1. A time-of-flight mass spectrometer having an energy supplier for giving ions to be analyzed a constant amount of energy to make the ions fly and a time-of-flight mass separator for separating the energy-given ions for each mass-to-charge ratio according to the difference in their flight time, wherein:
the mass separator includes a free-flight space in which ions are allowed to fly without being influenced by an electric field, a reflectron having a plurality of electrodes for creating an electric field which acts on the ions flying in the free-flight space to reflect the ions backward, and a voltage supplier for applying a direct-current voltage to each of the electrodes of the reflectron; and
the voltage supplier applies the direct-current voltage to each of the electrodes so that:
the electrostatic field created by the reflectron is virtually divided into a decelerating region for decelerating ions introduced thereinto and a reflecting region for reflecting backward the ions which have been decelerated through the decelerating region, the two regions being arranged along a traveling direction of the ions;
the potential distribution along a central axis of the electrostatic field in the decelerating region is either a potential distribution defined by one kind of function or a combination of potential distributions defined by a plurality of different kinds of functions along the central axis; and
the potential distribution along the central axis of the electrostatic field in the reflecting region is one kind of curved potential distribution for which a conditional equation to be satisfied by a flight time Tr(E) of the ions in the reflecting region is determined so that a total flight time required for an ion having an initial energy equal to a reference potential U0 set at a level equal to or lower than a maximal potential value Ud in the decelerating region to fly through a round-trip path including the free-flight space, will be equal to a total flight time required for an ion having an initial energy E higher than Ud to fly through a round-trip path including the free-flight space, a following equation is used as a relational equation for determining an inverse function x(U) of the curved potential distribution U(x) in the reflecting region realizing the flight time Tr(E), and an integral computation in that equation is either an analytic formula using a parameter defining the potential distribution of the electrostatic field in the decelerating field or a numerical solution obtained by a numerical computation:
x
\ue8a0
(
U
)
=
1
\u03c0
\ue89e
2
\ue89e
m
\ue89e
\u222b
0
U
\ue89e
T
r
\ue8a0
(
E
)
\ue89e
\uf74c
E
U
–
E
where m is a mass of an arbitrary ion of interest.
2. The time-of-flight mass spectrometer according to claim 1, wherein:
the decelerating region includes two-stage uniform decelerating electric fields defined by two kinds of functions each of which has a different linear potential gradient; and
with the reference potential U0 set to be equal to the maximal potential Ud of the decelerating region, the curved potential distribution along the central axis of the electrostatic field in the reflecting region is determined by an inverse function x(U) expressed as a following equation:
x
\ue8a0
(
U
)
=
L
\u03c0
\ue8a0
U
U
d
–
arctan
\ue89e
U
U
d
+
2
\ue89e
d
1
U
1
\ue89e
{
UU
d
–
(
U
+
U
d
)
\ue89e
\ue89e
arctan
\ue89e
U
U
d
}
–
2
\ue89e
(
d
1
U
1
–
d
2
U
2
)
\ue89e
{
UU
2
–
(
U
+
U
2
)
\ue89e
\ue89e
arctan
\ue89e
U
U
2
}
+
\u03c0
\ue89e
\ue89e
d
2
U
2
\ue89e
U
where L is a length of the free-flight space, d1 and d2 are ratios of lengths of the first-stage uniform decelerating electric field and the second-stage uniform decelerating electric field in the decelerating region to a length of the free-flight space, respectively, U1 is a potential height of the first-stage uniform decelerating electric field, and U2 is a potential height of the second-stage uniform decelerating electric field, hence Ud=U1+U2.
3. The time-of-flight mass spectrometer according to claim 2, wherein:
d1=d2=d; and
d is within the range of 0.01<d<0.5.
4. The time-of-flight mass spectrometer according to claim 2, wherein:
d1=d2=d; and
d has a value which satisfies a following equation:
d
=
u
2
3
2
\ue8a0
(
u
2
+
1
)
4
\ue89e
(
u
2
–
u
2
+
1
)
where u2=U2Ud.
5. The time-of-flight mass spectrometer according to claim 1, wherein:
the decelerating region includes two-stage uniform decelerating electric fields and an auxiliary free-flight space located between the two-stage uniform decelerating electric fields, the two-stage uniform decelerating electric fields being defined by two kinds of functions each of which has a different linear potential gradient, and the auxiliary free-flight space being free from influence of any electric field; and
with the reference potential U0 set to be equal to the maximal potential Ud of the decelerating region, the curved potential distribution along the central axis of the electrostatic field in the reflecting region is determined by an inverse function x(u) expressed as a following equation:
x
\ue8a0
(
u
)
=
L
\u03c0
\ue8a0
\u03c0
\ue89e
\ue89e
d
2
\ue89e
u
u
2
+
u
–
arctan
\ue89e
u
+
2
\ue89e
d
1
u
1
\ue89e
{
u
–
(
u
+
1
)
\ue89e
\ue89e
arctan
\ue89e
u
}
+
2
\ue89e
f
\ue89e
{
u
u
2
–
arctan
\ue89e
u
u
2
}
–
2
\ue89e
(
d
1
u
1
–
d
2
u
2
)
\ue89e
{
uu
2
–
(
u
+
u
2
)
\ue89e
\ue89e
arctan
\ue89e
u
u
2
}
where L is a length of the free-flight space, d1, f and d2 are ratios of lengths of the first-stage uniform decelerating electric field, the auxiliary free-flight space and the second-stage decelerating electric field in the decelerating region, respectively, U1 is a potential height of the first-stage uniform decelerating electric field, U2 is a potential height of the second-stage uniform decelerating electric field, hence Ud=U1+U2, and u=UUd, u1=U1Ud, and u2=U2Ud.
6. The time-of-flight mass spectrometer according to claim 5, wherein:
d has a value which satisfies a following equation:
d
=
(
2
\ue89e
f
+
u
2
3
2
)
\ue89e
(
u
2
+
1
)
4
\ue89e
(
u
2
–
u
2
+
1
)
provided that d1=d2=d.
7. The time-of-flight mass spectrometer according to claim 1, wherein:
the energy supplier includes a one-stage uniform accelerating electric field defined by a linear potential gradient sloped downward in a traveling direction of the ions, whereas the decelerating region includes two-stage uniform decelerating electric fields defined by two kinds of functions each of which has a different linear potential gradient; and
with the reference potential U0 set to be equal to the maximal potential Ud of the decelerating region, the curved potential distribution along the central axis of the electrostatic field in the reflecting region is determined by an inverse function x(u) expressed as a following equation:
x
\ue8a0
(
u
)
=
L
\u03c0
\ue8a0
\u03c0
\ue89e
\ue89e
d
2
u
2
\ue89e
u
+
u
–
arctan
\ue89e
u
+
(
a
u
a
+
2
\ue89e
d
1
u
1
)
\ue89e
{
u
–
(
u
+
1
)
\ue89e
\ue89e
arctan
\ue89e
u
}
–
2
\ue89e
(
d
1
u
1
–
d
2
u
2
)
\ue89e
{
uu
2
–
(
u
+
u
2
)
\ue89e
\ue89e
arctan
\ue89e
u
u
2
}
where Ua is a highest potential of the uniform accelerating electric field, L is a length of the free-flight space, a, d1, and d2 are a ratios of a lengths of the uniform accelerating electric field, the first-stage uniform decelerating electric field and the second-stage decelerating electric field in the decelerating region, respectively, U1 is a potential height of the first-stage uniform decelerating electric field, U2 is a potential height of the second-stage uniform decelerating electric field, hence Ud=U1+U2, and u=UUd, u1=U1Ud, u2=U2Ud and ua=UaUd.
8. The time-of-flight mass spectrometer according to claim 7, wherein:
d has a value which satisfies a following equation:
4
\ue89e
d
\ue89e
u
2
–
u
2
+
1
u
2
3
2
\ue8a0
(
u
2
+
1
)
=
1
–
2
\ue89e
a
u
a
provided that d1=d2=d.
9. The time-of-flight mass spectrometer according to claim 1, wherein:
the decelerating region includes a one-stage uniform decelerating electric field defined by a function having a linear potential gradient; and
with the reference potential U0 set to be equal to the maximal potential Ud of the decelerating region, the curved potential distribution along the central axis of the electrostatic field in the reflecting region is determined by an inverse function x(U) expressed as a following equation:
x
\ue8a0
(
U
)
=
L
\u03c0
\ue8a0
\u03c0
\ue89e
\ue89e
d
\ue89e
U
U
d
+
(
1
+
2
\ue89e
d
)
\ue89e
U
U
d
–
(
1
+
2
\ue89e
d
+
2
\ue89e
d
\ue89e
U
U
d
)
\ue89e
\ue89e
arctan
\ue89e
U
U
d
where L is a length of the free-flight space, d is a ratio of a length of the decelerating region to a length of the free-flight space, and d is set within a range of 0.2<d<0.8.
10. The time-of-flight mass spectrometer according to claim 9, wherein d is 0.25.
11. The time-of-flight mass spectrometer according to claim 1, wherein:
the energy supplier includes a one-stage uniform accelerating electric field defined by a linear potential gradient sloped downward in a traveling direction of the ions, and the decelerating region includes a one-stage uniform decelerating electric field defined by a function having a linear potential gradient; and
with the reference potential U0 set to be equal to the maximal potential Ud of the decelerating region, the curved potential distribution along the central axis of the electrostatic field in the reflecting region is determined by an inverse function x(u) expressed as a following equation:
x
\ue8a0
(
u
)
=
L
\u03c0
\ue8a0
\u03c0
\ue89e
\ue89e
du
+
u
–
arctan
\ue89e
u
+
(
a
u
a
+
2
\ue89e
d
)
\ue89e
{
u
–
(
u
+
1
)
\ue89e
\ue89e
arctan
\ue89e
u
}
where Ua is a highest potential of the uniform accelerating electric field, L is a length of the free-flight space, a and d are ratios of lengths of the uniform accelerating electric field and the decelerating region to a length of the free-flight space, respectively, u=UUd, and ua=UaUd.
12. The time-of-flight mass spectrometer according to claim 11, wherein:
d has a value which satisfies:
4d=1\u2212(2aua).
13. The time-of-flight mass spectrometer according to claim 1, wherein:
the voltage supplier uses resistive division to apply a voltage to at least one electrode among the plurality of electrodes constituting the reflectron, and the interval between the aforementioned one electrode and a neighboring electrode is adjusted so as to create a desired potential distribution.
14. The time-of-flight mass spectrometer according to claim 13, wherein:
the voltage supplier includes a ladder-type resistive divider circuit designed to separately apply a voltage to each of the electrodes other than those at both ends among the plurality of electrodes constituting the reflecting region in the reflectron.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A tap for a gas or liquefied gas cylinder, comprising:
a tap body defining a base end and a head end at the opposite ends of the tap body, and said tap body having a longitudinal bore extending therethrough and opening out at the base end and at the head end of the tap body;
a movable tap stem-closure element assembly tightly mounted within the tap body longitudinal bore and movable to open and close the tap, said tap stem-closure element assembly being supported within the longitudinal bore solely by the tap body which surrounds said movable assembly directly so as to provide only one single annular interfacial boundary to be sealed to prevent gas leakage at the head end of the tap body;
wherein said longitudinal bore has a sufficient diameter so that the tap stem-closure element assembly is adapted to be installed into the longitudinal bore through the base end portion of the tap body; and said tap further comprising
a fixed seat formed on a seat element that is separate from the tap body and adapted to be installed into the longitudinal bore through the base end portion of the tap body.
2. The tap according to claim 1, wherein the seat element is an elongated replaceable seat tube threaded into the longitudinal bore.
3. The tap according to claim 2, wherein the seat tube has an enlarged head accessible at the base end of the tap body to permit tightening and unscrewing of the seat tube.
4. The tap according to claim 1, wherein a seal means is provided between the seat element and the tap body.
5. The tap according to claim 3, wherein an annular gas passage is formed between the seat tube and the tap body, said gas passage being in communication on one side with the exterior of the tap at the base end thereof and at another side with a cavity formed in the tap body and adapted to receive a safety valve.
6. The tap according to claim 5, wherein the annular passage is formed by a length of reduced diameter portion of the seat tube, the seat of the seat tube being formed to ensure communication between the annular passage and the exterior of the tap at the base end of the tap body.
7. The tap according to claim 1, wherein a first radial abutment surface facing axially towards the seat element is formed between two portions of different diameter of the longitudinal bore and a second radial counter-abutment surface is formed on the movable assembly between the first radial abutment surface and the seat element, said second radial counter-abutment surface facing oriented towards the first radial abutment surface so as to retain the movable assembly within the longitudinal bore.
8. The tap according to claim 7, wherein the movable assembly is received with a sliding fit in at least one of the two portions of different diameter of the longitudinal bore.
9. The tap according to claim 8, wherein the movable assembly is provided with an outer thread screwed into an inner thread of at least one of the two portions of different diameter of the longitudinal bore.
10. The tap according to claim 9, wherein the movable assembly is threadedly engaged in the larger diameter portion of the longitudinal bore.
11. The tap according to claim 10, wherein the larger diameter portion of the longitudinal bore comprises a single internal thread whereinto the movable element and the seat element are threadedly engaged.
12. The tap according to claim 9, wherein the movable assembly comprising the tap stem and the closure element is formed of one single piece.
13. The tap according to claim 10, wherein the closure element of the movable assembly is a member separate from the tap stem.
14. The tap according to claim 13, wherein the two members constituting the movable element are unitary in rotation with one another, but the closure element is displaceable axially with respect to the tap stem.
15. The tap according to claim 14, wherein the closure element is threadedly engaged in the portion of larger diameter of the different diameter portions of the longitudinal bore and the tap stem is received with a sliding fit in at least one of the two portions of different diameter of the longitudinal bore.
16. The tap according to claim 13, wherein the seat tube is threadedly engaged in the same internal thread of the longitudinal bore as the closure element.
17. The tap according to claim 13, wherein the closure element is coupled to the tap stem so as to be axially displaceable therewith while permitting rotation of the tap stem with respect to the closure element.
18. The tap according to claim 17, wherein the tap stem is provided with an external thread that is threadedly engaged into the portion of smaller diameter of the different diameter portions of the longitudinal bore and wherein the closure element is received with a sliding fit in the portion of large diameter of the different diameter portions of the longitudinal bore.
19. The tap according to claim 1, wherein a sealing means is disposed between the movable assembly and the longitudinal bore.
20. A tap for a gas or liquefied gas cylinder comprising a tap body, a tap stem-closure element assembly movable between a closed position and an open position, and an annular element joined to the tap stem for rotation therewith and disposed exteriorly of the tap body, and an external ring disposed about the tap body and retained against rotation with respect thereto, said ring being mounted by a helical engagement means on the exterior of the annular element so that the ring effectuates an axial telescoping motion with respect to the annular element and the tap body in response to rotational movement of the tap stem and the annular element to cover or uncover a means for signaling the open position or the closed position of the tap.
21. The tap according to claim 20, wherein the indicating means is fixed stationary with respect to the tap body.
22. The tap according to claim 20, wherein the helical engagement means is an internal thread of the ring and an external thread of the annular element.
23. The tap according to claim 22, wherein the tap stem-closure element assembly is provided with an external thread in engagement with an internal thread formed in the interior of the tap body, and wherein the engaged threads of the ring and the annular element have a higher pitch than the engaged threads of the tap body and the tap stem-closure element assembly.
24. The tap according of claim 20, wherein the external surface of the tap body is provided with an hexagonal shape engaged by an internal portion of corresponding shape of said ring.
25. The tap according to claim 20, wherein the signaling means is provided on the external surface of the tap body, said signaling surface having a different color than adjoining parts of the tap and being concealed by the ring in the open position of the tap and exposed by the axial motion of the ring when the tap stem is rotated in the direction to close the tap.
26. The tap according to claim 20, wherein the signaling means is formed by the annular element joined to the tap stem for rotation therewith, said annular element having a different color than adjoining parts of the tap and being concealed by the ring in the closed position of the tap and partly exposed by the axial movement of the ring when the tap stem is rotated in a direction to open the tap.
27. The tap according to claim 20, wherein an actuating wheel is fixed to the tap stem to rotate the same.
28. The tap according to claim 27, wherein the actuating wheel is a member separate from the annular element joined to the tap stem for rotation therewith, and wherein the tap stem is provided with a weakening zone disposed approximately at the interface between the actuating wheel and the annular element.
29. The tap according to claim 27, wherein the actuating wheel and the annular element are formed of one single piece.