Properties of the β-delayed proton decay of ~(146)Ho

The proton-rich isotope 146Ho was produced via the fusion-evaporation reaction 92Mo (58Ni, 3p1n). The β-delayed proton decay of 146Ho was studied by proton-γ coincidence measurements using a He-jet tape transport system. The γ-transitions in 145Tb following the proton emissions were observed, and the β-delayed proton branching ratios to the final states in the grand-daughter nucleus 145Tb were determined. According to the relative branching ratios, the ground-state spin of 146Ho has been proposed and the possible configuration discussed.     

Properties of the β-delayed proton decay of 146Ho

The proton-rich isotope 146Ho was produced via the fusion-evaporation reaction ^92Mo （^58Ni, 3p1n）. The β-delayed proton decay of 146Ho was studied by proton-γ coincidence measurements using a He-jet tape transport system. The γ-transitions in ^145Tb following the proton emissions were observed, and the β-delayed proton branching ratios to the final states in the grand-daughter nucleus ^145Tb were determined. According to the relative branching ratios, the ground-state spin of 146Ho has been proposed and the possible configuration discussed.     

An Implantation and Detection System for Spectroscopy of 22,24Si

A new decay detection system with high detection efficiency and low detection threshold has been developed for charged-particle decay studies, including -delayed proton, decay or direct proton emission from proton-rich nuclei. The detection system was tested by using the -delayed proton emitter 24Si and was commissioned in the decay study of 22Si produced by projectile fragmentation at the First Radioactive Ion Beam Line in Lanzhou. Under a continuous-beam mode, the isotopes of interest were implanted into two double-sided silicon strip detectors, where the subsequent decays were measured and correlated to the preceding implantations by using position and time information. The system allows to measure protons with energies down to about 200 keV without obvious background in the proton spectrum. Further application of the detection system can be extended to the measurements of -delayed proton decay and the direct proton emission of other exotic proton-rich nuclei.     

β-delayed Multi-particle Emission From 31Ar

The β+ decay of 31Ar was investigated in an experiment at the GSI-FRS spectrometer.The ions of interest have been produced in the fragmentation of a 36Ar beam at 880 MeV/nucleon and implanted in a time projection chamber with optical readout. In addition to β -delayed one and two proton emission, for the first time the emission of -delayed 3 protons has been observed. The branching ratio for this decay mode is found to be (0.07 ± 0.02)%.     

Properties of the β-Delayed Proton Decay of 147Er

The β-delayed proton decay of 147Er is studied experimentally using the 58 Ni＋92Mo reaction at a beam energy of 383 MeV. Based on a He-jet apparatus coupled with a tape transport system, the β-delayed proton radioactivities both from the vδl/2 ground state and the vh11/2 isomer in 147 Er are identified by proton-7 coincidence measurements. By analyzing the time distribution of the 4＋ → 2＋-γ transition in the grand-daughter nucleus 146Dy, a half-life of 1.6 ± 0.2s is determined for the Vh11/2 isomer in 147 Er. The half-life for the ground state of 147Er is estimated to be 3.2±1.2 s.     

Beta Decay of Neutron—Rich Nucleus ^208Hg

The β- decaying γ scheme of the neutron-rich nuclide 208Hg has been determined for the first time.The 208 Hg was produced in multi-nucleon transfer reaction taking place in the bombardment of 18O-beam on natural lead target,and the Hg-element products were sepaated with a gas-thermochromatography technique.The γ-ray single and γ-γ coincident spectra were measured.A partial 208 Hg γ scheme was proposed.Twenty-six γ rays were assigned to follow the β- decay of 208Hg.At the same time,a new level structure of the daughter nucleus 208 T1 was constructed,in which three new levels at 1.725MeV.1.652MeV,and 1.362MeV were affirmed.The experimental 208Tl level structure was compared with a shell-model calculation.     

β-decay studies of the neutron-rich ~(18,21)N isotopes

The β-decay studies of neutron-rich 18,21N isotopes have been performed using β-n, β-γ, and β-n-γ coincidence methods. The 18,21N ions were produced by the fragmentation of the 22Ne and 26Mg beams, respectively, on a thick beryllium target. The time of flight of the emitted neutrons following the β-decay of 18,21N was measured by a neutron detector system with wide energy detection range and low-energy detection threshold. In addition, several clover germanium detectors were used to detect the β-delayed γ-r...     

Investigation of the anomaly in $\eta$-photoproduction off the neutron

Quasi-free photoproduction of wmesons off the neutron and off the proton has been studied using a deuterium target and bremsstrahlung photons produced by MAMI-C with incident energies up to 1.5 GeV. The wmesons were detected in coincidence with the recoil nucleons thus a fully exclusive measurement was performed. Preliminary results show a bump-like structure in the excitation function for the neutron close to W ≈ 1675 MeV which is not seen for the proton. Considering the experimental resolution and using a Breit-Wigner fit the width of this structure was approximated below 50 MeV.     

New Levels in ^118Pd Observed in the β Decay of Very Neutron-Rich ^118Rh Isotope

We investigate the β decay of very neutron-rich ^118Rh isotope using on-line mass-separated sources which are produced by applying 25 MeV proton induced symmetric fission of natural uranium at the IGISOL facility. The β-γ and γ-γ coincidence spectroscopy is employed to establish the level scheme of daughter nucleus ^118Pd. Five low-lying new levels are identified for the first time with tentative spin and parity assignments based on the even-mass Pd systematics.     

Observation of a Possible New Isomer in 175Ir

The neutron deficient nuclide 175Ir was produced by irradiation of 146Nd with 210 MeV 35Cl via a fusion-evaporation reaction channel. The reaction products were transported to a low-background location using a helium-jet recoil fast-moving tape-transport system for measurement. The experimental devices and data analysis method are introduced. Based on the decay-curve fitting of the β-delayed γ ray from 175Ir, realized by the least-square method, a new long-lived isomeric state of 175Ir is proposed and briefly discussed.     

Shell-Model Calculations of β Decays in 18N

We investigate β decays of the neutron-rich nucleus ^18 N and the structure of the daughter nucleus ^18 O using the shell model. The reduced transition strengths B（GT） and branching ratios of the/3 decays in ^18 N are calculated in the psd and spsdpf shell spaces with the WBT interaction. The calculations in the two different spaces are compared. The psd calculations obtain a better agreement with the observation of the β-delayed neutron emission, which seems to show that the observed properties of ^18 N and ^18 O are mainly produced by one particle being excited from the p-shell to the sd-shell.     

β-delayed neutron decay of 21N

The β-delayed neutron and γ spectra of neutron-rich nucleus ²¹N using β-γ and β-n coincidence measurements were presented in this paper. Thirteen new neutron groups ranging from 0.28 MeV to 4.98 MeV and with a total branching ratio 88.7±4.2% were observed. One γ transition among the excited states of ²¹O, and four γ transitions among the excited states of ²⁰O were identified in the β decay chain of ²¹N. The ungated half-life of 83.8±2.1 ms was also determined for ²¹N.     

A CVD diamond film detector for pulsed proton detection

A chemical vapour deposition （CVD） diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44% at 5 V/μm with the charge collection distance of 15.9 μm. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo （MC） simulation result. Its plasma time for a pulse with 4.85×10^5 protons is 1l.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 10^13 cm^-2. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection.     

Production and Identification of New Isotope ^265Bh（Z=107）

New Isotope ^265Bh was produced in bombardment of a ^243Am target with 168 MeV 26Mg ions. The experiment was carried out at the Sector Focus Cyclotron of Heavy Ion Research Facility in Lanzhou in 2003. The reaction products were transported and collected by using helium-jet technique and a set of rotating wheel system. Identification was made by observation of correlated a-particles between the new isotope ^265Bh and its ^261Db and ^257Lr daughter nuclei. A parent-daughter searching mode was used to facilitate detection of α-α correlations. A total of four pairs of PIPS detector (200mm^2 active area) were used to measure the kinetic energy of a particles. The a particle energy resolution was about 40 keV for the top detectors and 100 keV for the bottom detectors because of energy degradation in the polypropylene foil.     

ORNL-HRIBF 6GHzECR离子源的最新结果

Experimental studies were conducted to characterize and improve the performance of the flat-B ECR ion source.The emittance of the source was investigated for the first time.The output beam currents of high-charge-states of Ar(q>8)were nearly doubled by increasing the plasma electrode aperture from 4mm to 6mm in diameter.To investigate possible enhancements with broadband microwave radiation,a"white"Gaussian noise generator was employed with a TWT amplifier to generate microwave radiation with a bandwidth of～200MHz.The performance of the flat-B ECR ion source was found to be much better with narrow bandwidth radiation when the source was operated in the flat-B region.However,the ion beam intensities and charge state distributions were improved with the broadband radiation when the source was tuned off the flat-B region.     

Experimental measurement of radiation dose in a dedicated breast CT system

Radiation dose is an important performance indicator of a dedicated breast CT (DBCT). In this paper, the method of putting thermoluminescent dosimeters (TLD) into a breast shaped PMMA phantom to study the dose distribution in breasts was improved by using smaller TLDs and a new half-ellipsoid PMMA phantom. Then the weighted CT dose index (CTDI_w) was introduced to average glandular assessment in DBCT for the first time and two measurement modes were proposed for different sizes of breasts. The dose deviations caused by using cylindrical phantoms were simulated using the Monte Carlo method and a set of correction factors were calculated. The results of the confirmatory measurement with a cylindrical phantom (11 cm/8 cm) show that CTDI_w gives a relatively conservative overestimate of the average glandular dose comparing to the results of Monte Carlo simulation and TLDs measurement. But with better practicability and stability, the CTDI_w is suitable for dose evaluations in daily clinical practice. Both of the TLDs and CTDI_w measurements demonstrate that the radiation dose of our DBCT system is lower than conventional two-view mammography.     

Evolution of downsized crescent-shaped dune in wind tunnel experiment

The migration of a downsized crescent-shaped dune was investigated in a wind tunnel experiment.Quantified upwind influx and vertical oscillation of the sand bed were introduced to modulate the saturation level of the sand flux above the dune surface to affect dune evolution.The evolution was recorded by top-view photography and then abstracted as the evolution of self-defined characteristic quantities using a digital image processing algorithm.The results showed that,in contrast to the case for spanwise quantities,the evolution of streamwise quantities corresponds to a linear increase in the modulation magnitude more positively and in a monotonic and convergent manner.In contrast with quantities on the windward face,the changes in quantities with respect to the horns were nonmonotonic with time and almost uncorrelated with the variation in modulation strength,which reveals the distinctiveness of leeside evolution.     

Improved performance of P3HT：PCBM solar cells by both anode modification and short-wavelength energy utilization using Tb（aca）3phen

The performance of P3HT:PCBM solar cells was improved by anode modification using spin-coated Tb(aca)3phen ultrathin films. The modification of the Tb(aca)3phen ultrathin film between the indium tin oxide(ITO) anode and the PEDOT:PSS layer resulted in a maximum power conversion efficiency(PCE) of 2.99% compared to 2.66% for the reference device, which was due to the increase in the short-circuit current density(Jsc). The PCE improvement could be attributed to the short-wavelength energy utilization and the optimized morphology of the active layers. Tb(aca)3phen with its strong down-conversion luminescence properties is suitable for the P3HT:PCBM blend active layer, and the absorption region of the ternary blend films is extended into the near ultraviolet region. Furthermore, the crystallization and the surface morphology of P3HT:PCBM films were improved with the Tb(aca)3phen ultrathin film. The ultraviolent–visible absorption spectra,atomic force microscope(AFM), and X-ray diffraction(XRD) of the films were investigated. Both anode modification and short-wavelength energy utilization using Tb(aca)3phen in P3HT:PCBM solar cells led to about a 12% PCE increase.     

β-delayed fission of 228Ac

The basic process of an exotic decay mode namely β-delayed fission is simply introduced. The progress status of the study in the world is essentialized. The observation of β-delayed fission of ²²⁸Ac is reported. The radium was radiochemically separated from natural thorium. Thin Ra sources in which ²²⁸Ac was got through ²²⁸Ra →β^－228Ac were prepared for observing fission fragments from β-delayed fission of ²²⁸Ac. They exposed to the mica fission track detectors, and measured by an HPGe γ-ray detector. The β-delayed fission events of ²²⁸Ac were observed and its β-delayed fission probability was found to be (5±2)×10^－12.     

Experimental study on scintillation efficiency of ZnO:In to proton response

Film ZnO:In crystal is a good candidate for a scintillation recoil proton neutron detection system and the response of ZnO:In to protons is a crucial point. The energy response of ZnO:In to mono-energetic protons in the range of 10 keV-8 MeV was measured. The experiment was carried out in current mode, and Au foil scattering was employed, where the forward scattering protons were used for exciting the sample, and the backward scattering protons were used for monitoring the beam intensity. According to the result, the yield of light non-linearly depends on proton energy, and drops significantly when proton energy is low. The scintillation efficiency as a function of proton energy was obtained, which is very useful for researching the scintillation recoil proton neutron detection system.