J. Kaneko

Ground-state band of the neutron-rich transuranium nucleus 250Cm154

The ground-state band of the neutron-rich transuranium nucleus 250 Cm was established up to spin 12 by in-beam γ-ray spectroscopy using the two-neutron transfer reaction with a 248 Cm target and a 162 MeV 18 O beam. Deexcitation γ rays in 250 Cm were identified by selecting the kinetic energies of 16 O particles using Si Δ E – E detectors. The moment of inertia of 250 Cm 154 is considerably smaller than that of 248 Cm 152 , which supports the existence of the deformed subshell closure at N =152 in Cm isotopes.

In-beam γ-ray study of the neutron-rich nuclei 240U, 246Pu, and 250Cm produced by the (18O, 16O) reaction

We have measured deexcitation γ rays in the neutron-rich nuclei of 240U, 246Pu, and 250Cm produced by the (18O, 16O) two-neutron transfer reactions, in coincidence with the 16O particles using Si ΔE−E detectors. The γ rays in these nuclei were identified by selecting the kinetic energies of 16O particles, which correspond to the excitation energies in the residual nuclei below the neutron separation energies. The ground-state bands of 240U, 246Pu, and 250Cm were established up to 12+ states and the Kπ = 0− octupole band of 240U was established up to 9− states. The systematics of the moments of inertia of the ground-state bands for actinide nuclei shows that the deformed subshell closure at N = 152 is sustained for 96Cm isotopes and that it disappears for 94Pu isotopes.

Performance of the Belle silicon vertex detector

The performance of the Silicon Vertex Detector (SVD) in the Belle experiment is reviewed based on 6.8 fb/sup -1/ of data taken between October 1999 and July 2000. The main purpose of the SVD is to make precise measurements of the B decay vertex position, which are essential for the observation of CP asymmetries. Excellent vertex resolution and a good detection efficiency are required for the SVD. Basic performance parameters such as signal pulse height, noise, strip yield and intrinsic resolution are reported. The SVD performance parameters which are directly related to physics analysis such as track matching efficiency, impact parameter resolution and vertex resolution are also shown.

Numerical Studies on Dynamic Behavior of Air-Water Cross Flow Between Two Circular Interconnected Channels

The objective of this paper is to investigate the dynamic behavior of air-water fluid transfer across gap regions between fuel rods in LWR bundles, referred to as cross flow. A computational multifluid dynamic simulation of the cross flow is conducted by using an analysis code based on a three-dimensional two-fluid formulation plus an interface-tracking method. This code is applied to two-phase flows inside a single vertical cylindrical tube in order to perform wall friction sensitivity studies with a model that accounts for velocity gradients across boundary layers flowing on walls. Numerical analyses of two-phase cross flow across the gap region of two circular interconnected channels showed that the calculated turbulent mixing rates are in relatively good agreement with the results of experimental tests in the case of increased wall friction at low void fractions. On the other hand, at high void fraction, the agreement is not as good. Spectrum analyses of the calculated mixing velocities of both air and water across the gap region and the calculated differential pressure between channels showed a strong correlation between them. The present numerical study could demonstrate the following observations shown in previous experimental studies. (1) The fluctuation in differential pressure between channels is attributed to the passing of large bubbles through a channel. (2) The fluctuation in differential pressure primarily induces turbulent mixing phenomena.

Level-1 silicon vertex detector trigger at Belle

We present a newly developed fast trigger system that uses the silicon vertex detector (SVD) for the Belle experiment at the KEKB energy-asymmetric e/sup +/e/sup -/ collider. It is designed to issue the trigger with a latency of 1.85 /spl mu/s for the Belle central trigger system (GDL). The primary purpose of the SVD trigger is to reduce beam-induced background events by requiring tracks that come from the interaction point. The system receives trigger signals from VA1TA front-end integrated circuits, which read out signals on the silicon-strips. SVD tracks are constructed with them in combination with the trigger information of the central drift chamber (CDC), which is located outside the SVD. Performance of the SVD trigger is evaluated with collision data.