JP2007178329A - Positron lifetime measuring apparatus and measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device capable of measuring a positron lifetime by separating a positron beam source from a measuring sample, and having a half value width of a time resolution below 180 ps, and to provide a method of measuring the same. <P>SOLUTION: The device includes a positron beam source, a light detection device arranged in the state sandwiching the measuring sample between itself and the positron beam source, and a γ-ray detection device for detecting γ-rays generated when positrons entering the measuring sample from the positron beam source are annihilated in the measuring sample. The light detection device is characterized by detecting Cherenkov light generated when the positrons enter the measuring sample from the positron beam source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a positron lifetime measurement apparatus and measurement method, and more specifically, a positron lifetime measurement apparatus and measurement used for detection and evaluation of lattice defects and positronium in a substance as a sample to be measured, or for measuring a free volume of a polymer. Regarding the method.

  The positron lifetime measuring device is one of the most sensitive and effective methods for detecting and studying lattice defects such as vacancies and dislocations present in materials such as metals, semiconductors and compounds. The time at which the positron is incident on the sample to be measured and the time at which the incident positron collides with the electron in the sample to be measured and disappears are detected, and the frequency distribution of the time difference is taken to determine the lifetime of the positron.

For example, a sample 122 to be measured, such as an annealed copper plate, is placed in close contact with the ²² Na positron source 120 as shown in FIG. 8 (shown apart in FIG. 8). ^When positrons are emitted from the ²² Na positron beam source 120, 1.275 MeV nuclear γ rays are generated, and when these positrons disappear in the sample 122 to be measured, a pair of 0.511 MeV positron annihilation γ rays are generated. When the time when the positron is incident on the sample 122 to be measured is referred to as the start time, and the time at which the incident positron disappears in the sample 122 is referred to as the stop time, the time when the 1.275 MeV nuclear γ-ray is captured is started. The time and the time at which 0.511 MeV positron annihilation γ-rays are captured are regarded as the stop time, and the length of time that the positrons existed in the sample 122 to be measured can be measured from the difference between the stop time and the start time.

FIG. 7 shows an example of a conventional positron lifetime measuring apparatus 100 (see Patent Document 1). The positron lifetime measuring apparatus 100 includes the ²² Na positron beam source 120, a sample 122 to be measured that is placed in close contact with the ²² Na positron source, and a γ-ray detector 105 that captures γ-rays generated therefrom. The The γ-ray detection device 105 includes a scintillator 111 that captures 1.275 MeV nuclear γ-rays (start signal) from the positron source 120 and converts it into light, and 0.511 MeV that emits positrons annihilated in the sample 122 to be measured. And a scintillator 110 that captures the positron annihilation γ-rays (stop signal) and converts them into light. The scintillators 110 and 111 are made of, for example, BaF ₂ .

  In the γ-ray detection device 105, the light generated by the scintillators 110 and 111 is converted into an electrical signal by a photomultiplier tube (PMT) 112, and digitized by a digital oscilloscope 114 or a digitizer 116. It is transferred to a personal computer (PC) 118.

  The waveform of the photomultiplier tube is, for example, as shown in FIG. 9, and the time at which each scintillator 110, 111 captures γ rays can be specified from this waveform. First, since the interval between the points is generally about several hundred picoseconds (ps), the waveform is smoothed by, for example, averaging the total of several points, and then interpolated to convert to a continuous waveform. Next, the peak value of the waveform is obtained, and finally the position at which the waveform is, for example, 25% of the peak value is obtained to obtain the γ-ray capture time.

  By specifying the capture time of each of the two types of γ rays as described above, the stop time and start time of each positron can be measured, and the lifetime can be obtained. Then, by repeating the above steps, a positron lifetime histogram as shown in FIG. 10 can be obtained. From the half width of the obtained histogram, the time resolution (half width) of the positron lifetime measuring apparatus can be obtained as follows.

  First, the obtained positron lifetime histogram is fitted with the following function.

であり、Θ（ｔ−ｔ’）はヘビサイド関数である。

Θ (t−t ′) is a snake side function.

In Equation ₁ , τ ₁ represents the positron decay constant in the sample 122 to be measured, τ ₂ represents the positron decay constant in the ²² Na positron source 120, and τ _res represents the half width of the Gaussian distribution. τ ₁ can be defined as the positron lifetime in the sample to be measured, and τ _res can be defined as the time resolution (half-value width) of the positron lifetime measuring apparatus.

JP 2003-215251 A JP 2001-74673 A JP 2001-116706 A Research Institute of Electronics Technology Research Report No. 928 Ryoichi Suzuki 1991 Chapter 5

Above, ²² Na positron lifetime measurement method using positron source 120 of beta ⁺ decay, i.e. capturing the γ rays 1.27MeV emitted simultaneously with the positron emission from ²² Na positron source 120 selectively as an example This explains how to know the start time. However, this method has the following problems.

Since it is necessary to use the unsealed positron source 120 in close contact with the sample 122 to be measured, a radiation control area is required and the legal procedure is complicated. Further, when the sample 122 to be measured is measured in a special environment such as a high temperature, there arises a problem that ²² Na diffuses.

  In view of this, a method has been developed in which a positron beam is shortened (bunched) with RF (for example, see Non-Patent Document 1).

  However, when this method is used, the apparatus becomes very large. High performance can be obtained with an accelerator, but it costs billions of yen. If the positron source 120 is used, the cost can be reduced to about tens of millions of yen, but the measurement takes time because the number of positrons is reduced.

  References 2 and 3 include a positron beam source, an electromagnetic lens, a positron detector, and a γ-ray detector. The positron beam source is installed in the magnetic field of the electromagnetic lens and is measured. The positron detector is installed between the positron source and the material to be measured, and the positron flight path to the positron source and the material to be measured is maintained in a vacuum. A material evaluation apparatus is disclosed.

  That is, in the above invention, the positron generated from the positron beam source is transmitted through the plastic scintillator or the APD (avalanche photodiode) to obtain the start time. According to this method, it is not necessary to use a positron beam source in close contact with a sample to be measured, and the positron lifetime is measured by isolating the positron beam source and the sample to be measured without significantly reducing the number of effective positrons. Can do.

  However, there is a large variation in the energy of the positrons that have passed through the APD, which results in a variation in time. Therefore, energy selection by an electromagnetic lens is required. Also, the half width of time resolution is about 240 ps, which is not so good. In the above apparatus using a conventional non-sealed radiation source, 118 ps and 110 ps are possible as literature values.

  Accordingly, the present invention provides a high-performance positron lifetime measurement apparatus and measurement method that can measure the positron lifetime by separating the positron beam source and the sample to be measured and have a half-value width of time resolution of, for example, 180 ps or less. With the goal.

  Another object of the present invention is to provide a positron lifetime measuring apparatus capable of measuring the positron lifetime in a sample to be measured with a relatively inexpensive apparatus without using a large-scale apparatus such as an accelerator. is there.

  A positron lifetime measuring apparatus according to the present invention includes an apparatus positron beam source, a photodetection device disposed with the sample to be measured interposed between the positron beam source, and the sample to be measured incident from the positron beam source. A γ-ray detection device that detects γ-rays generated when positrons disappear in the sample to be measured, and the photodetection device receives the positron from the positron source into the sample to be measured. It is characterized by detecting Cherenkov light generated when the light is emitted. Cherenkov light is the start signal, γ-ray is the stop signal, and the lifetime of the positron in the sample to be measured is measured from the time difference when both signals are detected.

  The sample to be measured is transparent because it is necessary to extract and detect Cherenkov light generated in the sample to be measured.

  Further, the positron lifetime measuring apparatus of the present invention includes a positron beam source, a Cherenkov emitter disposed facing the positron source, and a positron emitted from the positron source passes through the Cherenkov emitter. And a photodetection device that detects Cherenkov light generated when the positron passes through the Cherenkov emitter in a sample to be measured facing the positron beam source via the Cherenkov emitter. And a γ-ray detection device that detects γ-rays generated when the light disappears. In this case as well, Cherenkov light is the start signal and γ-ray is the stop signal.

  The sample to be measured may be opaque. This is to detect Cherenkov light generated in the Cherenkov luminous body as a start signal.

  In the positron lifetime measuring apparatus according to the present invention, the γ-ray detection device may include a plurality of γ-ray detection means. Alternatively, the two γ-ray detection means may be arranged at positions facing each other with the sample to be measured interposed therebetween.

  The positron lifetime measuring apparatus of the present invention includes a digitizing means for digitizing a waveform signal detected by the photodetecting device and the γ-ray detecting device, and a waveform analyzing means for processing the digitized waveform signal to obtain a time spectrum. And can have. The digitizing means may be a digital oscilloscope, and the waveform analyzing means may be software analysis by a personal computer.

  In the positron lifetime measuring apparatus of the present invention, the half width of the time resolution of the time spectrum is preferably 80 ps or more and 180 ps or less, more preferably 80 ps or more and 110 ps or less.

  The positron lifetime method of the present invention includes a step of causing a positron to enter the sample to be measured, a step of detecting Cherenkov light generated when the positron is incident on the sample to be measured, and the positron being the sample to be measured. Detecting γ-rays that are generated when they disappear. In the present invention, the sample to be measured is transparent.

  Hereinafter, in the present specification, the positron lifetime method of the present invention is referred to as an “internal Cherenkov trigger method”.

  The positron lifetime method of the present invention includes a step of causing a positron to enter a Cherenkov emitter, a step of detecting Cherenkov light generated when the positron is incident on the Cherenkov emitter, and a passage through the Cherenkov emitter. Detecting γ-rays generated when the positrons disappear in the sample to be measured.

  Hereinafter, in the present specification, the positron lifetime method of the present invention is referred to as “external Cherenkov trigger method”. In the external Cherenkov trigger method, the sample to be measured may be opaque, and the Cherenkov illuminator is formed of a transparent substance.

  By using the positron lifetime measuring apparatus of the present invention, the positron lifetime can be measured by separating the positron beam source and the sample to be measured. Therefore, the positron lifetime in the sample to be measured can be measured even in a special environment such as a high temperature.

  Further, in the measurement of the positron lifetime by the positron lifetime measuring apparatus of the present invention, it was possible to obtain an extremely high time resolution with a half width of the time resolution of 100 ps to 150 ps.

  Further, in the positron lifetime measurement of the present invention, since a start signal can be obtained without capturing γ rays generated by annihilation of positrons in a positron beam source as in the prior art, there is little noise in the sample to be measured. The measurement result of the positron lifetime can be obtained only with this.

Furthermore, in the positron lifetime measurement by the external Cherenkov trigger method of the present invention, only a positron having a certain level or more of energy can generate Cherenkov light, so that the positron energy can be automatically selected to some extent, and high precision The positron lifetime can be measured.

  An embodiment of a positron lifetime measuring apparatus according to the present invention will be described with reference to the drawings. The same designations are used below for the elements already described as the prior art, but detailed illustration or description thereof is omitted. Further, the same reference numerals are used for the same reference numerals throughout the drawings.

  As shown in FIG. 1, the positron lifetime measuring apparatus 10 of the present embodiment includes a positron beam source 12, a photodetection device 14 having a measured sample 18 sandwiched between the positron beam source 12, and a measured object. A γ-ray detector 105 that detects γ-rays generated when the positrons incident on the sample 18 from the positron beam source 12 disappear in the sample 18 to be measured. The light detection device 14 can detect Cherenkov light generated when positrons are incident on the sample 18 to be measured from the positron beam source 12, and can obtain the time when the positrons are incident on the material 18 to be measured. Therefore, in this embodiment, Cherenkov light is the start signal and γ-ray is a stop signal.

  Here, Cherenkov light is an electromagnetic field created by charged particles that pass through when a charged particle passes through a transparent substance such as glass or water and the velocity of the charged particle exceeds the speed of light in the substance. Refers to ultraviolet light and visible light generated from the substance.

The sample 18 to be measured is preferably a substance that allows light having a large refractive index and a short wavelength to easily pass through, but is not particularly limited. For example, α-SiO ₂ , ice, glass, quartz, lucite, Cherenkov, etc. Any transparent material that can extract light to the outside may be used.

  The photodetection device 14 uses, for example, an MCP built-in photomultiplier tube, and captures Cherenkov light generated in the traveling direction of positrons in the sample 18 to be measured. The photodetection device 14 preferably has a high time resolution per photon of, for example, 30 ps and a large photon capturing surface, but is not particularly limited.

The positron beam source 12 may be a known device, for example, a ⁶⁸ Ge beam source having a γ ray shield. The positron beam source 12 is preferably a device capable of generating high energy positrons, but may be a device using ²² Na and is not particularly limited.

  As the γ-ray detection device 105, a known device can be used. For example, the γ-ray detection device 105 shown in FIG. 7 can be used in the prior art, and the γ-ray detection device 205 shown in FIG. A method for measuring the positron lifetime will be described.

  The positron lifetime measurement method of the present embodiment is a positron lifetime measurement apparatus 10 including a positron beam source 12, a light detection device 14, and a γ-ray detection device 205. A positron emitted from the positron beam source 12 is measured. A step of causing the light to enter the sample 18; a step of detecting the Cherenkov light generated when the light detection device 14 enters the positron into the sample 18 to be measured; and a step of annihilating the positron in the sample 18 to be measured. The γ-ray detecting device 205 detecting the generated γ-ray. As described above, the positron lifetime measurement method of this embodiment is referred to as an “internal Cherenkov trigger method”.

  As described above, the sample 18 to be measured is a transparent substance.

  The positron lifetime measuring apparatus 10 of this embodiment includes a digital oscilloscope (digitizing means) 114 for digitizing waveform signals detected by the light detection device 14 and the γ-ray detection device 205, and a waveform signal digitized by the digital oscilloscope 114. And a personal computer (waveform analyzing means) 118 for obtaining a time spectrum by processing.

  In FIG. 3, a photodetection device 14 (for example, a photomultiplier tube with a built-in MCP) and two photomultiplier tubes (hereinafter referred to as “PMT”) 112 are arranged in a substantially T shape, and each of the photodetection devices 14 and PMT112 is arranged. For example, FET voltage followers 210, 212, and 214 are provided as FET probes, and these outputs are input to the coincidence detection circuit 230 via discriminators (hereinafter referred to as “discs”) 220, 222, and 224. To do. Only when the coincidence detection of the disc 220 and the disc 222 or the disc 224 or all the three discs 220, 222, and 224 is obtained by the coincidence detection circuit 230, the digital oscilloscope 114 is triggered to capture the outputs of the light detection device 14 and the PMT 112. I have to.

The photodetection device 14 is, for example, an MCP built-in photomultiplier tube, and the two PMTs 112 are provided with a scintillator such as BaF ₂ on the measured sample 18 side.

  The positron lifetime measuring apparatus 10 of this embodiment is only when the photodetection device 14 detects Cherenkov light as a start signal and at least one of the PMTs 112 detects γ rays of a stop signal almost simultaneously (for example, within 100 ns). The digital oscilloscope 114 takes in the waveforms of the start signal and the stop signal. However, the coincidence detection circuit 230, discs 220, 222, 224 and the like are not essential components and can be omitted.

  Thereafter, the start signal obtained by the photodetector 14 and the stop signal obtained by the PMT 112 are analyzed by the personal computer 118 as described in the prior art, and the positron lifetime measurement in the sample 18 to be measured is repeated by repeating the positron lifetime measurement. Histograms and time spectral curves can be obtained.

  Next, a positron lifetime measuring apparatus according to another embodiment of the present invention will be described below with reference to FIG.

  The positron lifetime measuring apparatus 50 according to the present embodiment includes a positron beam source 12, a Cherenkov light emitter 16 disposed facing the positron beam source 12, and positrons emitted from the positron beam source 12 in the Cherenkov light emitter 16. A photodetection device 14 that detects Cherenkov light generated when it passes through, and a positron that has passed through the Cerenkov emitter 16 in a sample 20 to be measured that is disposed facing the positron beam source 12 via the Cherenkov emitter 16. And a γ-ray detection device 105 that detects γ-rays generated when annihilation disappears.

  Also in this embodiment, Cherenkov light is a start signal and γ rays are stop signals.

  The difference between the present embodiment and the above embodiment is that a Cherenkov luminous body 16 is disposed between the positron source 12 and the sample 20 to be measured. Cherenkov luminous body 16 is a transparent plate. The Cerenkov luminous body 16 is preferably a substance having a large refractive index and a short wavelength so that Cherenkov light is easily generated, but is not particularly limited. For example, acrylic, ice, glass, quartz Transparent materials such as are used. Since the Cherenkov light travels in the direction in which the positrons are incident, the measured sample 20 side of the Cherenkov light emitter 16 is covered with a reflective film such as an aluminum foil (not shown), and the Cherenkov light is light such as a photomultiplier tube with a built-in MCP. Reflect in the direction of the detection device 14.

  By the way, the energy of the positron that can generate Cherenkov light in the Cherenkov luminous body 16 is limited to a certain level or more. Therefore, in the present embodiment, by selecting the Cherenkov illuminant 16, it is possible to generate a start signal only for the positrons incident on the sample 18 to be measured at a high speed of a certain level or higher. Therefore, unlike the prior art (Patent Documents 2 and 3), it is not necessary to exclude low-speed incident positrons, and it is possible to automatically select incident positrons with uniform speed.

  Further, unlike the above embodiment, in the present embodiment, the sample 20 to be measured may be opaque. This is because Cherenkov light is generated by the Cherenkov light emitter 16 disposed between the positron beam source 12 and the sample 20 to be measured, and thus does not need to be extracted from the sample 20 to be measured. In the present embodiment, it is only necessary to detect only the γ rays generated when the positrons disappear from the sample 20 to be measured.

  The positron emitted from the positron beam source 12 first enters the Cherenkov light emitter 16, and the positron incident at a certain energy or more generates Cherenkov light in the Cherenkov light emitter 16. The Cherenkov light is reflected by a reflective film in front of the Cherenkov light emitter 16 and detected by a light detection device 14 such as an MCP built-in photomultiplier tube. The positrons that have passed through the Cherenkov illuminant 16 and the reflecting film are incident on the sample 20 to be measured, and γ-rays generated when they disappear in the sample 20 to be measured are detected by the γ-ray detector 105.

  The positron beam source 12, the light detection device 14, and the γ-ray detection device 105 used in the positron lifetime measuring device 50 of this embodiment may be basically the same as the device described in the above embodiment.

  The positron lifetime measurement method of this embodiment is the same as the positron lifetime measurement method of the above embodiment except that the Cherenkov light generated in the Cherenkov light emitter 16 is reflected and detected by the photodetector 14 as described above. . That is, in the positron lifetime measuring device 50 provided with the positron beam source 12, the light detection device 14, and the γ-ray detection device 105, the step of causing the positron emitted from the positron beam source 12 to enter the Cherenkov emitter 16, The detection device 14 detects Cherenkov light generated when positrons are incident on the Cherenkov illuminant 16, and γ generated when the positrons that have passed through the Cherenkov illuminant 16 disappear in the sample 20 to be measured. Detecting a line by the γ-ray detection device 105. The positron lifetime measurement method of this embodiment is called “external Cherenkov trigger method” as described above.

  The γ-ray detection device 205 described in the above embodiment may be used. Waveform analysis of the start signal obtained by the light detection device 14 and the stop signal obtained by the PMT 112 is performed, and the positron lifetime measurement is repeated in the sample 20 to be measured. A time spectrum curve of the positron lifetime at can be obtained.

  As mentioned above, although embodiment of the positron lifetime measuring apparatus and positron lifetime measuring method of this invention was described, this invention is not limited to the said embodiment and another Example. In FIG. 3, the γ-ray detection device 205 is arranged at a position where two PMTs (γ-ray detection means) 112 face each other with the sample 118 (18, 20) to be measured interposed therebetween, but one or three or more PMTs ( (γ-ray detection means). The more PMTs are arranged around the specimens 18 and 20 to be measured, the number of times of positron lifetime measurement per hour increases, and the measurement can be performed efficiently.

In addition, although the positron lifetime measuring apparatuses 10 and 50 of the present invention digitize the signal from the PMT 112 using the digital oscilloscope 114 or the digitizer 116, such a limitation is not particularly required. The scintillators 110 and 111 are not limited to BaF ₂ , and other types of scintillators may be used, and a timing discriminator such as an analog constant fraction discriminator (CFD) is used instead of the digital oscilloscope 114. A time difference wave height converter (TAC), or a multi-channel analyzer (MCA).

In addition, in the positron lifetime measuring apparatus of the present invention, the types of the positron beam source 12 and the photodetector 14 are not particularly limited, and the substances that form the Cherenkov emitter 16, the reflective film, and the sample to be measured are also particularly limited within the above range. However, the present invention can be implemented in variously modified, modified, and modified forms based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

Positron lifetime measurement was performed by the positron lifetime measuring apparatus 10 of the present invention shown in FIG. 1 (internal Cherenkov trigger method). A ⁶⁸ Ge ray source shielded with γ rays as the positron source 12, an MCP built-in photomultiplier tube as the photodetection device 14, BaF _{2 of} 28φ × 10 mm as the scintillator 110, and α-SiO ₂ as the sample to be measured. For the digital oscilloscope 114, WavePro 7100 manufactured by LeCroy was used, and for the photomultiplier tube (PMT) 112, H3378 manufactured by Hamamatsu Photonics was used.

  The distance between the positron beam source 12 and the sample 18 to be measured was 20 mm, the distance between the sample 18 to be measured and the photodetection device 14 was 20 mm, and the distance between the two scintillators 110 was 40 mm.

  Using the γ-ray detector 205 shown in FIG. 3, the positron lifetime in the sample 18 to be measured was measured as described in the above embodiment, and a time spectrum of the positron lifetime as shown in FIG. 4 was obtained.

In the positron lifetime spectrum of FIG. 4, the horizontal axis is a channel, and one channel corresponds to 10 ps. The vertical axis represents the count number (number of events) in the channel. The slope in the right direction from near the peak represents the lifetime of the positron. The sharper the peak, the better the performance of the device. As described above, the peak width and the decay curve of the positron are fitted to the data by the method of least squares, and the time resolution (half width) τ _res and the positron lifetime τ _{1 of the device} are obtained (see Equation 1).

In this example, the time resolution (half width) τ _res was 108 ps, which was very good time resolution as compared with the conventional positron lifetime measuring apparatus.

  The positron lifetime measurement was performed by the external Cherenkov trigger method using the positron lifetime measuring apparatus 50 of the present invention shown in FIG. For the positron beam source 12, the light detection device 14, the scintillator 110, the digital oscilloscope 114, and the photomultiplier tube (PMT) 112, the same devices as those in Example 1 were used. The Cherenkov luminous body 16 was an acrylic plate, and the sample 18 to be measured was covered with an aluminum foil to form a reflective film.

  The distance between the positron source 12 and the Cherenkov emitter 16 is 10 mm, the distance between the Cherenkov emitter 16 and the sample 18 to be measured is 10 mm, and the distance between the light detector 14 and the Cherenkov emitter 16 is 20 mm. The two scintillators 110 were opposed to each other with a measured sample 20 sandwiched between 40 mm.

  As the sample 20 to be measured, Cu without annealing and Cu annealed were used. The positron lifetimes in the sample 20 to be measured were measured for both of the samples 20 to be measured, and time spectra of positron lifetimes as shown in FIGS. 5 and 6 were obtained.

FIG. 5 is a positron lifetime spectrum in Cu without the former annealing. A positron lifetime τ ₁ of 193 ± 2 ps and a time resolution (half width) τ _res of 150 ps were obtained.

FIG. 6 is a positron lifetime spectrum in the latter annealed Cu. A positron lifetime τ ₁ of 154 ± 3 ps and a time resolution (half width) τ _res of 144 ps were obtained.

  As described above, using the positron lifetime measuring apparatus of the present invention, the half-width of the time resolution of the time spectrum of the time spectrum of 110 ps or less in the internal Cherenkov trigger method and 150 ps or less in the external Cherenkov trigger method is excellent. I was able to. If the internal Cherenkov trigger method is used, a half-value width with a time resolution of about 80 ps can be expected by selecting the sample 20 to be measured and improving the performance of the apparatus. Table 1 below compares the positron lifetime measurement method of the present invention (internal Cherenkov trigger method and external Cherenkov trigger method) and the above-described conventional positron lifetime measurement method.

  As is clear from Table 1, the positron lifetime measuring apparatus of the present invention has any one of the positron lifetime spectrum time resolution (half-value width), the size and cost of the apparatus, the measurement in a special environment, and the use of a sealed line source. From the viewpoint, it is understood that the apparatus is excellent.

  The technique according to the present invention is useful as a positron lifetime measuring apparatus for detecting the presence or position of defects in crystals such as atomic vacancies and dislocations and their positions. Further, it can be used for detection and evaluation of positronium in a sample to be measured, or measurement of free volume of a polymer.

The top view which shows the principal part of the positron lifetime measuring apparatus which performs the internal Cerenkov trigger method based on embodiment of this invention. The top view of the principal part of the positron lifetime measuring apparatus which performs the internal Cerenkov trigger method based on other embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The plane conceptual diagram which shows the whole positron lifetime measuring apparatus which concerns on embodiment of this invention. By internal Cerenkov trigger method, a positron lifetime spectra in alpha-SiO _2. It is a positron lifetime spectrum in Cu in the state which does not anneal by the external Cherenkov trigger method. It is a positron lifetime spectrum in annealed Cu by the external Cherenkov trigger method. The plane conceptual diagram of the conventional positron lifetime measuring apparatus. The conceptual diagram of the positron lifetime measuring apparatus using ²² Na. Waveform of γ rays detected by a photomultiplier tube (PMT). Positron lifetime spectrum (histogram) in annealed Cu.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 50: Positron lifetime measuring device 12 of this invention 12: Positron beam source 14: Photodetector 16: Cherenkov luminous body 18, 20, 122: Sample 100 to be measured 100, 200: Conventional positron lifetime measuring device 105, 205: γ Line detectors 110 and 111: Scintillator 112: Photomultiplier tube (PMT)
114: Digital oscilloscope 116: Digitizer (ADC)
118: Personal computer (PC)
120: ²² Na positron source 210: discriminator 212: coincidence detection circuit

Claims (11)

A positron source,
A photodetection device arranged with a sample to be measured between the positron source and
A γ-ray detector for detecting γ-rays generated when the positrons incident on the sample to be measured are extinguished in the sample to be measured, and
The photodetection device detects a Cherenkov light generated when the positron is incident on the sample to be measured from the positron beam source. The positron lifetime measuring apparatus according to claim 1, wherein the sample to be measured is transparent. A positron source,
A Cherenkov emitter disposed opposite the positron source;
A photodetection device that detects Cherenkov light generated when positrons emitted from the positron beam source pass through the Cherenkov luminous body;
A γ-ray detection device for detecting γ-rays generated when the positrons passing through the Cherenkov luminescent material disappear in a sample to be measured disposed opposite to the positron beam source via the Cherenkov luminescent material. When,
A positron lifetime measuring device with The positron lifetime measuring apparatus according to claim 3, wherein the sample to be measured is opaque. The positron lifetime measuring apparatus according to claim 1, wherein the γ-ray detection apparatus includes a plurality of γ-ray detection means. The positron lifetime measuring apparatus according to claim 5, wherein the two γ-ray detection units are arranged at positions facing each other with the sample to be measured interposed therebetween. Digitizing means for digitizing the waveform signals detected by the light detection device and the γ-ray detection device;
Waveform analysis means for processing the digitized waveform signal to obtain a time spectrum;
The positron lifetime measuring apparatus according to claim 1, comprising: The positron lifetime measuring apparatus according to claim 7, wherein a half-value width of time resolution of the time spectrum is 80 ps or more and 180 ps or less. The positron lifetime measuring apparatus according to claim 7, wherein a half-value width of time resolution of the time spectrum is not less than 80 ps and not more than 110 ps. Emitting positrons; and
Making the positron incident on a sample to be measured;
Detecting Cherenkov light generated when the positron is incident on the sample to be measured;
Detecting γ-rays generated when the positrons disappear in the sample to be measured;
A positron lifetime measuring method including: Emitting positrons; and
Making the positron incident on a Cherenkov emitter;
Detecting Cherenkov light generated when the positron is incident on the Cherenkov luminous body;
Detecting γ-rays that are generated when the positron that has passed through the Cherenkov luminescent material disappears in the sample to be measured;
A positron lifetime measuring method including:

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