Late Quaternary aeolian dust input variability on the Chinese Loess Plateau: inferences from unmixing of loess grain-size records

IEECAS SKLLQG

Experimental study of the beta-delayed neutron decay of N-21

The first spectroscopic study for the beta decay of N-21 is carried out based on beta-n, beta-gamma, and beta-n-gamma coincidence measurements. The neutron-rich N-21 nuclei are produced by the fragmentation of the E/A=68.8 MeV Mg-26 primary beam on a thick Be-9 target and are implanted into a thin plastic scintillator that also plays the role of beta detector. The time of flight of the emitted neutrons following the beta decay are measured by the surrounding neutron sphere and neutron wall arrays. In addition, four clover germanium detectors are used to detect the beta-delayed gamma rays. Thirteen new beta-delayed neutron groups are observed with a total branching ratio of 90.5 +/- 4.2%. The half-life for the beta decay of N-21 is determined to be 82.9 +/- 7.5 ms. The level scheme of O-21 is deduced up to about 9 MeV excitation energy. The experimental results for the beta decay of N-21 are compared to the shell-model calculations.

beta-delayed fission of Ac-228

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