Pan Qiangyan

Transmutation of nuclear wastes using photonuclear reactions triggered by Compton backscattering photons at the Shanghai laser electron gamma source

Based on the facility of the Shanghai Laser Electron Gamma Source (SLEGS), the transmutation for nuclear wastes such as Cs-137 and I-129 is investigated. It is found that nuclear waste can be transmuted efficiently via photonuclear reaction triggered by gamma photons generated from Compton backscattering between CO2 laser photons and 3.5 GeV electrons. The nuclear activities of Cs-137 and I-129 are evaluated and compared with the results of transmutation triggered by bremsstrahlung gamma photons driven by ultra intense laser. Due to the better character of gamma photon spectrum as well as the high brightness of gamma photons, the transmutation rate of Compton backscattering method is much higher than that of the bremsstrahlung method.

EC/β+ decay of six medium-heavy nuclei

Previous experimental results of (EC+beta(+)) decay for the medium-heavy nuclei reported by our group since 1996, including Er-153, Yb-157, Fr-209, Ce-128, Ce-130, and Pr-128 have been briefly summarized. The observed low-lying states in their daughter nuclei have been reviewed in a systematic way and compared with different model calculations. Finally, some questions have been put forward for further study and discussion.

Field emission enhancement of carbon nanotubes by surface modification

By employing a multi-walled carbon nanotube (MWCNT) film as the substrate, we obtain Fe tipped carbon nanorods or carbon nanoparticles grown on the outer walls of MWCNTs by combining sputtering deposition of Fe films and rf plasma enhanced chemical vapour deposition at high temperature. Scanning electron microscopy and high-resolution transmission electron microscopy are used to examine the structure of carbon nanorods and carbon nanoparticles. In addition, the formation mechanism is discussed briefly. The electron field emission tests indicate that the turn-on field (at 10 μA/cm2) of the treated MWCNT films decreases from 2.4 V/μm to 0.79 V/μm and the field emission current is relatively stable. The enhanced field enhancement factor, increasing emission densities coming from the grown nanorods and nanoparticles, and H terminated by H plasma all are responsible for the enhancement of the field enhancement factor.

New β-delayed proton decays in the rare-earth region near the proton drip line

The β-delayed proton precursors125Nd128Pm129Sm,137Gd and139Dy near the proton drip line were produced by the irradiation of92Mo,96Ru and106Cd with an36Ar beam, and conclusively identified for the first time by using proton-gamma coincidence in combination with a He-jet tape transport system. Their half-lives were determined to be 0.60(15)s,1.0(3)s,O.55(10)s,2.2(2)s and 0.6 (2)s, respectively. The measured energy spectra of β-delayed protons and estimated proton branching ratios to the final states in “daughter” nuclei for the precursors125Nd,129Sm,137Gd and139Dy, as well as the previously reported ones for the precursors135Gd and121Ce, were fitted by a statistical model calculation. The ground-state spins and parities of121Ce,125Nd,129Sm,139Gd,137Gd and139Dy were then assigned as 5/2±,5/2±, 1/2± (or 3/2+), 5/2+,7/2+- and 7/2, respectively. The consistency between the experimental spin-parity assignment and the predicted Nilsson diagrams indirectly indicates that the ground states of121Ce,125Nd,129Sm,135Gd,137Gd and139Dy are highly deformed with β2, - 0.3.

Measurement of PV asymmetry in n⃗ + p → d + γ and γ⃗ M+ d → n + p

The measurement of parity-violating (PV) observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons. Theoretical models describe the nucleon-nucleon weak interaction at low energies use a series of undetermined parameters. Two parity violating measurements have been considered: the capture of polarized slow neutrons on hydrogen ( + p ? d + ?) at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons ( + d ? n + p) at Shanghai Institute of Applied Physics. The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1 ? 10?8. The introduction of both experiments is presented.

Cross sections of barium isotopes in the interaction of 60 MeV/nucleon 18O with 238U

Barium isotopes were produced by 60 MeV/u 18O ion bombardment of natural uranium via 238U (18O, X) reactions. Ba sources were prepared by radiochemical separation, and measured by a HPGe detector. The cumulative cross sections were obtained by analysis of measured time sequence g-ray spectra. A double peak phenomenon in Ba isotope distribution was observed.

Radius studies of 8Li and 8B using the optical-limit Glauber model in conjunction with relativistic mean-field theory

We study the reaction cross sections (σR) and root-mean-square (RMS) radii of 8Li and 8B, the halo-like nuclei, with stable target 12C, 27Al and 9Be within the standard optical-limit Glauber model, using densities obtained from relativistic mean-field (RMF) formalisms and other types of distributions. It is found that the experimental σR can be reproduced well at high energy. The RMS radius and Δr extracted by RMF-theory and harmonic oscillator distribution are compared. We find that the RMS radius and Δr of 8B are larger than those of 8Li. In addition, we analyze in detail the relationship between σR and density distribution.

Determination of the stellar reaction rate for 12C（α,γ）16O： using a new expression with the reaction mechanism

The astrophysical reaction rate of 12C(?, ?)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9 = 0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(?, ?)16O reaction rates are calculated in the temperature range from T9 = 0.3 to 2 according to all the available cross section data. A new analytic expression of the 12C(?, ?)16O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3? fit errors, are obtained from fit to our calculated reaction rate from T9 = 0.3 to 2. Using the fit results, the analytic expression of 12C(?, ?)16O reaction rate is extrapolated down to T9 = 0.05 based on the underlying physics. The 12C(?, ?)16O reaction rate at T9 = 0.2 is (8.78 ? 1.52) ? 1015 cms?1 mol?1. Some comparisons and discussions about our new 12C(?, ?)16O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9 = 2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(?, ?)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(?, ?)16O reaction rates.