Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTowards a direct transition energy measurement of the lowest nuclear excitation in 229Th
89
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The isomeric first excited state of the isotope 229Th exhibits the lowest nuclear excitation energy in the whole landscape of known atomic nuclei. For a long time this energy was reported in the literature as 3.5(5) eV, however, a new experiment corrected this energy to 7.6(5) eV, corresponding to a UV transition wavelength of 163(11) nm. The expected isomeric lifetime is $tau=$ 3-5 hours, leading to an extremely sharp relative linewidth of Delta E/E ~ 10^-20, 5-6 orders of magnitude smaller than typical atomic relative linewidths. For an adequately chosen electronic state the frequency of the nuclear ground-state transition will be independent from influences of external fields in the framework of the linear Zeeman and quadratic Stark effect, rendering 229mTh a candidate for a reference of an optical clock with very high accuracy. Moreover, in the literature speculations about a potentially enhanced sensitivity of the ground-state transition of $^{229m}$Th for eventual time-dependent variations of fundamental constants (e.g. fine structure constant alpha) can be found. We report on our experimental activities that aim at a direct identification of the UV fluorescence of the ground-state transition energy of 229mTh. A further goal is to improve the accuracy of the ground-state transition energy as a prerequisite for a laser-based optical control of this nuclear excited state, allowing to build a bridge between atomic and nuclear physics and open new perspectives for metrological as well as fundamental studies.
rate research
Read More
The isoscaling is investigated using the fragment yield data from fully reconstructed quasi-projectiles observed in peripheral collisions of 28Si with 124,112Sn at projectile energies 30 and 50 MeV/nucleon. The excitation energy dependence of the isoscaling parameter beta_prime is observed which is independent of beam energy. For a given quasi-projectile produced in reactions with different targets no isoscaling is observed. The isoscaling thus reflects the level of N/Z-equilibration in reactions with different targets represented by the initial quasi-projectile samples. The excitation energy dependence of the isoscaling parameter beta_prime, corrected for the trivial 1/T temperature dependence, does not follow the trend of the homogeneous system above 4 MeV/nucleon thus possibly signaling the onset of separation into isospin asymmetric dilute and isospin symmetric dense phase.
Neutron kinetic energy spectra in coincidence with low-energy $gamma $-ray multiplicities have been measured around $Aapprox $ 110 in the $^{16}$O, $^{20}$Ne + $^{93}$Nb reactions in a compound nuclear excitation energy range of $approx $ 90 - 140 MeV. The excitation energy (temperature) and angular momentum (spin) dependence of the inverse level density parameter $k$ has been investigated by comparing the experimental data with statistical Hauser-Feshbach calculation. In contrast to the available systematic in this mass region, the inverse level density parameter showed an appreciable increase as a function of the excitation energy. The extracted $k$-values at different angular momentum regions, corresponding to different $gamma $-multiplicities also showed an overall increase with the average nuclear spins. The experimental results have been compared with a microscopic statistical-model calculation and found to be in reasonable agreement with the data. The results provide useful information to understand the variation of nuclear level density at high temperature and spins.
Reactions on the proton-rich nuclides drive the nucleosynthesis in Core-Collapse Supernovae (CCSNe) and in X-ray bursts (XRBs). CCSNe eject the nucleosynthesis products to the interstellar medium and hence are a potential inventory of p-nuclei, whereas in XRBs nucleosynthesis powers the light curves. In both astrophysical sites the Ni-Cu cycle, which features a competition between $^{59}$Cu(p,$alpha$)$^{56}$Ni and $^{59}$Cu(p,$gamma$)$^{60}$Zn, could potentially halt the production of heavier elements. Here, we report the first direct measurement of $^{59}$Cu(p,$alpha$)$^{56}$Ni using a re-accelerated $^{59}$Cu beam and cryogenic solid hydrogen target. Our results show that the reaction proceeds predominantly to the ground state of $^{56}$Ni and the experimental rate has been found to be lower than Hauser-Feshbach-based statistical predictions. New results hint that the $ u p$-process could operate at higher temperatures than previously inferred and therefore remains a viable site for synthesizing the heavier elements.
The nuclear modification factors R_{AA} and R_{CP} have been used to measure medium-induced suppression in heavy-ion collisions at sqrt{s_{NN}} = 200GeV which was among the earliest evidence for the existence of a strongly interacting medium called a quark-gluon plasma (QGP). Nuclear modification factors for asymmetric collisions (R_{dA}) have measured the Cronin Effect, an enhancement of high transverse momentum particle yields in deuteron-gold collisions relative to proton-proton collisions. A similar enhancement is observed in data presented in these proceedings and competes with the quenching caused by partonic energy loss in the QGP. In these proceedings we will present charged-hadron R_{CP} at mid-rapidity for sqrt{s_{NN}} = 7.7 - 62.4GeV as well as identified pi^{+}, K^{+}, and proton R_{CP}. Comparisons to HIJING motivate possible methods for disentangling competing modifications to nuclear transverse momentum spectra.
New results on the superdeformed $^{196}$Bi nucleus a re reported. We have observed with the EUROBALL IV $gamma$-ray spectrometer array a superdeformed trans ition of 124 keV which is the lowest observed energy $gamma$-ray in any superdeformed nucleus. We have de velopped microscopic cranked Hartree-Fock-Bogoliubov calculations using the SLy4 effective force and a realistic surface p airing which strongly support the $K^pi=2^-$($pi$[651]1/2$otimes u$[752]5/2) assignment of this su perdeformed band.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
