Neutron occupancy of the 0d5/2 orbital and the N = 16 shell closure in 24O - Archive ouverte HAL Access content directly
Journal Articles Physics Letters B Year : 2014

Neutron occupancy of the 0d5/2 orbital and the N = 16 shell closure in 24O

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K. Tshoo
  • Function : Author
Y. Satou
  • Function : Author
C.A. Bertulani
  • Function : Author
H. Bhang
  • Function : Author
S. Choi
  • Function : Author
T. Nakamura
  • Function : Author
Y. Kondo
  • Function : Author
S. Deguchi
  • Function : Author
Y. Kawada
  • Function : Author
Y. Nakayama
  • Function : Author
K.N. Tanaka
  • Function : Author
N. Tanaka
  • Function : Author
Y. Togano
  • Function : Author
N. Kobayashi
  • Function : Author
N. Aoi
  • Function : Author
M. Ishihara
  • Function : Author
T. Motobayashi
  • Function : Author
H. Otsu
  • Function : Author
H. Sakurai
S. Takeuchi
  • Function : Author
K. Yoneda
  • Function : Author
J. Gibelin
F.M. Marqués
  • Function : Author
  • PersonId : 941129
N.A. Orr
  • Function : Author
  • PersonId : 940479
T. Honda
  • Function : Author
T. Kobayashi
  • Function : Author
T. Sumikama
Y. Miyashita
  • Function : Author
K. Yoshinaga
  • Function : Author
M. Matsushita
  • Function : Author
S. Shimoura
  • Function : Author
D. Sohler
J.W. Hwang
  • Function : Author
T. Zheng
  • Function : Author
Z.H. Li
  • Function : Author
Z.X. Cao
  • Function : Author

Abstract

One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at Edecay=50±3 keV, corresponding to an excited state in 23O at 2.78±0.11 MeV, as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d -wave neutron knockout, providing support for a Jπ assignment of 5/2+. The associated spectroscopic factor was deduced to be C2S(0d5/2)=4.1±0.4 by comparing the measured cross section (View the MathML source) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0d5/2 orbital is in line with the N=16 shell closure in 24O.The neutron drip-line nucleus 24O, which has been studied extensively in recent years [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13] and [14], is now considered a doubly-closed-shell nucleus. In particular, the high excitation energy of the first 2+ state [7] and small quadrupole transition parameter [14] are strong indicators of an N=16 spherical shell closure. In addition, Kanungo et al. [8] found a large spectroscopic factor – C2S(1s1/2)=1.74±0.19 – for one-neutron knockout from 24O reflecting an almost complete occupancy of the 1s1/2 orbital.In this Letter we report on the spectroscopic factor for d5/2 neutron removal from 24O. The first excited state of 23O, which is neutron unbound [15], [13] and [16], was populated by one-neutron knockout from 24O with a proton target. The excitation energy, cross section, and longitudinal momentum distribution were determined and allowed the 0d5/2 neutron-hole nature of this state to be identified. The large spectroscopic factor deduced for this state is in line with the N=16 shell closure in 24O.The experiment was performed at the RIPS facility [17] at RIKEN. The experimental setup has been described in Refs. [14] and [18], and is depicted in Fig. 1. The secondary 24O beam was produced using a 1.5 mm-thick Be production target and a 95 MeV/nucleon 40Ar primary beam of ∼40 pnA. The average intensity of the 24O beam was ∼4 particles/sec. The momentum of the secondary beam was determined particle-by-particle by measuring the position at the dispersive focus F1 of RIPS with a parallel plate avalanche counter. The energy loss (ΔE ) and time-of-flight (TOF) were measured using 350 μm-thick silicon and 500 μm-thick plastic scintillator detectors, respectively, at the achromatic focus F2. The liquid-hydrogen (LH2) target [19] was installed at the achromatic focus F3. The effective target thickness and the mid-target energy of 24O were 159±3 mg/cm2 and 62 MeV/nucleon, respectively. The 24O beam incident on the target was tracked particle-by-particle by using two multi-wire drift chambers installed just upstream of the target. The target was surrounded by an array consisting of 48 NaI(Tl) crystals (DALI) to detect γ rays from de-excitation of the fragments.
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Dates and versions

in2p3-01090228 , version 1 (12-06-2015)

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Attribution - CC BY 4.0

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Cite

K. Tshoo, Y. Satou, C.A. Bertulani, H. Bhang, S. Choi, et al.. Neutron occupancy of the 0d5/2 orbital and the N = 16 shell closure in 24O. Physics Letters B, 2014, 739, pp.19-22. ⟨10.1016/j.physletb.2014.10.033⟩. ⟨in2p3-01090228⟩
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