Device for Constructing an Axonometric Image of a Signal on the Screen of a Cathode-Ray Tube During Measurement of Inhomogeneities in the Spatial Distribution of Radiation Fields

V. A. Vorob'ev, A. P. Laforov, O. V. Filondan

Presented by the joint seminar of the sectors [[unclear: DSN]] and MRD of the Nuclear Physics Research Institute

The purpose of studying the spatial distribution of radiation fields may be to obtain information on the radiation-beam intensity averaged over time or over some area, or to measure the magnitude and duration of inhomogeneities arising in the radiation field under consideration.

In the first case, integral methods for measuring radiation intensity may be used, based on ionization chambers, scintillation counters, X-ray films, and other types of radiation detectors. In the second case, it is necessary to have a detector or a detector system that records local changes in the radiation field occurring over a limited region of it or over a definite interval of time.

Information on a local change in the radiation field, recorded on X-ray film or by means of a television system, is based on obtaining a planar image of the radiation field, where regions of the radiation flux with different intensities correspond to an image on the film or on the screen of a cathode-ray tube of different density or brightness. To measure the magnitude of a local change in the radiation field in this case, it is necessary to use a method based on the application of special standards, which complicates and makes more difficult the investigation of the spatial distribution of radiation fields.

Fig. 1. Block diagram of the device

Fig. 3.

Fig. 2. Schematic circuit diagram of the STK.

In this case it is necessary to have a generalized picture of the spatial distribution of the investigated part of the radiation field in a form convenient for carrying out direct measurement of the quantities of its local variations.

The spatial distribution of the radiation field at any of its points is described by three variables. Two variables determine the coordinates of the point under consideration in the plane of the radiation field. The third variable is the quantity that determines the radiation field itself and, in our case, represents the radiation intensity at the point under consideration.

Below we describe a device developed by us that makes it possible to obtain a three-dimensional image of the radiation field being investigated. The construction of the image is based on the method of axonometric coordinate transformation \[1\].

The block diagram of the device is shown in Fig. 1. An X-ray vidicon with electrostatic beam deflection was used as the radiation detector, and the image indicator was a cathode-ray tube of type 13LK37. This combination made it possible to use only two voltage sweep generators.

The use of a small number of lines \(20\text{--}50\) determines the choice of an X-ray vidicon with electrostatic deflection, since, for increased clarity, there is no need to increase the number of lines above 50 and high resolution is not required; moreover, in order to record the radiation field between the lines, the “plans” can be shifted relative to one another.

The video signal is taken from the load resistance of the X-ray vidicon and is fed to video amplifier 5. After the amplifier, the signal of negative polarity is applied to coordinate-transformation system 6, to the two other inputs of which sawtooth voltages from the sweep generators \((8, 9)\) with amplitudes of 60 V are applied. The sweep voltages are simultaneously fed to phase inverters, whose loads are the deflecting plates of X-ray vidicon 1. To obtain an image of normal dimensions on the screen of the cathode-ray tube, signals with amplitudes up to 60 V must be applied to the deflecting plates. Therefore, the signals from the coordinate-transformation system are fed to vertical-deflection amplifier 3 and horizontal-deflection amplifier 2.

As the video-monitoring device one may use a standard oscilloscope of type EO-58, IO-4; then the above-mentioned

amplifiers for the beams. In order to obtain a stable image by lines and frames, a separate synchronization unit—9—is used in the device; it generates trigger pulses of frame and line frequency.

To blank the retrace strokes of the electron beams in the image dissector and in the CRT, the “blanking” unit—7—is used, which forms negative blanking pulses of frame and line frequency. The blanking pulses are summed in a pulse mixer made with active resistors, after which the blanking pulse with an amplitude of 60 V is fed to the CRT modulator and to a compensated voltage divider, whose output signal is applied to the image-dissector modulator.

As is clear from consideration of the operation of the device, the coordinate-transformation system converts three input signals, carrying information on the magnitude of the “inhomogeneity” of the radiation field, into two signals that are already “axonometric” in form.

In article [1] a mathematical relationship between such parameters was established, having the form

\[ \begin{aligned} Y &= y \operatorname{Cos}\alpha - x \operatorname{Sin}\beta \operatorname{Sin}\omega_{1} - z \operatorname{Cos}\gamma \operatorname{Sin}\omega_{2},\\ X &= x \operatorname{Cos}\beta \operatorname{Cos}\omega_{1} - z \operatorname{Cos}\gamma \operatorname{Cos}\omega_{2}. \end{aligned} \tag{1} \]

Here \(\alpha\), \(\beta\), \(\gamma\) are the angles of the vectors of the Cartesian coordinate axes \(ox\), \(oy\), \(oz\) with the projection plane \(XY\), and \(\omega_{1}\) and \(\omega_{2}\) are the angles formed by the projections of the coordinate axes of the Cartesian system with the \(OX\) axis belonging to the projection plane.

By specifying the angles \(\alpha\), \(\beta\), \(\gamma\), \(\omega_{1}\), \(\omega_{2}\), one can obtain the corresponding projection images for dimetry or isometry.

The basic circuit of the coordinate-transformation system is shown in Fig. 2.

The circuit was drawn up taking into account the fact that the video signal, corresponding to the function \(y(t)\), has negative polarity. This made it possible to dispense with two inverting blocks, which simplified the circuit.

In the system of equations (1), \(x(t)\) is the signal of an increasing sawtooth voltage of line frequency; \(y(t)\) is the video signal; \(z(t)\) is the signal of an increasing sawtooth voltage of frame-frequency

frequencies of the functions of the input parameters \(X(t)\), \(Y(t)\) are already complex signals.

An important feature of the functions \(x(t)\) and \(z(t)\) is that they specify the position of a point in space.

Let us consider the particular case of an isometric image of an inhomogeneity. For this case the system of equations (1) takes the form

\[ \begin{cases} Y = 0.816y - 0.408x - 0.408z,\\ X = 0.707x - 0.707z . \end{cases} \tag{2} \]

From the system of equations (2) it is evident that, in order to add the signals, amplitude values of 0.816 and 0.408 of the maximum values of the corresponding voltages are used.

The summators of the signals are implemented on double triodes of type 6N2P (tubes \(L_1, L_2, L_3\)). An inverter is made on tube \(L_4\). Cathode followers are made on tubes \(L_5, L_6, L_7, L_8\). They are necessary in order to avoid the shunting effect of the variable high-resistance resistors on one another.

Figure 3 shows an oscillogram of the axonometric image corresponding to a cavalier projection, that is, when

\[ \alpha = 0^\circ \qquad \beta = 0^\circ \qquad \gamma = 60^\circ \]

\[ \omega_1 = 0 \qquad \omega_2 = 45^\circ . \]

As tests have shown, the device described above makes it possible to detect and measure local changes in radiation fields amounting to 5–2% of the average value of the radiation intensity in the portion of the field under consideration.

In addition to using the instrument for studying radiation fields, it can also be applied in other cases when it is necessary to record changes in three or more independent parameters.

Literature

1. Laforov A. N., Naai I. E., Bylino N. M. Construction of axonometric images on the TsVM Minsk-2. Izv. ESTI TPI, 1970.

2. Nonopolskii V. A. Electron-beam oscillograph. Moscow, 1969.