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0.2

0.4

0.6

0.8

1.0

Gamma-Ray Energy (MeV)

Fig. 7.5. Time Resolution of a Ge(Li) Detector as a

Function of Energy.

For a detailed discussion of the Amplitude-Rise-Time-

Compensation (ARC) technique used in the 463 and

of other areas relating to timing with Ge(Li) detectors,

refer to the Bibliography at the end of this section.

FWHM =3.8 nsec -

FWTM =11.5 nsec-

1—q

Source: ""CO

Energy Window: 100 keV-1 MeV

Start Channel: Naton -136 with

RCA-8575 PM Tube

ORTEC 463 Discriminator

Calibration: 0.2 nsec/Channel

'•W.t

Channel Number

Fig. 7.6. Typical Timing Spectrum with Wide Dynamic

Range Using the System of Fig. 7.4.

7.3. TIMING WITH SURFACE BARRIER DETECTORS

The system shown in Fig. 7.7 can be used to check the

timing resolution of a surface barrier detector. An ORTEC

130 Surface Barrier Detector and Preamplifier is being

tested, with its response time compared to a l ight pulse

that is generated in an RCA Ga-As laser. The duration

of the light pulse can be 10 nsec or less, and its intensity

can be controlled by adjusting the voltage applied to

the laser. The detected light per laser burst can be

adjusted to correspond to an alpha energy if a weak

alpha source is placed in the vicinity of the detector.

With the single channel analyzer calibrated for an equiva

lent charged particle energy, a simulated timing test can

be performed for any energy.

For the ORTEC 130 Surface Barrier Detector system, as

for most surface barrier detectors, the rise time of the

TEKTRONIX

109

PULSER

RCA GA-AS

INJECTION LASER

ORTEC

457

TIMETO

PULSE HEIGHT

CONVERTER

MULTI

CHANNEL

ANALYZER

SURFACE BARRIER DETECTOR

ORTEC

130

ZIC^

130

PREAMP

))

PREAMP

5.9-Mev ALPHA SOURCE

INVERTING

TRANSFORMER

ORTEC

425

NANOSECOND

DELAY

ORTEC

455

CONST

FRACTION

TIMING SCA

ORTEC

463

CONST

FRACTION

DISCRIMI

NATOR

ORTEC

454

TIMING FILTER

AMPLIFIER

ORTEC

451

SPECTROS-

COPY

AMPLIFIER

Fig. 7.7. System for Testing Time Resolution of the ORTEC 130 Surface Barrier System.