The impact of ionizing radiation on video surveillance systems.

Today, the effect of temperatures on the operating parameters of video cameras has been analyzed in sufficient detail and various housings have been proposed. Some manufacturers have gone further and announced the creation of radiation-resistant video cameras. Such cases are no longer isolated, the equipment is actively advertised. It is often difficult for an installer to assess the type of degradation of product parameters created by ionizing radiation, as well as the level of ionizing radiation that causes deterioration of equipment parameters. Not to mention the required level of protection.
After all, as is known, under the influence of penetrating radiation the properties of almost all materials change: metals become less durable, glass loses its transparency, and the electrical characteristics of semiconductors deteriorate. When analyzing the radiation resistance of semiconductor devices, the main attention is paid to neutron, proton, electron and alpha radiation.

Sources of ionizing radiation
Ionizing radiation can be of artificial or natural origin. Outer space is a natural radiation environment in which galactic radiation acts – flows of protons, alpha particles and other heavy nuclei with energies of 102–1014 MeV and solar radiation (the source of solar radiation energy is a thermonuclear reaction – every second on the Sun ~6•1011 kg of hydrogen is converted into helium). A significant part of cosmic radiation is protons (about 90%). Processes on the Sun are irregular, manifesting themselves during periods of increased solar activity (up to 10 flares over several days per year). As a result of the capture of charged particles from outer space by the Earth's magnetic field, the Earth's radiation belts are formed. The radiation of the Earth's inner natural radiation belts consists of proton fluxes with energies up to 700 MeV and electrons with energies less than 1 MeV, while the Earth's outer belts consist of proton fluxes with energies up to 60 MeV and electrons with energies of 0.2–5 MeV. The Earth's radiation belts have a complex asymmetric structure determined by the structure of the Earth's magnetic field. As a result, the dose of ionizing radiation that onboard equipment can accumulate while in the Earth's radiation belt for 5 years is 5*104–2*105 rad. [1]. Ionizing radiation from outer space can have a noticeable effect on equipment located in mountainous areas.

Artificial radiation environments can be created for technological purposes.
A nuclear explosion is a source of a powerful gamma-radiation pulse and a fast neutron pulse that is delayed relative to the gamma-quanta. In nuclear power plants – continuous and pulsed nuclear reactors – the process of nuclear fission is accompanied by gamma-neutron radiation. In addition, sources of ionizing radiation are nuclear power plants, accelerators, gamma-installations, X-ray and other installations that create flows of electrons, gamma-quanta, neutrons, and heavy charged particles [1]. In industrial nuclear installations, devices are mainly exposed to neutron irradiation and gamma radiation. In this case, the neutron flux can be 1011 cm-2, and the gamma-quanta dose can be 104 rad.
Residual radiation is associated with artificial radioactivity induced by neutrons in the soil, building materials and other objects in the nuclear reaction zone, as well as fission fragments of nuclei with a long half-life. Residual radiation includes all gamma radiation that exists 15 seconds after the nuclear reaction. From this point of view, it is legitimate to create a radiation-resistant camera and special video surveillance systems for examining such objects. Such video cameras, which have a CCD matrix as a sensitive element, are resistant to gamma radiation of 105 rad.

In addition, when a metal anode (metal partition) is bombarded with a beam of electrons, gamma quanta or ions, the latter are slowed down inside the anode material and electromagnetic radiation is generated, called bremsstrahlung. Therefore, screens can often be sources of secondary radiation. When many materials are irradiated with neutrons and protons, nuclear reactions can occur, as a result of which the irradiated product becomes a source of gamma quanta or electrons.

Testing equipment for resistance to radiation
Such a detailed description of existing types of radiation was given in order to give an idea of ​​the complexity and large volume of methods for testing electronic equipment for radiation resistance.

It is impossible to simulate all the parameters of existing ionizing radiation under test conditions. The characteristics of the radiation generated by test simulation facilities differ from those that can actually affect the equipment. Therefore, when submitting information on the tests performed for radiation resistance, it is necessary to specify the characteristics of the simulation facility: energy and type of radiation, since different types of radiation interact with matter in different ways. There are sufficiently detailed GOSTs that describe the methods of testing products for resistance to the effects of radiation. In this case, tests for resistance to the effects of ionizing radiation of outer space and nuclear reaction radiation are given separately.

Interaction of ionizing radiation with substances
Let's analyze the effect of different types of radiation on the materials of electronic products. Currently, virtually all electronic components are made on the basis of semiconductors. Radiation emissions in semiconductor materials lose their energy mainly due to two physical processes: atomic collisions and ionization. During atomic collisions, the semiconductor atoms are knocked out of equilibrium positions in the crystal lattice, resulting in the formation of various types of defects. These are irreversible changes. These effects are mainly caused by heavy uncharged neutrons and protons.

During ionization, nuclear particles knock electrons out of atomic orbits, which increases the concentration of ions and free electrons in the crystal. These are mainly reversible effects, i.e., when the radiation exposure ceases, the ionization current disappears. The relative role of these mechanisms is determined by the nature of the radiation effect. Electrons and gamma quanta, being charged particles, lose their energy in semiconductors due to ionization. Protons, being charged particles, also cause ionization of matter. About 50% of the energy of fast neutrons is spent on elastic atomic collisions, leading to the displacement of atoms from the nodes of the crystal lattice. Protons transfer to the atoms of the irradiated substance less energy, compared to neutron irradiation, which is spent on their displacement. At the final stage, when the proton has a relatively low kinetic energy, it is able to capture an electron to form a hydrogen atom, which has sufficient kinetic energy to generate secondary radiation defects. After complete deceleration, the hydrogen atom turns into an impurity. Therefore, the same concentrations of radiation defects are introduced when irradiated with a significantly smaller flux of protons than neutrons [2].

The Effect of Radiation on Various Semiconductor Devices
The sensitivity of semiconductor devices to the effects of various types of radiation depends on the operating principle of the device. In devices that operate on the basis of volume effects, such as bipolar transistors, photodiodes degrade mainly due to volume radiation defects created by the displacement of atoms in their crystal lattice. Such devices experience significant degradation when irradiated with high levels of neutron fluxes (more than 1013 cm2) and protons (more than 1012 cm-2), which is clearly shown in Fig. 1. Radiation that causes mainly ionization effects does not lead to significant degradation of the device parameters. Fig. 2 shows that the decrease in the sensitivity of photodiodes when irradiated with ionizing radiation with a dose of 104–106 rad is only about 10%. As is known, some high-quality CCTV cameras use photodiodes as a sensitive element. The use of such structures is justified from many points of view [3].

The operation of charge-coupled devices (CCD) and CMOS is affected by both volume and surface defects. The operation of these devices is largely determined by surface effects. As is known, CCDs and CMOS matrices are most often used in video surveillance cameras. In addition, the reading electronics of video cameras are also based on CCDs and MIS microcircuits. In the degradation of these devices, the characteristics of which are determined by the properties of the semiconductor-dielectric interface, ionization processes play a significant role, changing the value of the built-in charge in the dielectric and increasing the density of surface defects. Currently, widely known methods are used to increase the stability and radiation resistance of CCDs — using a CCD with a built-in channel rather than a surface one (Fig. 3). Fig. 4 shows the dependence of the degradation of CCD parameters with a surface and built-in channel on radiation.
Also, to increase the radiation resistance of devices, an oxide is used, which initially creates a minimum level of tension between the semiconductor and the oxide, neutralizing surface states during ionization. Radiation-resistant oxide in tandem with electrodes made of specially selected materials form a radiation-resistant design of an MIS device. Since the MIS structure is created in a single technological process, all its elements influence each other at the manufacturing stage. The dependence of the voltage of flat zones under the aluminum and polysilicon electrodes of the CCD on the radiation dose is shown in Fig. 5.
It should be noted that CMOS electronics generally have sufficient radiation stability. That is, CMOS cells do not lose their functionality even when exposed to a dose of 106 rad (Fig. 6). Only the transfer characteristic shifts slightly.

Market View
Apparently, one of these methods is used to create radiation-resistant cameras. These video cameras, which have a CCD matrix as a sensitive element, are resistant to the effects of gamma radiation of 105 rad, which is almost 100 times higher than video cameras with conventional CCD matrices. Radiation resistance is achieved through the use of radiation-resistant elements (including the CCD matrix), as well as thanks to a specially developed method of circuit protection of the CCD matrix from the negative effects of ionizing radiation. According to the manufacturers (the scientific, production and commercial company «Telecort», created in 1992 from specialists of the «VNII Television» — formerly the main enterprise of the military-industrial complex of the USSR in the field of broadcasting, applied and special television, St. Petersburg), for example, in the KTA-J31 video camera, the possibility of subsequently increasing the radiation resistance to the level of 106 rad is provided.Funktel successfully supplies radiation-resistant video cameras to the radiation of a nuclear explosion. Resistance to the effects of radiation with a power of 102 rad/hour with a total dose during operation of 104 rad is achieved by using a special casing. Resistance to the effects of radiation with a power of 103 rad/hour with a total dose during operation of 105 rad is achieved by using specially manufactured radiation-resistant CCD matrices, vertical placement of video cameras in lead shells. In addition, direct hit of directed radioactive radiation on the CCD sensor is excluded by bending the optical axis with a mirror. Resistance to radiation with a power of 106 rad/hour with a total dose during operation of 108 rad is ensured by using a vidicon as a sensitive element instead of a CCD or CMOS matrix — an element containing a photoconductive target, which consists of a transparent metal film on the side of the projected image and a photoconductive layer located on it on the side of the electron-optical system. The design of these devices allows for their decontamination and provides protection against the penetration of radioactive dust into the devices.
The Russian company «Diakont» produces D70 video cameras with a 2/3″ vidicon based on CdSe, resistant to gamma radiation with a dose of 108 rad, with a gamma radiation power of 3*105 rad/hour. The same company produces video cameras that are radiation-resistant to the effects of a gamma radiation dose of 107 rad at a power of 105 rad/hour, type S90, with a sensitive element made on the basis of an APS sensor.

Conclusion
The issues of radiation resistance of video cameras and other security systems are a fairly new direction for the industry.
The statement of manufacturers and suppliers of video cameras that their video cameras have passed tests for radiation resistance, of course, requires clarification: what type of radiation resistance tests were conducted, what change in parameters under such impacts was accepted as acceptable, on what modeling installations creating particles, with what energy the tests were conducted.
CCD and CMOS matrices, widely used for video surveillance cameras, are very sensitive to the effects of ionizing radiation than discrete devices such as photodiodes. Therefore, video cameras with a sensitive element in the form of photodiodes have the greatest radiation stability. There are certain methods for producing radiation-stable CCD matrices, which are used to obtain radiation-stable matrices for video surveillance cameras designed to operate in fields of ionizing radiation.

Literature
1. Radiation Hardness in Optoelectronics. F. A. Zaitov, N. N. Litvinova, V. G. Savitsky, V. G. Sredin. Edited by V. G. Sredin. — M.: Voenizdat, 1987
2. The Effect of Penetrating Radiation on Electronic Products. V. M. Kulakov, E. A. Ladygin, V. I. Shakhovtsov, et al. Edited by E. A. Ladygin. – Moscow: Sov. Radio, 1980
3. Radiation effects in bipolar integrated circuits. V. N. Ustyuzhaninov, A. Z. Chepizhenko. – Moscow: Sov. Radio, 1989
4. Charge-coupled devices. Edited by D. F. Barb. – Moscow: Mir, 1982
5. A. A. Chernyshev, A. Z. Chepizhenko, Yu. A. Borisov, et al. Intermittent and stable failures in digital integrated circuits exposed to ionizing radiation. Foreign Electronic Technology, 1986, No. 7 (302)