AU626950B2 - Radiation detector - Google Patents

Description

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Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1953Z69 COMPLETE SPECIFICATION

(ORIGINAL)

626950 Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority 00 Q dated Art f me of Applicant: HOECHST AKTIENGESELLSCHAFT

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1dress of Applicant :50 Bruningstrasse, D-6230 Frankfurt/Main 80, Federal Republic of Germ any ;tual Inventor tidress for Service n" WERNER GROH, JOCHEN COUTANDIN, PETER HERBRECHTSMEIER and JURGEN THEIS WATERMARK PATENT TRADEMARK ATTORNEYS.

290 Burwood Road, Hawthorn, Victorie, Australia :omplete Specification for the invention entitled: 0 0 0 a RADIATION DETECTOR The following statement is a full description of this invention, including the best method of performing it known to .ii :r HOECHST AKTIENGESELLSCHAFT HOE 88/F 352 Dr.DA/je Description Radiation detector The invention relates to a detector for detecting invisible radiation and charged particles.

It is known that if light is irradiated laterally into an optical wave guide containing fluorescent dyestuffs, fluorescent radiation is produced which can be conducted to the end faces of the optical wave guide by total reflection (cf. Tanaka et al., SPIE, vol. 840, "Fiber Optic Systems for Mobile Platforms", page 19).

It is further known that polymer optical wave guides doped with a scintillating compound can be used to detect -radiation and charged particles (cf. H. Blumenfeld et :5 al., Nucl. Instr. Meth. A257 (1987), 603). A disadvantage of this method, however, is that the sensitive surface is restricted to geometries which can be produced from such t fibers. Thus, it is not readily possible, for example, to achieve the frequently used, circular, sensitive surface.

3 It ha5 also already been proposed to produce a light ::detector from a plate-like light-absorbing body and at least one optical wave guide connected thereto (cf.

'T Ca rs° Pe cc2ion -a l) The object was to find a detector for invisible radiation and charged particles which is distinguished by simplicity and flexible design possibilities.

It was found that the object can be achieved if at least one optical wave guide containing a fluorescent dyestuff is arranged parallel to the surface of a radiationabsorbing panel.

2 The invention consequently relates to the detector described in the claims.

The radiation-absorbing panel may have any desired form, preferably it is rectangular or round, in particular rectangular. The thickness is 0.1 to 3 mm, preferably 0.3 to 1 mm. The panel is composed of a carrier material, for example a polymer, doped with a luminescent compound.

Such panels may, for example, be the commercially available fluoroscopic screens.

Arranged parallel to the surface of the panel is at least one optical wave guide. Preferably, the optical wave guide is bonded to the surface. A single optical wave guide may also be replaced by a bundle of optical wave guides and the optical wave guide or guides may also be arranged between two panels so that the whole has a sandwich structure.

1 The optical wave guide may be a comnurercial fiber which is r preferably composed of a transparent polymer, for example polycarbonate, polystyrene or polymethyl methacrylate in 0 the core and a polymer cladding having a lower refractive index, for example a fluorinated acrylate.

The optical wave guide contains at least one fluorescent dyestuff, it being essential for the wave length range of the luminescent radiation from the panel to overlap with the wave length range of the absorption of the optical wave guide dyestuff. In the optical wave guide, the dyestuff may be contained in the core or in the C' E f cladding or in both. Suitable fluorescent dyestuffs are, in particular, organic compounds, for example perylene dyestuffs, benzoxanthenes, or, alternatively, inoxganic compounds, for example zinc sulfide.

If radiation of suitable wavelength, for example X-ray radiation, impinges upon the panel, luinescent light, which impinges with high intensity on the optical fiber, 4 -3is emitted in the panel. If the matching of the dyestuff in the fiber is such that the spectral emission range of the scintillator corresponds to the spectral absorption range of the optical fiber dyestuff, the light from the panel produces fluorescent radiation in the optical wave guide which is conveyed by total reflection and emerges at the end of the optical wave guide. At that point there is a photosensitive semiconductor component, for example a silicon diode, which detects the radiation. The diode may be of small area and therefore of the low-noise type.

In order to avoid any interfering irradiation of the optical wave guide with extraneous radiation, it can be surrounded with an absorbing layer, for example a black metal foil, on the side facing away from the panel.

Transparent layers for protection against mechanical or chemical stress or for checking the total reflection may i be deposited on the panel or on the optical wave guide.

In order to transmit the optical signal over a fairly large distance to the semiconductor component, lower- I attenuation optical wave guides composed of polymer or glass may be arranged at the end of the fluorescent optical wave guide.

4, The figures show examples of preferred embodiments of the i{ radiation detector according to the invention.

Figure 1 shows a detector in which a radiation-absorbing panal is joined to a bundle of optical wave guides arranged in parallel by the adhesive layer Figure 2 shows a detector in which two panels enclose the optical wave guides The joint is again achieved by the adhesive layer Advantages of the detector according to the invention are: i- Very large sensitive surface is possible which, in S- 4 addition, can be shaped in any desired manner by suitable masking. Irradiation- impermeable metal foils or adhesive films, for example, may be used for tasking.

Purely optical operation, i.e. no electrical leads are necessary at the site of the radiation detection. Use is therefore also possible in areas with an explosion hazard.

No, or only slight, alignment effort due to large detector surface.

Radiation detection possible from both sides of the panel.

The spectral sensitivity of the detector is selective in the absorption range of the scintillator in (5 the panel and may be matched to the measurement problem by choice of this scintillator.

t The luminescence quantum yield for electrons, protons, 7 -quanta or X-ray quanta can be optimized in different energy ranges by suitable choice of the fluoroscopic screen material or scintillator.

Example The core of a polymer optical wave guide having a polycarbonate core and poly(4-methyl-l-pentene) cladding was doped with a perylene dyestuff which absorbs in the 520i 580 nm wavelength range. The fiber diameter was 1 mm.

Nine optical wave guides each 15 cm long were arranged parallel to a strip and covered by two panels, each 1 cm x 2 cm in size, at one fiber end (Figure The panels Sare obtainable commercially as X-ray fluoroscopic screens and are composed of a (Zn, Cd)S:Ag pigment whose emission wavelength of 540 nm is in the absorption range of the optical wave guide dyestuff. Panels and fibers were M Ii

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5 bonded to one another and enclosed with a black thinwalled shrink-down tube for protection against cutside influences. At the fluoroscopic screen the fiber ends were reflection-coated in order to obtain maximum intensity at the photodiode.

Because of the relatively high attenuation of the fluorescent optical wave guide, it is advisable in the case of fairly long transmission paths to the photodiode to switch to untinted optical w;.\ve guides by means of a plug connection.

The table shows the result of a test measurement. The sensitive surface of the detector was exposed to an X-ray beam. Variation in the cathode current in the X-ray tube resulted in a linear dependence on voltage in the photo- S diode.

Table I C Cathode current Detector voltage [mA] [V] kV 40 kV (tube voltage) 0 0 i] 0.22 0.53 0.48 1.14 0.75 1.74 1.01 2.36 t 5 25 1.28 2.96 30 1.55 3.58 -r: 1 h

Claims (4)

1. A detector for detecting invisible radiation and charged particles, composed of a radiation-absorbing panel and at least one optical wave guide containing a fluorescent dyestuff joined thereto, wherein at least one optical wave guide is arranged parallel to the surface of at least one panel and said panel is doped with a luminescent compound which fluoresces in at least part of the absorption range of said fluorescent dyestuff in said optical wave guide.

2. The detector as claimed in claim 1, wherein a plurality of optical wave guides are arranged parallel to the surface of at least one panel.

3. The detector as claimed in claim 1, wherein at least one optical wave guide is arranged between two panels situated parallel to one another.

4. The detector as claimed in claim 1, wherein a plurality of optical wave guides are arranged between two panels situated parallel to one another. aa a .DATED this 2nd day of June, 1992. HOECHST AKTIENGESELLSCHAFT a a a a WATERMARK PATENT TRADEMARK ATTORNEYS a THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA DBM:KJS:JZ (Doc.16) AU4589389.WPC L b _LL I_