Complete spectroscopy of the 162Dy nucleus

Aprahamian, A.; Wu, Xiaofeng; Lesher, S. R.; Warner, D.D.; Gelletly, W.; Börner, H. G.; Hoyler, F.; Schreckenbach, K.; Casten, R. F.; Shi, Z.; Kusnezov, Dimitri; Ibrahim, Mohamed F.; Macchiavelli, A. O.; Brinkman, M.A.; Becker, J. A.

doi:10.1016/j.nuclphysa.2005.09.020

Cited by 27 publications

(36 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A partial level scheme with measured γ-ray transitions that are related to the isomer is shown in figure 5. The 504 keV and 380 keV transitions have been previously reported by Fields et al [7] and Aprahamian et al [9] although both works tentatively assigned the parent level as the (9 − ) member of a K π = (6 − ) band not detected in the present work. As the level is now shown to be isomeric, the earlier assignments need to be re-evaluated.…”

supporting

confidence: 69%

See 1 more Smart Citation

Discovery of a nonyrastKπ=8+isomer inDy162
Swan
¹
,
Walker
²
,
Podolyák
³

et al. 2011
Phys. Rev. C
10
0
4
0
View full text Add to dashboard Cite

The 160 Gd( 9 Be,α3n) 162 Dy reaction has been used to study high-spin states in 162 Dy. Pulsed beam conditions were utilised for enhanced isomer sensitivity. An isomer at 2188.1(3) keV with a half-life of 8.3(3) µs has been discovered and assigned K π = 8 + with a 2-quasineutron configuration. Among eleven γ-ray decay branches, an E2, ∆K= 8 transition to the ground-state band was observed with a reduced hindrance of fν =35, agreeing well with systematics correlating fν with the product of the valence neutron and proton numbers (NpNn) over an extended N, Z range. Small deviations from NpNn dependence are analysed for a range of 2-quasiparticle isomer decays, and interpreted as arising from a weak dependence on the isomer excitation energy relative to the yrast line.PACS numbers: 23.35.+g, 21.10.Ky, 23.20.Lv Understanding the decay rates from high-spin isomers in deformed nuclei remains a considerable challenge [1], and lacks an appropriate theoretical framework. Nevertheless, such isomers, apart from their own structural interest, may be important more generally -in astrophysical environments, at the limits of stability, and controversially, for novel energy storage applications [2]. The present work attempts to clarify the relative importance of some of the degrees of freedom involved in isomer deexcitation.The K quantum number is the projection of the angular momentum on the symmetry axis of the deformed nuclear shape. Half-life measurements for isomer decays that involve a change of K can establish the degree to which K is conserved. The reduced hindrance [1] for the isomeric state (f ν = F 1/ν W ) relates the Weisskopf hindrance factor for the decay (F W = T γ 1/2 /T W 1/2 ) to the K-forbiddenness (ν = ∆K − λ), where T γ 1/2 is the partial gamma half-life, T W 1/2 is the Weisskopf estimate, and λ is the γ-ray multipolarity. This systematic approach to categorising isomer decay rates can be extended by considering variables that reduce K-conservation by generating mixing [3].One form of K-mixing arises due to the Coriolis effect, which intensifies with decreasing neutron and proton number in the lower half of the N = 82 → 126 and Z = 50 → 82 shells due to the population of high-j, low-Ω orbitals. In contrast, greater axial asymmetry occurs with increasing neutron and proton number in the upper half of the shells, leading to an increase in K-mixing associated with γ-tunnelling, where γ is the axial asymmetry parameter. The systematic effect of Coriolis and γ-induced Kmixing may surprisingly be characterised through a single variable, the product of the valence neutron and proton numbers, N p N n , at least for 2-quasiparticle (2QP) iso- * Electronic address: t.swan@surrey.ac.uk mers decaying by E2 transitions [4]. The N p N n product has proven be useful in describing structural changes over extended regions [5]. For higher QP numbers there is a level-density effect that manifests as a dependence on the isomer's excitation energy relative to a rigid rotor (E − E R ), which is correlated with greater K-mixi...

show abstract

supporting

confidence: 69%

“…In the present work, all of the other direct isomeric branches, as well as the transitions above the isomer, are newly observed. The other parts of the level scheme are well established [7][8][9].…”

mentioning

confidence: 99%

Discovery of a nonyrastKπ=8+isomer inDy162
Swan
¹
,
Walker
²
,
Podolyák
³

et al. 2011
Phys. Rev. C
10
0
4
0
View full text Add to dashboard Cite

show abstract

“…4 shows the SMMC level densityρ(E x ) = ρ M=0 (E x ) (solid circles) and SMMC state density ρ(E x ) (open squares) of 162 Dy. We compare the SMMC level density with various experimental data sets: (i) level counting (solid histograms) [24,25], (ii) renormalized Oslo data (open circles) [26,27], and (iii) neutron resonance data (triangle) [28]. We find very good agreement between theory and experiments.…”

mentioning

confidence: 71%

“…We described . Also shown are experimental data sets for the level density: level counting at low excitation energies (histograms) [24,25], Oslo data at intermediate energies (open circles) [26,27], and the neutron resonance data (triangle) [28]. Bottom panel: thermal moment of inertia I of 162 Dy (solid circles) as a function of excitation energy Ex.…”

mentioning

confidence: 99%

Direct microscopic calculation of nuclear level densities in the shell model Monte Carlo approach

et al. 2015

View full text Add to dashboard Cite

Nuclear level densities are crucial for estimating statistical nuclear reaction rates. The shell model Monte Carlo method is a powerful approach for microscopic calculation of state densities in very large model spaces. However, these state densities include the spin degeneracy of each energy level, whereas experiments often measure level densities, in which each level is counted just once. To enable the direct comparison of theory with experiments, we introduce a method to calculate directly the level density in the shell model Monte Carlo approach. The method employs a projection on the minimal absolute value of the magnetic quantum number. We apply the method to nuclei in the iron region and to the strongly deformed rare-earth nucleus 162 Dy. We find very good agreement with experimental data and methods, including level counting at low energies, charged particle spectra and Oslo method data at intermediate energies, neutron and proton resonance data, and Ericson's fluctuation analysis at higher excitation energies. We also extract a thermal moment of inertia from the ratio between the state density and the level density, and observe that in even-even nuclei it exhibits a signature of a phase transition to a superconducting phase below a certain excitation energy. Introduction. The level density is among the most important statistical properties of atomic nuclei. It appears explicitly in Fermi's golden rule for transition rates and in the Hauser-Feshbach theory [1] of statistical nuclear reactions. Yet its microscopic calculation presents a major theoretical challenge. In particular, correlations have important effects on nuclear level densities but are difficult to include quantitatively beyond the mean-field approximation. The configuration-interaction (CI) shell model is a suitable framework, in which both shell effects and correlations are included. However, the dimension of the required model space increases combinatorially with the number of single-particle states and/or the number of nucleons, and conventional shell model calculations become intractable in medium-mass and heavy nuclei. This difficulty has been overcome using the shell model Monte Carlo (SMMC) approach [2][3][4][5]. The SMMC has proved to be a powerful method to calculate microscopically nuclear state densities [6][7][8][9][10][11].The SMMC method is based on a thermodynamic approach, in which observables such as the thermal energy are calculated by tracing over the complete many-particle Hilbert space at fixed number of protons and neutrons. Thus, the calculated density is the state density, which takes into account the magnetic degeneracy of the nuclear levels, i.e., each level of spin J is counted 2J + 1 times.However, experiments often measure the level density, in which each level is counted exactly once, irrespective of its spin degeneracy [12][13][14]. To make direct comparison of theory with experiments, it would be necessary to calculate the level density within the SMMC approach. A spin-projection method, introduced in Ref. 10...

show abstract

“…This essential element provides the only difference in the lowenergy spectra of molecules and of deformed nuclei. Indeed, there are no low-lying I π = 1 + states in deformed even-even nuclei [48,49].…”

Section: Spectramentioning

confidence: 99%

Effective field theory for finite systems with spontaneously broken symmetry

Papenbrock

Weidenmüller

2014

Phys. Rev. C

View full text Add to dashboard Cite

We extend effective field theory to the case of spontaneous symmetry breaking in genuinely finite quantum systems such as small superfluid systems, molecules or atomic nuclei, and focus on deformed nuclei. In finite superfluids, symmetry arguments alone relate the spectra of systems with different particle numbers. For systems with non-spherical intrinsic ground states such as atomic nuclei or molecules, symmetry arguments alone yield the universal features of the low-lying excitations as vibrations that are the heads of rotational bands. The low-lying excitations in deformed nuclei differ from those in molecules because of symmetry properties caused by pairing.

show abstract

Complete spectroscopy of the 162Dy nucleus

Cited by 27 publications

References 36 publications

Discovery of a nonyrastKπ=8+isomer inDy162
Swan
¹
,
Walker
²
,
Podolyák
³

et al. 2011
Phys. Rev. C
10
0
4
0
View full text Add to dashboard Cite

Discovery of a nonyrastKπ=8+isomer inDy162
Swan
¹
,
Walker
²
,
Podolyák
³

et al. 2011
Phys. Rev. C
10
0
4
0
View full text Add to dashboard Cite

Direct microscopic calculation of nuclear level densities in the shell model Monte Carlo approach

Effective field theory for finite systems with spontaneously broken symmetry

Contact Info

Product

Resources

About

Complete spectroscopy of the 162Dy nucleus

Cited by 27 publications

References 36 publications

Discovery of a nonyrastKπ=8+isomer inDy162Swan1, Walker2, Podolyák3 et al. 2011Phys. Rev. C10040View full textAdd to dashboardCite

Discovery of a nonyrastKπ=8+isomer inDy162Swan1, Walker2, Podolyák3 et al. 2011Phys. Rev. C10040View full textAdd to dashboardCite

Direct microscopic calculation of nuclear level densities in the shell model Monte Carlo approach

Effective field theory for finite systems with spontaneously broken symmetry

Contact Info

Product

Resources

About

Discovery of a nonyrastKπ=8+isomer inDy162
Swan
¹
,
Walker
²
,
Podolyák
³

et al. 2011
Phys. Rev. C
10
0
4
0
View full text Add to dashboard Cite

Discovery of a nonyrastKπ=8+isomer inDy162
Swan
¹
,
Walker
²
,
Podolyák
³

et al. 2011
Phys. Rev. C
10
0
4
0
View full text Add to dashboard Cite