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Note on high resolution measurements with a tandem accelerator
N U C L E A R I N S T R U M E N T S AND METHODS
Ix3 0973) 603-604; ©
NORTH-HOLLAND
P U B L I S H I N G CO.
NOTE ON HIGH R E S O L U T I O N M E A S U R E M E N T S WITH A T A N D E M ACCELERATOR* E. G. BILPUCH, F. O. PURSER, J. D. MOSES, T. D. HAYWARD +, H. W. NEWSON
Duke University and Triangle Universities Nuclear Laboratory, Durham, N.C., U.S.A. G . E . MITCHELL, D. A. OUTLAW and R. O. NELSON
North Carolina State University, Raleigh, N.C., U.S.A. and TUNL, Durham, N.C., U.S.A. Received 2 July 1973 The installation of a direct extraction negative ion source has led to significant improvements in high resolution measurements with a tandem accelerator. The intensities of both the experimen-
tal and associated (control) proton beams have increased by an order of magnitude; the overall measured resolution was improved to 425 eV.
In a r e c e n t a r t i c l e 1) w e d e s c r i b e d a s y s t e m w h i c h removed beam energy fluctuations from the interaction energy of the target. This system utilized an u n c h a r g e d c o n t r o l b e a m a s s o c i a t e d w i t h gas s t r i p p i n g o f t h e H i o n in t h e h i g h v o l t a g e t e r m i n a l o f a t a n d e m V a n d e G r a a f f . T e s t s o f this s y s t e m i n d i c a t e d t h a t it w a s possible to achieve overall e x p e r i m e n t a l energy spreads
o f ~ 600 eV f o r p r o t o n e n e r g i e s f r o m 2.0 t o 15.0 M e V . Using the charge exchange ion source then available, high resolution beam currents on target were limited t o less t h a n 0 . 4 / ~ A a n d t h e n e u t r a l b e a m c o m p o n e n t w a s u s u a l l y less t h a n 0.050/~A. T h e s e i n t e n s i t i e s w e r e adequate to d e m o n s t r a t e the feasibility of the m e t h o d but were too small to allow any extensive excitation function measurements. A d i r e c t e x t r a c t i o n n e g a t i v e i o n s o u r c e h a s since been installed which provides much larger high
* Work supported in part by the U.S. Atomic Energy Commission. t Now at Los Alamos National Laboratory 300
I
,
,
t
,
[
. S
i
i
,
i
I
54Fe (p, p) 54Fe
165 ° AE =q-25 eV
160 ° AE
= 625
eV
2OO to c~
E
,j
2D
b I©©
3.225
3.235 Ep (MeV)
3225
3.230 Ep ( M e V )
3.235
Fig. I. Differential cross section for elastic scattering of protons from 54Fe near a J" = 5/'2+ resonance at Ep = 3.229 MeV. The d.ata on the right were obtained with the high resolution system described in ref. 1. The resolution function used to obtain the fit shown was strongly asymmetric; the effective resolution width was 625 eV (fwhm). The data on the left were obtained with the direct extraction source and the high resolution system. The fit shown was obtained with a symmetric, gaussian resolution function and a resolution width of 425 eV (fwhm). Note that the improvement in the peak-to-valley ratio is greater than the fractional improvement in the resolution: the maximum observed cross section is a strongly non-linear function of the resolution width. 603
604
E . G . BILPUCH et al.
resolution b e a m currents. Target b e a m currents in excess o f 5.0 p A and neutral control b e a m currents greater than l p A are now routinely available. The isolated 5/2 + resonance in 55Co at a proton energy o f 3.229 MeV which was reported in reference 1 has been restudied to determine the effect of the new ion source upon a t t a i n a b l e resolution. A c o m p a r i s o n with the previously r e p o r t e d work is shown in fig. 1. The fits to b o t h o f these measurements were m a d e with a multi-level R matrix code in which the only u n k n o w n for this particular resonance is the experimental resolution. It is obvious from the figure that the newer d a t a on the left o f the figure exhibits far superior resolution. The original d a t a on the right required an a s y m m e t r i c resolution function with a net fwhm o f 625 eV. The newer d a t a as shown has been r e p r o d u c e d reasonably well with a gaussian resolution function
with a fwhm o f 425 eV. The relatively large a s y m m e t r y in the resolution function for the original d a t a can p r o b a b l y be attributed to straggling effects in the charge exchange gas o f the source. The high resolution system has since been used for a high resolution study o f the 1/2 + a n a l o g u e resonance in 92Mo at a p r o t o n energy of 5.3 MeV 2) and the feasibility o f high resolution excitation function measurements over extended portions o f the t a n d e m energy range has been demonstrated. References 1) T. G. Dzubay, E. G. Bilpuch, F. O. Purser, J. D. Moses, H. W. Newson and G. E. Mitchell, Nucl. Instr. and Meth. 101 (1972) 407. 2) E. G. Bilpuch, J. D. Moses, F. O. Purser, H. W. Newson, D. A. Outlaw, R. O. Nelson and G. E. Mitchell (to be published).
Ix3 0973) 603-604; ©
NORTH-HOLLAND
P U B L I S H I N G CO.
NOTE ON HIGH R E S O L U T I O N M E A S U R E M E N T S WITH A T A N D E M ACCELERATOR* E. G. BILPUCH, F. O. PURSER, J. D. MOSES, T. D. HAYWARD +, H. W. NEWSON
Duke University and Triangle Universities Nuclear Laboratory, Durham, N.C., U.S.A. G . E . MITCHELL, D. A. OUTLAW and R. O. NELSON
North Carolina State University, Raleigh, N.C., U.S.A. and TUNL, Durham, N.C., U.S.A. Received 2 July 1973 The installation of a direct extraction negative ion source has led to significant improvements in high resolution measurements with a tandem accelerator. The intensities of both the experimen-
tal and associated (control) proton beams have increased by an order of magnitude; the overall measured resolution was improved to 425 eV.
In a r e c e n t a r t i c l e 1) w e d e s c r i b e d a s y s t e m w h i c h removed beam energy fluctuations from the interaction energy of the target. This system utilized an u n c h a r g e d c o n t r o l b e a m a s s o c i a t e d w i t h gas s t r i p p i n g o f t h e H i o n in t h e h i g h v o l t a g e t e r m i n a l o f a t a n d e m V a n d e G r a a f f . T e s t s o f this s y s t e m i n d i c a t e d t h a t it w a s possible to achieve overall e x p e r i m e n t a l energy spreads
o f ~ 600 eV f o r p r o t o n e n e r g i e s f r o m 2.0 t o 15.0 M e V . Using the charge exchange ion source then available, high resolution beam currents on target were limited t o less t h a n 0 . 4 / ~ A a n d t h e n e u t r a l b e a m c o m p o n e n t w a s u s u a l l y less t h a n 0.050/~A. T h e s e i n t e n s i t i e s w e r e adequate to d e m o n s t r a t e the feasibility of the m e t h o d but were too small to allow any extensive excitation function measurements. A d i r e c t e x t r a c t i o n n e g a t i v e i o n s o u r c e h a s since been installed which provides much larger high
* Work supported in part by the U.S. Atomic Energy Commission. t Now at Los Alamos National Laboratory 300
I
,
,
t
,
[
. S
i
i
,
i
I
54Fe (p, p) 54Fe
165 ° AE =q-25 eV
160 ° AE
= 625
eV
2OO to c~
E
,j
2D
b I©©
3.225
3.235 Ep (MeV)
3225
3.230 Ep ( M e V )
3.235
Fig. I. Differential cross section for elastic scattering of protons from 54Fe near a J" = 5/'2+ resonance at Ep = 3.229 MeV. The d.ata on the right were obtained with the high resolution system described in ref. 1. The resolution function used to obtain the fit shown was strongly asymmetric; the effective resolution width was 625 eV (fwhm). The data on the left were obtained with the direct extraction source and the high resolution system. The fit shown was obtained with a symmetric, gaussian resolution function and a resolution width of 425 eV (fwhm). Note that the improvement in the peak-to-valley ratio is greater than the fractional improvement in the resolution: the maximum observed cross section is a strongly non-linear function of the resolution width. 603
604
E . G . BILPUCH et al.
resolution b e a m currents. Target b e a m currents in excess o f 5.0 p A and neutral control b e a m currents greater than l p A are now routinely available. The isolated 5/2 + resonance in 55Co at a proton energy o f 3.229 MeV which was reported in reference 1 has been restudied to determine the effect of the new ion source upon a t t a i n a b l e resolution. A c o m p a r i s o n with the previously r e p o r t e d work is shown in fig. 1. The fits to b o t h o f these measurements were m a d e with a multi-level R matrix code in which the only u n k n o w n for this particular resonance is the experimental resolution. It is obvious from the figure that the newer d a t a on the left o f the figure exhibits far superior resolution. The original d a t a on the right required an a s y m m e t r i c resolution function with a net fwhm o f 625 eV. The newer d a t a as shown has been r e p r o d u c e d reasonably well with a gaussian resolution function
with a fwhm o f 425 eV. The relatively large a s y m m e t r y in the resolution function for the original d a t a can p r o b a b l y be attributed to straggling effects in the charge exchange gas o f the source. The high resolution system has since been used for a high resolution study o f the 1/2 + a n a l o g u e resonance in 92Mo at a p r o t o n energy of 5.3 MeV 2) and the feasibility o f high resolution excitation function measurements over extended portions o f the t a n d e m energy range has been demonstrated. References 1) T. G. Dzubay, E. G. Bilpuch, F. O. Purser, J. D. Moses, H. W. Newson and G. E. Mitchell, Nucl. Instr. and Meth. 101 (1972) 407. 2) E. G. Bilpuch, J. D. Moses, F. O. Purser, H. W. Newson, D. A. Outlaw, R. O. Nelson and G. E. Mitchell (to be published).