ORTEC 473 User manual
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.
5.2.
INFMJT
CIRCUIT
Signals
are
accepted
through
CN1.
The
input
is
protected
against
large
amplitude
signals
by
Q1,
D1,
and
D2.
Resistor
R42
provides
SOfi
termination
for
the
input
signals
and
divides
the
input
amplitude
by
a
factor
of
2.
The
input
signals
can
be
monitored
at
TP1
on
the
front
panel.
The
signals
are
furnished
through
R45
and
buffer
Q5
into
the
lower
level
discriminator
and
through
R75
and
buffer
Q7
into
the
upper
level
discriminator.
The
signals
are
also
furnished
through
DL14
and
DL15
into
the
constant
fraction
discriminator
circuit.
5.3.
LOWER
LEVEL
DISCRIMINATOR
The
signal
through
05
is
furnished
to
pin
9
of
IC2A
and
its
level
is
compared
to
a
reference
level
at
pin
10.
Under
quiescent
conditions,
the
level
at
pin
9
is
less
negative
than
that
at
pin
10.
When
the
level
at
pin
9
exceeds
the
level
at
pin
10,
IC2A
changes
state
and
generates
a
response,
LLLE
for
lower
level
leading
edge,
used
to
reset
the
internal
logic
and
to
arm
a
zero
crossing
discriminator
in
the
constant
fraction
circuit.
The
response
remains
until
the
input
signal
level
decays
through
the
reference
level.
The
reference
level
at
pin
10
is
furnished
from
the
upper
level
adjustment
through
R43
and
R73
and
is
about
50%
of
the
upper
level
threshold.
A
calibrated
baseline
is
furnished
from
R160
and
R65
through
Q4.
5.4.
UPPER
LEVEL
THRESHOLD
The
signal
through
Q7
is
furnished
to
pin
9
of
IC4A
and
its
level
is
compared
to
a
reference
level
at
pin
10.
Under
quiescent
conditions,
the
level
at
pin
9
is
less
negative
than
that
at
pin
10.
When
the
level
at
pin
9
exceeds
the
level
at
pin
10
because
of
the
input
signal
amplitude,
IC4A
changes
state
and
generates
a
response,
ULLE
for
upper
level
leading
edge,
used
to
permit
an
output
signal
to
be
generated.
The
response
remains
until
the
input
signal
level
decays
through
the
reference
level.
The
reference
level
at
pin
10
is
furnished
from
the
R66, R67,
R69
circuit
through
Q6.
The
range
is
calibrated
by
R66
for
the
front
panel
level
control,
R67.
The
effective
range,
referred
to
the
input,
is
50
mV
through
5
V.
5.5.
CONSTANT
FRACTION
DISCRIMINATOR
Each
input
signal
is
applied
to
two
parallel
circuits.
One
circuit
delays
the
input
pulse
and
the
other
circuit
attenuates
the
signal.
The
delay
circuit
switch-selects
DL1,
DL2,
or
DL3
for
Ge(Li),
Scint,
or
Nal
respectively,
or
an
external
circuit
through
DL4
and
DL5
plus
whatever
amount
of
delay
is
connected
between
the
rear
panel
BNC
connectors.
The
attenuator
circuit
selects
R7
id
R14
for
Ge(Li),
R8
and
R15
for
Scint,
or
R9
and
R16
for
the
Nal
mode;
any
of
these
selections
provides
dc
fraction
of
32%.
The
value
of
the
dc
fraction
is
always
greater
than
the
effective
fraction,
f,
because
of
inherent
circuit
delays.
If
the
switch
selects
Ext,
the
attenuator
uses
RIO
through
R13
and
can
be
set
at
any
of
three
fractions
with
an
internal
jumper.
The
jumper
is
connected
for
a
fraction
of
30%
when
the
unit
is
shipped,
and
can
be
changed
to
either
20%
or
10%
if
desired.
A
differential
comparator,
IC1A,
accepts
the
two
signals
through
buffers
Q2
and
Q3,
and
determines
the
crossover
time
at
which
the
delayed
signal
amplitude
exceeds
the
prompt
attenuated
signal
amplitude.
Since
both
signals
are
the
result
of
the
same
input
pulse,
the
actual
peak
amplitude,
within
a
normal
range,
does
not
affect
the
relative
time
at
which
the
signal
is
recognized.
The
only
portion
of
the
input
pulse
the
is
used
for
Constant
Fraction
timing
derivation
is
the
rise
time.
Figure
5.1
shows
how
two
pulses
with
different
peak
amplitudes
will
generate
identical
timing
responses
in
101
A;
the
delayed
signal
is
furnished
to
pin
10
and
the
attenuated
signal
to
pin
9.
When
the
negative
amplitude
at
pin
10
exceeds
the
amplitude
at
pin
9,
IC1A
switches
states
and
does
not
switch
back
until
this
condition
is
reversed
at
the
end
of
the
input
pulse
decay.
The
result
is
that
the
C.
F.
Trigger
response
time
is
precisely
the
same
for
any
original
pulse
amplitude
within
the
normal
response
range
for
the
473.
The
pulse
that
is
formed
in
101A
is
shaped
in
101B
and
1010
and
furnished
to
gate
I03A,
and
the
circuit
is
stabilized
by
the
feedback
through
Q10
and
Q11
and
through
Q8
and
Q9;
R35
is
a
walk
adjust
control
that
sets
the
0.
F.
baseline
to
minimize
time
differences.
The
optimum
fraction
in
the
473
is
furnished
by
an
attenuator
that
divides
the
input
amplitude
by
the
proper
ratio.
The
appropriate
delay
is
selected
according
to
the
normal
rise
time
of
the
input
pulses,
and
this
varies
from
one
type
of
detector
to
another.
The
delay
for
Ge(Li)
uses
9'4"
of
50n
cable
for
a
delay
of
14
ns;
the
delay
for
Scint
uses
10-1/8"
of
cable
for
1.3
Pulse
A
Delaved
Attenuated
Delayed
Attenuated
Trigger
Time
Fig.
5.1.
Constant
Fraction
Trigger
Timing
for
Two
Different
Input
Pulse
Amplitudes.
ns;
the
delay
for
Nal
uses
15-1/4"
of
cable
for
1.9
ns.
In
the
external
circuit,
DL4
and
DL5
are
each
10"
of
cable,
so
the
total
delay
Is
3
ns
plus
whatever
amount
Is
added
between
the
rear
panel
connectors.
A
timing
pulse
at
pin
12
of
IC3A
Is
generated
In
response
to
a
negative-going
Input
variation
at
CN1,
whether
this
Is
a
real
signal
of
Interest
or
It
Is
simply
a
small-amplitude
pulse
—
generally
noise
—
that
Is
to
be
disregarded.
Gate
IC3A
will
have
been
aimed
I
>
pass
the
timing
signal
by
an
LLLE
response
for
a
signal
of
Interest.
5.6.
CONSTANT
FRACTION
OPERATION
Figure
5.2
Is
a
simplified
block
diagram
of
the
473
that
shows
selection
of
the
C.F.
mode
of
operation.
A
complete
block
r'
iqram,
473-0101-B1,
Is
Included
at
the
back
of
the
manual.
Constant
fraction
discrimination
provides
a
timing
pulse
for
each
Input
signal
variation,
whether
It
Is
converted
Into
an
output
signal
or
not.
The
function
described
In
Section
5.5
uses
the
CP
stage
In
Fig.
5.2
to
accomplish
this
signal
generation.
If
the
signal
Is
of
Interest,
It
will
have
triggered
the
LLLE
discriminator
prior
to
the
timing
pulse
so
gate
G1
(In
Fig.
5.2)
Is
armed
to
pass
the
timing
pulse.
After
a
delay
of
about
29
ns,
during
which
other
acceptance
criteria
are
checked,
the
timing
pulse
Is
furnished
to
gate
G2
(In
the
schematic,
this
Is
IC3B).
A
response
In
the
ULLE
circuit
must
have
triggered
FF
IC6B-IC6C
to
Indicate
that
the
Input
signal
amplitude
Is
sufficient
to
satisfy
the
amplitude
requirements,
and
the
timing
signal
passes
through
G2
and
G3
to
trigger
an
output
one-shot,
IC10A-IC10B,
and
generate
the
group
of
three
output
signals.
5.7.
SLO
R.T.
REJ
OPERATION
Operation
with
the
Slow
RIsetlme
Reject
circuit
Is
the
same
as
for
the
Constant
Fraction
operation
discussed
In
Section
5.6
except
that
the
timing
signal
Is
blocked
at
gate
G3
(Fig.
5.2)
If
the
signal
rise
time
Is
too
slow.
The
SRT
(slow
rise
time)
flip
flop,
IC7B-IC7C,
Is
reset
by
LLLE
and
Is
enabled,
through
IC8D,
to
be
set
by
FF
IC6B-IC6C.
The
SRT
flip-flop
must
have
been
set
by
the
time
the
timing
pulse
reaches
G3
(IC9A)
or
the
timing
pulse
wil
l
not
pass;
the
presumption
Is
then
that
the
rise
time
of
the
Input
pulse
was
too
slow
to
qualify
It
as
a
true
signal.
The
maximum
rise
time
from
LLLE
to
ULLE
Is
about
25
ns
to
permit
the
output
pulse
generation
to
occur.
CFandSRTR
7.5
ns
50
mV
SRTR
CF
and
LE
25
mV
CF
and
SRTR
Ge{Li)
14
ns
Scint
1.3
ns
Na)
1.9
ns
Ext
3
ns
+
external
delay
Nag
Out
-0
d/dt
OS
Pos
Out
Fig.
5.2.
Simplified
Block
Diagram
of
the
473
Constant
Fraction
Discriminator.
5.8.
LEADING
EDGE
OPERATION
Conventional
leading
edge
discrimination
can
be
selected
by
turning
the
mode
selector
switch
to
L.E.
This
enables
IC8C
and
completes
the
signal
path
from
ULLE
to
gate
G2
in
Fig.
5.2
through
the
delay,
DL9.
The
signal
path
starts
at
ULLE,
where
the
input
amplitude
triggers
a
response
when
it
exceeds
the
adjusted
Disc
level
setting.
It
is
delayed
while
FF
is
triggered
to
eriab'e
G2,
and
then
passes
through
G2,G3,
and
G4
to
generate
a
set
of
three
output
signals
and
the
deadtime
feedback
C
"'^•'Ol,
The
CF
response
is
not
effective
because
the
G1-to-G2
path
is
not
enabled.
SRT
is
set
to
enable
G3
each
time
a
FF
response
reaches
its
input
in
the
L.E.
mode,
and
it
is
reset
from
the
trailing
edge
of
LLLE.
The
FF
continues
to
toggle
between
reset
and
set
at
LLLE
and
ULLE
times,
but
it
enables
G2
each
time
there
is
a
ULLE
pulse
coming
through
the
delay
line.
5.9.
OUTPUT
PULSE
GENERATION
When
a
decision
has
been
made
to
generate
a
set
of
output
pulses,
the
signal
is
furnished
to
pin
5
of
IC9B(2).
The
signal
passes
through
IC9C(15)
to
trigger
both
NIM-standard
fast
negative
output
pulse
circuits
and
through
1090(14)
to
start
Schmitt
trigger
I010A
and
IC10B.
The
Schmitt
trigger
is
the
input
to
the
NIM-standard
slow
positive
output
generator.
One
fast
negative
output
generator
uses
012
and
013
as
a
current
switch.
The
current,
at
—16
mA,
normally
flows
through
012.
When
the
signal
is
furnished
from
1090(15),
012
is
turned
off
and
013
is
turned
on
to
furnish
the
current
through
CN2,
assuming
the
output
circuit
is
terminated
properly
in
50S2.
The
other
fast
negative
output
generator
uses
014
and
015
as
an
identical
current
switch
that
is
triggered
by
the
same
input
signal
from
1090(15)
to
switch
the
—16
mA
from
014
to
015
and
through
0N3
to
the
external
circuit.
The
Schmitt
output
at
101
OB(14)
is
furnished
to
the
positive
NIM
one-shot
circuit
that
includes
016,
017,
and
018.
When
the
signal
is
furnished
through
063
to
016,
the
output
at
CN4
rises
from
0
to
-1-5
V
for
a
period
of
about
500
ns.
The
Schmitt
output
at
IC10B(14)
is
also
coupled
back
to
pin
4
of
IC9B
to
hold
this
input
high
and
prevent
response
to
another
signal,
if
it
should
come
through
the
circuit,
before
a
controlled
dead
time
has
elapsed.
055
is
a
stretch
circuit
that
blocks
the
Schmitt
from
recovering
for
a
period
that
is
determined
by
the
selection
of
S1E.
When
switch
SI
selects
Ge(Li),
Scin,
or
Ext,
the
recovery
time
of
the
Schmitt
circuit
is
about
50
ns
but,
for
the
Nal
selection,
the
recovery
time
is
extended
to
about
1
us.
5.10.
EXTERNAL
SELECTIONS
If
the
detector
selector
switch
is
turned
to
Ext,
three
portions
of
the
internal
circuits
shown
in
Fig.
5.2
are
affected.
The
selection
of
is
dependent
on
the
addition
of
a
50ST
delay
cable
between
the
Ext
Delay
connectors
on
the
rear
panel,
and
the
cable
length
and
type
determines
the
amount
of
external
delay.
The
selection
of
the
dc
fraction
is
a
jumper
connection
at
one
of
three
alternate
locations
on
the
printed
circuit
board.
They
a>
'
located
h
tv
-en
the
front
corner
of
the
printed
circuit
board
nearest
SI
and
transistor
Q2,
and
are
numbered
"1",
"2",
and
"3"
Unless
otherwise
specified,
the
wire
lead
from
the
4th
position,
2nd
wafer,
of
the
detector
selector
switch
is
connected
to
point
"3"
for
a
30%
dc
fraction.
The
wire
lead
can
be
moved
to
point
"2"
for
20%
dc
fraction,
or
to
point
"1"
for
a
10%
dc
fraction
if
desired.
The
value
of
the
dc
fraction
is
always
larger
than
the
effective
fraction,
f,
because
of
the
inherent
circuit
delays.
an
alternate
fraction
is
selected,
readjust
the
constant
fraction
baseline
as
follows:
1.
Connect
a
50f2
terminator
on
the
Input
connector.
2.
Connect
a
digital
voltmeter
from
test
point
TP5
to
ground.
3.
Adjust
the
Walk
Adj
control
for
—1.25
V
at
TP5.
Since
the
basic
fraction
for
473
operation
in
Ge(Li),
Scint,
and
Nal
modes
is
32%
(dc),
the
Walk
Adj
setting
must
be
changed
again
if
the
detector
selector
switch
is
to
be
used
at
any
of
these
settings
after
the
Ext
adjustment
has
been
made.
The
remaining
portion
of
the
Fig.
5.2
circuit
that
is
affected
by
the
selection
of
Ext
is
the
duration
of
the
dead
time,
which
is
in
the
feedback
loop
from
the
Pos
Out
circuit
to
gate
G4.
Section
E
(the
last
wafer)
of
switch
81,
the
detector
selector,
completes
a
circuit
from
the
switch
wiper
to
ground
for
the
Ge(Li),
Scint,
and
Ext
settings,
and
the
resulting
controlled
dead
time
is
approximately
50
ns.
If
a
longer
dead
time
is
desired
for
Ext
operation,
the
grounded
connection
for
the
4th
switch
pciition
can
be
clipped
and
the
dead
time
will
then
be
approximately
1
iis,
the
same
as
for
Nal
operation.
5.11.
POWER
SUPPLIES
Two
power
supply
levels
are
generated
in
the
473
for
use
in
its
integrated
circuits.
One
is
at
—5.2
V
and
the
other
is
at
—2
V.
The
ac
input
power
line
is
connected
through
the
bin
and
power
supply
distribution
circuits
to
each
module
location.
It
is
accepted
from
this
circuit
into
the
primary
of
transformer
T1
on
the
473
chassis.
The
output
of
T1
is
full-wave
rectified
by
D5,
regulated
by
Q20
through
023,
and
filtered
by
C81.
T1,
D5,
and
C81
are
all
chassis-mounted
and
the
remaining
components
are
located
on
the
printed
circuit
board.
Using
the
—12
V
bin
power
dc
level
as
a
reference,
this
circuit
furnishes
the
—5.2
V
level
that
is
required
in
most
of
the
integrated
circuits.
Another
circuit
uses
the
—12
V
reference
and
reduces
the
level
from
—5.2
V
down
to
—2
V
for
other
operating
requirements.
025
is
the
series
pass
transistor
in
this
dropping
circuit
and
024
furnishes
the
reference
level
from
a
bleeder
in
the
—12
V
source.
Each
of
the
four
standard
dc
levels
(+12
V
and
±24
V)
are
accepted
from
the
bin
and
power
supply
through
four
separate
filter
networks
that
involve
LI
2
through
LI
5
and
C73
through
C80.
6.
APPLICATIONS
6.1.
TIMING
WITH
FAST
SCINTILLATORS
Figure
6.1
shows
a
typical
system
for
timing
with
fast
scintillation
detectors
such
as
Naton-136,
Pilot
B,
KL236,
NE-102,
NE-111, NE-213,
etc.
A
473
Constant
Fraction
Discriminator
is
used
in
each
of
the
two
channels
of
the
time
to
pulse
height
converter.
Figure
6.2
is
a
typical
timing
spectrum
that
was
taken
with
this
system.
A
plot
of
time
resolution
versus
dynamic
range
is
shown
in
Fig.
6.3
for
a
system
using
an
RCA
8850
photomultiplier
tube.
A
similar
plo'
for
the
RCA
8575
PMT
is
shown
in
Fig.
6.4.
The
output
pulse
from
the
RCA
8575
is
slightly
slower
than
that
from
the
h.
A
8850.
Because
of
this
risetime
difference,
the
best
timing
resolution
is
obtained
with
the
473
set
for
Scint
when
using
the
RCA
8850
and
set
for
Nal
when
using
the
RCA
8575.
The
input
to
the
473
should
have
approximately
5-V
pulses
for
the
Compton
edge
of
the
511-keV
gamma
from
^''Co
so
that
the
dynam'-:
i
nnge
can
be
100:1.
The
lower
level
discriminator
should
be
set
at
~50
mV.
For
some
tubes,
the
50i2
back
terminatioi
tI
to
the
tube
base
must
be
removed
to
accomplish
the
maximum
dynamic
range.
6.2.
TIMING
WITH
Nal(TI)
SCINTILLATORS
This
type
of
measurement
is
similar
to
timing
with
fast
scintillators
except
for
one
additional
problem
that
must
be
considered.
The
photoelec'ron
statistics
are
so
poor
for
low-energy
gamma-ray
work
that
individual
photoelectron
events
near
the
trailing
edge
of
the
Nal(TI)
pulses
will
trigger
the
473.
Thus
a
single
scintillation
event
can
produce
two
or
more
discriminator
output
pulses.
In
the
473
this
problem
is
overcome
by
using
the
Nal
mode
in
which
an
internal
dead
time
of
~1
IIS
is
generated.
The
473
can
then
be
operated
in
the
Nal
mode
and
be
used
successfully
on
even
longer
decay
scintillators,
but
the
internal
dead
time
may
have
to
be
increased
to
prevent
multiple
triggering.
Figure
6.5
is
a
typical
timing
spectrum
that
was
taken
with
a
Nal(TI)
detector,
based
on
triggers
from
a
KL236
detector.
Figure
6.6
is
a
plot
of
time
resolution
versus
dynamic
range
for
the
Nal(TI)
detector,
using
an
RCA
8575
PMT.
6.3.
TIMING
WITH
LARGE
Ge(Li)
DETECTORS
Figure
6.7
is
a
block
diagram
of
another
gamma-gamma
coincidence
system.
In
this
system
the
start
channel
uses
a
fast
scintillator
and
the
stop
channel
employs
a
large
coaxial
Ge(Li)
detector.
A
typical
timing
spectrum
for
a
narrow
dynamic
10
ORTEC
456
HVPOWER
SUPPLY
ORTEC
460
SPECTROS-
COPY
AMri'FIER
-2200V
Dynode
Anode
ORTEC
265
RCA
8850
PM
PM
BASE
V/,
ORTEC
473
CONST
FRACTION
DISCRIMI
NATOR
ORTEC
420A
SCA
Na
Source
*
Va
RCA
ORTEC
265
8850
PM PM
BASE
Dynode
Anode
1-
X
1-in.
NATON-136
Start
ORTEC
457
TIME
TO
PULSE
HEIGHT
CONVERTER
Stop
ORTEC
414A
COINCIDENCE
ORTEC
425
NANOSECOND
DELAY
ORTEC
420A
SCA
ORTEC
460
SPECTROS-
COPY
AMPLIFIER
ORTEC
456
HV
POWER
SUPPLY
-2200V
ORTEC
473
CONST
fraction
DISCRIMI
NATOR
ORTEC
113
SCINTILLA
TION
PREAMP
ORTEC
6220
MULTICHANNEL
ANALYZER
Fig.
6.1.
A
System
for
Gamma-Gamma
Lifetime
Measurement.
DDQ305BI
60Co
RCA
8850
Photomultiplier
Tube
1.1:1
Dynamic
Range
FWHM
193
ps
FWTM
373
ps
6,85
ps
per
channel
Fig.
6.2.
Timing
Over
a
Narrow
Dynamic
Range
with
the
System
of
Fig.
6.1.
1200
11
1000
800
8850
Tubes
ORTEC
9201
Bases
1"
X
1"
KL236
Scintillators
Co60
473
CF
Disc.
(CP
and
Scint
Modes)
H
600
400
200
8
nf>
1
;
1
2:1
5:1
10
:
1
Dynamic
Range
20
:1
50
:
1
100
:
1
Fig.
6.3.
Plot
of
Time
Resolution
vs
Dynamic
Range
Using
RCA
8850
Photomultiplier
Tube.
1200
1000
800
400
200
8575
Tubes
ORTEC
265
Bases
1"X
1"
KL236
Scintillators
Co60
473
CF
Disc.
(CF
and
Nal
Modes)
8136
Dynamic
Range
100;
1
Fig.
6.4.
Plot
of
Time
Resolution
vs
Dynamic
Range
Using
RCA
8575
Photomultiplier
Tube.
12
DOmSBSI
60Co
Start:
KL236
(1x1),
RCA
8575
Photomultiplier
Tube
FWHM
892
ps
FWTM
1.82
ns
9.7
ps
per
channel
Stop:
Nal
(1x1),
RCA
8575
Photomultiplier
Tube
50:1
Dynamic
Range
Fig.
6.5.
Typical
Timing
Spectrum
Over
a
Wide
Dynamic
Range
(50:1)
with
Nal(TI).
3.0
2.5
2.0
15
1.0
0
5
0
1
;
1
Resolution
vs.
Oynamic
Range
for
Co^^
Nal
-
Plastic
Start:
KL236
(1"
X
1")
Scint
8575
Tube
(-
2200
V)
473
(CF
and
Nal
Modes)
Stop;
1"
X
1"
Nal
(Bicron)
8575
Tube
(-2200
V)
473
(CF
and
Nal
Modes)
(Direct
from
Anode)
FWTM
(Extrapolated)
FWHM
(Extrapolated)
2
:
1
5:
1
10
:
1
20
:
1
Oynamic
Range
(Both
Side
Channels)
50
:
1
100:1
Fig.
6.6.
Plot
of
Time
Resolution
vs
Dynamic
Range
Using
Nal(TI)
and
RCA
8575
PMT.
range
(1.1:1)
is
shown
In
Fig.
6.8
for
both
the
CF
and
SRT
modes
of
operation.
A
similar
spectrum
for
a
wide
dynamic
range
(10:1)
is
shown
in
Fig.
6.9.
Note
that
the
SRT
mode
is
more
effective
on
wide
dynamic
ranges.
The
SRT
mode
can
provide
dramatic
improvement
In
timing
resolution
below
FW(1/10)M
and
makes
reliable
timing
data
possible
at
even
the
FW(1/100)M
level.
Typical
timing
resolution
data
for
various
sizes
of
Ge(Li)
coaxial
detectors
are
listed
in
Table
6.1.
The
SRT
mode
provides
improved
timing
resolution
by
rejecting
those
input
signals
with
an
excessively
slow
risetime.
Such
signals
are
generally
associated
with
detector
events
in
a
weak
field
region.
Since
these
events
can
represent
valid
data,
their
rejection
corresponds
to
a
reduction
In
detector
efficiency.
Since
the
473
mode
is
front
panel
selectable,
the
experimenter
can
select
either
SRT
for
best
timing
resolution
or
CF
for
best
timing
without
loss
of
efficiency.
13
ORTEC
4b6
HV
POWER
SUPPLY
1
by
1
in.
KL
236
Anode
ORTEC
RCA
265
8575
PM
BASE
PM
TUBE
ORTEC
473
CONST
FRACTION
DISCRIMI
NATOR
Ge(Li)
45CC
Na
Source
ORTEC
416A
GATE
AND
DELAY
GENERATOR
Start
ORTEC
457
TIME
TO
PULSE
HEIGHT
CONVERTER
Stop
ORTEC
455
CONST
FRACTION
TIMING
SCA
ORTEC
120A
PREAMP
ORTEC
452
SPECTROS-
COPY
AMPLIFIER
ORTEC
425
NANOSECOND
DELAY
ORTEC
473
CONST
FRACTION
DISCRIMI
NATOR
ORTEC
459
DETECTOR
BIAS
SUPPLY
won'
ORTEC
454
TIMING
FILTER
AMPLIFIER
Gate
ORTEC
6220
MULTI
CHANNEL
ANALYZER
Fig.
6.7.
Gamma-Gamma
Coincidence
System
Using
Plastic
Scintillator
and
a
Large
Ge{Li)
Coaxial
Detector.
1
Start:
KL236
(1x1),
RCA
8575
Photomultiplier
Tube
Stop:
Gel
Li)
Coax,
12.5%,
62.3
cc
1.1:1
Dynamic
Range
FWHM
FWTM
FW
1/100
M
CF
5.0
ns
10.0
ns
17.2
ns
SRT
5.0
ns
9.5
ns
17.6
ns
Fig.
6.8.
Timing
Spectrum
for
a
Narrow
Dynamic
Range
(1.1:1)
for
the
System
of
Fig.
6.7.
DDDRHHE5
22
Na
Start:
KL236,
RCA
8575
Ptiotomultipiier
Tube
Stop:
Ge(Li),
12.5%,
62.3
cc
10:1
Dynamic
Range
FWHM
FWTM
FW
1/100
M
CF
SRT
4.5
ns
4.4
ns
13.2
ns
9.4
ns
17.3
ns
Fig.
6.9.
Timing
Spectrum
for
a
Wide
Dynamic
Range
(10:1)
for
the
System
of
Fig.
6.7.
14
A
plot
of
the
percent
loss
of
511-keV
peak
counts
from
for
the
SRT
mode,
compared
to
the
CF
mode,
is
shown
In
Fig.
6.10
as
a
function
of
the
473
threshold
and
the
detector
size.
6.4.
TIMING
WITH
OTHER
DETECTORS
The
173
can
also
be
used
to
provide
timing
information
from
other
detectors
such
as
ORTEC
surface
barrier
detectors
and
I
v-cneigy
photon
detectors.
In
general,
when
the
454
Timing
Filter
Amplifier
is
used,
the
Ge(Li)
or
Ext
mode
on
the
473
will
pr:
'de
ti
ie
best
timing
resolution.
The
Scint
mode
or
the
Nal
mode
will
give
the
best
timing
resolution
for
signals
with
risetimes
in
the
low
nanosecond
range.
ORTEC
conducts
a
continuing
program
aimed
at
improving
timing
resolution.
Please
contact
an
ORTEC
representative
for
information
concerning
your
special
requirements.
Table
6.1.
Timing
Resolution
for
Various
Sizes
of
Ge(Li)
Coaxial
Detectors
Using
^^Na
and
the
System
of
Fig.
6.7.
Detector
Dynamic
Range
CF
Mode
SRT
Mode
FWHM
(ns)
FW(1/10IM
(ns)
FWHM
(ns)
FW(1/10)M
(ns)
FW(1/100)M
(ns)
8.6%
52.6
cc
1,1
:1
4.4
10.1
4.3
10.1
21.6
10:1
4.2
13.6
4.2
10.5
23.4
20:1
4.7
13.5
4.7
12.8
30.4
12.5%
1.1:1
5.0
10.0
5.0
9.5
17.6
10:1
4.5
13.2
4.4
9.4
17.8
62.3
cc
20:1
5.1
14.3
5.0
12.0
24.8
19.6%
1.1:1
7.9
16.4
8.1
16.0
27.3
10:1
8.4
24.0
7.9
17.0
30.0
103
cc
20:1
8.4
26.0
8.4
23.0
40.0
100
DO
-
40
20
19.6%,
103
cc
12.6%,
62.3
cc
8.6%,
52.6
cc
200
400
473
Threshold
Setting
(keV)
8136
600
Fig.
6.10.
The
Effect
of
473
Threshold
Setting
on
the
Apparent
Efficiency
of
Different
Ge(Li)
Detectors.
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