Rotatable support for selectively aligning a window with the channel of a probe

A mechanism is disclosed for selectively aligning one of two different radiation passing windows with the channel of a measuring device. The measuring device includes an elongated tubular probe having a channel formed therein. A spherical cap, having a diameter less than the diameter of the probe, is mounted to the end of the probe, and is rotatable between a first and second position. A pair of windows are mounted in the cap in a manner such that when the cap is oriented in the first position, the first window is aligned with the channel, and when the cap is oriented in the second position, the second window is oriented with the channel. In the preferred embodiment, an outer tubular member is mounted around the probe and includes axially projecting teeth which engage with a spur gear connected to the rotatable cap. The rotation of the outer tubular member relative to the probe drives the spur gear for rotating the cap.

The subject invention relates to a new and improved mechanism for 
selectively aligning a radiation passing window with a detecting device. 
The subject mechanism is designed to operate in low pressure conditions 
and is compact in construction to facilitate improved detection 
capability. 
BACKGROUND OF THE INVENTION 
In the prior art, many techniques have been developed for determining the 
composition of a sample. One of the more common techniques is spectroscopy 
wherein electromagnetic energy emitted from a sample is measured and 
evaluated to determine the elements contained in the sample. While there 
are many types of spectroscopic measurement methods, the subject invention 
is particularly adapted for use with X-ray detectors. In the latter 
technique, a detector is provided which senses X-rays emanating from a 
sample. 
Using an X-ray fluorescent analyzer, a spectrum associated with the sample 
can be generated. By analyzing the spectral data, the composition of the 
sample can be determined. 
X-ray detection equipment is typically designed to operate in conjunction 
with electron microscopes, such as scanning electron microscopes or 
transmission electron microscopes. The specimen chamber in these electron 
microscopes must be operated in a vacuum. This requirement imposes rather 
stringent design criteria on X-ray detection devices since they must be 
compatible with a vacuum environment. 
In the prior art, a number of X-ray detection devices have been developed 
for use with electron microscopes. The devices are generally provided with 
an elongated tubular member or probe, which is typically connected to some 
form of frame for housing the hardware of the device. The opposed free end 
of the tubular member is received in the specimen chamber of the electron 
microscope, and is sealed with a radiation passing window. The interior of 
the tubular member contains a channel for receiving the X-ray radiation 
entering the probe through the window. An X-ray sensor, such as a 
lithium-drifted silicon device, is mounted in the channel of the probe, 
behind the window. Since the sensor requires a vacuum to operate, the 
channel of the probe must be sealed and evacuated. 
As mentioned above, the free end of the probe is provided with some form of 
window to permit the X-ray radiation to enter the channel and reach the 
sensor. More particularly, a relatively thin window, formed for example, 
from aluminum foil, is provided to permit a high percentage of X-rays, 
emanating from the sample, to enter the channel. Unfortunately, a thin 
aluminum window, while effective for passing a large amount of radiation, 
is structually weak. This weakness would pose no difficulties if the 
window were never subjected to the strains of air pressure. However, in 
normal procedures, each time a new sample is introduced into the electron 
microscope, the specimen chamber must be exposed to full air pressure 
conditions. Since a vacuum is present in the channel of the probe, the 
thin film window is subjected to an extreme pressure differential when the 
microscope chamber is exposed to atmospheric pressure. This pressure 
differential will result in the rupture of the thin film window. If the 
thin film window is ruptured, the shock of the abrupt pressure change in 
the probe can damage the sensor. 
Accordingly, a means must be provided to prevent the rupture of the thin 
film window. This object is achieved in some prior art detectors by 
providing a second, thicker and stronger window, which will resist 
collapse when subjected to normal air pressure. The thicker window may be 
in the form of a beryllium foil, which will transmit a portion of the 
X-ray spectrum, particularly at higher energy levels. Since the beryllium 
window will pass some radiation, it can be used in many measurement 
situations. However, many test techniques require that lower level energy 
radiation be detected, such that a beryllium window alone is insufficient. 
In the prior art devices which rely on a two-window construction, a means 
must be provided for selectively aligning one of the two windows with the 
channel of the probe. In operation, the thicker beryllium window is 
initially aligned with the channel of the probe. After the sample has been 
placed in the electron microscope and the specimen chamber is evacuated, a 
mechanism must operate to move the thin aluminum film window into 
alignment with the channel. When the testing is complete, the beryllium 
window is moved back into alignment with the channel, prior to the 
pressurization of the chamber, thereby preventing the rupture of the thin 
film window. 
The mechanisms used in the prior art were capable of moving the thin film 
window into and out of alignment with the channel. However, the latter 
mechanisms tended to be relatively cumbersome, which inhibited optimum 
measurement capability. For example, one known device included the use of 
a large outer tube having both windows mounted thereon. The outer tube was 
disposed around the probe and mounted for rotational movement along an 
axis offset from the axis of the probe. By rotating the outer tube, the 
windows could be brought into selective alignment with the channel. 
Unfortunately, the use of the large outer tube added significantly to the 
total diameter of the probe. This extra size created some difficulties. 
More particularly, many electron microscopes could not accommodate a probe 
having a large diameter. In addition, because of the geometry of the 
specimen chamber, it was difficult to move a large diameter probe into 
close proximity with the sample. Since radiation levels fall off as 
function of the distance squared, it is highly desirable to be able to 
position the probe as close to the sample as possible. 
Some devices found in the prior art are provided with only a single, thin 
window. In the latter devices, the thin film window is protected by a gate 
valve. In use, when the specimen chamber is evacuated, the gate in the 
valve is retracted, exposing the window to permit radiation to pass into 
the probe towards the sensor. Thus, a functional window support can be 
manufactured which does not include a second, thicker window. However, a 
second, thicker window provides enhanced versatility by permitting sensing 
in some measurement situations. 
Accordingly, it is an object of the subject invention to provide a new and 
improved mechanism for selectively aligning at least one radiation passing 
window with the channel of a detector, that overcomes the shortcomings of 
the prior art devices. 
It is another object of the subject invention to provide a new and improved 
mechanism which is relatively compact in configuration, permitting the 
tubular probe to be moved relatively close to the sample for enhanced 
sensitivity. 
It is a further object of the subject invention to provide a new and 
improved mechanism, for selectively aligning one of two different windows 
with the channel, which is operable from a point spaced from the end of 
the probe. 
It is still another object of the subject invention to provide a new and 
improved mechamism for selectively aligning one of two different windows 
with the channel of a probe wherein at least one of said windows is 
readily replaceable. 
It is still a further object of the subject invention to provide a new and 
improved mechanism for selectively aligning one of two different windows 
with the channel of a probe which includes an interlock means to prevent 
the relatively fragile thin film window from being moved into alignment 
with the channel until a vacuum has been established in the specimen 
chamber of the microscope. 
SUMMARY OF THE INVENTION 
In accordance with these and many other objects, the subject invention 
provides for a mechanism capable of selectively aligning at least one 
radiation passing window with a channel of a detection device. The 
detection device includes a tubular probe, mounted to a frame, and having 
an elongated channel formed therein. An X-ray sensor is mounted within the 
channel. The free end of the probe can be introduced into the specimen 
chamber of an electron microscope whereby radiation emitted from a sample 
will enter the channel of the probe to reach the sensor mounted therein. 
In accordance with the subject invention, a cap is rotatably mounted at the 
free end of the tubular probe. The axis of rotation of the cap is 
perpendicular to the longitudinal axis of the probe. The cap is rotatable 
between a first and second position. The adjacent surfaces of the cap and 
the probe are provided with complementary spherical configurations. A 
means is provided to effect a seal between these adjacent surfaces. A 
first window is mounted on the cap and is located such that it will be 
aligned with the channel when the cap is oriented in the first position. 
Preferably, a second window is mounted in the cap in a manner to be 
aligned with the channel when the cap is oriented in the second position. 
In the preferred embodiment, a means is provided for rotating the cap. The 
rotation means includes a spur gear mounted to the cap. An outer tubular 
member is rotationally mounted around the inner tubular probe. The end of 
the outer tubular member adjacent the cap is provided with axially 
projecting teeth engageable with the spur gear. The rotation of the outer 
tube drives the spur gear, causing the rotation of the cap. 
A lever means may be connected to the outer tubular member at a point 
spaced from the cap to facilitate the rotational movement. In the 
preferred embodiment, a locking mechanism is provided to prevent the 
inadvertent alignment of the thin film window with the channel, unless the 
specimen chamber is evacuated, thereby reducing the likelihood of damage 
to the window. The preferred embodiment also includes a construction 
permitting the ready replacement of the thin film window. 
Further objects and advantages of the subject invention will become 
apparent from the following detailed description taken in conjunction with 
the drawings in which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, the subject invention relates to a new and 
improved mechanism 10 for selectively aligning one of two different 
radiation passing windows with the channel of a probe of a detector. In 
brief, the subject invention includes an inner tubular member or probe 20 
having an elongated channel 22 formed therein. Probe 20 projects through 
frame 26 and is connected to housing 46. The free end of probe 20 is 
provided with a cap 28 which is rotatably mounted thereto. Cap 28 can be 
provided with a removable insert 30 to facilitate the ready replacement of 
one of the windows. An outer tubular member 32 is mounted about probe 20 
and has axially projecting teeth 34 adapted to engage with the teeth of 
spur gear 36. The rotation of the outer tube 32 relative to the inner tube 
20 drives spur gear 36 for rotating the cap means, as described more fully 
hereinbelow. A lever 38 may be provided to facilitate the rotation of the 
outer tube. Preferably, a locking means 40 is provided to prevent the 
inadvertent rotation of the cap means. 
Having outlined the major components of the subject invention, the new and 
improved mechanism 10 will be described in greater detail. More 
particularly, and referring in addition to FIGS. 3 to 8, the subject 
invention is adapted for use with a detector designed for operation with 
an electron microscope. The inner tubular member or probe 20 is typically 
inserted within the specimen chamber of an electron microscope (not 
shown). The front plate or flange 44 of frame 26 is bolted to the outer 
cover of the specimen chamber of the microscope in a manner to create an 
airtight seal. The depth which the probe is introduced within the chamber 
can be controlled by adjusting the position of control housing 46. The 
housing, and the elements connected thereto, are slidable in the direction 
illustrated by arrows A in FIG. 1. As described more fully hereinabove, an 
accordian-type bellows 48 is provided to permit this adjustment. 
Referring to FIG. 4, it will be seen that probe 20 is provided with a 
channel 22 that opens outwardly toward the free end of the probe. X-ray 
radiation, which is received through the end of the channel, is 
transmitted therealong to a sensor 50, illustrated schematically. The 
sensor is typically a lithium-drifted silicon detector. 
In typical electron microscope devices, stray electrons will often enter 
the probe. If these electrons reach the sensor, they will interfere with 
the measurements. Accordingly, a pair of magnets 52 are mounted in the 
probe surrounding channel 22, in front of sensor 50. An iron ring 54 is 
mounted around the magnet to define pole positions. In operation, 
negatively-charged electrons are deflected by the magnets 52. The 
deflected electrons will pass into annular traps 56 preventing them from 
being detected by the sensor 50. 
In order to achieve satisfactory measurement, the internal chamber of the 
probe is maintained in a vacuum condition. Accordingly, cap 28 is 
configured to maintain the desired vacuum. As illustrated in FIG. 2, cap 
28 is provided with a spherical configuration, along the portions of the 
surface which contact the end surface 60 of probe 20. In addition, the end 
surface 60 of probe 20 is provided with a complementary spherical 
configuration, to facilitate the rotational movement between the cap 28 
and the probe 20. A means for sealing the end of the probe, such as an 
O-ring 62, is provided. 
As seen in the figures, the maximum diameter of cap 28 is less than the 
diameter of the cylindrical probe. By this arrangement, the probe may be 
used in conjunction with a specimen chamber having a relatively smaller 
entry port. In addition, the sensor 50 can be brought into closer 
proximity with the sample thereby enhancing sensitivity. 
Cap 28 is rotatably mounted to the end of tube 20, between a pair of 
axially projecting brackets 66. A pair of pins 68 are formed on cap 28, 
and are receivable in aligned apertures 70 provided in bracket 66. In the 
illustrated embodiment, cap 28 is rotatable through a 90.degree. arc, 
between a first position, shown in FIGS. 3 and 4, and a second position, 
shown in FIG. 5. As discussed more fully hereinbelow, radiation-passing 
windows located in cap 28 are disposed such that they will be selectively 
aligned with channel 22 in response to the rotation of the cap between the 
first and second positions. 
While the illustrated embodiment is depicted with a two-window 
construction, the scope of the subject invention is intended to cover 
other variations. As noted above, some devices may only require a single, 
radiation passing window which can be selectively moved into alignment 
with the channel. Also, a cap construction having three windows can be 
provided. Alternatively, a two-window cap, which is movable between three 
positions is also envisioned. Three positions would permit the cap to be 
oriented with both windows exposed allowing the windows to be serviced 
while the cap remains mounted to the probe thereby maintaining the vacuum 
within the channel. In the latter construction, cap 28 would be movable 
through an arc of 110 degrees with 55 degrees separating each orientation. 
As discussed above, in operation, probe 20 is mounted within the specimen 
chamber of an electron microscope. At the termination of each measurement 
cycle, when the chamber is opened to introduce a new sample, the probe is 
subjected to normal air pressure conditions. Accordingly, the end of the 
probe must be provided with a relatively rigid covering such that the 
vacuum generated in the channel 22 can be maintained. In the preferred 
embodiment of the subject invention, a relatively thick window 74 is 
mounted in the cap. Window 74 is preferably formed from a foil having a 
beryllium composition and is on the order of 8.5 to 12.7 microns thick. 
Since the beryllium window is relatively rigid, and not subject to 
rupture, it may be securely mounted in the cap. The beryllium window will 
pass a portion of the X-ray radiation and is therefore suitable for 
certain measurement applications. However, in many measurement situations, 
there is a need to provide a thin film window which will transmit a 
greater percentage of the lower energy X-rays. In the preferred embodiment 
of the subject invention, a thin film window 80 is provided which is 
replaceably mounted in the cap. Thin film window 80 may be formed from an 
aluminum foil having a thickness on the order of 2,000 angstroms or 0.2 
microns. However, where the pump of the electron microscope is capable of 
generating a very good vacuum, the "thin" window can be defined simply by 
an aperture. As can be appreciated, the latter construction is possible if 
the sensor will not be exposed to any damaging or interferring conditions 
present in the specimen chamber. 
While the subject invention is designed to reduce the likelihood of rupture 
of this thin film window 80, in some situations, rupture of the window is 
unavoidable. For example, if power is interrupted to an electron 
microscope, the vacuum may be inadvertently lost which could cause the 
rupture of the thin film window. Accordingly, the subject invention 
provides a means for ready replacement in the event that an unforeseen 
accidental rupture takes place. 
In accordance with the subject invention, thin film window 80 is mounted in 
a generally cylindrical, hollow insert 30. Insert 30 is receivable in an 
arcuate recess 82 formed in the cap 28. A circular aperture 84, formed in 
the bottom of cap 28, is adapted to tightly receive the end of insert 30. 
Preferably, insert 30 is formed with a pair of wedge tabs 85, which are 
adapted to abut the sidewall of recess 82 for enhancing the engagement 
between the insert and the recess. 
Insert 30 is also provided with a pair of aligned apertures 86. Apertures 
86 are disposed to be aligned with beryllium window 74 when the insert is 
mounted within the cap 28. Accordingly, X-ray radiation entering the probe 
along a path illustrated by arrow B in FIG. 4 can pass through apertures 
86 and beryllium window 74 into the channel to be detected by sensor 50. 
Of course, if the cap is only constructed with a single, thin window 
arrangement, there would be no need to provide apertures 86. 
As discussed above, after the probe and sample are placed within the 
electron microscope the specimen chamber is evacuated. At this time, the 
pressure differential between the specimen chamber and the channel of the 
probe is not severe. Accordingly, the relatively more fragile thin film 
window 80 can be used as an interface between the probe and the specimen 
chamber without fear of rupture. In order to place the thin window in 
place, cap 28 is rotated in a direction indicated by arrows C in FIG. 5. 
In this orientation, X-ray radiation traveling a path indicated by arrow D 
in FIG. 5, will pass through aperture 88 in the top of the insert and 
through the thin film window 80 towards detector 50. 
When the measurement of the sample is complete, cap 28 is rotated back to 
its initial position, illustrated in FIG. 4, prior to the repressurization 
of the specimen chamber. By this arrangement, the beryllium window is 
reoriented back into alignment with the channel such that the pressure 
differential, which is created when the vacuum in the chamber is released, 
will not damage or rupture thin film window 80. 
In addition to the new and improved mechanism 10 for housing the radiation 
transmitting windows, the subject invention further includes a new and 
improved means for rotating cap 28. The rotation means includes, a spur 
gear 36, having radially projecting teeth. Spur gear 36 is fixedly mounted 
to one of the pins 68 of cap 28. An outer driving tube 32 is mounted 
coaxially around tubular probe 20. Outer tube 32 is provided with a set of 
axially projecting teeth 34 disposed to be in engagement with the spur 
gear 36. The rotation of the outer tube 32 relative to the inner tube 
drives spur gear 36 which rotates cap 28. 
Since the portion of probe 20, located forward of mounting flange 44, is 
disposed within the evacuated specimen chamber of the electron microscope, 
the actuation means for rotating the cap must be located to the rear of 
the flange. Referring more particularly to FIGS. 1, 7 and 8, it will be 
seen that the actuation means includes an annular ring 90 fixedly mounted 
around outer tube 32. A radially projecting lever member 38 is provided to 
facilitate the rotation of the outer tube. 
In accordance with the subject invention, a locking means is provided to 
prevent the operator from inadvertently moving the thin film window into 
alignment with the channel prior to the establishment of a vacuum in the 
specimen chamber of the microscope. More particularly, a locking arm 94 is 
provided which is formed integrally with, and projects radially outwardly 
from annular ring 90. The free end of 94 is provided with a slot 96. The 
locking means further includes a solenoid 98 having a reciprocating 
plunger 100. Solenoid 98 is mounted in a manner such that plunger 100 is 
aligned with slot 96 of locking arm 94 when the cap 28 is in the first 
position. As long as plunger 100 is engaged with locking arm 94, the 
operator will be unable to rotate the outer tube 32 in an effort to move 
the cap into the second position, where the film thin window 80 would be 
subject to rupture. 
The operation of solenoid 98 is controlled by a switch (not shown). The 
switch, which is normally disabled, is connected to a pressure detector 
102. Pressure detector 102 is utilized to sense the pressure level in the 
specimen chamber. When the detector indicates that a vacuum has been 
established, an electrical signal is sent to enable the switch controlling 
solenoid 98. Thus, only after a vacuum has been established in the test 
chamber may the operator actuate the switch causing the plunger 100 in the 
solenoid to retract. Once the locking means has been disengaged, the outer 
tube 32 may be rotated, utilizing lever 38, to bring the thin film window 
into alignment with channel 22. 
In order to facilitate accurate alignment of the thin film window, a 
spring-biased button 104 is provided. More particularly, and as 
illustrated in FIG. 8, the spring-biased button 104 is intended to engage 
with a V-shaped detent 105, located radially inwardly from slot 96 on 
locking arm 94. When outer tube 32 is rotated to the second position, the 
engagement of the spring-biased button 104 with detent 105 will supply a 
positive locking sensation to the mechanism to alert the operator of 
proper alignment. 
As discussed above, the depth which the probe is introduced into the 
specimen chamber may be adjusted. Referring to FIG. 1, it will be seen 
that tube 32 projects through an aperture 106 in flange 44. The diameter 
of outer tube 32 is smaller than the diameter of aperture 106 such that a 
nonsealing mount is achieved. A metal accordian-type bellows 48 is affixed 
to the rear of flange 44 in a manner to form an air-tight construction. By 
this arrangement, the probe may be moved in an axial direction, in order 
to bring the end thereof into close proximity with the sample, for 
maximizing sensitivity. 
In summary, there has been disclosed a new and improved mechanism for 
selectively aligning a radiation passing window with the channel of a 
detector. More particularly, a tubular probe 20 is provided having a 
channel 22 therein. A cap 28 is rotatably mounted to the free end of the 
tubular probe 20. Cap 28, having a diameter less than the probe, is 
rotatable between first and second positions. In the preferred embodiment, 
a pair of radiation passing windows 74 and 80 are mounted in the cap in a 
manner such that one window will be aligned with the channel 22 of the 
tube when the cap is oriented in the first position, while the remaining 
window will be aligned with the channel when the cap is rotated to the 
second position. 
The subject invention further includes a means for rotating the cap 28 
which is spaced from the end of the probe. An outer tube 32 is mounted 
about the probe and includes axially projecting teeth which engage with 
the spur gear 36 connected to the cap. The rotation of the outer tube 32 
relative to probe 20 drives spur gear 36 for rotating cap 28. A lever 38 
is mounted to the outer tube 32 to facilitate its rotation. In a preferred 
embodiment, a locking mechanism is provided to prevent the operator from 
rotating the thin film window into alignment with the channel until a 
vacuum is established in the test chamber. 
While the subject invention has been described with reference to a 
preferred embodiment, it is to be understood that various other changes 
and modifications could be made therein, by one skilled in the art, 
without varying from the scope and spirit of the subject invention as 
defined by the appended claims.