BETATRON RADIATION ENERGY METER

A. P. GRIGOR’EV, N. V. NESTEROV

(Presented by the scientific seminar of the Scientific Research Institute of Electronic Introscopy)

Most betatrons used in industry, medicine, and scientific research are equipped with devices that make it possible to estimate the maximum energy in the spectrum of the betatron bremsstrahlung. Usually an indirect measurement method is used for this, i.e., some electrical parameter is measured (current, voltage) that is proportional to the measured quantity. Errors due to the measurement technique [1, 2] and due to the instability of the frequency and delay stages [4] were reduced to a considerable extent in a circuit in which the maximum energy is estimated from the voltage amplitude—an analogue of the magnetic field at the moment when the accelerated electrons are dumped onto the target [3].

A drawback of the above-mentioned circuits is the limitation of the range of measured energies either on the side of maximum [1, 2] or minimum energies [3, 4] (because of the use of switching devices); possible changes in the parameters (amplitude and duration) of the current pulse in the bias winding are not taken into account, which can make a noticeable contribution to the measurement error [5].

Fig. 1. Schematic diagram of the energy meter

The circuit of the energy meter given below (Fig. 1) is free of the indicated shortcomings. The circuit is built using semiconductor devices, since in the latest types of betatrons a transition has been made to semiconductor control circuits. The principle of operation of the circuit is analogous to the principle described in [3]; therefore its description is omitted here.

As can be seen from Fig. 1, the meter circuit consists of a flip-flop with separate triggering (\(T_1, T_2\)), to both inputs of which trigger pulses are applied. A pulse is applied to input A at the instant when the betatron magnetic field passes through zero (from the pulse amplifier of the peak transformer of the synchronization circuit); a pulse is applied to input B at the instant the radiation appears (from the FEC crystal sensor of the radiation dose-rate stabilization circuit or from another radiation receiver).

The gating circuit (\(T_4, T_5\)) is used instead of the switching device of the prototype circuit [3]; by means of emitter followers (buffer stages) on transistors \(T_3\) and \(T_6\), it is separated from the flip-flop and from the measuring device. A sinusoidal voltage—an analog of the field—is applied to the input of the gating circuit from the magnetic-field sensor; the required \(90^\circ\) shift is produced by means of an integrating RC circuit, while the integration error is reduced to a minimum by the measures described in [3].

The measuring device is made according to the simple circuit of a standard diode voltmeter with a closed input, which mainly determines the measurement error.

The meter circuit is easy to adjust and stable in operation.

REFERENCES

1. W. F. Westendorp. Rev. Sci. Instr., vol. 17, No. 6, 1946.
2. L. M. Anan’ev et al. Induction Electron Accelerator—Betatron. Moscow, Atomizdat, 1961.
3. V. I. Gorbunov et al. “Measurement Technology,” 1967, No. 1, 94–95.
4. V. I. Gorbunov et al. Electron Accelerators. Proceedings of the Fourth Interuniversity Conference. Moscow, “Vysshaya shkola,” 1964, 302–304.
5. A. A. Vorob’ev et al. Izvestiya TPI, vol. 156, Tomsk: TGU Publishing House, 1969, 224–225.