JPH0644079B2 - Phase zone plate for biological observation X-ray microscope - Google Patents

Description

TECHNICAL FIELD The present invention relates to a phase zone plate for a biological observation X-ray microscope. More specifically, the present invention is
The present invention relates to a phase zone plate for an X-ray microscope, which can be used in a wavelength range of 24 to 44Å, which enables high resolution observation of biological samples.

(Background Art) In academic research such as biology, biochemistry, and biophysics,
Also, in the development of biotechnology as an industrial technology, which has made great strides in recent years, we would like to observe the structure and intracellular movement of living biological samples, such as cell samples, at the molecular level with high resolution. Are increasing in demand.

Conventionally, as a method of observing a biological sample, a method using an optical microscope that focuses light with an optical lens and a method using an electron microscope that focuses an electron beam with an electromagnetic lens are known, but in the case of an optical microscope, You can see a living biological sample in a liquid, but the resolution is low (about 0.3 μm) due to the long wavelength of visible light, and the resolution is good (Å order) in the case of an electron microscope, but the sample is in vacuum. There is a problem that it cannot be used for samples containing liquid because it must be placed in

In addition, in the case of a cryo-electron microscope, which has been recently developed, it is possible to observe the stop motion while the biological sample is rapidly frozen and frozen, but it is not possible to observe the in-vivo movement. There was a problem.

On the other hand, X-rays have been used for a long time as a so-called X-ray fluoroscopic method because there exists a wavelength range in which X-rays are absorbed by a certain substance and not absorbed by another substance, depending on the type of the substance.

Due to the characteristics of this X-ray, it has been considered to utilize this X-ray for observing a living biological sample. In fact, for example, X-rays in the wavelength range of 24 to 44 Å are absorbed by proteins but not by water, and thus may be used for observing biological samples in water alive.

However, at present, this has not been realized yet. This is because there are some problems to be overcome.

Since X-rays cannot be focused by an optical lens or an electromagnetic lens, a unique focusing system is required, but this focusing system has not been developed.

Recently, it has been proposed to use a concave mirror (Walter type) or a Fresnel zone plate as a focusing system for an X-ray microscope, but a microscope having sufficient resolution has not been realized.

The Fresnel zone plate is attracting attention for its unique method, and is a clue for future development of an X-ray microscope. That is, as shown in FIG. 6 of the accompanying drawings, in this Fresnel zone plate, an annular zone (a) that shields X-rays and an annular zone (a) that passes X-rays are concentrically arranged alternately. The width of the X-rays passing through the ring zone (a) becomes narrower toward the periphery so that the X-rays gather at one point in the same phase. Assuming that the radii of the annular zones (a) and (b) are r ₁ , r ₂ , r ₃ , ... R _m , ..., R _n as shown in FIG. 6, the X-ray wavelength λ and the focal length f In between, for example, the Fresnel zone plate can be designed so that the relationship of r _m = m · f · λ is established.

This Fresnel zone plate has a function of collecting X-rays at a distance f (principal focus) in the rear f and diverging X-rays around the distance in the front f, so that it can be used as a convex lens or a concave lens. it can.

Further, this Fresnel zone plate has sub-focal points at distances f / 3, f / 5, ... (f / odd number) on the rear side and the front side, respectively.

In such a conventional Fresnel zone plate,
As is clear from FIG. 7 showing the cross section, about 50% of the incident X-rays are shielded, 25% pass straight without being diffracted, 10% is the main focus, and 5% is many. Dispersed in the subfocal, the remaining 15% diverge. For this reason, the condensing ratio of the optical lens is close to 100%, whereas in the case of the Fresnel zone plate, focusing the X-rays only 10% on the principal focal point is a major drawback. This drawback requires a strong X-ray source and a highly sensitive imaging medium, which delays the development of X-ray microscopes.

In order to overcome the drawback of the Fresnel zone plate having a low X-ray focusing ability, a new method called a phase zone plate has been proposed.

In FIG. 7, the reason why the shielding part (c) is necessary in the conventional Fresnel zone plate is that this shielding part (c) is temporarily used.
Considering a path that passes through to the focal point, the X-ray is out of phase with π radians from the X-ray collected through the transmission part (d), and the intensity at the focal point is weakened by the interference action. So it aims to prevent it.

As shown in FIG. 8, when the portion corresponding to the shielding portion of the Fresnel zone plate is replaced with a phase annular zone (e) which is transparent and has a function of shifting the phase by π radians, an X-ray is used. The phase shift of π radians caused by the path difference of the
The lines are in phase with each other and constructive interference occurs. The zone plate having such a configuration is called a phase zone plate.

According to such a concept of the phase zone plate, if the phase annular zone (e) is completely transparent, the X-ray focusing rate is 4
It will be improved to 0%.

However, in reality, these do not go beyond the scope of the idea, and no substances that are completely transparent to X-rays in the wavelength range of 24 to 44 Å suitable for observing biological samples have not been found. So far, the proposed phase zone plates include gold, silver, copper, carbon, silicon, beryllium,
It is made of aluminum, lithium fluoride, polystyrene, etc. In fact, it is only reported that silver was used to make a phase zone plate for 8Å.

For this reason, there has been a strong demand for development of a concrete one that makes use of the characteristics of the phase zone plate, and in particular for realization of a biological observation phase zone plate effective for X-rays having a wavelength of 24 to 44 Å.

(Object of the Invention) The present invention has been made in view of the above circumstances, and overcomes the drawbacks of the conventional microscope system for biological observation,
It is an object of the present invention to provide a new phase zone plate that can be used as an X-ray microscope for observing a living body with high accuracy and high sensitivity, because restrictions on the intensity of a light source and the sensitivity of an imaging medium are alleviated.

DISCLOSURE OF THE INVENTION The phase zone plate for a biological observation X-ray microscope of the present invention has a phase ring zone formed of any one of titanium, vanadium, and chromium in order to achieve the above object. It has a feature.

The phase annular is the size of the radius, as in the conventional Fresnel zone _{plate, r m = m · f ·} λ (r m: radius of the m-th ring zone from the center, f: focal length lambda: X-ray wavelength). Further, regarding the thickness, the following relationship is established. That is, the refractive index n of X-rays is smaller than 1 and depends on the wavelength λ. n
Can be calculated using the values of the real part f ₁ and the imaginary part f ₂ of the atomic scattering factor f = f ₁ + if ₂ for each wavelength. When an X-ray passes through a substance of thickness d, the phase advances by d · (1-n) · 2π / λ compared to when it passes through a vacuum of the same thickness. The band is π
= D (1−n) · 2π / λ, and can be determined by d = λ / 2 / (1−n).

In the present invention, titanium, vanadium or chromium is used as a material for forming the phase zone due to the characteristics and physicochemical stability with respect to X-rays. For each of these, the thickness of the phase zone with respect to the X-ray wavelength is used. Is shown in FIG. The correlation is shown for titanium (1), vanadium (2) and chromium (3). For example, when titanium (1) is used, it is 24-44Å
With respect to the X-ray wavelength of
The actual thickness can be determined from the balance with the light collection rate.

FIG. 2 shows the ratio R of the light collection rates of the phase zone plate of the present invention and the conventional Fresnel zone plate.

This R can theoretically be expressed as follows.

R = (1 + T) ² T = exp (−ρ · μ · d / 2) (ρ: material density, μ: material line absorption coefficient T: amplitude transmittance)
X-ray wavelength to be used, they want the focal length may be selected thickness d and condenser ratio described above in view of the limitations or the like in manufacturing R, and annular radius (r _m).

For example, X-ray wavelength λ = 36Å, focal length f = 10 mm,
When the number of zones n = 8, the minimum zone radius r ₁ = 6 μm, and the outermost zone radius r ₈ = 16.97 μm, the above R (concentration ratio) is 1 (T = 0, in the case of the conventional Fresnel zone plate). Radial X-ray intensity distributions on the focal plane for three cases, 4 (theoretical phase zone plate, T = 1) and R = 2.25 (T = 0.5, an example of the phase zone plate) Is FIG. 3.

Further, FIG. 4 shows an X-ray intensity distribution on the optical axis. The origin is the position of the zone plate and the main focus is at 10 mm. The other peaks are the subfocal points.

Based on such theoretical and practical considerations, the phase zone plate for the X-ray microscope of the present invention is constructed.

FIG. 5 shows an example of the construction of an X-ray microscope using this phase zone plate.

The example of FIG. 5 is constituted by an X-ray source (4), a focusing phase zone plate (5), a sample holder (6), an objective phase zone plate (7), an imager (8) and a vacuum chamber (9). Has been done.

X-rays in the desired wavelength range are absorbed by air and must be put into the entire vacuum chamber.

For this reason, when observing a living biological sample in a liquid, the sample holder (6) should be hermetically sealed and should have a window through which the X-rays used are passed. Further, if necessary, a passage that opens to the atmosphere outside the vacuum chamber (9) is provided.

The collecting phase zone plate (5) and also the objective phase zone plate (7) are formed by a ring of titanium, vanadium or chromium.

(Effect of the Invention) According to the present invention, as described in detail above, a phase zone plate used for a highly accurate and highly sensitive biological observation X-ray microscope is realized.

[Brief description of drawings]

FIG. 1 shows X for the phase zone plate of the present invention.
FIG. 6 is an X-ray wavelength / thickness correlation diagram showing the relationship between the line wavelength and the thickness of the phase zone. FIG. 2 is a light-collection ratio / wavelength correlation diagram showing the relationship between the light-collection ratio and the wavelength. 3 and 4 are intensity correlation diagrams showing the relationship between the X-ray intensity, the radius from the optical axis in the main focal plane, and the distance from the zone plate on the optical axis, respectively. FIG. 5 is a sectional view showing a configuration example of the X-ray microscope of the present invention. FIG. 6 is a front view of a conventional Fresnel zone plate. FIG. 7 shows a sectional view thereof. FIG. 8 is a sectional view of the phase zone plate. 1 ... Titanium, 2 ... Vanadium, 3 ... Chrome, 4 ... X-ray source, 5 ... Focusing phase zone plate, 6 ... Sample holder, 7 ... Objective phase zone plate, 8 ... Imaging device, 9 ... Vacuum chamber.

Claims (1)

[Claims] 1. A phase zone plate for a biological observation X-ray microscope, which comprises a phase ring formed of any one of titanium, vanadium and chromium.