^(209)Fr的能级结构研究

Level Structure in ^(209)Fr

利用能量为 90— 1 0 5MeV的16 O束流 ,通过197Au( 16 O ,4n)反应研究了2 0 9 Fr的高自旋态能级结构 .进行了γ射线的激发函数、γ γ延迟符合及γ射线的角分布测量 .首次建立了由 2 1条γ射线构成的2 0 9Fr的能级纲图 ,其中包括一个半寿命为 ( 52± 2 0 )ns的同质异能态 .基于2 0 9Fr与2 0 8Rn低位能级结构的相似性 ,用一个h9/ 2 价质子与2 0 8Rn激发态的弱耦合解释了2 0 9Fr的低位能级结构 .

The high-spin states of 209 Fr have been studied in the 197 Au( 16 O,4n) 209 Fr reaction at 16 O energies from 90 to 105 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions,γ-γ-t coincidences and γ-ray angular distributions were performed with 4 BGO(AC)HPGe detecters. A level scheme for 209 Fr with 21 γ rays was established for the first time,including a high-spin isomer with a measured half-life of (52±20)ns. Comparing with the low-lying level structure in 208 Rn,it may conclude that the low-lying levels in 209 Fr are formed by coupling the h 9/2 proton to the neutron hole excitations in 208 Rn. Thus,negative parities could be assigned tentatively to the low-lying states. The nucleus 209 Fr,with four valence neutron holes and five valence protons outside the closed-shell nucleus 208 Pb,also presents a competition between neutron-hole excitations and proton excitations in its low-lying level spectrum. Additionally,it should be pointed out that the higher-lying level structure in 209 Fr does not follow the excitation pattern of 208 Rn. We will pursue shell model calculations to interpret the level structure in 209 Fr.