Low-energy magnetic dipole response in 56Fe from high-resolution electron scattering

Abstract

The 56 Fe(e, e ) reaction has been studied for excitation energies up to about 8 MeV and momentum transfers q 0.4-0.55 fm −1 at the Darmstadt electron linear accelerator (DALINAC) with kinematics emphasizing M1 transitions. Additional data have been taken for q 0.8-1.7 fm −1 at the electron accelerator NIKHEF, Amsterdam. A PWBA analysis allows spin and parity determination of the excited states. For M1 excitations, transition strengths are derived with a DWBA analysis using shell-model form factors. The resulting B(M1) strength distribution is compared to shell-model calculations employing different effective interactions. The form factor of the prominent low-lying M1 transition at 3.449 MeV demonstrates its dominant orbital nature. It represents a major part of the scissors mode in 56 Fe.

Experiments on multiphonon states with proton–neutron mixed symmetry in vibrational nuclei

“…It dominates the M1 excitation strength distribution up to about 7 MeV [151,152]. Shell model calculations point to an orbital character of the M1 matrix element [152]. Gamma-ray transitions between that 1 + state and the two fragments of the proposed one-phonon 2 + 1,ms have not been observed so far.…”

“…The nucleus 56 Fe features a low-lying 1 + state at 3448 keV excitation energy. It dominates the M1 excitation strength distribution up to about 7 MeV [151,152]. Shell model calculations point to an orbital character of the M1 matrix element [152].…”

Magnetic dipole excitations ofCr50

“…As expected [13][14][15][16], this state is characterized by a strong M 1 transition to the ground state. The theoretical analysis [1,9,12] indicates that the 1 + sc in this mass region is of a mixed (orbital + spin) character, although with a dominant orbital contribution. Shellmodel calculations [9] demonstrate a considerable dependence of the description on a subtle balance of different effects such as equilibrium deformation, pairing, interaction parameters, etc.…”

“…Open-shell f p-shell nuclei are particularly important in this activity [9][10][11]. Description of these nuclei is rather * Electronic address: hari.vecc@gmail.com,hpai@ikp.tu-darmstadt.de complicated because here deformation and pairing effects come to play.…”

Weak Interaction processes in core-collapse supernova

“…A separation of spin and orbital pieces is further facilitated by the fact that the orbital part is strongly related to nuclear deformation [31]. For example, the scissors mode [32], which is the collective orbital M 1 excitation, has been detected in well-deformed nuclei like 56 Fe [33]. Thus one can expect that in spherical nuclei the orbital M 1 response is not only energetically well separated from the spin part, but also strongly suppressed.…”