Scintillation counting with an E.M.I. 5311 photomultiplier tube

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Material Information

Title:
Scintillation counting with an E.M.I. 5311 photomultiplier tube
Physical Description:
5 p. : ill. ; 27 cm.
Language:
English
Creator:
Allen, James S
Engelder, Theodore C
U.S. Atomic Energy Commission
Los Alamos Scientific Laboratory
Publisher:
U.S. Atomic Energy Commission, Technical Information Division
Place of Publication:
Oak Ridge, Tenn
Publication Date:

Subjects

Subjects / Keywords:
Scintillation counters   ( lcsh )
Photoelectric multipliers   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Bibliography:
Includes bibliographical references.
Statement of Responsibility:
by James S. Allen, Theodore C. Engelder.
General Note:
Cover title.
General Note:
"AECU-938."
General Note:
"November 3, 1950 TID Issuance Date."
General Note:
Work performed at Los Alamos Scientific Laboratory.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 005254599
oclc - 702220347
System ID:
AA00012259:00001


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UNITED STATES ATOMIC ENERGY COMMISSION


AECU-938


SCINTILLATION COUNTING WITH AN E. M. I. 5311
PHOTOMULTIPLIER TUBE


By
James S. Allen
Theodore C. Engelder


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November 3, 1950
[TID Issuance Date]


Los Alamos Scientific Laboratory


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IL Technical Information Division, ORE, Oak Ridge, Tennessee


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Reproduced direct from copy
as submitted to this office.


AEC, Oak Ridge, renn., 11-3-50-675-A24052















SCINTILLATION COUNTING WITH AN E. M. I. 5311 PHOTOMULTIPLIER TUBE*


James S. AllenI and Theodore C. Engelder2

University of California
Los Alamos Scientific Laboratory
Los Alamos, New Mexico


ABSTRACT

The EMI 5311 photomultiplier tube differs from the usual tube in that

the electrodes are of the Venetian blind type rather than sections of electron

optical lenses. This type of tube has been used as a scintillation counter

with trans-stilbene crystals. The shape of the scintillation pulse in charac-
-9 -8
terized by a rise time of 7. 2 x 10 sec. and a decay time of 1. 8 x 108 sec.,

It is concluded that this type of multiplication structure results in an un-

usually large spread in the transit time of electrons moving through the

structure.









* Work done under auspices of the Atomic Energy Commission.

I) Now at University of Illinois, Urbana, Illinois

2) Now at Yale University, New Haven, Connecticut








ARTICLE

A new type of photomultiplier tube has been described by Sommer and
(1)
Turk This tube has eleven multiplying electrodes of the Venetian blind

design and a flat, semi-transparent photocathode at the end of the tube en-

velope. The effective diameter of the photocathode is approximately one

inch and has a spectral response similar to that of the S-9 surface used

in the RCA 5819 tube.

The properties of this type of tube, used as a scintillation counter,

have been studied with the following arrangement. The potential divider for

the multiplier tube consisted of 12 330K resistors by-passed by 001 |if

condensors. The collecting electrode was connected to a distributed ampli-

fier by 150 feet of RG-7U cable and also to a trigger amplifier by 3 feet of

the same type of cable. Since these two cables were in parallel, the signal

at the multiplier output appeared across a load of 48 ohms. The output of

the final power amplifier was displayed on a 5XPII cathode ray tube. The

rise time of the signal amplifiers when connected to the scope was about
-9
3. 8 x 109 sec. (10 to 90% value).

Preliminary tests have indicated that voltages up to 5 K. V. may be

applied to the 5311 tube before breakdown occurs. In order to indicate the

characteristics of this tube as a scintillation counter, photographs have

been made of the noise pulses and scintillation pulses from a trans-stilbene

crystal.

The scope traces shown in Fig. 1 represent noise pulses observed

when the tube was operated at 3400 and at 5000 volts. The rise times of

these noise pulses are slightly longer than that of the distributed amplifier.

The most striking characteristic of these pulses is the long decay time of
-8
approximately 10-8 seconds.

The scintillation pulses shown in Fig. 2 were obtained when a trans-

stilbene crystal 5 mm thick was cemented with Canada balsam to the flat

photo-cathode. A source of Co60 gamma radiation was used to produce

the scintillations. As in the case of the noise pulses, the rise times are








longer than that of the amplifier. The decay times also appear to increase

with increasing voltage. For comparison, a trans-stilbene pulse observed

with an RCA 5819 tube operated at 1400 volts is included. In this case the

rise time of the pulse is almost exactly equal to that of the amplifier, and

the decay time agrees with published values The error in all measure-

ments is probably of the order of 15%.

The relatively long rise times and decay times of the pulses from the

5311 tube must be caused by an unusually large spread in the transit time of

the electrons passing through the multiplying electrodes. The most logical

explanation of this spread in time is that, as the voltage between stages is

increased, a greater proportion of the primary electrons incident upon a

given surface is scattered and finally reaches the next electrode ahead of

the secondaries ejected from this same surface. In addition to this spread

in transit time there is the usual variation caused by the combined effects

of different effective path lengths between successive electrodes and the

different emission velocities of the secondary electrons. The magnitude

of this latter effect is difficult to estimate without a knowledge of the po-

tential distribution within the Venetian blind electrodes.

We may conclude from these observations that the type of photo-

multiplier using the Venetian blind system of multiplication is character-

ized by unusually broad pulses. This will prove to be a serious limitation

to the resolving power of this tube when operated as a scintillation counter

using a fast crystal such as trans-stilbene. The tube should be entirely

suitable for use with slow inorganic crystals such as Thallium activated Nal.






(1) A. Sommer and W. E. Turk, Journ. of Sci Inst. 27 113, (1950)

(2) 0. Martinson, P. Isaacs, H. Brown and I. W. Ruderman, Phys. Rev.
79 178, (1950)









CAPTIONS


Fig. 1: Typical noise pulses from the E. M. I. 5311 photomultiplier tube.

The first trace, taken at 3400 V. indicates a rise time of
-9 -8
5.0 x 10 sec. and a decay time of 1.0 x 10 sec.. The second
-9
trace, at 5000 V., shows a rise time of 6. 0 x.10 sec. and a
-8
decay time of 1. 2 x 108 sec.. Rise times are taken from 10% to

90% pulse height, while decay times are measured to l/e, assuming

exponential decay.



Fig 2: Typical scope traces with a trans-stilbene crystal. Traces (a),

(b), and4c) were obtained with the E. M. I. 5311 tube, operated at

2800, 3500 and 4500 V, respectively. Trace (d), included for

comparison, is that obtained with, the RCA 5819, operated at
-9
1400 V. Rise and decay times are as follows: (a) TR = 7. 2 x 10 sec.,
-8 -9 -8
T = 8 x 10 sec.; (b) T = 7. 2 x 10 sec., T = 2. 8 x 10 sec.;

-9 -8 -9
(c) T = 6.6 x 109 sec., TD =3.2 x 108 sec.; (d) T = 4.0 x 0 sec.,

-9
T = 7. 0 x 10 sec. Note the amplifier and cable reflections which

become increasingly more prominent at higher voltages.























( a)








(b)


FIGURE 1









( a)


(b)







(C)






( d)


FIGURE 2
END OF DOCUMENT


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