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Bistirlich, J.; Crowe, K. M.; Parsons, A.S.L.; Skarek, P.; Truoel, P.

doi:10.1103/physrevlett.25.689

Cited by 40 publications

(6 citation statements)

References 19 publications

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“…The spin-flip transitions to low-lying unnatural-parity states show up in the ^Bei spectrum. The ^Bei spectrum is consistent with the data obtained for the C^C,'^N) reaction at 70 MeV/nucleon [11] which also has a spin selectivity of A5' = l. Indeed, the known 2 ~ component of the SDR [8,12,13] is clearly seen at Ex =4.37 MeV in the ^Bei spectrum. It is very interesting to note that broad structures are observed at Ex ==7.…”

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confidence: 89%

“…This peak has been reported to include the transitions to the 2~ (4.37 MeV) and 4" (4.52 MeV) states [15,18]. The former state has been assigned as the 2 " component of the SDR [8,12,13]. Observed Psf for the peak at Ex =4,5 MeV was found to be almost unity, from which we confirm that the peak consists predominantly of spin-flip transitions to the 2" (4.37 MeV) and 4" (4.52 MeV) states.…”

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Relative strength (ΔS=1)/[(ΔS=0)+(ΔS=1)] of isovector spin excitations in the high-lying resonance region ofC12

et al. 1991

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The relative strength (A5' = 1)/[(A5'=0)4-(A5'==1)] of isovector spin excitations, P^u in the highlying resonance region of '^C was investigated with the (^Li,''Be) reaction at EL =*26 MeV/nucleon and ^L =0° by separately measuring the (^Li,^Beg.s.) and (''Li,^Beo.43Mev) reaction channels with the ^Be-/ coincidence technique. The relative strength Psf was derived up to an excitation energy of 18 MeV in '^B and found to have a constant value of 0.4-0.5 for the continuum irrespective of excitation energy and 0.5 for the isovector dipole resonance centered at Ex =7.6 MeV. PACS numbers: 25.7aEf, 24.30.Cz, The relative strength (A5' = 1)/[(A5'=0) + (A5' = 1)] of spin excitations, P^u is defined aswhere a{/S.S =0) and G{/S.S = I) denote the cross sections resulting from AS'^O and A5' = l spin transfers in nuclei, respectively. Measurements of Fsf provide important information on the nuclear spin-isospin response function. So far, for isovector excitations, Psf has been investigated with the spin-flip probability, 5yvA^, observed by using polarized protons, especially, in the ^ji) reaction [1]. The relative strength Psf is directly related to 5' yvyv [2] aswhere a is the spin-flip probability for AS = 1 transitions and is expressed as a combination of Clebsch-Gordan coefficients [3,4]. Thus, the (p,Jt) reaction has been an excellent spectroscopic tool with AT^ = -1 for wellresolved states and isolated resonances. However, for excitations in a continuum where states excited via various values of AL, A/, and AS coexist, a nuclear structure model is needed in order to derive Psf from ^' yvA' , because a in Eq.(2) depends on AL and AJ as well as AS [3]. Therefore, in order to provide definite information on Psf for the continuum containing overlapping resonances, another tool is necessary, in which no nuclear structure model need be included. The (^Li,'^Be) reaction provides, independent of the nuclear structure model, the relative strength Psf even for the continuum and overlapping resonances. In this reaction, ^Be ejectiles are populated in either the ground state (y~;^Beo) or the first excited state (y ~,^;c=0.43 MeV; ^Bei) (ejectile excitation). Under the assumption of dominance of a one-step reaction process, the (^Li, ^Beo) reaction proceeds through either A5'=0 or 1, and the (^Li,^Bei) reaction proceeds predominantly through AS = 1 [5,6]. We have shown that these two reaction channels are separately measured by using a ^Be-/ coincidence technique [7]. Magnitudes of the A5=0 and AS = 1 excitations can be derived from transitions to a high-lying resonance region as well as discrete states by comparing the cross sections for the ^Beo and ^Bei reaction channels. Therefore, the (^Li,^Be) reaction is an unambiguous, ATz = -^\, probe for obtaining Psf, with typically better energy resolution than the (p,Ji) reaction because ^Be ejectiles may be detected by a magnetic spectrograph.In this Letter, we report on a measurement of the relative strength of isovector spin excitations in the continuum and giant resonance regions of ...

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confidence: 89%

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confidence: 99%

Relative strength (ΔS=1)/[(ΔS=0)+(ΔS=1)] of isovector spin excitations in the high-lying resonance region ofC12

et al. 1991

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“…9 Specifically, collective nuclear excitations are expected as final states of both reactions ( 1) and, (2), but are only observable. directly in ( 1).…”

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“…In -order to explain the total n1uon capture rate in 16 0, it was originally proposed that collective states were excited in process (2). 1° Further experi1nental evidence for such excitation has been meager and necessarily indirect.…”

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Photon Spectra from Radiative Absorption of Pions in Nuclei

et al. 1972

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“…Neutrons from the ground-state decay of the collective excitations observed in the Berkeley experiment are expected at energies of ~1 and ~4 MeV. 4 The 1-MeV neutrons are inaccessible to us as our neutron detection efficiency decreaces rapidly below 1.7 MeV. This limitation also prevents us from estimating the fraction of neutrons attributable to evaporation which should predominate below ~ 1 MeV.…”

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Radiative Pion Capture byC12

et al. 1972

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ENERGY 0.5 (MeV) 1.0 100 200 300 400 CHANNEL FIG. 2. Spectrum of electrons coincident with photons of ~ 75 keV. The data bars correspond to N±^M 9The dashed curve shows the shape of the " singles" spectrum observed with the same source, which consisted of a few milligrams of TlNO s powder spread over an area of 3 cm 2 .is in distinct contrast to the results of Goldman et alJ for other nuclides in this region. In the high-geometry measurements of Howe and Lan-ger, 2 coincidence summing between conversion electrons and j3 rays would provide a contribution consistent with the nonstatistical shape reported for the ground-state transition.The neutron-photon angular-correlation and energy spectrum of neutrons from radiative pion capture by carbon are presented and provide new evidence for excitation of a J 1 * = 1" axial-vector collective mode. Asymmetry in the angular correlation increases with neutron energy and is accounted for by direct neutron emission.The spin-isospin structure of the nuclear giant dipole resonance can be studied by radiative pion capture. 1 The capture rate is dominated by the same axial-vector operator that appears in muon capture 2 and in transverse electromagnetic interactions. 3 Thus these processes complement each other with pion and muon capture exciting the AT e = -1 analog states.A recent measurement 4 of the high-energy photon spectrum from radiative pion capture at rest by 12 C has disclosed resonances in 12 B at 4.8 and 8.2 MeV with widths of 0.45 and 1.1 MeV, respectively. The 4.8-MeV peak can be associated with the 19.4-MeV complex observed by electroexcnation of 12 c. 5,6 For a momentum transfer appropriate to pion capture (-120 MeV/c), this complex is dominated by the J* -2" giant magnetic quadrupole excitation. The resonance at 8.2 MeV corresponds to an excitation energy of 23.3 MeV in 12 C and may be due to excitation of a J 71 " = 1" axial-vector collective mode. This interpretation is supported by a high-resolution electroexcitation experiment on carbon, 6 where evidence was found that this spin-isospin mode is at 22.7 MeV, rather than at 25 MeV as suggested by particlehole calculations. 3 The energy spectrum of neutrons from radiative pion capture will also reflect the nature of the capture process. 7 Furthermore, the n-y angular correlation can be observed. This correlation will be isotropic when a large number of highly excited states participate leading to exaporation neutrons, strongly peaked near 180° when the neutrons are emitted directly, and symmetric about 90° when isolated nuclear states predominate. In the latter case information on the spin of the excited states can be obtained.To explore these possibilities experimentally we have measured the n-y angular correlation following radiative capture of stopped pions by 12 C, together with the energy spectrum of neutrons. Neutrons between 1.7 and 28 MeV were 108

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Radiative Pion Capture inC12

Cited by 40 publications

References 19 publications

Relative strength (ΔS=1)/[(ΔS=0)+(ΔS=1)] of isovector spin excitations in the high-lying resonance region ofC12

Relative strength (ΔS=1)/[(ΔS=0)+(ΔS=1)] of isovector spin excitations in the high-lying resonance region ofC12

Photon Spectra from Radiative Absorption of Pions in Nuclei

Radiative Pion Capture byC12

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