美国辐射剂量片FWT-60-00,FWT-60-20T,FW

FWT-60radiochromic剂量计系列是专为辐射加工。极薄，无色薄膜，逐步吸收剂量颜色变深蓝色。

该剂量计使用十六进制（羟乙基）aminotriphenylacetonitrile（HHEVC）染料FWT- 60系列。该剂量计分析是简单的使用光度计或分光光度计。一般使用的波长是510nm和600或605纳米。
 
 
   规格
 剂量计类型：radiochromic薄膜
 FWT品名：Radiachromic剂量计
 剂量范围：0.5-200 kGy (0.05-20 Mrad)

 剂量率依赖：10E12 Gy/sec (10E14 rads/sec)

型号

颜色峰值波长：605纳米
 波长的利益：510nm和600或605纳米
 色彩构筑时间：通常在1小时内
 颜色改变：未经辐照：清晰;照射：深蓝色
 紫外线灵敏度：当暴露在波长小于350纳米时着色。

包装规格：
 FWT，60-00：1厘米×1厘米×42-52微米，1000片/盒，每盒卖
 FWT- 60 -20T：10x 10厘米张，每张卖

 FWT- 60 -20F：15×15厘米，每张卖
 FWT- 60- 20：45x 15厘米的自定义尺寸，每张卖

This PAL discusses the use, handling, and calibration of the FWT
series of Radiachromic Dosimeters. It gives general use
guidelines as well as a wealth of information gathered over the
years from users and the manufacturers. Most of the
information needed to use these products is represented here.
I. GENERAL
A. Dosimeters
This sheet contains information on the FWT-60 series of
dosimeters. This includes:
FWT-60-00 1 cm x 1 cm square
FWT-60-20F 15 cm x 15 cm square
FWT-60-810 8-10 μm thick
FWT also manufactures the Opti-Chromic series of dosimeters
that are useful for lower doses than the FWT-60 series.
Dose range: 0.5 to 200 kGy; Dose rate independent to 1012 Gy s-1
B. Manufacturing
The FWT-60 series of dosimeters are manufactured by Far West
Technology (FWT) at its factory in Goleta, California, USA. The
manufacturing process involves many steps and is a proprietary
process. Each step of manufacturing is closely monitored for
quality. Below is a list of the steps used to manufacture the
dosimeters.
1. Manufacturing the Dye and its components. FWT
manufactures its own dyes that are used in the dosimeters.
This insures that the dye is of high purity and quality. The
nylon matrix that holds the dye goes through several
conditioning steps. Clear, blemish free dosimeters are the
result of the extra steps in the manufacturing procedures.
2. Solvent casting large sheets of dosimeters.
Dye/nylon/solvent solutions are evenly spread over
extremely flat sheets of glass. The solvents evaporate
leaving a free standing film which is then peeled from the
glass. The goal in casting the dosimeters is an even
thickness which is best performed by casting the
dosimeters in sheets. No other form of manufacturing has
been found that results in consistent even thickness
dosimeters.
3. Drying and aging the sheets. The sheets are not completely
dry after peeling. They are hung in cabinets with a
continuous airflow for 3 months to finish the drying/curing
process.
4. Cutting the sheets into proper dosimeter size. The sheets
are then cut into the required size. They are usually cut
into 1 cm x 1 cm squares for the FWT-60-00 dosimeters.
5. Inspecting and sorting each dosimeter. Each FWT-60-00
dosimeter is visually checked and sorted by thickness. The
thickness of the dosimeters is measured by very sensitive
instruments capable of measuring to 0.0001 mm.
6. Pouching and packing the dosimeters. Some dosimeters are
boxed in quantities of 1000. Others are put into foil
pouches, hermetically sealed and then boxed.
Of course shipping is an additional step that is handled by our
shipping department.
C. Chemical Composition
The FWT 60 dosimeters are composed of hexa(hydroxyethyl)
pararosaniline nitrile. The matrix that holds the dye is nylon.
The film has a density of approximately 1.15 g/cm3 and a
composition (by mass) of 63.7% C, 12.0% N, 9.5% H and 14.8% O.
D. Dosimeter lot numbering
The lot numbers are four digit numbers that are sequential
according to product production run numbers, thus film lots will
not necessarily have consecutive numbers. There is usually only
one lot per year and each number is unique.
II. HANDLING THE DOSIMETERS
A. Physical handling
The dosimeters are strong soft nylon films. They can be handled
by picking them up with your fingers, but this can be difficult
because they are so thin. Picking them up this way will leave
fingerprints which can change the optical density readings and
thus the exposure data. For these reasons we suggest that you
handle the dosimeters with round tipped tweezers, the tweezers
we use.
USING RADIACHROMIC DOSIMETERS PAL-1
PAL 1 USING RADIACHROMIC DOSIMETERS PAGE 2 OF 7
B. Ambient light
The dosimeters will change color from penetrating radiation and
from UV light below 370 nm. Most artificial lights contain some
light in this region and will cause a color change in the
dosimeters exposed to the light for very long. Sunlight of course
contains a large quantity of UV–even sunlight through a window
will contain enough UV to quickly alter the color of a dosimeter.
For this reason, we recommend a complete survey of the area
where the dosimeters will be exposed to all forms of light. If
the area uses fluorescent lights or has some daylight, then the
area will probably need filters.
A simple test for UV exposure is to place several uncovered
dosimeters of known optical density in the area where
dosimeters will be used. Leave the dosimeter in the work area,
exposed to ambient light, for 8 hours. If the density change
with the exposure is greater than 0.005 OD then the area needs
to be filtered. You may want to filter it even if the test shows
negative since accidental stray light can have quite an effect on
the dosimeter reading. For critical measurements we
recommend always filtering all light sources. This includes
lights on electronic equipment.
Filtering can consist of covering fluorescent tubes with filter
sleeves, covering windows with UV film, covering light fixtures
with UV film and purchasing UV free products. Filters are
available for fluorescent tubes, incandescent lamps and for
windows. All of these materials are designed to block UV light
and will do an adequate job of protecting your dosimeters from
exposure.
FWT sells both paper envelopes and aluminum laminate pouches
to protect the dosimeters when they are in use during
irradiation. See section C1 and C2 for information on these
products.
Exposing the dosimeters to visible light for prolonged periods (on
the order of days to weeks) may cause a decrease in sensitivity.
This can occur with no change in background OD. For this
reason, we recommend storing the dosimeters in the dark.
C. Packaging
The dosimeters should be protected during exposure. Abrasion,
UV light and dirt may all affect the final OD reading and thus the
calculated dose. Protecting the dosimeters is as simple as
putting them inside an envelope or a pouch. Envelopes protect
the dosimeter from UV, dirt and abrasion. Pouches also protect
them from humidity change.
1. Envelopes
While most envelopes will work to protect the dosimeters the
FWT-80 envelopes are designed specifically for protecting the
films. UV light can leak both around the flap and through the
corners of conventional envelopes. The FWT-80 envelopes have
a large safety flap to prevent UV light leaking through the top
and a wide fold at the bottom to cover the corners. The extra
thick paper helps to further block UV. They are approximately 1
inch square.
2. Pouches
The FWT-81 aluminized pouches offer the additional advantage
over the envelopes of humidity protection. One, two or three
dosimeters are placed inside the pouch and the pouch is
conditioned (See Section F) and then sealed with a rotary band
sealer. The pouches are used where the humidity cannot be
controlled during exposure or where a tight control on humidity
is necessary for critical readings.
D. Thickness gauge
The dosimeters can be measured for thickness using a thickness
gauge. Appendix II lists the equipment that we use at FWT to
measure the thickness of all dosimeters. The dosimeters are
sorted into the following average thickness bins 0.0425, 0.0435,
0.0445, 0.0455, 0.0465, 0.0475, 0.0485, 0.0495, 0.0505, 0.0515
and 0.0525 mm. Each thickness includes thicknesses in a 0.001
mm range. Thus 0.0425 mm thickness would include all the
thicknesses from 0.0420 to 0.0429 mm.
The probes we use are LVDT probes mounted on strong anvils to
keep low strain on probes because the equipment measures
down to 0.0001 mm. The dosimeters are manufactured of nylon
film and are physically soft; the probes used to measure the
thickness push into the film and displace it. Thus the thickness is
not the actual thickness, but rather the thickness under some
pressure. We use low pressure probes which in our experience
give the best reproducibility.
E. Storage
We recommend storing the dosimeters at 35-55% RH and 15-
30°C. This will assure a long shelf life. Higher temperatures or
higher humidity will shorten the shelf life. There is a natural
color development that takes place in the film over time and
poor storage conditions will speed this up. Under optimum
conditions the dosimeters should have a storage life of 3 to 5
years.
Low temperature will retard the aging process. Too low a
temperature can cause problems with condensation. High
temperatures will accelerate the aging which shows up as a
higher initial OD.
Prolonged storage at less than 10% RH can cause a permanent
change in sensitivity. High humidity above 70% can cause the
films to look cloudy and will cause them to stick together.
Exposure above 90% may cause a permanent change in
sensitivity.
F. Conditioning
For best dosimetry results the film should be conditioned to a
tight temperature and relative humidity range for 24 hours prior
to irradiation. We condition film at 47-53% RH and 65-70 °F.
Conditioning at a processing facility should be based on the
calibration conditions and the ambient conditions.
G. Marking the dosimeters
If you want to mark the dosimeters we recommend using an
extra fine tipped permanent marker. Write the number in the
corner away from the center so it will not influence the reading
in the reader. See Appendix II for the brands we recommend.
PAL 1 USING RADIACHROMIC DOSIMETERS PAGE 3 OF 7
III. USING THE DOSIMETERS
A. Temperature
The dosimeters have some temperature dependence. Figure 1
shows a typical temperature response curve of the dosimeters.
This curve is for a constant temperature during irradiation and
will vary lot to lot. Most dosimeters will be subject to a varying
temperature during irradiation.
B. Humidity
The dosimeters have humidity dependence. Figure 2 shows a
typical response of the dosimeters to variations in humidity.
This curve will vary lot to lot. For critical uses, the dosimeters
can be placed in hermetic pouches to stabilize the humidity
during irradiation.
C. Color development
The dosimeters may take some time to develop full color. This
time will vary depending on the humidity, exposure time, and
radiation energy. Typical times are from a few minutes to a few
hours. At 24 hours all the color will be developed. The
dosimeters can be easily tested to the local conditions by
reading some test dosimeters over a period and noting the
change. We generally recommend opening pouches for ½ to 1
hour prior to readout.
Generally lower humidity during irradiation will cause the
dosimeters to take longer to develop color. Higher dose rates
will also delay color change. With long irradiation times the
dosimeters may seem to develop quicker–this is because they
were developing as they were being irradiated.
The color change can be accelerated by heat treatment. Expose
them to 90°C for 2 to 3 minutes or 60°C for 5 to 15 minutes for
complete color development
CONDITIONS EFFECTS
HUMIDITY EFFECTS
0-10% RH Possible permanent change
in sensitivity
35-55 % RH Best storage condition
47-53 % RH Typical pre-irradiation
conditioning
70% RH Film sticks together
90-100 % RH Possible permanent change
in sensitivity
TEMPERATURE EFFECTS
5° C Water may condense on
film
15-30° C Best storage condition
60° C Heat treatment for color
development 5-15 minutes
at this temperature (If
needed)
90° C Heat treatment for color
development 2-3 minutes at
this temperature (If
needed)
Table 1 Temperature and Humidity Ranges and Their Effects
Figure 2 Graph of Typical Humidity Dependence
Figure 1 Graph of Typical Temperature Dependence
PAL 1 USING RADIACHROMIC DOSIMETERS PAGE 4 OF 7
IV. READING DOSIMETERS
A. Wavelengths of interest
The dosimeters have a peak wavelength for color change. This
peak is centered near 605 nm. The wavelengths to use for
reading the film are 510 nm and 600 or 605 nm. The two
wavelengths are used for different dose ranges.
WAVELENGTH DOSE RANGE
510 nm 10-200 kGy
600 nm or 605 nm: 1-30 kGy
B. FWT readers
The FWT readers are designed for reading the FWT dosimeters.
They read in units of Optical Density (OD, equivalent to
Absorbance) and are easy to use. The film holders are sized
correctly for the FWT-60 films and they provide a correct and
repeatable orientation with respect to the light path. Both
analog and digital models are available. Some models have
further processing capabilities. A product data sheet is available
for each model.
C. Using a spectrophotometer
If you want to use a spectrophotometer there are several points
that you should consider. The holder will need to be modified
to accommodate the dosimeters and should hold them in the
same position for each reading. The holder should also have
very little play to keep the angle of light perpendicular to the
film. The light beam needs to be small and centered on the
dosimeter.
The wavelengths in common use are 510 nm and 600 or 605 nm.
Photometers use 600 nm bandpass filters and
spectrophotometers are set to 605 nm with a narrow bandpass.
Whatever the wavelength or bandpass, it is important that it
be the same for both calibration and reading the routine
dosimeters.
Beware of contamination from UV or IR light. UV light may
color the dosimeter as it is being read. Some
spectrophotometers do not have IR or UV filters. Check with the
manufacturer. The UV component can be checked by placing a
dosimeter in the spectrophotometer and reading it over time. If
it changes, then there is a UV component in the instrument and
it needs an additional UV filter.
V. CALIBRATION
The FWT Radiachromic Dosimeters, when used to measure
absorbed dose, need to be calibrated. Far West Technology can
supply a dose calibration curve for the lot; however, it is a
typical calibration curve and not traceable to a national
standard. If your application requires more than an approximate
calibration we recommend a complete calibration of your
system, which includes the dosimeters and the reader(s) that
may be used. This section describes the techniques to calibrate
your dosimetry system.
A valuable reference is ISO/ASTM 51275, Standard Practice for
Use of a Radiochromic Film Dosimetry System, Annual Book of
ASTM Standards. Also useful is ISO/ASTM 51261, Guide for
Selection and Calibration of Dosimetry Systems for Radiation
Processing, and ISO/ASTM 51707 Guide for Estimating
Uncertainties in Dosimetry for Radiation Processing. If you have
stringent calibration requirements we recommend that you
purchase these references and use them in your calibration.
The dosimeters are manufactured in lots and each lot will need
to be calibrated separately. The lot number is clearly marked on
each box. Each reader, if more than one reader is used, will
also need to be calibrated. The general procedure for
calibration is as follows.
1. Determine how many calibration absorbed dose values are
needed. Choose a minimum of five absorbed dose values
covering the range of utilization with at least four absorbed
dose values per decade of absorbed dose range. For
example, if the range of utilization is 10 to 50 kGy, then
the absorbed dose values chosen might be 10, 20, 30, 40
and 50 kGy.
2. For each absorbed dose value you need a minimum of five
dosimeters. Add an additional set of 5 dosimeters for
control. Using the example above, this would be a total of
30 dosimeters (5 dose values x 5 dosimeters/dose value + 5
control dosimeters). All of these dosimeters should be from
the same lot. Visually inspect the dosimeters (gently
dusting any which need it). Identify the dosimeters by
writing a small number in the corner of the dosimeter using
a felt tip pen (extra fine permanent markers work best) or
label an envelope or pouch containing the dosimeter.
Measure the initial absorbance (background) in your reader.
The initial absorbance is A0. Measure A0 for each dosimeter
on each reader you are calibrating.
3. Send all the dosimeters to an irradiation facility whose
dose-rate is traceable to national or international
standards. Have them irradiate each set to the desired
absorbed dose. The control dosimeters should not be
irradiated but should be included for a check of the effects
of environmental conditions during transport.
Alternatively, irradiate the dosimeter in-house with
transfer standards that are traceable to national or
international standards.
4. Measure the post-irradiation absorbance, Af, of each
dosimeter and calculate the specific net absorbance, k, for
each dosimeter: k = (Af-A0)/t, where t is the thickness of
the film. (t may be an average thickness from the lot that
you used. Verify that the control dosimeters have not
experienced a significant change.
5. Plot the response curve versus absorbed dose. You may also
want to perform a regression analysis of the data using an
appropriate analytical form. If you are using regression
analysis we recommend that it be performed using
individual k values rather than averaging k values for a
given absorbed dose. Common forms are second and third
order polynomials and power series. Regression for power
series is discussed below.
6. Examine the calibration for goodness of fit. Repeat the
calibration procedure at intervals not to exceed 12 months
or after repair of the reader if the manufacturer
recommends it. In general, a lamp change will not require
recalibration.
PAL 1 USING RADIACHROMIC DOSIMETERS PAGE 5 OF 7
7. Calibrate all alternate and backup readers. If you have
other readers, calibrate them at this time using the same
set of calibration dosimeters. If your primary reader
cannot be used you will need to use your backup reader.
8. Keep your dosimeters. Store them in a stable environment
in the dark. They may be useful for checking the operation
of a reader in the future.
A. Curve fitting
Curve fitting is easiest using a spreadsheet program such as
Excel with graph features. To generate the calibration curve
plot the specific response (k) versus the dose. Using a trendline
with the equation display enabled you can obtain the calibration
equation of the best fit for each wavelength. Typical equation
types will be linear, 2nd order polynomial or 3rd order
polynomial. You may try different equations to obtain the best
fit. From the calibration equation you can then generate a look
up table for dose calculations.
Calculations can also be done by hand using linear regression.
B. Example
The data in Appendix I were used as a basis for a calculation of
the calibration equation by plotting Column E versus Column A.
Figure 1 shows a response curve derived from the table of data
in Appendix I. The data points are plotted using the table. A
trendline and equation can be added for analysis of curve fit and
trending.
Figure 4 below is a typical curve for the Radiachromic
Dosimeters. The net absorbance was read in an FWT reader and
shows the approximate net Optical Density (ΔOD, equivalent to
net Absorbance) expected for absorbed dose. Background has
been subtracted from these readings. The absorbed dose is
shown in both kGy and Mrads
TYPICAL RESPONSE CURVE @ 510 nm
y = 0.1439x + 0.502
R2 = 0.9887
0
1
2
3
4
5
6
7
8
9
0 10 20 30 40 50 60
ABSORBED DOSE, kGy
SPECIFIC ABSORBANCE, k
Figure 1 Typical Response Curve
Figure 2 Typical Response Curve in Various Units
PAL 1 USING RADIACHROMIC DOSIMETERS PAGE 6 OF 7
APPENDIX I
EXAMPLE OF WORKSHEET FOR CALIBRATION OF RADIACHROMIC
DOSIMETERS @ 510 nm
A B C D E
DOSE
D, kGy
THICKNESS
t, mm
INITIAL OD
Ao
FINAL OD
Af
NET OD/mm
k = (Af-
A0)/t
10 0.0465 0.054 0.151 2.08
10 0.0465 0.053 0.143 1.93
10 0.0465 0.058 0.149 1.95
10 0.0465 0.054 0.141 1.88
10 0.0465 0.063 0.160 2.08
20 0.0465 0.045 0.204 3.42
20 0.0465 0.053 0.207 3.32
20 0.0465 0.050 0.199 3.20
20 0.0465 0.046 0.216 3.64
20 0.0465 0.060 0.212 3.26
30 0.0465 0.051 0.216 4.52
30 0.0465 0.051 0.261 4.53
30 0.0465 0.057 0.298 5.19
30 0.0465 0.051 0.274 4.79
30 0.0465 0.057 0.267 4.52
40 0.0465 0.051 0.341 6.22
40 0.0465 0.047 0.346 6.45
40 0.0465 0.047 0.348 6.49
40 0.0465 0.052 0.361 6.63
40 0.0465 0.065 0.339 5.89
50 0.0465 0.048 0.404 7.67
50 0.0465 0.053 0.400 7.46
50 0.0465 0.062 0.430 7.92
50 0.0465 0.053 0.398 7.44
50 0.0465 0.057 0.429 7.98
0
(control)
0.0465 0.051 0.048 -0.07
0
(control)
0.0465 0.054 0.066 0.27
0
(control)
0.0465 0.043 0.049 0.13
0
(control)
0.0465 0.048 0.065 0.36
0
(control)
0.0465 0.055 0.056 0.02
A. The radiation dose that the dosimeters received.
B. The average thickness of the batch of dosimeters
C. The initial absorbance (background OD) before the dosimeters were irradiated.
D. The final absorbance (OD) after the dosimeters were irradiated.
E. The Net absorbance (ΔOD) per mm of thickness
Description of the columns in this table:
PAL 1 USING RADIACHROMIC DOSIMETERS PAGE 7 OF 7
APPENDIX II
THICKNESS GAUGES
Thickness gauges are available manufactured by:
Mitutoyo, 18 Essex Road, Paramus NJ 07652
Tel: 201-368-0525 Fax: 201-343-4969
These parts are available through machine shop suppliers. The
part numbers are:
Mu-Checker Digital Readout: 519-605 or 519-615
LVDT Probe: 519-890 or with lift: 519-891
Vacuum lift for use with 519-891: 523349
Digital Gauge Stand: 7004 (Includes flat anvil)
MARKING PENS
Sharpie Extra Fine Point Permanent Markers in black work very
well on the film dosimeters. The fine tip is small enough to
write small numbers. The manufacturer is Sanford and they are
available in most stationary stores.