Shani G. Radiation Dosimetry: Instrumentation and Methods
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470 Radiation Dosimetry: Instrumentation and Methods
geometry were examined. The numbers shown at the top
of Figure 10.70 are position groups which were introduced
to calculate the response at a certain depth from the mod-
erator surface along the x-axis as a function of the neutron
energy.
Figure 10.71 shows the counter responses as a func-
tion of the incident neutron energy obtained for the
x-proportional counter. Each of the curves shows the
detection counts at one of the five position groups, per
unit fluence at the center of the moderator, as a function
of the incident neutron energy. The energy resolution
seems to be rather poor because the response curves over-
lap considerably.
A rem counter with a response tailored to match the
shape of H
*
(10)/ as defined by ICRU and ICRP has been
developed by Burgkhard et al. [54] The rem counter LB
FIGURE 10.68 Smoothed responses of Bonner spheres as a function of the moderator diameter for two partial
3
He pressures and
incident neutron energies. The moderators consist of polyethylene with a specific mass density of 0.95 g cm
3
. The diameter of the
central detector is 3.2 cm. (From Reference [52]. With permission.)
FIGURE 10.69 A schematic drawing of the counter and the source-detector geometry. (From Reference [53]. With permission.)
Ch-10.fm Page 470 Friday, November 10, 2000 12:04 PM
Neutron Dosimetry 471
6411 consists of a polyethylene moderator sphere with a
diameter of 25 cm, a central cylindrical
3
He proportional
counter, and internal Cd absorbers and perforations. The
instrument has an integrated high-voltage supply and
signal processing and is connected to a microprocessor-
controlled portable data logger. Counter features are sum-
marized in Table 10.11.
The original data and the fitting results are shown in
Figure 10.72, which demonstrates the quality of the fitted
procedure, especially in the relevant high-neutron-energy
range. This fluence response has then been used to estab-
lish a numerical calibration factor for a broad calibration
field, N, defined as the ratio of the ambient dose equiva-
lent, H
*
(10), and the value indicated by the rem counter
in the calibration field, M, by integration:
(10.49)
(10.50)
where and are the neutron energy, the eval-
uated fluence response, and the spectrum, respectively.
and are taken as 1 meV and 20 MeV,
respectively.
FIGURE 10.70. Detection position profiles calculated with the Monte Carlo simulations or the responses as a function of the axial
position for various monoenergetic neutrons. The position profiles are shown for only the x-proportional counter. The numbers
indicate the position groups: (1)
13 cm to 7.8 cm, (2) 7.8 cm to 2.6 cm, (3) 2.6 cm to 2.6 cm, (4) 2.6 cm to 7.8 cm, and
(5) 7.8 cm to 13 cm, respectively. (From Reference [53]. With permission.)
FIGURE 10.71 Calculated responses for the five position groups shown in Figure 10.70 for the x-proportional counter as a function
of the incident neutron energy. (From Reference [53]. With permission.)
H
*
10() dE
n
h
*
E
n
()
E
n
E
n
()
E
n min
E
n max
MdE
n
R
E
n
()
E
n
E
n
()
E
n min
E
n max
E
n
R
,
En
E
nmin
E
nmax
Ch-10.fm Page 471 Friday, November 10, 2000 12:04 PM
472 Radiation Dosimetry: Instrumentation and Methods
Figure 10.73 shows the H
*
(10) response of the LB 6411
and the Leake counter, numerically calibrated in the bare
252
Cf spectrum. The LB 6411 shows a three-times-lower
over-response for intermediate neutrons and provides a
four-times-higher sensitivity than the Leake counter.
The so-called single sphere albedo counter makes use
of three active
3
He proportional counters as thermal
neutron detectors positioned in the center and on the sur-
face (albedo dosimeter configurations) of a polyethylene
sphere. The linear combination of the detector readings
allows for the indication of different quantities like H
*
(10),
D, and
, and reduces the energy dependence signifi-
cantly. [55]
The counter makes use of three
3
He tubes, one at the
center of a PE sphere, designated “c”, and two on the
surface, one just inside the moderator (albedo detector con-
figuration, designated “i”), front-shielded, and the other just
outside the moderator (detector configuration, designated
“a”, for thermal field neutrons), back-shielded by a boron-
plastic absorber (Figure 10.74). Detector positions, size, and
thickness of the boron absorber have been optimized to
simulate the KfK albedo dosimeter. Small
3
He proportional
counter tubes of the type Thomson 0.5 NH 1/1K, with an
effective height of 10 mm and a diameter of 10 mm com-
bined with a KfK-improved Thomson ACH amplifier, offer
a dose rate range from 1
Sv h
1
to 100 mSv h
1
with a
background rate of 0.01
Sv h
1
and a gamma discrim-
ination factor of 3 10
5
. The count rates of the three
detectors are indicated simultaneously.
The neutron dose equivalent was obtained by
a combination of the three detectors response (M(a), M(i),
and M(c)) (Figure 10.75) and the corresponding weighting
factor K.
(10.51)
For the estimation of the ambient dose-equivalent, fluence
to dose-equivalent conversion factors have been used,
based on the new
Q-L relationship recommended by
ICRP 60. The results in Figure 10.76 show that a sphere
diameter of 25 cm would result in a sufficient energy
response for H
*
(10), whereas a diameter of 27 cm would
improve the underestimation of the 30-cm sphere in the
energy range 0.1 to 1 MeV. The prototype with a diameter
of 25 cm is a compromise of energy response and weight
of the sphere.
The Andersson-Braun rem counter is widely
employed for radiation protection purposes, but its effi-
ciency shows a marked decrease for neutron energies
above about 10 MeV. A neutron monitor with a response
function extended up to 400 MeV has been achieved by
Birattari et al. [56] by modifying the structure of the
moderator-attenuator of a commercial instrument.
The Tracerlab NP-I Portable Neutron Monitor
Snoopy was chosen as a reference instrument for the
design of the extended range version. A moderator-atten-
uator structure was constructed to house the same BF
3
proportion counter. The new structure is obtained by
adding a layer of 1 cm of Pb around the boron plastic
attenuator (at a cost of about 8 kg of extra weight) and
shifting the outer polyethylene moderator 1 cm outward
(i.e., its thickness remains unchanged). Figure 10.77
shows a longitudinal cross section of the instrument. The
response function of the modified rem counter shows a
marked increase at high energies and no changes in the
other regions. This modified instrument was called the
Long Interval NeUtron Survey meter (LINUS). Figure
10.78 shows its calculated response function; the
response of the standard
A-B rem counter and the H
*
(10)
curve are also shown for comparison.
The response plotted in Figure 10.78 refers to lateral
irradiation of the monitor by a uniform and parallel
radiation field, i.e., the conditions under which H
*
(10)
is calculated. A response of 275 s
1
per mSv h
1
has
been adopted. The conversion coefficients from neutron
fluence to ambient dose equivalent were taken from
Stevenson. [57]
The Model NRD (Eberline [58]) neutron rem detector
is a nine-inch-diameter, cadmium-loaded polyethylene
sphere with a BF
3
lube in the center. This detector has
been shown to have an energy response which closely
TABLE 10.11
Essential Features of the LB 6411
Electronics Integrated high voltage supply and signal
processing, connected to a microprocessor-
controlled portable datalogger.
Physical basis
3
He proportional counter, moderating
polyethylene sphere of 25 cm diameter and
Cd absorbers.
Optimization Search for optimal physical instrument
parameters using detailed MCNP
modeling and the newest cross sections
(European Fusion File, EFF).
Experimental Monoenergetic neutrons from thermal
verification through 19 MeV at the PTB.
New quantity Ambient dose equivalent H*(10) for
indication neutrons according to ICRP 60 from
thermal to 20 MeV neutrons.
Low energy 10% to 30% in the energy range 50 keV
dependence up to 10 MeV.
High sensitivity 3 counts per nSva.
From Reference [53]. With permission.
H
10()
H
*
10() k
1
Ma() k
2
Mi() k
3
Mc()
Ch-10.fm Page 472 Friday, November 10, 2000 12:04 PM
Neutron Dosimetry 473
follows the theoretical dose from neutrons over the energy
range from 0.025 eV (thermal) to about 10 MeV. The BF
3
tube allows excellent gamma rejection. The detector is
identical to that of the Model PNR-4 portable neutron rem
counter. The detector specifications are:
1. Detector: BF
3
tube in nine-inch, cadmium-loaded
polyethelene sphere
2. Plateau: approximately 200 V with a slope of
5% per 100 V
3. Operating voltage: dependent on sensitivity of
counter and cable length; typically 1600 to
2000 V.
4. Directional response: within
10%
5. Energy range: thermal to approximately 10
MeV
6. Gamma rejection: up to 500 R/h, dependent on
high-voltage setting
7. Sensitivity: approximately 50 counts per minute
(cpm) per mrem/h (3000 counts per mrem)
8. Connector: MHV series coaxial
9. Energy response: see Figure 10.79
10. Size: 9 inches in diameter
10.5 inches high
(22.9 cm diameter
26.7 cm high)
11. Weight: 13.75 lb (6.3 kg)
Typical neutron plateau and gamma response of the NRD
neutron remdetector is shown in Figure 10.80.
FIGURE 10.72 Lower part: experimental (circles), calculated (dots), and evaluated neutron fluence responses for the LB 6411 (solid
line) and the Leake counter (dashed line) as a function of neutron energy. Upper part: response ratios of experimental and calculated
values to the filled values. (From Reference [54]. With permission.)
FIGURE 10.73 Ambient dose-equivalent response as function of neutron energy for the LB 6411 (solid line) and the Leake Counter
(dashed line), numerically calibrated (Equations 10.49 and 10.50 ) in a bare
252
Cf spectrum (histogram). (From Reference [54]. With
permission.)
Ch-10.fm Page 473 Friday, November 10, 2000 12:04 PM
474 Radiation Dosimetry: Instrumentation and Methods
FIGURE 10.74 Cross section of the dose rate meter using
3
He
detectors in the boron-plastic absorber configurations (i), (a), and (c)
in a polyethylene sphere. (From Reference [55]. With permission.)
FIGURE 10.75 Energy dependence of the fluence response M/ for the
3
He detectors for frontal (AP) irradiation of the detector
configuration (i) and (a) and for (c) in the PE spheres of different diameters. (From Reference [55]. With permission.)
FIGURE 10.76 Energy dependence of the dose equivalent response H(FIT)/H
*
(10) of the counter using different sphere diameters and
fits of the detector readings and frontal irradiation, based on the new
Q-L relationship of ICRP 60. (From Reference [55]. With permission.)
Ch-10.fm Page 474 Friday, November 10, 2000 12:04 PM
Neutron Dosimetry 475
FIGURE 10.77 Longitudinal cross section of LINUS. P, polyeth-
ylene; R, boron-doped synthetic rubber; L, lead; H, holes; D,
detector; C, connectors. (From Reference [56]. With permission.)
FIGURE 10.78 Response to lateral irradiation of LINUS. The response of a conventional A-B rem counter (the Tracerlab NP-1
Snoopy) and the H
*
(10) curve are shown for comparison. (From Reference [56]. With permission.)
FIGURE 10.79 Neutron energy response curve. (From Reference [58]. With permission.)
Ch-10.fm Page 475 Friday, November 10, 2000 12:04 PM
476 Radiation Dosimetry: Instrumentation and Methods
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FIGURE 10.80 Typical neutron plateau and gamma response. (From Reference [58]. With permission.)
Ch-10.fm Page 476 Friday, November 10, 2000 12:04 PM
477
Index
A
AAPM protocol, 171
Absorbed dose, 2
to air chamber factor, 31, 32, 96
calculation, 158
calibration factor, 21, 33, 166, 167
to dosimeter solution, 349
effect of on response of red Perspex dosimeter,
291
stopping power, 3–4
intercomparisons, in electron beams, 172
response of RCF with respect to, 315
value, 223
Accelerator
depth-dose curve in water for, 20
NPL linear, 342
photons produced by, 13
Accredited dosimetry calibration laboratory
(ADCL), 130
Acrylamide, index of refraction for, 417
Activation energy, 223
Active survey meter (ASM), 452
ADCL,
see
Accredited dosimetry calibration
laboratory
Agarose SeaPlaque, 413
Air-filled ion chambers, 190
Air kerma
calibration, 24, 152
calibration factor, 38, 93, 101, 103
formalisms, 31
rate, 178
ratio, 30
Alanine, 294, 297, 357, 358
All-scatter dose, 63
Alpha particles, 254, 287
Aluminum oxide dosimeters, 285
Ambient dose equivalent, 5
Amino acid, dissolved, 357, 358
Andersson-Braun rem counter, 472
Angle straggling, 427
Annealing
-irradiation-readout, 252
procedure, 232
treatment, pre-irradiation, 236
Antibodies, radiolabeled, 79, 80
ASM,
see
Active survey meter
Attix chamber, 204
Avogadro constant, 40
B
Back-diffusion, 119, 120
Backscatter
effects, 151
factor (BSF), 222, 283
air kerma–based, 103
variation of, 51
perturbation effects, 87
BANANA gel, 407
BANG,
see
Bis-acrylamide-nitrogen-gelatin
Base-plus-fog optical density, 306
Beam
calibration, 197
quality correction factor, 97
stop, 347
Beam’s-eye-view (BEV) planes, 308
Beginning of storage, 224
Beta dosimetry, 7
Beta emitters, 49
Beta energy, absorbed, 279
Beta irradiation, 290
Beta-ray dose backscatter factors, 51
BEV planes,
see
Beam’s-eye-view planes
Bhabha scattering, 14
Bias voltage, sensitivity vs., 373
Biological dosimetry, 8–9
Bis-acrylamide-nitrogen-gelatin (BANG), 407, 419
chemical composition of, 421
irradiation of, 405
polymer gel, 416
Bis monomer solutions, index of refraction for, 417
Boag
analytical formulas, 28
equation, 139
expressions, 125
formalism, 138
theory, 133, 134
Boltzmann constant, 225, 235, 250, 259
Bonner sphere (BS)
response, 469
spectrometer (BSS), 466
Boron-plastic absorber configurations, 474
BPS,
see
Brachytherapy planning system
Brachytherapy
dosimetry for, 56
photon energy, 390
planning system (BPS), 63
point source, 60
Ch-01.Index/frame Page 477 Friday, November 10, 2000 12:05 PM
478
Radiation Dosimetry: Instrumentation and Methods
radiation fields, 194
sources, use of diamond detector for dosimetry
of, 370
treatment-planning systems, computer-assisted,
282
Bragg
curves, 70
peak, 68, 267
Bragg-Gray
cavity, 53, 185, 206, 371
behavior, 52
theory, 354
conditions, ideal, 31
equation, 39, 152
principle, 96
relation, 228, 276
theory, 13, 72
bremsstrahlung, 13, 29, 31, 40, 375
charged particles lost by, 3, 180
contamination, 43
emission of, 43
facilities, pulsed, 376
fields, high-energy, 376
generation, 66
process, 14
production, 14, 164
secondary charged particles lost to, 36
tail, 174
transport, 16
x-rays, 236, 302
Broadband densitometer, 321
Brownian motion, 123
BSF,
see
Backscatter factor
BS response,
see
Bonner sphere response
BSS,
see
Bonner sphere spectrometer
Bubble
detectors, 459
dosimeters, 452, 454
lock, 183
Build-up cap, 110, 111, 115
Burlin
approach, 273
cavity
equation, 278
expression, 280
relation, 73
theory, 275
theory, 74, 75, 273, 278
C
Calcam chambers, 134
Calibration
curve, 326, 381
data, least-squares linear fit to, 311
factor(s)
absorbed-dose, 166, 167
air-kerma, 101, 102
cavity gas, 97, 204
dose, 167, 392
kerma, 178
polystyrene, 368
in phantom at depth, 163
ionization chamber, 162
LET, 241
methods, 173
run, 338, 340
Calorimeter(s), 344
core, 341
Domen’s, 331, 334
electron beam graphite, 341
graphite, 340
NPL, 342, 342
Ross’s, 334
system, 341, 342
thermal-defect, 345
water, 331, 335
Calorimetry, 331–347
graphite calorimeter, 340–343
other material calorimeters, 344–347
water calorimeter, 331–340
Capintec chamber, 166, 175
Carr-Purcell-Meiboom-Gill (CPMG) pulse
sequence, 419
Cavity
gas calibration factor, 97, 204
parameter, 76
radius, 54
theory, 10, 72, 184
CCD,
see
Charge-coupled device
CDM,
see
Classical Differential Method
CEA film, 302
Center of electron production (CEP), 114
Central axis percent depth dose, 86
CEP,
see
Center of electron production
Chamber(s),
see also
Ionization chambers
Attix, 204
Calcam, 134
Capintec, 166, 175
characteristics of commercial, 117
construction, knowledge of, 32
cooling of, 107
currents, inverse of, 134
diameter, 169
Exradin, 157, 175, 197, 349, 350
factor, dose-to-air, 105
Farmer, 105, 126
geometry, 149
HK, cross-sectional diagram of, 204
Holt, 166, 175
Markus, 119, 127, 154, 156
miniature Shonka thimble, 200
NACP, 95,133
necessity to calibrate, 206
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Index
479
NIST-calibrated cylindrical chamber, 164
over-response, 118
parallel-plate free-air, 133
plane-parallel, 125, 162, 164
PMMA-walled Farmer, 169
polarity effect, 145
ratio of perturbation factors for, 97
Scanditronix, 134
Shonka, 136
types tests, 190
Vinten, 148
walls, effect of density of, 119
Charge
carrier concentration, in high-purity silicon, 394
collection, 119
efficiency, 121, 362, 363
losses, 165
-loss mechanisms, 121
trapping, efficiency of, 372
Charge-coupled device (CCD), 313, 327, 413
Charged-particle equilibrium (CPE), 30, 73, 76
Chemical dosimetry, 349–359
Chromosome aberration analysis, 8
CIEMAT, 222
Classical Differential Method (CDM), 461–463
Code of practice, 25
Coefficient of general recombination, 134
Collecting electrode, 207
Collecting potentials, 129
Collection
efficiency(ies), 121, 123, 136
inverse of, 128
parallel-plate liquid-ionization chamber, 189
pulsed radiation, 124, 138
reciprocal of, 125
volume, 205
Compton interactions, 43, 74, 75
Computational dosimetry, 433
Computer-assisted brachytherapy treatment-plan-
ning systems, 282
Continuous radiation, 126, 135
Continuous slowing down approximation (CSDA),
44
Conversion factor, 177, 181, 215, 435
Cooling, reproducible, 256
Corona charging, 398
Correction(s)
energy, 231
factor(s), 93
behavior of, 101
calculation of for polymethylmethacrylate, 56
detector, 382
displacement, 101, 160
in-phantom calibration, 94
photon fluence perturbation, 352
stem, 111
variation of stem, 110
global stem 109
gradient, 158
heat-loss, 332
inverse-square law, 421
ion-recombination, 135
matrix, pixel-by-pixel nonuniformity, 314
perturbation, 154
photon attenuation, 158
recombination, 127
relative linearity, 315
replacement, 154, 157, 335
supralinearity, 252
values, fluence perturbation, 153
wall, 142
water proofing, 30
Coulomb
attraction, 123
collisions, 40
scattering, 71
Coumarin
emission, 356
spectra, irradiated, 356
Coumarin-3-carboxylic acid, 356, 357
Counting gas, 469
CPE,
see
Charged-particle equilibrium
CPMG pulse sequence,
see
Carr-Purcell-Meiboom-
Gill pulse sequence
CPU board, block diagram of, 213
CSDA,
see
Continuous slowing down approxima-
tion
Cylindrical ionization chambers, 100
D
Debye equation, 139
Deconvoluted glow curve, 239
DEF,
see
Dose enhancement factor
Delta-rays, 40
Densitometer(s)
laser-scanning, 302
LED, 319
LKB, 320
Depth-dose
curve, 305
distribution, 69
Depth-ionization curve, 27
Depth-scaling factor, 18
Detection
efficiency, 464
limit, 261
Detector(s)
board
external, 213
internal, 212
bubble, 459
configuration, 472
correction factor for, 382
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