Chang-Bum Moon

A new AMS facility in Korea

Abstract A new accelerator mass spectrometry (AMS) facility has been installed at the Inter-University Center for Natural Science Research Facilities (ICNSRF) of Seoul National University. In this report, an overview of the facility with its current status and prospects for the future will be presented.

Progress in sample preparation system for the Seoul National University AMS facility

Abstract The Seoul National University AMS Laboratory has developed a sample preparation system for AMS measurement. Graphite targets are prepared via the reduction of carbon dioxide over a Fe catalyst. The carbon dioxide gases are produced by combusting pretreated organic samples with CuO and silver wire in a sealed quartz tube. Each combustion produces ca. 2 mg of graphite that is loaded into the target. So far we have been successful in extracting and analyzing 12C− current up to 10 mA in stable condition by Cs sputtering onto the targets.

Energy transfer between host and dopant molecules in blue organic light-emitting devices

Blue organic light-emitting devices were fabricated with an activator of 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl doped into the various host materials such as N,N′-bis-(1-naphtyl)-N,N′-diphenyl-1,1-biphenyl-4,4′-diamine; 4,4′-bis(2,2′-diphenylyinyl)-1,1′-biphenyl; 2-methyl-9,10-di(2-naphthyl) anthracene; and 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene to investigate optical properties of blue light emission in the host-dopant system. By spectroscopic analysis based on multi-peak fits to the emission spectra, we found that energy transfer between the host and dopant molecules have a strong correlation with key features; current density, luminous efficiency, and color index for the devices. Among the present dopant-host systems, the TPBi molecule was found to be the best molecule as a host material for our devices. In contrast, the DPVBi host induced a complex excimer (electromer) leading to a shoulder spectrum with a longer wavelength emission. It was found that the electromer significantly affects the optical and electrical properties of the device.

White Organic Light-Emitting Diodes With Different Order of RGB-Emitting Layers

To achieve the emissive layers in white organic light-emitting diode (WOLED) for the three primary colors, DCJTB doped in Alq3, C545T doped in Alq3, and BCzVBi doped in MADN were applied for red, green, and blue emissive layer, respectively. By stacking all the red, green, and blue emissive layers in a single device, WOLED devices with the color coordinates close to (0.33, 0.33) were successfully fabricated. The structure of the blue–green–red (BGR) type of the three primary color WOLED device was NPB(700 Å)/MADN:BCzVBi-13%(210 Å)/Alq3:C545T-2%(30 Å)/Alq3:DCJTB-2%(60 Å)/Alq3(300 Å)/Liq(20 Å)/Al(1000 Å). Its maximum luminance and luminous efficiency were 25,680 cd m−2 and 3.79 cd A−1, as well as its white color coordinate was (0.32, 0.31) at 7 V. The structure of blue–red–green (BRG) type of the three primary color WOLED device was NPB(700 Å)/MADN:BCzVB-13%(210 Å)/Alq3:DCJTB-2%(30 Å)/Alq3: C545T-2%(60 Å)/Alq3(300 Å)/Liq(20 Å)/Al(1000 Å). Its maximum luminance and luminous efficiency were 26,010 cd m−2 and 4.95 cd A−1, as well as its white color coordinate was (0.33, 0.33) at 7 V. Both devices were successfully induced closer to the ideal white emissive lighting source, and three different peaks at 480 nm, 512 nm, and 616 nm could be confirmed at red, green, and blue region in electroluminescence (EL) spectra.

Spectroscopic study of white organic light-emitting devices with various thicknesses of emissive layer

White light-emitting devices based on a donor-acceptor structure were fabricated in order to investigate the dependence of the optical properties of white light emission on the thickness variance (15, 20, 25, and 30u2009nm) of the emissive layer. The emissive layer has a donor-acceptor system with the host 4,4′,4′′-tris(carbasol-l-nyl)triphenylamine molecule doped with 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) and 5,6,11,12-tetraphenylnaphtacene (Rubrene) molecules for blue and yellowish-green light activators, respectively. The characteristics of current density were analyzed by using a power function of applied field, J=σlEl+1 and the characteristic exponential function, J=J0(e(V-Vd)/V0-1). Through spectroscopic analysis, we obtained three physical quantities governing the device performance: 1) an effective conductivity, 2) a threshold potential, and 3) a characteristic potential barrier, which are associated with the trap-charge limited concentration in the bulk layer, the energy gap of t...

Energy measurement of 50 MeV proton beam with a NaI(Tl) scintillator

Abstract Energy measurement of 50 MeV proton beam produced on the AVF MC-50 Cyclotron was conducted using a detector telescope with a NaI(Tl) scintillator as an E counter. Protons of various energies, elastically and inelastically scattered from the 12 C target nucleus were measured at four different angles of 35°, 40°, 50° and 55°. We applied the chi-square method to determine the beam energy, which showed a well defined minimum chi-square corresponding to a beam energy of 49.6 ± 2.3 MeV at the 68% confidence level. Also the light output response of NaI(Tl) to proton energies between 31 and 44 MeV is linear within 0.5 MeV and is in good accord with the recent result of Romero et al. [Nucl. Instr. and Meth. A 301 (1991) 241].

Heavy-ion reactions of Cu with 135 MeV/nucleon 12C

Abstract Target residues from the interaction of copper with 135 MeV/nucleon 12C ions have been studied by off-line γ-ray spectroscopy. Cross sections, average forward ranges, and forward-to-backward ratios were measured for 44 products. The data were used to obtain the isobaric-yield distribution, the mean-linear-momentum transfer, and the mean excitation energy. The results are compared with the previous ones from low- and high-energy experiments. The plateau of the recoil-velocity distribution observed at lower intermediate energies disappears at the present energy. The mean excitation energy approaches the limiting value at the present energy. The cross sections of spallation products with mass numbers between 2 3 A target and A target are similar to those observed at relativistic energies, which suggests limiting fragmentation.

Rotational bands in115Sb

High-spin states of115Sb were studied by inbeamγ-ray spectroscopy using the89Y (29Si, 2pn) fusionevaporation reaction at a beam energy of 108 MeV. The experiments includedγ-γ coincidence and directional correlation of oriented nuclei (DCO) ratio measurements using six BGO Compton suppressed Ge detectors. An intruderΔJ=2 rotational band has been identified for the first time and it is interpreted as the h11/2 proton coupled to a two particle-two hole (2p − 2h) deformed state of the114Sn core. A ΔJ=1 rotational band based on the 2p − 1h, π{g72/2⊗g92/−1}, configuration has been extended to the 29/2+ state at an excitation energy of 5241 keV.

High-spin states of odd-odd156Ho

High spin states in the nucleus156Ho have been studied via the fusion-evaporation reaction140Ce(19F,3nγ)156Ho at the beam energy of 82 MeV.γ-γ coincidences, Eγ, Iγ and excitation functions have been measured. With two rotationally-aligned bands identified as π[h11/2]ν [i13/2], we found two new bands with a signature splitting, whose structure is believed to arise from either ν[h9/2] or ν[f7/2] coupled to π[h11/2]. Our placement of γ rays belonging to these new bands suggests that the previously known level scheme should be corrected. We also found many new low-energy γ rays in the low excitation energy. As compared to154Ho, the present nucleus with two more neutrons becomes more collective, and shows well-observed rotationally-aligned bands with a clear signature splitting.

Role Of Hexadecupole Deformation In The Shape Evolution Of Neutron-rich Nd Isotopes

A new isomer with ms half-life was observed in 160Nd at RIBF, RIKEN Nishina Center by using in-flight fission of 238U beam and a cluster-type Ge detector array, EURICA. The experimental results and a PSM calculation indicate that the isomer in 160Nd is a 2 quasi-particle excitation of nneutrons with a configuration of n1/2[521]x7/2[633] as the case in other N = 100 isotones. The E(4+)/E(2+) ratio of the ground-state band, 3.29, shows the 160Nd is well deformed and the ground band has a rotational nature. The 4- excitation of 160Nd showed an increase in energy byx18 100 keV compared to that of 162Sm as predicted by the PSM calculation. A PSM calculation was performed by changing input beta_4 value and confirmed that the large hexadecupole deformation in Nd was responsible for the increase of the isomer energy.