Shani G. Radiation Dosimetry: Instrumentation and Methods
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260 Radiation Dosimetry: Instrumentation and Methods
with
a
0
0.2677737343; a
1
8.6347608925; a
2
18.059016973; a
3
8.573328740; b
o
3.9584969228;
b
1
21.099653082; b
2
25.632956149; b
3
9.5733223454
where an upper bound for the error is:
(4.28)
Then one may rewrite Equation 4.25 as:
where only algebraic operations should be performed.
Applying the condition (4.28) to the arguments of
(z),
the error introduced in Equation 4.29 by the approxima-
tion of Equation 4.27 is negligible for temperatures (in K)
T 1.16 E, where E is the activation energy (in eV).
Glow-curve analysis of long-term stability of LiF:Mg,
Cu, P was compared by Duggan and Korn [32] to LiF:Mg,
Ti. Over a six-month period, the long-term stability of
LiF:Mg, Cu, P (GR-200A, Beijing, China) was compared
with LiF:Mg, Ti (GR-100, Beijing, China). Annealing at
220°C instead of the pre-set temperature of 240°C caused
an increase in the contribution from peak 3 in LiF:Mg,
Cu, P, causing the material to be more susceptible to fading
and peak-area interchanges. The response over time was
fitted to a simple exponential of the form:
(4.30)
with as the response at day
, t as time (days), and
T as the “half-life” of the response (days).
Two peaks were fitted for GR-200 and one (SC) or
three (FC) peaks were fitted for GR-100, depending on
the cooling regime. Program D is given by:
(4.31)
where
A area (counts); s frequency factor (s
1
); E
activation energy (eV); I intensity (counts s
1
); k Bolt-
zmann’s constant (eV K
1
); T temperature (K);
heat-
ing rate (K s
1
).
From Experiment A, “fading” of LiF:Mg,Cu,P over
six months, for a slow and fast cool-down, were 10% and
6%, respectively, compared with 10% and 14% for
LiF:Mg,Ti. From Experiment B, sensitivity changes of
LiF:Mg,Cu,P over six months, for a slow and fast cool-
down, were 3% and 7%, respectively, compared with 3%
and 19% for LiF:Mg,Ti.
Evolution of individual peak area over time in each
experimental arm A and B, is shown in Figures 4.49a
and b for LiF:Mg,Cu,P and in Figures 4.50a and b for
LiF:Mg,Ti. The peak fit for LiF:Mg,Cu,P (FC) was not as
good as with the rest of the study, and it is suspected that
first-order kinetics approximations may not be appropriate.
The total peak area, made up almost entirely of peak 4, was
very stable for this case. For LiF:Mg,Ti, for both cool-down
regimes, the sum of all peaks, (3 4 5) and (4 5),
remained unchanged within experimental uncertainty.
From this study it is clear that the mechanism respon-
sible for the decrease in TLD response is almost entirely
sensitivity changes caused by unstable unfilled trap (reac-
tions between defects) and cannot be explained by fading
(leakage of trapped charges) alone.
The detection limit (L
D
) and the determination limit (L
Q
)
in personal dosimetry were evaluated by Muniz et al. [33]
FIGURE 4.48 Background subtraction procedure: (i) heating
profile, (ii) LiF:Mg,Cu,P glow curves, (iii) second readout (X10),
and (iv) linear approximation of the residual signal in the region
of dosimetric peaks. (From Reference [31]. With permission.)
z() 210
8
if z 1()
It() I
M
E
kT
M
----------
E
kT
------
E
kT
M
----------
E
kT
M
----------
T
T
m
------
expexp
E
kT
M
----------
E
kT
------
exp
E
kT
------
(4.29)
10
4
RR
t
1 R
t
()t
2ln
T
--------
exp
R
t
IT() As
E
kT
---------
skT
2
E
----------------
E
kT
---------
expexpexp
0.9920 1.602
k
˙
T
E
------
Ch-04.fm Page 260 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 261
The reading cycles were linear at 7°C s
1
in a N
2
atmo-
sphere. LiF:Mg,Ti was heated up to 300°C, while
LiF:Mg,Cu,P was heated up to a maximum temperature
10°C higher than the detected position of the main dosi-
metric peak (peak 4), after which this temperature was
maintained for 5 s. For both materials, natural cooling
inside the reader was always used, resulting in a rather
rapid and reproducible cooling. Second readouts were per-
formed immediately after the first so that the zero-dose
signal could be estimated for the conventional analysis
method. No annealing other than the reading cycle was
used for the two materials.
The detection limit, L
D
, for any quantity that is mea-
sured with an analytical process is the smallest amount of
that quantity that can be detected at a specified confidence
level. The determination limit, L
Q
, specifies the minimum
dose that can be measured with a given predefined preci-
sion. Hirning [34a] deduced expressions for L
D
and L
Q
that are given by:
(4.32)
(4.33)
where t
n
and t
m
are one-sided Student-t factors for sample
sizes of n un-irradiated and m irradiated detectors at the 95%
confidence level; s
b
is the sample standard deviation of the
radiation background measurement,
K
b
; s
is the relative
standard deviation (variation coefficient) of the irradiated
dosimeters; and k
Q
is the desired precision (the inverse of
the maximum relative standard deviation).
The expression for the variance of a TLD reading
irradiated to a total air kerma K
t
is given as a function of
FIGURE 4.49 Evolution of individual peak area over time for
GR-200A (SC) for storage (a) post-irradiation (experiment A)
and (b) pre-irradiation (experiment B). Peaks were character-
ized by Equation 4.31. (From Reference [32]. With permission.)
L
D
2 t
n
s
b
t
m
2
s
2
K
b
()
1 t
m
2
s
2
-----------------------------------------
FIGURE 4.50 Evolution of individual peak area over time for
GR-100 for storage (a) post-irradiation (experiment A) and (b)
pre-irradiation (experiment B). A comparison is shown between
both cooling regimes. Peaks were characterized by Equation
4.31. (From Reference [32]. With permission.)
L
D
k
Q
2
s
2
K
b
k
Q
4
s
4
K
b
2
k
Q
2
s
b
2
1 k
Q
2
s
2
()[]
1 k
Q
2
s
2
--------------------------------------------------------------------------------------------------
Ch-04.fm Page 261 Friday, November 10, 2000 12:01 PM
262 Radiation Dosimetry: Instrumentation and Methods
the variance of null readings and of the relative vari-
ance observed for high air kerma :
(4.34)
If glow curves are to be analyzed with simplified
glow-curve analysis (GCA) methods, there is no need for
second readouts or for the use of undosed detectors. This
leads to a simplification of the above expression, as
n
does not exist. Then Equation 4.34 becomes:
(4.35)
It should be noted that the elimination of
n
in Equation
4.34 does not mean that the uncertainty of the zero dose
signals individual evaluation is zero, since it has an
obvious stochastic character. It simply reflects the fact
that GCA does not need zero-dose detectors or second
readouts.
According to the above, Equation 4.35 with the com-
plex
was considered in the deduction of the limits for
the GCA method. Using sample statistics, L
D
and L
Q
may
be given by: [33]
(4.36)
(4.37)
which are applicable for GCA methods.
Figure 4.51 shows the results for both
L
D
and L
Q
,
obtained with GCA methods on the left-hand side and
with conventional analysis on the right-hand side, for
LiF:Mg,Cu,P. Values of 3s
b
, obtained with either method,
are also presented in the figures, and it can be observed
that the use of this parameter for the detection limit under-
estimates it when the conventional approach is used, while
it is quite accurate in the GCA approach. As expected,
GCA-produced limits are always lower and the limits for
LiF:Mg,Cu,P are also lower than the limits for LiF:Mg,Ti.
Similar to LiF:Mg,Ti, LiF:Mg,Cu,P is available with
different thermal neutron sensitivities, depending on the
concentrations of LiF:Mg,Cu,P, i.e., 7.5%, 95.6%, and
0.07%, corresponding to TLD-100H, 600H, and 700H,
respectively. For use in personal dosimetry, the TLD pel-
lets are encapsulated in thin FEP-coated film and mounted
in a standard Harshaw aluminum substrate to form a TLD
card. The TL response of this material is extremely sen-
sitive to the readout temperature. [34]
A reader which uses a linear gas-heating technique that
combines the advantages of non-contact gas heating and
linear ohmic heating was described by Moscovitch. [34]
The reader incorporates a linear time-temperature-controlled
hot gas-heating technique. The reader can use either nitro-
gen or air for heating the TL elements. Heating rates may
be in the range of 1 to 50°C s
1
. The temperature is sensed
by individual thermocouples across the end of each nozzle
and is sent to a heater control board which compares the
measured temperature with that called for by the user-
defined heating profile (temperature as a function of time).
It then adjusts the current in the heating tubes to maintain
the temperature of the gas within 1°C of the specified
level. The TL-emitted light is measured using several pho-
tomultiplier tubes (PMT) that are thermoelectrically cooled
FIGURE 4.51 Results obtained with glow-curve analysis (left-hand side) and conventional analysis (right-hand side) of the glow
curves of LiF:Mg,Cu,P. Filled circles, detection limit; open squares, determination limit; open triangles, 3
s
b
values. Linear regression
fits are also presented. (From Reference [33]. With permission.)
()
2
()
2
t
2
n
2
2
K
t
2
t
2
2
K
t
2
L
D
GCA
t
n
s
b
1 t
m
s
---------------------
t
m
s
1 t
m
s
---------------------
K
b
L
D
GCA
k
Q
s
1 k
Q
s
----------------------
K
b
Ch-04.fm Page 262 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 263
to 12°C. The PMT signal is accumulated via the charge
integration technique.
The reader calibration factor for element position i,
RCF
i
, is defined as follows:
where is the average measured charge for that posi-
tion when a set of calibration dosimeters is exposed to a
known quantity of radiation
L.
The sensitivity of LiF(MCP) is approximately 25
times higher than the sensitivity of TLD-100, with a batch
homogeneity of 8% (one standard deviation). Once encap-
sulated in a TLD card, however, the relative sensitivity
drops to 10. The reason for this sensitivity decrease is that
the heating applied to the chip during manufacturing (the
encapsulation process) increases the temperature to
280–290°C for short periods of time. This results in per-
manent loss of sensitivity of the phosphor. [34]
A new environmental TLD dosimeter badge and dose-
computation algorithm based on LiF:Mg,Cu,P was
described by Perry et al. [35] LiF:Mg,Cu,P, with its high
sensitivity, tissue equivalence, energy independence, and
low fading characteristics, is a natural choice for environ-
mental dosimetry. The badge consisted of a card and a
plastic holder. The card contained four LiF:Mg,Cu,P ele-
ments encapsulated in Teflon. The elements were all 3.2 mm
square and 0.4 mm thick. The badge was symmetrical and
used four fillers to discriminate low-and high-energy
photons and to determine the directional dose equivalent,
H(0.07,
) and ambient dose equivalent (10).
The Type 8855 dosimeter is shown in Figure 4.52.
The filtration-covering element number 1 consists of
91 mg cm
2
Cu 240 mg cm
2
ABS plastic and is used
for low-energy photon discrimination. Element number 2
filtration consists of 1000 mg cm
2
PTFEABS plastic
and is used for ambient dose measurement. Element number
3 has 17 mg cm
2
of Mylar plus PTFE encapsulation and
is used for directional dose measurement. Element number
4 filtration consists of 464 mg cm
2
Sn 240 mg cm
2
ABS plastic and is used for intermediate energy photon
discrimination. The card identification is visible through a
red filter window located in the center of the front side of
the holder.
The graph in Figure 4.53 represents the photon energy
response of each of the elements in the dosimeter refer-
enced to
137
Cs for pure fields. The results show that with
light filtration, such as is the case in element 3, the energy
response of the dosimeter is relatively flat. Combined with
the response of elements with heavier filtration, ratios of
elements will give useful information as to what energy
is being measured in a blind test situation.
IV. CAF:Tm (TLD 300) DOSIMETER
TLD-300 dosimeters have been employed in high LET
radiotherapeutic fields generated by fast neutron, negative
pion, and heavy ion beams. By proper peak height analysis
FIGURE 4.52 Type 8855 dosimeter. (From Reference [35]. With permission.)
RCF
i
Q〈〉
i
L
Q〈〉
i
H
Ch-04.fm Page 263 Friday, November 10, 2000 12:01 PM
264 Radiation Dosimetry: Instrumentation and Methods
of the two main peaks of CaF
2
:Tm glow curves after such
irradiations, it is possible to separate the high and low
LET content of the radiation field. Therefore, the distri-
bution of the biological equivalent dose can be determined
in a single irradiation. The method was extended to a pre-
therapeutic proton field of 175-MeV maximum kinetic
energy by Hoffmann et al. [36] It turned out that in such
proton fields, the sensitivity of the high temperature
peak is constant; thus, the dose can be determined to an
accuracy of 4%. The sensitivity of the low temperature
peak decreases linearly to 50% as a function of , such
that the average linear energy can be determined to an
accuracy of 5 keV
m
1
.
The shape of the glow curve changes considerably
when the TLD-300 dosimeters are irradiated at different
positions along the depth dose. Figure 4.54 shows glow
curves taken with the same dose at 0.5, 17, and 19.5-cm
depth, which corresponds to 90 values of 4.5, 6.0, and
21.5 keV
m
1
. Whereas the sensitivity of the high-
temperature peak P2 remains constant, the sensitivity of
the low-temperature peak P1 decreases rapidly with
increasing LET. The decrease is steeper than measured
with negative pions, due to the different shape of the
microdosimetric spectra caused by secondary particles. It
is, however, similar to the LET dependence found in He
2+
beams because of the similarity of the spectra.
Peak 3 (P3) of TLD-300 was studied by Angelone
et al. [37] as a low-dose TL dosimeter. Measurements
showed that it is possible to reach, for the detection limit
(L
D
), a value of l.0 0.3
Gy. A reading cycle which
allows peak 3 to be read and the TLD-300 to be annealed
in the reader allows at least 9-fold reuse of TLD-300
before annealing at 400°C for 1 h is necessary. The resid-
ual TL signal was 0.5% of the TL signal of the irradiated
dosimeter. A slight decrease of the P3 TL signal with the
number of irradiation/reading cycles was also observed.
Since the glow curve of TLD-300 shows two well-
separated peaks, the so-called peak 3 (P3) and peak 5 (P5)
(the latter being sensitive to high LET particles), a reading
cycle able to read peak 3 alone was studied. After several tests
the following cycle was adopted: preheating at 80°C lasting
5°C s
1
; heating ramp of 5°C s
1
for 34 s, up to a maximum
temperature of 240°C; quick temperature rise (25° C s
1
)
up to 400°C; and annealing lasting 15 s (Figure 4.55).
The last step allows for P5 to be annealed in the reader.
The in-oven annealing procedure used in this work is 1 h
at 400°C.
A series of nine cycles (irradiation/preheating/read-
ing) were repeated, irradiating each time the same group
of 15 TLDs. The TL residual signal did not exceed 0.5%
of the last TL signal reading. It was also found that there
is a slight decrease of the P3 response as the number of
cycles increases. After nine cycles, a 4% decrease of the
FIGURE 4.53 Photon energy response of 8855 dosimeter. Elements i–iv indicated on curves. (From Reference [35]. With permission.)
FIGURE 4.54 TLD-300 glow curves taken at different posi-
tions along the depth-dose distribution with equal dose; val-
ues taken from the microdosimetric spectra taken at that
position. (From Reference [36]. With permission.)
y
D
y
D
Ch-04.fm Page 264 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 265
last measured signal, with respect to the first TL signal,
was observed.
Important parameters are the critical level (L
c
) and the
detection limit (L
D
). L
c
is the signal that provides a con-
fidence level of 1-
that the result is not due to a back-
ground fluctuation, while, as stated by Hirning [34a], L
D
is the smallest amount of signal that can be detected at a
specified confidence level.
The results for L
c
and L
D
are reported in Table 4.3. The
results clearly indicate that peak 3 of TLD-300 has a very
good performance as a low-dose detector. The measured
values are only twice that of LiF-600H and GR-206 and a
factor five above that of LiF-700H and GR-207, which
make peak 3 suitable for most low-dose measurements.
The TL response of CaF
2
:Tm to 0.7-MeV protons,
5.3-MeV particles, and 120-MeV
12
C ions has been inves-
tigated by Buenfil et al. [38] The area of peak 3 showed
a linear response as a function of fluence for all the flu-
ences studied, while peaks 5 and 6 followed a linear-
supralinear behavior. The departure from linearity occurs
at high doses, above 10
2
Gy.
Figure 4.56 shows a typical TLD-300 glow curve after
low LET irradiation (in this case,
60
Co gamma-rays) and
its deconvolution into peaks numbered 3 to 6. Figure 4.57
shows a typical glow curve after exposure to heavy charged
particles (in this case, 5.3-MeV particles). The differ-
ences between the glow curves displayed in Figures 4.56
and 4.57 explain the interest in TLD-300 as a dosimeter
for mixed field situations, where low and high LET con-
tributions need to be separated.
Hoffmann and Prediger [39] found that peak 5 has
constant sensitivity to gamma-rays and particles having
LET below about 30 keV m
–1
. Higher LET radiation is
less effective than gamma rays in activating peak 5.
Buenfil et al. confirmed their results since the highest LET
radiation in their data ( particles and
12
C) had about half
the peak 5 sensitivity than the one measured for protons.
Concerning peak 3, Hoffmann and Prediger reported a con-
tinuous loss of relative sensitivity as a function of the LET.
Loncol et al. [40] studied the peak 3 (150°C) and peak
5 (250°C) response of CaF
2
:Tm (TLD-300) to neutron and
proton beams, to analyze the effect of different radiation
qualities on the dosimetric behavior of the detector irradi-
ated in phantom. The study was extended to an experimental
12
C heavy ion beam (95 MeV/nucleon). The sensitivities of
peaks 3 and 5 for neutrons, compared to
60
Co, varied a little
with depth. A major change of peak 5 sensitivity was
observed for samples positioned under five leaves of the
multi-leaf collimator. While peak 3 sensitivity was constant
with depth in the unmodulated proton beam, peak 5 sensi-
tivity increased by 15%. Near the Bragg peak, peak 3
showed the highest decrease of sensitivity. The ratio of the
heights of peak 3 and peak 5 decreased by 70% from the
60
Co reference radiation to the
12
C heavy-ion beam.
Figure 4.58 shows the glow curves of two particular
samples positioned at the extreme depths in the phantom
FIGURE 4.55 Typical TL signal for TLD-300 irradiated at 1 mGy and read with the heating cycle reported in the text. The temperature
profile is also reported (right axis). (From Reference [37]. With permission.)
TABLE 4.3
Measured Critical Level (L
c
) and Detection Limit
(
L
D
), in
Gy, for the TLDs used by Angelone
Detector L
C
(
Gy) L
D
(
Gy)
TLD-300 0.5 1.0
TLD-700H 0.1 0.2
TLD-600H 0.25 0.50
GR-207 0.15 0.30
GR-206 0.26 0.52
Source: From Reference [37]. With permission.
Ch-04.fm Page 265 Friday, November 10, 2000 12:01 PM
266 Radiation Dosimetry: Instrumentation and Methods
FIGURE 4.56 Typical TLD-300 glow curve for low LET irradiation (
60
Co
irradiation). Deconvolution has been applied to separate
the curve into peaks 3 to 6. (From Reference [38]. With permission.)
FIGURE 4.57 Typical TLD-300 glow curve for high LET irradiation (
241
Am particles). Deconvolution has been applied to separate
the curve into peaks 3 to 6. (From Reference [38]. With permission.)
FIGURE 4.58 A glow-curve comparison for samples positioned at different depths in water, after irradiation in p(65) Be neutron
beam and in
60
Co beam. (From Reference [40]. With permission.)
Ch-04.fm Page 266 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 267
(2 and 15 cm) irradiated by the direct beam. The glow curve
issued from another chip irradiated in a cobalt beam was
also plotted. All the curves were normalized to a unit area
to allow the comparison between them. From these curves,
no major change of sensitivity was observed for peaks 3 and
5 at different positions in the direct neutron beam.
The glow curves of samples positioned at different
depths in the phantom irradiated by the unmodulated beam
showed that the height of peak 3 decreased relative to that
of peak 5 as the TLD position became deeper.
Figure 4.59 shows the proton energy as a function of
the peak height ratio in the unmodulated proton beam.
These results can be approximated with a second-order
polynomial fit. This curve can be used in order to estimate
the mean energy in the spread-out Bragg peak.
Figure 4.60 compares the glow curves of samples
positioned at the initial plateau (0.1 cm) and at the Bragg
peak (2.2 cm) of the unmodulated beam. The glow curve
shows an even more pronounced peak height change than
for the neutron and proton beams if compared to that for the
60
Co beam. As in the proton beam, the height of peak 3
decreased relative to that of peak 5 as the TLD position
approached the Bragg peak. Beyond the Bragg peak
(2.5 cm), the height of peak 3 increased again to 0.80, as
in the proton beam.
The glow-curve structure and kinetics parameters of
CaF
2
:Tm (TLD-300) were investigated by Jafarizadeh
[41] at a test dose of
90
Sr
rays. A new peak at 68°C,
called 1a, was recognized in the complex structure of the
initial part of the glow curve. By applying a thermal
FIGURE 4.59 Proton energy as a function of the peak height ratio (peak 3 to peak 5) for the unmodulated proton beam. The
experimental data were fitted with a second-order polynomial. (From Reference [40]. With permission.)
FIGURE 4.60 A glow curve comparison for samples positioned at different equivalent depths in water after irradiation in the
12
C
ion beam and in the
60
Co beam. (From Reference [40]. With permission.)
Ch-04.fm Page 267 Friday, November 10, 2000 12:01 PM
268 Radiation Dosimetry: Instrumentation and Methods
bleaching method using a heating rate of 2°C s
1
, seven
glow peaks (1a to 6) were separated at a temperature range
of 33 to 314°C.
Figure 4.61 shows the glow-curve structure of this
phosphor exposed for 10 min to a test dose of 30 mGy
of
rays, recorded at a heating rate of 2°C s
1
(a) imme-
diately, (b) after 1 h, (c) after 24 h of post-irradiation
time, and (d) immediately at a test dose of 80 mGy but
for a long exposure duration of 16 h. Seven glow peaks,
located at temperatures 68(1a), 80(1), 106(2), 145(3),
191(4), 243(5), and 273(6)°C, were obtained at a heating
rate of 2°Cs
1
.
The solution of the general order (GO) model formula
of May and Partridge [42] for a constant temperature
(isothermal decay) leads to Equation 4.38:
(4.38)
where A and B are constants and
t is the decay time.
The phototransferred thermoluminescence (PTTL)
of sintered pellets of natural CaF
2
from Brazil was com-
pared with that of CaF
2
doped with Ce
3
and/or Dy
3+
by
Nakamura et al. [43] It is shown that the excitation
spectrum provides a convenient way to find an optimum
condition of preheat treatment of sintered CaF
2
after UV
irradiation. The sintered CaF
2
containing a small amount
of Ce
3
0.2 mol% showed a strong glow peak around
90°C after UV irradiation. On co-doping with Dy
3+
in
CaF
2
:Ce
3
, the prominent glow peak shifts to 270°C. The
peak intensity shows a linear response to the UV irradi-
ation dose.
Figure 4.62 shows the glow-curve pattern of natural
CaF
2
, having been irradiated with x-rays to 25 Gy (a) and
UV light of 1.2 J (b). Although the TL intensity of UV
irradiation is smaller than that of x irradiation, the 260°C
peak is prominent compared with low-temperature peaks.
The inset shows the 260°C peak-intensity dependence on
the UV irradiation time over a wide range as t 0.8 to
103 min.
The 3.65-eV (340-nm) emission reveals a prominent
excitation peak at 4.00 eV (310 nm) for S-1 after heating
at 700°C for 5 min (Figure 4.63).The peak intensity
decreases after subsequent x irradiation (curve B). A
decreasing amount of Ce
3+
may correspond to the TL
intensity, since the Ce
3+
ion must return to the initial
state through a recombination with its counterpart. The
Ce
3+
peak height saturates around 310°C, and then the
peak height decreases with temperatures again (inset of
Figure 4.63).
Sintered CaF
2
was prepared containing a small amount
(0.2 mol%) of Ce
3+
(sample S-2). From the excitation
spectrum, the optimum temperature of S-2 was found to
be 320°C. A strong glow peak at 90°C was observed after
heating at 320°C and subsequent UV irradiation (solid
curves in Figure 4.64b).
FIGURE 4.61 Glow curves of CaF
2
:Tm exposed for 10 min to a test dose of 30 mGy of
rays , at a heating rate of 2°C s
1
: A,
immediately; B, after 1 h; C, 24 h after exposure of 60 mGy; and D, immediately after an exposure of 80 mGy but a long exposure
duration time of 16 h. (From Reference [41]. With permission.)
I
1b()1
ABt
Ch-04.fm Page 268 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 269
FIGURE 4.62 TL glow curves of as-received natural CaF
2
. (a) x irradiation of 25 Gy. (b) UV irradiation of 1.2 J. Inset shows a
relation between 260°C peak intensity and irradiation time of UV light. (From Reference [43]. With permission.)
FIGURE 4.63 Excitation spectra of 340-nm emission of Ce
3+
in sintered CaF
2
:CeO
2
.A: before; B: after x irradiation. Inset shows
the Ce
3+
peak height dependence on the treatment temperature after x irradiation. (From Reference [43]. With permission.)
Ch-04.fm Page 269 Friday, November 10, 2000 12:01 PM