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100MIDLAND

ROAD

OAK

RIDGE,

TENN.

37830

PHONE

(615)

482-4411

TWX

810-5

7

2-1078

INSTRUCTION

MANUAL

452

SPECTROSCOPY

AMPLIFIER

n

ci:ai\/iF='ArNiY

r-

ORTEC

452

SPECTROSCOPY

AMPLIFIER

Manual

Change

Sheet

May

19,1971

In

the

schematic,

452-0101-81,

please

make

the

following

changes:

Change

the

value

of

C12

from

430

to

470.

Change

the

value

of

C104

from

100

to

68.

Change

the

value

of

C105

from

68

to

39.

Change

the

value

of

C109

from

68

to

1000.

Add

a

capacitor,

C112,

15

from

pin

4

to

pin

3

of

Amp

2

(pin

3

is

not

shown

in

the

schematic

since

it

was

not

previously

used).

On

D20,

add

the

designation

1N5241,

and

delete

Q43.

In

Section

2

of

the

manual,

Specifications,

change

the

power

requirements

to

read:

+24

V,

120

mA;

+12

V,

45

mA;

-24

V,

130

mA;

-12

V,

30

mA.

INSTRUCTION

MANUAL

452

SPECTROSCOPY

AMPLIFIER

Serial

No.

Purchaser

Date

Issued

100

MIDLAND

RDAD

DAK

RIDGE,

TENN.

3783G

PHDNE

(615)

482-4411

TWX

B10-572-1D78

n

EGs.t3

cors/iF^Arsj-v

I

ORTEC

Incorporated

1970

Printed

In

U.

S.

A.

012571

TABLE

OF

CONTENTS

Page

WARRANTY

PHOTOGRAPHS

1.

DESCRIPTION

1

1.1

General

Description

1

1.2

Pole-Zero

Cancellation

1

1.3

Active

Filter

3

2.

SPECIFICATIONS

5

3.

INSTALLATION

7

3.1

General

3.2

Connection

to

Preamplifier

3.3

Connection

of

Test

Pulse

Generator

3.4

Connection

to

Power

3.5

Shaping

Considerations

3.6

Use

of

Delayed

Output

8

3.7

Output

Connections

and

Terminating

Considerations

8

3.8

Shorting

or

Overloading

the

Amplifier

Outputs

8

4.

OPERATING

INSTRUCTIONS

9

4.1

Initial

Testing

and

Observation

of

Pulse

Waveforms

9

4.2

Front-Panel

Controls

9

4.3

Front-Panel

Connectors

(All

Type

BNC)

9

4.4

Rear-Panel

Connectors

9

4.5

General

Considerations

for

Operation

with

Semiconductor

Detectors

10

4.6

Operation

in

Spectroscopy

Systems

12

4.7

Other

Experiments

13

4.8

Baseline

Restorer

(BLR)

14

4.9

Methods

of

Connection

to

Various

Analyzers

15

5.

CIRCUIT

DESCRIPTION

17

6.

MAINTENANCE

19

6.1

Test

Equipment

Required

19

6.2

Pulser

Modifications

for

Overload

Tests

19

6.3

Pulser

Test

19

6.4

Suggestions

for

Troubleshooting

21

6.5

Tabulated

Test

Point

Voltages

on

Etched

Board

22

SCHEMATIC

AND

BLOCK

DIAGRAM

452-0201-B1

ORTEC

452

Block

Diagram

452-0101-S1

ORTEC

452

Schematic

LIST

OF

FIGURES

Page

g.

1.1.

Clipping

in

an

Amplifier

Without

Pol6-Zero

Cancellation.

2

g.

1.2.

Differentiation

(Clipping)

in

a

Pole-Zero-Cancelled

Amplifier.

2

g.

1.3.

Pulse

Shapes

for

Good

Signal-to-Noise

Ratios.

3

g.

4.1

Typical

Effects

of

Shaping

Time

Selection

on

Output

Waveforms,

9

g.

4.2.

System

for

Measuring

Amplifier

and

Detector

Noise

Resolution.

10

g.

4.3.

Resolution

Effects

of

Capacitance.

10

g.

4.4.

Noise

as

a

Function

of

Bias

Voltage.

11

g.

4.5.

System

for

Measuring

Resolution

with

a

Pulse

Height

Analyzer.

11

g.

4.6.

System

for

Detector

Current

and

Voltage

Measurements.

11

g.

4.7.

Silicon

Detector

Back

Current

vs

Bias

Voltage.

12

g.

4.8.

System

for

High-Resolution

Alpha-Particle

Spectroscopy.

12

g.

4.9.

System

for

High-Resolution

Gamma

Spectroscopy.

12

g.

4.10.

Scintillation

Counter

Gamma

Spectroscopy

System.

13

g.

4.11.

High-Resolution

X-Ray

Energy

Analysis

System.

13

g.

4.12.

Gamma-Gamma

Coincidence

Experiment.

13

g.

4.13.

Gamma-Ray

Charged-Particle

Coincidence

Experiment

13

g.

4.14.

Gamma-Ray

Pair

Spectrometer.

14

g.

4.15.

General

System

Arrangement

for

Gating

Control.

14

g.

4.16.

Effects

of

Baseline

Restorer

on

Resolution.

14

g.

4.17.

Analyzer

Connection

with

No

Trigger

Required.

15

g.

4.18.

Analyzer

Connection

When

Trigger

Is

Required.

15

g.

6.1.

Pulse

Generator

Modifications.

19

g.

6.2.

Pole-Zero

Cancellation

of

a

Pulser

Output.

19

g.

6.3.

Circuit

Used

to

Measure

Nonlinearity.

20

g.

6.4.

Circuit

Used

to

Measure

Crossover

Walk

of

the

Amplifier

and

Single

Channel

Analyzer.

20

g.

6.5.

Circuit

Used

to

Measure

Crossover

Walk

of

the

Amplifier

Only.

21

g.

6.6.

Circuit

Used

to

Measure

Resolution

Spread

and

Amplitude

Changes

at

Various

Count

Rates.

21

STANDARD

WARRANTY

FOR

ORTEC

INSTRUMENTS

ORTEC

warrants

its

instruments

other

than

preampl

ifier

FET

input

transistors,

vacuum

tubes,

fuses,

and

batteries

to

be

free

from

defects

in

workmanship

and

materials

for

a

period

of

twelve

months

from

date

of

shipment

provided

that

the

equipment

has

been

used

in

a

proper

manner

and

not

subjected

to

abuse.

Repairs

or

replace

ment,

at

ORTEC

option,

wil

l

be

made

on

in-warranty

instruments,

without

charge,

at

the

ORTEC

factory.

Shipping

expense

wil

l

be

to

the

account

of

the

customer

except

in

cases

of

defects

discovered

upon

initial

operation.

Warranties

of

vacuum

tubes

and

semiconductors

made

by

their

manufacturers

wil

l

be

extended

to

our

custdmers

only

to

the

extent

of

the

manufacturers'

liabil

ity

to

ORTEC.

Specially

selected

vacuum

tubes

or

semiconductors

cannot

be

warranted.

ORTEC

reserves

the

right

to

modify

the

design

of

its

products

without

incurring

responsibil

ity

for

modification

of

previously

manufactured

units.

Since

installation

conditions

are

beyond

our

control,

ORTEC

does

not

assume

any

risks

or

l

iabil

ities

associated

with

methods

of

installation

or

with

instal

lation

results.

QUALITY

CONTROL

Before

being

approved

for

shipment,

each

ORTEC

instrument

must

pass

a

stringent

set

of

qual

ity

control

tests

designed

to

expose

any

flaws

in

materials

or

work

manship.

Permanent

records

of

these

tests

are

maintained

for

use

in

warranty

repair

and

as

a

source

of

statistical

information

for

design

improvements.

ORTEC

must

be

informed

in

writing

of

the

nature

of

the

fault

of

the

instrument

being

returned

and

of

the

model

and

serial

numbers.

Failure

to

do

so

may

cause

unnecessary

delays

in

getting

the

unit

repaired.

Our

standard

procedure

requires

that

instruments

returned

for

repair

pass

the

same

qual

ity

control

tests

that

are

used

for

new-production

instruments.

Instruments

that

are

returned

should

be

packed

so

that

they

wil

l

withstand

normal

transit

handl

ing

and

must

be

shipped

prepaid

via

Air

Freight

or

United

Parcel

Service

to

the

nearest

ORTEC

repair

center.lnstru-

ments

damaged

in

transit

due

to

inadequate

packing

wil

l

be

repaired

at

the

sender's

expense,

and

it

wil

l

be

the

sender's

responsibil

ity

to

make

claim

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

wil

l

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

normal

ly

l

iable

for

damage

in

shipment.

Packing

materials,

waybil

ls,

and

other

such

documentation

should

be

preserved

in

order

to

establ

ish

claims.

After

such

notification

to

the

carrier,

please

notify

ORTEC

of

the

circumstances

so

that

we

may

assist

in

dam

age

claims

and

in

providing

replacement

equipment

if

necessary.

■

MODEL

452

SPECTROSCOPY

AMPLIFIER

COARSE

GAIN

100

SHAPING

TIME

1.0

2.0

0.25

At

FINE

GAIN

0.5-1.5

POS

ii

nl

NEG

PZ

ADJ

INPUT

BIPOLAR

UNIPOLAR

OUTPUT

RANGE

-lOV

-t-iov

L

-6V

HI

LO

OUT

BLR

I

DELAY

IN

I

OUT

UNIPOLAR

<•

V

;

OUTPUTS

ilPOLAN

I

UNIl'OLAH

£

l)S

u

OUTPUT'.;

PilEIb'

POWEW

ORTEC

452

SPECTROSCOPY

AMPLIFIER

1.

DESCRIPTION

1.1

GENERAL

DESCRIPTION

The

ORTEC

452

Spectroscopy

Amplifier

is

a

double-width

NIM

module

with

a

versatile

combination

of

switch-

selectable

pulse

shaping

and

output

characteristics.

It

features

extremely

low

noise,

wide

gain

range,

and

excellent

overload

response

for

universal

appl

ication

in

high-resolu

tion

spectroscopy.

It

accepts

input

pulses

of

either

polarity

which

originate

in

germanium

or

sil

icon

semiconductor

detectors,

in

scintil

lation

detectors

with

either

fast

or

slow

scintillators,

in

proportional

counters,

in

pulsed

ionization

chambers,

in

electron

multipliers,

etc.

The

452

has

a

dc

input

impedance

of

approximately

lOOOfi

and

accepts

either

positive

or

negative

input

pulses

with

rise

times

<650

ns

and

fall

times

>25

/is.

Six

integrate

and

differentiate

time

constants

are

switch-selectable

to

provide

optimum

shape

for

resolution

and

count

rate.

The

first

differentiation

network

has

variable

pole-zero

cancella

tion

that

can

be

adjusted

to

match

preampl

ifiers

with

>25

IIS

decay

time.

The

pole-zero

cancellation

drastical

ly

reduces

the

undershoot

after

the

first

cl

ip

and

greatly

im

proves

overload

characteristics.

In

addition,

the

amplifier

contains

an

active

filter-shaping

network

that

optimizes

the

signal-to-noise

ratio

and

minimizes

the

overall

resolving

time.

Both

unipolar

and

bipolar

outputs

are

provided

simultaneously

on

the

front

and

rear

panels.

The

unipolar

output

should

be

used

for

spectroscopy

when

dc

coupl

ing

can

be

maintained

from

the

452

Ampl

ifier

to

the

analyzer.

A

BLR

(Base

Line

Restoration)

circuit

is

included

in

the

452

for

improved

performance

at

high

count

rates.

A

switch

on

the

front

panel

permits

this

circuit

to

be

switched

out,

set

for

low

count

rates,

or

set

for

high

count

rates.

When

using

the

direct-coupled

input

of

the

various

analyzers,

a

variety

of

voltage

requirements

exist.

To

meet

these

requirements

the

452

unipolar

output

can

be

selected

for

ful

l-scale

voltage

of

-3

V,

±6

V,

or

±10

V.

The

unipolar

output

dc

level

can

be

adjusted

from

-1

V

to

+

1

V.

This

output

permits

the

use

of

the

direct-coupled

input

of

analyzers

with

a

minimum

amount

of

interface

problems.

The

452

bipolar

output

may

be

preferable

for

spectroscopy

when

operating

into

an

ac-coupled

system

at

high

counting

rates.

The

452

can

be

used

for

crossover

timing

when

used

in

conjunction

with

an

ORTEC

407

Crossover

Pickoff

or

a

420A

or

455

Timing

Single

Channel

Analyzer.

The

ORTEC

Timing

Single

Channel

Analyzers

feature

a

minimum

of

walk

as

a

function

of

pulse

ampl

itude

and

incorporate

a

variable

delay

time

on

the

output

pulse

to

enable

the

cross

over

pickoff

output

to

be

placed

in

time

coincidence

with

other

outputs.

A

switch-selectable

2-jus

delay

is

provided

on

the

unipolar

output

to

aid

in

obtaining

the

proper

spacing

of

the

l

inear

pulse

in

a

coincidence-gated

system.

The

452

has

complete

provisions,

including

power,

for

operating

any

ORTEC

solid-state

preampl

ifier

such

as

the

109A,

113,

118A,

120, 124,

and

125.

Preamplifier

pulses

should

have

a

rise

time

of

0.25/ts

or

less

to

properly

match

the

amplifier

filter

network

and

a

decay

time

>25

iis

for

proper

pole-zero

cancellation.

The

452

input

impedance

is

1000^2.

When

long

preampl

ifier

cables

are

used,

the

cables

can

be

terminated

in

series

at

the

preamplifier

end

or

in

shunt

at

the

ampl

ifier

end

with

the

proper

resistors.

The

output

impedance

of

the

452

is

about

O.lfi

at

the

front-

panel

connectors

and

93T2

at

the

rear-panel

connectors.

The

front-panel

outputs

can

be

connected

to

other

equipment

by

single

cable

going

to

all

equipment

and

shunt

terminated

at

the

far

end.

If

series

termination

is

desired,

the

rear-

panel

connectors

can

be

used

in

connecting

the

452

to

other

modules

(see

Section

3).

Gain

changing

is

accomplished

by

varying

feedback

net

works.

These

networks

are

varied

in

such

a

manner

that

the

band

width

of

the

feedback

amplifier

stages

remains

essentially

constant

regardless

of

gain,

and

therefore

rise-

time

changes

with

gain

switching

(which

cause

crossover

walk)

are

limited

to

small

variations.

1.2

POLE-ZERO

CANCELLATION

Pole-zero

cancellation

is

a

method

for

eliminating

pulse

undershoot

after

the

first

differentiating

network.

The

technique

employed

is

described

by

referring

to

the

wave

forms

and

equations

shown

in

Figs.

1.1

and

1.2.

In

an

ampl

ifier

not

using

pole-zero

cancel

lation,

the

exponential

tail

on

the

preamplifier

output

signal

(usually

50

to

500/us)

causes

an

undershoot

whose

peak

ampl

itude

is

roughly

undershoot

amplitude

differentiation

time

differentiated

pulse

ampl

itude

preamplifier

pulse

decay

time

For

a

l-^ts

differentiation

time

and

a

50-/us

preamplifier

pulse

decay

time,

the

maximum

undershoot

is

2%

and

decays

with

a

50-/us

time

constant.

Under

overload

con

ditions

this

undershoot

is

often

sufficiently

large

to

saturate

the

ampl

ifier

during

a

considerable

portion

of

the

undershoot,

causing

excessive

dead

time.

This

effect

can

be

reduced

by

increasing

the

preampl

ifier

pulse

decay

time

(which

generally

reduces

the

counting

rate

capabil

ities

of

the

preamplifier)

or

compensating

for

the

undershoot

by

using

pole-zero

cancel

lation.

Pole-zero

cancel

lation

is

accompl

ished

by

the

network

shown

in

Fig.

1.2.

The

pole

[1/s

+

(I/To)]

due

to

the

preampl

ifier

pulse

decay

time

is

cancel

led

by

the

zero

[s

+

(/C/R2C1

)]

of

the

network.

In

effect,

the

dc

path

across

the

differentiation

capacitor

adds

an

attenuated

replica

of

the

preamplifier

pulse

to

just

cancel

the

negative

undershoot

of

the

cl

ipping

network.

eo

(t)

eo(t)=E„ax^

°

Undershoot

First

C'-PP®"

Charge

loop

^lippj^g

_

pulse

°P*P"< network

^

undershoot

Equations:

-t

Emax

X

G(t)

=

(t)

1

s

T-

X

—

=£^1

(s);

Laplace

Transform

rnox

j j

s

+

—

s

+

T

o

RiCi

To

-

h

Fig.

1.1.

Clipping

in

an

Amplifier

Without

Pole-Zero

Cancellation.

-t

max

Tt

To

,

, ,

—

„

_

To

e

—Tie

=

ei

where

Ti

=

Ri

Ci

o<K<1

®o

I

f/

^max

®

ei

(t)

No

Undershoot

Pole-zero

_.

,

cancelled

_

Clipped

pulse

Charge

loop

x

-

„i,hout

network

undershoot

1

K

Pole

zero

cancel

by

letting

s

+

—

=

s

+

-

T

o

R2C1

or:

1

s

-I-

R2C1

-max

1

Ri

+R2

s

+

—

s

+

To

R,R2C,

=

E^

(s);

Laplace

Transform

Tmax

^max

Ri

+

R2

1

s

+

^^^

s

+

R

£.

(s);

where

Rp

=

1R2

C|

RpCi

-t

^

RnCl

/

I

Tmax

®

~

(t)

Fig.

1.2.

Differentiation

(Clipping)

in

a

Pole-Zero-Cancelled

Amplifier.

Total

preamplifier-amplifier

pole-zero

cancel

lation

requires

that

the

preampl

ifier

output

pulse

decay

time

be

a

single

exponential

decay

and

matched

to

the

pole-zero-cancel

la-

tion

network.

The

variable

pole-zero-cancel

lation

network

allows

accurate

cancel

lation

for

all

preampl

ifiers

having

25

/is

or

greater

decay

times.

The

network

is

factory

ad

justed

to

50

/is,

which

is

compatible

with

al

l

ORTEC

FET

preamplifiers.

Improper

matching

of

the

pole-zero-cancella

tion

network

wil

l

degrade

the

overload

performance

and

cause

excessive

pileup

distortion

at

medium

counting

rates.

Improper

matching

causes

either

an

undercompensation

(undershoot

is

not

el

iminated)

or

an

overcompensation

(output

after

the

main

pulse

does

not

return

to

the

baseline

and

decays

to

the

baseline

with

the

preamplifier

time

constant).

The

pole-zero

adjust

is

accessible

from

the

front

panel

of

the

452

and

can

easily

be

adjusted

by

observing

with

an

oscilloscope

the

basel

ine

with

a

monoenergetic

source

or

pulser

having

the

same

decay

time

as

the

preamp

l

ifier

under

overload

conditions.

The

adjustment

should

be

made

so

that

the

pulse

returns

to

the

baseline

in

the

minimum

time

with

no

undershoot.

1.3

ACTIVE

FILTER

When

only

FET

gate

current

and

drain

thermal

noise

are

considered,

the

best

signal-to-noise

ratio

(Fig.

1.3)

occurs

when

the

two

noise

contributions

are

equal

for

a

given

pulse

shape.

The

Gaussian

pulse

shape

of

this

amplifier

requires

a

single

RC

differentiate

and

n

equal-RC

integrates,

where

n

approaches

infinity.

The

Laplace

transform

of

this

transfer

function

is

G(s)

=

1

[s-t(1/RC)

[s-(-(1/RC)]n

where

the

first

factor

is

the

single

differentiate

and

the

second

factor

is

the

n

integrates.

The

452

Active

filter

approximates

this

transfer

function.

CUSP

t>0

GAUSSIAN

1

s-r(1/RC)

[s+(1/RC)]"

GAUSSIAN

APPROXIMATION

FOR

n

=

2

1

s

+

(1/RC)

[s

+

(l/RC)]'

ACTIVE

FILTER

s

+

(1/RC)

_1+j

/=

VTT

200363

Fig.

1.3.

Pulse

Shapes

for

Good

Signal-to-Nolse

Ratios.