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Nasser Kalantar-Nayestanaki

Publications and source records attributed to Nasser Kalantar-Nayestanaki.

5 recordsLinked to original sources

A pathway towards decentralized studies of radioactive post-lead elements and their applications in beyond standard model physics

Molecules have proven to be sensitive tools for studying physics beyond the standard model, with heavy and deformed nuclei offering decisive sensitivity to parity- and time-reversal-violating effects. However, almost all elements beyond lead, occupying the 6p~to~5f atomic orbitals, lack stable isotopes, hence molecules containing them are referred to as radioactive molecules. Among those, radium monofluoride has seen particular interest, but to date, research on radioactive molecules has mainly been limited to large-scale nuclear facilities. Here, we present a scheme that allows efficient and fast harvest of radioactive ions (including short-lived Ra), and show ion gas-phase reaction studies of singly and doubly charged Ra, Po, and Pb ions with SF$_6$ gas inside an ion trap. Our results show that the chemical reaction rate of Ra$^+$ is in line with trends of other alkaline earth elements, further support by quantum chemical computations. The reaction Ra$^{2+}$ + SF$_6$ $\rightarrow$ RaF${^+}$ + SF$_5^{+}$ achieves an almost unity conversion efficiency, making it particularly suitable for the application for studies in physics beyond the standard model. The scheme enables future decentralized research avenues with short-lived radioactive molecules for fundamental physics research at laboratories without the need for local nuclear reactors or accelerators.

nucl-ex↗

Reconstructing charged-particle trajectories in the PANDA Straw Tube Tracker using the LOcal Track Finder (LOTF) algorithm

We present the LOcal Track Finder (LOTF) algorithm, a method that performs charged-particle trajectory reconstruction using the Straw Tube Tracker, one of the central trackers of the antiProton ANnihilation at DArmstadt (PANDA) detector. The algorithm builds upon the neighboring relations of the tubes to connect individual hits and form track candidates. In addition, it uses a local fitting procedure to handle regions where several tracks overlap and utilizes a system of virtual nodes to reconstruct the z-information of the particle trajectories. We generated 30,000 events to assess the performance of our approach and compared our results to two other track reconstruction methods. LOTF has (1) an average of 85\% of found tracks, (2) the largest number of Fully Pure tracks, (3) the lowest amount of incorrect reconstructions, and (4) is significantly faster than the other two approaches. Further, we compared the z-reconstruction performance with one of the two alternative methods and show that LOTF improves the median z-error by a factor of 8.7. Finally, we tested our method using 3,750 data sets composed of 4 events each, showing that our approach handles cases in which events are mixed. The raw (without parallelization) average reconstruction rate is about 68,000 hits/s, which makes the present algorithm promising for online data selection and processing.

hep-ex↗

Studying Gamow-Teller transitions and the assignment of isomeric and ground states at $N=50$

Direct mass measurements of neutron-deficient nuclides around the $N=50$ shell closure below $^{100}$Sn were performed at the FRS Ion Catcher (FRS-IC) at GSI, Germany. The nuclei were produced by projectile fragmentation of $^{124}$Xe, separated in the fragment separator FRS and delivered to the FRS-IC. The masses of 14 ground states and two isomers were measured with relative mass uncertainties down to $1\times 10^{-7}$ using the multiple-reflection time-of-flight mass spectrometer of the FRS-IC, including the first direct mass measurements of $^{98}$Cd and $^{97}$Rh. A new $Q_\mathrm{EC} = 5437\pm67$ keV was obtained for $^{98}$Cd, resulting in a summed Gamow-Teller (GT) strength for the five observed transitions ($0^+\longrightarrow1^+$) as $B(\text{GT})=2.94^{+0.32}_{-0.28}$. Investigation of this result in state-of-the-art shell model approaches sheds light into a better understanding of the GT transitions in even-even isotones at $N=50$. The excitation energy of the long-lived isomeric state in $^{94}$Rh was determined for the first time to be $293\pm 21$ keV. This, together with the shell model calculations, allows the level ordering in $^{94}$Rh to be understood.

nucl-ex↗

Compression-mode resonances in the calcium isotopes and implications for the asymmetry term in nuclear incompressibility

Recent data on isoscalar giant monopole resonance (ISGMR) in the calcium isotopes $^{40,44,48}$Ca have suggested that $K_τ$, the asymmetry term in the nuclear incompressibility, has a positive value. A value of $K_τ> 0$ is entirely incompatible with present theoretical frameworks and, if correct, would have far-reaching implications on our understanding of myriad nuclear and astrophysical phenomena. This paper presents results of an independent ISGMR measurement with the $^{40,42,44,48}$Ca($α,α^\prime$) reaction at $E_α= 386$ MeV. These results conclusively discount the possibility of a positive value for $K_τ$, and are consistent with the previously-obtained values for this quantity.

nucl-ex↗

Coulomb dissociation of $^{20,21}$N

Neutron-rich light nuclei and their reactions play an important role for the creation of chemical elements. Here, data from a Coulomb dissociation experiment on $^{20,21}$N are reported. Relativistic $^{20,21}$N ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the $^{19}\mathrm{N}(\mathrm{n},γ)^{20}\mathrm{N}$ and $^{20}\mathrm{N}(\mathrm{n},γ)^{21}\mathrm{N}$ excitation functions and thermonuclear reaction rates have been determined. The $^{19}\mathrm{N}(\mathrm{n},γ)^{20}\mathrm{N}$ rate is up to a factor of 5 higher at $T<1$\,GK with respect to previous theoretical calculations, leading to a 10\,\% decrease in the predicted fluorine abundance.

nucl-ex↗