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High-spin states of neutron deficient Trans-Lead nucleus $^{204}$At were populated up to $\sim 8\,{\rm MeV}$ excitation through the $^{12}$C + $^{197}$Au fusion evaporation reaction. Decay of the associated levels through prompt and delayed $\gamma$-ray emissions were studied to evaluate the underlying nuclear structure. The level scheme, which was partly known, was extended further. An isomeric $16^+$ level with observed lifetime $\tau=52 \pm 5\, {\rm ns}$, was established from our measurements. Attempts were made to interpret the excited states based on multi quasiparticle and hole structures involving $2f_{5/2}$, $1h_{9/2}$, and $1i_{13/2}$ shell model states, along with moderate core excitation. Magnetic dipole band structure over the spin parity range:~$16^+ - 23^+$ was confirmed and evaluated in more detail, including the missing cross-over $E2$ transitions. Band-crossing along the shears band was observed and compared with the evidence of similar phenomena in the neighbouring neutron deficient $^{202}$Bi, $^{205}$Rn isotones and the $^{203}$At isotope. Based on comparison of the measured $B(M1)/B(E2)$ values for transitions along the band with the semiclassical model based estimates, the shears band of $^{204}$At was established along with the level scheme., Comment: This preprint has not undergone peer review or any post-submission improvements or corrections. The Version of Record of this article is published in The European Physical Journal A and is available online at https://doi.org/10.1140/epja/s10050-022-00809-4

Intermetallic compounds Zr7Ni10 and Hf7Ni10 have been studied by perturbed angular correlation (PAC) spectroscopy considering the fact that Zr7Ni10 has application as hydrogen storage material in fuel cell. In stoichiometric Zr7Ni10, the phase Zr2Ni7 is found to be dominant (~38%) while a fraction of ~25% is found for the Zr7Ni10 phase at room temperature. In this compound, a phase due to Zr8Ni21 (~10%) is found from room temperature up to 773 K but, this is not found at 873 K and above. In the stoichiometric Hf7Ni10 sample, the phase due to Hf7Ni10 is found as a minor phase (~22%) at room temperature. In this system, no phase of Hf2Ni7 is observed but, a different phase due to HfNi3 is found to be dominant (~62%). It is found that the site fraction of Hf7Ni10 enhances with temperature at the expense of HfNi3 and this phase becomes predominant (~57%) at 673 K and above. The change of phase fractions of HfNi3 and Hf7Ni10 with temperature is found to be reversible. The phase components in Zr7Ni10 and Hf7Ni10 have been determined also from X-ray powder diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) measurements. Ab-initio calculations using the all electron full potential (linearized) augmented plane wave [FP-(L)APW] method, within the framework of the density functional theory (DFT), have been performed to determine the electric field gradients at the 181Ta impurity sites and therefrom to assign the different components observed from PAC measurements. Present experimental and calculated results of EFG support the Cmca space group for both Zr7Ni10 and Hf7Ni10 compounds., Comment: arXiv admin note: text overlap with arXiv:1712.04258

Time-differential perturbed angular correlation (TDPAC) measurements have been carried out in stoichiometric ZrNi$_3$ and HfNi$_3$ intermetallic compounds using $^{181}$Ta probe in the temperature range 77-1073 K considering the immense technological applications of Zr-Ni and Hf-Ni intermetallic compounds. In ZrNi$_3$, four components due to the production of Zr$_2$Ni$_7$, Zr$_8$Ni$_{21}$, Zr$_7$Ni$_{10}$ and ZrNi$_3$ have been found at room temperature. The HfNi$_3$ sample produces five electric quadrupole interaction frequencies at room temperature. The phase HfNi$_3$ is strongly produced in stoichiometric sample of HfNi$_3$ where two non-equivalent Hf sites are found to be present. Besides this phase, two other phases due to Hf$_2$Ni$_7$ and Hf$_8$Ni$_{21}$ have been found but, we do not observe any phase due to Hf$_7$Ni$_{10}$. X-ray diffraction, TEM/energy dispersive X-ray spectroscopy (EDX) and TEM-selected area electron diffraction (SAED) measurements were used to further characterize the investigated materials and it was found that these results agree with the TDPAC results. In order to confirm findings from TDPAC measurements, density functional theory (DFT) based calculations of electric field gradients (EFG) and asymmetry parameters at the sites of $^{181}$Ta probe nucleus were performed. Our calculated results are found to be in excellent agreement with the experimental results.

Numerous technological applications of Ni-based Zr and Hf intermetallic alloys promoted comprehensive studies in Zr$_8$Ni$_{21}$ and Hf$_8$Ni$_{21}$ by perturbed angular correlation (PAC) spectroscopy, which were not studied earlier until this report. The different phases produced in the samples have been identified by PAC and X-ray diffraction (XRD) measurements. Using $^{181}$Hf probe, two non-equivalent Zr/Hf sites have been observed in both Zr$_8$Ni$_{21}$ and Hf$_8$Ni$_{21}$ compounds. From present PAC measurements in Zr$_8$Ni$_{21}$, a component due to the production of Zr$_7$Ni$_{10}$ by eutectic reaction from the liquid metals is also observed. The phase Zr$_7$Ni$_{10}$, however, is not found from the XRD measurement. In Zr$_8$Ni$_{21}$, while the results do not change appreciably up to 973 K exhibit drastic changes at 1073 K. In Hf$_8$Ni$_{21}$, similar results for the two non-equivalent sites have been found but site fractions are in reverse order. In this alloy, a different contaminating phase, possibly due to HfNi$_3$, has been found from PAC measurements but is not found from XRD measurement. Density functional theory (DFT) based calculations of electric field gradient (EFG) and asymmetry parameter ($\eta$) at the sites of $^{181}$Ta probe nucleus allowed us to assign the observed EFG fractions to the various lattice sites in (Zr/Hf)$_8$Ni$_{21}$ compounds.

The lifetime of the 3163 keV, 7/2$^-$ isomeric state in $^{35}Cl$ that decays by a stretched M2 transition to the $3/2^+$ ground state, has been re-measured using the Doppler Shift Attenuation Method, by gating on the 1185 keV transition which directly feeds this state. This eliminates the uncertainties in the measurement arising from the direct feedings from the continuum. A mean life of 0.6$^{+0.5}_{-0.2}$ ps has been obtained from the present work. This is considerably smaller than the adopted value 45.3(6) ps. Implication of this major reduction in the lifetime has been pointed out., Comment: To be published in the Proc. of International Workshop on Nuclear Structure Physics at the Extremes: New Directions (NUSPE 05), 21-24 March, 2005, Shimla India