JP2019015743A - Radiation detector - Google Patents

Abstract

To provide a radiation detector capable of inhibiting TlBr crystal from being polarized and inhibiting electrodes from being corroded in atmosphere.SOLUTION: A radiation detector 1A includes a first electrode 10A, a second electrode 20A, and thallium bromide (TlBr) crystal 30 provided between the first electrode 10A and the second electrode 20A. The first electrode 10A has an alloy layer composed of alloy of thallium metal and another metal element. The second electrode 20A and a pad on a reading circuit board are electrically connected with each other, and they are mounted on the reading circuit board, and the second electrode 20A is sealed by resin.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radiation detector.

  The radiation detector detects radiation such as X-rays and gamma rays, and is used in a PET (Positron Emission Tomography) apparatus, a SPECT (Single Photon Emission Computed Tomography) apparatus, a gamma camera, a Compton camera, an imaging spectrometer, and the like. Can be.

  As a radiation detector, one using a thallium halide crystal (for example, thallium bromide, thallium iodide, thallium chloride, and a mixed crystal thereof) is known. As an example, a first electrode and a second electrode are used. The thing of the parallel plate-shaped structure by which the thallium bromide (TlBr) crystal | crystallization was provided in between is known (refer patent document 1, 2). One of the first electrode and the second electrode is used as an anode electrode, and the other is used as a cathode electrode. A radiation detector using a TlBr crystal can be manufactured inexpensively and easily, and has an advantage of high sensitivity. One or more electrodes may be further provided between the first electrode and the second electrode in order to control electrolysis or to electrostatically shield the electric field.

  The radiation detectors described in Patent Documents 1 and 2 use thallium electrodes made of only thallium (Tl) metal as the first electrode and the second electrode. By using a thallium electrode, polarization of the TlBr crystal can be suppressed and long-term stable operation of the radiation detector is possible.

Japanese Patent No. 5083964 JP 2006-80206 A

  When a thallium electrode is used as the first electrode and the second electrode in a radiation detector using a TlBr crystal, the thallium electrode rapidly corrodes and deteriorates in the atmosphere, and the characteristics of the radiation detector deteriorate. This also occurs when a metal layer such as gold is deposited on the thallium electrode. In order to suppress this deterioration, it is necessary to seal the thallium electrode with a resin or the like after manufacturing the radiation detector to improve moisture resistance and prevent oxidation and reaction with the air atmosphere.

  However, for example, when the radiation detector is mounted on the readout circuit board as a two-dimensional detector, electrical conduction between the electrode of the radiation detector and the pad of the readout circuit board is obtained by sealing with resin. Disappear. This hinders practical application of a radiation detector using a TlBr crystal.

  The present invention has been made in order to solve the above-mentioned problems, and radiation detection capable of suppressing deterioration of detector characteristics due to polarization of TlBr crystal and suppressing corrosion of electrodes in the atmosphere. The purpose is to provide a vessel.

  A radiation detector according to the present invention includes a first electrode, a second electrode, and a thallium bromide crystal provided between the first electrode and the second electrode. It has an alloy layer made of an alloy with a metal element, the second electrode and the pad on the readout circuit board are electrically connected to each other and mounted on the readout circuit board, and the second electrode is sealed with resin. It has been stopped. The second electrode may have an alloy layer made of an alloy of thallium metal and another metal element, or may be made of thallium metal.

  In the present invention, it is preferable that the alloy layer contains one or more metal elements of lead, silver, bismuth, and indium as the other metal elements. It is preferable that a low resistance metal layer made of a metal having a lower resistance than the alloy layer is provided on the surface of the alloy layer. The low resistance metal layer is preferably made of gold.

  In the present invention, it is preferable that a conductive intermediate layer for enhancing the adhesion between the alloy layer and the low resistance metal layer is provided between the alloy layer and the low resistance metal layer. The intermediate layer is preferably made of any one of chromium, nickel and titanium.

  In the present invention, it is preferable that a conductive underlayer for enhancing the adhesion between the thallium bromide crystal and the alloy layer is provided between the thallium bromide crystal and the alloy layer. The underlayer is preferably made of any one of chromium, nickel and titanium.

  The radiation detector of the present invention can suppress deterioration of detector characteristics due to polarization of the TlBr crystal and suppress corrosion of electrodes in the atmosphere.

FIG. 1 is a diagram illustrating a cross-sectional configuration of a radiation detector 1A according to the first embodiment. FIG. 2 is a diagram illustrating a cross-sectional configuration of the radiation detector 1B according to the second embodiment. FIG. 3 is a diagram illustrating a cross-sectional configuration of a radiation detector 1C according to the third embodiment. FIG. 4 is a diagram showing a cross-sectional configuration of the radiation detector 1D of the fourth embodiment. FIG. 5 is a diagram illustrating a cross-sectional configuration of a radiation detector 1E according to the fifth embodiment. FIG. 6 is a diagram showing a cross-sectional configuration of the radiation detector 1F of the sixth embodiment. FIG. 7 is a graph showing the content weight ratios of the Pb metal and the Tl metal in the alloy layer when the weight ratio of the Pb metal and the Tl metal as raw materials before alloying is set to various values. FIG. 8 is a graph showing the content weight ratios of Bi metal and Tl metal in the alloy layer when the weight ratios of Bi metal and Tl metal as raw materials before alloying are various values. FIG. 9 is a diagram showing a spectrum of 137Cs gamma rays obtained using the radiation detector of the example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

  FIG. 1 is a diagram illustrating a cross-sectional configuration of a radiation detector 1A according to the first embodiment. The radiation detector 1A is a flat plate detector including a first electrode 10A, a second electrode 20A, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10A and the second electrode 20A. It is. Of the two parallel surfaces of the TlBr crystal 30, the first electrode 10A is formed on one surface, for example, by vapor deposition, and the second electrode 20A is formed on the other surface, for example, by vapor deposition.

  The first electrode 10 </ b> A has an alloy layer 12. The second electrode 20 </ b> A has an alloy layer 22. The thickness of the alloy layers 12 and 22 is, for example, several tens nm to several hundreds nm. The alloy layers 12 and 22 are made of an alloy of thallium (Tl) metal and another metal element. The other metal element contained in the alloy together with the Tl metal may be arbitrary, but preferably one or more elements selected from lead (Pb), silver (Ag), bismuth (Bi) and indium (In) It is.

  The alloy layers 12 and 22 are made of an alloy such as Tl—Pb, Tl—Ag, Tl—Bi, Tl—In, Tl—Pb—Bi, or Tl—Pb—In. The alloy layers 12 and 22 contain Tl as a metal, and do not contain Tl only as a compound (for example, oxidation Tl, fluoride Tl, nitric acid Tl, etc.). The content ratio of Tl metal in the alloy layers 12 and 22 is a level at which Tl metal is detected by analysis by the fluorescent X-ray analysis (XRF) method. In addition, although the surface of the alloy layers 12 and 22 may be oxidized by touching air, the inside of the alloy layers 12 and 22 is not oxidized.

One of the first electrode 10A and the second electrode 20A is used as an anode electrode, and the other is used as a cathode electrode. Since thallium halide crystals exhibit ion conductivity, when a voltage is applied to the TlBr crystal 30, Tl ⁺ ions are accumulated to lower the cathode electrode, Br ^- ions are accumulated to lower the anode electrode. The radiation detector 1 </ b> A can detect radiation incidence by a current flowing between the two electrodes as an electron-hole pair generated by incident radiation moves according to an applied voltage.

Br ⁻ ions accumulated under the anode electrode combine with Tl metal contained in the anode electrode to form TlBr, and electrons are emitted at that time. Tl ⁺ ions accumulated under the cathode electrode combine with the emitted electrons to become Tl metal. Tl metal and TlBr produced by these reactions are not ions and have no charge. Therefore, polarization of the TlBr crystal 30 can be suppressed.

  Since the first electrode 10A and the second electrode 20A are not electrodes made of only Tl metal but electrodes made of an alloy of Tl metal and another metal element, corrosion in the atmosphere is suppressed, and sealing is performed with a resin or the like. There is no need to do. Therefore, the radiation detector 1A can be mounted on the readout circuit board.

  The first electrode 10A and the second electrode 20A made of an alloy of a Tl metal and another metal element have strong adhesion to the TlBr crystal 30 and peel off from the TlBr crystal 30 at a high temperature as compared with an electrode made only of the Tl metal. It is suppressed. For example, the reliability of the radiation detector 1A can be ensured even when the radiation detector 1A is at a high temperature when the radiation detector 1A is mounted on the readout circuit board.

  In addition, a radiation detector having an electrode made of only Tl metal needs to be subjected to aging (an operation in which voltage polarity is changed and applied alternately between electrodes) in order to stabilize the characteristics. On the other hand, a radiation detector having an electrode made of an alloy of a Tl metal and another metal element does not need to perform such aging and has a good energy resolution from the beginning.

  FIG. 2 is a diagram illustrating a cross-sectional configuration of the radiation detector 1B according to the second embodiment. The radiation detector 1B includes a first electrode 10B, a second electrode 20B, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10B and the second electrode 20B. Compared with the configuration of the first embodiment shown in FIG. 1, in the configuration of the second embodiment shown in FIG. 2, the low resistance metal layer 14 is formed on the surface of the alloy layer 12 in the first electrode 10B, for example, by vapor deposition. However, the second electrode 20B is different in that a low resistance metal layer 24 is formed on the surface of the alloy layer 22 by, for example, vapor deposition.

  The low resistance metal layer 14 is made of a metal having a lower resistance than the alloy layer 12. The low resistance metal layer 24 is made of a metal having a lower resistance than the alloy layer 22. The low resistance metal layers 14 and 24 may be a single layer or a plurality of layers. The thickness of the low resistance metal layers 14 and 24 is, for example, several tens nm to several hundreds nm. The metal of the low resistance metal layers 14 and 24 may be arbitrary, but gold (Au) is preferably used. By providing a low-resistance metal layer made of a low-resistance metal on the surface of the alloy layer, oxidation of the surface of the alloy layer is suppressed and, for example, resistance between a pad and an electrode on the readout circuit board is reduced. be able to.

  FIG. 3 is a diagram illustrating a cross-sectional configuration of a radiation detector 1C according to the third embodiment. The radiation detector 1C includes a first electrode 10C, a second electrode 20C, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10C and the second electrode 20C. Compared with the configuration of the second embodiment shown in FIG. 2, in the configuration of the third embodiment shown in FIG. 3, the intermediate layer 13 between the alloy layer 12 and the low-resistance metal layer 14 in the first electrode 10C. Is different in that the intermediate layer 23 is formed, for example, by vapor deposition between the alloy layer 22 and the low-resistance metal layer 24 in the second electrode 20C.

  The intermediate layer 13 is inserted in order to increase the adhesion between the alloy layer 12 and the low resistance metal layer 14. The intermediate layer 23 is inserted to increase the adhesion between the alloy layer 22 and the low resistance metal layer 24. The intermediate layers 13 and 23 have conductivity. The thickness of the intermediate layers 13 and 23 is, for example, several nm to several hundred nm. The material of the intermediate layers 13 and 23 may be arbitrary, but is preferably made of any one of chromium (Cr), nickel (Ni), and titanium (Ti).

  FIG. 4 is a diagram showing a cross-sectional configuration of the radiation detector 1D of the fourth embodiment. The radiation detector 1D includes a first electrode 10D, a second electrode 20D, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10D and the second electrode 20D. Compared with the configuration of the first embodiment shown in FIG. 1, in the configuration of the fourth embodiment shown in FIG. 4, an island-shaped thin film is formed between the TlBr crystal 30 and the alloy layer 12 in the first electrode 10 </ b> D. The underlayer 11 is formed by vapor deposition (resistance heating method), for example, and the first electrode 10D is formed in the gap between the island structures. Further, in the second electrode 20D, an underlayer 21 which is an island-shaped thin film is formed between the TlBr crystal 30 and the alloy layer 22 by, for example, vapor deposition (resistance heating method), and the second electrode 20D is formed in the gap of the island-shaped structure. Is different in that it is formed.

  FIG. 5 is a diagram illustrating a cross-sectional configuration of a radiation detector 1E according to the fifth embodiment. The radiation detector 1E includes a first electrode 10E, a second electrode 20E, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10E and the second electrode 20E. Compared with the configuration of the second embodiment shown in FIG. 2, in the configuration of the fifth embodiment shown in FIG. 5, an island-shaped thin film is formed between the TlBr crystal 30 and the alloy layer 12 in the first electrode 10 </ b> E. The underlayer 11 is formed by, for example, vapor deposition (resistance heating method), and the first electrode 10E is formed in the gap between the island structures. In addition, in the second electrode 20E, an underlayer 21 that is an island-shaped thin film is formed between the TlBr crystal 30 and the alloy layer 22 by, for example, vapor deposition (resistance heating method), and the second electrode 20E is formed in the gap between the island-shaped structures. Is different in that it is formed.

  FIG. 6 is a diagram showing a cross-sectional configuration of the radiation detector 1F of the sixth embodiment. The radiation detector 1F includes a first electrode 10F, a second electrode 20F, and a thallium bromide (TlBr) crystal 30 provided between the first electrode 10F and the second electrode 20F. Compared with the configuration of the third embodiment shown in FIG. 3, in the configuration of the sixth embodiment shown in FIG. 6, an island-shaped thin film is formed between the TlBr crystal 30 and the alloy layer 12 in the first electrode 10 </ b> F. The underlayer 11 is formed by, for example, vapor deposition (resistance heating method), and the first electrode 10F is formed in the gap between the island structures. In addition, in the second electrode 20F, an underlayer 21 that is an island-shaped thin film is formed between the TlBr crystal 30 and the alloy layer 22 by, for example, vapor deposition (resistance heating method), and the second electrode 20F is formed in the gap between the island-shaped structures. Is different in that it is formed.

  In the fourth to sixth embodiments, the underlayer 11 is inserted in order to increase the adhesion between the TlBr crystal 30 and the alloy layer 12. The underlayer 21 is inserted to increase the adhesion between the TlBr crystal 30 and the alloy layer 22. The underlayers 11 and 21 have conductivity. The thickness of the foundation layers 11 and 21 is, for example, several nm to several tens of nm. The material of the underlayers 11 and 21 may be arbitrary, but is preferably made of any one of chromium (Cr), nickel (Ni), and titanium (Ti).

  Next, an example of a method for manufacturing the radiation detector 1F of the sixth embodiment will be described. The other metal element contained in the alloy together with the Tl metal will be described as lead (Pb).

First, a TlBr crystal wafer is cut into an appropriate size (for example, a rectangle having a side length of about 10 to 20 mm) to form a TlBr crystal 30, and the surface of the TlBr crystal 30 is polished. The wafer may be cut after being polished. In addition, Tl metal and Pb element as raw materials are put into a tungsten boat at an appropriate weight ratio, and this boat is heated to alloy the Tl metal and Pb element in a vacuum tank depressurized to 10 ⁻³ Pa or less.

  The base layer 11 is thinly formed by vapor deposition on the polished surface of the TlBr crystal 30 using any one of Cr, Ni and Ti as an evaporation source. Thereafter, the alloyed metal in the boat is used as an evaporation source, and the alloy layer 12 is formed on the underlayer 11 by vapor deposition. By providing the base layer 11, the adhesive force between the TlBr crystal 30 and the alloy layer 12 can be increased.

  After the TlBr crystal 30 formed up to the alloy layer 12 is cooled, the intermediate layer 13 is thinly formed on the alloy layer 12 by vapor deposition using any one of Cr, Ni and Ti as an evaporation source. Thereafter, a low resistance metal layer 14 is formed on the intermediate layer 13 by vapor deposition using gold (Au) as an evaporation source. By providing the intermediate layer 13, the adhesion between the alloy layer 12 and the low-resistance metal layer 14 can be increased. Thus, the first electrode 10F is formed on one surface of the TlBr crystal 30.

  After sufficiently cooling the TlBr crystal 30 on which the first electrode 10F is formed, similarly to the ground surface 21 on the other polished surface of the TlBr crystal 30 facing the surface on which the first electrode 10F is formed, The alloy layer 22, the intermediate layer 23, and the low resistance metal layer 24 are sequentially formed by vapor deposition to form the second electrode 20F. The radiation detector 1F can be manufactured as described above.

  In addition, the adhesive force and electrical stability of the alloy layer 12 can be improved by heating the TlBr crystal 30 before, during or after the deposition of the alloy layer 12. Alternatively, the Pb metal is first deposited on the TlBr crystal 30 by vapor deposition and then the Tl metal is deposited by vapor deposition, or the Tl metal is first deposited on the TlBr crystal 30 by vapor deposition. The alloy layer 12 can also be formed by a method of forming a metal by vapor deposition.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, the first electrode may be an electrode having an alloy layer made of an alloy of thallium metal and another metal element, and the second electrode may be an electrode made of only thallium metal. In this case, for example, the first electrode may be exposed and connected to the pad of the readout circuit board, the second electrode may be directly connected to the pad of the readout circuit board, and the second electrode may be sealed with resin or the like. For example, an epoxy resin may be used as the sealing resin. In this case, by providing a base layer between the second electrode and the TlBr crystal, adhesion between the TlBr crystal and thallium metal can be improved as in the case of the alloy layer. The first electrode may be an electrode having an alloy layer made of an alloy of thallium metal and another metal element, and the second electrode may be an electrode made of gold.

  FIG. 7 is a graph showing the content weight ratios of the Pb metal and the Tl metal in the alloy layer when the weight ratio of the Pb metal and the Tl metal as raw materials before alloying is set to various values. The weight ratios of Pb metal and Tl metal before alloying were (a) 80:20, (b) 60:40, (c) 40:60, and (d) 20:80.

  FIG. 8 is a graph showing the content weight ratios of Bi metal and Tl metal in the alloy layer when the weight ratios of Bi metal and Tl metal as raw materials before alloying are various values. The weight ratios of Bi metal and Tl metal before alloying were (a) 80:20, (b) 60:40, (c) 40:60, and (d) 20:80.

  The weight ratio of each metal in the alloy layer shown in FIGS. 7 and 8 was measured using a fluorescent X-ray analyzer (ZSX Primus) manufactured by Rigaku Corporation. As shown in FIGS. 7 and 8, the weight ratio of each metal in the alloy layer does not necessarily match the weight ratio of each metal as a raw material before alloying. Therefore, in order to make the content weight ratio of each metal in the alloy layer a desired value, it is preferable to mix and alloy the raw materials before alloying at the weight ratio of each metal according to the desired value.

  FIG. 9 is a diagram showing a spectrum of 137Cs gamma rays obtained using the radiation detector of the example. FIG. 9A shows a spectrum when 5 minutes have elapsed since the start of operation, and FIG. 9B shows a spectrum when 6 hours have elapsed since the start of operation. The radiation detector used here has the structure of the first embodiment, and the alloy layer includes Tl metal and Pb metal at a weight ratio of 60:40 and has a thickness of 100 nm. The apparatus used for the spectrum measurement was a preamplifier (clear pulse 580 HP), a shaping amplifier (ORTEC 673), and a multi-channel analyzer (laboratory equipment 2100C / MCA). As shown in this figure, it was confirmed that the radiation detector of this embodiment can be operated continuously for 6 hours without sealing the electrodes with resin. In addition, the radiation detector of the comparative example having an electrode made of only Tl metal was corroded and blackened within 1 hour from the start of operation, and the characteristics deteriorated. Thus, the radiation detector of this embodiment can suppress the corrosion of the electrode in the atmosphere.

  Further, the adhesion force of the electrode to the TlBr crystal in the radiation detector was examined. The electrode of the example has the configuration of the second embodiment, and has a low resistance of 100 nm thickness made of gold on an alloy layer of 100 nm thickness containing Tl metal and Pb metal at a weight ratio of 60:40. A metal layer is provided. The electrode of the comparative example is obtained by providing a 100 nm thick low resistance metal layer made of gold on a 100 nm thick layer made of only Tl metal. A radiation detector was placed in an atmosphere at each temperature of 150 ° C., 175 ° C., and 200 ° C. for 1 minute to examine whether the electrode peeled off from the TlBr crystal. In the comparative example, the electrode was peeled off at a temperature of 150 ° C., whereas in the example, the electrode was not peeled off even at a temperature of 200 ° C. Thus, the radiation detector of this embodiment can suppress the peeling of the electrode from the TlBr crystal at a high temperature, and can ensure reliability.

  DESCRIPTION OF SYMBOLS 1A-1F ... Radiation detector, 10A-10F ... 1st electrode, 11 ... Underlayer, 12 ... Alloy layer, 13 ... Intermediate layer, 14 ... Low resistance metal layer, 20A-20F ... 2nd electrode, 21 ... Underlayer , 22 ... alloy layer, 23 ... intermediate layer, 24 ... low resistance metal layer, 30 ... thallium bromide crystal.

Claims (10)

A first electrode, a second electrode, and a thallium bromide crystal provided between the first electrode and the second electrode,
The first electrode has an alloy layer made of an alloy of thallium metal and another metal element,
The second electrode and a pad on the readout circuit board are electrically connected to each other and mounted on the readout circuit board, and the second electrode is sealed with a resin,
Radiation detector. The second electrode has an alloy layer made of an alloy of thallium metal and another metal element;
The radiation detector according to claim 1. The second electrode is made of thallium metal;
The radiation detector according to claim 1. The alloy layer contains one or more metal elements of lead, silver, bismuth, and indium as the other metal elements,
The radiation detector of any one of Claims 1-3. A low resistance metal layer made of a metal having a lower resistance than the alloy layer is provided on the surface of the alloy layer.
The radiation detector of any one of Claims 1-4. The low-resistance metal layer is made of gold;
The radiation detector according to claim 5. Between the alloy layer and the low-resistance metal layer, a conductive intermediate layer that increases the adhesion between the alloy layer and the low-resistance metal layer is provided,
The radiation detector according to claim 5 or 6. The intermediate layer is made of any one of chromium, nickel and titanium;
The radiation detector according to claim 7. Between the thallium bromide crystal and the alloy layer, a conductive underlayer is provided to increase the adhesion between the thallium bromide crystal and the alloy layer.
The radiation detector of any one of Claims 1-8. The underlayer is made of any one of chromium, nickel and titanium.
The radiation detector according to claim 9.

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