RU2522737C1 - Self-contained x-ray and ultraviolet radiation receiver - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: self-contained receiver for detecting X-ray and ultraviolet (UV) radiation includes a metal housing, a transparent dielectric substrate, a photosensitive layer made from an anomalously high photovoltage film and metal contacts, wherein a reflecting coating is placed between the transparent dielectric substrate and the metal housing, the receiver is provided with a hemispherical mirror cover, having a window which is transparent for X-ray and UV radiation.

EFFECT: high sensitivity when detecting X-ray and UV radiation.

2 cl, 2 dwg

Description

The invention relates to integrally-sensitive receivers of optical radiation and can be used to record x-ray and ultraviolet radiation.

A self-contained X-ray and ultraviolet radiation detector is known, which contains a sensitive element in the form of films with anomalous photovoltage (AFS films), metal contacts are created by a tin alloy with an admixture of 1% antimony or 1% gallium, and AFN films made from CdSe compounds were used as a sensitive element or CdTe: Ag 4 × 2 mm in size [Rakhimov N.R., Kasymakhunova AM, Usmanov Sh.Yu. A method of producing photogenerators / Patent RUz IAP 02610 dated 02.25.2003].

The disadvantage of this stand-alone X-ray and ultraviolet radiation receiver is the low sensitivity and not wide enough frequency range of the detected radiation, especially for recording X-ray and ultraviolet radiation in optoelectronic and robotic devices for receiving various light fluxes.

A self-contained X-ray and ultraviolet radiation detector based on films with anomalous photovoltage (AFN films) is adopted, which is taken as a prototype consisting of a metal body, a glass cover, metal contacts and a photosensitive layer of AFN film deposited on a transparent dielectric substrate [Rakhimov N. R., Seriouszov A.N. AFN films and their application / monograph. - Novosibirsk: SibNIA, 2005].

The disadvantage of this autonomous X-ray and ultraviolet radiation receiver is its low sensitivity due to the passage of the radiation flux through the photosensitive layer no more than once.

The claimed invention is directed to increasing sensitivity.

This result is achieved by the fact that a reflective coating is placed between the transparent dielectric substrate and the metal casing, the stand-alone X-ray and ultraviolet radiation receiver is equipped with a hemispherical mirror cover having a window transparent for x-ray and ultraviolet radiation.

Figure 1 shows the image of a stand-alone optical radiation receiver: 1 - a photosensitive layer of AFN film; 2 - transparent dielectric substrate, 3 - metal contacts; 4 - reflective coating; 5 - hemispherical mirror cover; 6 - metal case; 7 - a window transparent for x-ray and ultraviolet radiation. The reflective coating (4) and the hemispherical mirror cover (5) are made of osmium-silicon and osmium-scandium-silicon materials. The photosensitive layer is made as a scintillation layer based on AFN films of ZnSe and CdTe.

Figure 2 shows a diagram of a scintillation photosensitive layer based on Te-ZnSe. In this figure: 9 - a layer of zinc selenium (ZnSe), 10 - a layer of cadmium telluride (CdTe), 11 - conductive contacts.

The principle of operation of the stand-alone x-ray and ultraviolet receiver (figure 1) is as follows. Directional radiation Ф _о from the source of x-ray or ultraviolet radiation enters through the window (7). Getting on the photosensitive layer (1), this radiation is partially converted into a photo library and partially passes through this layer, then it is reflected from the reflective coating (4). The reflected part also passes through the photosensitive layer and is partially converted to a photocurrent, and the remaining part falls on the hemispherical mirror cover (5). This residual radiation, reflected from this cover, again falls on the photosensitive layer and is converted into a photocurrent. Due to repeated re-reflection, the conversion efficiency of x-ray or ultraviolet radiation into the photocurrent increases significantly.

Thus, the sensitivity of the stand-alone receiver of x-ray and ultraviolet radiation increases.

The principle of operation of the photosensitive layer is as follows. X-ray or ultraviolet radiation passes through both layers, (10 and 9) of the scintillator (figure 2), ionizes atoms and molecules and excites them. Excited atoms and molecules, returning to their original state, emit light that enters the cadmium telluride layer (10), which is an AFS film (CdTe). In this layer (10), due to the accumulation of charges, a photocurrent is generated. When a sensitive layer is illuminated by ultraviolet or X-ray fluxes, luminescence is generated in a layer of zinc selenium (ZnSe) (9).

An ultraviolet or X-ray beam passing through a scintillator transfers electrons from the valence band to the conduction band or from deep levels to the conduction band. Returning to the initial state due to the fact that radiative recombination occurs, these atoms emit light photons that fall on the AFN film of the (10) CdTe layer, and a photo signal arises which is taken from contacts (11) and, for example, recorded by an electrometer.

The AFD CdTe film detects luminescence of zinc selenium with low reflection losses from the ZnSe-CdTe boundary.

The reflection coefficient is calculated by the formula

, $$R=\frac{n_{\mathrm{one}}-n_2}{n_{\mathrm{one}}+{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="00000007.png"\; state="\{\{state\}\}">n</figure-callout>}}_2}=\frac{3.4-2.6}{7}=\frac{0.8}{7}\approx 0.1$$

,

where R is the reflection coefficient from the interface between ZnSe and CdTe; n ₁ is the refractive index of ZnSe; n ₂ is the refractive index of CdTe.

The reflection coefficient of known scintillation photodetectors takes into account reflection at the interface between ZnSe and air (n ₀ = 1), then R = 0.5. In the case under discussion, the loss of reflection photo signals is insignificant in comparison with the known receivers. Let us evaluate the change in the efficiency of a receiver with an AFS film:

L _R = R · L ₀ ,

L ' _R = (R-ΔR) L ₀ ,

where R is the reflection coefficient, L ₀ is the intensity of the incident light,

, $$T\text{'}\text{'}=\frac{L_0-L_R}{L_0}=\mathrm{one}-R$$

,

where T is the transmittance. Then

, $$T\text{'}\text{'}=\frac{L_0\left(R-\Delta R\right)L_0}{L_0}=\mathrm{one}-\left(R-\Delta R\right)$$

,

$$x=\frac{T\text{'}\text{'}}{T}\cdot \mathrm{one\; hundred}=\frac{\mathrm{one}-\left(R-\Delta R\right)}{\mathrm{one}-R}\cdot \mathrm{one\; hundred}\%=\left(\mathrm{one}+\frac{\Delta R}{\mathrm{one}-R}\right)\cdot \mathrm{one\; hundred}\%$$

;From here $$\Delta x=\frac{\Delta T}{T}=\frac{\Delta R}{\mathrm{one}-R}$$

;

; $$\Delta x=\frac{0.4}{\mathrm{one}-0.5}=0.8$$

;

those. efficiency is increased by 80%.

To determine the value of the photosignal, a photosensitive layer based on the AFN film of cadmium telluride is illuminated with ultraviolet light from the side of the ZnSe scintillator and the SF-26 spectrometer measures photo-emf, it was 200 mV (without the AFS layer - 120 mV). Then, the scintillator is excited by soft X-rays (URS-60 with a 0.4 VVV-4S tube, the voltage on the tube is 20 kV), and it turned out that the signal amplitude is 500 mV (without an AFS layer - 280 mV). The photo signal between the contacts is measured by an electrometer.

An x-ray mirror covers the hemispherical mirror cover from the inside (5). Also, a reflective coating (4) is made from an X-ray mirror. This X-ray mirror has a multilayer structure (up to several hundred layers), their production requires special conditions. Materials for creating reflective coatings must have ultra-high purity and are deposited on the mirror base by vacuum deposition. The wavelength range in which the mirror will operate, and additional conditions and requirements determine the choice of materials. For example, it can be osmium-cadmium and osmium-scandium-silicon. The reflection coefficient of such materials is extremely high.

To obtain AFN films and reflective surfaces, the VUP-2k vacuum system is used. A vacuum of the order of 10 ^-4 -10 ^-5 mm Hg is reached in the working chamber, the substrate temperature is 410-480 ° С. As substrates, glass plates with a size of 4 × 20 mm and a thickness of 2-5 mm are used. Before the vacuum evaporation process begins, the glass substrates are washed 2-3 times in boiling distilled water for 20-25 minutes and dried in an oven at a temperature of 150 ° C for 30 minutes, then they are fired at 250-300 ° C in a vacuum for 10 minutes.

Initially, to obtain a reflective layer, deposition of opposite layers of osmium-silicon and osmium-scandium-silicon materials is carried out on opposite sides of the substrate. The spraying process is carried out under a vacuum of 10 ^-4 -10 ^-5 mm Hg, the substrate temperature is 450 ° C.

In this case, the effective film thickness is ~ 1 μm.

In the last step, a reflective hemispherical cover (integrating cavity) is manufactured using the same technology as the reflective substrate. The spraying process is carried out under a vacuum of 10 ^-4 -10 ^-5 mm Hg, cover temperature 450 ° C.

The thickness of the reflective coating is also ~ 1 μm.

Based on the obtained elements, it is possible to develop a stand-alone optical radiation receiver.

As x-ray optics develops, the spectrum of materials used is much wider than the above, for example, osmium-silicon and osmium-scandium-silicon compositions are very effective in the long-wavelength part of the soft x-ray spectrum, and hafnium is very effective in the harder part of the x-ray spectrum its composition with other elements.

X-ray and optical are related in nature. Both types of radiation are electromagnetic radiation. X-rays are emitted with the participation of atoms or free electrons. X-ray photons have an energy of 100 eV to 250 KeV, which corresponds to radiation with a frequency of 3 × 10 ¹⁶ Hz to 6 × 10 ¹⁹ Hz (i.e., with a wavelength of 0.005-10 nm). Soft X-ray radiation is characterized by the lowest photon energy and radiation frequency (and the longest wavelength), and hard x-ray radiation has the highest photon energy and the radiation frequency (and shortest wavelength). Hard X-rays are used primarily for industrial purposes.

Thus, the proposed receiver can provide reception of both x-ray and ultraviolet radiation.

Therefore, residual x-ray or ultraviolet radiation, which was not converted along the path through the photosensitive layer (1) into the photocurrent, will be reflected first from the reflective coating (4), then from the hemispherical mirror cover (5), after which it will again fall onto the photosensitive layer (1) . This increases the portion of the light that is converted to a photocurrent. The photocurrent itself will increase proportionally, that is, with the same amount of x-ray or ultraviolet radiation that has fallen into the photodetector window (7), the photocurrent generated by this radiation will increase. Consequently, the sensitivity of the receiver will increase, since it is defined as the ratio of the photocurrent to the light flux that this photocurrent caused.

As a result, the task is solved.

The photosensitive layer (1) can be made, as in the prototype, in the form of AFN films from crystalline cadmium telluride [Rakhimov NR, Ushakov O.K. AFN-based optoelectronic sensors / monograph. - Novosibirsk: SSGA, 2010]. The reflective coating (4) and the hemispherical mirror cover (5) are made of osmium-silicon and osmium-scandium-silicon materials. The remaining elements can be performed by traditional technologies, as in the prototype. The transparent dielectric substrate (2) can be made, for example, of a glass plate. The metal case (6) can be made as in the prototype, or, for example, in the form of a shallow glass, equipped with a bracket for fixing.

Claims (2)

1. An autonomous receiver for detecting X-ray and ultraviolet radiation, including a metal case, a transparent dielectric substrate, a photosensitive layer of AFS film and metal contacts, characterized in that a reflective coating is placed between the transparent dielectric substrate and the metal case, the receiver is equipped with a hemispherical mirror cover, having a window transparent for x-ray and ultraviolet radiation. 2. The stand-alone X-ray and ultraviolet radiation receiver according to claim 1, characterized in that the reflective coating and the hemispherical mirror cover are made of osmium-silicon or osmium-scandium-silicon.

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