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The Water Cherenkov Detector Array (WCDA) is a major component of the Large High Altitude Air Shower Array Observatory (LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under construction. The WCDA is aimed at the study of TeV $\gamma$-rays. In order to evaluate the prospects of searching for TeV $\gamma$-ray sources with the WCDA, we present in this paper a projection for the one-year sensitivity of the WCDA to TeV $\gamma$-ray sources from TeVCat (footnote: http://tevcat.uchicago.edu) using an all-sky approach. Out of 128 TeVCat sources observable to the WCDA up to a zenith angle of $45^\circ$, we estimate that 42 would be detectable for one year of observations at a median energy of 1 TeV. Most of them are Galactic sources, and the extragalactic sources are Active Galactic Nuclei (AGN)., Comment: 10 pages,10 figures, it is to be published in Chinese Physics C

Lifetime measurements of $\ensuremath{\beta}$-decaying highly charged ions have been performed in the experimental storage ring (CSRe) by applying the isochronous Schottky mass spectrometry. The fully ionized $^{49}\mathrm{Cr}$ and $^{53}\mathrm{Fe}$ ions were produced in projectile fragmentation of $^{58}\mathrm{Ni}$ primary beam and were stored in the CSRe tuned into the isochronous ion-optical mode. The new resonant Schottky detector was applied to monitor the intensities of stored uncooled $^{49}\mathrm{Cr}^{24+}$ and $^{53}\mathrm{Fe}^{26+}$ ions. The extracted half-lives ${T}_{1/2}(^{49}\mathrm{Cr}^{24+})=44.0(27)$ min and ${T}_{1/2}(^{53}\mathrm{Fe}^{26+})=8.47(19)$ min are in excellent agreement with the literature half-life values corrected for the disabled electron capture branchings. This is an important proof-of-principle step towards realizing the simultaneous mass and lifetime measurements on exotic nuclei at the future storage ring facilities.

In this paper, we present direct mass measurements of neutron-rich $^{86}$Kr projectile fragments conducted at the HIRFL-CSR facility in Lanzhou by employing the Isochronous Mass Spectrometry (IMS) method. The new mass excesses of $^{52-54}$Sc nuclides are determined to be -40492(82), -38928(114), -34654(540) keV, which show a significant increase of binding energy compared to the reported ones in the Atomic Mass Evaluation 2012 (AME12). In particular, $^{53}$Sc and $^{54}$Sc are more bound by 0.8 MeV and 1.0 MeV, respectively. The behavior of the two neutron separation energy with neutron numbers indicates a strong sub-shell closure at neutron number $N$ = 32 in Sc isotopes., publised in Chinese Physics C Vol. 39, No. 10 (2015) 104001

The proton-rich isotope 133Sm was produced via the fusion evaporation reaction 40Ca + 96Ru. Its β-delayed proton decay was studied by p-γ coincidence in combination with a He-jet tape transport system, and half-lives, proton energy spectra, γ-transitions following the proton emission, as well as β-delayed proton branching ratios to the low-lying states in the grand-daughter nucleus were determined. Comparing the observed β-delayed proton branching ratios with statistical model calculations, the best agreement is found assuming that only one level with the spin of 3/2 in 133Sm decays or two levels with the spins of 1/2 and 5/2 decay with similar half-lives. The configuration-constrained nuclear potential energy surfaces of 133Sm were calculated using the Woods-Saxon-Strutinsky method, which suggests a 1/2- ground state and a 5/2+ isomer with an excitation energy of 120keV. Therefore, the simple (EC+β+) decay scheme of 133Sm in Eur. Phys. J. A 11, 277 (2001) has been revised. In addition, our previous experimental data on the β-delayed proton decay of 149Yb reported in Eur. Phys. J. A 12, 1 (2001) was also analyzed using the same method. The spin-parity of 149Yb is suggested to be 1/2-.

Excited states in 188Tl have been studied experimentally using the 157Gd (35Cl, 4n) reaction at a beam energy of 170MeV. A rotational band built on the πh 9/2 ⊗ νi 13/2 configuration with oblate deformation has been established for 188Tl. Based on the structure systematics of the oblate πh 9/2 ⊗ νi 13/2 bands in the heavier odd-odd Tl nuclei, we have tentatively proposed spin values for the new band in 188Tl. The πh 9/2 ⊗ νi 13/2 oblate band in 188Tl shows low-spin signature inversion, and it can be interpreted qualitatively by the two-quasiparticle plus rotor model including a J-dependent p-n residual interaction.

High-spin states in $^{187}\mathrm{Pt}$ have been studied experimentally using the $^{173}\mathrm{Yb}$($^{18}\mathrm{O}$, $4n$) reaction at beam energies of 78 and 85 MeV. The previously known bands based on the $\ensuremath{\nu}{i}_{13/2},\ensuremath{\nu}7/{2}^{\ensuremath{-}}[503]$, and $\ensuremath{\nu}{i}_{13/2}^{2}\ensuremath{\nu}j$ configurations have been extended to high-spin states, and new rotational bands associated with the $\ensuremath{\nu}3/{2}^{\ensuremath{-}}[512]$ and $\ensuremath{\nu}1/{2}^{\ensuremath{-}}[521]$ Nilsson orbits have been identified. The total Routhian surface calculations indicate that the transitional nucleus $^{187}\mathrm{Pt}$ is very soft with respect to $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ deformations. The band properties, such as level spacings, band crossing frequencies, alignment gains, and signature splittings, have been compared with the systematics observed in neighboring nuclei and have been interpreted within the framework of the cranked shell model. The rotational bands show different band crossing frequencies, which can be explained by the alignment either of ${i}_{13/2}$ neutrons or of ${h}_{9/2}$ protons. Importantly, evidence is presented for a $\ensuremath{\pi}{h}_{9/2}$ alignment at very low frequency in the $\ensuremath{\nu}7/{2}^{\ensuremath{-}}[503]$ band. The proton nature of the band crossing is strongly suggested by comparing the measured $B(M1;I\ensuremath{\rightarrow}I\ensuremath{-}1)/B(E2;I\ensuremath{\rightarrow}I\ensuremath{-}2)$ ratios with the theoretical values from the semiclassical D\"onau and Frauendof approach.

The concept of isochronous mass spectrometry (IMS) applying two time-of-flight (TOF) detectors originated many years ago at GSI. However, the corresponding method for data analysis has never been discussed in detail. Recently, two TOF detectors have been installed at CSRe and the new working mode of the ring is under test. In this paper, a data analysis method for this mode is introduced and tested with a series of simulations. The results show that the new IMS method can significantly improve mass resolving power via the additional velocity information of stored ions. This improvement is especially important for nuclides with Lorentz factor $\gamma$-value far away from the transition point $\gamma _t$ of the storage ring CSRe., Comment: published in Chinese Physics C Vol. 39, No. 10 (2015) 106201

We briefly reviewed and summarized the experimental study on $\ensuremath{\beta}$-delayed proton decays published by our group over the last 8 years, namely the experimental observation of $\ensuremath{\beta}$-delayed proton decays of nine new nuclides in the rare-earth region near the proton drip line and five nuclides in the mass 90 region with $N~Z$ by utilizing the $p\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence technique in combination with a He-jet tape transport system. In addition, important technical details of the experiments were provided. The experimental results were compared to the theoretical predictions of some nuclear models, resulting in the following conclusions. (1) The experimental half-lives for $^{85}\mathrm{Mo},\phantom{\rule{0.3em}{0ex}}^{92}\mathrm{Rh}$, as well as the predicted ``waiting point'' nuclei $^{89}\mathrm{Ru}$ and $^{93}\mathrm{Pd}$ were 5--10 times longer than the macroscopic-microscopic model predictions of M\"oller et al. [At. Data Nucl. Data Tables $66,131(1997)$]. These data considerably influenced the predictions of the mass abundances of the nuclides produced in the rp process. (2) The experimental assignments of spin and parity for the drip-line nuclei $^{142}\mathrm{Ho}$ and $^{128}\mathrm{Pm}$ could not be well predicted by any of the nuclear models. Nevertheless, the configuration-constrained nuclear potential-energy surfaces calculated by means of a Woods-Saxon-Strutinsky method could reproduce the assignments. (3) The ALICE code overestimated by one or two orders of magnitude the production-reaction cross sections of the nine studied rare-earth nuclei, while the HIVAP code overestimated them by approximately one order of magnitude.

Isochronous mass spectrometry (IMS) of heavyion storage rings is a powerful tool for the mass measurements of short-lived nuclei. In IMS experiments, masses are determined through precision measurements of the revolution times of the ions stored in the ring. However, the revolution times cannot be resolved for particles with nearly the same mass-to-charge (m/q) ratios. To overcome this limitation and to extract the accurate revolution times for such pairs of ion species with very close m/q ratios, in our early work on particle identification, we analyzed the amplitudes of the timing signals from the detector based on the emission of secondary electrons. Here, the previous data analysis method is further improved by considering the signal amplitudes, detection efficiencies, and number of stored ions in the ring. A sensitive Z-dependent parameter is introduced in the data analysis, leading to a better resolution of $^{34}$Ar$^{18+}$ and $^{51}$Co$^{27+}$ with A/Z=17/9. The mean revolution times of $^{34}$Ar$^{18+}$ and $^{51}$Co$^{27+}$ are deduced, although their time difference is merely 1.8 ps. The uncorrected, overlapped peak of these ions has a full width at half maximum of 7.7 ps. The mass excess of $^{51}$Co was determined to be -27332(41) keV, which is in agreement with the previous value of -27342(48) keV., 8 pages, 6 figures

Journal of physics / Conference series 1668, 012046 (2020). doi:10.1088/1742-6596/1668/1/012046, Published by IOP Publ., Bristol