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INSTRUMENTS

FOR RADIATION DETECTORS β Ι Ι ΐ A N D CONTROL SYSTEMS® H

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R. BENOIT*, E. DE BLUST*, L. ISABELLA**, V. MANDL*,

and G. MELANDRONE*

* Euratom

**CEI, Müan

ΛΛραΛ

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EUR 3063.e ELECTRONIC INSTRUMENTS FOR RADIATION DETECTORS AND CONTROL SYSTEMS by R. BENOIT*, E. DE BLUST*, L. ISABELLA**, V. MANDL* and G. MELANDRONE* * Euratom ** CEI, Milan

European Atomic Energy Community — EURATOM Joint Nuclear Research Center — Ispra Establishment (Italy) Chemistry Department — Nuclear Chemistry Brussels, August I960 — 34 Pages — 30 Figures — FB 50

Electronics instruments developed in the Nuclear Chemistry Laboratory of the Chemistry Department are described. They include low noise amplifiers for solid state detectors and gridded ionization chambers, fast electronics, power systems for the construction of lithium drifted semiconductors detectors and automatic controls for activation analysis and radiochemical separations.

EUR 3063.e ELECTRONIC INSTRUMENTS FOR RADIATION DETECTORS AND CONTROL SYSTEMS by R. BENOIT*, E. DE BLUST*, L. ISABELLA**, V. MANDL* and G. MELANDRONE* * Euratom ** CEI, Milan

European Atomic Energy Community — EURATOM Joint Nuclear Research Center — Ispra Establishment (Italy) Chemistry Department — Nuclear Chemistry Brussels, August 1966 — 34 Pages — 30 Figures — FB 50

Electronics instruments developed in the Nuclear Chemistry Laboratory of the Chemistry Department are described. They include low noise amplifiers for solid state detectors and gridded ionization chambers, fast electronics, power systems for the construction of lithium drifted semiconductors detectors and automatic controls for activat'on analysis and radiochemical separations.

EUR 3063.Θ

EUROPEAN ATOMIC ENERGY COMMUNITY - EURATOM

ELECTRONIC INSTRUMENTS FOR RADIATION DETECTORS

AND CONTROL SYSTEMS

by

R. BENOIT*, E. DE BLUST*, L. ISABELLA**, V. MANDL*, and G. MELANDRONE*

* Euratom **CEI, Milan

1966

Joint Nuclear Research Center Ispra Establishment - Italy

Chemistry Department Nuclear Chemistry

CONTENTS

1. Introduction 3

2. Low noise amplifiers for semiconductor detectors and gridded ionization chambers by R.Benoit and G.Melan-drone 3

3. Fast Electronics for time measurements with photo-multipliers and semiconductor detectors by L.Isabel­la and V.Mandi 7

4. Power Supplies and Control Systems for the construc­tion of Lithium Drifted Semiconductor Detectors by E. De Blust 12

5. Automatic Controls for the Act iva t ion Analysis and

Radiochemical Separa t ions by G.Melandrone 13

6. References H

7. Caption of f i gu re s 15

SUMMARY

Electronics instruments developed in the Nuclear Chemistry Laboratory of the Chemistry Department are described. They include low noise amplifiers for solid state detectors and gridded ionization chambers, fast electronics, power systems for the construction of lithium drifted semiconductors detectors and automatic controls for activation analysis and radiochemical separations.

1. INTRODUCTION

The aim of this paper is to describe briefly the electronic instruments which have been developed in the Nuclear Chemistry Laboratory during the last years. These instruments have been designed and built in con­nection with the research activities of the laboratory and are subdivided into the following branches:

Low noise amplifiers for semiconductor detectors and gridded ionization chambers. Past electronics for time measurements with photo-multipliers and semiconductor detectors. Power supplies and control systems for the construc­tion of lithium drifted semiconductor detectors. Automatic control for activation analysis and radio­chemical separations.

The main electrical characteristics of each instrument developed are indicated and for some of these the circuit diagram is given. Their performance in physical measure­ments are specified and other possible fields of applica­tion are mentioned.

All the instruments described have been tested for long periods of operation and have shown good reliabili­ty.

2. LOW NOISE AMPLIFIERS POR SEMICONDUCTOR DETECTORS AND GRIDDED IONIZATION CHAMBERS. by R.Benoit and G.Melandrone

Semiconductor detectors and gridded ionization cham­bers are characterized by extremely good intrinsic energy resolution. Our effort was focused on developing electro­nic instruments which could take full advantage of these characteristics. Por this purpose low noise charge and voltage sensitive preamplifiers, high gain linear ampli-

Manusc r ip t r e c e i v e d on June 6 , 1966 .

- k -

fiers, and pile-up detectors were developed.

2.1 Low noise charge sensitive preamplifiers for semiconduc­tor detectors.

Three types of charge sensitive preamplifiers for different types of semiconductor detectors have been built. They are:

a) preamplifiers for high capacitance and high leaka­ge current detectors such as surface barrier types

b) general purpose preamplifiers for medium capacitan­ce and medium leakage current, (small surface bar­rier and silicon lithium drifted detectors)

c) preamplifiers for low capacitance and low leakage current detectors, (germanium lithium drifted). The main electrical characteristics of these three

types of preamplifiers are given in Table 1.

TABLE 1

LOW NOISE PREAMPLIFIERS

Preamplifier type

a

b

c

Input tube

E810 F

E810 F

EC1000

Sensitivity in mV/MeV

in Ge

11,7

25

63,5

Output rise time in nsec

30

30

45

Noise in KeV at f.w.h.m. at zero ext. capacitance

3,5

2,5

1,4

Power supply

+270Vdc 20mA 6,3V ac

+270Vdc 20mA 6,3V ac

+270Vdc 20mA 6,3V ac

The schematic diagrams of the type a and b preampli­fiers are shown in Fig. 1. The first tube has been selec­ted and its operating conditions adjusted for low grid current and high transconductance so that a maximum signal to noise ratio is obtained with the type of detector desired. A semiautomatic curve tracer system has also been developed

- 5 -

for this purpose, and the tubes were aged for a period of 100 hours before being selected. The block diagram of this curve tracer system, with a typical plot of an EC 1000 tube, is shown in Fig. 2. The grid voltages,Vg, and the grid currents, Ig, for different plate voltages, Vp, are recorded on an X-Y plotter; first with the switch SW1 in pos. 1 and than in pos. 2. The grid current is proportional to the difference between plots 1 and 2, as shown by the dashed line. A type c preamplifier circuit is shown in Fig. 3· In this circuit a cascode input configuration with bootstrap has been used in order to increase the signal to noise ratio and the dynamic input capacitance. The performance of the type b and c preamplifiers is re­ported in Figs. 4 and 5. These show the resolution in KeV at FWHM (Full Width Half Maximum) for a germanium detector (W = 2.8 eV/electron-hole pair) vs. the shaping time con­stants. One RC differentation and one RC integration of equal time constant are considered and the curves aie plot­ted using the external capacity as a parameter. This mea­surement was performed by injecting a known quantity of charge at the preamplifier input and using the root mean square voltmeter method described by Gillespie(l) and Fairstein(2). in the upper parts of the Figures are shown the energy resolution vs. the total input capacitance mea­sured at the optimal time shaping constant.

The typical performance of these preamplifiers_is shown in Fig. 6 . In the upper part is reported an e spectrum of Cd1^9 performed with a b type preamplifier and a Silicon Lithium Drifted Detector cooled to -90°C. In the lower part is plotted an e spectrum of Cs137 per­formed with a c type preamplifier and the same detector as above cooled to -175°C.

2.2 Voltage sensitive preamplifiers for gridded ionization chambers.

Different types of preamplifiers with a cascode in­put, followed by a bootstrapped cathode follower, in or­der to increase the open loop gain, have been designed and tested. The following tubes have been used at the input: E180F, E83F, 404A, E88CC.

These have been selected for their high transcon-ductance to grid current ratio.

Typical characteristics of the triode connected E83F and of the E88CC are shown in figs. 7 and 8 , The o-perating points are selected at a grid bias corresponding

- 6 -

to the maximum of the grid current curve, (where elec­tronic current is negligible). The ratios of transcon-ductance vs. grid current for the two tubes these con­ditions are the following:

Vp in volts

50

60

70

80

90

gm in A/V/Ig i n A

E83F

0,544x 109

0,736x 109

0,738x 109

E88CC

3,6 χ 109

1,96x 109

1,17x 109

1,03x 109

The theoretical signal to noise ratio can than be cal­culated (taking into account the input capacitance of the tube), and the tube itself can be selected.

The best results were obtained with the preampli­fier shown in fig. 9 using an E88CC at the input. This tube was placed inside the ionization chamber in order to reduce the stray capacitances.

A typical alpha spectrum obtained with this pre­amplifier, using the best E88CC selected among twenty tested tubes and with RC pulse shaping, constants of Τ = RC int = RC diff = 2us, is shown in Fig. 10.

Fig. 11 shows the FWHM vs. shaping time constants f (r) of this preamplifier obtained by injecting a known charge from a pulse generator. The external capa­citance was 10 pF.

2.3 High gain linear amplifiers.

High gain amplifiers composed of a voltage sensitive input loop with independently variable RC integrating and differentiating time constants, and one main and one bia­sed post amplifier have been built. Two internal indepen­dent voltage supplies; one for biasing the semiconductor detectors and the other for operating an external pream­plifier, are also provided.

- 7 -

The gain is stabilized by internal feedback, and the principal characteristics of the amplifier and its different parts are reported in Table 2. These amplifiers are a modified version of the ORTEC Model 201 low noise amplifier in which a set of variable RC time constants and an input amplifying loop were added.

2.4 Pile-up detection circuit.

A pile-up detection circuit which rejects two or mo­re superimposed on closely spaced events in a time range from 5 to 500 usee was developed and is described in re­ference (3)· The circuit also provides the possibility of cancelling two or more pulses superimposed on their front edges and is used in connection with linear ampli­fiers described in Sec. 2.3. The schematic diagram is il­lustrated in Fig. 12.

3. FAST ELECTRONICS FOR TIME MEASUREMENTS WITH PHOTOMULTI-PLIERS AND SEMICONDUCTOR DETECTORS. by L.Isabella * and V.Mandi

A fast counting system in the time domain of nanose­conds has been developed. The input cricuits were desi­gned to work either with fast photomultipliers such· as types 56AVP and XP 1020 (manufactured by Phillips) or with semiconductor detectors. The parts were assembled in shiel­ded modular plug-in units and are operated from a common power-supply of -20, -10 and +10 Volts. Transistors and Germanium tunnel diodes were used, and the input and output impedance were kept at 50 ohm. Most signals have negative polarity, 0.5 V output amplitude, across a 50 ohm load. Coaxial 50 ohm transformers have also been built and are used to invert the signal polarities, when required.

The instruments which have been developed, and their main characteristics, are listed in Table 3· This equip­ment, up to now, has been used for time resolution mea­surements on fast photomultipliers (principally XP 1020) and for alpha-gamma and alpha-electron coincidences. The results obtained in the field of time resolution measure­ments with photomultipliers are reported in references(10) and (11). The half-life determination of the 73.6 KeV le­vel of Np239j performed by the delayed coicncidence tech­nique, is described in reference(4)· In this measurement a photomultiplier has been used for detecting the gammas and a surface barrier semiconductor detector for the alphas.

* CEI, Milano

I Oo I

TABLE 2 HIGH GAIN LINEAR AMPLIFIER

Part

Input lo­op (volta ge sensi­tive)

Main am­plifier

Post am­plifier (0-100V threshold)

Input polarity

positive or ne gative

positive

positive

Voltage gain

50 or 300

25,50,100 or 200

2,4,8 or 16

,

Rise time

0.1-0.15 usee

0.3usec

Time constants

0.22,0.33,0.47, 0.56,0.68,0.82, 1.2,1.4,1.6usec

no

no

Output pola­rity

output is in ternally con nected to the main ampi.

positive

positive

Dynamic range

0-15V

0-100V

0-100V

Integral li­nearity

+0.2$ of 95$ of the full range output

+0.25$ of the maximum output

+0.5$ of 80$ of the full range output

Alpha-electron and alpha-gamma coincidence measurements of Bi212 with Lithium Drifted Semiconductors detectors are still in progress. Refering to Table 3 both types of amplifiers were developed for semiconductor detectors since the gain of recent P.M.'s is sufficiently high so that no further amplification is necessary.

The discriminator, in its most recent version, uses a Ge 1N3716 tunnel diode with a peak current of 4.7 mA, and has a time walk of about 2 nsec for input signal am­plitudes from 100 to 500 mV. XP 1020 P.M. output pulses were used for this measurement and the test conditions are illustrated in Fig. 25. A hydrogen discharge lamp(4) was used to generate short light pulses, of about 1.5 nsec f.w.h.m., and a system of "polaroid" lenses was used to vary the light intensity over a central area of 1" diame­ter on the photocathode. This collimation was used to si­mulate the experimental conditions of the PM with a 1"x1" scintillator crystal and to avoid transit time jitter from the center to the border of the photocathode. The PM out­put controls the STOP input of the Time to Pulse Converter (TPC) which is started on each flash of the hydrogen lamp. These START signals are picked off by means of a capaciti­ve antenna which is sensitive to the current through the lamp. The output of the TPC is analyzed with a 256 channel pulse height analyzer.

Two different types of TPC have been developed. The first one is a START-STOP type, i.e. two inputs with dis­tinct characteristics are used and the signal at the START input must always precede the one at the STOP input. This converter also has a gate which can control the START si­gnal, and is triggered with an external pulse which normal­ly comes from a coincidence.

The second converter is of the pulse overlap type and the two inputs are symmetrical. In this circuit the coinci­dence is obtained from the same signals which enter the converter and a simpler circuit configuration is achieved with about the same performances as in the first type con­cerning the measured time internal, overall linearity, and stability.

Other instruments do not require special comment.

TABLE 3 FAST ELECTRONIC CIRCUITS

Type and model

Voltage divider for 56AVP P.M.

Voltage divider for XP1020 P.M.

Model 1 Pream­plifier

Model 10 Pream­plifier

Fast discrimina­tor D1

Double coinci­dence and Fan-out

Main characteristics

Bleeder current 3 mA, fast output from anode and slow out­put from dynode N°12

Bleeder current of 2 mA for the first 10 dynodes and 10 mA for the last three.Coaxial anode output (50 ohms) and slow output from dynode N° 10. positive or negative input polarity, 10 ohm input impedan­ce, voltage gain of about 70, output rise time 2 nsec, out­put polarity inverted with respect to the input, max. out. 0.7 Volts. input polarity negative, 50 ohm input impedance, voltage gain of 10, output rise time 1 nsec, output polarity ne­gative, max. output 1 Volt.

Minimum input threshold 1 mA across 50 ohms, signal length 2 nsec at f.w.h.m. Output rise time 3 nsec, duration 100 nsec standard, with possibility of inserting external de­lay lines for shorter lengths. Recovery time 150 nsec. Coincidence: resolving time 15 nsec, output signal 2V am­plitude, 200 nsec length. Fan-out: two identical circuits with two independent outputs; each output is about the sa­me as the input.

Remarks

see Fig. 13

see Fig. 14

see Fig. 15 and referen­ce (4).

modified version of the preamp. described in re­ference (5), see Fig. 16

see Fig.17 and reference (4).

see Fig.18, two symmetri­cal output channels, not indicated in the figure, are provided for each in­put.

TABLE 3 Continued

Type and model

Double pulse stretcher S1

Double linear Gate G1

Time to pulse height conver­ter C1

Time to pulse height conver­ter C10

Fast pile-up detector

High input im­pedance catho­de follower

Main characteristics

Accepts and delivers positive and negative signals, minimum in­put signal duration 1 nsec at f.w.h.m. gives 2 nsec output. Two identical circuits on same plug unit.

Gate normally closed, accepts negative input signals in 20-500 mV range; pedestal 1 mV Control signal positive 0.5V amplitude, must bracket and precede the input by 10 nsec. Start-Stop type, input negative, output either polarity. Time range: 50 nsec standard with possibility of obtaining longer ranges. Time resolution: 20 psec short period, 50 psec long pe­riod. Acceptance of the input signal can be controlled by an internal gate. Internal reset is provided. Output can be stretched.

Overlap type - output positive. Time range: 100 nsec when operated from D1 type discriminators. Time resolution: 30 psec short period; 100 psec long period.

Accepts signals from D1 discriminators and produces an output for each pair of input signals separated by 15 nsec to 1.5 nsec.Two identical units are built in the same plug and internally connec­ted to an OR circuit. Tube EC 1000 is used, output rise time 1 nsec, output impedance 70 ohms.

Remarks

based on the circuit de­scribed in reference 6 see Fig. 19.

based on the circuit de­scribed in reference 7, see Fig. 20 see Fig.21 and reference (4).

see Fig. 22

modified version of the circuit described in re­ference (8)., see Fig.23,

circuit described in refe­rence 9; see Fig. 24.

- 12 -

4. POWER SUPPLIES AND CONTROL SYSTEMS FOR THE CONSTRUCTION OF LITHIUM DRIFTED SEMICONDUCTOR DETECTORS. by E.De Blust

Three different power supplies for construction of silicon and germanium lithium drifted semiconductor de­tectors have been built. Two of these have a dc output and the third is pulsed. The outstanding characteristics are the following:

type A maximum dc output 500V 15W type Β maximum dc output 1000V 250W type C maximum pulsed output 600V 90W

frequency range from 1 to 1000 cycles/sec. The type A power supply has been developed in colla­

boration with the Research Reactor Service of the Reactor Physics Department and is described in reference (12). The block diagram of the part which has been built in this laboratory is shown in Fig. 26. The control voltage of the series control element is obtained by monitoring the cur­rent and the voltage across the semiconductor diode. These two variables are measured with logarithme sensitive cir­cuits and the power delivered to the diode, during the drifting process, is obtained by summing the two logarithms. The instrument is based on a similar type described in re­ference 03)· The type Β power supply has been developed for construction of large and thick lithium drifted detec­tors. The block diagram of the circuit is reported in Fig.27. The output power is controlled by varying the conduction angle of two Silicon Controlled Rectifiers (S.C.R.) which are placed in the primary winding of the transformer. These S.C.R. are triggered from a blocking oscillator with a re­petition frequency of 10 Kc/sec. The blocking oscillator is driven from a generator which delivers output pulses from 0 to 9 msec width, syncronized from 220 Va.c. The pulse width control is performed manually through an adjustable current feedback from the power output. This feedback acts as a security control during the drifting process and pre­vents any increase by more than 5$ of the rated value of the output current. The type C pulsed power supply has been built following the schematic of reference (14), and its block diagramm is re­ported in Fig. 28. The capacitor C is charged through an S.C.R. and a series inductance to an energy of 0.09 joule, and discharges into the semiconductor diode immersed in a boiling liquid. The output power is limited by a current interlock which controls the firing frequency of the S.C.R.

- 13

A separate circuit with control system is used for the immersion heater.

The semiconductor detectors constructed with these power supplier and their performance are described in re­ferences (15) and (16).

5. AUTOMATIC CONTROLS FOR THE ACTIVATION ANALYSIS AND RADIO­CHEMICAL SEPARATIONS. by G.Melandrone

In this field the following équipement has been built: a) a programmer for activation analysis by means of a 14

MeV neutron generator b) sample changers c) automatic equipment for radiochemical separations

The programmer has been developed and is used in con­nection with a 14 MeV neutron generator manufactured by IMICAM (Milano) and installed in this laboratory. It allows remote on-off control of the neutron flux, controls its focusing and gives the possibility of programming and recor­ding all data of interest over a set of operations.

The block diagram of the equipment is reported in Fig. 29· The program unit is triggered by the sample being ir­radiated, which switches an the neutron flux on arrival at the front of the generator and switches it off after with­drawal .

The sequence control counts and registers the following: a) the integrated neutron flux b) the transit time of the sample from the generator

to the gamma counter, and c) the sample activity at preset times (this operation

is continuously repeated so that half life measure­ments can be performed) The gas inlet control operates the pin-valve of the

deuterium bottle thai s allowing better control of the plas­ma. The focusing meter control the amount of defocussed deaterons, and keeps them to a minimum thus improving the neutron yield and ameliorating the neutron geometry.

A detailed description of this control system is given in reference (17). It was developed for routine analysis of oxygen in terphenils.

The sample changer and its control system are shown in the block diagram of Fig. 30. It may be operated either manually or from an external control unit which has been

- H -

built and is connected to the pulse height analyzer and to a timer.

The automatic equipment for radiochemical separa­tion can perform different chemical reactions.ltis com­posed of modular units which can be assembled and inter-conected in different ways, depending on the chemical se­paration desired. The equipment developed is composed of two types of modular units: 1) the pump with its program unit; 2) the fraction collector and series-parallel deviator.

The pump, which consists of a 30 ml glass syringe, is operated by a synchronous motor which drives the piston, and is controled by a unit assembled on a printed circuit card placed on the upper part of the pumping unit itself.

The fraction collector is composed of a chromatogra­phic column and a fraction collector. A three-way glass stopcock, driven by a micromator, can direct the column effluent to the collecting bottle or to another chromato­graphic column according to the program selected on the printed circuit card of the pumping unit.

The different ways of operation and the results ob­tained are described in reference (18).

More sophysticated automatic equipment has recently been developed in collaboration with the S.R.R. (Research Reactors Service) and consists of one programming and one operating unit. The program unit supplier a 24 Vdc volta­ge for operating up to sixteen various elements such as pumps, valves, heaters, fans, etc., at different preset time intervals and sequences. The program patter is engra­ved on a printed circuit card. A complete chemical process is contained on such a card.

The operating unit contains the pumps and valves which are used to start, regulate and stop the various reagents along the analytical line, and to control the line itself. The pump is of a peristalic type and is operated by a step­ping motor driven by a 24 V variable frequency generator contained in the program unit. The speed of the pump can be varied in five steps between 0.2 and 4 ml/min by chan­ging the control frequency on the programming card.

A detailed description of the equipment and its appli­cations is given in reference (19)·

6. ACKNOWLEDGEMENTS The authors wish to acknowledge many helful discus­

sions with Prof.Bertolini and aredndebited for helful ad­vices and equipment loans to their collegues.

15

6- REFERENCES

1. A.B.Gillespie; Signal, Noise and Resolution in Nuclear Counter Amplifiers; p. 83, Pergamon Press 1953·

2. E.Pairstein; IRE Trans. Nucl. Sci. NS-8 N°1, 129 (1961). 3. G.Bertolini, V.Mandi and G.Melandrone; Nucl. Instr. and Meth.

29, 357 (1965). 4. G.Bertolini, V.Mandi, A.Pedrini, L.Stanchi; Report EUR 2274 e

(1965). 5. H.G.Jackson; Nucl. Instr. and Meth. 33, 161, (1965). 6. K.B.Keller; Rev. Scient. Instr. 35, 1360 (I964). 7. M.Feldman; Rev. Scient. Instr. ¿6, 241 (1965). 8. H.Weisberg; Nucl. Instr. and Meth. 32, 138 (I965). 9. C.Cottini, E.Gatti, V.Svelto, P.Torri, F.Vaghi; Misure di tem­

po con rivelatori a semiconduttore, Rapporto CISE R-72 (1962). 10. G.Bertolini, M.Cocchi, V.Mandi, A.Rota; to be published in

Nucl. Instr. and Methods. 11. G.Bertolini, M.Cocchi, V.Mandi, A.Rota; to be published in IEEE

Trans, on Nuclear Science. 12. E.De Blust, M.Galli, A.Garroni; private comunication. 13. G.Deamaley; J.C.lewis; A.E.R.E. report R 4335. 14. G.L.Miller, B.D.Pate and S.Wagner IEEE Trans. Nucl. Sci. NS-10

N° 1 (1963) 220. 15. G.Bertolini, F-Cannellani, W.Fumagalli, M.Henuset and G.Restelli

report EUR 2580 e. (1965) 16. F.Cappellani, W.Fumagalli and G.Restelli; Nucl. Instr. and Meth.

37, 352 (1965). 17. F.Girardi, J.Pauly, E.Sabbioni; report EUR 2290.f. (1965) 18. F.Girardi, M.Merlini, J.Pauly, R.Pietra; Radiochemical Methods

of Analysis, Vol. II IAEA 1965. 19. F.Girardi, G.Guzzi, J.Pauly, R.Pietra; Intern. Conf. Modern Trends

in Activation Analysis, College Station, Texas; USA 1965.

16

7 -CAPTIONS OF THE PIGURES

Fig. 1 Schematic diagram of the charge sensitive preamplifier type a and b.

Fig. 2 Block diagram of the semiautomatic curve tracer system and a typical plot of a EC1000 tube.

Fig. 3 Schematic diagram of the charge sensitive preamplifier type c.

Fig. 4 Resolution at f.w.h.m. vs. shaping time constant for ty­pe b preamplifier.

Fig. 5 Resolution at f.w.h.m. vs. shaping time constants for type c preamplifier.

Fig. 6 Typical performance of the charge sensitive preamplifiers upper part: Cd"!09 e~ spectra performed with type b pream­plifier lower part Cs137 e~ spectra performed with type c preamplifier.

Fig. 7 Typical Ip vs. Vg and Ig vs. Vg characteristic of E83F tube (triode connected).

Fig. 8 Typical Ip vs. Vg and Ig vs. Vg characteristic of E88CC tube.

Fig. 9 Schematic diagram of a voltage sensitive preamplifier for gridded ionization chambers.

230 Fig.10 Alpha spectra of Th , voltage sensitive preamplifier of

Fig.9 was used for this measurement. Fig.11 FWHM vs. equal integrating and differetiantiating time

constants. Fig.12 Schematic diagram of the pile-up detector. Fig.13 Voltage divider for 56AVP photomultiplier. Fig.14 Voltage divider for XP 1020 photomultiplier. Fig.15 Model 1 Preamplifier. Fig.16 Model 10 Preamplifier. Fig.17 Fast discriminator D1 . Fig.18 Double coincidence and fan-out. Fig.19 Double pulse stretcher. Fig.20 Linear Gate. Fig.21 Time to pulse height converter C1. Fig.22 Time to pulse height converter C10.

17 -

Fig. 23 Fast pile-up detector. Fig. 24 High input impedance cathode follower. Fig. 25 Experimental arrangement for testing the discriminator sle­

wing characteristics. Fig. 26 Block diagram of the type A constant dc power supply for

construction of the lithium drifted semiconductor detectors. Fig. 27 Block diagram of the type Β constant dc power supply for

construction of lithium drifted semiconductor detectors. Fig. 28 Block diagram of the type C pulsed power supply for construc­

tion of lithium drifted semiconductor detectors. Fig. 29 Block diagramm of the programmer for activation analysis by

means of the IMICAM neutron generator. Fig. 30 Block diagram of the sample changer and control system.

.16K ' 5W ¿ μ Ρ

I 350V

22K TOOK"»-.—AV—Ψ

82K 5W 100

-ΛΛΛ Ç- E288CC

TEST a5pF

® I I -

^O- I -Ci) E 188 CC 1

Q_ _

"=*=·

220 W . + 270V

8 M F

350 V

lOOOpF

Φ INPUT | 2000V

)1G 5-500M

E 810 F

J6 ^ F

6V

22 pF Type b

HI—— NPO ¿7pF Type a

01

Hl-^) 27K>5W

3 5 0 V 0 U T P U T

^.pp

Fig. 1 CHARGE SENSITIVE LOW NOISE PRE-AMPLIFIER (E 810 F) TYPE a AND b

Y=Ip Fig. 2

SEMI-AUTOMATIC CURVE TRACER

EC 1000 [ ip . f (Vg)l

TYPICAL PLOT

TESTED TUBE

■X=Vg

a2K/|W i.MF/350 V

22K*

INPUT

®— 500 ρ F

lOOOV < ,_ 5 G

~ | 0047μF

1M < wtlf

[ DETECTOR

(Tl BIAS

E 288 CC

EC 1000

-Il—Il— l8pF 13 Ρ F

ι- 270 V

e uF

350 V

0.1|iB

27K

3W \y^@

OUTPUT

Fig. 3 CHARGE SENSITIVE LOW NOISE PRE-AMPLIFIER (EC1000) TYPE C

FV Ke

9 "I exl

8 -J ex·

/HM ext V.Ge \ \ = 2UpF Λ

=15.2 p F \ \

ext = Ç2pF>> \ \

7-

6 -

5 -

4 -

3 -

2 -

1 .

ext.OpF \ \

o; 0.2

= 28.2 pF

0.4

FWHM = f ( t )

CUB 16 3.2

3-

2"

1 -

0H

FWHM

KeVGe

- II

/ FWHM = f (Co + Cext)

/ Co+Cext/pF

10 20 l io ¿0 50 60

Jl/ c

°

JW Fig. t,

^ ¡ y RESOLUTION AT F.W.H.M.

5 5 5 ^ VS. SHAPING TIME CONSTANTS

FOR TYPE b PREAMPLIFIER ANO F.W.H.M

VS. INPUT CAPACITANCES

ω 12.8 t / j l S

40 Co + Cext/pF

Fig. 5 RESOLUTION AT F. W. H. M. VS. SHAPING TIME CONSTANTS FOR TYPE C PREAMPLIFIER ANO F. W. H. M. VS INPUT CAPACITANCES

Vus

E83F(triode connected)

Curves : Ι ρ = f (Vg )

lg = g(Vg)

Vp in parameter

Fig. 8

E88CC Curves : Ip »f(Vg)

ig=g(Vg)

Vp in parameter

Fig. 9 LOW NOISE PREAMPLIFIER (VOLTAGE SENSITIVE) .2?ον

2,2 mA

I 8

Test f 20pF

~ (The capacitances are expressed in^ iF)

C= 200 ρ F-capacitance of the connected cable C<=:500pF 2O000V

Counts

300

200

100

Th-230 do

A+2°/.C2H î 1,4Atm. Collector voltage 1800V

W . = T

int.= 2

^ S

Fig. 10

ALPHA SPECTRUM OF Τ h 230

PERFORMED WITH VOLTAGE SENSITIVE

PREAMPLIFIER OF Fig. 9

-23,6 kev

1

Po-210

23,6 kev

100 150 200 Channel 250

-10V o

2.2K

Disen Width ^i sec

- 5 V Q

1K% ^ 2 2 K ή J T 2 2 Κ

Dead Time 1000p 5K^*JASY29 Coarse us.

ÍUÍOÀ t2N4C 4 if: 2200p a015

-O -20V

0026 InhibitOFF

:560K 4.7 μ sec.

, Delay Line

]K< 800p :ικ

:ικ 1K

Λ _ 1 "»1 IU» V-TT^ A A A . | |

Hl ·-" ~ °" HCV —II '-EN 404

47'θρ O-mPrOoN I N

^ N ¿ 0 "2 2 0 P

' S

No Pile UP ^ Out. o )

1

ó -10V

10Turns Helipot

Dead Time Fine

-10V -20V

+10V

100p 1 K

L - l | - t - W V \ r - I C 2 N Ä 0 A'

IOK:

Fig. 12

PILE-UP DETECTOR

-10V'

82Κξ. $2.2K

A1G26

„6.8Kp

'2N404

►10K

18-1

Fig. 11

LOW NOISE PREAMPLIFIER FOR IONIZATION CHAMBER FWHM = f ( τ ) with 10pF external capacitance

^ 17-

I χ £ 16-li_

15-

U -

13-

T 2 3

T u

~r 5 6

Tint.=Tdiff.=T()jS)

CATHODE

FOCUSING ELECTRODE

(20)

65)

γ « f " V W — @ -HV 100pF| I 25KpF - X .

ACCELERATING ELECTRO ° E W -DEFLECTOR ODDDOO

©

D,

D2

D*

© Fig. 13

VOLTAGE DIVIDER FOR 56 AVP P. M.

® © ©

°5 0-

D7 B-

©

©

; 3 9 K

•39K

•39K

•39K

•39K

©

° 9 Β ­

ΟΙΟ D -

© 47K«

(Watt)J

© lOKpF τ fP

IKpF

IKpF

47KpF

bn D,2

013

DW

©

©

— W W lKdWatt)

100PFJI M

X±nl lOKpF

lOKpF

5 6 K > 20KPF1 (2Watt)i

33K> (1Watt)< 5 K P F OUT

-^-, I±=33pF

47ΚρΠ

50 ohm FAST OUT

Fig. U VOLTAGE DIVIDER FOR XP 1020 P. M.

Fig. 15

MODEL 1 PREAMPLIFIER

IN © -

«SM

-20V®—fO-

: 3.3K

2,2 κ

4.7K

: WK JoijiF IC

^ - T j - ^ - î N S i e

OL

|:15K Ï I K

I 1G26

-tø ©+10V

A7 »00 pF

i£ :

: 3·

3 Κ ::3.3K _ _68pF

_MICA

IN o — m n m ^ r ^ i u r o n s — ι © OUT .10V .0, =^ I K p F ^ ^ z . s

*7μΗ <7μΗ _ IN o rorm*YinrwsBV^-r 1 ©OUT

-20V .01 =j= ,K|f=t i 25

IN®

1G26

—TWOT^-f-W «-+12V

=0.1 ■ 1G26

-12V

"0.1

Λ1Ν753

Fig. 16

MODEL 10 PREAMPLIFIER

Fig 17

FAST DISCRIMINATOR D 1

: MK ικ: :.

, ¡ V T » * t = *: ÎM

TD= 1N356Ï

t : OC it,

1N3716

OCii

220

1 %*-

■ \2*

V'

?"

6κ ¿270 ¿ e . r

fcL

iVK «

<"

:,«

■Î'

2N708 . Κ2

* ™8

(—®0UT

AU transistors ore 2N976

unless otherwise specified

rVD^FDIOO

D3= S570G

FIG. 18

DOUBLE COINCIDENCE AND

FAN-OUT

22pF

1KpFr—|H I N ® ||-—MWV—

J-Hr^s?

22 pF

IKpFl— \ \~ | D2

Τ, - 2N917 D1-D2-FDIOO

W2N976 D3-D (-S555G

T4 - TX833

T5 - 2N708

OUT

RISE TIME ADJ.

FIG. 19

PULSE STRETCHER

10 V

3.9K:

ICKpF

SIGNAL IN ® -

+ J_i7pF_[_

IOKPFT^VVJ"

IN ® t—II MWr-'— 11

10

K f 0.1

Οι

r-W-f

GATE

100

0.4S>uH

ï-τ , T, 3-

51 -WA-

ΚΚφ

10V

15K

1K φ

220

® SIGNAL OUT

Tt-Tj-Tj = 2N976

Di = S555G FIG. 20

LINEAR GATE

T,.1 j . t i . .Tn .T i4.JN7794 T2.T5.T6.T?.T,2 .2N70 Τβ = AFY19 T 9 .2N404 T10=Tt7.Tl9=OC141 l i3. l2o.2N9H T,6.2N71I

Φ

STOP ©

100 pf

¿126.. i0·5 cLi

0 i " =L

oj

LXJH^

®

GATE © -

SIART®

I -i ι

2 3 ( 5 W » t t )

«,» V

—it—ι Γ 220pr

| K i FOVOulf

< — <

■£]£

KXWpf

i / U

47(5W)

ΛΛτν-t

J GATE

^2 K

ON L »

i = — C L J " I [ '12

Ttl \

10 0,11

JLUr

«i

Τ Γ

I0K Ν

Β ON -«OFF

STRETCHER

22pf

ieo £„ | U K f * 1.2 K I f

¡ ! ¿ 22K> '=^= 1,2«

S 5706

) 1K

MVv * f 15

ΙΟΟμΗ

-VW

STRETCHER l \ 0,01

1N<M

«3.3K <2,2K ^

'i-L

ï i 2.2K

@ — I I — CT

" Η W x°

•I «ï 6ÍKpF V '

0,1 ?'« =p0.' ¡Mo =L i

(D

4 7 K

■AW-

-^3jT] Γ_ * U M

iks.in.ocn

- O 20v

Í— — o - iu

® <S)0UT(*)

τ

<Q)OUT<-)

-Οίον

FIG. 21 TIME TO PULSE HEIGHT CONVERTER C 1

IN .1 Di

f—Ihj-w-50:

0.1 Dj -ίΙ-τ-Οτ-t~*ï

so; 470

ON U OFF

-10V Di-D2-D3-HPA210^ D4-Q690T TrT2-2N918 T3-TA-2N2894

-10V

0.01 —1|—®OUT

FIG. 22

TIME TO PULSE CONVERTER CIO

A1G26

vk Jzsop—Ih-wvv i 220

1 ¥

1G26

From unit I identical to > f-the above one @ ^yy ..

+4.5V

L_.

0.1

ÍK 65K:

I H i n I D e L

7.-!^.s;

c

J4N711 ° °

4=io

2N708 |

OUT

4-TT®

σο ξ κ

® f6V

lOnF

B IAS®-

5nF |

2.2M

H·

1.2pF=±=

TEST C 2.2M

022M 022 M

EC10O0

MSflW—s^—► 6.3V

ι—vagua, ! * " " I 5nF

U K 2 W

t OUT

75

-150V

FIG. 24

HIGH INPUT IMPEDANCE CATHODE FOLLOWER

FIG. 23

FAST PILE-UP DETECTOR

LIGHT ABSORBER

FIG. 25

EXPERIMENTAL ARRANGEMENT FOR TESTING THE DISCRIMINATOR SLEWING CHARACTERISTIC

o 500 V

SERIES CONTROL

ELEMENT AMPLIFIER

PRESET POWER

LOG. I

DRIFTED SILICON DIODE

FIG. 26

TYPE "A" CONSTANT POWER SUPPLY FOR CONSTRUCTION OF THE LITHIUM DRIFTED SEMICONDUCTOR DETECTORS

o + OUTPUT

MONOSTABLE BLOCKING OSCILLATOR

VARIABLE WIDTH PULSE GENERATOR

(o to9 msec.)

MAINS SYNCHRONISATION

FIG. 27

TYPE "Β- CONSTANT POWER SUPPLY FOR CONSTRUCTION OF LITHIUM DRIFTED SEMICONDUCTOR DETECTORS

S.C.R

+ 300V ,

220 V a c

SCOPE ©MONITORING

BLOCKING OSCILLATOR

FIG. 28

TYPE"C*PULSED POWER SUPPLY FOR CONSTRUCTION OF LITHIUM DRIFTED SEMICONDUCTOR DETECTORS

FIG. 29

PROGRAMMER FOR ACTIVATION

ANALYSIS BY MEANS OF THE

IMICAM NEUTRON GENERATOR

" IMICAM"

NEUTRON

GENERATOR

FOCUSING

METER

GAS INLET

CONTROL

NEUTRON FLUX

COUNTER

SAMPLE ACTIVITY

COUNTER

NEUTRON FUJX ON-OFF

CONTROL

100c/sec

CLOCK

GENERATOR

- I SEQUENCE

CONTROL

PROGRAM

UNIT

'

T I M E R

FROM RABBIT

CONTROL

"" TO SCALER

„ AND PRINTER

INTERLOCK

FOP

MA

ST

■ — *

WARD

NUAL

ART

ROTATING SAMPLE

CHANGER

1

FORWARD

MOTOR

SAMPLE

REMOVAL

MOTOR

1 STA RT

,

BACKWARD

MOTOR

INTERL

SAMPLE

INSERTION

MOTOR

MA t vlUAL

«« START

3CK

POSITION

SENSOR

SAMPLE CHANGER

AND CONTROL SYSTEM

iff»

mmm

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