Theoretical description of dipole resonance?s (DR) in electroexcitation cross sections of open shell nuclei ⁴⁴ Ca and ²⁶Mg was performed in a ?particle-core coupling? (PCC) version of Shell Model.

Both nuclei under investigation have non-filled valence shells. The basic configuration of DR calculations for both nuclei were built on those states of residual nuclei which have non vanishing spectroscopic factor of pick-up reaction. The main difference in direct reaction spectroscopy for nuclei with closed and open shells manifests in a quantity of residual nuclei states displayed in pick-up reactions. For example in ⁴⁴ Ca(p,d) ⁴³ Ca reaction about 20 states of ⁴³ Ca are observed. The energies of residual states with noticeable specrtoscopy extend from 0 up to 11 Mev. For ²⁶Mg the range of residual nuclei energies is almost the same as for ⁴⁴ Ca. Dipole resonances in ⁴⁴ Ca and ²⁶Mg have two isospin branches.

The investigation of electroexitation cross sections for dipole resonances include calculation of transverse (E1) and longitudinal (C1) form factors. The first one at momentum transfer q=E_exc represents photoexcitation cross section.

The results of E1 and C1 form facrors estimation in PCC version of SM could be summed up as follows:

1. The width of resonance?s in open shell nuclei is larger than in closed shell nuclei.
2. The configuration splitting clearly seen in closed shell nuclei as two peaks formed by transition from valence and more deep shells is broken in open shell nuclei. The transitions from non filled shell and upper filled one are mixed.
3. The T_> isospin branch in ²⁶Mg exhausts about 35% of the E1 strength. The T_> (T=3) branch of ⁴⁴Ca electrodisintegration has only about 10% of total strength.