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Register a new userNuclear level density of $^{69}$Zn from gamma gated particle spectrum and its implication on $^{68}$Zn(n, $gamma$)$^{69}$Zn capture cross-section
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Evaporated $alpha$-spectra have been measured in coincidence with low energy discrete $gamma$-rays from residual nucleus $^{68}$Zn populated in the reaction $^{64}$Ni($^9$Be,$alpha$n)$^{68}$Zn at $E(^9$Be) = 30 MeV producing $^{73}$Ge compound nucleus. Low energy $gamma$-gated $alpha$-particle spectra, for the first time, have been used to extract the nuclear level density (NLD) for the intermediate $^{69}$Zn nucleus in the excitation energy range of E $approx$ 5-20 MeV. The slope of NLD as a function of excitation energy for $^{69}$Zn matches nicely with the slope determined from RIPL estimates for NLD at low energies and the NLD from neutron resonance data. Extracted inverse NLD parameter (k = A/$widetilde{a}$) has been used to determine the nuclear level density parameter value $a$ at neutron separation energy $S_n$ for $^{69}$Zn. Total cross-section of $^{68}$Zn(n,$gamma$) capture reaction as a function of neutron energy is then estimated employing the derived $a(S_n)$ in the reaction code TALYS. It is found that the estimated neutron capture cross-section agrees well with the available experimental data without any normalization. The present result indicates that experimentally derived nuclear level density parameter can constrain the statistical model description of astrophysical capture cross-section and optimize the uncertainties associated with the astrophysical reaction rate
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A study of the $beta$ decay of the proton-rich $T_{z}$ = -2 nucleus $^{56}$Zn has been reported in a recent publication. A rare and exotic decay mode, $beta$-delayed $gamma$-proton decay, has been observed there for the first time in the $fp$ shell. Here we expand on some of the details of the data analysis, focussing on the charged particle spectrum.
Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from $beta$-stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus $^{60}$Zn. We have determined the nuclear level density of $^{60}$Zn using neutron evaporation spectra from $^{58}$Ni($^3$He, n) measured at the Edwards Accelerator Laboratory. We compare our results to a number of theoretical predictions, including phenomenological, microscopic, and shell model based approaches. Notably, we find the $^{60}$Zn level density is somewhat lower than expected for excitation energies populated in the $^{59}$Cu(p,$gamma$)$^{60}$Zn reaction under rp-process conditions. This includes a level density plateau from roughly 5-6 MeV excitation energy, which is counter to the usual expectation of exponential growth and all theoretical predictions that we explore. A determination of the spin-distribution at the relevant excitation energies in $^{60}$Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate for the $^{59}$Cu(p,$gamma$)$^{60}$Zn reaction rate at X-ray burst temperatures.
Cross section measurements of the $^{58}$Ni($alpha$,$gamma$)$^{62}$Zn reaction were performed in the energy range $E_{alpha}=5.5-9.5$ MeV at the Nuclear Science Laboratory of the University of Notre Dame, using the NSCL Summing NaI(Tl) detector and the $gamma$-summing technique. The measurements are compared to predictions in the statistical Hauser-Feshbach model of nuclear reactions using the SMARAGD code. It is found that the energy dependence of the cross section is reproduced well but the absolute value is overestimated by the prediction. This can be remedied by rescaling the $alpha$ width by a factor of 0.45. Stellar reactivities were calculated with the rescaled $alpha$ width and their impact on nucleosynthesis in type Ia supernovae has been studied. It is found that the resulting abundances change by up to 5% when using the new reactivities.
Transfer reactions provide information about the single-particle nature of nuclear levels. In particular, the differential cross sections from these measurements are sensitive to the angular momentum of the transferred particle and the spectroscopic factor of the populated level. However, the process of extracting these properties is subject to uncertainties, both from experimental and theoretical sources. By integrating the distorted wave Born approximation into a Bayesian model, we propagate these uncertainties through to the spectroscopic factors and orbital angular momentum values. We use previously reported data of the proton pickup reaction $^{70}$Zn$(d, ^3!text{He}) ^{69}$Cu as an example. By accounting for uncertainties in the experimental data, optical model parameters, and reaction mechanism, we find that the extracted spectroscopic factors for low lying states of $^{69}$Cu are subject to large, asymmetric uncertainties ranging from $35 %$ to $108 %$. Additionally, Bayesian model comparison is employed to assign probabilities to each of the allowed angular momentum transfers. This method confirms the assignments for many states, but suggests that the data for a state lying at $3.70$ MeV is better characterized by an $ell = 3$ transfer, rather than the previously reported $ell = 2$.
We report the observation of a very exotic decay mode at the proton drip-line, the $beta$-delayed $gamma$-proton decay, clearly seen in the $beta$ decay of the $T_z$ = -2 nucleus $^{56}$Zn. Three $gamma$-proton sequences have been observed after the $beta$ decay. Here this decay mode, already observed in the $sd$-shell, is seen for the first time in the $fp$-shell. Both $gamma$ and proton decays have been taken into account in the estimation of the Fermi (F) and Gamow Teller (GT) strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.
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