ORTEC 276 Service manual

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ORTEC

Model

276

Photomultiplier

Base

Operating

and

Service

Manual

Model

276

Photomultipller

Base

Operating

and

Service

Manual

Printed

In

U.S.A.

ORTEC®

Part

No.

733130

0405

Manual

Revision

D

Advanced

Measurement

Technology,

inc.

a/k/a/

ORTEC®,

a

subsidiary

of

AMETEK®.

Inc.

WARRANTY

ORTEC*

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

a

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,

by

telephone

[(865)

482-4411]

or

by

facsimile

transmission

[(865)

483-2133],

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

designated

ORTEC

repair

center.

The

address

label

and

the

package

should

include

the

Return

Authorization

Number

assigned.

Instruments

being

returned

that

are

damaged

in

transit

due

to

inadequate

packing

will

be

repaired

at

the

sender's

expense,

and

it

will

be

the

sender's

responsibility

to

make

claim

with

the

shipper.

Instruments

not

in

warranty

should

follow

the

same

procedure

and

ORTEC

will

provide

a

quotation.

Damage

in

Transit

Shipments

should

be

examined

immediately

upon

receipt

for

evidence

of

external

or

concealed

damage.

The

carrier

making

delivery

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

notification

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.

Copyright

©

2005,

Advanced

Measurement

Technology,

Inc.

All

rights

reserved.

*ORTEC®

is

a

registered

trademark

of

Advanced

Measurement

Technology,

Inc.

All

other

trademarks

used

herein

are

the

property

of

their

respective

owners.

CONTENTS

WARRANTY

ii

SAFETY

INSTRUCTIONS

AND

SYMBOLS

iv

SAFETY

WARNINGS

AND

CLEANING

INSTRUCTIONS

V

1.

DESCRIPTION

1

2.

SPECIFICATIONS

2.1.

PHOTOMULTIPLIER

TUBE

BASE

2.1.1.

PERFORMANCE

2.1.2.

CONTROL

2.1.3.

INPUT

2.1.4.

OUTPUTS

2.2.

PREAMPLIFIER

2.2.1.

PERFORMANCE

2.2.2.

OUTPUT

2

2.2.3.

INPUTS

2

2.3.

ELECTRICAL

AND

MECHANICAL

2

3.

INSTALLATION

2

3.1.

DETECTOR

MOUNTING

2

3.2.

SYSTEM

CONNECTION

2

3.3.

INITIAL

ADJUSTMENTS

;

2

4.

OPERATION

3

4.1.

CALCULATION

OF

RESPONSE

OF

SCINTILLATOR/PHOTOMULTIPLIER

3

4.2.

TIMING

APPLICATIONS

5

4.2.1.

TYPICAL

FAST-SLOW

COINCIDENCE

SYSTEM

5

4.2.2.

GAMMA-GAMMA

COINCIDENCE

SYSTEM

FOR

THE

HIGH-PURITY

GERMANIUM

(HPGe)

DETECTOR

6

4.3.

SCINTILLATION

SPECTROSCOPY

6

5.

MAINTENANCE

7

5.1.

FACTORY

REPAIR

...

.

..

...

.

.

.

8

6.

BIBLIOGRAPHY

9

IV

SAFETY

INSTRUCTIONS

AND

SYMBOLS

This

manual

contains

up

to

three

levels

of

safety

instructions

that

must

be

observed

in

order

to

avoid

personal

injury

and/or

damage

to

equipment

or

other

property.

These

are:

DANGER

Indicates

a

hazard

that

could

result

in

death

or

serious

bodily

harm

if

the

safety

instruction

is

not

observed.

WARNING

Indicates

a

hazard

that

could

result

in

bodily

harm

if

the

safety

instruction

is

not

observed.

CAUTION

Indicates

a

hazard

that

could

result

in

property

damage

if

the

safety

instruction

is

not

observed.

Please

read

all

safety

instructions

carefully

and

make

sure

you

understand

them

fully

before

attempting

to

use

this

product.

In

addition,

the

following

symbol

may

appear

on

the

product:

ATTENTION

-

Refer

to

Manual

A

DANGER

-

High

Voltage

Please

read

all

safety

instructions

carefully

and

make

sure

you

understand

them

fully

before

attempting

to

use

this

product.

SAFETY

WARNINGS

AND

CLEANING

INSTRUCTIONS

DANGER

Opening

the

cover

of

this

instrument

is

likely

to

expose

dangerous

voltages.

Disconnect

the

instrument

from

all

voltage

sources

while

it

is

being

opened.

WARNING

Using

this

instrument

in

a

manner

not

specified

by

the

manufacturer

may

impair

the

protection

provided

by

the

instrument.

Gleaning

instructions

To

clean

the

instrument

exterior:

•

Unplug

the

instrument

from

the

ac

power

supply.

Remove

loose

dust

on

the

outside

of

the

instrument

with

a

lint-free

cloth.

,

^

x

_i

»

i

4;^^

•

Remove

remaining

dirt

with

a

lint-free

cloth

dampened

in

a

general-purpose

detergent

and

water

solution.

Do

not

use

abrasive

cleaners.

CAUTION

To

prevent

moisture

inside

of

the

instrument

during

external

cleaning,

use

only

enough

liquid

to

dampen

the

cloth

or

applicator.

Allow

the

instrument

to

dry

completely

before

reconnecting

it

to

the

power

source.

lA

1

ORTEC

MODEL

276

PHOTOMULTIPLIER

BASE

1.

DESCRIPTION

The

ORTEC

276

Photomultiplier

Base

is

designed

to

provide

a

near-optimum

voltage

distribution

for

essentially

all

10-stage

photomultiplier

tubes

that

fit

the

standard

14-pin

tube

socket.

The

unit

has

a

self

contained

low-noise

integrating

preamplifier

that

provides

gain

and

line

drive

capability

for

the

output

signal

from

the

last

dynode.

The

preamplifier

is

de

coupled

to

simplify

pole-zero

cancellation

in

the

main

amplifier.

The

anode

signal

is

capacitively

coupled

to

an

output

BNC

connector

for

use

in

coincidence

timing

or

linear

pulse-height

analysis.

A

TEST

input

is

provided

to

allow

pulser

calibration

and

testing.

A

FOCUS

control

on

the

rear

panel

is

for

optimizing

the

photocathode

first-dynode

electrical

field.

Some

of

the

photomultiplier

tubes

with

which

this

PM

base

is

compatible

are:

•

RCA:

4518,

5819,

6217,

6342A,

6655A,

7326,

8053,

8054,

and

8055

•

Philips:

XP-1000

to

1005

and

XP-1031

through

1033

•

EMI:

9536,

9578,

9579,

and

9708

Series

•

CBS:

7817,

7818,

7819,

and

GL-1004

to

1012

•

Dumont:

6292,

6363,

and

6364

The

unit

is

also

compatible

with

other

10-stage

tubes

not

listed

above.

Compatibility

can

be

determined

by

comparison

with

those

listed.

2.

SPECIFICATIONS

2.1.

PHOTOMULTIPLIER

TUBE

BASE

2.1.1.

PERFORMANCE

Design

Resistor

divider

bleeder

connected

to

14-pin

standard

PM

tube

base

for

10-stage

tubes.

Total

resistance

1.49

MQ,

with

bleeder

current

of

1.33

mA

when

maximum

high

voltage

of

2000

V

is

applied.

Voltage

Distribution

Coefficient

Linear

to

all

stages

with

focus

adjustment

on

the

grid.

2.1.2.

CONTROL

FOCUS

Single-turn

locking

potentiometer

on

panel

for

external

adjustment

of

PM

tube

grid

potential.

2.1.3.

INPUT

HIGH

VOLTAGE

Type

SHV

connector

on

panel

accepts

operating

voltage

for

distribution

to

PM

tube;

+2000

V

maximum.

2.1.4.

OUTPUTS

ANODE

Type

BNC

connector

on

panel

furnishes

PM

tube

anode

negative

output

pulse

for

use

primarily

as

a

timing

signal;

Z,,

=

1

kO

ac-coupled.

LAST

ANODE

Connected

internally

to

preamplifier

input.

2.2.

PREAMPLIFIER

2.2.1.

PERFORMANCE

Input

Directly

from

last

dynode

of

photomultiplier

tube.

Conversion

Gain

Nominally

5

pV/eV

using

a

2

X

2-in.

Nal(TI)

crystal

and

a

photomultiplier

tube

gain

of

10®.

Rise

Time

<100

ns

for

a

fast

rise

time

test

pulse.

Fall

Time

Constant

50

ps.

Integral

Nonlinearity

<±0.02%,

0

to

+10

V.

Output

Polarity

Positive.

Output

Noise

<50

pV

rms.

Saturation Level

+10

V

into

open

circuit;

+5

V

into

93

Q

load.

Gain

Temperature

Coefficient

<±0.005%/°C,

0to50°C.

2.2.2.

OUTPUT

PREAMP

Type

BNC

connector

on

panel

furnishes

preamplifier

positive

output

pulse

for

use

primarily

as

an

energy

analysis signal.

=

93

0

de

coupled.

2.2.3.

INPUTS

Power

Cable

3-m

(10-ft)

captive

cable

terminates

in

Amphenol

17-20090

connector

to

accept

operating

power

for

the

preamplifier

circuits.

Compatible

with

all

ORTEC

main

amplifiers

and

with

an

ORTEC

114

Preamplifier

Power

Supply.

test

Type

BNC

connector

on

panel

accepts

test

pulses

from

an

ORTEC

Pulse

Generator

for

testing

and

calibration.

Nominal

100-Q

charge

termination

built

into

preamplifier

circuit.

2.3.

ELECTRICAL

AND

MECHANICAL

Power

Requirements

Preamplifier

+24

V,

16

mA;

-24

V,

16

mA.

PM

Tube

Base

+2000

V

maximum

(use

rate

voltage

for

the

PM

tube

that

is

installed).

Weight

Net

0.65

kg

(1.5

lb).

Shipping

1.3

kg

(3.0

lb).

Dimensions

5.58

cm

(2.2

in.)

diam

x

10.1

cm

(4.0

in.)

long

plus

3-m

(10-ft)

captive

power

cable.

3.

INSTALLATION

3.1.

DETECTOR

MOUNTING

Normally

with

10-stagephotomultipliers

the

amount

of

signal

current

through

the

tube

is

small;

therefore,

it

is

quite

practical

to

run

positive

high

voltage

on

the

tube

with

the

cathode

at

ground

potential.

This

means

that

when

the

detector

is

mounted

to

the

photocathode,

very

little

attention

need

be

paid

to

the

probability

of

leakage

currents

being

created

across

the

glass

envelope,

since

the

voltage

potential

should

be

zero.

In

many

cases

where

this

PM

base

is

used,

the

detector

is

mounted

to

the

photomultiplier

in

an

integral

package.

When

a

scintillator

is

mounted

on

a

photomultiplier,

the

combination

must

be

made

light-tight

to

ensure

low

noise

and

to

eliminate

the

possibility

of

photomultiplier

damage.

The

most

common

practice

to

make

the

detector/photomultiplier

light-

tight

is

to

carefully

wrap

it

with

a

good-quality

black

electrical

tape.

Another

is

to

use

an

aluminum

can

cover

and

to

tape

it

a

the

entrance.

3.2.

SYSTEM

CONNECTION

If

it

is

desired

to

test

and

calibrate

the

system,

connect

a

pulser

to

the

test

input.

A

1-V

test

pulse

should

yield

a

1-V

pulse

on

the

preamplifier

output.

The

test

input

is

internally

terminated

in

93

Cl.

Connect

a

high

voltage

power

supply

to

the

high

voltage

input

connector

and

ensure

positive

polarity

of

the

high

voltage

supply.

Connect

the

preamplifier

signal

to

the

energy

analysis

system

and

connect

the

anode

signal

to

either

a

timing

or

energy

analysis

system.

Use

high-quality

coaxial

cable

and

terminate

the

anode

signal

cable

in

its

characteristic

cable

impedance.

3.3.

INITIAL

ADJUSTMENTS

The

only

adjustment

on

the

PM

Base

is

the

FOCUS

control,

which

optimizes

the

photocathode/first-

dynode

electrical

field.

1

2.

3.

4.

5.

Plug

a

photomultiplier

detector

into

the

unit

and

ensure

it

is

light-tight.

Connect

the

positive

high

voltage

supply.

Place

a

radiation

source

in

the

vicinity

of

the

scintillation

detector.

Observe

the

preamplifier

output

on

a

sensitive

range

of

an

oscilloscope

and

slowly

increase

the

high

voltage.

If

there

is

a

very

large

amount

of

unipolar

grass

(circuit

noise),

there

is

possibly

a

light

leak.

Cover

the

PM

tube

with

a

black

cloth

to

see

whether

the

grass

diminishes;

if

it

does,

the

photomultiplier

was

seeing

the

ambient

light

and

should

be

rechecked

for

proper

covering

to

eliminate

the

light

leak.

With

the

high

voltage

at

the

desired

level,

observe

the

pulses

which

are

radiation-induced

scintillations

and

adjust

the

FOCUS

control

to

obtain

maximum

pulse

amplitude.

This

is

the

proper

setting;

lock

the

adjustment

with

the

potentiometer

lock

nut.

4.

OPERATION

Once

the

steps

outlined

in

Section

3

of

this

manual

are

performed,

the

unit

is

ready

for

use.

High

voltage

may

be

applied

and

adjusted

for

the

appropriate

gain

associated

with

the

specific

experiment.

The

gain

will

vary

by

a

factor

of

approximately

2

for

each

high-voltage

change

of

100

V.

NOTE:

It

is

advisable

to

operate

the

high

voltage

at

the

minimum

practical

value

when

the

high

count

rates

are

to

be

experienced,

since

count

rate

tolerance

is

a

direct

function

of

the

photomultiplier

gain.

4.1.

CALCULATION

OF

RESPONSE

OF

SCINTILLATOR/PHOTOMULTIPLIER

Table

4.1

lists

the

decay

constants

of

some

of

the

more

common

scintillators.

The

first

three

scintillators

are

crystals.

Naton-136,

Pilot

B,

and

NE-102

are

plastics,

and

the

last

two

are

liquid

scintillators.

The

decay

time

is

responsible

for

a

finite

rise

time

on

the

leading

edge

of

L(t)

(refs.

12,

21,22):

t2

is

the

fast

decay

component

which

is

mot

noticeable

at

the

output

of

the

photomultiplier;

Tj

and

T4

are

the

slow

components

(important

for

n-y

discrimination

with

NE-213,

NE-218,

and

Stilbene).

Where

measured

values

were

not

given,

the

letters

N.G.

have

been

entered.

The

parameter

P

is

the

number

of

photo

electrons

released

at

the

photocathode

per

unit

energy.

This

figure

is

affected

by

the

efficiency

and

spectral

response

of

the

photocathode

(refs.

22,

23,

26,

27)

and

hence

is

somewhat

characteristic

of

the

photomultiplier

used.

However,

it

provides

a

reasonably

good

guide

for

comparing

the

light

output

of

scintillators.

In

Table

4.1,

P

is

listed

as

a

fraction

of

the

value

for

anthracene;

P(anihracene)

's

~700

eV/

photoelectron

for

S-11

photocathode

material.

Table

4.1.

Scintillator

Decay

Times.

Scintillator

Decay

Time

Constants

(ns)

P/P(an>wac*n*>

ri

ri

T3

Tt

Nal(TI)

250

(24)*

2.40

Anthracene

(25)*

N.G.

29.3

1.00

Stilbene

(23)*

0.1

4.05

33

270

0.64

Naton-136

(22)"

0.4

1.6

10

0.37

Pilot

B

(22)"

0.4

1.6

9.5

0.41

NE-102

(25)*

N.G.

2.51

N.G.

0.65

NE-213

(23)*

1.66

3.16

32.3

270

0.47

NE-218

(23)*

1.76

3.58

36.5

288

0.56

The

thickness

of

the

scintillator

is

frequently

chosen

according

to

the

required

stopping

power.

The

flight

time

of

the

radiation

(gamma

rays

or

neutrons)

across

the

scintillator

normally

becomes

a

limitation

on

the

time

resolution

as

the

thickness

is

increased.

Usually

detection

efficiency

must

be

compromised

for

good

time

resolution.

The

scintillator

geometry

and

the

coupling

to

the

phototube

must

be

carefully

considered:

If

the

light

can

travel

a

variety

of

path

lengths

before

being

collected,

an

additional

contribution

to

the

time

resolution

will

result.

Light

collection

is

widely

discussed

in

the

literature

(refs.

15,17-19,

28,29).

Table

4.2

lists

the

characteristics

of

several

types

of

photomultipliers.

It

is

noteworthy

to

observe

that

the

gain

of

theses

tubes

ranges

from

-0.5

x

10®

to

2.5

x

10®.

This

gain

is

strongly

affected

by

the

age

of

the

tube

and

the

temperature

and

will

change

by

a

factor

of

-2

for

each

100-V

change

in

high

voltage.

For

response

calculations

there

are

several

approximations

that

will

aid

in

a

quick

"ballpark"

answer:

1.

Conversion

for

absorbed

energy

(eV)

to

photons

(p)

for

anthracene

is

-70

eV/p

(ref.

35).

2.

Conversion

of

photons

to

photoelectrons

for

S-11

photocathode

material

is

-10%

(ref.

37).

3.

100%

of

photons

are

collected

on

the

photocathode

and

100%

of

cathode-emitted

photoelectrons

are

collected

on

the

first

dynode.

The

function

for

the

total

charge

output

now

becomes

Q„

=

A

X X

X

G

X

q

(coulombs)

(1)

where

Qo

E

P/Pa

'See

Bibliography

PC,

■eff

output

charge

in

coulombs

absorbed

energy

in

detector

in

eV

detector

efficiency

compared

to

anthracene

from

Table

4.1

photomultiplier

gain

from

Table

4.2

or

from

manufacturer's

data

charge

per

electron

1.6

x

10'^®

coulomb

efficiency

of

photocathode

or

-10%

for

S-11.