EG&G ORTEC 474 Operating And Service Manual - Page 10

Browse online or download pdf Operating And Service Manual for Amplifier EG&G ORTEC 474. EG&G ORTEC 474 13 pages. Tinning filter amplifier

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456

HIGHVOLTAGE

POWERSUPPLY

1-bv 1- in. KL236

459

DETECTOR

BIAS SUPPLY

265

BASE

RCA

8575

TUBE

Anode

SCINTIL

PREAMI

LATION

'LIFIER

460

OELAY-LINE

AMPLIFIER

473A

CONSTANT-

FRACTION

DISCRIMINATOR

^^Na Source

425A

NANOSECOND

DELAY

GeaO COAXIAL

DETECTOR

473A

CONSTANT-

FRACTION

DISCRIMINATOR

120-4

PREAMPLIFIER

474

TIMING

FILTER

AMPLIFIER

Start ^ f

^ Stop

TIMING SCA

457

TIME-TO

PULSE HEIGHT

CONVERTER

414A

FAST

COINCIDENCE

551

TIMING SCA

460

OELAY'LINE

AMPLIFIER

6240B

MULTICHANNEL

ANALYZER

8169

Fig. 7.1. Gamma-Gamma Coincidence System Using a Piastic Scintiilator and a Large

Ge(Li) Coaxial Detector.

uses a fast plastic scintiilator and the stop channel uses

a coaxial germanium detector. Excellent timing spectra

have been obtained by combining the pulse shaping avail

able with the 474 together with the use of the slow-rise-

time (SRT) reject circuitry in the constant-fraction dis

criminator. The SRT circuitry is most effective when used

with a wide dynamic range of energies. It can provide

dramatic improvement in timing resolution below the

FWHM level and makes reliable timing data possible at

even the FW(1/100)M level.

The SRT circuitry in the constant-fraction discriminator

can provide improved timing resolution by rejecting those

logic pulses that result from leading-edge timing in the

instrument. Since the input signals that cause leading-

edge walk represent valid energy information, use of the

SRT circuitry results in a loss in the counting efficiency of

the system.

A system for measuring the lifetimes of excited states at

extremely low energies is similar to the system shown in

Fig. 7.1. In this configuration the coaxial Ge(Li) detector

and preamplifier are replaced with a Ge(Li) low-energy

photon spectrometer (LEPS) detector and preamplifier.

7.3.

NANOSECOND FLUORESCENCE

SPECTROMETRY

The ORTEC 9200 Nanosecond Fluorescence Spectrom

eter is used in lifetime measurements of excited molecular

states. In the specific application where the molecular

structure is studied, the experimenter seeks to verify a

complex model of a particular molecule or to determine

how a particular molecule is altered by its surroundings.

This type of experiment requires that the total efficiency,

the exact energy, and the complete time function involved

in the de-excitation of an electronic state be known so that

the e,xperimental results can be fit precisely to a model.

Figure 7.2 shows the 9200 System, and Fig. 7.3 shows the

detailed lifetime characteristics of a 0.1 N solution of

quinine sulfate in sulfuric acid that was excited with im

pulses of light at approximately 340 nm with the 9200

System. The quantity of information available from such a

lifetime measurement is illustrated by this set of data.