ORTEC 473 - Fig. 6.5. Typical Timing Spectrum over a Wide Dynamic Range (50:1) with Nal(TI); Fig. 6.6. Plot of Time Resolution Vs Dynamic Range Using Nal(TI) and RCA 8575 PMT

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.