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LEGAL NOTICE
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огу че
JUL 22 1965
(Paper - Second International Meeting on Accelerator Targets Designed
for the Production of Neutrons, June 21-22, 1965, Grenoble, France)
CONF-6506355/
(pin)cr Cross Section from Threshold to 2.25 MeV
stil
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J. H. Gibbons and R. L. Macklin
Oak Ridge National Laboratory
Cak Ridge, Tennessee
MASTER
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Abstract
internetoverk
The absolute (p,n) total cross section for "v(p,n) has been
sig
measured from threshold to 2.25 MeV with an accuracy of 5:40. The cross
inde
section measured with an ~ 15 keV thick target fluctuates appreciably
sutini inimicis
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despite the ~1 keV-level spacing observed using a thin target. The soull
change of neutron energy with emission angle make this reaction a good 41
monoenergetic source.
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mimo termine their
PATENT CLEARS APPROVED. JING SECTION
PATENT CLEARANCE OBTAINED. RECEASE TO
THE PUBLIC IS APPROVED. PROCEDURES
ARE ON FILE IN THE RECEIVING SECTION,
Research sponsored by the U.S. Atomic Energy Commission under contract
with the Union Carbide Corporation.
A
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Introduction: The use of the "v(pin) reaction as a neutron source
in the 10-700 keV energy range has recently been reviewed.
Earlier
measurements of forward yield and angular distributions have shown a very
complicated resonance structure not fully resolved at I keV resulution.
However, the variation of neutron energy with laboratory Angie is surti -
cient to provide a continuous neutron flux, reasonably uniform uver a band
of energies, when the 41 yield is used (see reť. 3 for example). While
the neutron yield can be found for a particular target and bombardment by
measuring the per radioactivity produced, this may not always be us con-
venient as the use of a proton current integrator together with the target
thickness and the, (p,n) croße section.
sperimental: The equipment used was substantially the same as
that described in an earlier report.“ We used the proton beam from the
CRNL 5.5 M Van de Graaff accelerator, vacuum evaporated natural vanadiuin
targets on Pt backings, and the graphite sphere 48 neutron detector.” The
particular target used in this measurement (F48. 1) was (226 + 7) ug/cm² v
by weight. Crystal growth gives a small variation of thickness and our
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estimate of this effect from experience with thinner targets is indicated
in Fig. 1. The proton beam was collimated and passed electron scraper and
bias slits before entering the ~ 1 meter long target tube. The relative
yield at several energies was checked during the course of the measurement
and was repeatable to about 3%.
Results: The cross section obtained is given in Fig. 1. It is
clear from an examination of our earlier work that each peak ouserved is
due to several resonances. For example, the peak neur 1.63 MeV is due
.
A
to about 15 resonances. Thus the cross section shape will vary with target
GA
- 3 -
thickness. The results of Harris, et al., are also plotted on Fig. 1.
The agreement between these two measurements varies from goud (1.6") to 1.7 MeV
and 1.9 to 2.1 MeV) to relatively poor elsewhere. The disagreement for
E. > 2.15 MeV may be partially due to the different target thicknesses used
but there is no apparent explanation for the other areas of disagreement.
In contrast to this, our data are in good
agreement over the entire
energy interval measured with the results of Johnson, Gulonsky and Ulrich,"
who used a 45 neutron detector whose efficiency vs energy was callbrated
**.
,
with a manganese bath. We estimate our errors (s.1). ) to be approximately
as follows: target thickness (3%), proton beam current (1%), detector
efficiency (s 3%), accelerator energy stability (~ 1 kev), counting statistics
(< 1%). Thus the relative cross section should be accurute to about (+ 2%)
and the absolute cross section to about (+ 5%).
Conclusion: The total cross section is only about I mu for the
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production of about 100 keV neutrons, compared to several hundred mb for
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no reason
T(p,n) and 'L(P,n) reactious; but the target atomic weight 18 such that
the full 4x solid angle can be used without introducing large energy spreads.
While the effective cross section 18 somewhat dependent upon target thickness
the results, given proton current and target thickness, should allone...(486.).
n t av dissez étrang
neutron yield determination for E5 2.2 MeV accurate 'o less than 17%.
Acknowledgements: The authors greatly appreciate conversations
in aria
with H. Grench and C. H. Johnson.
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4
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References:
1.
K. K. Harris, H. A. Grench, R. C. Jolmson and K. J. Vaugha, Nuci. Instr.
and Methods 33, 257 (1965).
2. J. H. Gibbons, R. L. Macklin and E. W. Schmitt, Phys. Rev. 100, 167 (1965).
3. K. K. Harris, H. A. Grench, R. G. Johnson, F. J. Vauglun, J. H. Ferziger
and R. Sher, submitted for publicatior in Nucl. Phys.
4. J. H. Gibbons and R. L. Macklin, Phys. Rev. 114, 571 (1999).
5. R. L. Macklin, Nucl. Phys. 1, 33(1957).
6. C. H. Johnson, A. Galonsky and J. P. Ulrich, Phys. Rev. 109, 1243 (1998).
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Fig. 1. The
Figure Caption:
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to Harris, et al.
agreement with the results herein reported.
The data of Johnson, et al. are in good
solid line simply connects data points. The open circles are due
for a given proton energy is dependent upon target thickness.
v(pin)cr total cross section. The cross section value
The
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TARGET: 226mg/cm2 (AV) V ON PI
n tendimento delle
traitement and co
thinkimakasini yaration de
Les contenitoring
CROSS SECTION (mb)
قفسه سینوسیله
ESTIMATED
RESOLUTION
-
I
1.5
1.7
1.9
2.1
2.3
LABORATORY PROTON ENERGY AT TARGET CENTER (MeV)
v5(pen) Cp54 Average Cross Section as a
Function of Proton Energy.
END
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DATE FILMED
9/ 24/65





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