Monte Carlo Simulation of in situ Gamma-Spectra Recorded by Na I(Tl) Detector in the Marine Environment

To develop a NaI （T1） detector for in situ radioactivity monitoring in the marine environment and enhance the confidence of the probability of the gamma-spectrum analysis, Monte Carlo simulations using the Monte Carlo N-Particle （ MNCP ） code were performed to provide the response spectra of some interested radionuclides and the background spectra originating from the natural radionuclides in seawater recorded by a NaI （T1） detector. A newly developed 75 mm × 75 mm NaI （T1） detector was calibrated using four reference radioactive sources 137Cs, 60Co, 40K and 54Mn in the laboratory before the field measurements in seawater. A simulation model was established for the detector immersed in seawater. The simulated spectra were all broadened with Gaussian pulses to reflect the statistical fluctuations and electrical noise in the real measurement. The simulated spectra show that the single-energy photons into the detector are mostly scattering low-energy photons and the high background in the low energy region mainly originates from the Compton effect of the high energy y-rays of natural radionuclides in seawater. The simulated background spectrum was compared with the experimental one recorded in field measurement and they seem to be in good agreement. The simulation method and spectra can be used for the accurate analysis of the filed measurement results of low concentration radioactivity in seawater.

Multiple Shoots Propagation with Bioreactor Culture of Labisia pumila(Bl.) F. Vill.

This study was to establish the micropropagation system of Labisia pumila （Bl.） F. Vill. and explore the feasibility of mass production of its multiple shoots by bioreactor culture. [Method] The effects of cytokinin or cytokinin/auxin mixture solution at different concentrations on its shoot growth and propagation by nodal segment culture were tested. In order to mass-proliferate its shoots, multiple shoots were suspension-cultured on Murashige and Skoog （MS） liquid medium in the bioreactor. [Results] Thidiazuron （TDZ） showed the highest cytokinin-like activity and the number of its shoots at the TDZ concentration of 0.1 mg/L was the maximum up to 21.5 shoots per explant, without the TDZ effect on shoot elongation, but zeatin signifcantly promoted the shoot elongation and each explant grew 6.8 relatively long shoots at 5.0 mg/L of zeatin. There was no signifcant effect on shoot propagation on induction medium supplemented with auxin. By inoculating 10 g/L （260 shoots） of multiple shoots into 3 L airlift bioreactor containing 2 L MS liquid medium supplemented with 0.1 mg/L TDZ for solution culture, 6 100 multiple shoots with a fresh weight of 183.13 g were harvested. After explant regeneration was conducted in MS solid medium, the regenerated plants were transplanted into flowerpot and the morphologically normal and healthy plants were obtained. [Conclusion] The development of bioreactor technology was conducive to the high efficiency propagation of L. pumila shoot.