Ma Ke-Yan

Designing of the 14 MeV neutron moderator for BNCT

In boron neutron capture therapy (BNCT), the ratio of the fast neutron flux to the neutron flux in the tumor (RFNT) must be less than 3%. If a D-T neutron generator is used in BNCT, the 14 MeV neutron moderator must be optimized to reduce the RFNT. Based on the neutron moderation theory and the simulation results, tungsten, lead and diamond were used to moderate the 14 MeV neutrons. Satisfying RFNT of less than 3%, the maximum neutron flux in the tumor was achieved with a three-layer moderator comprised of a 3 cm thick tungsten layer, a 14 cm thick lead layer and a 21 cm thick diamond layer.

High-Spin Level Scheme of 120I

Excited states in 120I are investigated utilizing in-beam gamma-ray spectroscopy following the 114Cd(11B,5n) reaction at 70 MeV bombarding energy. A level scheme is constructed with states up to 9 MeV. The levels are classified into several bands and their possible configurations at low spins are discussed briefly Based on the linking transitions between different bands at higher spins, the excitation energy of the previously reported T1/2 = 53 min isomer is ascertained to be 72 keV. Evidence showing the existence of an isomer at an excitation energy of 6.4 MeV is presented.

Clarification of Confusion in Level Scheme of 124Cs

Low-lying and high-spin states of 124Cs are studied through the 116 Sn(11 B,3n)124 Cs reaction at a beam energy of 45 MeV. Several new linking transitions are observed, including three transitions between the yrast and πh11/2 ⊗ νd3/2 bands and two transitions between the yrast and πh11/2 ⊗ ν(d5/2, g7/2) bands. These transitions fix the excitation energy of the yrast band and its decay path, and confirm the existence of eight E1 linking transitions between the yrast and πh11/2 ⊗ ν(d5/2, g7/2) bands observed before. These E1 linking transitions infer the octupole correlation in Cs. The decay paths of the yrast band are investigated, and discrepancies in the level scheme of 124Cs in the latest two studies are clarified. The reason for the discrepancies is discussed. A new decoupled band is established and temporarily assigned as the unfavored signature partner of πh11/2 ⊗ νd3/2 configuration.

High-Spin States in the Odd-Odd Nucleus 92Nb

High spin states of the odd-odd nucleus 92Nb are investigated using the 82Se (14N, 4n)92Nb reaction at a beam energy of 54 MeV. The level scheme of the 92Nb was extended up to Jπ =(16+) at about 7.3 MeV and Jπ=(21−) at about 9.7 MeV. According to systematic analyses and a comparison with the neighboring nucleus, the higher spin states could be interpreted by the multi-particle excitations in the π(f5/2,p3/2,p1/2,g9/2)⊗ν(p1/2,g9/2,d5/2, g7/2) configuration space.

New high spin level scheme of 87Sr

High spin states of the odd-A 87Sr were populated by the fusion-evaporation reaction 82Se(9Be,4n) 87Sr at a beam energy of 46 MeV. Excited levels of 87Sr have been extended up to an excitation energy of 7.4 MeV at spin 31/2ħ. The coupling of a g9/2 neutron hole to the yrast states of the 88Sr core can account for the low-lying states in 87Sr. The structure of the higher spin states is discussed by analogy with those of the neighboring odd-A N = 49 isotones and possible configurations are proposed.

Doublet bands in 128La and systematic features of energy separation of doublet bands observed in the A∼130 mass region

High spin states of 128La have been studied through the fusion-evaporation reaction 118Sn(14N, 4n)128La at a beam energy of 69 MeV. A positive-parity side band with the same configuration as that of the yrast band has been identified. Moreover, it is noted that the energy separation ΔE(I) = E(I)side − E(I)yrast of all doublet bands reported in odd-odd nuclei in the A~130 mass region exhibit a staggering pattern systematically, and they stagger up at even-spin and stagger down at odd-spin.

Yrast Band in 122I and Band Termination

High spin states of the odd-odd nucleus 122I have been investigated via the fusion-evaporation reaction 116Cd(11B, 5n) at a beam energy of 68 MeV. The yrast band is extended up to Iπ = (29+). The band termination at Iπ = (22+) reported in previous studies is confirmed and interpreted as arising from a shape change from collective prolate to noncollective oblate according to Total-Routhian-Surface (TRS) calculations. In addition, the Iπ=(29+) state is assigned to the [πh11/2(πg7/2)2]23/2-⊗[(νh11/2)3(νd5/2)2]35/2− configuration corresponding to the full alignment of all valance nucleons outside the semi-closed shell.

High-k Structures in 124Cs

High spin states in the odd-odd nucleus 124Cs have been investigated through the fusion-evaporation reaction 116Sn(11B, 3n)124Cs with a beam energy of 45 MeV. A new rotational band is established and assigned as the high-k configuration of πg9/2[404]9/2+⊗νh11/2[523]7/2−. Some structures linking to this band have also been observed. According to the results of the excitation energy systematics, the lowest level of this band is assigned as 9-, and the 8- isomer bandhead has not been observed. Another isomer with a half life of 6.3 s has also been observed with its new decay paths established. Its excitation energy is raised by 79 keV, but its Iπ is not changed.

Magnetic Dipole Band in 113In

High spin states in the odd-A nucleus 113In have been investigated using the reaction 110Pd(7Li, 4n) at a beam energy of 50 MeV. A new positive parity dipole band with the configuration of π(g9/2)−1 ⊗ ν(h11/2)2 ⊗ ν(g7/2)2 is established. The effective interaction V(θ) values of this band have been successfully described by a semiclassical geometric model based on shear mechanism, which show that the dipole band has the characteristics of magnetic rotation. In addition the collective rotational angular momentum for this band is extracted. The results show that the core contribution increases gradually with the increase of the rotation frequency.

High-Spin Structure in Odd-Odd 160Lu Nucleus

The high-spin states of 160Lu are populated by the fusion-evaporation reaction 144Sm(19F,3n)160Lu at beam energies of 90 and 106 MeV. A new level scheme of 160Lu is established. A possible isomeric state based on the πh11/2⊗νh9/2 configuration is observed. The new decoupled band with the configuration of πd3/2[411]1/2+⊗νi13/2[660]1/2+ is established, and the configurations of these similar decoupled bands in the neighboring odd-odd 162−166Lu nuclei are suggested. A positive parity coupled band is assigned as the πd5/2[402]5/2+⊗νi13/2[660]1/2+ configuration.