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Lee, P. S.

Publications and source records attributed to Lee, P. S..

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Isomeric and beta-decay spectroscopy of 173,174 Ho

β-decay spectroscopy of 173,174 Ho (Z = 67, N = 106,107) was conducted at Radioactive Isotope Beam Factory at RIKEN by using in-flight fission of a 345-MeV/u 238 U primary beam. A previously unreported isomeric state at 405 keV with half-life of 3.7(12) μs and a spin and parity of (3/2 + ) is identified in 173 Ho. Moreover, a new state with a spin and parity of 9 - was discovered in 174 Er. The experimental log ft values of 5.84(20) and 5.25(18) suggest an allowed-hindered β decay from the ground state of 174 Ho to the K π = 8 - isomeric state in 174 Er. Configuration-constrained potential energy surface (PES) calculations were performed and the predictions are in reasonable agreement with the experimental results.

150 ≤ A ≤ 189↗
DOE OSTI2018

β - γ and isomeric decay spectroscopy of 168 Dy

Here, this contribution will report on the experimental work on the level structure of 168 Dy. The experimental data have been taken as part of the EURICA decay spectroscopy campaign at RIBF, RIKEN in November 2014. In the experiment, a 238 U primary beam is accelerated up to 345 MeV/u with an average intensity of 12 pnA. The nuclei of interest are produced by in-flight fission of 238 U impinging on Be target with a thickness of 5 mm. The excited states of 168 Dy have been populated through the decay from a newly identified isomeric state and via the beta decay from 168 Tb. In this contribution, scientific motivations, experimental procedure and some preliminary results for this study are presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

94 {beta}-Decay Half-Lives of Neutron-Rich 55Cs to 67Ho: Experimental Feedback and Evaluation of the r-Process Rare-Earth Peak Formation

The β-decay half-lives of 94 neutron-rich nuclei 144$-$151 Cs, 146$-$154 Ba, 148$-$156 La, 150$-$158 Ce, 153$-$160 Pr, 156$-$162 Nd, 159$-$163 Pm, 160$-$166 Sm, 161$-$168 Eu, 165$-$170 Gd, 166$-$172 Tb, 169$-$173 Dy, 172$-$175 Ho, and two isomeric states 174m Er, 172m Dy were measured at the Radioactive Isotope Beam Factory, providing a new experimental basis to test theoretical models. Strikingly large drops of β-decay half-lives are observed at neutron-number N = 97 for 58 Ce, 59 Pr, 60 Nd, and 62 Sm, and N = 105 for 63 Eu, 64 Gd, 65 Tb, and 66 Dy. Lastly, features in the data mirror the interplay between pairing effects and microscopic structure. r-process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system

Wu, J.↗
DOE OSTI2016

Long-lived K isomer and enhanced γ vibration in the neutron-rich nucleus 172 Dy: Collectivity beyond double midshell

The level structure of 172Dy has been investigated for the first time by means of decay spectroscopy following in-flight fission of a 238U beam. A long-lived isomeric state with T1/2 = 0.71(5) s and Kπ = 8- has been identified at 1278 keV, which decays to the ground-state and γ -vibrational bands through hindered electromagnetic transitions, as well as to the daughter nucleus 172Ho via allowed β decays. The robust nature of the Kπ = 8- isomer and the ground-state rotational band reveals an axially-symmetric structure for this nucleus. Meanwhile, the γ -vibrational levels have been identified at unusually low excitation energy compared to the neighboring well-deformed nuclei, indicating the significance of the microscopic effect on the non-axial collectivity in this doubly mid-shell region. The underlying mechanism of enhanced γ vibration is discussed in comparison with the deformed Quasiparticle Random-Phase Approximation based on a Skyrme energy-density functional.

172Dy↗
DOE OSTI2016

A light-stimulated synaptic transistor with synaptic plasticity and memory functions based on InGaZnO{sub x}–Al{sub 2}O{sub 3} thin film structure

In this work, a synaptic transistor based on the indium gallium zinc oxide (IGZO)–aluminum oxide (Al{sub 2}O{sub 3}) thin film structure, which uses ultraviolet (UV) light pulses as the pre-synaptic stimulus, has been demonstrated. The synaptic transistor exhibits the behavior of synaptic plasticity like the paired-pulse facilitation. In addition, it also shows the brain's memory behaviors including the transition from short-term memory to long-term memory and the Ebbinghaus forgetting curve. The synapse-like behavior and memory behaviors of the transistor are due to the trapping and detrapping processes of the holes, which are generated by the UV pulses, at the IGZO/Al{sub 2}O{sub 3} interface and/or in the Al{sub 2}O{sub 3} layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1980

Optimal regulation in systems with stochastic time sampling

An optimal control theory that accounts for stochastic variable time sampling in a distributed microprocessor based flight control system is presented. The theory is developed by using a linear process model for the airplane dynamics and the information distribution process is modeled as a variable time increment process where, at the time that information is supplied to the control effectors, the control effectors know the time of the next information update only in a stochastic sense. An optimal control problem is formulated and solved for the control law that minimizes the expected value of a quadratic cost function. The optimal cost obtained with a variable time increment Markov information update process where the control effectors know only the past information update intervals and the Markov transition mechanism is almost identical to that obtained with a known and uniform information update interval.

Montgomery, R. C.↗
NASA NTRS1978

Simulation of distributed microprocessor-based flight control systems

The aim of the present paper is to demonstrate, within the framework of a digital flight control system, the method of simulating the information exchange between a microcomputer and a supervisory computer, and between microcomputers working on separate control tasks. A gradient technique is described that considers the trade-off between the objectives of the control system and the information exchange requirements.

Lee, P. S.↗
NASA NTRS1977

Information distribution in distributed microprocessor based flight control systems

This paper presents an optimal control theory that accounts for variable time intervals in the information distribution to control effectors in a distributed microprocessor based flight control system. The theory is developed using a linear process model for the aircraft dynamics and the information distribution process is modeled as a variable time increment process where, at the time that information is supplied to the control effectors, the control effectors know the time of the next information update only in a stochastic sense. An optimal control problem is formulated and solved that provides the control law that minimizes the expected value of a quadratic cost function. An example is presented where the theory is applied to the control of the longitudinal motions of the F8-DFBW aircraft. Theoretical and simulation results indicate that, for the example problem, the optimal cost obtained using a variable time increment Markov information update process where the control effectors know only the past information update intervals and the Markov transition mechanism is almost identical to that obtained using a known uniform information update interval.

Montgomery, R. C.↗