Lifetime measurements of excited states in neutron-richAr44,46populated via a multinucleon transfer reaction

Abstract

Lifetimes of low-lying excited states of the neutron-rich 44,46 Ar nuclei, populated via multinucleon transfer reactions, are measured by means of the differential recoil distance Doppler shift method. The extracted electromagnetic transition probabilities are compared with previous intermediate-energy Coulomb-excitation measurements and with large-scale shell-model calculations. The increase in the deduced B(E2; 2 + → 0 +) transition probability from 44 Ar to the closed-shell nucleus 46 Ar contradicts the earlier results of Coulomb-excitation experiments. Shell-model calculations using different effective interactions agree with the new measured values.

Coulomb excitation ofCa44andAr46

“…A B(E2; 0 is derived for 46 Ar, in relative to the one of 473 (20) [22]. Since the latter value has a very large error bar, results remain almost compatible within 2σ .…”

Single-particle structure atN=29: The structure ofAr47and first spectroscopy ofSGade1, Tostevin2, Bader3 et al. 2016Phys. Rev. CSelf Cite15050View full textAdd to dashboardCite

“…While some observables, for example those re-lated to the masses of the Ar isotopes around N = 28 [13], are well described, calculations appear to over-predict the B(E2) excitation strength to the first 2 + state [2,[14][15][16]. This result is not without controversy, on the experimental side, where an excited-state lifetime measurement yields higher collectivity, in agreement with the shell model [17], but is at odds with several Coulomb excitation measurements that consistently yield a lower B(E2) value [2,14,16]. Using an inverse kinematics 46 Ar(d, p) reaction, states in 47 Ar with significant singleneutron spectroscopic strength were measured [18] and were used in the development of the SDPF-U SM effective interaction [11].…”

Low-lying2+states generated bypn-quadrupole correlation andN=28shell quenching

“…The single-particle states more than 7.5 MeV above the chemical potential are not shown, due to the cutoff energy in the pairing channel [33]. 48 48 Ca, although they have large discrepancy [8,49].…”

“…The lifetime measurement [8] experiments [5,6], B(E2) ∼ 196 (218) e 2 fm 4 . In all cases we tested, the low-lying strengths are less than 200 e 2 fm 4 , and hence supports the smaller value of B(E2) reported by Coulomb excitation.…”

“…One of the interesting examples is the N = 28 shell gap which is known to be quenched in the vicinity of 44 S and which has been given considerable experimental [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and theoretical attention [22][23][24][25][26][27][28][29][30][31][32]. Since the the orbital angular momenta of f 7/2 and p 3/2 differ by two, the quench of the N = 28 shell gap will lead to the strong quadrupole correlation of neutrons.…”