Background technology
X ray is widely used in modern medical diagnosis and treatment, especially oncotherapy.
In prior art, there is bremsstrahlung (a kind of radiation that high energy charged particles produces when slowing down suddenly) and produce X ray in high-power electron beam bombardment target in target.High-power electron beam is generally accelerated to be formed by accelerator high pressure, and target can be made up of materials such as such as tungsten, gold, thallium, iron, copper, nickel.
During high-power electron beam bombardment target, the conversion efficiency producing X ray is very low, and usually only have about 15%, most of energy of high-power electron beam is all absorbed by target, produces heat.The dose rate provided when machine foresees larger (x-ray dose that the unit interval produces), then require that the incident power of high-power electron beam is larger, accumulate in heat on target also more simultaneously, if heat can not be distributed in time, then can cause the thawing of target material surface, puncture time serious, permanent use, target material surface is oxidized, produces distortion, cause reduce the useful life of target, greatly reduce actinotherapeutic fail safe.Therefore the heat radiation of target becomes a problem demanding prompt solution.
A kind of x-ray target assembly (prior art one) is had in prior art, as shown in Figure 1, target assembly comprises the target 11 (such as tungsten target) be exposed in air and the heat-conducting metal 12 with high thermal conductivity, heat-conducting metal 12 has groove 14, target 11 is arranged in groove 14, the lower surface of target 11 and fit in the bottom of groove 14, upper surface is for receiving the bombardment of high-power electron beam; In addition, cooling water pipeline 13 is embedded with in heat-conducting metal 12.By said structure, the heat accumulating in target 11 lower surface can be conducted to rapidly cooling water pipeline 13 by heat-conducting metal 12, is distributed by the effect of cooling water in cooling water pipeline 13.
The defect of this target assembly is: one is because target contacts with air, adds that target is subject to bombardment spot temperature higher, causes this position to be easily oxidized, to be easily corroded; Two is that the heat radiation of target is bad, and in order to ensure its useful life, can only reduce the incident power of high-power electron beam, to ensure that target assembly is in safe temperature range in use, this makes the dose rate of X ray be restricted.
Another kind of x-ray target assembly (prior art two) is had in prior art, as shown in Figure 2, target 11, on the basis of prior art one, is placed in the vacuum environment Q of accelerator by this target assembly, can prevent surface oxidation and the surface corrosion of target like this.On the one hand, the technique be installed in vacuum environment by x-ray target assembly is more complicated; On the other hand, this target assembly does not solve in prior art one bad problem of dispelling the heat, and causes this target assembly can not use when the high-power incidence of high-power electron beam.
Summary of the invention
The invention provides a kind of new target assembly, while the oxidation by bombardment position preventing target and surface corrosion, can there is good radiating efficiency, promote the x-ray dose rate of target assembly, and structure is simple.
For solving the problem, the invention provides a kind of x-ray target assembly, comprising target, described target has the first surface receiving high-power electron beam bombardment, and described first surface has by bombardment position; Also comprise heat-conducting layer, described heat-conducting layer at least covers described by bombarding position and fitting by bombarding position with described.
Optionally, described target assembly is fixed target or rotary target.
Optionally, described heat-conducting layer covers described first surface.
Optionally, the conductive coefficient of described heat-conducting layer is greater than 15W/mK, and the density of described heat-conducting layer is less than 19g/cm3.
Optionally, also comprise radiating part, described target has the second surface opposing with described first surface, and described second surface and described radiating part are fitted.
Optionally, described radiating part has groove, and described target and described heat-conducting layer are positioned at described groove, and the sidewall of described heat-conducting layer and described groove is fitted.
Optionally, in described radiating part, there is at least one cooling passage.
Optionally, the material of described radiating part is heat-conducting metal.
Optionally, the material of described heat-conducting layer is the material modified of graphite or graphite, or is oxidation resistant metal or alloy.
Optionally, described heat-conducting layer comprises basal layer and anti oxidation layer, and described basal layer is beryllium, iron, or beryllium, iron material modified at least one; Described basal layer is at least fitted by bombarding position with described, and described anti oxidation layer is positioned at described basal layer and described being subject to is bombarded opposing side, position, covered described basal layer and fit with described basal layer.
Compared with prior art, technical scheme of the present invention has the following advantages:
At the bombardment position that is subject to of target, heat-conducting layer is set, heat-conducting layer make target by bombardment position and air exclusion, and the heat by bombardment position can be gone out by Quick diffusing, therefore can while the oxidation preventing target to be subject to bombard position and surface corrosion, promote the incident power of high-power electron beam, improve x-ray dose rate.
Embodiment
For enabling above-mentioned purpose of the present invention, feature and advantage more become apparent, and are described in detail specific embodiments of the invention below in conjunction with accompanying drawing.
Embodiment one
The present embodiment provides a kind of x-ray target assembly 100, with reference to Fig. 3, comprises target 101, heat-conducting layer 102 and radiating part 103.
Shown in composition graphs 4-5, target 101 has the first surface 101a and the second surface 101b opposing with first surface 101a that receive high-power electron beam bombardment, first surface 101a has by bombardment position A, and heat-conducting layer 102 covers first surface 101a and fits with first surface 101a.
Heat-conducting layer 102 is the critical components in the present embodiment structure, and in theory, the condition of choosing of heat-conducting layer 102 material is: conductive coefficient is the bigger the better, density is the smaller the better, thickness is the smaller the better.In the present embodiment, the material selection graphite of heat-conducting layer 102 or the material modified of graphite.
The material of radiating part 103 is heat-conducting metal, one surface has groove 103a; There is in radiating part 103 at least one cooling passage 104, fill cooling fluid in cooling passage 104, such as water etc.Target 101 and heat-conducting layer 102 are positioned at groove 103a, fit in the second surface 101b of target 101 and the bottom of groove 103a, and heat-conducting layer 102 is fitted with the sidewall of groove 103a.Heat-conducting layer 102 is after absorbing the heat on first surface 101a, by the position that heat-conducting layer 102 and groove 103a sidewall are fitted, promptly heat can be passed to radiating part 103, then by radiating part 103, heat be passed to cooling fluid, the circulation eventually through cooling fluid distributes.
The capacity of heat transmission of graphite or graphite modified material is very good, and its thermal conductivity has obvious anisotropic, its thermal conductivity along crystal bedding angle is perpendicular to several times or the decades of times of the thermal conductivity of crystal bedding angle, therefore, the crystal bedding angle arranging heat-conducting layer 102 is parallel with the first surface 101a of target, utilize the above-mentioned character of graphite, the heat accumulated in by bombardment position A can be conducted to radiating part 103 fast along the direction being parallel to first surface 101a.
Here the heat conductivility of graphite is simply compared with the heat conductivility of air.For any conduction material, its thermal conductivity (heat of conduction in the unit interval) is defined as:
In above formula, the equation left side is thermal conductivity, and κ is conductive coefficient, and A is heat-conducting area, and Δ T is temperature difference (namely during conduction material generation effect, the temperature drop to thermal source is formed), and x is the thickness of conduction material.Air conductive coefficient is in normal conditions 0.024W/mK, and the conductive coefficient of graphite is 151W/mK.Suppose that A with x is identical, when temperature is 600K, graphite can reach 892W/mK along the thermal conductivity of crystal bedding angle, it is about 30,000 times of air conduction rate, for target 101 for tungsten target, on target 101, cladding thickness is the heat-conducting layer 102 of the graphite material of 0.5mm, as calculated, when incident electron power is 1000W, the temperature drop by bombardment position A can reach 230 ~ 260 degrees Celsius.Apparently, for air, heat-conducting layer 102 has better heat-conducting effect, effectively can reduce the heat accumulation of first surface 101a, therefore can apply the incident power of higher high-power electron beam to target assembly, improve x-ray dose rate.
In addition; due to its thermal conductivity perpendicular to first surface 101a direction, to be comparatively parallel to first surface 101a direction lower; heat-conducting layer 102 can keep higher temperature gradient in this direction; the side surface temperature making heat-conducting layer 102 and target 101 opposing is lower, protects graphite surface, makes it be not easy to suffer erosion with this.
Heat-conducting layer 102 is except playing except the effect of transferring heat; also has another one effect; be exactly first surface 101a and the air of isolated target 101, the first surface 101a of target 101 can be prevented to be oxidized and surface corrosion, target 101 is played a very good protection.Because graphite itself has non-oxidizability, therefore the heat-conducting layer 102 of graphite material is also not easy oxidized corrosion, has longer useful life.
Verify that (density of graphite linings is 2.26g/cm to the heat-conducting layer of graphite material for the impact of the bundle spot of electron beam and photons spectrum below
3).
When the thickness adopting MC algorithm (Marching Cubes, marching cubes algorithm) to calculate heat-conducting layer 102 in the present embodiment is 0.5mm, halved tie spot expands effect.As shown in Figure 6, abscissa represents radius R (unit is cm), and ordinate represents energy flow, and (unit is Mev/cm
2), point-like curve a, solid line shape b represent the bundle spot of conventional target component design (without heat-conducting layer) and the design of the present embodiment target assembly respectively.As can see from Figure 6, two curves a, b overlap substantially, so be shown as a curve in the drawings.That is, in the present embodiment, the impact of heat-conducting layer 102 halved tie spot is negligible, such as, adopts bundle spot to be 1mm in this experiment, and energy is that the electron beam of 6Mev is incident, and electron beam, through after heat-conducting layer 102, is still 1mm in the bundle spot size on target 101 surface.
Fig. 7 shows the impact of heat-conducting layer 102 on photons spectrum, wherein abscissa represents energy (unit is Mev), ordinate represents relative intensity, point-like curve aa represents the photons spectrum of conventional target component design (without heat-conducting layer), real line-like curve bb represents the present embodiment and to hit the photons spectrum of component design, as can see from Figure 7, the peak value of two curves overlaps substantially, and therefore heat-conducting layer 102 also can be ignored the impact of photons spectrum.
As can be seen here, in the present embodiment, the impact of heat-conducting layer 102 on target assembly performance is negligible.
In other embodiments, the thickness of heat-conducting layer can choose other values as required.
Wherein, target assembly can be fixed target or rotary target.With reference to Fig. 4, when target assembly is fixed target, be usually located at the central area of target 101 by bombardment position A; With reference to Fig. 5, when target assembly is rotary target, form an annular by bombardment position A.
In other embodiments, the area of heat-conducting layer also can be less than the area of first surface, but must ensure that heat-conducting layer at least covers by bombardment position and fits with by bombarding position; Target and heat-conducting layer directly can also be arranged at the surface of radiating part, and not necessarily need to arrange in a groove, as long as ensure that heat-conducting layer and radiating part have fitting part; In addition, according to the cooling requirements of target, also can not arrange radiating part, now can arrange heat-conducting layer and only cover by bombardment position, the heat now by bombardment position can be dispersed in air by heat-conducting layer.
Embodiment two
The difference of the present embodiment and embodiment one is, with reference to shown in Fig. 4-5 composition graphs 8, heat-conducting layer 102 structurally comprises basal layer 102a and anti oxidation layer 102b, and basal layer 102a is beryllium, iron, or beryllium, iron material modified at least one.
Wherein, basal layer 102a at least with by bombarding position A fits, and anti oxidation layer 102b is positioned at basal layer 102a and is subject to bombard the opposing side of position A, cover basal layer 102a and fit with basal layer 102a.
If based on the beryllium of layer 102a, the material modified of iron inherently there is non-oxidizability, then can save the setting of anti oxidation layer 102b.
In order to reduce the bundle spot of heat-conducting layer 102 on incident beam and the impact of power spectrum, heat-conducting layer 102 at least demand fulfillment: the conductive coefficient of heat-conducting layer 102 is greater than 15W/mK, density is less than 19g/cm3, and the thickness of heat-conducting layer 102 determines according to the density of selected materials and conductive coefficient.
Although the present invention discloses as above, the present invention is not defined in this.Any those skilled in the art, without departing from the spirit and scope of the present invention, all can make various changes or modifications, and therefore protection scope of the present invention should be as the criterion with claim limited range.