investigating the subshell closure at n=34
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J. J. Valiente Dobón (INFN-LNL, Italy) A. Obertelli (CEA, Saclay, France) D. Sohler (ATOMKI, Hungary)
A. Algora (CSIC, Valencia) and the PRESPEC Collaboration
Investigating the subshell closure at N=34
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Overview
• Physics Motivation– Knockout 54,55Sc– (p,p’) neutron rich Ti isotopes.
• Experimental details• Beam time request
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Nuclei in the fp shell
TiSc
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Indication of shell gapsEnergies and B(E2) values
B(E2) valuesEnergy
N=28
N=32
Energies and B(E2) values are complementary to study in detail shell evolution.
34 KB3G: A. Poves, et al., Nucl. Phys. A (2001).
GXPF1A: M. Honma et al., Phys. Rev. C (2002); Eur. Phys. J. A (2004).
50Ca
52Ca
54Ca
Ene
rgy
N=34
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N=34 subshell gap
T. Otsuka et al., PRL95 232502 (2005)
Monopole effect of the tensor interaction in shell evolution
NeutronProton
f7/2
f5/2
p1/2
•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?
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What is know in the region?
D. Napoli et al., Journal of Physics: Conference Series 49 (2006) 91.
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)
Vanadium isotopes
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What is known in the region?
P. Maierbeck et al., Phys. Lett. B 675 (2009) 22.
•Semi-inclusive momentum distribution to the gs of 55Ti
•The data established the ground state of 55Ti is 1/2- in agreement with GXPF1A.
Titanium isotopes
•Beta decay of 56Sc populate
56Ti.
•Beta –delayed γ ray at 1127 keV assigned 2+ → 0+ in 56Ti
•Midway between GXPF1 and KB3G predictions.
S.N. Liddick et al., PRL92, 072502 (2004)
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What is known in the region?
f7/2p3/2f5/22
p3/2f5/22
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)
Scandium, calcium isotopes
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What is known in the region?
M. Rejmund et al., PRC76 021304(R) (2007)
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.
Calcium isotopes
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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).
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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.
54Sc are known two states: 110 keV (7 ± 5μs) and 247 keV (β decay)
55Sc no excited states known
3/2-
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Titanium isotopes, mass deformation
•Use of global optical potentials•Proton deformation known from B(E2) – Mp
2=B(E2)•Obtain mass deformation from inclusive cross section measurement (p,p’)
•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
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Experimental details
•Primary beam 86Kr at 400MeV.A – Primary target 1.6 mg/cm2 9Be
•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
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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 (H2 vs 9Be : 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.
H2 target
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Knockout 54Ti →53Sc
3/2-
Neutron contribution from the sd shell → Increase of exclusive σ for excited states
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Beam time request
We considered 1010pps
Reaction Cluster HECTOR52Ti(p,p’) 520 23054Ti(p,p’) 2400 115056Ti(p,p’) 310 140
1p-2p AGATA HECTOR
54Sc 2000 940
55Sc 630 280
We will apply for 6 days of beam time
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• 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:• nucleus core can be excited• Possible multiple scattering INCL4, developed by J.Cugnon, A.Boudard
ref: Phys. Rev. C66 (2002)
Cross section calculations
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• 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
Cross section calculations
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Cr(p,p’) case
N. Aoi et al., PRL102, 012502 (2009)
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Optical potential for 46,48,50Ti
100MeV proton elastic scattering
Woo et al., PRC29, 794 (1984)
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Effective charges fp shell
Lifetimes isotones 51Sc and 50Ca
•Ti isotopes not well reproduced either with IS or IS+IV effective charges
•Recent work suggests orbital dependence
PRL102, 242502 (2009)
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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 transitionmatrices 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.
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Titanium isotopes
IS: εn=0.5 εp=1.5
IS+IV: εn=0.8 εp=1.15
A. Poves, et al., Phys. Rev. C 72, 047302 (2005).
•Staggering in the B(E2) not well reproduced (IS, IS+IV)•Not exclusive for models