Shani G. Radiation Dosimetry: Instrumentation and Methods
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290 Radiation Dosimetry: Instrumentation and Methods
with the general formula (K, Na) X
n
AlSi
3
O
10
(OH,F)
2
, where
X corresponds to Al
3
, Mn
2
, Mn
2
, Fe
2
, Fe
3
, Mg
2
, Ti
4
,
or Li
, depending on the mica type. These minerals are
classified according to crystallographic criteria in dioctahe-
dral (D-micas like muscovite and sericite) and trioctahedral
(T-micas like phlogopite and lepidolite). The results provide
evidence of the presence of several thermoluminescence
(TL) glow peaks induced after laboratory trituration (tribolu-
minescence) of the non-irradiated mica samples.
Figure 4.101 displays the data representing the effects
of beta and gamma irradiation on the TL signal for the
three mica samples with a lower percentage of scattering
(5%) and no fading. The samples used for Figures
4.101a, b, and c were Mos-1, Seri, and Flo-1, respec-
tively. As can be seen, the TLI of the samples is complex,
showing the presence of different, complex glow peaks
in the range 100 to 450°C. Beta irradiation of muscovite
samples was found to induce a prominent glow peak,
presumed to be complex, between 150 and 170°C, with
a large high temperature signal.
Metal alloy oxides, ceramics, glass, and various
papers (carton, filter paper, typewriting paper) have been
investigated by Stenger et al. [72] as possible thermolu-
minescent (TL) detectors or indicators for gamma and
electron radiation technology process control. Results
show that there is a good correlation between TL
response and absorbed dose in the range 0.1 Gy–15 kGy.
Electrochemically oxidized aluminum alloys (E-ALO)
can be used in the dose range from 0.1 Gy to 5 kGy.
Above 5 kGy they have a non-linear TL response to
50 kGy (Figure 4.102). The useful dose range of ceram-
ics is 100 Gy–8 kGy; the sensitivity of ceramics is similar
to that of Al
2
O
3
; and the linear range is 100–400 Gy.
The dose response curve of glass demonstrates high
nonlinear character; glass can store dose information for
10 years.
PERSPEX DOSIMETERS (CHANGE IN LIGHT ABSORPTION)
White Perspex pieces of different thicknesses were exam-
ined by Amin et al. [73] for their dosimetric properties in
industrial radiation processing. Light absorption of Per-
spex depends on the dose at which the Perspex is irradi-
ated. The wavelength used for the readout was 314 nm.
Pre-irradiation storage under different conditions had no
effect on absorbed doses. The post-irradiation studies indi-
cate that the specific absorbance decreases increasingly
with storage time. White Perspex of 2-mm thickness could
be employed as a suitable dosimeter to measure absorbed
dose reproducibly within the common working range of
10–50 kGy.
FIGURE 4.94 340-nm TSL response of CaSO
4
doped with:
curve A, Dy
3
; B, Tm
3
; C, Ho
3
; D, Er
3
; and E, Gd
3
. Curve
F shows the response with undoped CaSO
4
. (From Reference
[67]. With permission.)
FIGURE 4.95 RE
3+
TSL response of CaSO
4
doped with: curve
A, Dy
3
; B, Tm
3
; C, Ho
3+
; D, E
3+
; and E, Gd
3+
. (From Refer-
ence [67]. With permission.)
Ch-04.fm Page 290 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 291
The absorption spectra of both irradiated and un-
irradiated local white Perspex materials of two different
thicknesses are shown in Figure 4.103. The white Perspex
irradiated to 10 kGy gives the absorption spectrum shown,
yielding a well-defined peak at 314 nm. The dose-response
curves of local white Perspex of two different thicknesses
(2 mm and 2.5 mm) and Harwell red Perspex were
obtained by irradiating them at different radiation doses, as
shown in Figure 4.104. The dose response of white Perspex
of 2-mm thickness is better-defined up to 50 kGy, compared
with that of 2.5-mm thickness (Figure 4.104). This property
may make the former more suitable for use as a dosimeter
in the range of 10–50 kGy for industrial radiation process-
ing than the Perspex of 2.5-mm thickness, which is unsuit-
able for use beyond 35 kGy.
The effect of absorbed dose on the response of a red
Perspex dosimeter was studied by Al-Sheikhly et al. [74]
Red 4034 Perspex (Batch AW) was irradiated at several
doses from 10 to 50 kGy and at three dose rates from
0.83 to 8.6 Gys
1
(3.0 to 31 kGy h
1
). Although it has
been reported that there is only slight temperature depen-
dence of response over the temperature range 20–43°C
during irradiation, the effect of elevated temperatures
during the period immediately after irradiation may
cause errors in dose interpretation related to calibration
and storage at ambient laboratory temperatures (e.g.,
23°C). The Harwell red 4034 Perspex (Batch AW)
dosimeters were kept in hermetically sealed aluminum
polymer sachets until read with a Gary Model 219 spec-
trophotometer.
Figure 4.105 shows the net absorption spectra of red
4034 Perspex (Batch AW), irradiated at a controlled tem-
perature of 22°C, to a series of five doses, at the three
indicated dose rates. The vertical “error bar” on each data
point shows the estimated random uncertainty (1
) of 5
replicate samples at each dose and dose rate. The net absor-
bance per unit thickness (A cm
1
) was obtained by placing
the un-irradiated sample (having the mean value of absor-
bance, 0.0585) in the reference beam of the spectro-
photometer. The results show that the higher the dose rate,
FIGURE 4.96 TL glow curves of BaSO
4
:Eu (0.5 mol%) prepared by recrystallization, co-precipitation, and sintering methods. (From
Reference [68]. With permission.)
FIGURE 4.97 TL glow curves of BaSO
4
:Eu,P prepared by: 1,
(---) recrystallization; 2, (- . - . - ) co-precipitation; 3, ( — )
sintering; and 4, (-..-..-) CaSO
4
:Dy. (From Reference [68]. With
permission.)
A
0
Ch-04.fm Page 291 Friday, November 10, 2000 12:01 PM
292 Radiation Dosimetry: Instrumentation and Methods
the lower the gamma-ray sensitivity of the dosimeter. This
finding is at an overlapping higher dose- rate range.
VII. ELECTRON SPIN RESONANCE
DOSIMETRY
Electron spin resonance (ESR) is a well-documented
technique applied to the study of defects related to para-
magnetic impurities in insulators. ESR data can provide
definite information on the structure of the dopant sur-
roundings, such as the distribution of charge over the
surrounding nuclei, charge and aggregation state of impu-
rity, and characterization of new paramagnetic centers if
produced during irradiation.
Splittings between electron energy levels of the
defect/impurity is seen due to the interaction of the
uncompensated (paramagnetic) electronic spin with crys-
tal fields, nuclear spins, and the applied magnetic field.
FIGURE 4.98 TL glow curves of BaSO
4
:Eu,Na (0.5, 0.2 mol%) prepared by recrystallization, co-precipitation, and sintering methods.
(From Reference [68]. With permission.)
FIGURE 4.99 TL glow curves of Sr
3
(PO
4
): Eu
2
measured after beta irradiation of 0.4-Gy dose at RT. () blue emission band
(below 450 nm), (x) red emission band (between 500 and 650 nm). (From Reference [69]. With permission.)
Ch-04.fm Page 292 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 293
A free ion having a resultant electron spin (s 1/2),
applied magnetic field (H
A
) removes spin degeneracy and
splits the energy level into two spin non-degenerate levels
characterized by m
s
12 and 1/2. The extent of split-
ting is E = g
B
H
A
, where
B
= e 2m
e
c is the Bohr
magneton and g (Landé g factor) = 2 for a free electron.
If electromagnetic radiation (microwave) is impressed
upon the material, then it will be strongly absorbed (res-
onance absorption) if its frequency
is
(4.62)
or
(4.63)
As for a free electron, g 2, and if
10
10
Hz, then H
A
3570 gauss. It is convenient to use a fixed frequency and
vary the magnetic field H
A
to observe spin resonance.
Thermal treatment of irradiated (10
6
R) TLD-100
powder and the consequent shape and size of the ESR
signal have been utilized [75] to study the defect structures
responsible for TL emission. In Figure 4.106, g values for
different observed signals are shown. These are deter-
mined using the known signal position of DPPH (diphenyl
picryl hydrazyl; g = 2.0036) as the calibration point (g
marker). This is measured experimentally by placing a
quartz tube containing DPPH in the second cavity while
the irradiated sample powder, in a clean and dry matching
quartz tube, is placed in the first cavity of the dual-cavity
ESR spectrometer. The difference of the g factor as compared
to its free-electron value (
g 2), i.e., g g
bound
g
free
) is
a measure of the strength of binding of the electron within
the defect. The sign of g gives the charge state of the
defect. The electron gives a negative, and a hole gives a
positive, value of g. The observation of a broad ESR
band is usually related to the presence of centers in a
precipitate or colloid form. The precipitates form during
the irradiation, a fact which can be verified as the ESR
band grows in intensity during the first few irradiation
cycles, after which the saturation is exhibited.
FIGURE 4.100 Glow curves of KMgF
3
:Yb. (From Reference
[70]. With permission.)
h
g
B
H
A
h
gH
A
h
B
()v 7.14 10
7
cgs()
FIGURE 4.101 Thermoluminescence signals of three micas:
(a) Mos-1, (b) Seri and (c) Flo-1. The solid line (—) represents the
nonirradiated sample, The dash-dotted line (— • — ) represents the
beta-irradiated sample, and the dashed line (— —) represents the
gamma-irradiated sample. (From Reference [71]. With permission.)
Ch-04.fm Page 293 Friday, November 10, 2000 12:01 PM
294 Radiation Dosimetry: Instrumentation and Methods
The dosimetric properties of purified cellulose mem-
brane were investigated by Wieser and Regulla [76] for
high-level dosimetry. The response of the cellulose radicals
in terms of absorbed dose in water was determined in the
dose range 1–500 kGy. The ESR spectra were analyzed
with respect to the radicals’ stability under different tem-
perature and humidity conditions.
The use of ESR spectroscopy in the field of dosimetry
provides excellent precision and applicability over a wide
dose range from 0.1 Gy to about 1 cGy. The ESR quan-
tification of the radiation-induced free radical in, for
example, the amino acid alanine has meanwhile proved to
be of reference-class quality for high-level dosimetry, i.e.,
in the range 10 Gy to 0.5 MGy, covering photons and
electrons. [76]
Purified cellulose membranes supplied in sheets of
15
30 cm
2
and 18
m thickness contain 7.5% water
and 12% glycerine. The irradiations were performed
with
60
Co gamma rays. The dose rate was 15 kGy/h and
the temperature in the irradiation chamber was 40°C.
The samples were irradiated in the range from 1 kGy
to 500 kGy in PMMA containers. The spectrum of a
sample measured 4 days after irradiation with 20 kGy
is shown in Figure 4.107. It has a total spread of 5.5
mT, and the ratios of the peak amplitudes are approxi-
mately 1:3:7:3:1. The central peak is positioned at g
2.0027. Immediately (15 minutes) after irradiation, the
amplitudes in the range of 2 mT around the center of
the spectrum are increased by about. 40% and the center
is slightly shifted to a higher field (g 2.0032). The
peak amplitudes increase linearly with absorbed dose up
to about 50 kGy, leading to a saturated level at about
500 kGy (Figure 4.108).
FIGURE 4.102 Dose response curves of E-ALO disks, gamma rate: 120 kGy/h. (From Reference [72]. With permission.)
FIGURE 4.103 Absorption spectra of local white Perspex.
(From Reference [73]. With permission.)
Ch-04.fm Page 294 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 295
Of all living tissues in the body, only dental enamel
retains indefinitely the history of its radiation exposure.
The effect of ionizing radiation on many crystalline
materials is to produce free electrons that can be trapped
in defects in the crystal lattice. The lifetime of these traps
is long and can provide a history of radiation effects.
Both electron spin resonance (ESR) and thermolumines-
cence have previously been used to examine the trapped
electrons in calcified tissues. [77]
When irradiated to high doses, tooth enamel shows a
strong signal, which has been investigated previously in
dental enamel and hydroxyapatite and identified as the
FIGURE 4.104 Dose-response curves of local white and Harwell red Perspex. (From Reference [73]. With permission.)
FIGURE 4.105 Net absorption spectra produced by gamma-ray
irradiation of red 4034 Perspex, Batch AW, to the indicated
doses, at three dose rates (temperature during irradiation: 22°C).
(From Reference [74]. With permission.)
FIGURE 4.106 Central ESR signals from LiF (TLD-100) powder
after irradiation to 10
6
R (shown at half-intensity) and after anneal-
ing at 280°C for 10 min. (From Reference [75]. With permission.)
Ch-04.fm Page 295 Friday, November 10, 2000 12:01 PM
296 Radiation Dosimetry: Instrumentation and Methods
carbonated radical with a g of 2.002. At low doses (less
than 100 cGy), however, this radiation signal is masked by
a signal which is due to the native crystal structure itself
and is thought to be due to electrons in deep traps in the
crystal at a g of 1.996.
Figure 4.109 shows the ESR signals from enamel sam-
ples irradiated with doses of up to 10 Gy and the ESR
signal of an un-irradiated sample (patient B). A good
correlation was found between the strength of the ESR
signal and dose up to 20 Gy.
Although ESR dosimetry is a widely accepted means
of rapid and early detection of absorbed radiation doses,
it does possess two important disadvantages, limited sen-
sitivity and lack of portability. The low sensitivity exists
primarily because of the small interaction between the
magnetic dipole moment of the trapped electron and the
externally applied magnetic field that is required to
observe the ESR signal. The magnitude of the associated
energy-level transitions is proportional to the product of
FIGURE. 4.107 The ESR spectrum of cellulose measured at room temperature 4 days after irradiation with 20 kGy. (From Reference
[76]. With permission.)
FIGURE 4.108 Dose-response curve of gamma-irradiated cellulose membranes. Prior to irradiation the samples were stored at room
conditions. (From Reference [76]. With permission.)
FIGURE 4.109 ESR signals of tooth enamel samples irradiated
with doses of
60
Co gamma-rays up to 10 Gy. (From Reference
[77]. With permission.)
Ch-04.fm Page 296 Friday, November 10, 2000 12:01 PM
Thermoluminescent Dosimetry 297
these two quantities and is only 10
6
that of readily
observable optical transitions in an atom.
The lack of portability and general applicability of
ESR in dental enamel for radiation dosimetry exists for
two reasons. First, because of the large externally applied
magnetic field strength required to observe the ESR signal,
a wide array of laboratory equipment is used. Second, the
large sample size required (typically 0.1 g) necessitates
the use of extracted teeth.
The use of electron spin resonance (ESR) dosimetry
is also proposed in radiation therapy and accident dosim-
etry. Experimental investigation preparation procedures
FIGURE 4.110 Dose dependence of the ESR signal amplitude of alanine-polyethylene dosimeters. The full line represents the
second-order polynomial fitting function; error bars indicate overall uncertainty (95% confidence level). (From Reference [78]. With
permission.)
FIGURE 4.111 Response of crystalline quartz powder dosimeter (in terms of total amplitudes of the g
2
and g
3
ESR line signals of
the quartz center) as a function of the gamma-ray absorbed dose .The inset shows the ESR spectrum of the center in crystalline
quartz powder at an absorbed dose of 10 MGy (measurement at ambient room temperature). (From Reference [79]. With permission.)
E
1
E
1
Ch-04.fm Page 297 Friday, November 10, 2000 12:01 PM
298 Radiation Dosimetry: Instrumentation and Methods
of alanine-polyethylene solid state dosimeters (SSD) with
optimized characteristics were defined, both modifying the
commonly used blend composition and preparation and
choosing the best ESR spectra recording conditions. [78]
Dose response to
60
Co was studied by Bartolotta et al.
[78], irradiating groups of three dosimeters to dose values
between 0.5 and 30 Gy. Up to 2 Gy, the signal is almost
comparable with BG and no accurate dose measurements
are possible. In the 2–30 Gy dose range, ESR amplitude
values can be fitted with a second-order polynomial; dif-
ferences between given and recalculated doses were always
less than 4% (Figure 4.110). [78]
SiO
2
has been introduced for use at very high doses
(10
5
to 5 10
7
Gy) [79] and at relatively high tem-
peratures (up to 200°C). The preferred method of anal-
ysis in this case is ESR spectrometry. Figure 4.111
shows the ESR response properties of this system,
where the silica material is fine-grain pure crystalline
quartz, and free-radical centers consist of oxygen
vacancies ( centers) in the SiO
2
lattice. This dosi-
meter shows an irradiation temperature coefficient of
6.5 10
5
% C
1
. It can be optimally stabilized by a
short heat treatment at 300°C between irradiation and
ESR signal analysis.
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