Investigation of Compound Elastic Scattering Near Isobaric Analog Resonances with Polarized Protons

Kretschmer, W.; Graw, G.

doi:10.1103/physrevlett.27.1294

Cited by 41 publications

(3 citation statements)

References 9 publications

(4 reference statements)

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“…We have used both methods: First we have applied the method of Henneck and Graw, 11 where a combination of the normalized variances of cr and uA yields the relative direct contribution y D to the reaction without any assumption about the effective number of spin channels iV eff 0 We then checked the consistency of this method by describing the extracted cP l with the optical potential obtained by fitting the artifically energy-averaged observable (cx(0)A(0)) which contains no compound-nucleus contribution. 10 A target nucleus 30 Si was chosen because in the energy region of interest (JE P = 9.8 MeV) all final levels of the competing (P?P')> (P,n), and (p,a) compound -nucleus reactions were known and therefore the Hauser-Feshbach cross section a HF could be calculated explicitly without the introduction of free parameter s c Finally, W aa was calculated as the ratio a CE /a HF 0…”

Section: W Kretschmer and M Wanglermentioning

confidence: 99%

Model-Independent Determination of the Compound-Elastic Enhancement Factor in a Polarized-Proton Fluctuation Experiment

Kretschmer¹,

Wangler²

1978

Phys. Rev. Lett.

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fits of the folding model with no density dependence. Using the obvious relation Ar m 2 =Zr p 2 + Nr n 2 and the value 1 r^Ca) =3.386 fm one obtains r"( 48 Ca) -r,( 48 Ca) =0.17± 0.10 fm. Table II compares the present results with previous ones, all of which were obtained using simple analytic functions for the nuclear-matter distribution. If the uncertainties obtained in the present work are typical of the uncertainties that should have been quoted for previous results, then all seemingly conflicting results are in agreement with each other. We thank Professor Dr. G. Schatz and Professor Dr. P. Brix for their encouraging interest and the cyclotron crew for good cooperation. An unambiguous and model-independent separation of direct and compound elastic cross section was performed by a simultaneous fluctuation analysis of the cross section and the analyzing power for the reaction 30 Si(/> pol ,£ 0 ) 30 Si. The compound elastic cross section was calculated by means of Hauser-Feshbach theory without any adjustable parameters. Comparison of experiment with the calculation results in a compound-elastic enhancement factor of 2.09±0.14 for this strong-absorption, many-channel case.In this Letter we report definitive experimental evidence for a factor-of-2 enhancement of the compound elastic cross section (a CE ) over the Hauser-Feshbach 1 cross section (a HF ) in a reaction with many strongly absorbing channels. This so-called compound-elastic enhancement factor W acc =(j CE /a m has been the subject of considerable theoretical efforts. 2 " 6 In the many-channel, strong-absorption limit most theorists now agree that W aa should be two irrespective of the number of direct reaction channels. Previous attempts to determine W aa experimentally have been performed only with unpolarized protons yielding a large model-dependent error. 7 In the best of these experiments Ernst, Harney, and Kotajima 7 have confirmed the effect of channel self-correlation (W cca > 1) but their values of W aa ranged from 1.6 to 3.5. Thus a clear statement about the validity of the underlying compound-nucleus theories was not possible. Since the enhancement factors derived from these theories are widely used, 8 * 9 it is important to have a much more critical test.A model-independent separation of a CE and a DI (DI indicating the direct part of the cross section), necessary for an accurate determination of W«a> can be performed by measuring both the differential cross section a and the analyzing power A (9) either in an energy-averaged experiment 10 or in an Ericson fluctuation experiment 11 on a spin-0 target nucleus. We have used both methods: First we have applied the method of Henneck and Graw, 11 where a combination of the normalized variances of cr and uA yields the relative direct contribution y D to the reaction without any assumption about the effective number of spin channels iV eff 0 We then checked the consistency of this method by describing the extracted cP l with the optical potential obtained by fitting the artifically energy-average...

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Section: W Kretschmer and M Wanglermentioning

confidence: 99%

Model-Independent Determination of the Compound-Elastic Enhancement Factor in a Polarized-Proton Fluctuation Experiment

Kretschmer¹,

Wangler²

1978

Phys. Rev. Lett.

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“…The requirement of maximizing the CN cross section in the channels coupled through the isobaric analogue resonance is met by nuclei in the vicinity of mass 90, for which comparatively few neutron channels are open. Several experimental groups have measured the angular distribu tion, analyzing power, spin-flip probability, spin-flip asymmetry, and cross-correlation functions fo r the outgoing protons (Kretschmer & Graw 1971, Albrecht et al 1973, Graw et a1 1974, Blanke et a1 1975, Davis et al 1975, Clement et al 1977, Haynes et al 1976, Feist et al 1977, King & Slater 1977. Typically, the cross section is written in the form 2.3, and two different fits to the data are performed: one is based on the expression for <a;b N > where DI are neglected, and one is based on Equation 6.3.…”

Section: Intermediate Structurementioning

confidence: 99%

Untitled

1979

Annu. Rev. Nucl. Part. Sci.

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“…For elastic proton scattering from 88 Sr and 90 Zr near the d 5/2 IAR at E p = 5.07 and 4.707 MeV, preliminary fits based on visual agreement have been presented previously. 3 In this Letter, the results of a x 2 fit procedure are reported for these IAR and also for IAR's observed with the spin-1" target 89 Y for the doublet (d 5/2 ®V) with spin 2" and 3** at £^ = 4.822 and 5.023 MeV, respectively, and with 92 Zr for the spin-| + (d 5/2 ) 3 ground-state analog at E p = 5.044 MeV. A detailed description of these experiments is given elsewhere.…”

mentioning

confidence: 99%

Investigation of Internal Isospin Mixing of Isobaric Analog Resonances from Polarized-Proton Experiments

Graw

Kretschmer

1973

Phys. Rev. Lett.

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Investigation of Compound Elastic Scattering Near Isobaric Analog Resonances with Polarized Protons

Abstract: A rather model-independent separation of direct and compound elastic cross sections has been obtained from the analysis of elastic scattering of polarized protons near the lowest d 5 / 2 isobaric analog resonances in 89 Y and 91 Nb.

Cited by 41 publications

References 9 publications

Model-Independent Determination of the Compound-Elastic Enhancement Factor in a Polarized-Proton Fluctuation Experiment

Model-Independent Determination of the Compound-Elastic Enhancement Factor in a Polarized-Proton Fluctuation Experiment

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Investigation of Internal Isospin Mixing of Isobaric Analog Resonances from Polarized-Proton Experiments

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