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ORNØ 437
CONF-593-66
DTIEP
OCT 51964
(For Presentation at the Conference on the Automatic Acquisition and Reduction
of Nuclear Data, Karlsruhe, Germany, July 13-16, 1964).
*
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THE USE OF MULTIPARAMETER DISPLAYS IN STUDIES OF RADIOACTIVE NUCLEI*
G. Davis O'Kelley
Oak Ridge National Laboratory
Oak Ridge, Tennessee, U. S. A.
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Introduction
During the past year, considerable experience has been gained in applying
to studies of nuclear disintegration schemes a multiparameter pulse-height analyzer
with a 20,000-worà, ferrite-core memory and a storage capacity of 10° counts per
channel. The basic configuration of 100 x 200 channels can be rearranged into
other arrays, all with provision for subgrouping and dynamic routing into desired
subgroups. Flexible automatic programming features are also incorporated. Several
2-4
general descriptions of this instrument have now been published."
Nuclear spectroscopy with a multiparameter analyzer involves many explorato-y
aspects; therefore, setup time may often exceed the actual data acquisition time
by a large factor. Further, much of the setup time actually may arise from the
inherent complexity of multiparameter experiments themselves. For these reasons,
it is necessary that the data be stored in a sorted array, and that the entire
contents of the memory be displayed, so the experimental situation may be assessed
at any time from setup to completion.
•е
The X-Y Map Display
The 20,000-channel analyzer uses two 12-in. diameter cathode-ray tubes” (CRT).
Long-persistence phosphors (type P-7) are required because the time to generate a
scan of 20,000 channels is about 1 sec.
A two-dimensional X-Y "map" display is generated on one CRT by scanning a
plane in X each time the Y address is increased by one ("scan X-Y"); similarly,
planes in Y can also be sequentially scanned for increments of X ("scan Y-X").
Dots representing the X-Y channel coordinates may be intensified by using either
a linear or logarithmic voltage analog of the number of events stored. A variable
window discriminator provides additional intensification for analog voltage pulses
falling within the window. If the CRT intensity control is turned down to suppress
Research sponsored by the U. S. Atomic Energy Commission under contract with
the Union Carbide Corporation.
Dual appointment, University of Tennessee, Knoxville.
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the intensity modulation from the data analog signal, then the effect of the window
discriminator is to generate an adjustable contour line on the map.
The two photographs in Fig. 1 illustrate typical contour and intensity modulated
map displays for a moderately complex gamma-gamma coincidence spectrum. The data
were recorded with two 3 in. x 3 in. NaI(Tl) detectors at 180°, each 10 cm from an
Y source. The fast coincidence circuit was disabled for this demonstration, so
the slow coincidence alone (2 I ~1 u sec) would give rise to prominent random
coincidence peaks at 0.899-0.899 and 1.83-1.83 MeV. In Fig. 1(a) the photograph
shows a display using the linear analog voltage for intensification of the X-Y dot
pattern. The photograph shows the 0.511-0.511 MeV positron annihilation coinci-
dences to be very intense, due to the 180° detector geometry. Other prominent
coincidences fall at 0.899-0.511, 0.899-0.899, and 0.899-1.83 Mev. The contour
level was set too high in this illustration to show the 1.83-1.83 MeV random
coincidence events.
With practice, an X-Y contour display can be extremely useful in making rapid
decisions during the setup of an experiment. Inter-detector scattering, for example,
exhibits a very characteristic pattern on the X-Y map."
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Single-Spectrum Representation and Display Correlation
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The second CRT displays conventional single-spectrum plots of counts vs.
channel number. In either the "Scan X-Y" or "Scan Y-X" modes, the respective X or
Y planes are displayed in rapid succession as the map display is being generated
on the other CRT. If desired, a static display of any X or Y plane can be dis-
played by means of address selector pushbuttons. Conventional display overlap
features are also provided.
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A digital marker helps to tie the single-spectrum display and the X-Y map
2.
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together. The marker appears on the map as a line of adjustable brightness, and
can be moved from one X (or Y) address to another, until the desired memory plane
is brightened. The address is then read from digital switches. Also provided is
another digital marker which intensifies every tenth address in X and Y; the result
on the map display is a superimposed reference grid in multiples of 10 x 10 channels.
When the contour circuit is in use, the dots on the single-spectrum display
are intensified if their data analog voltages fall within the contour window in-
terval. Thus, it is possible to check the setting of the display controis for
such artifacts as display "overflow", while at the same time monitoring the posi-
tion of the contour window. Several examples of correlations between displays
will be described below.
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The ºy data of the previous illustration have been used in Fig. 2. Part (a)
shows a contour map display of the data; (b) shows a single-spectrum display for
a scan in X for a Y address near the peak at Ey = 0.9 MeV. The highly intensified
dots mark the position of the contour window.
Figure 3 illustrates the contour display obtained if a narrow contour is set
much lower on the analog voltage from the data of Figs. I and 2. The contour now
outlines the "foothills" of the three-dimensional surface, including not only the
bases of the full-energy coincidence peaks, but also the surface due to coincidences
with Compton electron and pair-annihilation escape peaks. Also noted are low-
intensity peaks arising from coincidences with scattered photons, position annihi-
lation, and pair annihilation escape from NaI(Tl) in various combinations. To show
how these spectra may be assessed, a marker is shown running along the X direction
for Ey = 0.9 MeV.
Even when statistics are relatively poor, considerable detail still may be
gleaned from a careful study of the display. Figure 4 shows data from a gamma-gamma
coincidence study of 17-sec - Tc. The analyzer stored the ungated, or "totals",
spectra from the X and Y amplifiers on a time-sharing basis with the storage of
coincidences in the matrix.”* The photograph of Fig. 4(a) is a double exposure
taken at two settings of the contour level. The first level is set high, to
emphasize the elliptical locus of 0.54-0.59 MeV events, which demonstrates that
these gamma rays are in coincidence. When the contour level is set lower, a promi-
nent peak at 1..5 MeV is seen. With the marker set to scan in the y direction, the
X address was adjusted until the marker passed through the 1.5-MeV peak. The in-
tensified spot on the single-spectrum display of the X totals (Fig. 4(b ) ) shows
immediately that the marker is set to the peak at 0.54-MeV, and not at 0.59 MeV,
confirming that the 1.5-MeV gamma ray is in sürong coincidence with 0.54 MeV.
3,4
Oblique Projections
The X deflection, Y deflection, and data analog voltages can be combined to
form a display which approximates the representation of a three-dimensional sur-
face known in graphic arts as an "oblique projection". If the two-paramuter
correlation does not contain many peaks, and if the peaks ai'e not very different
in height, then this type of display may aid in orienting the viewer to the three-
dimensional nature of two-parameter data. However, present experience indicates
that for detailed evaluation of complex two-parameter data over a wide dynamic
range, the map display with adjustable contour appears to be superior. In some
cases it may prove useful to use the two methods in combination.
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An oblique projection of the "y data used in previous illustrations is shown
in Fig. 5(a). A startling three-dimensional effect is manifested ior "ridges" due
to Compton electron spectra and the small 1.8-1.8 MeV random coincidence peak.
The intense peak corresponding to the 0.511-0.511 MeV coinciderces rises very
high, and is discerned chiefly as a void in the coinc: dence surface. In Fig. 5(b),
the planes at Ey = 0.90 and 1.8 MeV have been intensified by use of the marker.
64.
Multiple Spectra
The large memory of the two-parameter analyzer is particularly well suited
to storage of large numbers of conventional single-para:neter spectra. Either
manually or via the automatic sequence programmer, it is possible to record 100 X
"totals" (i.e., ungated) spectra of 200 channels each, 50 of 400 euch, or 20 of
1000 each. When beginning a new decay scheme study, it is essential that the
purity of the source be carefully investigated. In carrying out an investigation
of short-lived species, it is difficult to check the purity of typical sources
rapid.ly and conveniently by conventional methods.
A technique which has proved useful in such situations is illustrated in
Fig. 6. A mixed source containing 12.9-hr 64cu, 5.1-min Ocu, and 18-min "Rb
was measured on a 3 in. x 3 in. NaI(Ti) spectrometer. The automatic programmer
caused the 20,000-channel analyzer to record X totals for 10 sec of live time;
at the end of the count, the Y address was increased by ore, and 40 sec of clock
time after the beginning of the first count, the second count started. This timing
pattern was repeated until 100 spectra, !0 sec apart and 200 channels each, had
been recorded.
The illustration shows how the data may be readily interpreted on the display.
In Fig. G(a) one of the early spectra is shown. Using the marker, an X address
in each of the 5 prominent peaks was identified. Next the single-spectrum display
was set up to scan Y (i.e., time) for each of the X addresses marked in Fig. 6(a).
Since a logarithmic ordinate was chosen, the resulting display in (b) yields a
decay curve for each cf the 5 peaks in the gamma-ray spectrum. Curve l shows that
the peak at 0.511 MeV is due to "Cu, with some background contribution from the
short-lived species. The curves numbered 2, 4, and 5 all exhibit the same half-
life, 18 min, and hence are identified as due to °°Rb. The curve 3 has two com-
ponents, one of 5.1 min, and a tail of 10 min. This indicates that the 1.04-MeV
peak arises from a "cu peak added to a Compton electron background from ºy gamina
rays. An inspection of various X planes during the decay of this peak confirmed
WO.S
the decay curve analysis.
-5-
References
3.
1. Model MP-204 RT, Victoreen Instrument Company, 5806 Hough Avenue, Cleveland,
Ohio.
2. C. D. Goodman, G. D. O'Kelley, and D. A. Bromley, "A 20,000-Channel Pulse-
Height Analyzer with Two-Coordinate Address", in J. B. Birks, editor,
Proceedings of the Symposium on Nuclear Instruments, Harwell, September 1961,
pp. 197-8, Academic Press, New York, 1962.
D. A Bromley, C. D. Goodman, and G. D. O'Kelley, "Multiparameter Analysis
in Accelerator Studies in Nuclear Physics", in L. J. Lidofsky, editor,
Proceedings of the Conference on the Utilization of Multiparameter Analyzers
in Nuclear Physics, Grossinger, N. Y., November 12-15, 1962, pp. 35-48,
Columbia University Report CU(PNPL)-227; also published as U. S. Atomic
Energy Commission Report NYO-10595.
4. G. D. O'Kelley, D. A. Eromley, and C. D. Goodman, "The Role of Multiparameter
Pulse-Height Analyzers in Radioactivity Studies", ibid., pp. 49-56.
5. Type 24881P7, General Electric Co., Cathode Ray Tube Dept. 2081, Syracuse,
New York.
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Figure Captions
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Fig. 2. Photographs of the X-Y map display of data recorded with two 3 in. x
3 in. NaI(Tl) detectors at 180° from an "Oy source. (a) Contour dis-
play, with window discriminator set on linear voltage analog of counts
stored. (b) Dot pattern with linear voltage analog for dot intensifi-
cation.
Fig. 2. Illustration of contour generation. The °°y data of Fig. I were used.
(a) Contour map display. (b) Single-spectrum display at E, ~ 0.9 Mev.
Intensified dots mark the position of the contour window discriminator.
Fig. 3. Contour display of the "Y data in Fig. 1, when a narrow contour window
is set low on the linear analog voltage. A digital marker is shown set
to a Y address corresponding to an energy of about 0.9 MeV.
Fig. 4. Gamma-gamma coincidence data on 100Tc. (a) Contour set high to emphasize
coincidences between 0.54-0.59 MeV, and also set low to outline the
1.5-MeV peak. The digital marker is centered on the peak at Ey = 1.5 Met
(b) The bright spot on the X totals spectrum shows that the marker is set
on the 0.54-MeV peaii.
Fig. 5. (a) Oblique projection of the °°y gamma-gamma coincidence data in Fig. 1.
(b) Sare as (a), except intensified markers have been superimposed at
Ey ~ 0.9 and 1.8 Mev.
Fig. 6. Display of information from storage of multiple X totals spectra.
(a) Single-spectrum display of the plane at Y = 0. (b) Scan in the Y
direction for each of the X addresses selected by the five marker dots
in (a). See text.
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LEGAL NOTICE

This report was prepared as an account of Governinont sponsored work. Neither the United
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disseminates, or provides access to, any Information pursuant to his employment or contract
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END