Complete Spectroscopy of an Isobaric Analog Resonance with the(e,e′p)Reaction

Abstract

It is demonstrated by the example of the E x 16.28 MeV, J p ; T 1 2 ; 6 state in 90 Zr that a highresolution 90 Zr͑e, e 0 p͒ 89 Y experiment can provide a nearly model-independent full characterization of all relevant spectroscopic properties of an isobaric analog state. The proton angular correlation data and branching ratios determine the total and partial widths into radiative and particle decay channels. A phenomenological wave function is deduced from the form factor. [S0031-9007(97)02985-2] PACS numbers: 24.30. Gd, 25.30.Dh, 27.60.+j The advent of new high-resolution continuous-wave electron beam facilities in nuclear research has, as one of its main purposes, to measure the excitation and deexcitation properties of nuclear levels by coincidence measurements [1]. One major success of such ͑e, e 0 x͒ experiments, where the inelastically scattered electron and the heavy particle x neutron, proton, a particle, etc., are detected, has been the ability to decompose overlapping giant resonance strength of different multipolarities, either from form factor [2][3][4][5] or from angular correlation [6-9] data. Because of the combination of an electromagnetic probe and a background-free response due to the coincidence technique the deduced strengths in terms of sum rules are the most reliable available for stringent tests of nuclear model predictions, and many discrepancies between different experiments in the literature using hadronic probes could be resolved.It has also been advocated that such coincidence experiments should be able to isolate and identify narrow, weak levels buried in the continuum and allow one to determine their decay properties which reveal subtle nuclear structure information. Since one can selectively excite different multipoles by varying the momentum transfer, it has been emphasized that electroexcitation provides a powerful, versatile probe. In this Letter, we report results where we have, for the first time, exploited the full potential of this probe to extract the structural details of a single level of long-standing interest.Black and Tanner [10] were the first to observe a narrow resonance ͑G ഠ 70 keV͒ in the 89 Y͑p, g 0 ͒ reaction at an excitation energy of 16.28 MeV in 90 Zr. This level, located just above the peak of the giant dipole resonance (GDR) has since been the subject of numerous experimental investigations, viz. with the ͑p, p 0 ͒ [11], ͑p, g͒ [12], ͑e, p͒ [13,14] and ͑g, p͒ [15] reactions. The latest information [16] on this nuclear level is summarized in Fig. 1. There, the shaded area represents the GDR with isospin T , 5, which predominantly decays by neutron emission to levels in 89 Zr. The 16.28 MeV state is the isobaric analog (IAS) of a level at 3.160 MeV in 90 Y with spin-isospin quantum numbers J p 1 2 and T 6, respectively. Because of isospin selection rules only decay by proton or g emission is expected for this T . state. So far, one component of this level was deduced [10] to be a p2d 3͞2 particle configuration coupled to the 89 Y ground state wave function,...

Giant Resonances in the Doubly Magic NucleusC48afrom the (e,Strauch1, Neumann-Cosel2, Rangacharyulu3 et al. 2000Phys. Rev. Lett.Self Cite465340View full textAdd to dashboardCite

“…level, and no branches to T , T 0 levels are observed. While the power of the ͑e, e 0 p͒ reaction for the detailed spectroscopy of IAR in heavy nuclei has recently been demonstrated [34], the present results prove that the same also holds for ͑e, e 0 n͒ experiments.…”

Direct-decay properties of giant resonances

“…Assuming that the isobaric analog state exhausts 100% of the Fermi strength, one can express the IVGDR > strength function (corresponding Being motivated by the experimental results of Ref. [16], where one of 1 − IAR in 90 Zr…”

Deuteron Breakup in theH2(e,e′Neumann-Cosel1, Richter2, Schrieder3 et al. 2002Phys. Rev. Lett.Self Cite151160View full textAdd to dashboardCite

“…Further details of the ͑e, e 0 p͒ detection setup can be found in Refs. [14,15]. The kinematic variables are described in the inset of Fig.…”