Photon strength functions

The excitation and deexcitation of the atomic nucleus by electromagnetic radiation are fundamental processes in reactions of this many-body quantum system. At high excitation energy and high level density of the nucleus, nuclear reactions are described by statistical models. These models use photon strength functions to describe the average transition strengths in a certain range of excitation energy.

The experimental determination and the theoretical understanding of the properties of photon strength functions have attracted increasing interest because of their importance for the accurate description of photonuclear reactions and the inverse radiative-capture reactions, which play a central role in the synthesis of the elements in various stellar environments in the universe.

Photon strength functions are determined in experiments using various types of nuclear reactions, such as photon scattering, neutron capture and light-ion induced reactions:

- Photon-scattering experiments are carried out at the bremsstrahlung facility γELBE of HZDR and at the HIγS facility of TUNL/Duke UNiversity Durham, North Carolina.
- Neutron-capture is used in experiments at research reactors that deliver thermal or cold neutrons, for example at ILL Grenoble, IKI Budapest or UJV Rez (Prague).
- Experiments using light-ion reactions are performed at ion accelerators, for example at the cyclotron of Oslo University.

In addition, photon strength functions are calculated using theoretical nuclear-structure models to better understand their properties.

According to the growing importance of photon strength functions for fundamental research as well as for applications, the Nuclear-Data Section of the International Atomic Energy Agency (IAEA) initiated a
"Coordinated Research Project on Photonuclear Data and Photon Strength Functions" (CRP F41032).
The goal of this CRP was the generation of a reference data base for photon strength functions from various kinds of experiments, published in:

IAEA Photonuclear Data Library 2019
T. Kawano, Y.S. Cho, P. Dimitriou, D. Filipescu, N. Iwamoto, V. Plujko, X. Tao, H. Utsunomiya, V. Varlamov, R. Xu, R. Capote, I. Gheorghe, O. Gorbachenko, Y.L. Jin, T. Renstrøm, K. Stopani, Y. Tian, G.M. Tveten, J.M. Wang, T. Belgya, R. Firestone, S. Goriely, J. Kopecky, M. Krticka, R. Schwengner, S. Siem, M. Wiedeking
Nuclear Data Sheets 163, 109 (2020).

Reference database for photon strength functions
S. Goriely, P. Dimitriou, M. Wiedeking, T. Belgya, R. Firestone, J. Kopecky, M. Krticka, V. Plujko, R. Schwengner, S. Siem, H. Utsunomiya, S. Hilaire, S. Peru, Y.S. Cho, S.M. Filipescu, N. Iwamoto, T. Kawano, V. Varlamov, R. Xu
European Physical Journal A 55, 172 (2019).

Publications about experiments using light-ion reactions:

Nuclear level densities and gamma-ray strength functions in ^147,149Sm isotopes
F. Naqvi, A. Simon, M. Guttormsen, R. Schwengner, S. Frauendorf, C.S. Reingold, J.T. Burke, N. Cooper, R.O. Hughes, S. Ota, A. Saastamoinen
Physical Review C 99, 054331 (2019).

Nature of low-lying electric dipole resonance states in ⁷⁴Ge
D. Negi, M. Wiedeking, E.G. Lanza, E. Litvinova, A. Vitturi, R.A. Bark, L.A. Bernstein, D.L. Bleuel, S. Bvumbi, T.D. Bucher, B.H. Daub, T.S. Dinoko, N. Erasmus, J.L. Easton, A. Görgen, M. Guttormsen, P. Jones, B.V. Kheswa, N.A. Khumalo, A.C. Larsen, E.A. Lawrie, J.J. Lawrie, S.N.T. Majola, L.P. Masiteng, M.R. Nchodu, J. Ndayishimye, R.T. Newman, S.P. Noncolela, J.N. Orce, P. Papka, L. Pellegri, T. Renström, D.G. Roux, R. Schwengner, O. Shirinda, S. Siem
Physical Review C 94, 024332 (2016).

Completing the nuclear reaction puzzle of the nucleosynthesis of ⁹²Mo
G.M. Tveten, A. Spyrou, R. Schwengner, F. Naqvi, A.C. Larsen, T.K. Eriksen, F.L. Bello Garrote, L.A. Bernstein, D.L. Bleuel, L. Crespo Campo, M. Guttormsen, F. Giacoppo, A. Görgen, T.W. Hagen, K. Hadynska-Klek, M. Klintefjord, B.S. Meyer, H.T. Nyhus, T. Renstrøm, S.J. Rose, E. Sahin, S. Siem, T.G. Tornyi
Physical Review C 94, 025804 (2016).

Low-energy enhancement in the γ-ray strength functions of ^73,74Ge
T. Renstrøm, H.-T. Nyhus, H. Utsunomiya, R. Schwengner, S. Goriely, A.C. Larsen, D.M. Filipescu, I. Gheorghe, L.A. Bernstein, D.L. Bleuel, T. Glodariu, A. Görgen, M. Guttormsen, T.W. Hagen, B.V. Kheswa, Y.-W. Lui, D. Negi, I.E. Ruud, T. Shima, S. Siem, K. Takahisa, O. Tesileanu, T.G. Tornyi, G.M. Tveten, M. Wiedeking
Physical Review C 93, 064302 (2016).

Experimentally constrained (p,γ)⁸⁹Y and (n,γ)⁸⁹Y reaction rates relevant to the p-process nucleosynthesis
A.C. Larsen, M. Guttormsen, R. Schwengner, D.L. Bleuel, S. Goriely, S. Harissopulos, F.L. Bello Garrote, L.A. Bernstein, Y. Byun, T.K. Eriksen, F. Giacoppo, A. Görgen, T.W. Hagen, M. Klintefjord, H.T. Nyhus, T. Renstrøm, S.J. Rose, E. Sahin, S. Siem, T.G. Tornyi, G.M. Tveten, A.V. Voinov, M. Wiedeking
Physical Review C 93, 045810 (2016).

Partial cross sections of the ⁹²Mo(p,γ) reaction and the γ strength in ⁹³Tc
J. Mayer, S. Goriely, L. Netterdon, S. Peru, P. Scholz, R. Schwengner, A. Zilges
Physical Review C 93, 045809 (2016).

Publications about neutron-capture experiments at the Budapest research reactor:

The role of magnetic dipole strength functions in ¹¹⁴Cd(γ,γ') and ¹¹³Cd(n,γ) reactions
R. Massarczyk, G. Schramm, T. Belgya, R. Schwengner, R. Beyer, D. Bemmerer, Z. Elekes, E. Grosse, R. Hannaske, A.R. Junghans, Z. Kis, T. Kögler, C. Lorenz, K. Schmidt, L. Szentmiklosi, A. Wagner, J.L. Weil
Physical Review C 93, 014301 (2016).

Electromagnetic dipole strength up to the neutron separation energy from ¹⁹⁶Pt(γ,γ') and ¹⁹⁵Pt(n,γ) reactions
R. Massarczyk, G. Schramm, A.R. Junghans, R. Schwengner, M. Anders, T. Belgya, R. Beyer, E. Birgersson, A. Ferrari, E. Grosse, R. Hannaske, Z. Kis, T. Kögler, K. Kosev, M. Marta, L. Szentmiklosi, A. Wagner, J.L. Weil
Physical Review C 87, 044306 (2013).

Dipole strength in ⁷⁸Se below the neutron-separation energy from a combined analysis of ⁷⁷Se(n,γ) and ⁷⁸Se(γ,γ') experiments
G. Schramm, R. Massarczyk, A.R. Junghans, T. Belgya, R. Beyer, E. Birgersson, E. Grosse, M. Kempe, Z. Kis, K. Kosev, M. Krtika, A. Matic, K.D. Schilling, R. Schwengner, L. Szentmiklosi, A. Wagner, J.L. Weil
Physical Review C 85, 014311 (2012).

Publications about model calculations of magnetic dipole strength functions:

Evolution of low-lying M1 modes in germanium isotopes
S. Frauendorf, R. Schwengner
Physical Review C 105, 034335 (2022).

Low-energy magnetic dipole strength in cadmium isotopes
R. Schwengner
Physical Review C 105, 014303 (2022).

Exploring enhanced low-energy magnetic dipole strength in photon scattering
R. Schwengner, G. Rusev
Physical Review C 100, 054320 (2019).

Low-energy magnetic dipole radiation in open-shell nuclei
R. Schwengner, S. Frauendorf, B.A. Brown
Physical Review Letters 118, 092502 (2017).

Low-energy behavior of E2 strength functions
R. Schwengner
Physical Review C 90, 064321 (2014).

Low-energy enhancement of magnetic dipole radiation
R. Schwengner, S. Frauendorf, A.C. Larsen
Physical Review Letters 111, 232504 (2013).