EG&G ORTEC 260 User manual

too MIDLAND ROAD. OAK RIDGE TENNESSEE, 37830
AREA CODE [phone] TWX 810-572-1078
INSTRUCTION
MANUAL
260
TIME
PICKOFF
UNIT
AN COMPANY

INSTRUCTION MANUAL
260
TIME PICKOFF UNIT
S^al No.
Purchaser
Date Issued
ORTEC
INCORPORATED
P. 0. BOX 0
OAK RIDGE, TENNESSEE 37830
Telephone [phone]
TWX 810-572-1078
@ ORTEC Incorporated 1966
Printed In U«S«Aa

TABLE OF CONTENTS
Page
WARRANTY
PHOTOGRAPH
1. DESCRIPTION 1-1
2. SPECIFICATIONS 2-1
3. INSTALLATION INSTRUCTIONS 3-1
4. OPERATING INSTRUCTIONS 4-1
4.1 Initial Checkout and Familiarization 4- 1
4.2 Application Notes 4- 1
5. CIRCUIT DESCRIPTION 5-1
6. MAINTENANCE INSTRUCTIONS 6-1
6.1 Testing Performance 6- 1
6.2 Calibration Adjustments 6- 1
6.3 Suggestions for Troubleshooting 6- 1
SCHEMATIC
ORTEC 260 Time Pickoff 260-Sl

LIST OF FIGURES AND ILLUSTRATIONS
Page
Figure 2-1. Plof of ORTEC 260 Threshold SensiH vify vs Det-ector Capacity 2-2
Figure 2-2. Typical Block Diagram for Timing With Semiconductor Detectors 2-3
Figure 4-1. Pileup Reduction With 260 and 404 4 -2
Figure 4-2. A Method of Pulse Shape Discrimination 4-3
Figure 4-3. Charged-Porticle Identification by Time-of-Flight 4-4
Figure 4-4. Beam Pulse Time Pickoff System (T = O) for Pulsed Accelerators 4-5

A NEW STANDARD TWO-YEAR WARRANTY FOR ORTEC ELECTRONIC INSTRUMENTS
ORTEC warrants its nuclear instrument products to be free from defects in workmanship and materials, other
than vacuum tubes and semiconductors, for a period of twenty-four months from date of shipment, provided
that the equipment has been used in a proper manner and not subjected to abuse. Repairs or replacement, at
ORTEC option, will be made without charge at the ORTEC factory. Shipping expense will be to the account
of the customer except in cases of defects discovered upon initial operation. Warranties of vacuum tubes and
semiconductors, as made by their manufacturers, will be extended to our customers only to the extent of the
manufacturers' liability to ORTEC. Specially selected vacuum tubes or semiconductors cannot be warranted.
ORTEC reserves the right to modify the design of its products without incurring responsibility for modification
of previously manufactured units. Since installation conditions are beyond our control, ORTEC does not
assume any risks or liabilities associated with methods of installation other than specified in the instructions,
or installation results.
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
ORTEC instruments not in warranty may be returned to the factory for repairs or checkout at modest expense
to the customer. Standard procedure requires that returned instruments pass the same quality control tests as
those used for new production instruments. Please contact the factory for instructions before shipping
equipment.
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 we may assist in damage claims and in providing replacement equipment if necessary.

'I '
4".'
TIME PICKOFF UNIT
[-- >
I—DETfcCTOR PRbAMP
MODEL 260
I I I II I

1 -1
}
INSTRUCTION MANUAL
ORTEC 260 TIME PICKOFF UNIT
1. DESCRIPTION
The ORTEC 260 Time Pickoff Unit- is designed to obtain a timing signal directly from a
semiconductor detector without significantly altering the energy resolution qualities of
the detector-linear-amplifier system. It consists of a pulse transformer, a wide-band
transistor amplifier, a tunnel diode discriminator, and a line driver buffer. The unit is
connected in series between a detector and a charge-sensitive preamplifier; i.e., the
pulse current from the detector flows through the primary of the pulse transformer en
route to the preamplifier.
The 260 derives its power and discriminator control bias from a remote location via a
shielded multiconductor cable. The necessary power and control bias are provided by a
403A Time Pickoff Control . All signal input and output connections are of a BNC type.
The 260 may be used in conjunction with photomultipliers to obtain timing signals frpm
either the anode or dynode simply by reversing the order of connections to the transformer
primary. This unit provides the necessary functions of amplification and low amplitude
triggering required for signal leading edge time measurements with low gain (10-stage)
photomultipliers. (Refer to section 4.2(2).)
The 260 may also be used in conjunction with electrostatic-inductive pickup to derive
a timing pulse corresponding to T = 0 for pulsed accelerators. (Refer to section 4.2 (4).)
The physical dimensions of the unit are 6 x 4 x 1.7 (4.45 x 10.2 x 15.30cm).
I (
*

2 - 1
I
2. SPECIFICATIONS
2.1 Input Polarily-
2.2 Input Signal Amplitude-
2.3 Sensitivity
2.4 Time Pickoff Effect on
Energy Resolution
■Either positive or negative by reversing the order of
connections to the input transformer primary. Connect
negative input to BNC (CN-1) labeled DET., and posi
tive input to BNC (CN-2) labeled PREAMP.
-Dependent on input impedance of ORTEC 260 amplifier,
which may be changed by simple plug-in of a resistor.
Signal input to the amplifier should not exceed 2V| i.e.,
I2 Rj ^2V, 1^ = 1 .5 I2; therefore, I] (max) ^.5/Rj.
I] and I2 refer to the primary and secondary pulse
transformer currents.
-See figure 1.
-Refer to table 1.
2.5 Energy Variation Effect on
Time Resolution
2.6 Threshold Range-
2.7 Output
2.8 Power Requirements-
2.9 Signal Connections
2.10 Transformer Insulation—
-Refer to table 2.
-s 15.1
-Negative 500 mV (voltage drive, Zq~5 ohms), Tj. ^
1.2 nsec. Pulse width ~10 nsec (variable)
-+ 12V at 40 mA or - 12V at 40 mA, plus discriminator
bios current. All power is provided by a Time Pickoff
Control Unit (ORTEC 403A) via a multiconductor
shielded cable.
-BNC type
-1 kV
Table 1. Time Pickoff Effect on Energy Resolution (RC Mode)
(Typical Measurement)
Detector
Pulser Width
Pulser Width
Capacity Without Time Pickoff With Time Pickoff
(pF)
(keV) (keV)
0
5.9
7.3
20 6.05
7.8
50
7.35
8.9
100
8.85
11.0
200 12.1
14.7
Note: The detector capacity indicated is in addition to approximately 25 pF cable capacity.

2-2
I
Table 2. Signal Energy Effect on Pickoff Output Time
(Typical Measurement)
Signal Amplitude
Time Shift
Jitter (FWHM)
(MeV, Si Detector)
(nsec)
(psec)
0.25 (Threshold)
0
150
0.5
1.2 86
1.25
1.9
73
2.5 2.5
68
5.0
2.7 62
Note: The pulse generator used is a mercury-switch, delay-line type (T^ <0.3 nsec).
600
LU
-J
3
O-
s
CM
U
UJ
H-
o
>
<D
>-
o
CSC
LU
z
LU
Q
_J
o
X
OO
LU
CC
X
400
200
c
)
.
ORTEC
*0017 0
100
200
500
SIMULATED DETECTOR CAPACITY
Figure 2-1
Plot of ORTEC 260 Threshold Sensitivity vs Detector Capacity

2-3
2-0= son
I 1
CHARGE
TERMINATOR
CHARGE-SENSITIVE
PREAMPLIFIER
LINEAR
AMPLIFIER
DETECTOR
I
ANALYZER,
ETC,
PARTICLE
BEAM
PREAMP DET.
POWER a CONTROL BIAS
ORTEC
200172
OUTPUT
>—a
PRECISION
PULSE GEN
FA^OUJ_^F^^R
7 outputs}
INPUT A
403A
TIMING SIGNALS
Figure 2-2
Typical Block Diagram for Timing Wifh
Semiconductor Detectors

3 - 1
3. INSTALLATION INSTRUCTIONS
3.1 CAUTION: Before applying a pulser or connecHng to a photomultiplier, refer to
section 2.2.
3.2 Connect the 260 between the detector and charge-sensitive preamplifier input
as indicated by the arrows at the two input BNC connectors. The inputs are
indicated for electron signal collection. (See block diagram, figure 2.)
3.3 Connect a precision pulse generator via a charge terminator in parallel with the de
tector as shown in the block diagram (figure 2).
3.4 Connect the power coble between 260 and 403A Time Pickoff Control Unit.
3.5 Connect 50-ohm coaxial cable from 260 output to input of fanout buffer of Time
Pickoff Control, to scope input, or to other time monitoring point. The coaxial
cable should be terminated at the receiving end.
3.6 Control of the 260 Time Pickoff is now handled completely by the 403A Time Pickoff
Control Unit.
3.7 Set the Control Unit discriminator level (R9) at 1000.
3.8 Turn on Control Unit power.
3.9 The discriminator level may now be adjusted to the energy level desired. The dis
criminator should trigger on amplifier noise when the level is set very near zero.

4- 1
4. OPERATING INSTRUCTIONS
4.1 Initial Checkout and Familiarization
(1) Connect the unit as described in the installation instructions (section 3). (The
detector need not be connected for checkout.) In some applications, it may be
desirable to replace the charge-sensitive preamplifier by a fixed-capacity,
delay-line terminating impedance, or short-circuit terminator. Use a pulser such
as the ORTEC 204 or 419 Precision Pulse Generator or any mercury switch delay-
line pulser with a rise time of less than 2 nanoseconds. If a delay-line pulser is
used, set the pulse width to 2-10 nanoseconds, and use a terminating impedance in
place of the charge-sensitive preamplifier.
(2) Adjust the pulser amplitude to the equivalent of ~10 mV into 100 ohms before
connecting to the 260. (Refer to section 2.2.)
(3) Connect pulser, turn on power to Time Pickoff Control, and adjust the discriminator
level to obtain an output pulse. If a precision pulse generator is used, it may be
calibrated in energy and then the pulser becomes an energy reference to both the
energy analysis system and the discriminator of the 260.
4.2 Application Notes
Refer to the next four pages for four different applications using this equipment.

4-2
APPLICATION NOTES
(1) Inspecfion and Pileup Reduction
Figure 3 is a block diogrom of the experimental setup for removing from a spectrum
those pulses which have the wrong amplitude because of multiple pulses arriving
in a detector within a period of time corresponding to the linear amplifier resolving
time. This is especial ly important when pulse height analysis is performed on a
complicated spectrum containing many pulse amplitudes and widely varying relative
rates. Inspection by this method reduces the relative pileup time from 3.3 microseconds
for a double-del ay-line clipped amplifier with 1-microsecond clipping lines to
approximately 250 nanoseconds. This is a reduction factor of approximately 12 in the
number of counts in any random sum or difference peak.
DETECTOR
I'
-OAOltr
CHARGE
SENSITIVE
LINEAR
PREAMP
427
LINEAR
DELAY
INPUT
MULTICHANNEL
ANALYZER
POWER 4 CONTROL BIAS
Zo= I 403A
50 ohm
-Lfl ) i—jFAN OUT
BUFFER
FAST AMP
260
TIME PICKOFF
INSPECT
^NGLES J
TIMING CIRCUIT
(TPHC, COINC., ETC.)
SINGLES
SCALER
LINEAR SIGNAl
LINEAR (DELAYED)
TIME PICKOFF OUTPUT
INHWIT PULSE
UNEAR SIGNAl
LINEAR (OaAYED)
TIME PICKOFF OUTPUT
INHIBIT PULSE
r/
1
i/
(-
\\
V
• -x
1
1..
..J
1
Figure 4-1
Pileup Reduction With 260 and 404A

4-3
APPLICATION NOTES
(2) Pulse Shape Discrimination
A method of scintillation counter pulse shape discrimination which has many advantages
is shown in block diagram form in figure 4. Some of these advantages are:
4
(a) high count rate capability (s2 x 10 cps),
(b) wide dynamic range ma^v^E^ min >20:1),
(c) low neutron threshold (E^^ <300 keV),
(d) simple to set up and monitor,
(e) may be performed with a 10-stage photomultiplier. When the 260 is used for this
purpose, i.e., with a photomultiplier, care should be exercised to prevent excessive
input signal. (Refer to section 2.2.)
This method of pulse shape discrimination can also be used with semiconductor detectors.
When it is desired to measure particles of the same energy but differing range (e.g., alphas
in the presence of protons), the depletion depth can be adjusted to stop the alphas but not
the protons. Proton pulses will then consist of a fast portion, corresponding to collection
of signal deposited in the depletion zone, and a slow portion, corresponding to signal
collected by diffusion from the field-free undepleted regions. Elimination of the undesired
proton pulses can thus be performed by pulse shape discrimination.
£N£l9Cf SIGNAL
LIN£AR SIGNAL
VIAPIN
AMP.
AMP.
4 20
TIMING
S.C.A
TIMING SIGNAL
4 OS A
TIME
P/CKOPr
CONTROL
26-4
OP see
POWER* eiAS
DELAY 4
PM.T.
ST/lBENE op NC-^/S
XlHTIUMi
TS/GNAL
ANODC SIGNAL
PA ST
DISC.
TIMING SIGNAL
CO PO OUTPUT
(r- PAY)
ALTERNATE METNOO
T> SIGNAL
GATE OP ROUTE
4S7
4Z0
T.RH.C.
3.C.A.
OP "71 SIGNAL
711
PULSE NEIGNT
CO PO OUTPUT
(NCUTPON)
TIME DIAGRAM
Figure 4-2
A Method of Pulse Shape Discrimination

4- 4
APPLICATION NOTES
(3) Charged-Particle Identification by Time-of-Flight
The advent of the 260 opens up a new realm of exploration in charged-particle
spectroscopy by allowing simultaneous high-resolution energy analysis and sub-
nanosecond time resolution measurements of charged particles, A block diagram of
electronics needed to perform such measurements with a pulsed accelerator is shown
in figure 5.
MODEL 622 PULSED
CHARGE
DETECTOR
ADC 2
ADC I
50A
260
260
Zo ' SO A
Ho = 50 A
STOP
START
Ho • 50 A
DELAY
Ho • 50 A
425
TIME TO
HEIGHT
CONVERTER
MULTIPARAMETEF
ANALYZER
403A
403A
Figure 4-3
Charged-Particle Identification by Time-of-Flight

4-5
APPLICATION NOTES
(4) Beam Pulse Time Pickoff for Pulsed Accelerators
There are many applications where timing experiments are performed with high-energy
particles. It is sometimes difficult to obtain a timing signal, indicating the time the
beam burst strikes the target (T = O), of sufficient accuracy, and independent of
machine parameters. A method for obtaining a T = O pulse which meets the criteria
for accuracy and stability, and is also simple to install, is shown in the block diagram
in figure 6. The beam pulse pickup is an electrostatic-inductive pickup which is
installed in the beam tube. (Further information will be supplied upon request.) For
this application, an estimate of the required minimum beam pulse peak current (Ip)
may be based upon V(min), the maximum sensitivity of the 260, which is approximately
200pV into 50 ohms. Assuming that the pickup capacitance (Cp) is ~5 pF, we require,
for the minimum beam charge to provide the driving signal,
Q (min) = C V (min) = I A t
P P
= (5 X 10"^^ F) (2 X 10""^ V) = 1 X 10"^^ coul.
For a pulse width of 5 nsec, this gives:
I =Q(raln) = 2x10"^ A.
p Z1—
PULSED
BEAM
BEAM
PULSE
PICKUP
SIGNAL
G=)
Zo= son
A
TARGET
POWER & CONTROL
TIMING
SIGNALS
Figure 4-4
Beam Pulse Time Pickoff System (T = O) for Pulsed Accelerators

5- 1
5. CIRCUIT DESCRIPTION
The circuit consists of a current transformer, two amplifier stages, a remotely controlled
tunnel diode discriminator, and an emitter follower for a line driver and buffer.
The current pulse from a detector flows through the transformer primary, induces in the sec
ondary a corresponding secondary current and therefore a voltage across Rj. Rj may take
on any value from zero impedance to open circuit, where the input impedance will be
determined total ly by the input impedance of Q1 . Since Q1 senses the voltage generated
across the input impedance, the sensitivity will vary directly with Rj. As mentioned at
other places in the manual, plug-in jacks are provided so that Ry may be changed.
The amplifier must have a negative input voltage at the base of Ql, but since the trans
former primary has both ends available, a signal of either polarity may be processed by
interchanging the role of CN-1 and CN-2. (Refer to section 2.1.)
The amplifier consists of two identical stages, each consisting of a fed-back cascode driven
by an emitter follower.^ The first stage is composed of Ql, Q2, and Q3, where the degenera
tive feedback is obtained by the 10-ohm emitter resistor, R5. The bypassing capacitor,
C4, serves to increase the high-frequency response without affecting the midfrequency gain.
The output of the second amplifier stage, consisting of Q5 and Q6, feeds the tunnel diode
discriminator, Dl. The bias current for D1 is derived from a Time Pickoff Control Unit.
The discriminator output pulse width may be changed, as desired, by changing L3, since the
pulse width is determined by the L/R time constant composed of L3 and R15. Plug-in jacks
are provided for easy interchange. Increase L3 to obtain a wider pulse.
Q7 is an emitter follower used to drive the coaxial line and to prevent any delay-line
reflections from retriggering the discriminator.
' C. W. Williams and J. H. Neiler, IRE Trans. Nucl. Sci. NS-9 (1962) p. 1.

6 - 1
6. MAINTENANCE INSTRUCTIONS
6.1 Testing Performance
Many methods of testing the unit may be used for convenience, although only one
method will be described here. The steps are given for clarity.
(1) Connect the 260 to the Time PIckoff Control Unit as described In sections
3.4 and 3.7.
(2) Use a 50-ohm mercury switch delay-line pulse generator, with the pulse width
set In the range of 2-10 nanoseconds. Trigger an oscilloscope externally from the
pulse generator trigger output. Attenuate the pulser output signal to obtain a
negative 5 mV signal when Rj s IK ohms.
(3) Terminate CN-2 In 50 ohms.
(4) Connect the pulser signal to CN-1.
(5) Connect the 260 output signal to the Input of the oscilloscope (terminate delay
line).
(6) Turn on the Time PIckoff Control Unit; there should be an output from the 260
at this time.
(7) Adjust the pulser ourput to obtain an Input signal of 0.3 mV; the 260 discriminator
should trigger on this signal at a discriminator level setting above noise.
(8) Increase the signal Input as desired; the threshold should cover a range of 15:1
In signal amplitude.
6.2 Calibration Adjustments
The only Internal adjustments are Interchange of Rj to vary Input Impedance, and
Interchange of L3 to vary output pulse width.
6.3 Suggestions for Troubleshooting
If no output pulse Is obtained, check the cable connections between the Time PIckoff
Control Unit and the Time PIckoff. Adjust the discriminator level control to near zero
and check for output pulses. (Discriminator should free-run.) If the discriminator free-
runs, check the Input connections for contact and polarity. If the trouble Is still not
located, perform a voltage check and compare the results with the values listed In table
3. Transistor failures may not be detected In a voltage check; therefore, transistors
Q1 through Q6 should be tested separately.
If the discriminator falls to free-run, the trouble must be discriminator associated, so
check the voltages and compare them with those In table 3. If the trouble Is still not
located, check the tunnel diode, D1.

6-2
E - Emitter
Table 3. Typical Voltage Tests
B = Base
ORTEC 260
C = Collector
Location
Check Point
Average Voltages
P-3
Pin E
+ 11 .9
P-3
Pin B
- 11.9
B-
bus
- 11.6
B +
bus
+ 11 .5
Q1 E
- 0.7
Q4
E - 0.88
Q3
B
+ 4.7
Q6
B
+ 4.9
Q2
E
- 1 .5
Q5
E
- 1.6
Q3
C
+ 8.7
Q6
C
+ 8.6
Q7
C - 10.6
Q7
E
+ 0.6
Note: All voltages are read from chassis ground with vtvm.

APPLICATION NOTE
Gamma-Gamma Coincidence with Ge(Li-drift) Detectors
The advent of large-volume Ge(Li-drift) detectors
Makes coincidence experiments involving these very
high-resolution devices feasible. The desirabi l ity of
such experiments has long been unquestioned. Cross
over timing may be used for these experiments; how
ever, optimization of energy resolution necessitates
long col lection times and therefore large ampl ifier
shaping time constants which increase the broadening
of the time distribution. The second disadvantage of
of the crossover pickoff technique is that the timing
signal is derived from the 50% point of the col lection
function. This means that if the collection function
varies, as it does with these devices, there is a time
shift (walk) introduced. ''^
The recommended procedure is to uti l ize a leading
edge trigger device such as the Model 260 Time Pick-
off which may be set to trigger at a smal l fraction of
the total energy. Since Ge(Li-drift) detectors charac
teristical ly have long col lection time (>30 nsec) and
energy resolution is of the utmost importance, the
Time Pickoff should be connected between the pre
ampl ifier and the shaping ampl ifier. By this method,
a low triggering threshold may be achieved with no
energy resolution degradation and the time resolution
is affected only slightly by the preampl ifier rise time.
In this appl ication the plug-in inductor (L3) in the
Model 260 Time Pick'off should be changed to~4.7
fxH to prevent multiple trigger on the wide input
signal.
Ge(Li'DPirT)
DLTCCTOR-YZm
SOURCE- *
N».l(TI)SaN'^^
rULATOR
P/A QASE^,
POWER
/IS>
PREAM/
r^r —
-PHOTO MULT
TUBE
~\ Ee5.2e7
ENERGY
rZ/HE
427
LINEAR
DELAY
A POLAR
SHAPihiG:?——►
APR,
420
TIMING
S.CA.
4/9
260
Pulse
T/ME
GEN P/CKOFF
4/7
PAST
O/SC.
42 6
RELAY
403A
T/ME
P/CNOFF
CONTROL
STOP
437
T.PPC.
4ZO
SC.A.
409 , ^
SLOW \Z/NEAR
CO/NC. GATE
r]
A
PfiEAMP
POWER
410
SHAPIM
AMP.
420
TIMING
S.C.A.
NALYZE T/ME
OR ENERGY
R. L. Graham, et al., IEEE Trans. Nucl. Sci.
NS-I3(I): 12 (Feb. 1966)
G. T. Ewan, R. L. Graham and i. K. MacKenzie,
IEEE Trans. Nucl. Sci. NS-I3(3):297 (June 1966)