US 3400265 A
Description (OCR text may contain errors)
Sept. 3, 1968 Y. HOUBART X-RAY SPECTROMETRY APPARATUS HAVING BOTH INTERCHANGEABLE SPECIMENS AND RADIATION SOURCES Filed March 30, 1965 2 Sheets-Sheet l POWER PACK VACUUM PUMP Sept. 3, 1968 Y. HOUBART 3,400,265
X-HAY SPECTROMETRY ARATUS HAVING BOTH ERCHANGEABLE SPECIM AN ADIATION SOURC Filed March 30, 1965 2 Sheets-Sheet 2 United States Patent 3,400,265 X-RAY SPECTROMETRY APPARATUS HAVING BOTH INTERCHANGEABLE SPECIMENS AND RADIATION SOURCES Yvan Houbart, Liege, Belgium, assignor to Centre National de Recherches Metallurgiques, Brussels, Belgium, a Belgian corporation Filed Mar. 30, 1965, Ser. No. 443,822
Claims priority, applicatiotrilltielgium, Apr. 1, 1964,
6 Claims. 61. 250-495 ABSTRACT OF THE DISCLOSURE The present invention relates to X-ray spectrometry and more particularly to an apparatus for X-ray spectrometry having a rotatable turret in which at least two specimens can be placed.
One particular object of the invention is the provision of a spectrometer which is universal in the sense that it can either be used for bombarding a specimen with electrons so that X-rays are produced or for projecting X- rays on to the specimen so that a fluorescence technique can be used.
A further object of the invention is to provide an improved apparatus in which the specimen under examination is maintained in the same evacuated space as a source of electrons or X-rays for the examination of the specimen, so that X-rays are projected through an aperture onto a detecting device comprising a crystal and a counter. The detecting device is in a prolongation of the evacuated space of the electrons or X-rays source. Thus, the entire X-ray path is under vacuum and the only absorbing matter is the window of the counter.
Yet a further object of the invention is the provision of a device for examination by X-ray techniques in which the space to be evacuated is as small as possible, and in which the volume put under atmospheric pressure when a specimen is introduced or removed is reduced to a minimum and does not include the space surrounding the electron or X-ray generating means.
In order to explain a specific embodiment of the invention it is proposed to describe a previously proposed device as protected by Belgian Patent 634,419 and then to describe how the present invention may be employed as a modification of the basic structure of the device forming the subject matter of the Belgian patent specification.
Accordingly FIGURES 1 and 2 are respectively a sid view and partial section of the device described in the Belgian patent specification, and is a view of the turret from below. 65
FIGURE 3 is a view on the line III-III of FIGURE 1.
FIGURES 4 and 5 are views of part of the novel spectrometer forming the subject matter of the present invention in accordance with two vertical sections at right angles to each other.
FIGURES 6 and 7 correspond to FIGURE 5 but ShOW the apparatus equipped for projecting a beam of electrons Patented Sept. 3, 1968 Fr I onto a specimen, and for projecting X-rays onto it, respectively.
Referring now to the drawings of the previously proposed device and more particularly to FIGURE 1 it Will be seen that the spectrometer represented comprises a non-rotatable base portion B and a rotatable turret T. The base portion B has a vertically extending aperture 2 reaching as far as an oblique upper face 11 of the base portion. This aperture 2 contains an electron gun 6 with a vertical axis 1. The lower part of the electron gun is put in communication with a vacuum pump indicated diagrammatically while it is connected with a power pack indicated diagrammatically also. The turret T is carried by a ball bearing 31 mounted in a recess 32 in the upper part of the base portion and is held down by a stud 14 on which a nut 30 is screwed. A rim 13 projects above the oblique face 11 and surrounds partly the turret T.
The turret T has three circular apertures 16 in which specimens such as 8 can be carried by specimen holders 17 at such a distance from the axis 3 of rotation of the turret that as the turret is rotated they can be brought into position over the electron gun 6. Each specimen is covered by a cap such as 18 with sealing means 19.
When the turret is in the position shown in FIGURE 1 air can only be exhausted from under the specimen which is over the opening 20 of the base B. This opening is connected to a vacuum rotary pump and air can be exhausted by means of an electromagnetic valve.
In order to prevent air leaking from one specimen to another through the space between the turret and the base, I provide a special joint moulded in only one piece and comprising an outer circular sealing ring 23, an inner one 24, and six radial strips with fiat flanges 25.
Both parts of this special sealing unit are fitted into circular and radial grooves of the turret (27, 25 FIG. 2); fiat flanges are held down by little plates of steel and such as screws 26 in such a manner that the entire sealing device rotates with the turret when it is turned. It will be easily understood that with such a sealing device, the circular apertures 16 containing specimen holders 17 and specimens 8 are enclosed into approximately trapezoidal spaces avoiding air leakages from outside or from another specimen holder to any one of the other specimen holders when the turret is in position and clamped down by means of the nut 30. If leaks begin to appear the nut 30 can be tightened or the sealing device can be replaced, an operation which only takes a few minutes.
What must still be understood is that apertures 20 and 21 in the base B are connected to two high vacuum devices, independent from each other, each device comprising a vacuum rotary pump and a diffusion pump in the purpose to obtain a 1O mm. Hg vacuum.
To operate the apparatus, specimens are placed in the holes 16 and the different pumping devices are started. When vacuum of 10* mm. Hg is obtained in apertures 2 and 20, the power pack creates a potential dilference between the filament 5 of the electron gun and the specimen 8 of about 10 kilovolts so that the electron bombardment of the specimen produces X-rays which emerge through an aperture 9 in the side of the base. I remind that this aperture 9 is in direct communication with the detecting device, which is of no interest for this present invention. When satisfactory information has been obtained from the specimen opposed to the filament in the aperture 2, the turret is turned through in a clockwise direction. In this way, the specimen just examined comes over the aperture 21 where it can be removed by acting the electro magnetic valve connecting the aperture 21 only to the atmospheric pressure.
In the same way, the specimen which was under 10- mm. Hg over the aperture 20 comes over aperture 2 and can be examined. Similarly, the specimen which was primarily over the aperture 21 under 10 mm. Hg comes over aperture 20 where it will be prepared to the vacuum of 10 mm. Hg necessary for the examination.
Each time a specimen is removed from the specimen holder 17 in the aperture 16 over the aperture 21, it can be replaced by another one and, after replacing the cap 18 with sealing means 19, air can be exhausted to mm. Hg by means of the vacuum rotary pump.
In this way, once the first cycle accomplished, the unit becomes a semi-automatic device.
A disadvantage of the known apparatus just explained is the fact that, regarding the electron bombardment, the specimen must be good electrical conductor.
Powders and insulators may be examined using this high vacuum device with the condition of replacing the electron bombardment by photon bombardment (X-ray fluorescence technique).
Accordingly, I have altered the design of the base B so that the aperture 2 (see FIGURES 4 and 5) is in fact a blind hole open at its top end. Towards the bottom end of the aperture 2 I provide two conical holes 41 and 42 (see FIGURE 5) in the part of the base surrounding the aperture 2, whose axes 43 and 44 are radial with respect to the vertical axis 45 of the aperture 2 and meet the axis 45 at vertically spaced positions. The angle of the axis of rotation of the turret is 45 to the vertical.
These conical holes enable me to mount an electron gun 48 (see FIGURE 6) in the base so that electrons can be shot up from an emitter 49 while directed by a concentrating head 50, onto the specimen and strike the specimen and then emerge through the window 9 along the line 46 as X-rays after striking the specimen. When this is done it is necessary to plug the left hand conical hole 41 hermetically with a bung 47 as shown in FIG- URE 6.
On the other hand when I wish to examine a specimen by an X-ray fluorescence technique, I replace the electron gun 48 by an electron gun 54, as shown in FIGURE 7, which has an emitter 55 and a concentrating head 56 and sends out electrons towards the axis 45 of the aperture 2. In the hole 41 previously occupied by the bung 47 I place an anti-cathode 52 with a pyramidal end piece whose faces make an angle of about 45 to the vertical and have inserts of tungsten or chromium or alternatively electrolytic deposits of these metals. In this case a beam of electrons from the gun 54 impinges on the anti-cathode and the resulting beam of X-rays passes upwards and impinges against the bottom face of the specimen 8. The resulting beam of secondary X-rays is reflected and then emerges from the apparatus through the aperture 9. The anti-cathode 52 has a space for the circulation of water cooling. Electron gun 54 is insulated from the base B. The emitter of the gun can be a heated filament connected with the power pack through a flexible cable.
While I have described particular forms of my invention in detail so that those skilled in the art can readily put my invention into practice, it is to be understood that the scope of the monopoly I seek in the United States is to be defined by the gist and scope of the following patent claims.
1. In an apparatus for examining a specimen by bombardment with radiation, comprising a non-rotary base with a horizontal lower face and an upper face inclined at an acute angle to said lower face, an aperture opening upwardly through the upper face, a rotatable turret mounted over the upper inclined face, at least two specimen holders in the turret, at such distances from the axis of rotation of the turret that the specimens can be aligned with the aperture in the base and means for evacuating the aperture and preventing air from coming into contact with the lower face of the specimen, the improvement in which the aperture in the base plate is formed as a hole open at its upper end and closed at its lower end and having provision therein to enable at least one source of radiation to be introduced into the said aperture through the side walls thereof.
2. An apparatus as claimed in claim 1 in which one source of radiation comprises an electron gun.
3. An apparatus as claimed in claim 1 in which an electron gun and an anti-cathode are introduced through the side walls of the aperture, in diametrically opposed relationship so as to bombard the sample with X-rays.
4. An apparatus as claimed in claim 3 in which the anti-cathode has a pyramidal end.
5. An apparatus as claimed in claim 1 in which the sources of radiation are introduced through holes, the axes of which are perpendicular to the axis of the aperture.
6. An apparatus as claimed in claim 1 in which an electron gun and an electron gun/anticathode combination are used together to bombard the sample simultaneously with electrons and X-rays.
References Cited UNITED STATES PATENTS 3,073,951 1/1963 Burdg 25041.9 3,099,743 7/ 1963 Ichinokawa 25049.5
RALPH G. NILSON, Primary Examiner.
A. L. BIRCH, Assistant Examiner.