The inorganic fraction of biochar played the dominant role in the Pb(ii) removal mainly via inner-sphere complexation and precipitation while the organic carbon sorbed Pb(ii) via intrinsic chemical affinity and/or electrostatic attraction.

A defect dynamic model is proposed for the positive synergistic effect of neutron- and γ-ray-irradiated silicon NPN transistors. The model considers a γ-ray-induced transformation and annihilation of the neutron-induced divacancy defects in the p-type base region of the transistor. The derived model of the base current predicts a growth function of the γ-ray dose that approaches exponentially an asymptotic value, which depends linearly on the neutron-induced initial displacement damage (DD) and a linear decay function of the dose whose slope depends quadratically on the initial DD. Variable fluence and dose neutron-γ-ray irradiation experiments are carried out, and we find all of the novel dose and fluence dependence predicted by the proposed model are confirmed by the measured data. Our work, hence, identifies that the defect evolution under γ-ray irradiation, rather than the widely believed interface Coulomb interaction, is the dominating mechanism of the synergistic effect. Our work also paves the way for the modification of displacement defects in silicon by γ-ray irradiation.

E − (red) due to a "phonon-kick" mechanism. The other three conversion processes in (c) and (b) are also enhanced by the recombination because of the vibrational excitations of the spring-like chemical bonds.

The synergistic effects of neutron and gamma ray radiated PNP transistors are systematically investigated as functions of the neutron fluence, gamma ray dose, and dose rate. We find that the damages show a 'tick'-like dependence on the gamma ray dose after the samples are radiated by neutrons. Two negative synergistic effects are derived, both of which have similar magnitudes as the ionization damage (ID) itself. The first one depends linearly on the gamma ray dose, whose slope depends quadratically on the initial displacement damage (DD) and can be attributed to the healing of neutron-radiation-induced defects in silicon. The second one has an exponential decay with the gamma ray dose, whose amplitude shows a rather strong enhanced low-dose-rate sensitivity (ELDRS) effect and can be attributed to the passivation of neutron-induced defects near the silica/silicon interface by the gamma-ray-generated protons in silica, which can penetrate the silica/silicon interface to passivate the neutron-induced defects in silicon. The simulated results based on the proposed model match the experimental data very well, but differ from previous model, which does not assume annihilation or passivation of the displacement defects. The unraveled defect annealing mechanism is important because it implies that displacement damages can be repaired by gamma ray radiation or proton diffusion, which can have important device applications in the space or other extreme environments. Unirradiated Samples Fluence: 0 n/cm 2 Fluence: 2 10 13 n/cm 2 Fluence: 3 10 13 n/cm 2 Fluence: 5 10 13 n/cm 2 LDR: 2.2mrad(Si)/s LDR: 2.2mrad(Si)/s LDR: 2.2mrad(Si)/s LDR: 2.2mrad(Si)/s HDR: 10rad(Si)/s HDR: 10rad(Si)/s HDR: 10rad(Si)/s HDR: 10rad(Si)/s Step 1:Neutron irradiation Step 2:Gamma irradiation FIG. 2. (color online) Flowchart of the neutron/gamma radiation experiments. For each of the eight radiation conditions, 2 chips with 8 PNP transistors are used.

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