Shengyun Zhu

EXPERIMENTAL VERIFICATION OF HEAVY ION IRRADIATION SIMULATION

The heavy ion irradiation simulation of neutron and/or proton irradiation has been verified experimentally by the detailed study of radiation damage in α-Al2O3 irradiated at the equivalent dose by 5.28×1015cm-285 MeV19F ions and by 3×1020cm-2 En≥1MeV neutrons, respectively. The radiation damage created by irradiation was examined by a positron annihilation lifetime technique. The positron annihilation parameters of lifetime and intensity obtained for both irradiations in α-Al2O3 are all in good agreement. This demonstrates that the heavy ion irradiation can well simulate the neutron and/or proton irradiation.

Behavior of Boron Implanted in Semiconductor Si

Using β-NMR with 12B nuclei the temperature dependence of the lattice locations of boron implanted in Si is studied. At low temperature almost 100% of the implanted B is in either substitutional site or nonsubstitutional site. Above 260 K, the nonsubstitutional B rapidly becomes undetectable and disappears at a temperature higher than 325 K due to the fast spin-lattice relaxation. Above 450 K, the fraction of substitutional B increases to 100%. These experimental results are consistently explained by the thermal atomic jump and the dissociation of the defect associated with the nonsubstitutional B.

RADIATION EFFECTS IN STAINLESS STEEL AND TUNGSTEN FOR USE IN THE ADS SPALLATION NEUTRON SOURCE SYSTEM

Radiation effects have been studied in modified 316L stainless steel and commercially available stainless steel and tungsten by the heavy ion irradiation simulation and positron lifetime techniques. The experimental results show that the radiation resistant property of stainless steel is much better than that of tungsten, and the modified 316L stainless steel is the best among them. The stainless steel is a good choice for the beam window material of the ADS spallation neutron source system, and the modified 316L stainless steel is the best choice.

g-Factor measurements of rotational states in 84,86Zr

The g-factors of the positive parity yrast rotational states in 84,86Zr have been precisely measured using a TMF-IMPAD method. The measured g factors indicate the proton alignment followed by neutron alignment in the g9/2 high-j shell for 84Zr and the neutron alignment followed by proton alignment for 86Zr. The present results also reveal the structure transition at N=46 for Zr isotopes.

Effect of triple ion beams on radiation damage in CLAM steel

The effect of triple ion beams has been investigated by simultaneous and sequential irradiations of gold, hydrogen and helium on radiation damage in the CLAM steel developed in China. The depth profile measurements of positron annihilation Doppler broadening S parameter were carried out as a function of slow-positron beam energy to examine the produced radiation damage. The experimental results show clearly the synergistic effect of displacement damage and hydrogen and helium on the formation of radiation damage. The synergistic effect of simultaneous triple ion beam irradiation of gold, hydrogen and helium ions was found to suppress the radiation damage in the CLAM steel due to the helium and/or hydrogen filling of vacancy clusters.

Nuclear Spin Alignment of 12,13B Produced in Heavy Ion Collisions

The nuclear spin alignments of the β-emitting fragments 12B(Iπ=1+, T1/2=20.2 ms) and 13B(Iπ=3/2−, T1/2=17.4 ms) produced in the 100A-MeV 13C, 15N + 9Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO2, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for P and A are almost the same, there may be some depolarization mechanism in the collision process itself.

Hyperfine Interactions of N Isotopes in TiO2 and Quadrupole Moment of 16N

Hyperfine interactions of 12,14N in BN(hexagonal) crystal were studied by detecting β-NQR(12N) and FT-NMR(14N). A β-NMR of 16N (Iπ=2−,T1/2=7.13 s) in MgO crystal was detected to determine the magnetic moment of 16N to be |μ(16N:2−)|=(1.986±0.001)μN. Also, the β-NQR of 12,16N in TiO2 crystal were detected to determine |Q(16N:2−)|=(17.9±1.7) mb. An abnormally small effective charge for neutrons is required to account for |Q(16N:2−)|.

Irradiation Hardening and Indentation Size Effect of the 304NG Stainless Steels After Triple Beam Irradiation

The nuclear grade 304NG stainless steel (SS) has been developed in the past several decades as the new generation of internal material in light water reactors. The irradiation effects of domestic 304NG SS were simulated by the triple ion beam irradiation on the heavy ion, hydrogen and helium triple ion beam irradiation platform at China institute of Atomic Energy. The irradiation experiments were carried out with various doses (6, 15, 30 and 150 dpa at 300 ℃) and temperatures (300, 350, 400, 450 ℃ with 6 dpa). The depth-dependent hardness and elastic modulus of the specimens before and after irradiation were measured by nanoindentation with the continuous stiffness measurement technique. For the specimens irradiated at 300 ℃, the hardness generally increases with the increasing dose. The depth-dependent hardness in the micro-indentation region (indentation depth h > 100 nm) of those specimens with dose less than 30 dpa can be well explained by Nix & Gao formulae of the indentation size effect. For the specimens irradiated at different temperatures, the hardening effect can be observed for all specimens for indentation depth beyond 1 μm and the hardness decreases with increasing irradiation temperature. However, as the irradiation temperature elevates or the dose increases up to 150 dpa, the hardness for the indentation depth h < 500 nm deviates significantly from the projection of the Nix & Gao model. The surface morphology observed by SEM and the S parameters extracted from the slow positron annihilation Doppler broadening indicate that the drastic reduction of hardness those specimens with indentation depth h < 500 nm can be attributed to the change of surface morphology.

Electromagnetic Moments of Proton-Rich {sup 28}P and Decomposition of Its Spin

The magnetic moment of 28P(Iπ = 3+, T1/2 = 270.3 ms) has been measured precisely by means of β‐NMR technique. The obtained magnetic moment is |μ(28P)| = 0.3115 (34) μN. Combined with the magnetic moment of its mirror partner 28Al, the nuclear spin I = 3 is decomposed into its 4 components. The measurement of the Q moment has also been tried. From the preliminary NQR spectrum, it was found that the quadrupole coupling constant eqQ/h may be slightly larger than the prediction, which may show enhancement of the Q moment.