ASTM E1654-94(R2021) pdf free download

ASTM E1654-94(R2021) pdf free download.Standard Guide for Measuring Ionizing Radiation-Induced Spectral Changes in Optical Fibers and Cables for Use in Remote Raman FiberOptic Spectroscopy
5. Apparatus
5.1 The test schematic is shown in Fig. 1. The following list identifies the equipment necessary to accomplish this test procedure. 5.2 Light Source—A laser source shall be used for the Raman analysis, and the wavelength must be chosen so that the fluorescent signals from the optical components (especially the spectral activator sample and optical fibers) are minimized, and so that the wavelength corresponds to the spectral sensitivity of the detection scheme. Typically, the wavelength range ex- ploited spans from 0.4 µm to 1.06 µm. The laser source must have sufficient power to obtain the desired minimum signal- to-noise ratio (S/N) (see 10.3). 5.3 Focusing/Collection Optics—A number of optical ele- ments are needed for the launch and collection of light radiation into and from the optical fibers (interfacing, sample and reference), and other instrumentation (light source, spectrograph, detector). The minimal requirement for these elements shall be that the numerical aperture of the compo- nents are matched for efficient coupling. Optics may also be necessary to enhance the interaction of the input light with the spectral activator. 5.4 Interfacing Optical Fiber—The primary requirement of the interfacing optical fiber is to provide the minimum power to the activator sample at the proper wavelength(s). The fiber length may be adjusted so that the power requirements are met. 5.5 Light Radiation Filtering—It is important that all neigh- boring laser lines are removed from the source beam prior to interaction with the spectral activator. This can be accom- plished before or after the interfacing optical fiber. Placement of the filter before the interfacing fiber will eliminate the neighboring laser lines, but any fluorescence and Raman scattering due to the fiber or associated optics will be allowed to interact with the sample. Placement of the laser pass filter after the interfacing fiber is preferable because it will eliminate any signals created within the fiber. If it is necessary to place the filter before the interfacing fiber, then the fiber should be kept as short as possible (several metres).5.6 Spectral Activator Sample—The spectral activator used must demonstrate a strong, well-characterized Raman spectral signal. The sample may be either liquid, gas, or solid, depend- ing on the requirements of the optical fiber arrangement. It is recommended that a liquid be used, since the Raman scattering in the proposed configuration will launch similarly into the sample and reference fibers. Standard recommended samples are: acetonitrile, benzene, and carbon tetrachloride. The sample should be contained in a standard spectroscopic rectangular silica cuvette. 5.7 Optical Interconnections—The input and output ends of the interfacing, reference, and sample optical fibers shall have a stabilized optical interconnection, such as a clamp, connector, splice, or weld. During an attenuation measurement, the interconnection shall not be changed or adjusted. 5.8 Irradiation System—The irradiation system should have the following characteristics: 5.8.1 Dose Rate—A Co 60 or other irradiation source shall be used to deliver radiation at dose rates ranging from 10 Gy (SiO 2 )/min to 100 Gy (SiO 2 )/min. (See Note 2.) 5.8.2 Radiation Energy—The energy of the gamma rays emitted by the source should be greater than 500 KeV to avoid serious complications with the rapid variations in total dose as a function of depth within the test sample. 5.8.3 Radiation Dosimeter—Dosimetry traceable to Na- tional Standards shall be used. Dose should be measured in the same uniform geometry as the actual fiber core material to ensure that dose-buildup effects are comparable to the fiber core and the dosimeter. The dose should be expressed in gray calculated for the core material. 5.9 Temperature-Controlled Container—Unless otherwise specified, the temperature-controlled container shall have the capability of maintaining the specified temperature to 23 °C 6 2 °C. The temperature of the sample/container should be monitored prior to and during the test. 5.10 Collection Optics into Detection System—An appropri- ate collection configuration shall be used at the distal end ofthe sample and reference optical fibers. It is recommended that the collection and focusing optic(s) is f/number matched to the numerical aperture of the fibers and detection system. 5.10.1 Raman analysis requires that the laser line be elimi- nated prior to detection. A laser reject (or long pass filter) must be used at the entrance to the detection system. The filter should pass all energy at 500 cm −1 below the laser excitation line. The filter should be placed between the optical elements prior to the spectrometer.