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Measured cross section of the 151 Eu(α, γ) 155 Tb reaction. The last three rows show the average results of the measurement carried out at the same energy.
Source publication
In order to extend the experimental database relevant for the astrophysical
gamma-process towards the unexplored heavier mass region, the cross sections of
the 151Eu(alpha,gamma)155Tb and 151Eu(alpha,n)154Tb reactions have been
measured at low energies between 12 and 17 MeV using the activation technique.
The results are compared with the predictio...
Contexts in source publication
Context 1
... the lowest measured energies only upper limits could be given to the partial cross sections to the ground or m2 states. Tables 2 and 3 show the results of the 151 Eu(α, γ) 155 Tb and 151 Eu(α,n) 154 Tb cross section measurements, respectively. The effective center of mass energies in the second columns take into account the energy loss of the beam in the target which was between 15 and 35 keV. ...
Context 2
... the final uncertainties the independent uncertainties have been added quadratically. The uncertainties for each data point given in Tables 2 and 3 are not independent as they contain both the independent uncertainties (like the counting statistics) and the common systematic uncertainties. ...
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Citations
... Gyürky et al. measured the cross sections for the 151 Eu (α, γ) reaction using the activation technique at energies between E cm = (12 -17) MeV [9]. Furthermore, they performed statistical model calculations and found that the predictions are overestimated by a factor of 2. Kiss et al. employed the activation technique to measure the cross sections for the reaction 162 Er (α, γ) at the astrophysically relevant energies of E cm = (11.21 ...
... The σ exp were taken from Refs. [9,10,12,15]. Fig. (1) depicts the cross sections for all p-nuclei under investigation for the different α-OMPs. The rms values were calculated for the suitable combinations. ...
... The σ exp were taken from Refs. [9,10,12,15]. Furthermore, we have computed the nuclear reaction rates using the model combinations with the least rms errors. The nuclear reaction rates are critical for the descriptions of stellar models. ...
Investigation of the cross sections for (α, γ) reactions for p-nuclei 90Zr, 121Sb, 151Eu, and 162Er was conducted by varying
different α- Optical Model Potentials (OMPs) for a set of Level Density Model (LDM) and Radiative Strength Function
(RSF). The calculations were performed within the framework of TALYS-1.96 code, with the primary inputs being the
OMP, the LDM, and the RSF. We have fine-tuned the input models of TALYS-1.96 to regenerate the experimental data of
cross sections. The present investigation was analyzed based on the root mean square error (rms). Good agreement was
achieved for all nuclei under study using various model combinations. Based on the radiative capture cross sections, we
have computed the rates which can be used as inputs to various astrophysical models.
... However, the practical application of 155 Tb is constrained by the difficulties associated with its production. It can be obtained in reactions under the action of protons [6][7][8] and deuterons [9][10][11] on isotopes of gadolinium, alpha particles on isotopes of europium [8,12,13]. Most of these reactions lead to the simultaneous formation of neighboring radionuclides. ...
Introduction
¹⁵⁵Tb (T1/2 = 5.32 d) is considered both as a promising Auger electron emitter and as a diagnostic pair for other therapeutic terbium radionuclides. Despite several methods for its production proposed, it remains scarcely available. Most of the methods using low-energy protons and deuterons beams result in a high content of radionuclidic impurities. High purity ¹⁵⁵Tb can be obtained using high-energy proton beams combined with online mass separation of products, but the method remains inaccessible to most potential consumers. We have proposed an indirect method for the production of ¹⁵⁵Tb via formation of ¹⁵⁵Dy (T1/2 = 9.9 h), which can be implemented using medium energy alpha particles beam.
Methods
Gadolinium oxide targets of natural isotopic composition were irradiated by 60 MeV alpha particles beam on a U-150 cyclotron of the National Research Center “Kurchatov Institute”. The cross sections of nuclear reactions were measured by the stack foil technique, detecting the gamma radiation of the activation products. Gd, Tb, and Dy were separated by extraction chromatography using the LN Resin sorbent in nitric media. The isolated dysprosium fraction was stored for a day, and the formed ¹⁵⁵Tb was isolated by the same method.
Results
The cross sections for the formation of ¹⁵⁹Gd, ¹⁵³⁻¹⁵⁶Tb, and 155,157Dy under irradiation by alpha particles of a gadolinium target of natural isotopic composition in the energy range 20–60 MeV have been measured. The ¹⁵⁵Dy yield on a thick target at 60 MeV was 35 MBq/μAh, which makes it possible to obtain 1 GBq ¹⁵⁵Tb as a result of 12-hour irradiation with a beam current of 50 μA. Extraction chromatography on LN Resin sorbent in nitric enabled quick and efficient separation of Gd, Tb, and Dy. The radiochemical yield of Dy was 95%, for Tb > 95%. The main radionuclidic impurity is ¹⁵³Tb (T1/2 = 2.34 d; <5.4% of ¹⁵⁵Tb activity).
Conclusions
The developed method allows the production of therapeutic amounts of ¹⁵⁵Tb with acceptable radionuclidic purity without the need for isotopically enriched materials.
The amount of ¹⁵⁵Tb is sufficient for its use in Auger therapy, as well as for preclinical studies of the suitability of SPECT preparations in laboratory animals. Nevertheless, to obtain higher activities, a longer irradiation time and a higher projectile current are proposed.
The ¹⁵³Tb radionuclide present in the final preparation has a shorter half-life than the target radionuclide, and its hard γ-lines have a probability of emission of less than 1%, from which it can be concluded that the negative effect will not be significant. However, a product of this purity and type of contamination requires additional testing for toxicity in living organisms. The final sample also includes a certain amount of ¹⁵⁷Tb (T1/2 = 71 a, the only γ-line 54.5 keV Iγ = 0.0084%), which will complicate the labeling conditions. Thus, more research is needed in the labeling area.
It should be noted that the use of gadolinium enriched in the ¹⁵⁵Gd or ¹⁵⁶Gd nuclide as a target will help not only reduce the amount of impurities but also increase the yield of ¹⁵⁵Tb.
... Despite the fact that various theoretical and experimental investigations of α-induced reaction relevant to the production of p-nuclei (see e.g., Refs. [22][23][24][25][26][27][28][29][30][31][32][33][34][35] and references therein) have been performed in order to considerably enhance the reliability of the nuclear physics inputs to the Hauser-Feshbach (HF) statistical model [36], the calculations of nucleosynthesis have still been suffered from a pronounced underproduction of the most abundant p-isotopes in the light and intermediate regions [37][38][39]. ...
The present paper examines the effect of temperature-dependent repulsive core potential on the fusion reactions of the \(\alpha \) particle relevant to the production of p-nuclei such as \(^{154}\)Sm, \(^{162}\)Dy, \(^{166}\)Er, and \(^{197}\)Au. For this purpose, the \(\alpha \)-nucleus potentials making use of the double folding model with the density-dependent CDM3Y3 interaction plus the temperature-dependent repulsion (CDM3Y3+Repulsion) are employed. In addition, three nuclear level density (NLD) models of Fermi-Gas (FG), Hartree–Fock BCS (HFBCS), and exact pairing plus independent-particle model (EP+IPM) are used to describe the temperature-dependent excitation energy of the compound nucleus produced in the fusion reaction. The results obtained show that temperature has a significant effect on the repulsive core potential, and different NLD models predict different fusion potentials, especially at high temperatures and near the center point (origin) of the interaction. Going further away from the origin, the repulsive core potential decreases to approximately zero near the barrier region, while at sufficiently far distances, it is least affected by nuclear temperature. The calculated fusion cross sections using the CDM3Y3+Repulsion potential are only affected by the diffuseness parameter of the repulsive potential \(a_\mathrm{{rep.}}\) in the region above the Coulomb barrier, and a good agreement with the experimental data is found at \(a_\mathrm{rep.}=0.35\) fm. Hence, the effect of repulsive potential on the \(\alpha \)-induced reactions is only justified as a correction term, which is added to resolve the Pauli principle problem. This conclusion is in line with those reported previously using similar formalism but for other fusion reactions of heavy nuclei.
... Encouraged by this successful application of the pBTM for 197 Au + α, we have calculated σ reac for a series of αinduced reactions of heavy target nuclei above A = 150. Fig. 2 shows that the predictions from the pBTM are in excellent agreement with recent experimental data [35][36][37][38][39][40][41][42]. Typical deviations are less than a factor of two which is marked as grey-shaded uncertainty band in Fig. 2. No parameter adjustment to reaction cross sections is necessary for the present calculations because the real part of the ATOMKI-V1 potential is completely constrained from elastic scattering and an imaginary part is not required in the simple pBTM. ...
... As an alternative to the statistical model, a simple barrier transmission model is suggested where the total reaction cross section is calculated from the transmission through the Coulomb barrier in a real (Color online) Total reaction cross section σreac (given as astrophysical S-factor) for α-induced reactions above A = 150. The pBTM predicts practically all experimental data [35][36][37][38][39][40][41][42] within a factor of two (grey shaded). The dotted lines show the results from the many-parameter AOMP of [20]. ...
The prediction of stellar ($\gamma$,$\alpha$) reaction rates for heavy nuclei is based on the calculation of ($\alpha$,$\gamma$) cross sections at sub-Coulomb energies. These rates are essential for modeling the nucleosynthesis of so-called $p$-nuclei. The standard calculations in the statistical model show a dramatic sensitivity to the chosen $\alpha$-nucleus potential. The present study explains the reason for this dramatic sensitivity which results from the tail of the imaginary $\alpha$-nucleus potential in the underlying optical model calculation of the total reaction cross section. As an alternative to the optical model, a simple barrier transmission model is suggested. It is shown that this simple model in combination with a well-chosen $\alpha$-nucleus potential is able to predict total $\alpha$-induced reaction cross sections for a wide range of heavy target nuclei above $A \gtrsim 150$ with uncertainties below a factor of two. The new predictions from the simple model do not require any adjustment of parameters to experimental reaction cross sections whereas in previous statistical model calculations all predictions remained very uncertain because the parameters of the $\alpha$-nucleus potential had to be adjusted to experimental data. The new model allows to predict the reaction rate of the astrophysically important $^{176}$W($\alpha$,$\gamma$)$^{180}$Os reaction with reduced uncertainties, leading to a significantly lower reaction rate at low temperatures. The new approach could also be validated for a broad range of target nuclei from $A \approx 60$ up to $A \gtrsim 200$.
... On the other hand, measured experimental cross sections are needed to be extrapolated to the astrophysical energies, because most of the experiments have been performed at higher energies than astrophysical energies [11][12][13][14][15][16]. An alternative method to the extrapolation of the experimental cross sections to lower energies is to calculate the cross sections theoretically by using the best nuclear parameters that are deduced from the comparison of the experimental results at energies close to the astrophysical energies. ...
The theoretical cross section calculations for the astrophysical $p$ process are needed because the most of the related reactions are technically very difficult to be measured in the laboratory. Even if the reaction was measured, most of the measured reactions have been carried out at the higher energy range from the astrophysical energies. Therefore, almost all cross sections needed for $p$ process simulation has to be theoretically calculated or extrapolated to the astrophysical energies. The $^{112}$Sn($\alpha$,$\gamma$)$^{116}$Te is an important reaction for the $p$ process nucleosynthesis. The theoretical cross section of the $^{112}$Sn($\alpha$,$\gamma$)$^{116}$Te reaction was investigated for different global optical model potentials, level density and strength function models at the astrophysically interested energies. Astrophysical $S$ factors were calculated and compared with experimental data available in EXFOR database. The calculation with the optical model potential of the dispersive model by Demetriou et al., and Back-shifted Fermi gas level density model and Brink-Axel Lorentzian strength function model best served to reproduce experimental results at astrophysically relevant energy region. The reaction rates were calculated with these model parameters at the $p$ process temperature and compared with the current version of the reaction rate library Reaclib and Starlib.
... Comparisons of theoretical predictions with the few available data at low energy (see section 6.3.1) revealed a mixed pattern of good reproduction and some cases of maximally 2 − 3 times overprediction of the (α,γ) cross sections when using the "standard" potential of [135] (see, e.g., [140][141][142][143][144] and references therein; see also section 7.2). So far, the only known example of a larger deviation was found in 144 Sm(α,γ) 148 Gd (determining the 144 Sm/ 146 Sm production ratio in the γ-process, see section 4.2) where the measured cross section is lower than the standard prediction by more than an order of magnitude at astrophysical energies [139], inexplicable by global potentials and also not reproduced using a potential independently derived from elastic α-scattering at higher energy [145]. ...
... On the other hand, particle emitting reaction cross sections, such as (p,n), (α,n) or (α,p), have also been measured along with the (p,γ) or (α, γ) reactions, or on their own right. These reactions can provide valuable additional The measured cross section data can be found in [139][140][141][142][143][169][170][171][172][173][174][175][176][177][178]. ...
A small number of naturally occurring, proton-rich nuclides (the p-nuclei) cannot be made in the s- and r-processes. Their origin is not well understood. Massive stars can produce p-nuclei through photodisintegration of pre-existing intermediate and heavy nuclei. This so-called γ-process requires high stellar plasma temperatures and occurs mainly in explosive O/Ne burning during a core-collapse supernova. Although the γ-process in massive stars has been successful in producing a large range of p-nuclei, significant deficiencies remain. An increasing number of processes and sites has been studied in recent years in search of viable alternatives replacing or supplementing the massive star models. A large number of unstable nuclei, however, with only theoretically predicted reaction rates are included in the reaction network and thus the nuclear input may also bear considerable uncertainties. The current status of astrophysical models, nuclear input and observational constraints is reviewed. After an overview of currently discussed models, the focus is on the possibility to better constrain those models through different means. Meteoritic data not only provide the actual isotopic abundances of the p-nuclei but can also put constraints on the possible contribution of proton-rich nucleosynthesis. The main part of the review focuses on the nuclear uncertainties involved in the determination of the astrophysical reaction rates required for the extended reaction networks used in nucleosynthesis studies. Experimental approaches are discussed together with their necessary connection to theory, which is especially pronounced for reactions with intermediate and heavy nuclei in explosive nuclear burning, even close to stability.
... In recent years, a number of α-beam activation measurements have been conducted for targets relevant to the p process [4][5][6][7][8][9][10][11][12]. Cross sections of the corresponding (α,x) reactions were measured at, or close to, the astrophysically relevant energy. ...
The statistical Hauser-Feshbach (HF) model performs poorly in calculating the (γ, α) rates that are critical to the p process. Experimental work on elastic scattering of the tellurium isotopic chain [A. Palumbo et al. (unpublished)] provided a new parametrization of the α-optical potential and consequently new HF calculations of the (α,x) cross sections on 120−130Te. However, reliable experimental cross sections of these isotopes have not been measured at energies relevant to the p process. To test the reliability of the HF calculations, we measured the (α,n) cross sections on 120Te, one of the p nuclei, using the activation technique. The results are compared with the HF model calculations.
In this work, we examine cross sections for (α, γ) reactions on p-nuclei, including 90Zr, 121Sb, 151Eu, and 162Er at astrophysically relevant energies. By using our recently developed α optical model potential (α-OMP), the (α, γ) cross sections were calculated within six models of radiative strength functions (RSF) which consisted of the microscopic HFB-QRPA model based on the BSk-14 Skyrme force, the HF-BCS theory using Skyrme parameters, the EGLO model, SMLO model, the empirical SMLO (SMLOg) and global semi-microscopic (D1M-QRPAg) models. The numerical results is then compared to the measured data of (α, γ) cross sections. For the considered (α, γ) reactions, the EGLO, SMLO, and HFB results are typically greater than the measured data. In addition, the comparison has indicated that the RSF models of SMLOg and D1M-QRPAg best fit the measured data with rms smaller than 0.2 within our proposed α-OMP. Therefore, for the (α, γ) reactions on the selected targets, RSF models of SMLOg and D1M-QRPAg are strongly recommended. The results are significant for a further systematic examination to evaluate which RSF model is most appropriate for studying (α, γ) reactions on p-nuclei in general.
The production possibility of 161Tb and 155Tb by irradiating of natural dysprosium with gamma rays obtained by decelerating an electron beam with an energy of 55 MeV has been demonstrated experimentally. The yield of 161Tb was 14.4 × 103 Bq × μA-1 × h-1 × cm2 × gDy2O3-1. Simultaneously, upon irradiation, 155Dy is formed with the yield of 25 × 103 Bq × μA-1 × h-1 × cm2 × gDy2O3-1, which leads to the formation of 1.6 × 103 Bq × μA-1 × h-1 × cm2 × gDy2O3-1 of 155Tb. It has been shown that the isolation of terbium radioisotopes from tens of mg of dysprosium target can be achieved by extraction chromatography, and final separation yield was 39%. The impurity of 160Tb is 7.3% of the 161Tb activity at EOB.
The present paper proposes an improved version of the α-nucleus optical model potential (α-OMP), in which the real part of the potential is determined by the double-folding calculation using the density-dependent CDM3Y1 interaction plus a repulsive potential. The imaginary part of the α-OMP is treated by a Woods-Saxon form with energy-dependent depth, while its real part is corrected by including the contribution of the dispersion relation derived from the strong variation of the potential at energies in the vicinity of the Coulomb barrier. The proposed potential is validated by calculating the (α,n) and (α,γ) cross sections on different target nuclei and the obtained results are compared with those predicted by the recent α-OMP suggested by Avrigeanu, as well as the available experimental data. The impacts of the energy-dependent imaginary part and the real dispersive term on the α-induced cross sections are also investigated. The results obtained show that the proposed α-OMP together with that of Avrigeanu describe reasonably well the experimental cross sections of all (α,n) reactions being considered. In addition, the imaginary part of the proposed potential has a strong energy-dependent effect on the α-induced cross section in the energy region below the Coulomb barrier, in particular for radiative α-capture reactions. Two potentials also describe well the cross sections of (α,γ) reactions after rescaling the radiative γ width. This leads to our conclusion that the present α-OMP can provide precise α widths for the study of reactions relevant to the production of p nuclei, and therefore more intensive theoretical research on the radiative strength functions is required.
