Transmitting-type target and X-ray generation tube provided with transmitting-type target
A transmissive-type target includes a target layer, and a transmissive substrate configured to support the target layer. The transmissive substrate has a pair of surfaces facing each other and is formed of polycrystalline diamond. In the transmissive substrate, one of the pair of surfaces includes polycrystalline diamond having a first average crystal grain diameter which is smaller than a second average crystal grain diameter of polycrystalline diamond included on the other surface opposing thereto. The target layer is supported by any one of the pair of surfaces.
1. A transmitting-type X-ray target comprising:
a target layer; and
a transmissive substrate configured to support the target layer,
wherein the transmissive substrate includes a first surface and a second surface facing each other and is formed of polycrystalline diamond,
wherein the first surface includes polycrystalline diamond having a first average crystal grain diameter which is smaller than a second average crystal grain diameter of polycrystalline diamond included in the second surface, and
wherein the target layer is supported by the first surface which includes the polycrystalline diamond having the first average crystal grain diameter, such that a grain diameter of the polycrystalline diamond increases from the first surface towards the second surface.
2. The transmitting-type target according to claim 1 , wherein an average line density of grains of the polycrystalline diamond decreases from the first surface towards the second surface.
3. The transmitting-type target according to claim 1 , wherein a ratio of the first average crystal grain diameter to the second average crystal grain diameter is 0.75 or lower.
4. The transmitting-type target according to claim 3 , wherein the ratio of the first average crystal grain diameter to the second average crystal grain diameter is 0.2 or lower.
5. The transmitting-type target according to claim 1 , wherein the first average crystal grain diameter is between 5 μm and 50 μm.
6. The transmitting-type target according to claim 1 , wherein the second average crystal grain diameter is 100 μm or larger.
7. The transmitting-type target according to claim 1 , wherein the transmissive substrate has column-shaped crystal grains extending in a substrate thickness direction from the first surface toward the second surface.
8. The transmitting-type target according to claim 1 , wherein the target layer is supported by the second surface which includes the polycrystalline diamond having the second average crystal grain diameter.
9. The transmitting-type target according to claim 8 , wherein the transmissive substrate is a self-contained diamond formed by being deposited on a seed crystal substrate by the chemical vapor-phase deposition method and removing the seed crystal substrate,
wherein the first surface is a surface on the side of a growing surface side of the self-contained diamond, and the second surface is a seed crystal substrate side surface of the self-contained diamond.
10. The transmitting-type target according to claim 1 , wherein a ratio of the second average crystal grain diameter to the first average crystal grain diameter is 1.3 or higher.
11. The transmitting-type target according to claim 10 , wherein the ratio of the second average crystal grain diameter to the first average crystal grain diameter is 5 or higher.
12. The transmitting-type target according to claim 1 , wherein a crystal grain field of the polycrystalline diamond forming the transmissive substrate contains sp2 bonding.
13. The transmitting-type target according to claim 12 , wherein the sp2 bonding is determined by Raman shift of 1580 cm −1 in a Raman spectrometry.
14. The transmitting-type target according to claim 1 , wherein the polycrystalline diamond forming the transmissive substrate has a crystal grain diameter distribution in the substrate thickness direction, and
the average crystal grain diameter Dm is determined by the following expression when the crystal grain diameter distribution is sampled by the number of samples n in a crystal grain diameter axis
D
m
=
∑
i
=
1
n
(
D
i
S
i
)
∑
i
=
1
n
(
S
i
)
where a crystal grain diameter larger than a crystal grain diameter D i-1 and not larger than D i is D i , a cumulated surface area larger than the crystal grain diameter D i-1 and not larger than D i is S i , i is an integer from 1 to n, and a crystal grain diameter D 0 is an actual number not smaller than 0.
15. The transmitting-type target according to claim 14 , wherein the average crystal grain diameter is determined by an electron backscattering diffraction method.
16. The transmitting-type target according to claim 1 , wherein the transmissive substrate is self-contained diamond formed by being deposited on a seed crystal substrate by a chemical vapor-phase deposition method and removing the seed crystal substrate,
wherein the second surface is a surface on the side of a growing surface side of the self-contained diamond, and the first surface is a seed crystal substrate side surface of the self-contained diamond.
17. The transmitting-type target according to claim 1 , wherein the target layer contains at least one metal material selected from a group consisting of tungsten, tantalum, and molybdenum.
18. The transmissive target according to claim 17 , wherein the target layer contains a carbide of the selected metal material.
19. The transmitting-type target according to claim 1 , wherein the thickness of the transmissive substrate is between 0.3 μm and 3 mm.
20. The transmitting-type target according to claim 1 , wherein the thickness of the target layer is between 1 μm and 12 μm.
21. The transmitting-type target according to claim 1 , wherein the crystal grain diameter of the polycrystalline diamond is smaller on the first surface that supports the target layer than the crystal grain diameter on the second surface opposed thereto.
22. An X-ray generation tube comprising:
transmitting-type target;
an electron emitting source having an electron emitting portion configured to emit electrons toward the target layer; and
an enclosure having an evacuated internal space,
wherein the electron emitting portion and the target layer are arranged in the internal space or on an inner surface of the enclosure, and
wherein transmitting-type target comprises:
a target layer; and
a transmissive substrate configured to support the target layer,
wherein the transmissive substrate includes a first surface and a second surface facing each other and is formed of polycrystalline diamond,
wherein the first surface includes polycrystalline diamond having a first average crystal grain diameter which is smaller than a second average crystal grain diameter of polycrystalline diamond included in the second surface, and
wherein the target layer is supported by the first surface which includes the polycrystalline diamond having the first average crystal grain diameter, such that a grain diameter of the polycrystalline diamond increases from the first surface towards the second surface.
23. An X-ray generation apparatus comprising:
an X-ray generation tube according to claim 22 ;
a drive circuit electrically connected to the target layer and the electron emitting portion respectively and configured to output a tube voltage applied between the target layer and the electron emitting portion.
24. An X-ray imaging system comprising:
an X-ray generation apparatus according to claim 23 ; and
an X-ray detector configured to detect an X-ray emitted from the X-ray generation apparatus and transmitted through a subject.