A radiation induced light wavelength shifter and an apparatus for detecting radiation and transmitting detected signal through an optical fiber are disclosed. A radiation induced light wavelength shifter used in such apparatus comprises a cylindrical scintillator, a fluorescent optical fiber an end of which is inserted into the scintillator, the fluorescent optical fiber extending out of the scintillator, a light shielding member covering the scintillator and the fluorescent optical fiber, and a light reflecting material covering the scintillator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a radiation-detecting light-transmission 
apparatus for use in nuclear power plants, radiological facilities, and 
the like which deal with radiation and radioactive substances. 
2. Description of the Related Art 
Scintillation detectors, semiconductor detectors, and the like have been 
used for detection of radiation and measurement of radiation in nuclear 
power plants, radiological facilities, non-destructive inspection 
technology, particle accelerating facilities, cyclotron radiation 
facilities, and so forth in which radioactive substances have to be 
handled. It should be noted that the term "radiation" used herein means 
alpha rays, beta rays, gamma rays, neutron rays, and X rays, individually 
or collectively. 
In such scintillation detectors, a detecting section is composed of a 
scintillator and a photomultiplier tube assembled together, while in the 
semiconductor detectors, the detecting section is composed of a 
semiconductor sensor, high voltage power circuits, and signal circuits 
combined with one another. Detection signals are sent to a counting 
section through the signal circuit. The detection signals are analyzed by 
a single channel analyzer with count rates. Alternatively, they undergo 
spectral analysis treatment by a multi-channel wave height analyzer. 
When a detecting and counting section are desired to be separated from each 
other in the conventional detectors before mentioned, a power cable and an 
electric signal cable are used therebetween. In place of the electric 
signal cable, it has been recently proposed that electric signals are 
converted into light signals at the detecting section and thereafter the 
light signals are transmitted through an optical fiber cable. In either of 
such systems, the detecting section has a power supply, and hence some 
countermeasures against noise problems are needed. In an improvement for 
alleviating noise problems, it has been attempted that a scintillator and 
a photomultiplier tube, which are usually placed adjacent to each other, 
are spaced apart from each other and connected by a bundle of optical 
fibers or an optical pipe, and that a power supply is removed from the 
detecting section, and the light from the scintillator is transmitted 
directly to the photomultiplier tube without conversion. However, such an 
attempt has not been successfully employed in commercial applications. 
Also, in Japanese Patent Application No. 1-336296 filed by the same 
applicants on Dec. 27, 1989 (Japanese Laid-Open Patent Publication No. 
3-242590), a microlens is employed to connect an end of one or more 
fluorescent optical fibers of a radiation induced light wavelength shifter 
with one optical fiber. In such structure, the wavelengths of the light 
emitted by the scintillator are shifted by the fluorescent optical fiber, 
and the output light of the fluorescent optical fiber is optically 
transmitted for a long distance to the counting section which is spaced 
apart therefrom. 
As described above, conventional devices or apparatuses such as the 
detecting section of the scintillation detector and the semiconductor 
detector need power supplies in their detecting section and signals are 
converted electronically therein. Thus, under adverse environmental 
conditions, such as high temperature atmosphere or strong magnetic fields, 
it happen that the photomultiplier tube and the semiconductor do not work 
properly and measuring operation is adversely affected. 
To overcome such a problem, a design in which the detecting section and the 
counting section are sufficiently spaced apart from each other with a long 
cable may be implemented. Such design, however, includes a long signal 
line exposed to a surrounding electromagnetic field and/or induction 
noise, thereby requiring another countermeasure. 
Incidentally, when the conventional apparatuses are used in water, they 
require a waterproof structure and careful handling since the detecting 
sections have high voltage power supplies. Accordingly, a detector which 
does not require such a waterproof structure, a long electric cable, or a 
power supply in the detecting portion has been needed for long time. 
In the invention in the above-mentioned patent application which invention 
was proposed so as to solve such problems, a radiation induced light 
wavelength shifter 10, as shown in FIG. 14, comprises a cylindrical or 
columnar scintillator 11, reflecting sheets 12a and 12b, and a transparent 
layer 13. When radiation enters the scintillator 11, it emits light. The 
optical reflecting sheets 12a and 12b are disposed on the upper and lower 
surface of the scintillator 11, respectively. The transparent layer 13 is 
disposed on the outer periphery of the scintillator 11. 
Fluorescent optical fibers 14a-14c are wound around and on the outer 
periphery of the transparent layer 13 disposed on the scintillator 11. The 
fluorescent optical fibers 14a-14c are housed together with the 
scintillator, in a reflecting casing 17. The fluorescent optical fibers 
14a-14c are, at one end, optically connected to optical transmission 
fibers 15a-15c through microlenses 16a-16c, respectively. 
The object of winding the fluorescent optical fibers 14a-14c around the 
outer periphery of the scintillator 11 is to increase the incidence area 
for light, namely, the amount of incident light into the optical fibers, 
because the amount of light entering the fluorescent optical fibers 
14a-14c is proportional to the incidence area through which the light 
passes. 
Another problem has been found. Winding of the fluorescent optical fibers 
14a-14c around the cylindrical scintillator 11 tends to adversely affect 
the refractive index of the fluorescent optical fibers 14a-14c. In 
addition, a relatively larger amount of light leaks out of the bent 
fluorescent optical fibers 14a-14c themselves and at the connection 
portions to the microlenses 16a-16c. Besides, the focus of the microlenses 
16a-16c is inclined to deviate from the respective optical axes of the 
optical transmission fibers 15a-15c. Consequently, transmission loss is 
relatively large. Moreover, since light emitted by the scintillator 11 
only enters the inner half side of the fluorescent optical fibers 14a-14c 
which are wound around the scintillator 11, the fluorescent optical fibers 
14a-14c cannot efficiently shift the wavelengths of all the light, emitted 
by the scintillator 11, thereby providing an insufficient amount of light 
shifted in wavelength. 
Moreover, winding the fluorescent optical fibers 14a-14c around the 
scintillator 11 with large contact length needs increases the size of the 
scintillator 11. Furthermore, when the microlenses 16a-16c are used, it is 
rather impossible to individually place the focus of the microlenses 
16a-16c in complete alignment with the optical axes of the optical 
transmission fibers 15a-15c. In this case, it is also very difficult to 
connect or disconnect the optical transmission fibers 15a-15c as 
transmission paths to or from the radiation induced light wavelength 
shifter 10. 
SUMMARY OF THE INVENTION 
The object of the present invention which has been made in view of the 
above-mentioned state of art is to provide a compact and light-weight 
radiation-detecting apparatus which is capable of shifting wavelengths and 
performing optical transmission free of influence from electromagnetic 
fields, induction noise, and the like with efficiency and without a 
dedicated power supply. 
The present invention provides a radiation induced light wavelength shifter 
comprising: a columnar scintillator; a fluorescent optical fiber which is 
axially inserted into the scintillator, said fluorescent optical fiber 
extending out of the scintillator; and a light shielding member covering 
said scintillator and said fluorescent optical fiber. 
Since the fluorescent optical fiber is disposed along the axial center of 
the cylindrical scintillator, the light emitted by the scintillator can be 
received from all peripheral directions of the fluorescent optical fiber. 
The present invention also provides a radiation-detecting 
light-transmission apparatus comprising: a columnar scintillator; a 
fluorescent optical fiber which is axially inserted into the scintillator, 
said fluorescent optical fiber extending out of the scintillator; a light 
shielding member covering said scintillator and said fluorescent optical 
fiber; a light reflecting material surrounding said scintillator arranged 
in said light reflecting member; and an optical transmission fiber which 
is connected to the other end of said fluorescent optical fiber through an 
optical connector, said optical transmission fiber transmitting light 
generated in said fluorescent optical fiber. 
The light reflected by the light-reflecting material surrounding the 
cylindrical scintillator is collected toward the axial center, the 
fluorescent optical fiber can efficiently receive the light emitted by the 
scintillator. Thus, the shifting of wavelengths of the light and the 
transmission of optical signals can be realized with efficiency. The 
sensitivity of the counting section at a later stage can be improved. 
The present invention further provides a radiation-detecting 
light-transmission apparatus comprising: a plurality of the radiation 
induced light wavelength shifters, each radiation induced light wavelength 
shifter comprising a columnar scintillator, a transparent optical member 
surrounding said cylindrical scintillator, a fluorescent optical fiber 
which is inserted substantially coaxially into said scintillator and emits 
light upon receiving light from the scintillator, an optical connector 
connected to the other end of the fluorescent optical fiber, a light 
reflecting material covering an outer circumferential and end surfaces of 
said transparent optical member, and a light shielding casing covering 
said scintillator and said fluorescent optical fiber; a collimator having 
a plurality of substantially parallel through holes for holding said 
radiation induced light wavelength shifters; a light shielding casing 
covering said plurality of said radiation induced light wavelength 
shifters received in said through holes; and a plurality of light 
transmission fibers each connected separately to an end of said 
fluorescent optical fiber through an optical connector so that light 
generated in each fluorescent optical fiber is transmitted through each 
optical transmission fiber. 
With this construction, a two dimensional pattern of radiation doses can be 
detected quickly. Also, since a bundle of fluorescent optical fibers whose 
light receiving window is larger than the light emitting window of the 
cylindrical scintillator can be connected, almost all light emitted by the 
scintillator undergoes the wavelength shifting process with efficiency. In 
addition, because a bundle of optical transmission fibers with a light 
receiving surface which is larger than the end surface of the fluorescent 
optical fibers can be connected, almost all the light whose wavelengths 
have been shifted by the fluorescent optical fibers can be efficiently 
transmitted. Thus, without losing information on radiation energy, the 
radiation detection signals can be transmitted. 
Furthermore, radiation detection signals from each radiation induced light 
wavelength shifter can be transmitted as separate signals. In addition, 
information such as two-dimensional radiation dose distribution can be 
transmitted to a remote place without a power supply.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the accompanying drawings, an embodiment of the present 
invention will be described. 
FIG. 1 is a cross-sectional view showing the structure of a radiation 
induced light wavelength shifter 20. The radiation induced light 
wavelength shifter 20 comprises an end plug portion 21, a cylindrical 
scintillator 22, a fluorescent optical fiber 23, a scintillator housing 
24, a joint 25, an optical connector housing 26, a rear panel 27, and an 
optical connector 28. The cylindrical scintillator 22 is contained in a 
casing whose outer periphery is coated with a reflecting material made 
from fluororesin or the like. The fluorescent optical fiber 23 is, at one 
end, coaxially disposed in the scintillator 22. The scintillator housing 
24 covers the outer periphery of the scintillator 22 and is provided with 
the end plug portion 21 at an end thereof. 
In the figure, the scintillator 22 is constructed of a pair of 
semi-cylinders made of thallium (Tl) doped sodium iodide (NaI) or the 
like. Each of the semi-cylinders has, at and along an axial center of a 
circle defined thereby, a semi-cylindrical groove with a radius of 
approximately 0.5 mm and is covered with a transparent member 29 which is 
quartz glass etc. The pair of semi-cylinders form, in combination, a full 
cylindrical structure which defines a hole with a diameter of 
approximately 1 mm along a central axis. The fluorescent optical fiber 23 
is inserted and disposed in and through the axial hole. 
The kinds of the scintillator 22 usable in this invention include an 
inorganic scintillator, an organic scintillator, and a liquid 
scintillator, etc. With respect of the property of scintillator 22, the 
only requirement is that the spectrum of wavelengths of light which can 
excite the scintillator 22 should coincide with the spectrum of 
wavelengths of light excited by the fluorescent optical fiber 23. Thus, 
various combinations may be available depending on the type of radiation 
to be detected and the characteristics of light emitted or produced by the 
scintillator to be used. 
In addition, since the light wavelength shifter 20 is connected to an 
optical transmission fiber 30 as a transmission path via the optical 
connector 28, an optical combination of the scintillator 22 and the 
fluorescent optical fiber 23 is made to provide a wavelength band with 
less transmission loss in the optical transmission fiber 30. 
The optical connector 28 before-mentioned comprises a guide tube 31 and an 
outer sleeve 32. The guide tube 31 is integrally constructed of a flange 
31a, a cylinder 31d, and another cylinder 31b. The flange 31a is 
positioned at the exterior of the guide tube 31. The cylinder 31d is 
positioned on the side of the flange 31a near the scintillator 22 and has 
a hole of a diameter of approximately 2 mm. The cylinder 31b is positioned 
between the optical transmission fiber 30 and the flange 31a, and has a 
hole which gradually narrows toward the optical transmission fiber 30 from 
approximately 2 mm to 1 mm. In addition, the cylinder 31b has threaded 
outer surface and a fiber sleeve 31c of relatively smaller diameter. 
The outer sleeve 32 is of cylindrical shape so as to be screwed onto the 
cylinder 31b of the guide tube 31 and has thread formed in the outer 
periphery thereof. By engaging a put 34 on the thread with a washer 33, 
the guide tube 31 and the outer sleeve 32 can be fixed to the rear panel 
27. 
As described herein before, the fluorescent optical fiber 23 is disposed in 
the scintillator 22 with one end coated with the reflecting material. The 
other end of the fluorescent optical fiber 23 is inserted into the guide 
tube 31 through the hole of the cylinder 31d. In addition, the fluorescent 
optical fiber 23 in the guide tube 31 is fixed by a cushion member 35 
which is made of rubber or the like is inserted into a clearance at the 
mouth of the hole in the cylinder 31d. 
The mouth or opening of the optical insulating tube 37 described later, the 
cushioning member 35 and the cylinder 31d of the guide tube 31 are 
optically insulated by optical insulating substance 36 which are made of 
silicone rubber or the like. 
The other end surface of the fluorescent optical fiber 23 is located at an 
appropriate point protruding slightly more than the end of the fiber 
sleeve 31c of the guide tube 31 comprising the optical connector 28, and 
abraded after heat treatment so as to decrease the emission angle of the 
light. The guide tube 31 and the outer sleeve 32 are designed to be 
connected by a screw engagement as a combined structure in which the 
center of the optical axis at the other end surface of the fluorescent 
optical fiber 23 is nearly aligned with the center of the outer sleeve 32. 
In addition, the scintillator 22 contained in the transparent layer 29 
which is made of quartz is designed to form a cylindrical structure 
defining, at its axial center, a hole with a diameter of approximately 1 
mm when the pairs of the semi-cylinders are put together as described 
above. The fluorescent optical fiber 23 is inserted, at one end, in the 
axially central hole of the scintillator 22 and is covered by the optical 
insulating tube 37 over the outer periphery between the guide tube 31 of 
the optical connector 28 and the mouth of the hole of the scintillator 22. 
A light-reflecting material made, for example, of magnesia (MgO) is coated 
on and over the outer peripheral surface of the scintillator 22 encased in 
the transparent case 29. Alternatively, a rubber strip which reflects and 
insulates light may be wound around the scintillator 22. The 
light-reflecting material mentioned above is also attached to opposite 
ends of the transparent case 29 so as to reflect the light emitted by the 
scintillator 22 and prevent the light from leaking out. 
In the conventional apparatus shown in FIG. 14, an optical paste which is 
made of silicone grease or the like is applied to optical connecting 
portions so as to prevent light from scattering and improve linear 
transparency. In the present invention, it is rather preferable that light 
emitted by the scintillator 22 enters the fluorescent optical fiber 23 
through the whole clad surface, as much as possible, at right or inclined 
incident angle. Accordingly, unlike the conventional apparatus, an optical 
paste is not applied to the gap between the scintillator 22 and the 
fluorescent optical fiber 23, so as to help the reflected or scattered 
light from the scintillator 22 to enter the fluorescent optical fiber 23 
at various angles. 
Referring-to the drawing, the casing of the radiation induced light 
wavelength shifter 20 comprises the end plug 21, the scintillator housing 
24, the joint 25, the optical connector housing 26, the rear panel 27, the 
washer 33, and the nut 34, each of which may be made of aluminum or the 
like. 
The end plug 21 is a cap which optically insulates and hermetically closes 
one end of the scintillator housing 24. The end plug 21 has a thread on 
its inner surface and may be connected to the scintillator housing 24 in a 
thread engagement. 
As illustrated in the drawing, the scintillator housing 24 is in a 
cylindrical shape, and has the end plug 21 at an end and, at the other 
end, thread to be screwed into the joint 25. The joint 25 is to used for 
connecting the scintillator housing 24 and the optical connector housing 
26 and is made of aluminum. Further, the joint 25 is a cylindrical 
structure which has, on an inner and outer surface, threads to be used to 
connect the scintillator housing 24 and the optical connector housing 26, 
respectively. 
The optical connector housing 26 houses the fluorescent optical fiber 23 
between the scintillator 22 and the optical connector 28. The optical 
connector housing 26 is associated with the rear panel 27 so as to form a 
cylindrical body with a closed bottom. The optical connector housing 26 
also has, at an end apart from the rear panel 27, a thread which, in turn, 
is engaged with the joint 25. 
The portion where the transparent case 29 meets the optical insulating tube 
37 on the fluorescent optical fiber 23 through the light-reflecting 
material is fixed with epoxy resin or the like. As shown in the figure, 
the optical insulating material 36 is deposited over this portion. When 
the fluorescent optical fiber 23 is arranged as shown in the figure, a 
part of the thread on the outer surface of the outer sleeve 32 projects 
from the hole of the rear panel 27 of the optical connector housing 26. 
The optical connector 28 shown in the drawing comprises the guide tube 31 
and the outer tube 32. The optical transmission fiber 30, which functions 
as an optical transmission path, is connected to the optical connector 28 
described above through a receiving optical connector section 43 which, in 
turn, comprises a receiving optical connector 41 and a fiber sleeve 42. 
Some of commercially available optical connectors may be used as the 
optical connector 28 and the receiving connector portion 43. Such optical 
connectors are widely used for connecting optical transmission fibers and 
can be easily attached and detached. With these optical connectors, 
optical fibers with an equal diameter can be very easily connected. 
The material for the optical transmission fiber 30 is generally composed of 
an optical fiber 30a and an outer sheath 30b. The optical transmission 
fiber 30 is made up from the material so as to connect the receiving 
optical connector 41 and the fiber sleeve 42 by peeling an end of the 
outer sheath 30b and baring the optical fiber 30 therein. Thereafter the 
bared end of the optical fiber 30a is inserted into the fiber sleeve 42 
until the outer sheath 30b is inserted into and stopped by the fiber 
sleeve 42. Thus, the end surface of the optical transmission fiber 30a is 
located out of the fiber sleeve 42. Under such condition, the end of the 
optical fiber 30a is cut in the vicinity of the connecting end of the 
optical transmission fiber 30, and then a cut surface is heat treated and 
abraded so as to make smaller the angle of light emission from the optical 
transmission fiber. Finally the fiber sleeve 42 in which the outer sheath 
30b is inserted lightly compressedly deformed around its center so that 
the optical fiber 30a is fixed. 
Though not shown in the drawing, the other end of the optical transmission 
fiber 30 bears the same treatment so that it is connected to an adapter 
(not shown), 
The connection of the optical connector 28 and the receiving connector 
portion 43 is made by fixing the receiving optical connector 41 to the 
outer sleeve 32 of the optical connector 28 by thread means in a thread 
engagement. At this point, the end surface of the fluorescent optical 
fiber 23 which slightly protrudes from the fiber sleeve 31c of the guide 
tube 31 should be faced, as close as possible, to the end surface of the 
optical fiber 30a in the fiber sleeve 42 in the receiving connector 43 in 
such a way that the optical axis of the fluorescent optical fiber 23 may 
align with that of the optical transmission fiber 30 without contact 
therebetween. 
Thus, the power of emitted light by the fluorescent optical fiber 23 
efficiently enters into the optical transmission fiber 30. It is desirable 
that the diameter of the fluorescent optical fiber 23 is the same as that 
of the optical transmission fiber 30. When, however, the numerical 
aperture and the angle of light emission of the fluorescent optical fiber 
23 and the optical transmission fiber 30 are different from each other, it 
is necessary that the diameter of the optical transmission fiber 30 should 
be designed to be larger than that of the fluorescent optical fiber 23. 
As described above, the radiation induced light wavelength shifter 20 has 
an aluminum casing, as the outermost member, housing almost all the 
members thereof and is optically insulated by sealing. In addition, as the 
optical insulating tube 37, the optical insulating material 36, and so 
forth insulates external light, noise generated in the scintillator 22 and 
the fluorescent optical fiber 23 can be great by reduced. 
Furthermore, in the radiation induced light wavelength shifter 20, the 
scintillators 22 are formed in a cylindrical structure so that light 
generated around the axial center of the scintillator 22 is reflected at 
the reflecting member disposed on the periphery, repeatedly scattered and 
concentrated into the axial center region in the scintillator 22. 
Accordingly, the radiation induced light wavelength shifter 23 can collect 
light generated at the fluorescent optical fiber 23 with less losses. 
In the structure before mentioned, when radiation enters and excites the 
scintillator 22 to emit light, the light emitted enters through the clad 
surface of the fluorescent optical fiber 23 toward the core thereof. The 
wavelength of the incident light is efficiently shifted to a longer 
wavelength band according to light excitement and wavelength shifting 
function of the fluorescent optical fiber 23. Then the light is collected 
by the fluorescent optical fiber 23 and transmitted to the output terminal 
to which the optical connector 28 is optically connected. 
Moreover, the output light of the fluorescent optical fiber 23 enters the 
optical transmission fiber 30 by the optical connector 28 with less loss. 
Thus, optical signals can be sent to an optical power meter or a 
photomultiplier tube (not shown) disposed at the other end of the optical 
transmission fiber 30 without using a power supply. 
Next, with reference to FIG. 2, the details of connecting structure between 
the optical transmission fiber 30 and the optical power meter in a 
counting section or a sensor section of the photomultiplier tube connected 
to the other end of the optical transmission fiber 30 will be described. 
The sensor in the counting section may be a commercially available 
photomultiplier tube which counts the number of electric pulses which is 
proportional to the quantity of the light received. Alternatively, the 
sensor may be an optical power meter measuring the quantity of the light 
by means of photosemiconductor. 
In such cases, some improvements shown in FIG. 2 are needed to connect the 
output end of the optical transmission fiber 30 and an optical sensor (for 
example, in the photomultiplier tube or optical power meter). Describing 
structurally, the output end of the optical transmission fiber 30 is 
composed of a fiber sleeve 52 and a receiving optical connector 53. The 
structure of the output end of the optical transmission fiber 30 is the 
same as that of the input end thereof connected to the optical connector 
28 of the radiation induced light wavelength shifter 20. 
An adapter 55 connected to the fiber sleeve 52 and the receiving connector 
53 is of cylindrical shape with an end plate which, in turn, is provided 
with a cylindrical connection tube 54 integrally formed in axial alignment 
relationship. The connection tube 54 has a thread formed on the outer 
surface so as to be connected to the receiving optical connector 53. 
When the receiving optical connector 53 is screwed and fastened to the 
connection tube 54, the fiber sleeve 52 protrudes from the inner end of 
the connection tube 54 toward the open end of the adapter 55. Thus, the 
end surface of the fiber sleeve 52 is positioned as close as possible to 
the input window of the sensor section 56 and faces the input window 
without contact. 
Next, a measuring operation with the apparatus described before will be 
described. 
FIG. 3 is a schematic diagram for explaining how radiation is detected. 
When the scintillator 22 is exposed to radiation, it emits fluorescent 
light. The fluorescent light enters the periphery of the fluorescent 
optical fiber 23, namely, the clad 23b at a right or other angle and 
thereafter excites the fluorescent substance in the core 23a. The emitted 
light is collected and transmitted to the fiber end where the light is 
output. 
Thus, the light is output from the fluorescent optical fiber 23 with 
wavelengths which are more suitable for transmission after being shifted 
from those of the input light. As a result, the output density has been 
relatively increased. 
FIG. 4 shows an example of emission spectrum of the scintillator as a 
function of wavelength. When gamma rays enter the scintillator 22 made of 
thallium (Tl) doped sodium iodide (NaI) which has the spectrum shown in 
the figure, the scintillator 22 emits light with a peak in photointensity 
at a wavelength of 410 nm. In FIG. 4, the thallium doped sodium iodide is 
designated as NaI(Tl). 
FIG. 5 shows an example of emission spectrum of the fluorescent optical 
fiber 23 as a function of wavelength. As seen from the figure, the 
fluorescent optical fiber 23 emits light with a peak in photointensity at 
a wavelength of about 500 nm. 
FIG. 6 is a table in which the relation between a wavelength band of 
exciting light and that of emitted light for the fluorescent optical fiber 
23 are shown. Since the scintillator 22 shown in FIG. 4 emits light in 
wavelength band from 300 nm to 550 nm with a peak at a wavelength of 410 
nm, it is found that a fluorescent optical fiber designated as product 
number F201 with exciting light in a wavelength band from 400 nm to 460 nm 
is suitable as that to be used with the scintillator 22. The fluorescent 
optical fiber F201 emits light in wavelengths ranging from 495 nm to 550 
nm with a peak at a wavelength of approximately 520 nm. The light emitted 
from the fluorescent optical fiber 23 is in green color and has been 
shifted to a longer wavelength band by the fluorescent optical fiber 23. 
It should be noted that there are different types of scintillator which 
emit light in different wavelengths and a fluorescent optical fiber may be 
selected so as to match with the emitted light wavelengths of the 
scintillator used. 
FIG. 7(a) is a graph giving the relation between transmissible wavelengths 
and their transmission losses in plastic optical transmission fibers. In 
the vicinity of wavelength of 410 nm, the transmission loss of the 
fluorescent optical fiber 23 is as high as approximately 400 dB/km. On the 
other hand, in the vicinity of wavelength of 520 nm, the transmission loss 
of the fluorescent optical fiber 23 is approximately 150 dB/km. Thus, it 
is clear that signals can be transmitted in a wavelength band with a low 
transmission loss according to the present invention. 
Thus, it has been found that the wavelengths of light emitted by the 
fluorescent optical fiber 23 are more suitable for transmitting signals 
than those of light emitted by the scintillator 22 which represent 
radiation intensity detecting signals. 
FIG. 7(b) is a graph showing the relation between wavelengths of light 
transmitted and its optical transmission loss in an optical fiber 
substantially made of quartz. In the vicinity of wavelength of 520 nm of 
the light emitted by the fluorescent optical fiber 23, the transmission 
loss is as low as approximately 10 dB/km. The graph shows that the quartz 
optical fiber can transmit the light emitted by the fluorescent optical 
fiber 23 in a wavelength band with lesser transmission loss. Accordingly, 
it is to be appreciated that the quartz optical fiber is suitable for 
signal transmission over long distances compared to the plastic optical 
transmission fibers. 
With the use of the optical transmission fiber 30 as a signal transmission 
path, transmitted signals are not affected by electric noise unlike in 
electrical signal cables. In addition, since the radiation induced light 
wavelength shifter 20 outputs light itself, a power supply for 
amplification and signal transmission can be advantageously omitted. 
The radiation induced light wavelength shifter 20 provided with the optical 
connector can be very easily manufactured. In addition, it is advantageous 
that the radiation induced light wavelength shifter 20 can be easily 
attached to and detached from the optical transmission fiber 30 and can do 
signal transmission without amplifying electric noise. 
Accordingly, by temporarily detaching the optical transmission fiber 30 
from the radiation induced light wavelength shifter 20, passing the fiber 
30 through a narrow place or a narrow hole in a wall, and attaching again 
the fiber 30 to the radiation induced light wavelength shifter 20, the 
counting section which tends to be affected by environmental noise (such 
as electric noise) can be spaced far apart from objects to be detected. 
With such an arrangement, radiation measurements which have been difficult 
with conventional apparatuses under electromagnetic environment or in 
water can be carried out with ease. 
As described above, since the transmission loss in the fluorescent optical 
fiber 23 is large and hence not suitable for optical transmission, the 
optical transmission fiber 30 is alternatively used by being connected to 
the fluorescent optical fiber 23 through the above-mentioned optical 
connector. For signal transmission for short distances, an inexpensive 
plastic optical transmission fiber may be selected, while for signal 
transmission for a long distance, a quartz optical transmission fiber may 
be preferred in spite of expansiveness. 
FIG. 8 is a block diagram showing the general scheme of a photoelectric 
conversion processing section 61 as a measuring and testing unit connected 
to the optical transmission fiber 30. The photoelectric conversion 
processing section 61 comprises a photoelectric converting section 62, a 
processing section 63, and an indicating section 64. In the section 61, 
the photoelectric converting section 62 converts optical signals received 
from the optical transmission fiber 30 into electric signals, and the 
processing section 63 determines the value of the electric power in the 
electric signal obtained in the photoelectric converting section 62 by 
signal processing and converts the value of the electric power into that 
in digital form. The indicating section 64 outputs and indicates the value 
of the electric intensity gained in the processing section 63. 
FIG. 9 is a graph showing test results obtained with the detecting and 
testing unit shown in FIGS. 1 and 8. The length and outer diameter of the 
cylindrical scintillator 22 of the radiation induced light wavelength 
shifter 20 used was 20 cm and 0.8 cm, respectively, The diameter of the 
fluorescent optical fiber 23 was 1 mm. The length of the optical 
transmission fiber 30 was 10 m. In this test, cobalt 60 (.sup.60 Co) which 
radiates gamma rays was used, The horizontal axis of the graph gives dose 
equivalent rates, whereas the vertical axis thereof gives counting rates 
(counts/minute). As illustrated in the graph, increases in the 
dose-equivalent rate are proportional to increases in the counts by the 
detecting unit. Accordingly, the illustration shows that the radiation 
induced light wavelength shifter 20 according to this invention can be 
used as a radiation counter. 
Next, with reference to FIGS. 10 and 11, radiation measurements and their 
results carried out by using the apparatus according to the present 
invention in the vicinity of a top portion of a nuclear fuel assembly laid 
in a water pool of a nuclear power plant will be described hereinafter. 
In this test, the length of the cylindrical scintillator 22 used was 2 cm, 
the outer diameter thereof being 0.8 cm, the diameter of the fluorescent 
optical fiber 23 used being 1 mm. Waste nuclear fuel emitted strong 
radiation in the water pool 70. 
In this test, the radiation induced light wavelength shifter (hereinafter 
referred to as "detector") 20 was fixed in an upper portion of a through 
hole defined at a center of a cylindrical lead collimator 75 received in a 
cylindrical vessel 71. The optical transmission fiber 30 was extended to 
the outside of the cylindrical vessel 71 and connected to a counter 
section (not shown). In the counter section the number of electric pulses 
received is counted by a photoelectron multiplying tube. 
The lead collimator 75 is a conventional member generally used to improve 
the directivity of the detector 20 and to distinguish a radiation source 
to be measured from the others. In this test, to distinguish the nuclear 
fuel element assembly to be measured in the water pool 70 from the others, 
the lead collimator 75 was placed to improve the downward directivity of 
the detector 20. 
The cylindrical vessel 71 which contains the detector 20 was hung and 
lowered from the water level of the water pool 70 to a position near the 
top of the fuel assembly in the water by a rope. 
FIG. 10(a) shows a situation in which the cylindrical vessel 71 containing 
the detector 20 is hung in the water pool 70. For the measurements, the 
cylindrical vessel 71 was positioned at the location in positions 50 cm 
and 30 cm apart from the top of the nuclear fuel assembly placed in the 
water pool 70. At these positions, radiation was measured. 
FIG. 10(b) is a cross-sectional view showing the cylindrical vessel 71 
which contains the detector 20 and the lead collimator 75, the detector 20 
being received in a center hole of the lead collimator 75. 
FIG. 10(c) is showing an arrangement of the nuclear fuel assemblies each 
placed in the water pool 70. In an actual water pool, the nuclear fuel 
assemblies are normally held in individual storage racks, one by one. FIG. 
10(c) shows individual racks each designated by symbol A to F. In this 
case, the nuclear fuel assemblies are separately contained in the racks B, 
C, D, and F, while an activated substance other than nuclear fuel 
assemblies is contained in the rack G. In the drawing, the racks A, E are 
empty. 
FIG. 11 shows graphs giving test results by the detector 20 contained in 
the cylindrical vessel 71 which travelled in a horizontal direction at 
predetermined time intervals. In these graphs, the horizontal axis 
indicates horizontal distances, whereas the vertical axis shows normalized 
values of the count rate (normalized counts per unit time), 
FIG. 11(a) shows measurement results obtained at positions 50 cm vertically 
apart from the top of the nuclear fuel assembly, namely, at 6.5 m from a 
water level. A lead plug was used. On the other hand, FIG. 11(b) shows 
measurement results obtained at positions 30 cm vertically apart from the 
top portion of the nuclear fuel element assembly, namely, at 6.7 m from a 
water level. A lead plug was also used. 
These measurement results represent peak values just above the nuclear fuel 
assembly. The more the detector 20 approaches to the nuclear fuel 
assembly, the more the peak value in the count rate increases. Thus, it 
was shown that the detector 20 can accurately measure radiation from the 
nuclear fuel assembly. It should be noted that the vertical scale in FIG. 
11(a) is different than that in FIG. 11(b). This is because the 
measurement positions in FIG. 11(b) are closer to the nuclear fuel 
assembly than those in FIG. 11(a). 
From the experimental results before described, it should be appreciated 
that the radiation induced light wavelength shifter 20 according to the 
present invention successfully works as a practical radiation measuring 
system. In addition, while the radiation induced light wavelength shifter 
20 is very light and compact, it can measure radiation without any 
influence from environmental conditions (for example, the existence of 
water or electromagnetic field). 
Although the above-described radiation induced light wavelength shifter 20 
has only one scintillator 22 as a detector, the size of the scintillator 
22 may be made smaller and then a plurality of such scintillators can be 
used in an arrayed arrangement. 
In this case, the scintillator 22 may be a plastic scintillator tube with 
an inner diameter of 1 mm and an outer diameter of 2 mm instead of the 
thallium doped sodium iodide (NaI:Tl) as described above. A 
light-reflecting material is disposed on the outer periphery of the 
plastic scintillator tube. 
Thus, as schematically shown in FIGS. 12 and 13, provided is a 
radiation-detecting light-transmission apparatus comprising: a rectangular 
collimator 76 having 20.times.20 through holes 77 arranged in a matrix 
pattern; 20.times.20 radiation induced light wavelength shifters 20 
disposed in the 20.times.20 through holes, each wavelength shifter 
comprising a columnar scintillator having a light-reflecting material 
disposed on an outer peripheral surface thereof, the scintillator being 
adapted to emit light by incident radiation, a fluorescent optical fiber 
whose one end axially extends to the scintillator, the fluorescent optical 
fiber being adapted to emit light by the light received from the 
scintillator, and an optical connector connected to the other end of the 
fluorescent optical fiber; an optical shielding casing for entirely 
covering the 20.times.20 radiation induced light wavelength shifters; and 
20.times.20 optical transmission fibers 30 connected to said other end of 
each of the fluorescent optical fibers through the 20.times.20 optical 
connectors, the 20.times.20 optical transmission fibers being adapted to 
transmit received light to an outside of said apparatus. 
The radiation detection signals of the radiation induced light wavelength 
shifters can be transmitted as discrete signals. In addition, information 
such as two-dimensional distribution of radiation dose can be transmitted 
to a remote place without necessity of a power supply.