ORTEC 473 Manuel utilisateur

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PriniPd

in

U.S.A.

Model

473

Constant

Fraction

Discriminator

This

manual

applies

to

instruments

"Rev.

01"

(on

rear

panel)

Copyright

1975,

ORTEC

Incorporated

2318

04C

0875

ORTEC

473

CONSTANT

FRACTION

DISCRIMINATOR

Manual

Change

Sheet

September

24,

1975

KCN

473-02

On

.scTu-m.it

i

c

473-01U1-SI

,

rhangi^

tiic

(k'scriptlon

Cor

Q2

and

Q3

from

MI'S23()9

(I'/N

47H45)

To

MI'SC'Fil

(I'/N

480

39)

Change

the

flagged

note

from

4

to

()

and add

note

6:

Selecteil

-

ORTEC

J'art

Number

48039

-

Violi't.

October

28,

1975

ECN

473-3T

On

schematic

473-0101-Sl,

change

the

values

of

the

following

parts:

Change

C63

from

1000

pF

to

27

pF.

Change

R123

from

2K

to

1.5K.

CONTENTS

Page

WARRANTY

w

PHOTOGRAPHS

. .

VI

1

GENERAL

^

1.1.

Functional

Description

^

1.2.

Physical

Description

^

2.

SPECIFICATIONS

2

2.1.

Performance

-

2.2.

Controls

»

2.3.

Signal

Input

_

2.4.

Signal

Outputs

2

2.5.

External

Delay

2

2.6.

Electrical

and

Mechanical

2

3.

INSTALLATION

3

3.1.

General

2

3.2.

Connection

to

Power

3

3.3.

Input

Connection

3

3.4.

Output

Connections

|

'

'

3

3.5.

External

Control

3

4.

OPERATION

4

5.

THEORY

OF

OPERATION

4

5.1.

General

4

5.2.

Input

Circuit

g

5.3.

Lower

Level

Discriminator

g

5.4.

Upper

Level

Threshold

g

5.5.

Constant

Fraction

Discriminator

g

5.6.

Constant

Fraction

Operation

|

]

c

5.7.

Slo

R.T.

Rej

Operation

g

5.8

Leading

Edge

Operation

g

5.S

Output

Pulse

Generation

g

5.10.

External

Selections

g

5.11.

Power

Supplies

g

6.

APPLICATIONS

g

^.1.

"^'ming

with

Fast

Scintillators

g

sj.2.

Timing

with

Nal(TI)

Scintillators

9

6.3.

Timing

with

Large

Ge(Li)

Detectors

9

6.4.

Timing

with

Other

Detectors

! !

!

14

7.

CALIBRATION

.,g

7.1.

Equipment

Required

.jg

7.2.

Preliminary

Procedure

7.3.

Leading

Edge

Discriminator

Test

15

7.4.

Scintillation

Mode

Walk

Test

15

7.5.

NaI

Mode

Walk

Test

17

7.6.

Ge(Li)

Mode

Walk

Test

'

]

1g

7.7.

Factory

Repair

^

ig

BIBLIOGRAPHY

20

APPENDIX

20

Replaceable

Parts

Block

Diagram

and

Schematic

473-0101-B1

473-0101-S1

ILLUSTRATIONS

Fig.

b.1.

Constant

Fraction

Trigger

Timing

for

Two

Different

Input

Pulse

Amplitudes

G

Fig.

5.2.

Simplified

Block

Diagram

of

the

473

Constant

Fraction

Discriminator

7

Fig.

6.1.

A

System

for

Gamma-Gamma

Lifetime

Measurement

10

Fig.

6.2.

Timing

Over

a

Narrow

Dynamic

Range

with

the

System

of

Fig.

6.1

10

Fig.

6.3.

Plot

of

Time

Resolution

vs

Dynamic

Range

Using

RCA

8850

Photomultiplier

Tube

11

Fig.

6.4.

Plot

of

Time

Resolution

vs

Dynamic

Range

Using

RCA

8575

Photomultiplier

Tube

11

Fig.

6.5.

Typical

Timing

Spectrum

Over

a

Wide

Dynamic

Range

(50:1)

with

Nal(TI)

12

Fig.

6.6.

Plot

of

Time

Resolution

vs

Dynamic

Range

Using

Nal(TI)

and

RCA

8575

PMT

12

Fig.

6.7.

Gamma-Gamma

Coincidence

System

Using

Plastic

Scintillator

and

a

Large

Gel

Li)

Coaxial

Detector

13

Fig.

6.8.

Timing

Spectrum

for

a

Narrow

Dynamic

Range

(1.1:1)

for

the

System

of

Fig.

6.7

13

Fig.

6.9.

Timing

Spectrum

for

a

Wide

Dynamic

Range

(10:1)

for

the

System

of

Fig.

6.7

13

Fig.

6.10.

The

Effect

of

473

Threshold

Setting

on

the

Apparent

Efficiency

of

Different

Ge(Li)

Detectors

.

.

14

Fig.

7.1.

Test

Setup

for

Leading

Edge

Discriminator

Mode

Calibration

16

Fig.

7.2.

Test

Setup

for

Scintillation

Mode

Walk

Test

17

Fig.

7.3.

Test

Setup

for

Nal

Mode

Walk

Test

18

Fig.

7.4.

Test

Setup

for

Ge(Li)

Mode

Walk

Test

19

STANDARD

WARRANTY

FOR

ORTEC

INSTRUMENTS

warrants

that

the

items

will

be

delivered

free

from

defects

in

material

or

workmanship.

ORTEC

makes

no

other

warranties,

express

or

implied,

and

specifically

NO

WARRANTY

OF

MERCHANTABILITY

OR

FITNESS

FOR

A

PARTICULAR

PURPOSE.

ORTEC's

exclusive

liability

is

limited

to

repairing

or

replacing

at

ORTEC's

option,

items

found

by

ORTEC

to

be

defective

in

workmanship

or

materials

within

one

year

from

the

date

of

delivery.

ORTEC's

liability

on

any

claim

of

any

kind,

including

negligence,

loss

or

damages

arising

out

of,

connected

with,

or

from

the

performance

or

breach

thereof,

or

from

the

manufacture,

sale,

delivery,

resale,

repair,

or

use

of

any

item

or

services

covered

by

this

agreement

or

purchase

order,

shall

in

no

case

exceed

the

price

allocable

to

the

item

or

service

furnished

or

any

part

thereof

that

gives

rise

to

the

claim.

In

the

event

ORTEC

fails

to

manufacture

or

deliver

items

called

for

in

this

agreement

or

purchase

order,

ORTEC's

exclusive

liability

and

buyer

s

exclusive

remedy

shall

be

release

of

the

buyer

from

the

obligation

to

pay

the

purchase

price.

In

no

event

shall

ORTEC

be

liable

for

special

or

consequential

damages.

QUALITY

CONTROL

Before

being

approved

for

shipment,

each

ORTEC

instrument

must

pass

a

stringent

set

of

quality

control

tests

designed

to

expose

any

flaws

in

materials

or

workmanship.

Permanent

records

of

these

tests

are

maintained

for

use

in

warranty

repair

and

as

j

source

of

statistical

information

for

design

improvements.

REPAIR

SERVICE

If

It

becomes

necessary

to

return

this

instrument

for

repair,

it

is

essential

that

Customer

Services

be

contacted

in

advance

of

Its

return

so

that

a

Return

Authorization

Number

can

be

assigned

to

the

unit.

Also,

ORTEC

must

be

informed,

either

in

writing

or

by

telephone

[(615)

482-4411],

of

the

nature

of

the

fault

of

the

instrument

being

returned

and

of

the

model,

serial

,

and

revision

(

Rev

on

rear

panel)

numbers.

Failure

to

do

so

may

cause

unnecessary

delays

in

getting

the

unit

repaired.

The

ORTEC

standard

procedure

requires

that

instruments

returned

for

repair

pass

the

same

quality

control

tests

that

are

used

for

new-production

instruments.

Instruments

that

are

returned

should

be

packed

so

that

they

will

withstand

normal

transit

handling

and

must

be

shipped

PREPAID

via

Air

Parcel

Post

or

United

Parcel

Service

to

the

nearest

ORTEC

repair

center.

The

address

label

and

the

package

should

include

the

Return

Authorization

Number

assigned.

Instruments

being

returned

that

are

dama

.

;d

:r

ransit

due

to

inadequate

packing

will

be

repaired

at

the

sender's

expense,

and

it

will

be

the

sender's

responsibility

to

make

ci,

n

with

the

shipper.

Instruments

not

in

warranty

will

be

repaired

at

the

standard

charge

unless

they

have

been

grossly

misused

or

mishandled,

in

which

case

the

user

will

be

notified

prior

to

the

repair

being

done.

A

quotation

will

be

sent

with

the

notification.

DAMAGE

IN

TRANSIT

Shipments

should

be

examined

immediately

upon

receipt

for

evidence

of

external

or

concealed

damage.

The

carrier

making

del

ivery

should

be

notified

immediately

of

any

such

damage,

since

the

carrier

is

normally

liable

for

damage

in

shipment.

Packing

materials,

waybills,

and

other

such

documentation

should

be

preserved

in

order

to

establish

claims.

After

such

noqfication

to

the

carrier,

please

notify

ORTEC

of

the

circumstances

so

that

assistance

can

be

provided

in

making

damage

claims

and

in

providing

replacement

equipment

if

necessary.

CONSTANT

FRAaiON

DISC

SCINTx

»-Nal

DISC

LEVEt

EXT

DELAY

iSk:

I

1

ORTEC

473

CONSTANT

FRACTION

DISCRIMINATOR

1.

GENERAL

1.1.

FUNCTIONAL

DESCRIPTION

Thu

ORTEC

473

Constant

Fraction

Discriminator

provides

logic

outputs

that

are

used

for

precise

timing

measurements.

The

outnuts

are

derived

from

input

pulses

that

originate

in

almost

any

style

of

nuclear

detector.

The

Constant

Fraction

technique

i.'s

I

io

obtain

the

timing

signals

ensures

accuracy

and

precision

through

a

wide

dynamic

range

of

input

signal

amplitudes.

Sliaping

details

are

selected

with

a

front

panel

switch.

The

switch

settings

are

marked

Ge(Li),

Scint,

and

Nal,

for

the

positions

that

are

most

appropriate

to

these

types

of

detectors,

and

Ext

for

normalizing

the

operating

characteristics

to

other

applications.

Since

the

switch

selections

differ

only

in

the

delay

time,

f^,

used

for

the

Constant

Fraction

technique,

the

indicated

detector

types

are

general

classifications

rather

than

being

strict

selections.

The

characteristics

of

each

type

of

detector

differ

through

a

very

wide

range

and

cannot

be

served

by

any

unique

delay

time.

But

the

473,

including

its

Ext

selection,

can

be

used

to

optimize

the

operation

for

any

specific

detector

experimentally.

When

the

collection

times

in

the

detector,

and

therefore

the

rise

times

of

its

output

pulses,

vary

through

a

wide

time

range,

it

is

often

advantageous

to

connect

the

detector's

preamplifier

output

through

an

ORTEC

454

Timing

Filter

Amplifier

before

it

reaches

the

input

of

the

473.

The

454

can

also

be

used

to

amplify

preamplifier

output

signals

if

they

do

not

have

sufficient

amplitude

to

drive

the

473

with

the

signals

that

represent

energies

of

interest.

In

addition

to

the

basic

Constant

Fraction

timing

signal

derivation,

the

473

permits

selection

of

a

Slo

R.T.

Rej

(slow

rise-time

signal

reject)

operating

mode

so

that

an

input

signal

with

a

rise

time

that

is

too

slow

to

provide

accurate

timing

information

will

be

rejected.

When

this

variation

from

the

basic

Constant

Fraction

mode

is

selected,

each

input

signal

with

a

rise

time

g'eater

than

about

25

ns,

measured

between

the

C.F.

pickoff

discriminator

level

and

the

front

panel

adjusted

Disc

Level,

will

not

generate

an

output.

The

C.F.

pickoff

discriminator

level

is

automatically

adjusted

at

50%

of

the

front

panel

adjusted

Disc

Level.

Although

signal

rejection

reduces

the

efficiency

of

operation,

the

timing

resolution

of

the

remaining

output

signals

is

improved

by

using

this

mode

when

there

are

slow

rise-time

signals.

The

mode

selector

switch

also

includes

a

setting

for

L.E.

(Leading

Edge)

discriminator

operation.

In

this

mode

the

Constant

Fraction

circuitry

is

bypassed

and

the

unit

operates

as

a

conventional

leading

edge

discriminator.

The

shaping

selector

switch

at

the

top

of

the

front

panel

has

no

effect

during

L.E.

operation

except

that

the

input

count

rate

is

limited

to

1

MHz

if

the

switch

is

set

at

Nal;

otherwise

the

input

count

rate

limit

is

about

20

MHz.

The

adjustments

and

selections

are

usually

quite

simple.

Just

select

the

appropriate

detector

identification,

set

the

Disc

Level

for

the

lowest

energy

of

interest,

select

the

desired

mode

of

operation,

and

connect

the

input

and

output

cables.

The

473

then

provides

the

timing

signals

with

excellent

precision

and

stability,

suitable

for

even

the

most

sophisticated

time

spectioscopv

measurements.

For

convenience,

monitor

test

points

are

included

for

inspection

of

input

and

output

signals.

The

appropriate

delay

and

attenuation

conditions

are

selected

according

to

the

detector

type.

The

maximum

benefits

of

using

the

Constant

Fraction

technique

are

obtained

without

any

unnecessary

calculations.

But

there

is

also

a

provision

for

external

control

to

permit

■xperimenf

iiion

or

to

provide

for

those

unusual

conditions

that

require

delays

or

fractions

other

than

the

standard

valuris

that

are

swi

i

lected.

Although

th-

switch

selections

do

not

include

surface

barrier

detectors,

the

473

serves

this

class

of

detectors

equally

for

time

derivation

signals.

There

are

two

general

types

of

surface

barrier

detectors,

one

includes

a

shaping

preamplifier

such

as

is

included

in

the

ORTEC

130

Detector-Preamplifier

Timing

System,

and

the

other

provides

a

long-time

constant

decay

for

the

preamplifier

output

signals.

If

a

130

System,

or

equal,

is

used

and

it

furnishes

sufficient-amplitude

signals

of

interest

to

the

473,

either

the

Scint

or

the

Nal

switch

selection

may

provide

the

best

operation.

Otherwise,

if

an

ORTEC

454

Timing

Filter

Amplifier

is

used

to

amplify

the

130

output,

the

473

may

operate

satisfactorily

with

either

Ge(Li)

or

Nal

timing,

or

it

may

be

necessary

to

switch

to

Ext

and

adjust

the

Any

other

surface

barrier

detector

output

should

be

shaped

(and

amplified

if

nec

essary)

with

a

454,

and

the

best

operation

with

the

473

may

be

provided

by

Ge(Li),

Nal,

or

Ext

timing.

1.2.

PHYSICAL

DESCRIPTION

The

473

is

a

single-width

NIM-standard

module

that

must

be

installed

in

a

bin

and

power

supply

for

operation.

All

of

the

normally-used

connections

and

controls

are

located

on

the

front

panel.

When

external

control

is

to

be

used,

the

adjusted

delay

can

be

provided

by

connecting

the

appropriate

length

of

RG-174

cable

between

two

BNC

connectors

on

the

rear

panel

and

the

effective

constant

fraction

can

be

selected

with

a

jumper

on

the

printed

circuit

board

inside

the

module.

The

required

operating

power

will

be

furnished

from

the

bin

and

power

supply

into

which

the

module

is

installed.

2.

SPECIFICATIONS

2.1.

PERFORMANCE

INPUT

PULSE

CHARACTERISTICS

Accepts

negative

pulses

to

5

V

without

saturation;

protected

to

100

V

for

duty

cycle

of

10%;

f^<1

ns.

DISCRIMINATOR

RANGE

-50mVto-5V.

WALK

AND

DYNAMIC

RANGE

Ge(Li)

Mode

2

ns

for

range

of

100

mV

to

5

V

with

40-ns

f^.

Scint

Mode

200

ps

for

range

of

50

mV

to

5

V

(including

test-attenuator

walk)

with

1-ns

t^.

Nal

Mode

<'

500

ps

tor

range

of

50

mV

to

5

V

with

5-ns

TEMPERATURE

CHARACTERISTICS

Disc

Level

Drift

typically

<0.5

mV/°C,

0

to

50°C.

Propagation

Delay

Stability

typically

within

<15

ps/°C,

10

to

40°C.

PULSE

PAIR

RESOLUTION

Internal

circuitry

limits

pulse

pair

resolution

to

50

ns

minimum

for

Ge(Li),

Scint,

or

Ext

operation

and

to

1

/js

minimum

for

Nal

operation

to

prevent

multiple

triggering

on

slow-decay

signals.

PROPAGATION

DELAY

For

Scint

mode,

500

mV

input

with

t^.

~1

ns;

typically

63

ns

for

C.F.

or

Slo

R.T.

Rej,

43

ns

for

L.E.

2.2.

CONTROLS

SHAPING

SELECTOR

4-position

front

panel

switch

selects

the

optimum

constant

fraction

timing

signal

derivation

according

to

the

type

of

signal

that

originates

in

a

class

of

detectors.

Ge(Li)

Selects

the

delay

and

fraction

for

optimum

time

resolution

for

signals

from

lithium-drifted

germanium

detectors.

Scint

Selects

the

delay

and

fraction

for

optimum

time

resolution

for

signals

from

fast

plastic

scintillators.

Nal

Selects

a

delay

and

fraction

for

optimum

time

resolution

for

signals

from

a

Nal(TI)

or

similar

scintillation

detector.

Also

selects

an

internal

dead

time

of

~1

ps

to

prevent

multiple

triggering

on

slow-decay

signals.

Ext

Permits

selection

of

any

desired

delay

>~3

ns

by

controlling

the

length

of

coaxial

cable

attached

between

rear

panel

connectors;

also

permits

internal

jumper

selection

of

fraction

at

10%,

20%,

or

30%.

DISC

LEVEL

10

tuin

piecision

locking

pot(Mitiomet(M

iidjusls

li

iggei level

ol

sigiiiil

Input

disctirninatoi

Ihioiigh

iIm;

lange

50

inV

to

5

V,

lh(.'

constant

Itaction

(lickoH

disctimitialor

is

st.'t

automatically

at

50%

ol

the

adjusted

li^vt.'l.

TIMING

MODE

SELECTOR

3

position

switch

selects

the

operating

mode.

C.F.

Selects

the

basic

Constant

Fraction

mode

for

timing

signal

derivation.

Slo

R.T.

Rej

Selects

the

Constant

Fraction

mode

with

automatic

cancellation

of

response

if

the

input

signal

fails

to

rise

from

the

con'

nt

fraction

pickoff

level

to

the

signal

input

discriminator

level

within

~25

ns.

L.E.

Sole!

'

e

Leading

Edge

discriminator

mode

and

bypasses

the

constant

fraction

portions

of

circuitry.

2.3.

SIGNAL

INPUT

INPUT

F;

i

panel

BNC

connector

accepts

input

signals

from

a

fast

preamplifier

or

from

a

shaping

amplifier

such

as

the

ORTEC

454;

de

coupled

and

baseline-restored;

normal

range

from

Disc

Level

setting

to

—5

V;

Z|^

50n.

Reflections

typically

<10%

to

—5

V

with

>1

ns.

Directly

compatible

with

current

pulses

from

PM

tube

anodes.

2.4.

SIGNAL

OUTPUTS

NEG

Two

NIM-standard

fast

negative

logic

output

signals

generated

separately

and

furnished

through

two

BNC

connectors

on

front

panel;

nominally

—16

mA

(800

mV

on

50S2

load);

width

<10

ns;

<2.5

ns.

PCS

One

NIM-standard

slow

positive

logic

output

signal

furnished

through

BNC

connector

on

front

panel;

nominally

+5

V;

width

500

ns;

<25

ns;

<10ri.

2.5.

EXTERNAL

DELAY

IN

AND

OUT

A

pair

of

BNC

connectors

on

the

rear

panel

permit

any

length

of

RG-174

cable

to

be

connected

as

an

external

delay

line;

total

delay

equals

external

delay

plus

3

ns

(internal

circuitry).

2.6.

ELECTRICAL

AND

MECHANICAL

POWER

REQUIRED

+24

V,

10

mA;

-24

V,

75

mA;

+12

V,

21

mA;

-12

V,

150

mA;

115

V

ac,

42

mA.

3.

INSTALLATION

3.1.

GENERAL

The

473

is

used

in

conjunction

with

an

ORTEC

401/402

Bin

and

Power

Supply,

which

is

intended

for

rack

mounting.

Therelore

if

vacuum

tufte

etiuipment

is

operated

in

the

same

rack,

there

must

be

sufficient

cooling

with

circulating

air

to

prevent

any

localized

heating

of

the

all-transistorized

circuitry

used

throughout

the

473.

The

temperature

of

equipment

mounted

in

racks

can

easily

exceed

the

recommended

maximum

limit

of

120"F

(50"C)

unless

these

precautions

are

taken.

3.2.

CONNECTION

TO

POWER

Always

turn

off

power

for

the

Power

Supply

before

inserting

or

removing

modules.

The

ORTEC

400

Series

of

modular

instruments

is

designed

so

that

the

Power

Supply

cannot

be

overloaded

when

there

is

a

full

complement

of

modules

in

the

Bin.

Since,

however,

this

may

not

be

true

when

the

Bin

contains

modules

other

than

those

of

ORTEC

design,

use

the

convenient

test

points

on

the

front

panel

of

the

401/402

to

check

each

Power

Supply

voltage

level

after

all

modules

have

been

inserted.

3.3.

INPUT

CONNECTION

The

Input

circuit

of

the

473

is

designed

for

use

with

500

cable.

The

input

impedance

is

50O;

so

no

external

terminator

is

required

for

this

connection.

The

input

can

come

from

a

detector

or

photomultiplier

directly,

provided

that

the

negative

input

pulse

will

have

sufficient

amplitude

to

exceed

a

Disc

Level

setting

in

the

473.

When

an

amplitude

requires

amplification

or

when

additional

pulse

shaping

is

required

[such

as

with

Ge(Li)

coaxial

detectors]

,

an

ORTEC

454

Timing

Filter

Amplifier

can

be

used

between

the

detector

and

the

input

to

the

473.

3.4.

OUTPUT

CONNECTIONS

There

are

three

outputs

on

the

473,

and

all

connectors

are

located

on

the

front

panel.

Two

of

these

are

NIIVl-standard

Fast

Negative

pulses

that

are

generated

separately

and

are

therefore

completely

isolated.

The

third

is

a

NIM-standard

Slow

Positive

pulse.

All

three

pulses

are

furnished

for

each

input

pulse

that

exceeds

the

Disc

Level

setting

unless

it

has

a

slow

rise

time

and

the

front

pane

mode

switch

selects

Slo

R.T.

Rej.

The

Fast

Ner;

•

ve

output

pulses

are

intended

for

timing

applications

such

as

the

Start

and

Stop

inputs

to

a

time

to

pulse

height

converter.

Either

or

both

may

be

used

and

the

alternate

connector

does

not

need

to

be

terminated

when

it

is

not

being

used.

Since

the

NIM-standard

Fast

Negative

pulse

is

a

current

pulse

and

since

it

is

intended

for

use

with

a

50JT

load,

you

should

use

500

cable

to

connect

it

to

the

point

where

it

will

be

used

and

that

point

must

be

terminated

in

50O.

Normally

the

instrument

that

receives

the

pulse

will

have

a

50O

input

impedance;

if

it

does

not,

use

an

external

termination

at

the

output

end

of

the

cable.

The

NIM-standard

Slow

Positive

output

pulses

can

be

used

for

coincidence

work

or

can

be

counted

directly

in

a

sealer

or

ratemeter.

It

is

normal

to

use

930

cable

to

transfer

this

voltage

pulse

that

is

furnished

through

the

output

impedance

of

<!10J2.

For

cable

lengths

longer

than

2

meters

(~7

ft)

it

is

recommended

that

the

cable

be

terminated

in

its

characteristic

impedance.

This

output

can

also

drive

a

terminated

50J2

cable,

but

with

a

slightly

reduced

amplitude.

3.5.

EXTERNAL

CONTROL

If

the

optional

external

control

is

selected

in

lieu

of

one

of

the

identified

detector

types,

the

fraction

can

be

changed

from

its

factory-connected

30%

to

either

20%

or

10%

by

moving

a

jumper

on

the

printed

circuit.

In

addition

to

the

optional

fraction

S'

ipction,

it

is

necessary

to

connect

a

length

of

RG-174

50f2

cable

between

the

Out

and

In

connectors

on

the

rear

panel.

The

aujusted

delay

will

be

equal

to

3

ns

plus

the

cable

delay,

which

is

125

ps/inch.

4.

OPERATION

After

the

473

has

been

installed

and

interconnected

as

described

in

Section

3,

the

only

operating

functions

that

are

required

are

the

setting

of

the

detector

selector

switch,

adjustment

of

the

Disc

Level

control,

and

selection

of

the

desired

operating

mode.

f

Mi

ially

the

detector

selector

switch

can

be

set

at

the

switch

position

that

identifies

the

type

of

detector

being

used,

hovvever,

the

only

differences

between

the

three

switch

positions

marked

for

detector

types

are

the

effective

delay

time

that

will

be

used

for

constant

fraction

pickoff

and

the

controlled

dead

time

duration

in

the

output

circuit.

If

the

switch

is

set

at

Nal,

the

dead

time

for

each

output

pulse

will

be

1

fis

regardless

of

the

mode

by

which

the

output

was

generated.

The

controlled

dead

time

is

50

ns

for

any

of

the

other

three

switch

settings.

For

reference,

the

selectable

delay

times

are

14

ns

for

Ge(Li),

1.3

ns

for

Scint,

and

1.9

ns

for

Nal.

Shaping

that

is

provided

by

the

preamplifier

may

affect

the

relation

between

the

optimum

switch

selection

and

the

actual

class

of

detector

that

is

being

used.

If

the

switch

is

set

at

Ext,

the

delay

time

can

be

any

amount

greater

than

the

3

ns

built-in

delay

that

is

a

part

of

the

circuit

leading

to

and

from

the

rear

panel

connectors.

One

additional

function

is

selectable

when

the

Ext

setting

is

used,

and

this

is

the

effective

fraction;

the

basic

setting

of

a

jumper

on

the

printed

circuit

selects

30%,

but

the

jumper

can

be

moved

to

select

20%

or

10%

if

desired.

See

information

in

Section

5,

Theory

of

Operation,

for

changing

the

jumper

selection

of

the

effective

fraction.

The

function

of

the

Disc

Level

adjustment

is

to

permit

selection

of

signals

with

amplitudes

of

interest

and

to

eliminate

response

to

signals

with

smaller

amplitudes.

The

proper

setting

of

this

control

depends

on

the

range

of

signal

amplitudes

that

are

furnished

into

the

input.

The

control

range

is

from

50

mV

to

5

V,

with

the

10-turn

potentiometer

used

for

precise

setting

and

excellent

repeatability.

For

most

applications,

the

mode

selector

will

be

set

at

C.F.,

for

Constant

Fraction

operation.

If

the

input

signal

rise

times

tend

to

vary

through

a

wide

range,

such

as

the

signals

that

can

be

furnished

from

a

large-volume

coaxial

germanium

detector,

the

switch

can

be

turned

to

Slo

R.T.

Rej

to

operate

as

a

Constant

Fraction

discriminator

but

to

also

reject

input

pulses

with

too

slow

a

rise

time

so

that

the

timing

spectrum

has

a

better

resolution.

The

mode

switch

can

be

turned

to

L.E.

to

select

conventional

leading

edge

discriminator

operation.

If

the

detector

selector

switch

is

set

at

Nal,

the

internal

dead

time

is

held

at

1

(is

so

the

maximum

input

count

rate

is

limited

to

1

MHz.

But

if

the

detector

selector

switch

is

set

in

any

other

position,

the

dead

time

is

50

ns,

permitting

response

to

an

input

count

rate

up

to

20

MHz.

The

other

functions

selected

by

the

detector

switch

have

no

effect

during

L.E.

operation

because

the

constant

fraction

portion

of

the

473

circuits

is

bypassed.

5.

THEORY

OF

OPERATION

5.1.

GENERAL

The

circuits

of

die

473

are

shown

in

block

diagram

473-0101-81

and,

in

more

detail,

in

schematic

473-0101-S1.

Both

of

t

'.Gse

drawip'"^

are

included

at

the

back

of

the

manual.

The

input

is

furnished

simultaneously

to

three

internal

circuits.

One

circuit

is

a

lower

level

leading

edge

discriminator

that

defines

the

onset

of

a

signal

of

interest

and

arms

internal

logic

circuits

in

the

module.

A

second

circuit

is

an

upper

level

leading

edge

discriminator;

each

input

signal

must

exceed

this

level

in

order

that

an

output

will

be

generated.

The

third

circuit

is

a

constant

fraction

discriminator

that

provides

a

precise

timing

recognition

for

the

input

signal.

A

front

panel

Disc

level

control

effectively

adjusts

the

response

threshold

for

both

the

lower

level

and

upper

level

discriminators.

The

nominal

range

for

this

control

is

50

mV

to

5

V,

associated

with

the

upper

level

threshold

range;

the

threshold

for

the

lower

level

discriminator

is

automatically

adjusted

at

about

50%

of

the

upper

level

so

that

it

is

triggered

earlier

on

the

leading

edge

of

the

input

pulse.

When

an

output

is

generated,

it

furnishes

two

independent

NIM-standard

fast

negative

signals

and

one

NIM-standard

slow

positive

signal.

The

leading

edges

of

the

three

output

signals

are

coincident.

A

feedback

in

the

output

trigger

circuit

ensures

the

generation

of

only

one

output

pulse

in

each

of

the

three

output

signal

paths.

The

Constant

Fraction

mode

of

operation

can

be

used

either

with

or

without

the

Slow

Risetime

Reject

feature.

When

Slo

R.T.

Rej

is

selected

with

the

front

panel

mode

switch,

the

C.F.

timing

signal

is

not

generated

if

the

rise

time

of

an

input

pulse

is

too

slow.

The

Leading

Edge

mode

of

operation

does

not

use

the

slow

risetime

reject

feature.