Abstract:
The present invention has an object to provide an X-ray fluorescence spectrometer capable of preventing a decrease in analysis precision of light elements whose atomic number is less than 23 and making helium gas replacement for the inside of an analysis chamber more efficient. An X-ray fluorescence spectrometer of the present invention includes: an X-ray tube  12  for irradiating a sample S on a sample stage  14  with a primary X-ray, the sample stage  14  having an X-ray passing port  141;  a detector  13  for detecting a fluorescent X-ray emitted from the sample S; an analysis chamber  16  having an introduction port  17  for the primary X-ray emitted from the X-ray tube  12  and a detection port  181  for the detector  13,  the analysis chamber  16  containing an internal space including an optical path of the primary X-ray from the introduction port  17  to the X-ray passing port  141  and an optical path of the fluorescent X-ray from the X-ray passing port  141  to the detection port  181;  first and second introduction pipes  201  and  202  for introducing helium gas supplied from a helium gas cylinder  22  into the analysis chamber  16  through the introduction port  17  and the detection port  181,  respectively; and a flow rate control valve  24  for controlling a helium gas flow rate in each of the first and second introduction pipes  201  and  202.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an X-ray fluorescence spectrometer which detects the wavelength (energy) and the intensity of a peak of a fluorescent X-ray that is generated from a solid, powder, or liquid sample when the sample is irradiated with an X-ray, and thus performs a qualitative/quantitative analysis of light element components whose atomic number is less than 23 in the sample. 
       BACKGROUND ART 
       [0002]    An X-ray fluorescence spectrometer irradiates a sample in an analysis chamber with a primary X-ray emitted from an X-ray source, detects a fluorescent X-ray emitted from the irradiated sample by means of a detector, measures the wavelength (energy) and the intensity of a peak of the fluorescent X-ray, and thus performs a qualitative/quantitative analysis of element components in the sample. Here, if the atmospheric air exists in an optical path of the primary X-ray from the X-ray source to the sample as well as in an optical path of the fluorescent X-ray from the sample to the detector, the primary X-ray and the fluorescent X-ray are absorbed and attenuated by the atmospheric air. In particular, light elements whose atomic number is less than 23 each generate a fluorescent X-ray with a long wavelength (low energy), and are strongly influenced by such absorption by the atmospheric air. To deal with this, in the case where light elements are contain d in an analysis target, the atmosphere inside the analysis chamber is replaced with helium gas which absorbs less X-ray than the atmospheric air. 
         [0003]    The analysis chamber is provided with a gas supply port and a gas outlet, and helium gas is supplied from the gas supply port while the atmospheric air is pushed out from the gas outlet, whereby the atmosphere inside the analysis chamber is replaced with the helium gas. In addition to the gas supply port and the gas outlet, the analysis chamber is provided with opened parts such as an introduction port for the primary X-ray emitted from the X-ray source and a detection port for the detector. Hence, conventionally, in order to prevent gases from flowing in and out through the opened parts, the opened parts are each covered by a thin organic whereby the helium gas replacement work is made more efficient (see Patent Literature 1). 
         [0004]    In the above-mentioned conventional method, however, although organic films that absorbs less X-ray are used, the light elements, which each emit a fluorescent X-ray with a longer wavelength (lower energy) by irradiation with the primary X-ray, a e significantly influenced by the X-ray absorption due to the existence of the organic films in the optical path of the primary X-ray and the optical path of the fluorescent X-ray. 
       CITATION LIST 
     Patent Literature 
       [0005]    [Patent Literature 1] JP 2001-349852 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    The present invention has an object to provide an X-ray fluorescence spectrometer capable of enhancing the analysis precision of light elements whose atomic number is less than 23 and making helium gas replacement for the inside of an analysis chamber more efficient. 
         [0007]    Solution To Problem 
         [0008]    An X-ray fluorescence spectrometer according to the present invention, which has been made in order to achieve the above-mentioned object, includes: 
         [0009]    a) an X-ray source for irradiating a sample with a primary X-ray; 
         [0010]    b) a detector for detecting a fluorescent X-ray that is emitted from the sample when the sample is irradiated with the primary X-ray; 
         [0011]    c) an analysis chamber having an introduction port for the primary X-ray emitted from the X-ray source and a detection port for the detector, the analysis chamber confining a space including an optical path of the primary X-ray from the introduction port to the sample and an optical path of the fluorescent X-ray from the sample to the detection port; 
         [0012]    d) first introduction means for introducing helium gas into the analysis chamber through the introduction port; 
         [0013]    e) second introduction means for introducing helium gas into the analysis chamber through the detection port; and 
         [0014]    f) flow rate control means for controlling a flow rate of the helium gas that is introduced into the analysis chamber by each of the first introduction means and the second introduction means. 
         [0015]    In the above-mentioned X-ray fluorescence spectrometer, it is preferable that the flow a control means include: first flow rate control means for controlling the flow rate of the helium gas that is introduced into the analysis chamber by the first introduction means; and second flow rate control means for controlling the flow rate of the helium gas that is introduced into the analysis chamber by the second introduction means. According to such a configuration, the flow rate of the helium gas that is introduced into the analysis chamber through each of the introduction port and the detection port can be adjusted as appropriate, depending on the positions, structures, or other factors relating to the introduction port and the detection port. 
         [0016]    Moreover, it is preferable that: the first introduction means include a first introduction pipe having an inlet-side end part connected to a helium gas supply source and an outlet-side end part connected to the introduction port; the second introduction means include a second introduction pipe having an inlet-side end part connected to the helium gas supply source and an outlet-side end part connected to the detection port; and the X-ray fluorescence spectrometer further include atmospheric air introduction means for forcibly introducing an atmospheric air into the analysis chamber from at least one of the first introduction pipe and the second introduction pipe. 
         [0017]    According to such a configuration, the time required to replace helium gas in the analysis chamber with the atmospheric air can be reduced. Moreover, helium gas remaining in the introduction port and the detection port can be reliably replaced with the atmospheric air, and hence influences of helium gas when the sample is analyzed under the atmospheric air can be eliminated. 
       Advantageous Effects of Invention 
       [0018]    According to the present invention, the first introduction means and the second introduction means are provided, and helium gas is introduced from the introduction port for the primary X-ray and the detection port for the detector that are opened parts of the analysis chamber. Hence, in the insides of these opened parts where gas replacement is conventionally difficult, the atmosphere can be efficiently replaced with helium gas. Accordingly, the time before the fluorescent X-ray intensity of each light element detected by the detector becomes stable from a helium gas introduction start can be reduced, the analysis time can be reduced, and the analysis processing capability can be enhanced. 
         [0019]    Moreover, the helium gas replacement rates of the introduction port for the primary X-ray and the detection port for the detector are enhanced compared with those in conventional cases. Hence, the fluorescent X-ray intensity of each light element detected by the detector increases, and the analysis sensitivity and the analysis precision can be enhanced. 
         [0020]    Further, unlike conventional X-ray fluorescence spectrometers, a member that absorbs X-rays does not exist on the optical paths of the primary X-ray and the fluorescent X-ray. Hence, decrease in the intensity of the primary X-ray radiated to the sample and in the intensity of the fluorescent X-ray that is emitted from the sample and is detected by the detector is prevented, and the qualitative/quantitative analysis precision of light element components whose atomic number is less than 23 in the sample is further enhanced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a schematic configuration diagram of an X-ray fluorescence spectrometer according to a first embodiment of the present invention. 
           [0022]      FIG. 2A  is a diagram illustrating a relation between a helium gas flow rate and a helium gas replacement rate when helium gas is introduced into a chamber of a conventional X-ray fluorescence spectrometer, and  FIG. 2B  is a diagram illustrating a relation between a helium gas flow rate and a helium gas replacement rate when helium gas is introduced into a chamber of the X-ray fluorescence spectrometer according to the present embodiment. 
           [0023]      FIG. 3A  is a diagram illustrating a temporal change in fluorescent X-ray (Na—Kα) intensity of the conventional X-ray fluorescence spectrometer, and  FIG. 3B  is a diagram illustrating a temporal change in Na—Kα intensity of the X-ray fluorescence spectrometer according to the present embodiment. 
           [0024]      FIG. 4A  is a diagram illustrating a temporal change in fluorescent X-ray (S—Kα) intensity of the conventional X-ray fluorescence spectrometer, and  FIG. 4B  is a diagram illustrating a temporal change in fluorescent X-ray (S—Kα) intensity of the X-ray fluorescence spectrometer according to the present embodiment. 
           [0025]      FIG. 5  is a schematic configuration diagram of the conventional X-ray fluorescence spectrometer. 
           [0026]      FIG. 6  is a schematic configuration diagram of an X-ray fluorescence spectrometer according to a second embodiment of the present invention. 
           [0027]      FIG. 7  is a schematic configuration diagram of an X-ray fluorescence spectrometer according to a third embodiment of the present invention. 
           [0028]      FIG. 8  is a schematic configuration diagram of an X-ray fluorescence spectrometer according to a fourth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0029]    Hereinafter, some specific embodiments of the present invention are described with reference to the drawings. 
       First Embodiment 
       [0030]      FIG. 1  is a diagram illustrating a schematic configuration of an X-ray fluorescence spectrometer according to a first embodiment of the present invention. The X-ray fluorescence spectrometer  10  of the present embodiment is an X-ray fluorescence spectrometer of under irradiation type, and includes: an X-ray tube  12  for generating a primary X-ray; a detector  13  (for example, a semiconductor detector, a proportional counter) for detecting a fluorescent X-ray secondary X-ray) generated from a sample; a sample stage  14  having an X-ray passing port  141 , and other components. 
         [0031]    A lower part of the sample stage  14  is provided with an analysis chamber  16 . The analysis chamber  16  is provided with an introduction port  17  for the primary X-ray and a housing  18  to which a leading end part of the detector  13  is attached. The primary X-ray emitted from the X-ray tube  12  enters the analysis chamber  16  from the introduction port  17 , passes through the analysis chamber  16 , and is radiated to a sample S held by the sample stage  14  through the passing port  141 . Moreover, the leading end of the housing  18  is provided with a detection port  181 , and the fluorescent X-ray that is emitted from the sample S and comes out from the passing port  141  passes through the analysis chamber  16 , and enters the detector  13  through the detection port  181 . 
         [0032]    The inside of the analysis chamber  16  is in communication with a helium gas cylinder  22  that is a helium gas supply source, through an introduction pipe  20 . A flow rate control valve  24  is set to the introduction pipe  20 , the degree of opening of the flow rate control valve  24  is adjusted by an instruction from a control device  25 , and helium gas is introduced at an appropriate flow rate into the analysis chamber  16 . 
         [0033]    A guide bush  171  is attached to a lower wall  161  of the analysis chamber  16  near the introduction port  17 , and the guide bush  171  is provided with a first gas introduction port  162 . 
         [0034]    Moreover, the housing  18  is provided with a second gas introduction port  164 . The introduction pipe  20  extending from the helium gas cylinder  22  is brandied into two halfway, and leading end parts of the branch pipes  201  and  202  are connected to the first gas introduction port  162  and the second gas introduction port  164 , respectively. The branch pipe  201  and the branch pipe  202  correspond to a first introduction pipe and a second introduction pipe of the present invention, respectively. The flow rate control valve  24  is set to the introduction pipe  20  upstream of (on the helium gas cylinder  22  side from) the branch pipes  201  and  202 . 
         [0035]    In the X-ray fluorescence spectrometer  10  configured as described above, a helium gas replacement rate (He replacement rate Its examined when helium gas was introduced into the analysis chamber  16  while a helium gas flow rate from the introduction pipe  20  was changed. Here, a powder sample of sodium sulfate (Na 2 SO 4 ) obtained by press working was used, and the He replacement rate was obtained in the following manner from values (actual measurement values obtained by measuring a Na—Kα, intensity and a S—Kα intensity under this condition. 
         [0036]    The fluorescent X-ray intensities of Na—Kα and S—Kα when the atmosphere inside the analysis chamber  16  is replaced with helium gas can be theoretically expressed by the following Expression (1) and Expression (2). 
         [0000]      (Na—Kα intensity)=(Na—Kα intensity in vacuum)×(attenuation rate of primary X-ray)×(attenuation rate of Na—Kα)   (1)
 
         [0000]      (S—Kα intensity)=(S—Kα intensity in vacuum)×(attenuation rate of primary X-ray)×(attenuation rate of S—Kα)   (2)
 
         [0037]    In Expression (1) and Expression (2), the attenuation rate of the primary X-ray and the attenuation rates of Na—Kα and S—Kα represent the rates of attenuation by helium gas. That is in the case where the atmosphere inside the analysis chamber  16  is completely (100%) replaced with helium gas, theoretically, a value obtained by multiplying the Na—Kα intensity in vacuum by the rates of attenuation of the primary X-ray and Na—Kα by helium gas is an actual measurement value of the Na—Kα intensity, and a value obtained by multiplying the S—Kα intensity in vacuum by the rates of attenuation of the primary X-ray and S—Kα by helium gas is an actual measurement value of the S—Kα intensity. 
         [0038]    Because the Na—Kα intensity and the S—Kα intensity in vacuum of a fluorescent X-ray emitted from sodium sulfate, the rates of attenuation of these Na—Kα and S—Kα by helium gas, and the rate of attenuation of the primary X-ray by helium gas are known, the rate (He replacement rate) at which the gas in the chamber  16  is replaced with helium gas can be obtained from the actual measurement values of Na—Kα and S—Kα. 
         [0039]    In actuality, because the atmosphere inside the analysis chamber  16  under atmospheric pressure is replaced with helium gas, the actual measurement values of the Na—Kα intensity and the S—Kα intensity are influenced due to absorption of the primary X-ray and the fluorescent X-ray by the atmospheric air in the analysis chamber  16 . In view of this, in the present embodiment, a data table showing a relation between: the actual measurement value of Na—Kα and the actual measurement value of S—Kα, and the He replacement rate was created considering attenuation of the prima. X-ray, Na—Kα, and S—Kα by not only helium gas but also the atmospheric air, and the data table was stored in advance in a memory, whereby the He replacement rate was obtained from the actual measurement value of Na—Kα and the actual measurement value of S—Kα. 
         [0040]      FIG. 2A  and  FIG. 2B  each illustrate a relation between the helium gas flow rate and the He replacement rate. Moreover,  FIG. 3A  and  FIG. 3B  each illustrate a change in Na—Kα intensity from a helium gas introduction start, and  FIG. 4A  and  FIG. 4B  each illustrate a change in S—Kα intensity from the helium gas introduction start.  FIG. 2A ,  FIG. 3A , and  FIG. 4A  illustrate results obtained by a conventional X-ray fluorescence spectrometer  100  (see  FIG. 5 ; hereinafter, referred to as a conventional apparatus), and  FIG. 2B ,  FIG. 3B , and  FIG. 4B  illustrate results obtained by the X-ray fluorescence spectrometer  10  of the present embodiment (hereinafter, referred to as a present apparatus), when helium gas is introduced from the gas introduction port provided to the lower wall  161  of the analysis chamber  16 . Moreover, in  FIG. 2A  and  FIG. 2B , the horizontal axis represents the He flow rate (L/min), and the vertical axis represents the He replacement rate (%). It is assumed in  FIG. 2A  and  FIG. 2B  that the Na—Kα intensity and the S—Kα intensity when the inside of the analysis chamber  16  is in a vacuum state are each represented by 100%. Moreover, in  FIG. 2A  and  FIG. 2B , the He replacement rate on the detector  13  side (between the sample and the detector) is represented by *, and the He replacement rate on the primary side (between the X-ray tube and the sample) is represented by ♦. 
         [0041]    As is apparent from  FIG. 2A  and  FIG. 2B , in the conventional apparatus, the He replacement rate on the primary side was lower than that on the detector  13  side at every He flow rate, and, particularly, the He replacement rate on the primary side was extremely low at a He flow rate of 0.5 to 1.5 L/min. In comparison, in the present apparatus, the He replacement rate on the primary side was slightly lower than that on the detector  13  side at a He flow rate of 0.5 to 1.5 L/min, but was considerably improved. Moreover, the He replacement rates on the detector  13  side and on the primary side were substantially the same as each other at the He flow rates of 1.5 L/min or more, and were equal to or more than 90%. 
         [0042]    Moreover, as is apparent from  FIG. 3A ,  FIG. 3B ,  FIG. 4A , and  FIG. 4B , the fluorescent X-ray intensities of Na—Kα and S—Kα of the present apparatus were higher than those of the conventional apparatus immediately after the He introduction start, at every He flow rate. Further, in the conventional apparatus, the fluorescent X-ray intensities of Na—Kα and S—Kα did not reach an equilibrium (stable) state even after the elapse of 300 seconds from the He introduction start. In comparison, in the present apparatus, the fluorescent X-ray intensities of Na—Kα and S—Kα reached an equilibrium state after the elapse of about 100 seconds from the He introduction start, at the He flow rates of 1.5 L/min or more. Accordingly, it is understood that the present apparatus can reduce the time required for the He replacement work, compared with the conventional apparatus. 
         [0043]    The following is understood from the above. In the present embodiment, the first gas introduction port  162  is provided near the introduction port  17  for the primary X-ray, the second gas introduction port  164  is provided to the housing  18  for the detector  13 , and He is introduced into the analysis chamber  16  through this introduction port  17  and the detection port  181  for this detector  13 . Helium gas replacement is difficult for the introduction port  17  for the primary X-ray and the detection port  181  for the detector  13  due to their structures, and the He replacement rates of these portions are low in conventional cases. On the other hand, in the present embodiment, the He replacement rates of the introduction port  17  and the detection port  181  for the detector  13  can be enhanced. As a result, the fluorescent X-ray intensity of each light element detected by the detector  13  increases, and hence the detection sensitivity and the analysis precision can be enhanced. Moreover, because efficient helium gas replacement is possible for the introduction port  17  and the detection port  181  for the detector  13 , the time until the fluorescent X-ray intensity becomes stable (reaches an equilibrium state) after helium gas is introduced can be reduced, and the analysis time can be reduced. As a result, the amount of sample analysis per unit time can be increased, and the sample measurement capability can be enhanced. 
       Second Embodiment 
       [0044]      FIG. 6  illustrates an X-ray fluorescence spectrometer  10 A according to a second embodiment of the present invention. In the X-ray fluorescence spectrometer  10 A, flow rate control valves  24 A and  24 B are set to the branch pipes  201  and  202  of the introduction pipe  20 , respectively instead of the flow rate control valve  24 . The degrees of opening of the flow rate control valves  24 A and  24 B are individually adjusted by instructions from the control apparatus  25 . According to such a configuration, in the present embodiment, the amount of helium gas passing through the branch pipe  201  and the branch pipe  202  can be individually adjusted. Hence, for example, in the case where the introduction port  17  has a more complicated structure than that of the detection port  181  and helium gas less easily flows into the analysis chamber  16  from the introduction port  17 , the helium gas flow rate in the branch pipe  201  is set to be higher than that in the branch pipe  202 , whereby the amount of helium gas that is introduced into the analysis chamber  16  from the introduction port  17  can be made equal to the amount of helium gas that is introduced into the analysis chamber  16  from the detection port  181 . 
       Third Embodiment 
       [0045]      FIG. 7  illustrates an X-ray fluorescence spectrometer  10 B according to a third embodiment of the present invention. The X-ray fluorescence spectrometer  10 B is different from the X-ray fluorescence spectrometer  10  of the first embodiment in that: a switching control valve  30  is set to the introduction pipe  20  between the helium gas cylinder  22  and the flow rate control valve  24 ; and a compressor  32  is connected to the switching control valve  30 . When helium gas is introduced into the analysis chamber  16 , the switching control valve  30  is switched to communicate the helium gas cylinder  22  with the introduction pipe  20 . When an analysis is performed under the atmospheric air, the switching control valve  30  is switched to communicate the compressor  32  with the introduction pipe  20 . 
         [0046]    The present embodiment can produce the following functions and effects. That is, in the case where an analysis is performed inside which the analysis chamber  16  is replaced with helium gas, next analysis is then performed under the atmospheric air, the inside of the analysis chamber  16  (optical system) is exposed to the atmosphere, but helium gas remaining in the introduction port  17  and the housing  18  may not be completely discharged, and may remain as residual gas. If the analysis is performed in this state, the fluorescent X-ray intensity of each light element detected by the detector  13  becomes higher than that in the case where the analysis is performed inside which the analysis chamber  16  is completely replaced with the atmospheric air, and a quantitative analysis result of each light element is varied by depending on the residual amount of helium gas. In a quantitative analysis using a fundamental parameter (FP) method, quantitative analysis results of light elements significantly influence those of other heavy elements, and hence the unstable quantitative analysis results of the light elements are not preferable. 
         [0047]    To deal with this, in the present embodiment, in the case where an analysis is performed under the atmospheric air, the atmospheric air can be forcibly introduced into the analysis chamber  16  by the compressor  32 . Accordingly, helium gas remaining in the introduction port  17  and the housing  18  in the leading end part of the detector  13  can be efficiently replaced with the atmospheric air, and hence the quantitative analysis precision can be enhanced. Moreover, the time required to replace the atmosphere inside the analysis chamber  16  with the atmospheric air can be reduced. 
       Fourth Embodiment 
       [0048]      FIG. 8  illustrates an X-ray fluorescence spectrometer  10 C according to a fourth embodiment of the present invention. The X-ray fluorescence spectrometer  10 C has a configuration in which the switching control valve  30  and the compressor  32  are set to the introduction pipe  20  of the X-ray fluorescence spectrometer  104  (see  FIG. 6 ) of the second embodiment. Such a configuration can also produce functions and effects similar to those produced by the apparatus  10 B according to the third embodiment. 
         [0049]    The present invention is not limited to the above-mentioned embodiments, and can be variously modified. For example, in all the above-mentioned embodiments, the present invention is applied to a so-called X-ray fluorescence spectrometer of under irradiation type in which the sample placed on the upper surface of the sample stage is irradiated with the primary X-ray from below the sample stage. Alternatively, the present invention can also be applied to: an X-ray fluorescence spectrometer of top irradiation type in which the sample is irradiated with the primary X-ray from above; and an X-ray fluorescence spectrometer of side irradiation type in which the sample is irradiated with the primary X-ray from the side. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10 ,  10 A,  10 B,  10 C . . . X-ray Fluorescence Spectrometer 
           12  . . . X-ray Tube 
           13  . . . Detector 
           14  . . . Sample Stage 
           141  . . . X-ray Passing Port 
           16  . . . Analysis Chamber 
           162  . . . First Introduction Port 
           164  . . . Second Introduction Port 
           18  . . . Housing 
           181  . . . Detection Port 
           20  . . . Introduction Pipe 
           201 ,  202  . . . Branch Pipe 
           22  . . . Helium Gas Cylinder 
           24  . . . Flow Rate Control Valve 
           25  . . . Control Device 
           30  . . . Control Valve 
           32  . . . Compressor