Isospin symmetry in nuclear transitions from pion scattering

Peterson, R. J.

doi:10.1103/physrevc.48.1128

Cited by 18 publications

(14 citation statements)

References 72 publications

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“…For 10,12,14,16,18 C isotopes, measured values are taken from Refs. [12,23,26,[37][38][39]. The dashed lines are to guide the eye and reflect that M 2 p practically becomes constant and M 2 n shows a linear increase above N = 14.…”

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confidence: 99%

“…Furthermore, the available experimental M 2 n values of 16,20 C (98 ± 17 and 292 ± 52 fm 4 ) are very close to the shell model calculations with the reduced effective charges (139 and 260 fm 4 ). We also note that unlike in the C isotopes, the linear increase of M 2 n breaks in the O isotopes because of the N = 14 subshell closure (M 2 n = 42.8 ± 2.2, 186 ± 10, 248 ± 63, and 75 ± 43 fm 4 for 16,18,20,22 O, respectively [21,39,[44][45][46][47]). The fact that the polarization charges have decreased to less than half of the standard values indicates that the coupling of the valence neutrons to the core has become weaker, or in other terms, the valence neutrons have decoupled to some extent from the nuclear core.…”

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Persistent decoupling of valence neutrons toward the dripline: Study ofC20byγspectroscopy

et al. 2009

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The very neutron-rich nucleus 20 C has been investigated by inelastic scattering on 208 Pb and liquid hydrogen targets. Through distorted wave analysis, the reduced electric quadrupole transition probability B(E2; 0 + g.s. → 2 + 1 ) < 18.4 (stat) e 2 fm 4 and the neutron transition probability M 2 n = 292 ± 52 (stat) fm 4 have been derived. A simple shell model calculation has shown a need for a factor of about 0.4 decrease of the normal polarization charges to elucidate the results. This is interpreted as a decoupling of the valence neutrons from the nuclear core in carbon isotopes heavier than 14 C.Nuclei close to the dripline are especially important in nuclear structure studies and have been extensively investigated because their properties significantly differ from those of the stable isotopes. One of the most exotic phenomena is the neutron halo, which is formed by the extremely weakly bound neutrons that decouple from the nuclear core [1] leading to the appearance at low excitation energies of a soft dipole mode [2]. A few years ago, the decoupling of more strongly bound neutrons in heavy carbon and boron isotopes was reported [3-6], which was observed as a reduction of the quadrupole polarization charge of the neutrons. This suppression of the polarization charge was associated with the extended distribution of the valence neutrons [7-9] detected in reaction cross section measurements [10]. This might also be accompanied with the change of the structure of the giant quadrupole resonance in neutron-rich nuclei [7,8,11].Recently, the lifetime of the 2 + 1 state in 16 C has been remeasured, and the decoupling phenomenon has been questioned [12]. In the present paper, we report on a study of the neutron and proton transition strengths and polarization charges investigated by inelastic scattering processes in the heavy carbon isotope 20 C, lying next to 19 C which shows halo characteristics in its ground state [13][14][15]. Our aim is to provide evidence that the decoupling phenomenon exists in the carbon isotopic chain.The experiment was carried out at RIKEN Nishina Center, where a 40 Ar primary beam of 63 MeV energy and 700 pnA intensity was delivered to a 0.2 mm thick 181 Ta production target in which various isotopes were created via the fragmentation process. The RIKEN isotope separator (RIPS) [16] analyzed the momentum and mass of the ejectiles. For purifying purposes, an aluminum wedge degrader of 221 mg/cm 2 thickness was put at the momentum dispersive focal plane (F1). The fragment separator was operated at its full 6% momentum acceptance in order to achieve a 20 C beam intensity as high as around 10 particles per second (pps). The resultant cocktail beam also included 17 B, 19 C, 21 N, and 22 N isotopes with a total intensity of 100 pps. The identification of these incident beam constituents could be performed on an event-by-event basis using energy loss ( E), time-of-flight (TOF), and magnetic rigidity (Bρ) information [17]; however, only TOF and E were used in the real runs since the parallel plate...

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Persistent decoupling of valence neutrons toward the dripline: Study ofC20byγspectroscopy

et al. 2009

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“…leading to the lowest 3 − state in 40 Ca and the lowest 2 + and 3 − states in 42,44,48 Ca and 54 Fe were computed by the DWBA method using the zero-range code DWUCK4 due to Kunz [11]. The motivation is that these are good vibrational states [12] and strongly excited in the inelastic scattering of pions. One therefore expects under a strong absorption situation a simple relationship between the elastic S-matrix elements and the inelastic ones [13] so that the extent of applicability of the conventional DWBA method and in effect the local optical model may be tested.…”

Section: Inelastic Scatteringmentioning

confidence: 99%

“…Deformation parameters are extracted in each case and shown in table 4. Calculations were normalized to the data in the same angular range as used in [6,7,12]. Fits to the shape of the data in general are clearly better with parameter set 1, with our preferred value of r u near 1.5 fm.…”

Section: Inelastic Scatteringmentioning

confidence: 99%

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Local optical model studies of pion-nucleus scattering

Akhter

Sultana

Gupta

et al. 2001

J. Phys. G: Nucl. Part. Phys.

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Local optical model calculations have been carried out for elastic and inelastic scattering of π ± from 40,42,44,48 Ca and 54 Fe at pion energies atop, above and below the resonance. The elastic studies resulted in considerable ambiguities in the parameter values. Using the best-fit parameters, zero-range DWBA calculations have been carried out for inelastic scattering of π ± leading to the lowest 2 + and 3 − states of these nuclei. Transition strengths extracted from inelastic scattering, compared with known values, remove the ambiguity found for elastic scattering, making the simple model useful for other reaction studies with pions.

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