JPS62177473A - Radiation sensor - Google Patents

Abstract

PURPOSE:To eliminate a time difference among images as to energy subtraction and to improve an SN ratio by extracting signals by the kinds of energy from radiation which contains various energy and is made incident once. CONSTITUTION:A mixed phosphor 1 is formed in a pentagonal shape by mixing CaWO4 and ZnS:Cu:Al which have different energy absorption characteristics to obtain one pixel, which is arrayed with light shield plates 2 interposed. At the time of this phosphor 1 is excited with an X ray, an image by fluorescence differing in spectrum is led out of photomultiplier tubes 5 and 6. Namely, plural kinds of images having different X-ray spectra are led out at the same time by performing X-ray exposure once. Therefore, the X-ray exposure needs to be performed only once for energy subtraction, so an image having no time difference is obtained and the SN ratio is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a radiation sensor for detecting radiation such as X-rays and γ-rays.

2. Description of the Related Art Conventional radiation sensors that are sensitive to radiation in a wide energy range are mainly used. Therefore, when performing so-called energy subtraction, for example, the subject is exposed to X-ray tubes several times while varying the tube voltage, obtaining several image signals, and these are appropriately calculated to determine the bone structure. Only areas with relatively similar X-ray absorption coefficients, such as soft tissues and other tissues, are extracted.

Problems to be Solved by the Invention However, when several images are obtained by irradiating X-rays with different tube voltages several times during energy subtraction, a time lag occurs between each image. Furthermore, when imaging with a high tube voltage, information from low-energy X-rays contained in the spectrum is removed by subsequent calculation processing, and is also rejected by filtering the X-rays when they enter the sensor. As a result, the utilization efficiency of X-rays is poor and the S/N ratio is deteriorated.

The present invention provides a radiation sensor that can extract signals for each energy from a single incidence of radiation containing various energies, thereby eliminating the time lag of each image in the energy subtraction, and improving the utilization efficiency of xVj. The goal is to increase the signal-to-noise ratio and improve the S/N ratio.

Means for Solving the Problems The radiation sensor according to the present invention uses a mixed phosphor that is a mixture of several types of phosphors that have different energy absorption edges and different emission colors, and a radiation sensor that emits light when the mixed phosphor is excited by radiation. The device includes means for color-separating the emitted light and means for converting the separated light of each color into electrical signals.

The energy absorption properties of a working phosphor depend strongly on the absorption edge of the contained elements, especially those of high atomic number. For example, when comparing CaWO4 and ZnS:Cu:Al as phosphors, CaWO4 has a sharp peak at 69°52KeV, which is the absorption edge of W, as shown in Figure 1A, and it has a sharp peak at 69°52KeV on the higher energy side. absorption is high. On the other hand, ZnS:Cu
: In case of Al, 69.52KeV as shown in Figure 1B
The absorption edge of Zn is 9,66KeV, which corresponds to
, and decreases uniformly for higher energies.

Therefore, CaWO with different energy absorption characteristics
When a mixed phosphor is made by mixing ZnS:Cu:Al and ZnS:Cu:Al, and when this mixed phosphor is excited by X-rays, a signal containing more information about high energy is obtained from the former than the latter, and conversely, a signal containing more information about high energy is obtained from the latter. From the former, it is possible to obtain a signal containing more information regarding low energy than from the former.

Since each of these phosphors emit light of a different color, the signals can be separated using a color filter or the like. In the above example as well, the emission of CaWO4 has a peak at a wavelength of 420 nm, and the emission of ZnS:Cu:Al has a peak at a wavelength of 530 nm, so they can be separated using a color filter.

Since the difference in energy is converted into a difference in the emission spectrum of the phosphor in this way, a high-energy signal and a low-energy signal can be simultaneously extracted with one radiation irradiation.

Embodiment The radiation sensor shown in FIG. 2 is an embodiment configured as an X-ray line sensor, and includes, for example, CaWO4 and ZnS:
A mixed phosphor 1 of Cu:Al is formed into a pentagonal shape for one pixel, and is arranged in a line with a light shielding plate 2 in between. And wavelength 420nm and wavelength 530n respectively.
A photomultiplier tube 5.6 is optically coupled to each side of the pentagonal mixed phosphor mass through a color filter 3.4, for example blue and green, which passes light of m.

The radiation sensor shown in FIGS. 3 and 4 is configured as an X-ray surface sensor, and the mixed phosphor 7 formed into a plate shape with a large area is composed of, for example, Ca WO4 and Z.
It is formed by mixing nS:Cu:Al. Images of light emitted from these phosphors with different spectra are captured by the color image pickup tube 8, and by obtaining video signals of each color, images of X-rays with different energies are taken out. In FIG. 4, color separation is performed by a color filter 3.4, and an image brightness intensifier tube 9 is used instead of a color image pickup tube.
．． 10 and image pickup tubes 11 and 12. In this case, since the image brightness intensifier tube 9.10 is used, the sensitivity can be improved.

According to these radiation sensors, each signal containing information regarding radiation of each energy can be obtained. In other words, several images corresponding to several images taken by irradiating several types of X-rays with different X-ray spectra can be obtained by one X-ray irradiation. Therefore, by processing the output signals of these radiation sensors, it is possible to perform energy subtraction without time lag in each image, or to create an image in an arbitrary human X-ray spectrum in an isometric manner. In the case of energy subtraction, only one X-ray exposure is required, which is advantageous in terms of time and dose utilization, increases the S/N ratio, and reduces the burden on the X-ray tube and the like.

The phosphors to be mixed are desirably phosphors that each have an absorption edge near the lower limit of the required energy band, have different emission spectra, and are not mutually excited by the spectra.

Note that although an example in which two types of phosphors are mixed is shown above, it goes without saying that three or more types may be used.

Effects of the Invention According to the radiation sensor of the present invention, signals can be extracted for each energy by one incidence of radiation containing various energies.

[Brief explanation of drawings]

FIG. 1 is a graph showing the absorption characteristics of each phosphor for explaining this invention, FIG. 2 is a schematic perspective view of one embodiment of this invention, and FIGS. 3 and 4 are graphs showing other embodiments. FIG. 3 is a schematic perspective view of an example. 1.7... Mixed phosphor 2... Light shielding plate 3.4...
・Filter 5.6...Photomultiplier tube 8...Color image pickup tube 9, lO...Image brightness multiplier tube 11.12.
・・Image tube

Claims (1)

[Claims] (1) A mixed phosphor in which several types of phosphors having different energy absorption edges and different emission colors are mixed together, a means for color-separating the emitted light when the mixed phosphor is excited with radiation, and the separated phosphor. A radiation sensor having means for converting light of each color into electrical signals.