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MASTER
LOW ENERGY NUCLEAR RESEARCH
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CESTI PXICKS
CESTI PS
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H.C. Sc
C$3.00, MN 165
e-of-Flight Experiments
Bxperimente*
P. H. Stelson
Oak Ridge National Laboratory
vak Ridge, Tennessee
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Nanosecond beam pulsing and precise flight timing
techniques are now widely used for investigating nuclear
reactions in which fast neutrons are emitted. The gradual
improvements in time-of-flight techniques are such that it
is possible in many cases to resolve neutron groups with a
precision comparable to that obtained by the magnetic anal-
ysis of charged particles from nuclear reactions. I vill
confine my discussion to recent results obtained for (pon)
and (dgn) reactions which have so far received the most
attention. Similar techniques apply and have been used to
study (He3,n) and (a,n) reactions. In fact future work with
the (Hey,n) reaction might be especially rewarding because
it involves the transfer of a pair of protons and is analo-
gous to the interesting (t,p) reaction. Of course, pulsed
(pon) and (d,n) reactions are widely used as neutron sources
for measurements of neutron reactions. The use of this
technique ior i: alastic neutron scattering measurements will
be discusseä at this conference by A. B. Smith.
LEGAL NOTICE
This report was jropared as an account of Govorament sponsored work. Neithor tho Valtod
Sutos, por the Commission, nor any person acting on behalf of the Commission:
A. Makes ay warranty or represenution. expressed or impliod, with respect to tla uccu-
racy, completeness, or usefulness of the information contained in the report, or that the we
of any information, apparatus, mothod, or procoss disclosed in this report may not Irfringo
B. Askumos any liabilities with respect to the use of, or for damages resulting from the
use of coy Information, apparatus, method, or process disclosed in thio roporto
As used in the above, “person acting on behalf of the Commissioa" includes any em-
ployoo or contractor of the Commission, or employee of such contractor, to tho oxtont that
such omplsyed or contractor of the Commission, or employee of much coatricJr preparat,
disseminates, or provides rccosa to, kay Information pursuant to his employment or contract
with the Commission, or his employment with such contractor.
privately ownod rights; or
A survey of recent literature indicates that nano-
second beam pulsing work is done on about a dozen Van de
Graaffs (single-ended or tandem), on several cyclotrons and
on at least one linear accelerator. The different acceler-
ators produce pulse widths which vary from several nano-
seconds down to a fraction of a nanosecond and peak currents
which vary from 5 mA down to 30 UA. The spacing of pulses
varies from 200 nsec to 2000 nsec.
WASTA
ST
th
What are the limitations on energy resolution ob-
tained by the time-of-flight method? The answer must
necessarily be rather complicated because there are at least
nine factors which must be considered and balanced
Research sponsored by the U.S. Atomic Energy Commission
under contract with Union Carbide Corporation
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DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED
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LOW ENERGY NUCLEAR RESEARCH
judiciously to obtain a near optimum situation. Even so,
the particular arrangement chosen probably won't be optimum
for all neutron energies of interest. There are of course
limitations such as target thickness and intrinsic energy
spread of the accelerated beain which are common to other
types of experiments. Of special interest to us are those
factors which involve time meası dement. Since the energy
resolution, En/AEn, depends on toi/Atn we can increase the
rezolution either hy increasing tn (increasing the flight
patn) or by decreasing Atn. Bearing in mind that the neutron
flux varies inversely with the square of the flight path,
it beconies clear that it is advantageous to decrease At,
rather than to increase tn. Although the above arguniant is
an overs implification of the actual situation, it is never-
theless roughly correct and hence it explains the strong
emphasis of trying to achieve small Aty values in time-of-
flight work.
It is straightforward to calculate the expected
neutron energy spread, AEn, which results from a given over-
all timing uncertainty, Atn, for a given neutron energy and
flight path. Some typical values are shown in graphical
form in Fig. 1. The straight lines on the log-log scale
give the values of En as a function of En for several
different flight paths. We assume & timing width of Insec;
the values can be directly scaled up or down for other values
of Atn. Of central importance in time-of-flight work is the
fact that AEn is proportional to Em 19. For example, if the
flight path is 5 meters and Atn is 1 nsec, then AEn changes
from 6 to 500 keV as En changes from 1 to 20 MeV. "A flight
path of 40 meters is required to give 60 keV for AEn at
En = 20 MeV.
The timing spread of a monoenergetic neutron group
is caused by a) the time width of the beam pulse, b) the
finite detector thickness, and c) the timing accuracy of the
detector and associated electronics system. Of these the
simplest to discuss is the time spread caused by the finite
detector thickness. Plastic scint, illators of l. to 2-inch
thickness are typical in fast neutron time-of-flight work.
It takes a l-MeV neutron 1.8 nsec to move 1 inch. A 20-MeV
neutron will move 1 inch in 0.4 nsec. In Fig. 1 we show a
dashed curve for a 5-meter flight path in which an additional
time spread due to a l-inch thick detector is folded into .
the basic l nsec width. In this example the detector thick-
ness is the chief limitation for neutron energies below I
Mev. In many experiments we wish to detect a wide range
of neutron energies. We see that it is then difficult to
achieve a well-matched system. We want a thick detector for
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LOW ENERGY NUCLEAR RESEARCH
high energy neutrons to increase the detection efficiency
and yet a thick detector severely limits the energy reso-
lution for low-energy neutrons. If the detector thickness
is an important contributor to the energy resolution for a
given neutron energy and it is desired to decrease En, it
is advantageous from a counting rate point-of-view to de-
crease the detector thickness rather than to increase the
flight path.
Plastic or liquid scintillators coupled to fast photo-
multipliers are almost universally used to detect the fast
neutrons and hence the time response of these detectors is
of great linpor'ance to time-of-flight work. I will not have
the time to discuss this subject, in detail; there are several
good articles on this subject. --* A rather flat continuous
distribution of pulse heights result from the fast neutron
interaction with the scin-illator and in order to maintain
a high counting rate it is desirable to use a wide dyr.amic
range of pulse heights for timing. In considering the time
response of the detector it is useful to distinguish "time
jitter" from "time walk." By time jitter we mean the vari-
ation in timing of pulses which have the same pulsa height.
If the scintillator area is not large and if the pulses used
for timing are restricted to a small range of the larger
pulses, then it is possible to detect neutrons of several
y with a time jitter well under 1 nsec. Time jitter
increases for lower energy neutrons and for larger area
detectors.
1927
The rise time of the pulse from the detector is
governed by a) the decay time of the scintillator (typically
2 to 4 nsec), b) the time taken by the photons to arrive at
the photocathode (not negligible when large area scintil-
lators and light pipes are used), and c) the rise time of
the photomultiplier (typically 2 nsec). The rise time of
the pulses is therefore several nanoseconds and if we measure
time by triggering at a given pulse height there will be
appreciable time walk for pulses of different size. In
principle, time walk is not a limitation on timing accuracy,
it merely requires an elaborate system for recording the
information. At Oak Ridge we use leading edge timing and
we store a 2-dimensional array in which the time spectra are
sorted according to scintillator pulse height. The individ-
ual time spectra are then appropriately walk corrected and
collapsed into a single time spectrum
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LR
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There are timing systems in use which do not require
two-dimensional storage. By the use of the "fast crossover"
LOW ENERGY NUCLEAR RESEARCH
technique one can eliminate time walk but only at the ex-
pense of increased tim: jitter.
In our work at Oak Ridge we have used an NE-213 liquid
scintillator with 1-inch thickness and 4-1/2-inch diam
which is mounted directly onto a 58 AVP photomultiplier.
When we set the trigger level to respond to energy pulses
greater than 0.5 MeV we find that the timing resolution for
several Mev energy neutrons is approximately 1 nsec. Similar
results are obtained by others, for example, C. J. Oliver,
et al.5
The final necessary ingredient for fast neutron time-
of-flight work is an accelerated pulsed peam. A van de
Graaff accelerator produces a dc beam characterized by a .
certain energy homogeneity, angular divergence, spot size
and intensity which taken together indicates the quality of
the ion beam. Fowler and Good" have emphasized that the
production of a time-modulated beam invariably reduces the
quality of the beam. Careful consideration should be given
to the pulsing system to achieve a desirable balance between
the beam burst duration and the decrease in beam quality.
For example, in an attempt to achieve better energy reso-
lution by producing sharp time bursts through strong klystron
bunching one might in fact find poorer energy resolution be-
cause the bunching process produces an appreciably larger
energy spread in the incident ion beam.
The Mobley magnetic compression method has proved to
be a popular and reliable method for achieving sharp ion
bursts with Van de Graaff accelerators. The actual per-
formance of a Mobley system has been described by Cranberg,
et al. An rf ion source and a beam chopper, located in
the high voltage terminal, produce pulses of 10 nsec width
and 1000 nsec spacing. After acceleration the Mobley
magnet system compresses the pulses to about I nsec width..
The peak current is several mA.
It is well-known that Mobley time compression is
paid for by an increase in the beam divergence. However,
one should also note that in the system described by
Cranberg, et al. there is a considerable increase in ion
energy spread caused by the electrostatic beam deflector
needed to fan curs the beam prior to entrance into the
Mobley magnet. The energy homogeneity is decreased to 1
part in 250. This is to be compared with values of 1 part
in 1000 to 2000 which are commonly realized with dc beams
from Van de Graaffs.
LOW ENERGY NUCLEAR RESEARCH
An alternative method for producing nanosecond
pulsing for Van de Graaffs has been developed at Oak Ridge.
A duoplasmatron ion source, a beam chopper, and & klystron
buncher are located in the terminal of the Van de Graaff.
The characteristics of this system for our 3-MV Van de Graaff
has been described in detail by Moak, et al. This system
produces a pulse with width Sinsec and a peak current of 10
mA. Since one achieves tiine compression by energy modu-
lation of the particles within a given pulsc, one expects
to pay for the time compression by an increase in the energy
spread of the ion beam. In Fig. 2, I show a test made a
couple of years ago. The narrow resonance in the Cabo
reaction was measured with a chopped beam of 9 nsec pulse
width. The indicated bean energy spread was 0.4 kev. The
klystron buncher was then turned up until the pulses on
the scope had a width of 1.5 nsec and the narrow resonance
was again measured. The measured energy spread was 1.8
keV. Thus the klystron buncher reduces the energy homoge-
neity from 1 part in 4000 to l part in 1000.
A beam pulsing system similar to that described by
Moak, et al. has been in operation for about two years on
the 6-MV Van de Graaff at Oak Ridge. One recent improve-
ment made to both machines was the installation of a beam
pulse diverter or "ccunt down" system in each terminal.
This allows the experimenter to turn a knob on the control
console and thereby select the time interval between
pulses from among the values 500, 1000, 2000, ---, to
16,000 nsec.
Nanosecond pulsing systems have been developed for
several tandem Van de Graaffs. Because one must work with
a negative ion beam, the peak currents for tandems are down
I to 2 orders of magnitude from those obtained with single-
ended Van de Graaffs. An early pulsing system is described
by Lefevre, et al.9. The negative ions are obtained by charge
exchange. The beam is klystron bunched at the low-energy
end of the tandem and is then rf chopped at the high-energy
end. The system produced pulses of 2 nsec width and peak
current of 30 HA. The Aldermaston tandem_Uydd also uses a
negative ion beam obtained by charge exchange. However in
the Aldermaston system the beam is first chopped and then
klystron bunched at the low-energy end. They report pulses
of 2.5 nsec width and about 50- to 90-uA peak current. The
pulsing system which has recently becor operational for
the Oak Ridge tandemd. uses direct extraction of a negative
ion beam from a duoplasmatron ion source. The beam is then
chopped and klystron bunched at the low-energy end of the
tandem. This pulsing system produces pulses which are 0.8
LOW ENERGY NUCLEAR RESEARCH
nsec wide and 400 ulo peak current and spot size of 5 mm.
The natural phase bunching in cyclotrons results in
a time-structured accelerated beam which may be quite suit. .
able for neutron time-of-flight work. Anderson and co-workers
have done extensive neutron time-of-flight work with the small
variable energy cyclotron at Livermore. -5 I do not know the
characteristics of their pulsed beam.
(pin) Reactions
I now want to discuss some (p,n) measurements done
with the 6-MV Van de Graaff at Oak Ridge. Figure 3 shows &
time-of-flight spectrum (converted to pulse height) observed
when 3-MeV protons hit a thin Cuotarget. Four neutron
groups are observed which result from the excitation of the
ground state and 3 low-lying excited states in Znos. Although
g-n pulse shape discrimination was used (liquià scintillator
NE213), there is still a small residual y-ray peak. For this
experiment the spacing between beam pulses was 222 nsec and
the flight path was about 9 meters. Whenever the time
differenc: between the fastest and slowest neutrons detected
is larger than the time between beem pulses then we have
what we call a "wrap around" situation. In Fig. 3, they rays
actually get to the detector 3 cycles earlier than the ground
state neutrons. The y-ray peak is narrow compared to the
neutron peaks and this shows that, the beam pilse width and
electronic time spread are small contributions to the width
of the neutron peaks. The flight time of the ground state
neutron group is about 700 nsec (E = 0.88 MeV). The ub-
served width is 3.4 nsec or 9 kev." This width is believed
to be the result of 3 approximately equal contributions:
a) the energy spread from target thickness (nomiral value
5 keV or 1.9 nsec), b) the energy spread in the beam pulse
(estimated at 5 keV or 1.9 nsec), and c) the timing spread
caused by the l-inch thick detector (1.9 nsec or 5 kev).
One can therefore obtain a neutron energy resolution
of about 10 keV for neutron groups with energies between 0.5
and 1 MeV. As we have seen the resolution becomes less im-
pressive for higher energy neutrons. This is illustrated in
Fig. 4 which shows once again a time-of-flight spectrum for
Cub5 but at a higher bombarding energy of 4.36 MeV. NOW
the neutron groups labelled 0, 1, 2 and 3 are not nearly so
well resolved (En = 2.2 MeV). On the other hand neutron
groups labelled 15 and 16 correspond to neutrons leaving
the Znº, nucleus in excited states at 1.6 MeV with an energy
separation of only 15 key. By bombarding at successively
higher proton energies we can gradually move up the region
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LOW ENERGY NUCLEAR RESEARCH
of good energy resolution and in this way examine the level
structure in the residual nucleys. This has been done for
the targets v51, 0053, M55, 0039, and Cu65 all of which have
fairly low (p,n) thresholds.
Co59(,
To 122ustrate the results I will discuss the
,n)Ni59 reaction. High resolution work on the states.
in Ni59 is also available from the N158(d,p)N159 reaction. 14
Figure 5 shows a time-of-flight spectrum for Ep = 4.359 MeV
(the (p,n) threshold is about 1.8 MeV). There is some "wrap
around" complication in this spectrum. Neutron group 20 is
merged with group 1. The "wrap around" groups can be dis-
entangled because the data is recorded in a 2-dimensional
array. Those peaks due to lower energy neutrons have smaller
pulse heights. The peak labelled 7 and 8 is too wide for a
single neutron group and is assumed to be a close doublet.
Figure 6 is a time-of-flight spectrum taken at the
higher proton energy of 4.765 MeV. Notice that there is a
weak peak (5) on the side of the strong peak (6). Figure
7 is a composite of 3 time-of-flight spectra taken at the
still higher energies of 5.771, 5.366, and 6.045 MeV. The
peaks are labelled with the excitation energies in the Ni
nucleus. These spectra serve to examine the level structure
in Nil at excitation energies of 2.9 to 3.6 Mev. Tlie close.
lying states at 3.035 and 3.047 MeV are resolved in the top
spectrum but are merged to single peak at the next higher
proton energy. Similarly the states at. 3.298 and 3.305 MeV
are a broad peak in the top spectrum, then separate in the
center spectrum and again merge in the bottom spectrum.
We note that new groups corresponding to higher excited
states emerge as the proton energy is increased.
Ni
The ground state of Co39 is 7/2”. Assuming the
validity of the statistical model, we can use proton pene-
trabilities from the optical model to calculate the relative
populations of different it states in the compound nucleus.
Such a distribution is shown for 5-Me V protons in Fig. 8.
States with spins 3 to 5 are the most likely. The
results have shown that the state labelled 5
in Fig. 6 has an d = 1 stripping pattern. It must then be
a 3/2“ or 1/2“ state. The small intensity of this state
in the (p,n) reaction strongly suggests that the state is a
1/2“ state. Other known 3/2- states are more strongly
excited. Higher & waves and hence lower neutron penetra-
bilities are required to excite a 1/2" residual state. For .
example the compound nucleus state 4 can decay to a 1/2
state only by g-wave neutrons whereas it can decay to
state by dawave neutrons.
LOW ENERGY NUCLEAR RESEARCH
Figure 9 is a graphical summary of the excited states
in N159 observed with the (p,n) reaction. We have also
shown the level structure obtained by
used the (d,p) reacticn on Ni>. There is good agreement .
for the first 6 excited states. At higher energies there
are definite differences in the level structures obtained in
the two experiments.
Figure 9 also shows some preliminary results obtained
by looking at the 7 rays with a Ge detector when protons
bombard a coo tai get. At these low proton energies neutron
emission is strongly favored and hence most of the observed
ny rays come from the decay of excited states in Ni>9. The
C059(p,ny) results in Fig. 9 indicate the levels for which
q rays have been identified.
Next I want to briefly discuss the yos(.n)zrºy
reaction which has been studied by Kim and Robinson. 15
Figure 10 shows the low-lying states of Zro e ground
state and first excited state are kr.own to be 9/27 ang 1/2",
respectively. Goodmando has measured the z
ion and found b = ? for the transferred neutron to the
second excited state at 1095 key. The yo9(p,n)Zr89 was
used to try to decide whether this second excited state was
1/2 or 3/2. The relative differential cross sections
were measured at several proton energies. An example of
these results is shown in Fig. 11. Hauser-Feshbach pre-
dictions are shown for 3/2 (solid curve) and 1/2- (dashed
curve). Clearly the shape and magnitude of the differential
cross section indicate that the second excited state is 3/2º.
As a final topic on (pen) reactions I will briefly,
discuss some work by Kim, Kernell, Robinson, and Johnson'!
which uses the neutron
h uses the neutron decay of an analog resonance to make
spin and parity assignments to residual excited states.
Figure 12 shows the Sn19(p,n)Sb119 yield as a function of
proton energy. The strong resonance is identified as the
analog of the ground state in Snt. The idea of the
experiment is to measure the neutron spectra both on and off
the analog resonance. When off the resonance the compound
states from which the neutrons decay will be typically
distributed over a range of Jh. However, the analog reson-
ance selectively enhances of compound states. As a result
the neutron decay to the residual states in Sb 1.19 would be
expected to differ when on and off the analog resonance. .
This is illustrated in Fig. 13. For example, the groups
ng and have different relative heights when on resonance
and off resonance. This type of experiment plus some addi-
tional angular distribution measurements has led to spin
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LOW ENERGY NUCLEAR RESEARCH
and parity assignments for the levels fed by the neutron
groups 110, nul, n12, and n13.
(d,n) Reactions
The Q-values for (pen) reactions for many nuclei are
so negative that the (p,n) reaction cannot be studied with a
low-energy accelerator. In contrast, the (a,n) reaction
generally has a positive Q-value and hence (d,n) reactions
offer a more extensive range of application for low-energy
accelerators. The problem with (d,n) reactions is that the
Q-value may be so large and positive that the neutron groups
with high energy may not be adequately resolved by the time-
of-flight method. Long flight paths are required. The (den)
work done with the 3-MV Van de Graaff at Harwell has used a
15-meter flight path.
In the recent (,11) work done at Oak Ridge we have
used the experimental arrangement shown in Fig. 14. The 6-
MV Van de Graaff is a vertical machine. The beam analyzing
magnet is o!) a gun mount which permits the beam to be sent
in different directions. To change the angle at which the
neutrons from a (d,n) reaction are detected we rotate the
beam arialyzing magnet. The shielded detector which is
mounted on a polar coordinate system (carriage mounted on a
horizontal beam which is in turn supported by a pivot point
and circular rail) requires only slight adjustment to allow
the detector to view the new target position. This system
allows flight paths of up to 15 meters.
Now the simplest thing to do with the (d,n) reaction
is to use it to locate levels in the residual nucleus. How-
ever, one would also like to use stripping theory to get in-
formation on the spins and parities of the states and possi.
bly also spectroscopic factors. The difficulty is that at
low bombarding energy the reaction is likely to be a mixture
of direct and compound nucleus reactions. If this is the
case one may still be able to make a qualitative interpre-
tation which will select l values. The spectroscopic factors
will be more difficult. As an example, Paul and Montague?
e studied the Ne22(d,n)Na3 reaction at Ea = 3 MeV and
have used the strong peaking at forward angles to pick out
de = 0 proton transfer.
Davies, et al. 19 have studied the si2(d,n)p29
reaction at both 4 and 5 MeV incident deuteron energy. They
found a j-dependence for the stripping patterns. It is also
interesting to note that they found different spectroscopic
factors at 4 and 5 MeV. They believe that at 5 MeV the
10
LOW ENERGY NUCIEAR RESEARCH
spectroscopic factors are probably reliable (relatively,
small compound gucleus contribution). Buccino, et al.20 also
studied the siz(d,n)P<9 reaction at the higher energies of
7, 9, and 10 MeV. Their results are in agreement with those
obtained by Davies, et al.
It is clear that a great deal more (a,n) work on
nuclei is desirable in order to have information on the
proton states in nuclei which is comparable in quality and
quantity to what is now known for the neutron states. In
recent years the (He),a) reaction has proved to be an attrac-
tive alternative to the (d,n) reaction. At present the
theoretical interpretation of the (1,n) reaction is probably
more reliable than that for the (He,d) reaction. The study
,n) reactions on the medium and heavy weight nuclei will
probably require deuteron energies in the tandem van de
Graaff range.
OT l.Lav+
27
Lawergren, Morrison, and Ferguson have used the
(d,n) geaction to study the excitation of analog states.
The Na }(d,n)Mg24 and A127 (a,n)si28 reactions excite states
in Mg24 and 5:28 which are the analogs of the low-lying
states in Na24 and A220. They have compared the spectro-
scopic factors for excitation of the anajpg states to those
previously obtained for the states in Na<4 and A120 from the
(d,p) reaction. Lawergren, et al. point out that the energy
resolution available for investigation of the analo states
is especially good because the neutrons leading to these
states (for the cases studied) have low energy
An example of a (d,n) time-of-flight spectrum taken
recently at Oak Ridge is shown in Fig. 15 for a Niyo target.
The neutron groups leading to the low-lying states of Cuy
are very well resolved. Some preliminary angular distribution
for the ground state and first three excited states of Cupy
are shown in Fig. 26. The ground and first excited states
P3/2 and P states and one sees a strong stripping
pattern for the neutrons going to these states.
Blairs has used the (He",d) reaction to look at
states in Cu39. A strong state at 3.9 MeV was identified
as the analog of the ground state of Ni59. Rosner, et al.23
concluded that states at 3.90, 4.32, and 4.37 MeV are ex-
cited in the (He),d) reaction and are to be identified as
the analogs of the first 3 states in Nipy. However,
Morrison and Schiffer24 also studied the (He",d) reaction
and found a somewhat more complicated situation. Our results
from the (d,n) work are in general agreement with the work of
Morrison and Schiffer. The spectrum shown in Fig. 15
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LOW ENERGY NUCLEAR RESEARCH
indicates a number of strong peaks in the region from 3.5 to
4.5 MeV. In fact, Morrison and Schiffer found states at
3.56, 3.59, 3.76, 3.90, 3.92, 4.01, 4.06, 4.12, 4.32 and
4.36 MeV and these values correspond quite well with those
shown in Fig. 15.
During this talk I have referred to (p,n) and (d,n)
work at Oak Ridge. I therefore want to acknowledge my co-
workers, Y. Cassagnou, F. Perey, J. Biggerstaff, A. Marusak,
K. Dickens, W. Kinney, and J. McConnell.
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LOW ENERGY NUCLEAR RESEARCH
References
1. A Schwarzschild, Nucl. Instr. and Methods 21, 1 (1963).
2. G. Present, A. Schwarzschild, I. Spirn, and N.
Wotherspoon, Nucl. Instr. and Methods 31, 71 (1964).
3. E. Gatti and V. Svelto, Nucl. Instr. and Methods 30,
213 (1964).
4. C. W. Williams, "Timing with Photomultipliers", ORTEC
News (March 1967). Oak Ridge, Tennessee.
C. J. Oliver, B. Collinge, and G. Kaye, Nucl. Instr. and
Methods 50, 105 (1967).
7, 245 (1960).
7.
L. Cranberg, R. A. Fernald, F. S. Hahn, and E. F.
Shrader, Nucl. Instr.. and Methods 12, 335 (1961).
C. D. Moak, W. M. Good, R. F. King, J. W. Johnson, H. E.
Banta, J. Judish, and W. H. duPreez, Rev. Sci. Instr.
35, 672 (1964).
9. H. W. Lefevre, R. C. Borchers, and C. H. Poppe, Rev.
Sci. Instr. 33, 12.31 (1962).
10.
J. H. Anderson and D. Swann, Nucl. Instr. and Methods
30, 1 (1964).
11. D. Dandy and D. P. Hammond, Nucl. Instr. and Methods 30,
23 (1964).
12.
C. D. Moak (private communication).
13.
See, for example, c. Wong, J. D. Anderson, J. W.
McClure and B. Pohl, Phys. Rev. 156, 1266 (1967).
E. R. Cosman, C. H. Paris, A. Sperduto, and H. A. Enge,
Phys. Rev. 142, 673 (1966).
15. H. J. Kim and R. L. Robinson (submitted to Phys. Rev.).
16. C. D. Goodman, Bull. Am. Phys. Soc. 9, 106 (1964).
17. H. J. Kim, R. L. Kernell, R. L. Robinson, and C. H.
Johnson (private communication).
..
. usar o x..
so
..
."
13
LOW ENERGY NUCLEAR RESEARCH
18. E. B. Paul and J. H. Montague, Nucl. Phys. 54, 497
(1964).
19. W. G. Davies, W. K. Dawson, G. C. Neilson, and K.
Ramavataram, Nucl. Phys. 76, 65 (1966).
S. G. Buccino, D. S. Gemmell, L. L. Lee, Jr., J. P.
Schiffer, and A. B. Smith, Nucl. Phys. 86, 353 (1966).
21.
B. Lawergren, G. C. Morrison, and A. T. G. Ferguson,
page 739, Conference on Isobaric Spin, Academic Press
(1966).
22.
A. G. Blair, page 115 Proceedings of "Nuclear Spectro-
scopy with Direct Reactions" ANL-6878 (1964).
23. B. Rosner, C. H. Holbrow, and D. J. Puller, page 595,
Conference on Isobaric Spin, Academic Press (1966).
.
24. G. C. Morrison and J. P. Schiffer, page 748, Conference
on Isobaric Spin, Academic Press (1966).
Tu
*
LOW ENERGY NUCLEAR RESEARCH
Figure Captions
Fig. 1 Plots of the neutron energy spread AE, (in kev)
as a function of neutron energy (in MeV) for different
flight paths which results from a timing uncertainty Aty
of Insec. The dashed curve shows the Er for a 5 meter
flight path which results from an additional timing spread
caused by a 1 inch thick detector.
Fig. 2 Narrow
) resonance which was measured
with and without klystron bunching to study the increase
in beam energy spread caused by the bunching.
Fig. 3 Time-of-flight spectrum for the Cu65(p,n)zn65
reaction.
Fig. 4 Time-of-flight spectrum for the Cuos(p,n) 7.nº
reaction. The flight path was about 6 meters. The arrows
indicate the neutron groups going to excited states in
znos (ground state group labelled o).
Fig. 5 Time-of-flight spectrum for th
reaction. Flight path is 6 meters.
Fig. 6 Time-of-flight spectrum for th
reaction. Flight path is 6 meters.
for the C.59(pın)N:59
Fig. 7 Three time-of-flight spectra for the
C059(p,n)Niby reaction. The arrgys indicate the excitation
energies of the states in the Ni?9 nucleus. Only those
neutron groups leading to rather high excited states are
shown.
Fig. 8 Relative population of gr states for 5 MeV
protons on Copy. The statistical assumption is made and
the transmission coefficients are obtained from an optical
model.
Fig. 9 Summary of levels in Ni59 observed by the
C059(p,n) reaction. The levels obtained by the Ni) (d,p)
reaction are also shown. Levels identified by observing
they rays in a Ge detector spectrum are shown.
Fig. 10 Level diagram for Zr89.
LOW ENERGY NUCLEAR RESEARCH
Fig. 11 Relative differential cross sections for the
con groups leading to the ground state and first two
excited states in Zr89. The curves are theoretical
predictions of the Hauser-Feshbach theory. The dashed
curve is for the assignment 1/2" and the solid curve is
for the assignment 3/2º for the second excited state.
Fig. 12 (pon) reaction cross sections for Sn 17
and Sn119 in the vicinity of the of analog resonance.
ig. 13 Neutron time-of-flight Spectra for the
Sn119(p,n) reaction taken on-resonance and off-resonance.
Fig. 14 Schematic diagram of the experimental neutron
time-of-flight arrangement on the Oak Ridge 6 MV Van de
Graaff. The observation angle is changed by rotating
the beam analyzing magnet.
Fig. 15 An example of a Ni'°(d,n) time-of-flight
spectrum. This spectrum was obtained with 1 hour of
running time.
Fig. 16 Some preliminary angular distributions for
the ground and first 3 excited states in Cu59 obtained
from the Ni?(d,n) reaction at Ea = 4.946 MeV.
ORNL-DWG 67-6380

En (kev)
5 meters
x 10 meters
20 meters
40 meters
0.1
0.2
0.5
1
2
En (MeV)
5
10
20
50
Figil
ORNL-DWG 67-6379:

Como
C310, y) RESONANCE
_ En= 1.747 MeV
• NO KLYSTRON BUNCHING
9 nsec PULSE
• KLYSTRON BUNCHING
1.5 nsec PULSE
- ENERGY SPREAD: 0.1%
relative counts
H
unie
0.40 keV
-1.80 keV
20.190
20.200
20.210
20.220
PROTON RESONANCE FREQUENCY
.
.
. L
.
..,
1
.
'
N
2
.
water
.
SM
ORNL-DWG 67-6378
.
.
Cu65(e,n) Zn65
Ep = 3.08-Mev
_D=9 meters, 8 = 25 -
G.S.
I En=0.880
In 700 nsec
i Atn= 3.4nsec
Aen=9kev
0.115-MeV
counts/channel
0.060-MeV
0.210-MeV
y's
WWW
60
70
80
90
100
110 120 130 140
CHANNEL NUMBER
150
160
170
180
190 200

4 x 103
ORNL-DWG 66-3672
- 65 Cule, n 165 zn
Ep = 4.36 Mev –
O
2
14 + y's
bobo
counts
do N o an
10 L
o
20
40
60
80
100
120
140
160
180
200
220
240
260

CHANNEL
Nowe
ORNL-DWG 66-3675
o
– 59 colp, n) 59 Ni
Ep = 4.359 Mev
N
o
counts
Oo 206
oooo
0086
Ō
0000027
on
N
o
20
40
60
80
100
120 140
CHANNEL
160
180
200
220
240

ORNL-DWG 66-3673
IL
-
counts
oli
oo po o
No 0 N
59colp, n) 59 Ni
Ep = 4.765 MeV
10°/
.
0
20
40
60
80
100 120
CHANNEL
140
160
180
200
220
240

.
Ep=6.045 Mey
Ep=5.866 Me
Ep=5.771 MeV
م
3
.
638
150
ر
3
.
453
3
.
417 سه
200
3.556
3
.
382 ما
-ه
3
.
528
سه
3
.
357
3.515
3.343
250
3.305
3.298
ا
م (
3
.
175
59cole,n) 59Ni Flight Path 7.9 meters.
CHANNEL NUMBER
300
التمر -

23.047
350
- 3.035
400
2.900
ORNL-DW6 67-4736
450
ORNL-DWG 66-3669
59c0 + P; 16+ = 72
Ep = 5.0 MeV 7
0+ 0- 9+ 1. 2+ 2- 3+ 3- 4+ 4- 5+ 5- 6+ 6- 7+ 7-

Relative Population of jt States.
Www
TI
.
introl
ORNL-DWG 67-4735.
1
58Ni (d,p) 59 Ni
I
| || || | | || | 5 i (d,p)Beni
I I L 5900(0,0 %) 59Ni
| || UTI | 5°C(0,959 Ni
||
2.6
2.8
3.0 3.2 3.4
EXCITATION (MeV)
3.6
3.8
|
I
58Ni(d,p)59Ni
||
.
ll
|| IIII
I III
IllIII
||| sexi (0.9)”Ni
1 5°co(0,0 2150Ni
||| secole,n39ni
I
I
3.0
2.0
EXCITATION (MeV).
ORNL-DWG 67-4799
097 +p, Qion) =- 3.63 MeV
d AND a.
90Zr +p AND
90 Zr +3 He
1645 keV ?
1465 keV?
1095 kev na,
595 keV 12
en=9
bn=1
bin=4-
mino
En =1.4 Mev
Enq=0.9 Mev
En = 2.0 Mev

G.S. 9
8977
-
.
..
*
.
.
ELLA!
ORNL-DWG 67-4522
89712,n)89Zr*
En=5.770 MeV
ASSUMED 1"=3/2
ASSUMED 1"=12
89Zr* (1095-kev)


897r* (595-keV, 12)
RELATIVE 0(0)

89Zr(g.s., 2+1
0
40
80
120
160
Oc.m. (deg)
.
.
.
.
.
.
ORNL-DWG 65-472R

ô
Pepe
L
ô
Hot
o 119 Snip, n) 11956
117Sn(e, n)947 Sb
Ô
o
10
Ñ
olan
Ô
o (millibarns)
0
至至至
​0
A
N
4.9
4.2
4.3
4.4 4.5 4.6 4.7
PROTON ENERGY (MeV)
4.8
4.9
5.0
13
ORNL-DWG 67-4802

112Snip, n) 19 sb'
FLIGHT PATH = 6m
8 = 90°
OFF-RESONANCE
An3 (24)
no (5)
1.7408
ng(23) 7 no
NEUTRON COUNTS
ON-RESONANCE
*
**
.
o
20
40
60
80
180 200
220 240 260
100 120 140 160
CHANNEL NUMBER
13
ORNL-DWG 67-1338
-6 meters ---
-7 meters -
VO
CARRIAGE
ON
TARGET
.

---
|NEUTRON FLIGHT PATH
PIVOT
DETECTOR
DETECTOR
SHIELDING
BEAM
ANALYZING
MAGNET

- CARRIAGE TRACK
SHIELDING
WALL

counts/channel
& na ar na dno a e
30
50
74.358
F74.3081
-4.265 ||
70
+4.106
100
11873.893
150
3.654 |||
1433.427
200
CHANNEL NUMBER
250
10
IMPURITY?
A=750
FLIGHT PATH = 12.65 m
Ep=4.946 Mev
E58 Ni (d,n 59 Cu
300
2239 2.299_
11 S
IMPURITY?
129616
350
Set 1.375
ORNL-DWG 67-4737
400
#
GROUND
STATE
ORNL-DWG 67-4734


58Nild, n) 59cu
TG.S.
0.479-MeV STATE
: 0(0)
-


0.895-MeV STATE —
4.375-MeV STATE
0 (0)
0
40
:
80 120
BLAB (deg)
160
0
40
80 120
PLAB (deg)
160
.
:
TTTT
115,-
AL
'
.
EL.
2.23
Ajk
!
.
L
T
.
.
14.1!1
Wyn
?
A
1
.
**
**
**
.,
*
:.
:.:.
::1:.:.
"
11
2
ST
1
wa
.
X2
"
'
.
END

11?
DATE FILMED
10 / 3 /67








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.
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