Nucl. Tracks Radiat. Meas., Vol. 20, No. 2, pp. 383--387, 1992 Int. J. Radiat. ,4ppL Instrum., Part D Printed in Great Britain

0735-245X/92 $5.00 + .00 © 1992 Pergamon Press Ltd

SHORT COMMUNICATION

DESIGN A N D CONSTRUCTION OF AN ELECTROCHEMICAL ETCHING POWER SUPPLY

GUILLERMO ESPlNOSA,* FRANCISCO FERN~,NDEZ and VICTOR M. CASTA~O Instituto de Fisica, U.N.A.M., Apartado Postal 20-364, 01000 Mexico, D. F. Mexico

(Received 13 January 1992)

Almtrmet--An original design for a high-voltage power supply for electrochemical etching of latent nuclear tracks is presented. The device is analysed in terms of each of its block components and its performance with and without loading. Some of the main advantages of the design, besides the electronic performance, are its portability and low power consumption.

1. INTRODUCTION

FOR ~ ~ working in the field of particle track detection, efficient etching of plastic (polymeric) detectors is a well-known problem. Indeed, it is sometimes difficult to decide whether to use chemical or electrochemical etching, when processing time and cost are considered.

Since the introduction of electrochemical etching (ECE) in the 1970s (Tommasino, 1970; Tommasino and Armellini, 1973), a number of systems intended to produce dielectric breakdown (also known as treeing) have been developed, especially in the case of polymeric detectors which are widely used nowa- days in a variety of applications such as particle accelerators, nuclear reactions, personal and environ. mental dosimetry, radon measurements and, in general, in every case where solid state nuclear track detectors (SSNTDs) are utilized (Tayyeb et al., 1988).

The main advantage of ECE is that it allows an enlargement of the latent track produced by radi- ation. This, associated with some physicochemical parameters such as the concentration of the etchant solution, temperature, wave form, frequency and voltage, gives the possibility of determining the characteristics of the incident radiation (i.e. energy, nature, etc.). Generally speaking, one of the most important parameters to be taken into account when designing a workable ECE system is the high- voltage high-frequency power supply. In this present work we report our design of a high-voltage power supply that requires low power for operating and which can be used both in field or in laboratory conditions.

2. GENERAL DESCRIPTION OF T H E

ELECTRONIC SYSTEM

As already mentioned, various interesting designs for high-voltage power supplies have been reported in the literature during the last 20 yr (Matiullah et al.,

1987; Tommasino, 1970; Tommasino and Armellini, 1973). Nevertheless, it is still a challenge for elec- tronics designers to offer a power supply with a high adaptability to the available ECE chambers, flexi- bility in its voltage and frequency ranges and, above all, absolute control over all the detectors to be recorded.

Our present design has been developed through various stages in the generation of the signal as well as high-voltage production. We mention this because it could prove interesting to know our experi- ences for people thinking of building their own dedicated power supply. In 1975, the first prototype was built, based upon a commercial television "fly- back". This power supply produced an acceptable high-voltage but the output power was rather low and the signal was distorted. After this attempt a solenoid from an automobile was utilized and a high voltage was achieved; the efficiency, however, was extremely low and the treeing was not obtained in most cases. Further, Lawrence Livermore National Laboratory technology (Griffith and McMahon, 1982) was used successfully and it was possible to handle up to 50 detectors at a time. Unfortunately, the current employed and the heat dissipated were too high.

The current design, based on an output trans- former built with materials designed for good per- formance at high frequencies, utilizes integrated

*CICESE Graduate Student.

383

384 G. ESPINOSA et al.

| i

- i

i i

0 ii'

circuits and solid-state components which provide an excellent response for practical applications. Figure i shows a block diagram of the whole system. In what follows we shall describe briefly each one of the blocks in the system. A list of components is given in the Appendix.

I

i r~

"O

3. DESCRIPTION OF THE CIRCUITS

(a) Figure 2 shows that inverting system circuitry provides 125V r.m.s. 60Hz from a 12.5V d.c. bat- tery. It is useful for autonomy performance or when power line failure occurs.

(b) Low-voltage power supplies: these are con- ventional power supplies which provide the biasing for the security system (12V d.c.), the oscillator (75 V d.c.) and the power stage (175V d.c.). The corresponding low-voltage power supply circuit is schematically depicted in Fig. 3.

(c) Oscillator: Fig. 4 shows the circuit of an oscil- lator with fixed frequency, variable amplitude and impedance matching. The technology used is basi- cally a RC circuit with a transistor connected in common-emitter mode. An interesting feature of the circuit is the variable resistance (0--4.7 kl'l) which allows a fine tuning (_+400Hz) of the nominal frequency value given by

f = 1/2~ RCx/6

(in our case f = 2 kHz). As can be observed from Fig. 4, this circuit includes

an impedance matching stage via a PNP transistor. (d) Power stage: this circuit, also shown in Fig. 4,

consists of two pans: one dedicated to phase separ- ation and the other to high voltage (power). The first part required a transformer with central derivation in the secondary and the following characteristics:

(i) the primary coil was tuned at 2 kHz by using a capacitor (C = 0.01 •F);

(ii) the nucleus constant is equal to K = 6.9073 x 10 -7 H (turn)-2;

(iii) for each phase, a relationship of primary-to. secondary turns was 1:1/2; and

(iv) wire caliber AWG 32 was utilized. For the power stage, a "push-pull" (Millman and

Halkias, 1972) circuit type "B" was constructed. This kind of amplification stage allows one to reach an efficiency of 78.5%, which is 28.5% higher than that of class "A".

(e) High-voltage transformer: it was necessary tc build a special transformer to raise the input voltage up to a range from 350 V to 6 kV and 25 mA at the output (all these data without loading). The nucleus of the transformer was designed according to the relation:

L = #AN2/I,

where L is the inductance, ~ the magnetic per. meability, A the cross-section of the nucleus, N the

DESIGN A N D CONSTRUCTION OF AN ECE POWER SUPPLY 385

z~

I2

c3 It: ~,c, 1 1 8 ~ 6 5 1 I I Lc.1 I . , , z~

FIG. 2. Security system.

oa

G? .S,a. . [_ , .<" [

J-~ I I .!a-}- i :

r" r ' B I

DI;

D3 ~.

X Y to transient detector dy.

O * 11'5 Vdc

:i)'Z o "~0 *TSVdc

D S ~ ' ~ - - 6 *12~c

J_.

FIG. 3. Diagram of the low-voltage power supply.

to security fly. X Y I I . . . . . . . . . . . . . . . . . . . . . . . . . . . . I

.12Vdco *l't5 Vdco RI9 *75Vdcc t ~ ~V-

. . . . . . . T--J, , . , c~82

°" ; i

I

29

:GI6 ;r5' D6;

O

12 H.V. OUTPUT

_ i _ O

FIG, 4. Diagram showing the oscillator and impedance matching stage, phase separation and power stages. A security system is provided in the high-voltage output.

number of turns of the coil and I the total length of the wire that forms the coil.

(f) Security system: as can be observed from Fig. 1, this block really corresponds to a feedback stage. It consists, as depicted in Fig. 4, of three parts: a sensor circuit that activates the a.c.-d.c, converter when a

short circuit occurs; a current amplifier and, finally, a reed relay.

(g) Security relay: this is, as can be seen in Fig. 1, an intermediate stage between the line and the low- voltage power supplies and is activated in the event of a sudden voltage increase by the security system

386

(a)

~ 2

(b)

G. ESPINOSA et al.

~ SKHz

2,0KHz

t,0KHz

0,SKHz

0,5 I L5 2 2.5 3 3,5 4 4,5 5

VOLTAGE ACROSS ECE CELL (KW)

: ~ X [ I ' , I x T [

I I I I I I I [ I J 1 2 3 4 5 6 7 8 9 10

NUMBER OF CHAMBERS

FIG. 5. Plots of the output voltage of the power supply described for (a) no loading applied and (b) a load (i.e. an

ECE cell) connected.

(see section (f)). As can be observed in Fig. 3, the circuit has a reset button to re-activate the system after a failure.

point out that the development of instrumentation in the field will lead necessarily to a deeper understand- ing of the track detection process.

Acknowledgements--The authors wish to thank Mr Jos6 I Golzarri, Ms Rosa Lima and Mr Jorge Barreto for theil technical support.

REFERENCES

Castafio V. M. and Bribiesca A. (1989) Computer- aided design and analysis of electronic circuits for instrumentation and control. Comp. Phys. Jul/Aug, 69-72.

Griflith R. V. and McMahon T. A. (1982) Progress on development of a passive, personnel neutron dosimeter/spectrometer. In Dospec. Proc. of the 9t~ DOE Workshop on Personnel Neutron Dosimetry, pp. 103-119. Battelle Memorial Institute.

Matiullah, Taylor C. and Durrani S. A. (1987) An inte- grated-circuit-based variable power supply for elec. trochemical etching. Nucl. Tracks Radiat. Meas. 13, 67-70.

Millman J. and Halkias C. C. (1972) Integrated Electronics. McGraw-Hill Kogakusha, Tokyo.

Tayyeb Z. A., AI-Khalifa I. J. M., Khalifa M. S. and Durrani S. A. (1988) Thermoluminescence response ol CR-39 to fl-particles and ?-rays. NucL Tracks Radiat. Meas. 15, 787-790.

Tommasino L. (1970) Electrochemical etching of damage track detectors by H.V. pulse and sinusoidal wave forms. CNEN Report RT/PROT (71), 1.

Tommasino L. and Armellini G. 0973) A new etching technique for damaged track detectors. Radiat. Eft. 20, 253-255.

4. PRACTICAL APPLICATIONS AND FINAL R E M A R K S

The behavior of the system was tested in order to ensure a good response of the circuits. Figure 5(a), for instance, shows plots of the voltage delivered by the system as a function of the frequency. Figure 5(b) corresponds to the case in which the ECE cell was connected to the power supply. Obviously, the load- ing represents a diminishing in the efficiency of the output power, as can be further observed in the plot, where the voltage with a load connected is drawn against the free-load voltage. In an ideal case, there should not be a decrease in the delivered power.

Finally, in the authors' opinion, this type of design represents an alternative to some of the systems already available, and a number of deeper studies, such as obtaining the transfer function of the total circuit and analysing the stabifity of the components under different loading regimes. In principle this is not an easy task, given the relative complexity of the circuit; however, some powerful software techniques available today (Castafio and Bribiesca, 1989) make it possible to analyse fully these kinds of circuits with the aid of a digital computer. Besides the obvious academic interest of these studies, it is important to

APPENDIX: LIST OF COMPONENTS

Capacitors

CI: 4.7 #F, 63 V (electrolytic) C2, C16: 0.47 #F, 250V C3: 1 nF, 50 V C4: 3.3 #F, 63 V (electrolytic) C5: 2.2 #F, 250V C6, C7, C8, C12, C|3, C14, CI7, C18- 10nF, 250V C9: 470t~F, 200 V (electrolytic) C10: 10 #F, 100 V (electrolytic) C11: I0 #F, 25 V (electrolytic) C15: 100/~F, 63 V (electrolytic).

Rectifiers diodes DI, D2, D3, D4, D5, D6: 1N4007.

Transistors QI, Q6, Q10, QI 1, QI2: BC.547C Q2, Q7: BD235 Q3, Q4: TIPI42 Q5: TIPS0 Q8, Q9, Qg': TIP54.

Resistors (0.5 watt, unless otherwise specified) RI: 150 RI5: 56K R2, R7: 10 K RI6: 2.2 K R3: 1.8 K RI7: 18 K R4: 2.7 K RIg: 5 K pot R5: 4.7K pot R19: 100K R6, RII: 47K R20: 4.7K prese!

D E S I G N A N D C O N S T R U C T I O N O F A N ECE P O W E R S U P P L Y 387

R8: 5.6 K R21, R22: 3.3 K R9: 220 R23: 2 K RI0: 1.5 K 17,24, R25: 10 RI2: 100, 1W R26: 50M RI3: 22K, I W R27: 33K RI4: 47 K, 1 W R28, R29: 100K.

Transformers TI: phase separator for AC187/88 complementary

transistors. T2: primary 20V r.m.s.c.t.; secondary 125V r.m.s.;

120 watts. T3: primary 125 V r.m.s.; secondary 18V r.m.s.; 6watts.

T4: primary 200 turns AWG28; secondary 2 x 100 turns AWG28. Laminated iron core.

T5: primary 2 x 140 turns AGW22; secondary 4900 turns AGW28. Laminated iron core.

Relays U 1: 2P 1 T, 12 Vac coil U2: IPIT reed, 5 V d.c. coil.

Zener diodes Z 1 : I N4739 ZA: Z2: 1N4732 Z5: Z3: 1N4761

IN4743 IN4735