sciences ~Trieste, Italy!. T. M.
Piters is grateful to CONACyT for a Cátedra Patrimonial de
Excelencia Nivel II Grant and to ANUIES ~México! for the
funding provided via the SUPERA Program.
1
I. Aguirre de Carcer, G. Lifante, F. Cussó, F. Jaque, and T. Calderón,
Appl. Phys. Lett. 58, 1825 ~1991!.
2
A. Camacho, G. Mũnoz, J. Rubio, J. Garcia, H. Murrieta, and J. Hernández, J. Mater. Sci. Lett. 7, 437 ~1988!.
3
I. Aguirre de Carcer, F. Cussó, F. Jaque, E. España, T. Calderón, G.
Lifante, and P. D. Townsend, J. Phys. D 26, 154 ~1993!.
4
E. Buenfil and E. Brandan, Health Phys. 62, 341 ~1992!.
5
R. Aceves, R. Pérez Salas, and M. Barboza-Flores, J. Phys., Condens.
Matter 6, 10 397 ~1994!.
6
R. Pérez-Salas, R. Meléndrez, R. Aceves, R. Rodrı́guez, and M. BarbozaFlores, J. Phys., Condens. Matter 8, 4983 ~1996!.
7
H. Nanto, K. Murayama, T. Usuda, S. Taniguchi, and N. Takeuchi, Radiat. Prot. Dosim. 47, 281 ~1993!.
8
H. Nanto, K. Murayama, T. Usuda, F. Endo, Y. Hirai, S. Taniguchi, and
N. Takeuchi, J. Appl. Phys. 74, 1445 ~1993!.
9
R. Pérez Salas, R. Meléndrez, R. Aceves, and M. Barboza-Flores, Appl.
Phys. Lett. 63, 3017 ~1993!.
10
R. Meléndrez, R. Pérez-Salas, L. P. Pashchenko, R. Aceves, T. M. Piters,
and M. Barboza-Flores, Appl. Phys. Lett. 68, 3398 ~1996!.
11
J. Rubio, J. Phys. Chem. Solids 52, 101 ~1991!.
1070
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