ASTM E1654-94(2004)
(Guide)Standard Guide for Measuring Ionizing Radiation-Induced Spectral Changes in Optical Fibers and Cables for Use in Remote Raman FiberOptic Spectroscopy
Standard Guide for Measuring Ionizing Radiation-Induced Spectral Changes in Optical Fibers and Cables for Use in Remote Raman FiberOptic Spectroscopy
SIGNIFICANCE AND USE
Ionizing environments will affect the performance of optical fibers/cables being used to transmit spectroscopic information from a remote location. Determination of the type and magnitude of the spectral variations or interferences produced by the ionizing radiation in the fiber, or both, is necessary for evaluating the performance of an optical fiber sensor system.
The results of the test can be utilized as a selection criteria for optical fibers used in optical fiber Raman spectroscopic sensor systems.
Note 1—The attenuation of optical fibers generally increases when they are exposed to ionizing radiation. This is due primarily to the trapping of radiolytic electrons and holes at defect sites in the optical materials, that is, the formation of color centers. The depopulation of these color centers by thermal or optical (photobleaching) processes, or both, causes recovery, usually resulting in a decrease in radiationinduced attenuation. Recovery of the attenuation after irradiation depends on many variables, including the temperature of the test sample, the composition of the sample, the spectrum and type of radiation employed, the total dose applied to the test sample, the light level used to measure the attenuation, and the operating spectrum. Under some continuous conditions, recovery is never complete.
SCOPE
1.1 This guide covers the method for measuring the real time, in situ radiation-induced alterations to the Raman spectral signal transmitted by a multimode, step index, silica optical fiber. This guide specifically addresses steady-state ionizing radiation (that is, alpha, beta, gamma, protons, etc.) with appropriate changes in dosimetry, and shielding considerations, depending upon the irradiation source.
1.2 The test procedure given in this guide is not intended to test the other optical and non-optical components of an optical fiber-based Raman sensor system, but may be modified to test other components in a continuous irradiation environment.
1.3 The values in SI units are to be regarded as standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E1654 −94(Reapproved2004)
Standard Guide for
Measuring Ionizing Radiation-Induced Spectral Changes in
Optical Fibers and Cables for Use in Remote Raman
FiberOptic Spectroscopy
This standard is issued under the fixed designation E1654; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope EIA-455-57Optical Fiber End Preparation and Examination
EIA-455-64 Procedure for Measuring Radiation-Induced
1.1 This guide covers the method for measuring the real
Attenuation in Optical Fibers and Cables
time,insituradiation-inducedalterationstotheRamanspectral
2.3 Military Standards:
signal transmitted by a multimode, step index, silica optical
MIL-STD-2196-(SH)Glossary of Fiber Optic Terms
fiber. This guide specifically addresses steady-state ionizing
radiation (that is, alpha, beta, gamma, protons, etc.) with
3. Terminology
appropriatechangesindosimetry,andshieldingconsiderations,
3.1 Definitions—Refer to the following documents for the
depending upon the irradiation source.
definition of terms used in this guide: MIL-STD-2196-(SH)
1.2 The test procedure given in this guide is not intended to
and Guide E1614.
test the other optical and non-optical components of an optical
fiber-based Raman sensor system, but may be modified to test 4. Significance and Use
other components in a continuous irradiation environment.
4.1 Ionizing environments will affect the performance of
1.3 The values stated in SI units are to be regarded as
optical fibers/cables being used to transmit spectroscopic
standard. No other units of measurement are included in this
information from a remote location. Determination of the type
standard.
and magnitude of the spectral variations or interferences
produced by the ionizing radiation in the fiber, or both, is
1.4 This standard does not purport to address all of the
necessary for evaluating the performance of an optical fiber
safety concerns, if any, associated with its use. It is the
sensor system.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4.2 The results of the test can be utilized as a selection
bility of regulatory limitations prior to use.
criteria for optical fibers used in optical fiber Raman spectro-
scopic sensor systems.
2. Referenced Documents
NOTE 1—The attenuation of optical fibers generally increases when
2.1 ASTM Standards:
theyareexposedtoionizingradiation.Thisisdueprimarilytothetrapping
E1614 Guide for Procedure for Measuring Ionizing
ofradiolyticelectronsandholesatdefectsitesintheopticalmaterials,that
Radiation-Induced Attenuation in Silica-Based Optical
is, the formation of color centers.The depopulation of these color centers
Fibers and Cables for Use in Remote Fiber-Optic Spec-
by thermal or optical (photobleaching) processes, or both, causes
troscopy andBroadband Systems recovery, usually resulting in a decrease in radiationinduced attenuation.
Recovery of the attenuation after irradiation depends on many variables,
2.2 EIA Standards:
including the temperature of the test sample, the composition of the
2.2.1Test or inspection requirements include the following
sample, the spectrum and type of radiation employed, the total dose
references:
applied to the test sample, the light level used to measure the attenuation,
and the operating spectrum. Under some continuous conditions, recovery
is never complete.
This guide is under the jurisdiction of ASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
5. Apparatus
mittee E13.09 on Fiber Optics, Waveguides, and Optical Sensors.
Current edition approved Nov. 1, 2004. Published January 2005. Originally
5.1 ThetestschematicisshowninFig.1.Thefollowinglist
approved in 1994. Last previous version approved in 1999 as E1654–94 (1999).
identifies the equipment necessary to accomplish this test
DOI: 10.1520/E1654-94R04.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
procedure.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
Available from Electronic Industry Association, Engineering Dept., 2001 Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
Pennsylvania Ave., NW, Washington, DC 20006. dodssp.daps.dla.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1654−94(2004)
FIG. 1 Test Configuration
5.2 Light Source—A laser source shall be used for the 5.3 Focusing/Collection Optics—A number of optical ele-
Ramananalysis,andthewavelengthmustbechosensothatthe ments are needed for the launch and collection of light
fluorescentsignalsfromtheopticalcomponents(especiallythe radiation into and from the optical fibers (interfacing, sample
spectralactivatorsampleandopticalfibers)areminimized,and and reference), and other instrumentation (light source,
sothatthewavelengthcorrespondstothespectralsensitivityof spectrograph, detector). The minimal requirement for these
the detection scheme. Typically, the wavelength range ex- elements shall be that the numerical aperture of the compo-
ploited spans from 0.4 to 1.06 µm. The laser source must have nents are matched for efficient coupling. Optics may also be
sufficientpowertoobtainthedesiredminimumsignal-to-noise necessary to enhance the interaction of the input light with the
ratio (S/N) (see 10.3). spectral activator.
E1654−94(2004)
5.4 Interfacing Optical Fiber—The primary requirement of 5.10.1 Raman analysis requires that the laser line be elimi-
the interfacing optical fiber is to provide the minimum power natedpriortodetection.Alaserreject(orlongpassfilter)must
to the activator sample at the proper wavelength(s). The fiber be used at the entrance to the detection system. The filter
−1
lengthmaybeadjustedsothatthepowerrequirementsaremet. should pass all energy at 500 cm below the laser excitation
line. The filter should be placed between the optical elements
5.5 Light Radiation Filtering—Itisimportantthatallneigh-
prior to the spectrometer.
boring laser lines are removed from the source beam prior to
5.11 Optical Detection—An optical detector with a known
interaction with the spectral activator. This can be accom-
responseovertherangeofintensitiesthatareencounteredshall
plished before or after the interfacing optical fiber. Placement
be used. A typical system for Raman might include a single-
of the filter before the interfacing fiber will eliminate the
neighboring laser lines, but any fluorescence and Raman point detector (that is, PMT) or a multichannel analyzer (that
is, CCD array). The spectrograph must exhibit fast scanning
scattering due to the fiber or associated optics will be allowed
to interact with the sample. Placement of the laser pass filter capabilities. As Fig. 1 indicates, it is recommended that a
single-imaging spectrometer be used with a 2D CCD detector
aftertheinterfacingfiberispreferablebecauseitwilleliminate
any signals created within the fiber. If it is necessary to place so that the output from the reference and sample fibers can be
evaluated simultaneously. Two spectrometers operating simul-
the filter before the interfacing fiber, then the fiber should be
taneously may also be used.
kept as short as possible (several metres).
5.11.1 The optical detection system must be capable of
5.6 Spectral Activator Sample—The spectral activator used
−1
obtainingtheRamanspectrumfrom500to3000cm fromthe
must demonstrate a strong, well-characterized Raman spectral
excitation frequency.
signal. The sample may be either liquid, gas, or solid, depend-
5.12 Recorder System—Asuitable data recording, such as a
ing on the requirements of the optical fiber arrangement. It is
computer data acquisition system, is recommended.
recommendedthataliquidbeused,sincetheRamanscattering
in the proposed configuration will launch similarly into the
5.13 Ambient Light Shielding—The irradiated fiber length
sample and reference fibers. Standard recommended samples
shall be shielded from ambient light to prevent photobleaching
are:acetonitrile,benzene,andcarbontetrachloride.Thesample
byanyexternallightsourcesandtoavoidbaselineshiftsinthe
should be contained in a standard spectroscopic rectangular
zero light level. An absorbing fiber coating or jacket can be
silica cuvette.
used as the light shield provided that it has been demonstrated
to block ambient light and its influence on the dose within the
5.7 Optical Interconnections—The input and output ends of
fiber core has been taken into consideration.
the interfacing, reference, and sample optical fibers shall have
astabilizedopticalinterconnection,suchasaclamp,connector,
NOTE2—Theaveragetotaldoseshouldbeexpressedingray(Gy,where
splice, or weld. During an attenuation measurement, the 1 Gy=100 rads) to a precision of 65%, traceable to national standards.
For typical silica core fibers, dose should be expressed in gray calculated
interconnection shall not be changed or adjusted.
for SiO , that is, Gy(SiO ).
2 2
5.8 Irradiation System—The irradiation system should have
6. Hazards
the following characteristics:
5.8.1 Dose Rate—ACo orotherirradiationsourceshallbe 6.1 Carefully trained and qualified personnel must be used
used to deliver radiation at dose rates ranging from 10 to 100
to perform this test procedure since radiation (both ionizing
Gy (SiO )/min. (See Note 2.) and optical), as well as electrical, hazards will be present.
5.8.2 Radiation Energy—The energy of the gamma rays
7. Test Specimens
emitted by the source should be greater than 500 KeVto avoid
7.1 Sample Optical Fiber—The sample fiber shall be a
serious complications with the rapid variations in total dose as
previously unirradiated step-index, multimode fiber. The fiber
a function of depth within the test sample.
shall be long enough to have an irradiated test length of 50 6
5.8.3 Radiation Dosimeter—Dosimetry traceable to Na-
5 m and to allow coupling between the optical instrumentation
tionalStandardsshallbeused.Doseshouldbemeasuredinthe
outside the radiation chamber and the sample area.
same uniform geometry as the actual fiber core material to
ensure that dose-buildup effects are comparable to the fiber
7.2 The test specimen may be an optical-fiber cable
core and the dosimeter. The dose should be expressed in gray
assembly, as long as the cable contains at least one of the
calculated for the core material.
specified fibers for analysis.
5.9 Temperature-Controlled Container—Unless otherwise
7.3 Test Reel—The test reel shall not act as a shield for the
specified, the temperature-controlled container shall have the
radiation used in this test or, alternatively, the dose must be
capability of maintaining the specified temperature to 23 6
measured in a geometry duplicating the effects of reel attenu-
2°C. The temperature of the sample/container should be
ation. The diameter of the test reel and the winding tension of
monitored prior to and during the test.
the fiber can influence the observed radiation performance,
therefore, the fiber should be loosely wound on a reel diameter
5.10 Collection Optics into Detection System—Anappropri-
exceeding 10 cm.
atecollectionconfigurationshallbeusedatthedistalendofthe
sampleandreferenceopticalfibers.Itisrecommendedthatthe 7.4 Fiber End Preparation—Prepare the test sample such
collection and focusing optic(s) is f/number matched to the thatitsendfacesaresmoothandperpendiculartothefiberaxis,
numerical aperture of the fibers and detection system. in accordance with EIA-455-57.
E1654−94(2004)
7.5 Reference Fiber—The reference fiber shall have the sample. Position the sample and reference fibers to collect the
same requirements as the sample fiber. It should have similar spectral energy scattered (see Note 3).
characteristics, be packaged in the same configuration, and
10.3 Positionthelightexitingthefibersforcollectionbythe
should be used in an identical fashion as the sample fiber
detectionscheme.Thespectraobtainedthroughthesampleand
except for the radiation exposure.
reference fibers must exhibit a minimum signal-to-noise ratio
(S/N)of9priortoirradiationfortheprimaryRamanpeaks(see
8. Radiation, Calibration, and Stability
Note 4).
8.1 Calibration of Radiation Source—Make calibration of
10.4 Stabilize the test sample in the temperature chamber at
the radiation source for dose uniformity and dose level at the
23 6 2°C prior to proceeding (see Note 5).
location of the device under test (DUT) and at a minimum of
10.5 Obtain the system stability and baseline.
four other locations, prior to introduction of fiber test samples.
The variation in dose across the fiber reel volume shall not 10.6 RecordtheRamanspectrumfromthetestsampleprior
exceed 610%. If thermoluminescent detectors (TLDs) are to, and for the duration of the ionizing radiation cycle. Also
used for the measurements, use four TLDs to sample dose recordtheoutputspectraforatleast3600saftercompletionof
the irradiation process (see Note 5). Also record the spectrum
distribution at each location. Average the readings from the
multipleTLDsateachlocationtominimizedoseuncertainties. of the reference signal before and during both the irradiation
time and the recovery time after completion of the irradiation.
To maintain the highest possible accuracy in dose
measurements, do not use the TLDs more than once. TLDs The reference path is used to monitor for any system fluctua-
tions for the duration of a measurement.
should be used only in the dose region where they maintain a
linear response.
10.7 Take each spectral scan long enough to obtain the
necessary S/N ratio.
8.2 Measure the total dose with an irradiation time equal to
subsequent fiber measurements. Alternatively, the dose rate
10.8 Test Dose—Determine adverse effects due to the expo-
may be measured and the total dose calculated from the
sure to ionizing radiation by subjecting the test sample to one
product of the dose rate and irradiation time. Source transit
of the dose rate/total dose combinations specified in Table 1.
time (from off-to-on and on-to-off positions) shall be less than
10.9 Sample Number—Test three samples (see Note 6).
5% of the irradiation time.
10.10 Test Results Format—Depict the Raman spectra for
8.3 Stability of Radiation Source—The dose rate must be
both the reference and sample
...
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