Investigating the subshell closure at N=34 J. J. Valiente Dobón (INFN-LNL, Italy) A. Obertelli (CEA, Saclay, France) D. Sohler (ATOMKI, Hungary) A. Algora (CSIC, Valencia) and the PRESPEC Collaboration
Physics Motivation Knockout 54,55Sc (p,p’) neutron rich Ti isotopes. Experimental details Beam time request Overview
Nuclei in the fp shell Ti Sc
Indication of shell gaps Energies and B(E2) values Energy B(E2) values Energies and B(E2) values are complementary to study in detail shell evolution. N=28 N=32 N=34 54Ca Energy 52Ca 50Ca KB3G: A. Poves, et al., Nucl. Phys. A (2001). 34 GXPF1A: M. Honma et al., Phys. Rev. C (2002);Eur. Phys. J. A (2004).
f5/2 p1/2 f7/2 Proton Neutron N=34 subshell gap Monopole effect of the tensor interaction in shell evolution T. Otsuka et al., PRL95 232502 (2005) • Posible subshell closure between p3/2-p1/2 and f5/2 • Atraction between the f7/2 and f5/2 • Does 54Ca present N=34 subshell?
What is know in the region? Vanadium isotopes N=32 N=34 The experimental data in comparison with the Shell Model calculations suggest the N=32 subshell gap for 55V but there is no evidence for N=34 for the 57V (N=34) D. Napoli et al., Journal of Physics: Conference Series 49 (2006) 91.
What is known in the region? Titanium isotopes • Beta decay of 56Sc populate56Ti. • Beta –delayed γ ray at 1127 keV assigned 2+ →0+in 56Ti • Midway between GXPF1 and KB3G predictions. • Semi-inclusive momentum distribution to the gs of 55Ti • The data established the ground state of 55Ti is 1/2- in agreement with GXPF1A. P. Maierbeck et al., Phys. Lett. B 675 (2009) 22. S.N. Liddick et al., PRL92, 072502 (2004)
2 pf7/2np3/2f5/2 2 np3/2f5/2 What is known in the region? Scandium, calcium isotopes 52Sc 51Ca States with predominant νf5/2 predict that the p1/2-f5/2 energy difference might be smaller that the one predicted by GXPF1A. Nevertheless this does not rule out the possible N=34 shell gap, since the change in the gap still gives good description of 54Ca. B.Fornal et al., PRC77, 014304 (2008)
What is known in the region? Calcium isotopes A SM interpretation of the experimental levels shows that the energy spacing between the p1/2 and f5/2 is almost constant up to 52Ca, and when extrapolated to 53,54Ca shows that N=34 might not be a magic number. M. Rejmund et al., PRC76 021304(R) (2007)
Beyond mean field and N=34 Beyond mean field: variation after projection effects were considered as well as simultaneous projection of angular momentum and particle number for the Gogny force. These results support a N =32 shell closure and predict the nonexistence of a shell closure at N=34 T.R. Rodriguez and J.L. Egido PRL99, 062501 (2007).
Investigating the N=34 with knockout We propose the study of the neutron-rich Z=21 isotopes 54,55Sc in order to disentangle the evolution of πf7/2 –νf5/2 monopole tensor interaction, that might give rise to the subshell closure N=34. 3/2- 54Sc are known two states: 110 keV (7 ± 5μs) and 247 keV (β decay) 55Sc no excited states known
Titanium isotopes, mass deformation • We propose to extract the mass deformation in 52,54,56Ti via (p,p’) • A final 25% uncertainty is expected for the final mass distribution • Inclusive total cross section already tells us about the neutron proton deformation • Use of global optical potentials • Proton deformation known from B(E2) – Mp2=B(E2) • Obtain mass deformation from inclusive cross section measurement (p,p’)
Experimental details • Primary beam 86Kr at 400MeV.A – Primary target 1.6 mg/cm29Be • Standard FRS setting on 56Ti + AGATA + LYCCA0 + H2 target • Rate S2 ~ 105 Hz • Knockout: Glauber-type and beyond Glauber cross section calculations give the inclusive cross sections: • σ(1p) ≈ 12 mb, σ(2p) ≈ 0.3 mb • Inelastic scattering: ECIS code σ(p,p’)≈ 1mb
H2 target • Advantages of a pure H2 target • both knockout and (p,p’) • “no” carbon-induced background • less neutron-induced background in spectra • minimal energy loss for a given thickness (H2vs9Be : 4) optimal statistics with preserved Doppler correction • CEA-Saclay LH2 target • dedicated to PRESPEC and fast beam campaigns • pure liquid hydrogen target (20 degrees Kelvin) • thickness from 5 mm to >100 mm / radius of 35 mm • free environment around the target / 100 m Mylar Prototype 100 mm-long, 15-mm radius • G-PAC 37 (october 2009) • a parasitic-beam experiment / A. Obertelli et al.
Knockout 54Ti →53Sc 3/2- Neutron contribution from the sd shell → Increase of exclusive σ for excited states
Beam time re quest We considered 1010pps We will apply for 6 days of beam time
Cross section calculations INCL4, developed by J.Cugnon, A.Boudardref: Phys. Rev. C66 (2002) • intranuclear cascade (INCL4) and evaporation (ABLA) • Semi-classical treatment: path of each particule is known • Consistent approach for both hydrogen and heavy-ion induced knockout Beyond Glauber approximation: • nucleuscorecanbeexcited • Possible multiple scattering
Cross section calculations • Monte-Carlo:100000 events • 22 reactions compared with large panel of projectile, target and energies (from 50 AMev to 1 AGeV) • Agreement within a factor of 2 Calculations by C. Louchart, CEA Saclay
Cr(p,p’) case N. Aoi et al., PRL102, 012502 (2009)
Optical potential for 46,48,50Ti 100MeV proton elastic scattering Woo et al., PRC29, 794 (1984)
Effective charges fp shell Lifetimes isotones 51Sc and 50Ca PRL102, 242502 (2009) • Ti isotopes not well reproduced either with IS or IS+IV effective charges • Recent work suggests orbital dependence
Investigating the Ti isotopes (p,p’) • The (p,p') study you can deduce the nuclear mass instead of the nuclear charge: In common nuclei neutron and proton transition matrices are similar due to strong p-n correlation. • The inelastic scattering depends on the p and n deformation lengths (for a given optical model parameters) • The p deformation parameter δp~sqrt(B(E2)) • Therefore we can obtain the δn from the cross section measured • The result is model dependent: potential parameters, radius • A final 25% uncertainty is expected for the final neutron deformation length • The cross section is 1mb if we consider similar deformations for n and p and 12mb if the neutron deformation is as large as expected by Grodzin’s rule.
Titanium isotopes IS: εn=0.5 εp=1.5 • Staggering in the B(E2) not well • reproduced (IS, IS+IV) • Not exclusive for models IS+IV: εn=0.8 εp=1.15 A. Poves, et al., Phys. Rev. C 72, 047302 (2005).