Kanungo Rituparna, Chiba Masami, Iwasa Naohito, Nishimura Shunji, Ozawa Akira, Samanta Chhanda, Suda Toshimi, Suzuki Takeshi, Yamaguchi Takayuki, Zheng Tao, Tanihata Isao
RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan.
Phys Rev Lett. 2002 Apr 8;88(14):142502. doi: 10.1103/PhysRevLett.88.142502. Epub 2002 Mar 22.
The longitudinal momentum (P(axially)) distributions of one- and two-neutron removal fragments ((21,22)O) of 23O from the reaction with a C target at 72 A MeV have been measured for the first time using a new direct time-of-flight method with nearly full acceptance for the breakup fragments. The unexpectedly narrow width of 21O ( 115 +/- 34 MeV/c in FWHM) is consistent with two neutrons occupying the 2s(1/2) orbital in 23O. This indicates modification of core (22O) structure for neutron halo-like sd shell nuclei near the drip line. This also suggests the lowering of the s orbital providing a justification for the N = 16 magic number.
首次使用一种新的直接飞行时间方法，对在72 A MeV下与碳靶反应产生的(^{23}O)的单中子和双中子移除碎片（((^{21,22}O))）的纵向动量（(P(轴向))）分布进行了测量，该方法对破裂碎片几乎具有完全接受度。(^{21}O)出人意料的窄宽度（半高宽为115±34 MeV/c）与两个中子占据(^{23}O)中的(2s_{1/2})轨道一致。这表明在滴线附近类似中子晕的sd壳层核的核心（(^{22}O)）结构发生了改变。这也暗示了s轨道的降低，为N = 16幻数提供了一个理由。
