Experimentally constrainedHo165,166(n,γ)rates and implications for thesprocess

Abstract

The γ -ray strength function and the nuclear level density of 167 Ho have been extracted using the Oslo method from a 164 Dy(α, pγ ) 167 Ho experiment carried out at the Oslo Cyclotron Laboratory. The level density displays a shape that is compatible with the constant temperature model in the quasicontinuum, while the strength function shows structures indicating the presence of both a scissors resonance and a pygmy dipole resonance. Using our present results as well as data from a previous 163 Dy(α, pγ ) 166 Ho experiment, the 165 Ho(n, γ ) and 166 Ho(n, γ ) eellian-averaged cross section (MACS) uncertainties have been constrained. The possible influence of the low-lying, long-lived 6 keV isomer 166 Ho in the s process is investigated in the context of a 2M , [Fe/H] = −0.5 asymptotic giant branch star. We show that the newly obtained 165 Ho(n, γ ) MACS affects the final 165 Ho abundance, while the 166 Ho(n, γ ) MACS only impacts the enrichment of 166,167 Er to a limited degree due to the relatively rapid β decay of the thermalized 166 Ho at typical s-process temperatures.

Uncertainties of nuclear level density estimated using Bayesian neural networks*

“…For the test sets, the NLD of 233 U-239 U and experimental data with 63 Ni, 70 Ni, and 167 Ho [26][27][28] are used. The MAEs of both the training and test sets are listed in Table 1.…”

“…To further test the predictions from the BNN models, we investigate the NLD for 63 Ni, 70 Ni, and 167 Ho [26][27][28] in Fig. 4.…”

“…In this study, we propose a BNN model to investigate the NLD and verify whether it can be used to make reliable predictions. The training set used in the BNN contains 282 nuclides, including six theoretical NLD models (BSFGM, GCM, GSM, HF-BCS, Gogny-HFB, and Skyrme-HFB), with Z , A taken from the TALYS 1.95 code [44], and the experimental 53-nuclide database measured using the Oslo method [26][27][28]. Approximately 70000 data points are used for training set.…”

“…2. The red solid lines are the mean values of the different nuclei, the dash lines and circles are the data of the models and Oslo experiment [26][27][28]. The pink band represents the 95% confidence interval, showing the uncertainty in the predictions of the BNN, which provides the uncertainty among all models and experimental data.…”

“…In this study, a BNN is used to train a set of NLDs that are uniformly described over a large range, considering the NLD calculated by the theoretical model and obtained experimentally using the Oslo method [26][27][28]. By training a neural network for the identification and reconstruction of the NLD, we can explore the model uncertainties in a comprehensive manner and provide a modelindependent method for the study of the NLD.…”