Nano-crystallize materials have been known for decades to potentially owe the novel self-healing ability for radiation damage, which has been demonstrated to be especially linked to preferential occupation of interstitials at grain boundary (GB) and
promoted vacancy-interstitial annihilation. A major obstacle to better understanding the healing property is the lack of an atomistic picture of the interstitial states near GBs, due to severely separation of the timescale of interstitial segregation from other events and abundance of interstitials at the GB. Here, we report a generic self-blocking effect of the interstitial cluster (SIAn) near the metallic GB in W, Mo and Fe. Upon creating a SIAn near the GB, it is immediately trapped by the GB during the GB structural relaxation and blocks there, impeding GBs further spontaneous trapping of the SIAn in the vicinity and making these SIAns stuck nearby the GB. The SIAn in the stuck state surprisingly owes an exceptionally larger number of annihilation sites with vacancies near the GB than the SIAn trapped at the GB due to maintaining its bulk configuration basically. Besides, it also has an unexpectedly long-ranged repelling interaction with the SIA in the bulk region, which may further affect the GBs trap of the SIAn. The self-blocking effect might shed light on more critical and extended role of the GB in healing radiation-damage in NCs than previously recognized the GBs limited role based on GBs trap for the SIA and resulted vacancy-SIA recombination.
Design of nuclear materials with high radiation-tolerance has great significance1, especially for the next generation of nuclear energy systems2,3. Response of nano- and poly-crystals to irradiation depends on the radiation temperature, dose-rate and
grain size4-13. However the dependencies had been studied and interpreted individually, and thus severely lacking is the ability to predict radiation performance of materials in extreme environments. Here we propose an operational window for radiation-resistant materials, which is based on a perspective of interactions among irradiation-induced interstitials, vacancies, and grain boundaries. Using atomic simulations, we find that healing grain boundaries needs much longer time than healing grain interiors. Not been noticed before, this finding suggests priority should be thereafter given to recovery of the grain boundary itself. This large disparity in healing time is reflected in the spectra of defects-recombination energy barriers by the presence of one high-barrier peak in addition to the peak of low barriers. The insight gained from the study instigates new avenues for examining the role of grain boundaries in healing the material. In particular, we sketch out the radiation-endurance window in the parameter space of temperature, dose-rate and grain size. The window helps evaluate material performance and develop resistant materials against radiation damage.
We derive a new method to improve the statistics of identified particles at high transverse momentum (pt) using online-triggered events by the Barrel Electro-Magnetic-Calorimeter (BEMC) detector. The BEMC is used to select hadronic interaction and en
ergy deposit from showers created by charged hadrons ($pi^{pm},K^{pm}$ and $p$($bar{p}$)) in the BEMC. With this trigger, the statistics of the high pt particles are significantly enhanced by about a factor of 100 with selection efficiency up to 20%. In addition, resonant states ($rho^0$, $K^{star}$) and weak-decay V0 (Ks and La(aLa)) can be constructed by selecting the BEMC-trigger hadron as one of its daughters. We also show that the trigger efficiency can be obtained reliably in simulation and data-driven approaches.
The study of hadron spectra at high $p_{T}$ in p+p collisions provides a good test of perturbative quantum chromo-dynamic calculations (pQCD) and baseline for measurements of nuclear modification factors in Au+Au collisions. Using events triggered by
the Barrel Electro-Magnetic Calorimeter, identified charged hadron transverse momentum ($p_T$) spectra are measured up to 15 GeV/$c$ at mid-rapidity ($mid ymid$ $<$ 0.5) and neutral kaon $p_T$ spectra up to 12 GeV/$c$ in p + p collisions at $sqrt{s_{NN}}$ = 200 GeV. The particle ratios of $p/pi^{+}$, $bar{p}/pi^{-}$ and $K^{pm,0}$ / $pi^{pm}$ in p + p collisions are shown and compared with next-to-leading order pQCD calculations. In central Au+Au collisions, we report nuclear modification factors ($R_{AA}$) for pion, kaon, proton and $rho$ and discuss several model calculations: color-charge dependence of jet quenching and jet conversion. Finally, centrality dependence of $R_{AA}$ at high $p_T$ ($>$ 5.5 GeV/c) for kaon are compared with that of pion in Au + Au collisions at 200 GeV.
We derive a method to improve particle identification (PID) at high transverse momentum ($p_T$) using the relativistic rise of the ionization energy loss ($rdE/dx$) when charged particles traverse the Time Projection Chamber (TPC) at STAR. Electrons
triggered and identified by the Barrel Electro-Magnetic Calorimeter (BEMC), pure protons and pions from $Lambdato p+pi^{-}$ ($bar{Lambda}to bar{p}+pi^{+}$), and $K^{0}_{S}topi^{+}+pi^{-}$ decays are used to obtain the $dE/dx$ value and its width at given $betagamma=p/m$. We found that the deviation of the $dE/dx$ from the Bichsel function can be up to $0.4sigma$ ($sim3%$) in p+p collisions at $sqrt{s_{NN}}=200$ GeV taken and subsequently calibrated in year 2005. The deviation is approximately a function of $betagamma$ independent of particle species and can be described with a function of $f(x) = A+frac{B}{C+x^{2}}$. The deviations obtained with this method are used to re-calibrate the data sample from p+p collision for physics analysis of identified hadron spectra and their correlations up to transverse momentum of 15 GeV/$c$. The ratio of $e^{-}/e^{+}$ (dominantly from $gamma$-conversion) is also used to correct the residual asymmetry in the negative and positive charged hadrons due to momentun distortion in the STAR TPC.
We report an extension of charged kaon transverse momentum ($p_T$) spectra at mid-rapidity ($mid ymid <$ 0.5) up to 15 GeV/$c$, neutral kaon $p_T$ spectra up to 12 GeV/$c$ using events triggered by the Barrel Electro-Magnetic Calorimeter (BEMC) from
p+p collisions at $sqrt{s_{NN}}$ = 200 GeV. The $K^{pm}/pi^{pm}$ and $K^{0}/pi^{pm}$ at high $p_T$ are compared in p+p and Au+Au collisions, and nuclear modification factor ($R_{AA}$)for pion, kaon, proton and rho are discussed. The $R_{AA}$ for kaon in central collisions are consistent with theory calculation having jet conversion in a plasma of quarks and gluons.
We report the transverse momentum (pT) distributions for identified charged pions, protons and anti-protons using events triggered by high deposit energy in the Barrel Electro-Magnetic Calorimeter (BEMC) from p + p collisions at psNN = 200 GeV. The s
pectra are measured around mid-rapidity (|y|<0.5) over the range of 3<pT<15 GeV/c with particle identification (PID) by the relativistic ionization energy loss (rdE/dx) in the Time Projection Chamber (TPC) in the Solenoidal Tracker at RHIC (STAR). The charged pion, proton and anti-proton spectra at high pT are compared with published results from minimum bias triggered events and the Next-Leading-Order perturbative quantum chromodynamic (NLO pQCD) calculations (DSS, KKP and AKK 2008). In addition, we present the particle ratios of pi-/pi+, pbar/p, p/pi+ and pbar/pi- in p + p collisions.
