In-beam  -ray spectroscopy of neutron-rich nuclei in the uranium region through the heavy-ion transfer reaction ISHII Tetsuro Japan Atomic Energy Agency JAEA H. Makii, M. Asai, H. Koura, K. Tsukada, A. Toyoshima, M. Matsuda, T. Shizuma, S. Ichikawa Tokyo Institute of Technology S. Shigematsu, T. Kohno National Defense Medical Colledge A. Makishima Komazawa Univ. J. Kaneko, M. Ogawa Osaka Univ. I. Hossain, Ibaraki Univ. H. Toume JAEA-Tokai Tandem Accelerator

Where are deformed / spherical shell gaps ? high-L (k 17/2 ) orbitals ? ► In-beam  -ray spectroscopy using heavy-ion transfer reactions U, 244 Pu, 248 Cm targets; ( 18 O, 16 O), ( 18 O, 20 Ne) selection of reaction channels using Si  E-E ► First  -ray measurements of 236 Th, 240,242 U, 246 Pu, 250 Cm - establishment of ground-state bands up to 12 + states ► Systematics of E(2 1 + ) in the neutron-rich U region - disappearance of N=152 deformed shell gap at 94 Pu - possibility of the spherical shell gap at N=164 for 256 U 164 Nuclear structure at the largest neutron number

 - stability More Neutron-rich than the  -stability ( 18 O, 16 O) 2n stripping ( 18 O, 20 Ne) 2p pickup Ds 184 T 1/2 ~300y

18 O beam Cm target (0.8mg/cm 2 )  3mm, 45kBq 4 Si  E-E telescopes  E: 75  m thickness 6 Ge detectors  eff = 0.2 MeV 1.3 MeV Experimental setup

O N C B Be F Si E-  E PLOT 248 Cm( 18 O, 16 O) 250 Cm; 2neutron-stripping  E ∝ AZ 2 /E E-  E Plots &  -ray spectra of 250 Cm 154  ~0.5mb

248 Cm( 18 O, 16 O) 250 Cm; 2neutron-stripping Complete selection of  -rays in residual nuclei by measuring outgoing particles - Z, A, and kinetic energies - Si E-  E PLOT gate E x of 250 Cm < S n E-  E Plots &  -ray spectra of 250 Cm 154

Level schemes of 240 U, 246 Pu and 250 Cm by ( 18 O, 16 O)

Level Schemes of 236 Th and 242 U by ( 18 O, 20 Ne)

if deformed shell gap exists, pairing energy gap (  ) moment of inertia (E 2+ ) Five new data cranking model Experiment Calculation Sobiczewski et al., PRC 63(2001) Moments of inertia and N=152 deformed shell

Narrower energy gap at N=152 for 94 Pu Experiment 245 Pu 151 1/2[620] 9/2[734] present in-beam  -ray data combined with the (d,p) data at ANL in ’70s

Possibility of spherical shell closure of N=164 in the U region pairing energy gap (  ) moment of inertia (E 2+ ) U 164 is spherical ？ Minimum Deformed shell gap N=126

S.P.E. calculated by Koura-Yamada potential (modified Woods-Saxon)

Summary First measurements of deexcitaion  -rays in 5 neutron-rich nuclei in the U region ( 18 O, 16 O) 2n-strippping; 240 U, 246 Pu and 250 Cm up to 12 +  ~0.5mb ( 18 O, 20 Ne) 2p-pickup ; 236 Th and 242 U up to 10 + and 8 +  ~  b - complete selection of  -rays by Z and M by measuring the outgoing particles with Si  E-E 250 Cm 154 : first in-beam  -ray study beyond N=152 Disappearance of N=152 deformed shell gap for 94 Pu - from the systematics of the E(2 1 + ) energies and from the single particle levels in 245 Pu 151 Possibility of the spherical shell closure of N=164 - supported by the calculation using the Koura-Yamada potential 240 U: T. Ishii et al., Phys. Rev. C 72 (2005) (R) 250 Cm: T. Ishii et al., J. Phys. Soc. Jpn. 75 (2006)