FIG 8 - uploaded by Ann Cecilie Larsen
Content may be subject to copyright.
![(Color online) Level densities at the neutron separation energy extracted from known D 0 values (filled symbols) [47]. The systematics (solid lines) are taken from Ref. [35] with all values scaled by a factor of 0.618. The estimate for 160 Dy (open circle) is taken from the scaled curve.](profile/Ann-Cecilie-Larsen/publication/324690865/figure/fig4/AS:618424338243595@1524455260668/Color-online-Level-densities-at-the-neutron-separation-energy-extracted-from-known-D-0.png)
(Color online) Level densities at the neutron separation energy extracted from known D 0 values (filled symbols) [47]. The systematics (solid lines) are taken from Ref. [35] with all values scaled by a factor of 0.618. The estimate for 160 Dy (open circle) is taken from the scaled curve.
Source publication
The photo-neutron cross sections of $^{162,163}\rm{Dy}$ have been measured for the first time in an energy region from the neutron threshold ($S_n$) up to $\approx$ $13$~MeV. The ($\gamma$,n) reaction was induced with quasi-monochromatic laser Compton-scattered $\gamma$ rays, produced at the NewSUBARU laboratory. The corresponding $\gamma$-ray stre...
Contexts in source publication
Context 1
... α is the slope correction and δ is an energy shift. These calculations reproduce the overall shape of the experimental data very well for the even-even isotopes; the case of 164 Dy is shown in Fig. 7. For the odd isotopes, the shape of the NLD is less compatible with the data; we have chosen to still apply (see text). the spin distribution of Ref. [46] to provide an anchor point at S n for the normalization of the NLD, but use the constant- temperature model for the interpolation as described in the following paragraph. The spin cutoff parameter σ H (E) is ex- tracted from the HFB calculations by a fit of Eq. (8) for each excitation-energy bin. Table I lists the D 0 and σ J values at S n used to determine the level density ρ(S n ) with a and E 1 parameters taken from Ref. [35]. The additional E d and σ d values are used to get the energy dependence according to Eq. (9). Also, the parameters α and δ are given. The D 0 and Γ γ (S n ) values are taken from s-wave neutron capture reac- tions reported in the RIPL-3 compilation [47]. As 159 Dy is un- stable, no neutron capture data is available for 160 Dy and we therefore use arguments from systematics. Figure 8 demon- strates how ρ(S n ) is estimated for 160 ...
Similar publications
Arms control treaties are necessary to reduce the large stockpiles of the nuclear weapons that constitute one of the biggest dangers to the world. However, an impactful treaty hinges on effective inspection exercises to verify the participants’ compliance to the treaty terms. Such procedures would require verification of the authenticity of a warhe...
Arms control treaties are necessary to reduce the large stockpiles of the nuclear weapons that constitute one of the biggest dangers to the world. However, an impactful treaty hinges on effective inspection exercises to verify the participants' compliance to the treaty terms. Such procedures would require verification of the authenticity of a warhe...
Citations
... The neutron yield cross section experimentally determined by the number of incident LCS γ rays (N γ ), the areal density of target nuclei (N t ), and the number of neutrons detected (N n ) represents a quantity that is expressed by folding the photoneutron emission cross section σ (E γ ) with the energy distribution of the LCS γ -ray beam [32]): ...
... Experimentally, cross sections are determined in the monochromatic approximation, which we plot at the maximum energy of the LCS γ -ray beam E max as the experimental cross section, σ E max exp . Photoneutron emission cross sections σ (E γ ) in Eq. (1) were unfolded at E max with the deconvolution method [32]. The method was routinely applied to the data of Ni [33], Tl [34], and Ba [35] isotopes. ...
... The maximum energy of the incident LCS γ -ray beams in the current experiment was changed in rather small increments and the interpolation was done with a third-order polynomial in numerical iterations of solving a set of linear equations (Eq. (3) of Ref. [32]) toward a convergence of the reduced χ 2 to unity. This ensures that no spurious fluctuations are caused by the choice of parameters for the cubic spline. ...
Photoneutron emission cross sections were measured for C13 below 2n threshold using quasimonochromatic γ-ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. The data show fine structures in the low-energy tail of the giant-dipole resonance; the integrated strength of the fine structure below 18 MeV is intermediate among the past measurements with bremsstrahlung and the positron annihilation γ rays. We compare the photoneutron emission data with the talys statistical model calculation implemented with the simple modified Lorentzian model of E1 and M1 strengths. We also compare the total photoabsorption cross sections for C13 with shell model and antisymmetrized molecular dynamics calculations as well as the statistical model calculation. We further investigate the consistency between the present photoneutron emission and the reverse C12(n,γ) cross sections through their corresponding astrophysical rate.
... In order to find σ , we utilize a folding iteration method. The main features of this method are as follows [34]: ...
In this work, we present new data on the W182,183,184(γ,n) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and γ-ray strength function of W186 from data on the W186(α,α′γ)W186 reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the W186(γ,n) cross section with our new W182,183,184(γ,n) and (α,α′γ)W186 data sets, we have deduced the W186γ-ray strength function in the range of 1<Eγ<6 MeV and 7<Eγ<14 MeV. Our data are used to extract the level density and γ-ray strength functions needed as input to the nuclear-reaction code talys, providing an indirect, experimental constraint for the W185(n,γ)W186 cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 database, our results are on average lower for the relevant energy range kBT∈[5,100] keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao et al. [At. Data Nucl. Data Tables 76, 70 (2000)] and the cross section experimentally constrained on photoneutron data of Sonnabend et al. [Astrophys. J. 583, 506 (2003)] are significantly higher than our result. The lower value by Mohr et al. [Phys. Rev. C 69, 032801(R) (2004)] is in very good agreement with our deduced MACS. Our new results provide an improved uncertainty estimate for the (n,γ)W186 reaction rate, which is one important ingredient in simulations for investigating the neutron density and the Os186,187 production in the s process.
... Here, E x , J and π may be averaged out using the generalized Brink-Axel hypothesis [14,15], shown to hold for Dy nuclei [16], and it is usually sufficient to consider dipole radiations E1 and M 1 that dominate in the quasicontinuum region (see, e.g. Ref. [17]). ...
... This is to be compared to the B SR calculated by integrating the SLO fit of the SR using the parameters in Table II between 0 and 10 MeV, giving a value of 6.3(10) µ 2 N . The latter value assumes the E1 contribution stemming from the GEDR tail to be smaller than for the former value, and is comparable to values obtained for 163,164 Dy by Renstrøm et al. [16]. ...
The $\gamma$-ray strength function and the nuclear level density of $^{167}$Ho have been extracted using the Oslo method from a $^{164}\text{Dy}(\alpha,p\gamma)^{167}$Ho experiment carried out at the Oslo Cyclotron Laboratory. The level density displays a shape that is compatible with %can be approximated with the constant temperature model in the quasicontinuum, while the strength function shows structures indicating the presence of both a scissors and a pygmy dipole resonance. Using our present results as well as data from a previous $^{163}\text{Dy}(\alpha,p\gamma)^{166}$Ho experiment, the $^{165}\text{Ho}(n,\gamma)$ and $^{166}\text{Ho}(n,\gamma)$ 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 2~$M_\odot$, [Fe/H]=-0.5 AGB star. We show that the newly obtained $^{165}\text{Ho}(n,\gamma)$ MACS affects the final $^{165}$Ho abundance, while the $^{166}\text{Ho}(n,\gamma)$ MACS only impacts the enrichment of $^{166,167}$Er to a limited degree due to the relatively rapid $\beta$ decay of the thermalized $^{166}$Ho at typical $s$-process temperatures.
... For example, the Oslo group calculated the global level density parameter by using a systematic equation in which the level density parameters of isobars are the same, i.e., a = 0.21A 0.87 with A being the mass number, but Fig. 2 of Ref. [16] demonstrates that the level density parameters of isobars can differ from each others up to 25%, and even more in some specific cases. In 2018, the Oslo group re-analyzed their previously conducted experiment and updated the experimental NLDs of 161−164 Dy nuclei [17]. However, the heat capacities of these Dy isotopes have not yet been reexamined. ...
... In the present work, we calculate the heat capacities of 161−164 Dy nuclei using the most recent recommended NLD data in Ref. [17] in combination with the BSFG NLD model with energy-dependent parameters. The updated heat capacities will be compared with those reported in 2003 and 2012 in Refs. ...
... The damping parameter γ in Eq. (4) determines how rapidly a approaches a. In the present work, we take the values of δW from RIPL-3 database [22], and consider a, E 1 , and γ to be free parameters, whose values are determined by fitting the BSFG NLD to the experimental NLD data given in Ref. [17] for 161−164 Dy. The spin cut-off parameter σ is determined using the following equation [19] σ 2 = 0.0888A 2/3 a(E − E 1 ) . ...
This work presents the updated heat capacities of \(^{161-164}\)Dy nuclei in the nuclear temperature region from 0 to 1 MeV. The updated heat capacities are obtained within the canonical ensemble method making use of the most recent and recommended experimental nuclear level density (NLD) data together with those calculated within the back-shifted Fermi gas (BSFG) model with energy-dependent parameters. By comparing the updated heat capacities with the un-updated ones, which are obtained by using the old experimental NLD data and the BSFG with energy-independent parameters, we found that the updated and un-updated heat capacities are almost identical at low temperature, but differ from each others at high temperature. This discrepancy can be interpreted by the damping of nuclear shell structure with increasing the excitation energy. Besides, we observe that the S-shape in the updated heat capacities is much more pronounced in even-even Dy isotopes than in even-odd ones, whereas the un-updated heat capacities do not clearly exhibit this S-shape. Therefore, the updated heat capacities should provide a more convincing evidence for the signature of pairing phase transition in nuclear systems.
... This region of the nuclear chart is interesting because of the variety in deformation (from close-to-spherical to well-deformed prolate shapes [1]), and it is an ideal region for studying nuclear statistical properties (see, e.g., Refs. [2][3][4][5][6]). ...
... While the SR has been observed in many even-even and odd-even nuclei (see, e.g., Refs. [6,8]), it has not yet been studied thoroughly in odd-odd ones, with the notable exception of the two-step cascade experiment on 160 Tb by Kroll et al. [9]. While many studies have been carried out using the nuclear resonance fluorescence (NRF) technique (see Ref. [8] and references within), this technique has usually been applied in the low excitation-energy region. ...
... As already mentioned, NFR experiments have revealed a total strength of ≈3 μ 2 N for well-deformed rare-earth nuclei. In contrast, experiments utilizing the two-step cascade method following neutron capture [14][15][16] have found about twice the integrated strength, which is also the case for data analyzed with the Oslo method [3,4,6,[17][18][19][20][21][22]. One possible explanation for this discrepancy is related to the different moments of inertia the nucleus attains for ground-state excitations and quasicontinuum decay (for which in the latter case, many quasiparticles are involved; see, e.g., Uhrenholt et al. [23]). ...
The γ-strength function and the nuclear level density for the odd-odd, rare-earth nucleus Ho166 have been extracted from Dy163(α,pγ)Ho166 data using the Oslo method. A structure at ≈3 MeV in the γ-strength function is interpreted as the M1 scissors resonance. By employing three different methods we find that its strength depends rather strongly on the modeling of the E1 strength, while its centroid does not. The Ho166 scissors resonance parameters are consistent with previous results on other rare-earth nuclei.
... The neutron yield cross section experimentally determined by the number of incident LCS γ rays (N γ ), the areal density of target nuclei (N t ), and the number of neutrons detected (N n ) represents a quantity that is expressed by folding the photoneutron emission cross section σ (E γ ) with the energy distribution of the LCS γ -ray beam [32]): ...
... Experimentally, cross sections are determined in the monochromatic approximation, which we plot at the maximum energy of the LCS γ -ray beam E max as the experimental cross section, σ E max exp . Photoneutron emission cross sections σ (E γ ) in Eq. (1) were unfolded at E max with the deconvolution method [32]. The method was routinely applied to the data of Ni [33], Tl [34], and Ba [35] isotopes. ...
... The maximum energy of the incident LCS γ -ray beams in the current experiment was changed in rather small increments and the interpolation was done with a third-order polynomial in numerical iterations of solving a set of linear equations (Eq. (3) of Ref. [32]) toward a convergence of the reduced χ 2 to unity. This ensures that no spurious fluctuations are caused by the choice of parameters for the cubic spline. ...
Photoneutron emission cross sections were measured for $^{13}$C below $2n$ threshold using quasi-monochromatic $\gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. The data show fine structures in the low-energy tail of the giant-dipole resonance; the integrated strength of the fine structure below 18~MeV is intermediate among the past measurements with bremsstrahlung and the positron annihilation $\gamma$ rays. We compare the photoneutron emission data with the {\sf TALYS} statistical model calculation implemented with the simple modified Lorentzian model of $E1$ and $M1$ strengths. We also compare the total photoabsorption cross sections for $^{13}$C with the shell model and antisymmetrized molecular dynamics calculations as well as the statistical model calculation. We further investigate the consistency between the present photoneutron emission and the reverse $^{12}$C(n,$\gamma$) cross sections through their corresponding astrophysical rate.
... In order to find σ, we utilize a folding iteration method. The main features of this method are as follows [31]: 1) As a starting point, we choose for the 0th iteration, a constant trial function σ 0 . This initial vector is multiplied with D, and we get the 0th folded vector σ 0 f = Dσ 0 . ...
In this work, we present new data on the $^{182,183,184}$W($\gamma,n$) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and $\gamma$-ray strength function of $^{186}$W from data on the $^{186}$W($\alpha,\alpha^\prime\gamma$)$^{186}$W reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the $^{186}$W($\gamma,n$) cross section with our new $^{182,183,184}$W($\gamma,n$) and ($\alpha,\alpha^\prime\gamma$)$^{186}$W data sets, we have deduced the $^{186}$W $\gamma$-ray strength function in the range of $1 < E_\gamma < 6$ MeV and $7 < E_\gamma < 14$ MeV. Our data are used to extract the level density and $\gamma$-ray strength functions needed as input to the nuclear-reaction code \textsf{TALYS}, providing an indirect, experimental constraint for the $^{185}$W($n,\gamma$)$^{186}$W cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 data base, our results are on average lower for the relevant energy range $k_B T \in [5,100]$ keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao \textit{et al.} and the cross section experimentally constrained on photoneutron data of Sonnabend \textit{et al.} are significantly higher than our result. The lower value by Mohr \textit{et al.} is in very good agreement with our deduced MACS. Our new results could have implications for the $s$-process and in particular the predicted $s$-process production of $^{186,187}$Os nuclei.
... where we consider a normalized energy distribution with E mi S kn D(E γ , E mi )dE γ = 1. The above treatment has been successfully applied for photoneutron cross section measurements in the vicinity of the S n , where the electromagnetic interaction of the incident beam generates secondary photons with energies below photonuclear reaction thresholds [47]. However, the spectral condition no longer holds with the increase in the maximum energy of the incident LCS γ-ray beam. ...
... As the high energy GDR peak region folds with the low energy tail of the LCS beam, large fractions of the measured photoneutron reaction yields are generated by the tail of the energy distribution, especially for the (γ, n) channel. The experimental excitation function is obtained by unfolding the measured cross section, following the iterative procedure described in Ref. [47]. It is seen that the accuracy of the unfolded results is highly dependent on the good characterization of the LCS γ-ray spectra. ...
Intense, quasi-monochromatic, polarized $\gamma$-ray beams produced by Compton scattering of laser photons against relativistic electrons are used for fundamental studies and applications. Following a series of photoneutron cross section measurements in the Giant Dipole Resonance energy region performed at the NewSUBARU synchrotron radiation facility, we have developed the eliLaBr Monte Carlo simulation code for characterization of the scattered $\gamma$-ray photon beams. The code is implemented using Geant4 and is available on the GitHub repository (https://github.com/dan-mihai-filipescu/eliLaBr). Here we report the validation of the eliLaBr code on NewSUBARU LCS $\gamma$-ray beam flux and spectral distribution data and two applications performed with it for asymmetric transverse emittance profiles electron beams, characteristic for synchrotrons. The first application is based on a systematic investigation of transverse collimator offsets relative to the laser and electron beam axis. We show that the maximum energy of the LCS $\gamma$-ray beam is altered by vertical collimator offsets, where the edge shifts towards lower energies with the increase in the offset. Secondly, using the eliLaBr code, we investigate the effect of the laser polarization plane orientation on the properties of the LCS $\gamma$-ray beams produced with asymmetric emittance electron beams. We show that: 1. The use of vertically polarized lasers contributes to the preservation of the LCS $\gamma$-ray beam maximum energy edge by increasing the precision in the vertical collimator alignment. 2. Under identical conditions for the electron and laser beams phase-space distributions, the energy spectrum of the scattered LCS $\gamma$-ray beam changes with the laser beam polarization plane orientation: the use of vertically polarized laser beams slightly deteriorates the LCS $\gamma$-ray beam energy resolution.
... We, therefore, study the transition cross-sections and probabilities, photon strength functions, transition strengths, isospin character, and collectivity of the predicted E1 responses. 162,163 Dy isotopes [18]. Several theoretical works have calculated the GDR structures of the Dy isotopes using two different approaches [16,19]. ...
... On the other hand, experimental effort for the PDR in heavy, strongly deformed nuclei is still inadequate [29,30]. Some experimental studies can be mentioned in the literature where the low-lying dipole strength of the deformed nuclei was investigated up to 7.4 MeV [18,27]. If one considers the limitations of available experimental techniques, the theory is one of the most possible ways to investigate the PDR mode in well-deformed nuclei [17,[24][25][26][31][32][33][34][35][36][37][38][39][40]. ...
... Only for this nucleus, there is limited experimental data for photo-absorption cross sections up to 14 MeV. As can be seen from figure 2, our results for 162 Dy partly agree with the available experimental data from [18]. Due to the small numbers of experimental cross sections data, such comparison is not much reliable. ...
The excitation of pygmy dipole resonance (PDR) and giant dipole resonance (GDR) in even-even ¹⁵⁴⁻¹⁶⁴ Dy isotopes is examined through quasiparticle random-phase approximation (QRPA) with the effective interactions that restores the broken translational and Galilean invariances. In each isotope, an electric response emerges by showing ample distribution at energies below and above 10 MeV. We, therefore, study the transition cross sections and probabilities, photon strength functions, transition strengths, isospin character, and collectivity of the predicted E1 responses.
... For a detailed discussion and implementation of the Oslo method, see Ref. [24]. In this work, data from 56 Fe [30], 92 Zr [31], and 164 Dy [32] have been reanalyzed with the Oslo method using an intrinsic spin-distribution for the absolute normalization at S n . The γ SFs of those nuclei may therefore deviate slightly from results presented in previous publications. ...
... More details on the extraction of NLDs and γ SFs for 56 Fe, 92 Zr, and 164 Dy are discussed in Refs. [30][31][32]. ...
... This makes 164 Dy a feasible case for applying the shape method to the 164 Dy( 3 He, 3 He ) experimental data, measured with the CACTUS and SiRi arrays, from Refs. [32,56,57]. Furthermore, there are two interesting features in the previous findings of the γ SF: (i) a scissors resonance at E γ = 2.83(8) MeV is built on the tail of the giant dipole resonance and (ii) it has been speculated that an enhancement exists around E γ = 6-7 MeV due to the E 1 pygmy resonance [32]. ...
The shape method, a novel approach to obtain the functional form of the γ-ray strength function (γSF), is introduced. In connection with the Oslo method the slope of the nuclear level density (NLD) and γSF can be obtained simultaneously even in the absence of neutron resonance spacing data. The foundation of the shape method lies in the primary γ-ray transitions which preserve information on the functional form of the γSF. The shape method has been applied to Fe56, Zr92, and Dy164, which are representative cases for the variety of situations encountered in typical NLD and γSF studies. The comparisons of results from the shape method to those from the Oslo method demonstrate that the functional form of the γSF is retained regardless of nuclear structure details or Jπ values of the states fed by the primary transitions.
