252Cf-plasma desorption mass spectrometry multistop time digitizer

Internutional Journal of Muss Spectrometry madIon Physics, 53 (1983) 353-362 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

252Cf-PLASMA

DESORPTIDN

MASS

SPECTROMETRY

MULTISTOP

TIME

353

DIGITIZER*

B.T. Turk*,' R.D. Macfarlane' and C.J. McNeal' 1 Lawrence Berkeley Laboratory, Berkeley, California 94720 (U.S.A.) 2 Department of Chemistry, Texas A&M University, College Station, Texas

77843

(U.S.A.) ABSTRACT 252A multistop time digitizer is described which was designed specifically for Cf-plasma.desorption time-of-flight mass spectrometry. The digitizer is a high resolution time intervalometer capable of measuring the times of a number of stop events following a common start. A resolution of 78.125 ps is achieved. The time range can be varied from 5 ms to 320 ms in 16 steps. stop event processing time takes less than one microsecond, enabling high resolution measurements of closely spaced bursts of events. The digitizer consists of the following three modules. A clock module provides the accurate time reference including a precision time calibrator. An analog module contains a special tandem stretcher by which the high resolution and low differential nonlinearity are achieved. A digital module comprises the counting, logic and interface circuits. Up to four complete digitizers can be housed in and powered by a standard CAMAC crate.

INTRODUCTION Since of-flight studying The

its introduction mass

nonvolatile

principle

into two 252Cf

electric evacuated

penetrate

field

fast shape

electric

pulse

but vary

is minimized

These

which

in amp1 itude.

by the employment

in Fig.

particle

molecular

252Cf

the

foil,

in an down

an

an ion detector

The detector

generates

The pulses

have

due to the change

fraction

weights.

from

on a thin

to travel

timefor

disintegrates

fragments

reaching

particle.

in timing

of constant

method

are accelerated

of its mass.

The error

1.

deposited

and directed

of each

higher

Fission

particles

of each

is a function

at the arrival

with

has been

masses,

desorption

as a unique

directions.

charged

to their

those

is shown

in opposite

The time-of-flight

at the end of the tube

1), the 252 Cf-plasma recognized

especially

the sample

ions.

according

tube.

(ref.

quickly

a spectrometer

going

molecular

was

molecules,

of such

fragments

source

producing

in 1974

spectrometry

a

similar

in amplitude

discriminators.

*Dedicated to Prof. R.D. Macfarlane on the occasion of his 50th birthday and presented at a symposium held in his honor at College Station, Texas USA 15-19 May 1983. 0020-7381/83/$03.00

0 1983 Elsevier Science Publishers B.V.

354

FISSION FRAGMENT DETECTOR SAMPLE --CL3-----------------

ION DETECTOR I,

252

-‘, Cf SOURCE

/

F

CHARGED

m* -

E”““‘,

CONSTANT FRACTION DLSCRIMINATOR

-5

-

-

General

Since

the

consists detector gration

DATA

fragments

placed

on the

pulses

their

are amplified the high

detector between register interface plotted

other toward

and

then

(ref.

5).

the

generates

same time

source the

to a data are

first

sorted

or further

fragment

are

generated

fragment

detector

fraction

discriminator

A signal

from

stored

processor

ions

the disinte-

ions

Each digitized

is first

a fission

fission

digitizer.

the digitizer.

peaks,

The

of molecular

registers

molecular

in a constant

time

stop

a burst

directions,

ion detector.

reshaped

The events of time

that

of the '5*Cf

the

subsequent

transferred

as spectra

side at

system.

in opposite

multistop

stops

and

start

and

then

resolution

discriminator the

event

traveling

a pulse

travel

of a PDMS

fission

of two

REGISTER

INTERFACE

diagram

spontaneous

by producing

and start start

block

d

AMPLlFlER

RECORDING

1.

a

\

STOP

MULTISTOP TIME DIGITIZER

Fig.

-

CONSTANT FRACTION DlSCRlMlNATOR

7

START

AMPLIFIER

-

time

the

to

ion

interval

in a derandomizing

data

via an appropriate out

by the computer

calculated

to generate

and

then

the mass

spectra. 252

A new multistop Cf-plasma

original

time

desorption

experiment,

digitizer, experiment,

reported

designed

in 1980

is described

by Macfarlane

(ref.

specifically

in this

paper.

11, a modified

for

the

In the E.G.&,

Inc.

355 TDC 100 Time nuclear

Digitizer physics

and deadtime

time-of-flight

of 4 ps after

described

(ref.

15 events

per each

report

3) having

It's deadtine

provided

they

the digitizer problem

frequency

Fig.

2.

MULTISTOP Basic 3).

'fraction These

by more stability

an excellent

time-to-digital

(ref. 4), which

described

of stop

events

can

differential

The

time

precis?on

linearity

systems.

by implementing

in effect

in this from

the 900 ns.

increases

to 1280b

(fig.. 2)

be processed,

calibration

of

reference

has often

resolution

a technique

up to

5 us to

50 MHz

which

High

of 125 ps was

to process

ranges

of a built-in

conversion

are achieved

capacity

in 16 time

number

than

system

designed

been

and

General

block

DIGITIZER operation

diagram

GENERAL

low

MHz

the actual

clock

The counting

of the period

of time

is essentially interval

is expressed

of an internal

are counted

Time

Digitizer.

DESCRIPTION

of the digitizer

The time measured

increments

of a PDMS Multistop

until

is initiated

frequency

a stop

analogous

in increments pulse

reference

a

of dual

of 50 MHz.

stop watch. (fig.

Any

timing

ps and

The digitizer

is 900 ns.

originally

It had a resolution

Another

of 675

ps (LSB)

inherent

deadtime

interpolation

period.

of 78.125

separated

in other

event.

a resolution

has

and

The TDC 100 was

experiments.

stop

are

oscillator

conversion

each

timing

has a resolution

320 ns.

clock

used (ref. 2).

was

to a mechanical

by a start equal

clock

is received.

pulse

to a fixed oscillator.

One of the

356 problems

was

how

counting

and

thus

can

arrive,

and

of

accurately.

an

already

no

stop

Stop that

the

EVENT CLEAR 5 MASTER CLEAR YA5TE;E;;;ISTER

Fig.

In

to

the

both

number

storage

data

The different

and

data

b

time

some

the

the

time.

stops

processing

of

stop

not

of

During

counting

maximum does

The

range.

takes

the

number

time

pulse

limit

thi

s

continues

rate,

the

rate.

digitizer

the

number as clock

of

of

size

the

time

range,

The

clock

room

for

in

here

system.

the

of

three

it

calibrating

can

the and

modular.

The

Inexpensive

Commercial

a clock the

digitizer

is

be easily is of

intended

available events,

deadconform

provide

interfaced

hardware

de-randomizing

stop

modules

CAMAC crates

low,

for

use

with

a

at

with

a rea-

temporary

processor. basic

a separate

interconnections.

of

resolution is

This and

fast

to

dissipation

incremental

expansion.

additional

transfer

power

described

system

YIVIV

digitizer.

and

processors.

for

with

the

v

“I

VIVY

cost,

consists

serving

v

CAMAC standard

contained

minimum

C v

diagram

data

both and

and

Any

”

processing

modern

storage

clock’s

system

stopping

start.

although

be accepted,

IY

used

cost,

actually

the

pulse

determines

keep

power

of

sonable

stop

thus

be made.

an external

the

data

timing

to

widely the

without to

deadtime

between

must

during

accepted

8

Basic

a trade-off time

time

external

IO

order

stop reference

S

IllPUT

3.

the time

can

a STOP

out the

each’ start,

deadtime

provided

read

lose

after

storage

short

to

units.

module. The

units

pul se generator,

Each They are

are

unit

is

conceptually

designed

a frequency an analog

to

require

standard interpolator

a

module

367 module

for processing

start

and

stop

arithmetic,

logic

and

interface

counters, been

selected

have

been

50 MHz logic

desirable

is the

for instance,

operated

correction

for the difference

frequency

Range

time

shorter

ranges

interval

pulse

reached.

are used,

A master

all

of 335.36

clear

state,

functions

A number

frequencies

ms

is covered

of 5.12

vs can

cannot

be stopped

sequence

is then

awaiting

a new start

and resets

of interpolation

and

have

been

used

and digitization

interva'ls smaller

were

digitized

factor

by much

of 256 would

frequency

were

long conversion closely

greatly

spaced

of statistically Substantial interpolation Two

successive

conversion starting

the same

are

results

as though

the digitizer

It would

take

to the reference

prohibitive

5.12

in typical pulses

of an experiment

sufficient

data.

reduction

interpolations

deadtime.

was

are

Additional

often

accomplished

smaller

than

sufficient conversion

of a new event

over-

while

the

incre-

a method a full

good

of

period

results

time

interval

a stretching

the 50 MHz

reference

is paralyzed period

occur.

Such

needed

pulse

to drasticalJy time the

reduction second

to stretch

by

Such

measurements a deadtime

would

for the accumulation

by multiple

the clock

for the

of 20 ns.

time-of-flight

of stop

the conversion

very

ps in order

frequency

of time

intervals

restored

MHz.

bursts

deadtime

than

For instance,

the length

of time

with

frequency.

process,

time,

close

times

increase

reference

stretching

an interval

previously

to 256 x 50 = 12,800

of the conversion

256 times where

produce

of the

employed

6).

was the same as if the whole measured

higher

increased

As a result duration

has been

by a

is

ctear

to increase

stretching

result

For

initiated

For instance,

linear

clock

A

immediately.

(ref.

The

number.

master

of the time measurements

7,2,8).

pulses.

the digitizer

A manual

resolution

(refs.

as a

the end of the range

mental

of the reference

Also,

clock

50 MHz

Once

generated

of time

serve

binary

pulse.

no

units.

by a 32-bit

the digitizer

techniques

can

be preselected_ until

and

is necessary.

coarse

can

simultaneously.

to the other

by counting

and

standard

calibrated

any one of the group

is defined

any multiple

are operating

the reference

has

would

counting

frequency

automatically

50 MHZ

frequency

Schottky

supplied

in individual

containing

lower stop deadtime,

and

low-power

digitizers

become

supplying

the digitizer

to the armed rules

source,

of the digitizer

maximum start

several

a higher

resolution

an externally

the digitizers

a group .of digitizers

when

master

higher

module

For the clock,

Although

of convenient

Alternatively

when,

thus

timit

and a digital

circuits.

standard.

for achieving

practical

circuits.

be used, When

as the frequency

events

successive period

reduce

(ref. the

is possible

stage

4).

by

of processing

the

358 preceding

event

in 73.125

ps incremental

frequency

50 MHz),

pointed

been

resolution Short i.e.

is still with

at the same same

the stop

events.

The

input

as soon the

Since

stop

the start other

events

interpolation,

digitizers

thermal

stop

rate

digitizer

rates

remained with

,thru the same The clock

processing module A front

an external

frequency

digitizer(s). module.

An

lO-position

front

supplied

NIM pulses,

the calibrator frequency and

source

stop

inputs

digitized frequency,

with

The start

tandem

precision

advantage, and

to the start to the stop

interpolator between

thereafter

drift

In

a change

the start

not affect

starts

and

imperfect Also,

because

does

a71

the stop

is compensated.

error.

time

and

the

stops

a quick

pass

simplifying expands

end of a measured

counter,

of the input

output

can

be used

of stops

with

and reliable

own clock

of the digitizer

the small time

time

interval.

same by a

frequency

stable

up to

of fast

Therefore,

as the external

for driving

following

procedure

trouble-shooting

in the

programmable is a train

the calibrator

from

another

frequency.

and

in case

an output

at any

of the calibrator

frequency

provided

Also,

operates

the digitizer's

the operation

are

is located

is as accurate

compared

reference

switch

or for driving

calibrator

Any number

When

internal mode

the digitizer.

nth cycle

The calibrator

possible

50 MHz

The output separation

interpolator

and the stop

same

the start

interpolators,

change

The calibrator

pulse

greatly

important

switched

of time

is a divide-by-n

every

the calibrator,

US for the

assigned

The

thermal

monitoring

after

the digitizer.

the clock,

As has

range.

because

for

frequency

of the digitizer.

making

ns each.

of both

then

and stop

and operation

is used

externally.

used.

5.12

interpolator

rate

an accurate

switch.

and the measured

calibrating driving

for

output

time

source

The event

the calibrator

appearing

start

additional

input

source

panel

first and

of the

interpolator

independent

BasicaTly,

100 MHz,

panel

is available

result

route.

contains

oscillator. the clock

dual

320

of the difference

is a major

the same.

stretchers (reference

another

is completed.

drift

separate them

can cause

a common

are

the end of the

thermal

between

yields

circuits

is a function

employing

tracking

of average pulse

until

require

measurement

conversion

time

of only

for the interpolation

of the time

the measured

16-time

frequency.

be used

as the start

would

interpolation

interpolator

at the beginning

successive

deadtime

stretcher

reference can

input serves

step

of the dual

circuit

Two

of the time measurements

a the conversion

out a single

deadtime

the

in progress. resolution

the start

a start

can be

reference

for checking output

is in full

and

is used

for

synchronism

and repair. fractions These

remaining fractions

at the are,

of

359

smaller

course, explained

the measured

time

synchronism counting after

with

another enabled

(and the

stop

counters

clock

the counting

After

start

is

event

(defining

(T,, T2, T3)

pulses

gating

start-stop

control

separation

is then

in the

is computed

cleared

(640 ns),

counting

a clear

(CR) for

time

as soon

of the

interpolator

to the

counter

counting before

data

exactly

original

"Fine"

amount

conversion

input

of the

and

greatly

the

counter

is generated

last

range. stop

stop

the control input

the end of stop event

can

to the auxiliary logic

routes

(VR) while again

remains

stop

counting

was

events

immediately

events

and

to the have

is again

continued.

is still

enabled

The AC is

counter,

referred

interpolator

counter

the

is completed.

to the master

how many The

taking

a new stop

are digitized

in

deadtime.

in the digitizing

in the adder

after

restarts

thus

is already

subsequent

the conversion

an

is switched

the start

register

is added

the master

"fine"

interpolator

Two close

be accepted.

place

after

periods

the counting

no matter

"fine"

take

when

The master

enabled

back

to the master

the end of the time

and requires

The control

is lost

input

conversion

later.

temporarily

no time

and

During

interpolation

interpolator

is given

is accepted.

This

(AC).

start

this,

leaves Soon

the

pulse before

data

range.

enables

register

pulses.

and

The time

reducing

operations

time

After

pulse.

the stop can

stop

of clock

and

in

The 640 ns of the auxiliary

interpolator

transferred

the operation.

and the stop the

event

start

is

the

"coarse"

counter

"fine"

input

of time

afterwards

counter

start

Although

The

auxiliary

been digitized cleared

"coarse" is also

"coarse"

counter.

sequence

by the

the counting

counting

(MIX).

is switched

stop

32 clock

it resumes the 32nd

timing

counting

as first

the

start

for a period

is digitized

immediately

(CR) signal

Detailed

preventing

is completed. place

The

events.

in the auxiliary

to the master

input

stop

Also

first

counter

added

and

event

640 ns the main

to master

the stop

The master counter

tandem,

pulses

start

module.

is started

takes

now be accepted.

event

stretcher

stop

pulses

interpolator

for the rest of the digitized

auxiliary

place,

The

counting

is also

enables

disabled

after

The

(CL), also

logic

counting)

320 ns. time

both

start

the auxiliary

counting

pulse.

of 32 preset

start

additional

master

of any

gating

These

2).

The

logic

in the

periods

"coarse"

"fine"

logic

(fig.

serves

by the control

of any

start

reference

from

three

module.

is completed.

interpolator

first

acceptance

and

(CK)

in the logic

of this

a start

event. same

"fine"

Basically, generates

the clock

counting

The operation

period.

section.

interval),

operation

each

The

than a clock

in the next

(AD) as soon

of an event.

as the

"fine"

The arithmetic

register

is

360 strobed

in.

binary

Eventually,

number

that

the

and

register

simultaneously bursts

of

remains

by closely

Basic

pulse

every

used of

lasts (line

7)

is

the

acceptance

the

end

new start

the

first

the

one

end

externally

stop

event

monitoring

(line each

8)

Master

The

digitizer

10)

are

or

a stop

least

a few

last

about

generated

by

the

tandem

in

progress.

can

be con-

the

is

output accepted

events,

purposes.

when

the

start

6).

An

internal

which

clear is

at

the

i.e.

and

interpolation,

(line

of

pulse

This

of

digitizer.

pulse

conversion

ns.

when

input

be gated,

appear

is

800

signal

range

event.

next

but

remained

The

third

to

still

storage.

the

process stop

is

is

arriving

at

the

gate

which

ready

starting

data

the

digitizer

pulse

transfer, for

automatically

generated ready

accepted event

prepares

then

there accepted

still

since stop Next

retain

overload

a and

all The

busy.

(line

12), The

data at

at

processing meeting

event

data

with

stops

busy

conversion

register.

Such

The

,h).

shown,

coincident

be accepted,

accepted

registers

not

another of

in

The

low.

for

clear

(line

is

external

master

or

about

the

gate

stop

signal

counting

end of

the

range.

(c,f

produces the

and

time

next

pulses

rejected interpolator

stop

busy

to

a busy

event

pulses

stop

the

at

time

stop

The

ately

the

or

advised stop

for

the

acceptance

times

marked

at of

a

pulse.

Random n.

the

the

should

start

corrections,

logic,

at

by of

fixed

start

pulse

is

in

can

a

be retained

operation

inputs

of

the

and

stretcher

time-of-flight stop

as

can

remain

gating

a start

is

events

and

LED display microsecond

memory

The

a coincident

An event

one

events

external

stop

by

panel than

stop

type

start

edge

generates of

two

a typical

Any

deadtime

end

the

in

front less

expected.

previous

Roth

either

fast

folIowed

of

3.

leading

generated

is

to

for

the

and

events

pulse

module

until

both

of

time

external

logic

as

the in

only

are

be conditioned

this

on

A “FIFO” events

afterwards.

of

veniently

since

Fig.

the

interpolator

appears

be transferred

externally.

The

The

in

before

duration

can

stop

long

may

nanoseconds

gating

digitizer.

applied

nanoseconds five

the

shown

acceptance

gate

be cleared

sequence

is

their

can

as

time

result

data

spaced

disabled

digitizer

the

the

buffer

10)

no external at

k was

eligible two

conditions

still

preceding can

be

required

to is

in

processed,

into the

but

arriving

at

stops.

Event

13)

data

the

time remained

m was busy

signal

d is

register

(line

14).

(line

14). in

because (line

to

memory,

stored

the

sent cleared

buffer

range

accepted

is

until

rejected

by monitoring

at

buffer

processor

strobed

immedi-

The

the

a,

because

stop

(line

the

external

came

inspected

into ready

retains

an

The

from

are

conditions.

strobed

also

11) rejected

pulse.

register

register

clear

stop

the is

(line

internally

start

the

transfer

g (1 ine

b are

the

data

and

stop

the

4) event

the all remains busy

by

361 an oscilloscope.

CONCLUSION Several

of the digitizers

the Department typical is the

of Chemistry,

positive

at full

above

2440.659

distribution it.

resolution

distributions

Texas

ion rhodamine

ion time

spectrum

have

built

A&M

Na+

used

and

for

Cf-PDMS 1).

the calibrating

experiments

The portion lower

and the calculated

mass

primary

calibration

points

at

of

The

in Fig. 4.

Time-of-flights

ps/channel.

measured

(ref.

is shown

ns intervals

ions were

252

for the

University

66 spectrum in 7.25

H+ and

of 70.125

were

ns were

been

a

part

of spectra

of H+ and

Na+

of 1106,911

ns and

calculated.

415

355

371 399 3B7 424 III,

100

150

200

250

300

I

350

MASS

400

w’4500 5 4000 c 3500 5 3000 0: 2500 g 2000 v) 1500 g 1000 g 500 u 4000

Fig. 4.

4500

5000

252Cf-PDMS

5500 TIME

positive

OF

6000 FLIGHT

ion spectrum

6500 (nssc)

7000

of Rhodamine

7500

6000

66.

ACKNOWLEDGEMENTS This work and

was

Development

by the Texas National Health

Group,

A&M

Science (GM-26096),

to a company product

performed

as part

of the Lawrence

Research

Foundation

Foundation and

of the program

(Grant

the Robert

or product

by the University

name

does

Berkeley under

not

imply

to the exclusion

Electronics

Laboratory,

Contract

CHE-82-06030), A. Welch

of the

and was

Research supported

No. 263-79-C-0652,

the

tile rlational Institutes

Foundation approval of others

(Grant

A-258).

or recommendation that

may

of

Reference of the

be suitable.

362 REFERENCES R.D. Macfarlane, D.F. Torgerson, Int. J. Mass. Spectrom, and Ion Phys., 21 (1976) 81-92. 8. Turko, Multiple Stop Clock for Neutron Time-of-Flight Measurements, Bulletin of the American Physical Society, Series II, Vol. 16, No. 1 (56-57), January 1971. R.F. Bonner, D.V. Bowen, B.T. Chait, A.B. Lipton and F.H. Field, High Performance Digital Timing System, Analytical Chemistry, Vol. 52, No. 12 (136-140), October 1980. B. Turko, Spaceborne Event Timer, IEEE Trans. Nucl. Sci,, NS-27, No. 1 (309-404), February 1980. Internal Report. Description of Data Acquisition in 252Cf-PDMS, Department of Chemistry and Cyclotron Institute, Texas A&M University. D-F. Porat, Review of Sub-Nanosecond Time Interval Measurements, IEEE Trans. Nucl. Sci., Vol. 20, No. 5 (36-511, October 1973. R. Nutt, Digital Time Intervals Meter, Rev. Sci. Instr. Vol. 39, No. 3 (1342-1345), September 1968. B. Turko, A Picosecond Resolution Time Digitizer for Laser Ranging, IEEE Trans. Nucl. Sci., Vol. NS-25, No. 1 (75-80), February 1980. B. Turko, A Modular 125 ps Resolution Time Interval Digitizer for 10 MHz Stop Burst Rates and 33 ms Range, IEEE Trans. Nucl. Sci., Vol. NS-26, NO. 1 (737-745), February 1979.