Optical waveguides – Optical waveguide sensor
Patent
1998-06-01
2000-03-21
Ullah, Akm E.
Optical waveguides
Optical waveguide sensor
G02B 600
Patent
active
060411503
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national stage of PCT/DE/96/02321 filed Dec. 2, 1996 and based on German national application 195 45 060.4 of Dec. 2 1995 under International Convention.
The invention relates to a sensor having a radiation sensitive light waveguide for measuring a tissue equivalent radiation dose.
BACKGROUND OF THE INVENTION
From DE 39 29 294 A1, it is known to provide a mirror on such a light waveguide at one end and to couple light into it at the other end.
The light coupled into the light waveguide travels through it to the mirrored end, is reflected and travels back in the opposite direction through the light waveguide as a result.
The intensity of the reflected light is measured. If such a light waveguide is subjected to an ionizing radiation, the light damping in the waveguide is thus altered and so is the light intensity. The intensity change is a measurement of the radiation dose.
Light waveguides which, because of their composition, enable a tissue equivalent measurement of the radiation dose have a relatively low detection sensitivity.
The detection sensitivity can be increased by the use of long radiation-sensitive light waveguides. However, that increased detection sensitivity is connected with a correspondingly smaller local resolution.
In order to be able to measure approximate tissue equivalents with satisfactory local resolution and detection efficiency, according to German Patent application DE 195 03 647A1, two differently radiation-sensitive light waveguides are used.
However, the use of two waveguides, because of the large spatial requirements by comparison to a single waveguide also is detrimental with respect to the local resolution. Even here, proportionally longer light waveguides must be used with correspondingly poorer local resolution.
OBJECT OF THE INVENTION
The object of the invention is to provide a sensor for measuring a tissue equivalent dose which does not have the aforedescribed drawbacks.
SUMMARY OF THE INVENTION
The object is attained with a sensor for measuring a tissue-equivalent radiation dose which comprises a radiation-sensitive light waveguide, means for coupling the light into and out of the waveguide and mirroring provided on both ends of the radiation-sensitive light waveguides. The mirror on one or both ends of the radiation-sensitive light waveguide is formed as totally reflective. The radiation-sensitive light waveguide can have a pointed end and the point can be pyramidal.
As a tissue equivalent measurement radiation-sensitive light waveguide (sensor fiber), a glass fiber has been found to be suitable that is free from heavy doping elements. Suitable doping elements are especially lithium, magnesium and sodium.
The tissue equivalent measuring, radiation-sensitive light waveguide has on its end surface reflectors. To be able to couple light into and use of the light waveguide, it is especially provided that at least one end surface is only partly mirrored. Through the unmirrored part, the light can enter or leave the radiation-sensitive light waveguide.
By contrast to the state of the art represented by DE 39 29 294, only a part of the light coupled into the light waveguide is prematurely permitted to escape after traversing the radiation-sensitive light waveguide (back and forth travel with a fully mirrored end surface). The other part is reflected back and forth a multiplicity of times. The construction resembles a laser cavity. The light path is elongated in this manner and thus the sensitivity is improved.
The coupling of a sensor fiber (radiation sensitive light waveguide) to a radiation resistant transmission fiber cannot be carried out with the usual splicing methods of light waveguide technology since that would damage the mirror layer. In effect coupling is required to avoid direct reflection at the front mirror layer and to minimize leakage in the cavity. To insure a high precision coupling, the fiber to be coupled must be precisely aligned with the opening in the mirror on the
Buker Harald
Hasing Friedrich Wolfgang
Pfeiffer Frank
Dubno Herbert
Forschungszentrum Julich GmbH
Ullah Akm E.
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