Advances in photonuclear reactions and astrophysical nucleosynthesis at USC

Wen Luo

School of Nuclear Science and Technology, University of South China

Email address: wen.luo@usc.edu.cn; wenluo-ok@163.com

The 8^th International Workshop on Nuclear Dynamics in Heavy-ion Reactions (IWND2026), Aug. 21-25, Taiyuan, China

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• Background and motivation
• (γ, n) reaction experiments and (γ, f) reaction simulations
• Astrophysical reaction rates and nucleosynthesis calculations
• (n, γ) cross section inferences for unstable nuclei
• Summary and Outlook

Outline

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• Background and motivation
• (γ, n) reaction experiments and (γ, f) reaction simulations
• Astrophysical reaction rates and nucleosynthesis calculations
• (n, γ) cross section inferences for unstable nuclei
• Summary and Outlook

Outline

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High-temperature gas-cooled reactor

Space reactor

Fusion

Nuclear cross section data research covers the entire “spectrum” from particle and nuclear physics to large-scale engineering applications.

Significance of nuclear reaction cross section data

courtesy of R. R. Xu, CIAE

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• These cross-section data serve as critical input parameters in nuclear astrophysical network simulations, and thus play an essential role in advancing our understanding of the evolution of the universe.
• Direct measurements of neutron capture cross sections in the stellar energy range (from eV to several MeV) are largely restricted to stable and long-lived nuclei. For unstable nuclei, how to infer the neutron capture cross sections is becoming an important topic.

Significance of nuclear reaction cross section data

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Significance of nuclear reaction cross section data

• Considerable or notable differences exist between the evaluated and measured data in both neutron and photon induced reaction cross sections.
• A lot of efforts (experiments and calculations) are required to reduce uncertainties and meanwhile to resolve these discrepancies.

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• On the proton-rich side of the β-stability line, there are 35 neutron-deficient isotopes ranging from ⁷⁴Se to ¹⁹⁶Hg. These nuclides cannot be synthesized via the s-process or r-process, and are thus termed p-nuclides.
• In the late evolutionary stages of massive stars and core-collapse supernovae, the p-process (or γ-process) is postulated to consist of a series of photodisintegration reactions, including (γ, n), (γ, p), and (γ, α) channels.

The γ-process: Origin of the p-nuclei

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• Background and motivation
• (γ, n) reaction experiments and (γ, f) reaction simulations
• Astrophysical reaction rates and nucleosynthesis calculations
• (n, γ) cross section inferences for unstable nuclei
• Summary and Outlook

Outline

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gs

Particle separation energy ~8MeV

^AX

γ´

n or p or f

β

Photodisintegration

Photofission

Nuclear resonance fluorescence

Photoactivation

Photonuclear reaction

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gs

Particle separation energy ~8MeV

^AX

Laser Compton scattering

Geant4-MCLCSS，NIMA 660, 108 (2011); Physica Scripta 89, 075208 (2014)

γ´

n or p

β

Nuclear resonance fluorescence

G4-NRF，Scientific Reports 11, 1306 (2021)

Photodisintegration

G4-GENBOD, NIMA 849, 49 (2017)

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Photoactivation and transport

G4Evaporation class

G4Transportation class

or f

Photofission

G4-GFDPO, NIMA1062, 169222 (2024)

Photonuclear reaction

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⁶³Cu：Nucl. Sci. Tech. 36, 34 (2025) Cover Article

⁶⁵Cu：Chin. Phys. C 50, 064002 (2026)

^natLu：Euro. Phys. J A 62, 63 (2026)

⁷⁶Ge, ¹⁹F：In preparation, experiment is ready

^164m,gHo：Front. Astron. Space Sci. 10, 1265919 (2023)

²⁷Al：Nucl. Phys. A 1043, 122834 (2024)

^152m,150mEu：Acta Phys. Sin. 75, 140102 (2026) Cover Article

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^164m,gHo ²⁷Al ^152m,150mEu

2023 2024 2025 2026 and later

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⁶³Cu ⁶⁵Cu ^natLu ⁷⁶Ge, ¹⁹F

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Experimentally measured photonclear cross sections

Xingguang-III facility

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Open to Users‌

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Peking University CLAPA1：200 TW 5 J, 30 fs, 5 Hz

(γ, x) cross section measurement of ²⁷Al (@ CLAPA facility, Peking University)

(Use: γ-ray flux monitoring; photonuclear data)

M.Z. Wang, W. Luo* , X. Q. Yan*, et al. Nucl. Phys. A 1043, 122834 (2024)

²⁷Al case

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The IRs of ^152mEu exhibit significant dependence on the γSF and NLD, which still have room for improvement in accurately describing Eu isotopes.

Luo K.J. … Yan X.Q.*, Luo W.*, Gu Y.Q. , Acta  Phys.  Sin. 75 (2026) 140102 Cover Article

The IR value for ^152m2,m1Eu is 0.046 ±0.006 @ E_e = 200 ±28 MeV

Photonuclear excitation of ^152m,150mEu (@ CLAPA facility, Peking University)

(Use: nuclear model constraints; p-nucleus ¹⁵²Gd nucleosynthesis?)

^152m,150mEu case

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Experimental methods built by the SLEGS team

Experimentally measured photoneutron cross sections

³He flat-efficiency detector ³He detector efficiency γ-ray spectrum from LaBr₃/BGO

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Z.C. Li, W. Luo*, G. T. Fan* et al., NST 36 (2025) 34. Cover Article

Y.L. Shen, Z.C. Li*, W. Luo* et al., CPC 50 (2026) 064002.

Z.C. Li, W. Luo*, G. T. Fan* et al., EPJA 62 (2026) 63.

Photoneutron cross sections of ^63,65Cu and ^natLu (@ SLEGS facility)

（Use: nuclear fuel cladding, structural and shielding materials）

• These photoneutron cross sections have a small uncertainty of 5%, which are helpful to resolve discrepancies among existing experimental data.

^63,65Cu and ^natLu cases

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Some of our measured data are accepted by the EXFOR database

https://www-nds.iaea.org/exfor/servlet/X4sSearch5?sort=entry&name=Zhi-Cai%20Li&aini=

https://www-nds.iaea.org/exfor/servlet/X4sSearch5?sort=entry&name=Wang&aini=M.Z.

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UML class diagram for adding the GammaFission process in Geant4

GammaFission simulation program Geant4-GFDPO

SXM, Wen Luo* et. al., NIMA 1062, 169222 (2024)

Photofission of actinide nuclides

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Mass yield and charge distributions of fission fragments

Photofission of actinide nuclides

SXM, Wen Luo* et. al., NIMA 1062, 169222 (2024)

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Average multiplicity and energy of prompt neutrons and gammas

Photofission of actinide nuclides

WJH, Wen Luo* et. al., Sci. Data (under review)

Preliminary result

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Identification of actinide nuclides using their delayed γ signatures

Simulated spectrum for delayed γ-ray emissions

WMZ, Wen Luo* et al., NST 36 (2025) 162.

Photofission of actinide nuclides (application)

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Vortex γ-induced fission for actinide nuclides

The vortex light carrying orbital angular momentum (OAM) can selectively excite isovector giant resonances with higher multipolarity, providing an unprecedented new probe for the precise detection of nuclear internal structure and specific quantum states.

Question: May OAM γ photons still enhance the photofission cross section?

Z. W. Lu, et al., PRL 131 (2023) 202502

M. Wei, et al., PRL 136 (2026) 025001

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Calculated cross sections for microscopic single nucleus

KXZ, W. Luo* … et al., Physics Letters B 880 (2026) 140735

Vortex γ-induced fission for actinide nuclides

Calculated cross sections for macroscopic target

The cross-section ratio for the macroscopic target satisfies:

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A novel approach to infer the polar-angle parameter of vortex photons

Vortex γ-induced fission for actinide nuclides

KXZ, W. Luo* … et al., Physics Letters B 880 (2026) 140735

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• Background and motivation
• (γ, n) reaction experiments and (γ, f) reaction simulations
• Astrophysical reaction rates and nucleosynthesis calculations
• (n, γ) cross section inferences for unstable nuclei
• Summary and Outlook

Outline

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Significant discrepancy between the theoretical and observed abnudances for some p-nuclei.

​

Possible reasons may be:

• Uncertainty of theoretical models
• Not include specific reaction pathways, etc

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How could we do:

• Experimentally Constraining Models
• Summing contributions from all populated states
• Taking some isomeric states as separated species

L. Roberti… A. Psaltis et al, A&A 677, A22 (2023)

Astrophysical reaction rates and nucleosynthesis calculations

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Astrophysical reaction rates and nucleosynthesis calculations

Astrophysical reaction rates：

H. Y. Lan, W. Luo* et al., Phys. Rev. C 98, 054601 (2018)

⁹⁸Ru： Y. Guo, Z. C. Li*, W. Luo* et al., (In preparation)

⁹²Mo：W. R. Fan, W. Luo* et al., Phys. Rev. Res 5, 043120 (2023)

¹¹²Sn：H. C. Liu, W. Luo* et al.,

The Astrophys. J. 1007, 74 (2026)

Phys. Rev. Res

Phys. Rev. C

​

Phys. Rev. C

​

The Astrophys. J.

^93mMo：Z.Q. Zhang, Y. Yuan, W. Luo* et al., (In preparation)

Isometric state contribution：

H. Y. Lan, W. Luo* et al., Phys. Rev. C 105, 044618 (2022)

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Comparison of (γ, p/α) cross sections calculated with different OMPs

• The significant discrepancies among the (γ, α) cross sections indicate that the α-OMP in the astrophysical energy region is not yet well determined.

Photodisintegration of p-nuclei in nuclear astrophysics (ground state)

LHY, Wen Luo* et al., Physical Review C 98, 054601 (2018)

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• Experimental measurements of photodisintegration cross sections are necessary to constrain the OMPs of charged particles. This could help to reduce the uncertainties in the reaction rates for p-nucleus nucleosynthesis.

Photodisintegration of p-nuclei in nuclear astrophysics (ground state)

LHY, Wen Luo* et al., Physical Review C 98, 054601 (2018)

OMPs exert a significant influence on the (γ, α) and (γ, p) reaction rates of p-nuclei.

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Effect of nuclear structure parameters on the contribution of (γ, p/α)L0i reaction channels (where L0i denotes the residual nucleus in the i-th excited state, and L00 denotes the ground state)

The excited-state contribution to photodisintegration is most sensitive to the OMPs. Direct measurements of these reactions are meaningful for further constraining the OMPs.

Photodisintegration of p-nuclei in nuclear astrophysics (ground and excited states)

LHY, Wen Luo* et al., Physical Review C 105, 044618 (2022)

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Contribution of (γ, p/α)L0i reaction yields to the total yield

Blue shaded area: single reaction channel

Yellow shaded area: two reaction channels

Pink shaded area: more than two channels

Photodisintegration of p-nuclei in nuclear astrophysics (ground and excited states)

LHY, Wen Luo* et al., Physical Review C 105, 044618 (2022)

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Chipps et al. from ORNL performed measurements of the (γ, p) and (γ, α) reactions on ¹⁰²Pd using the HIγS facility

K. A. Chipps*, et al. Physical Review C 114, 015804 (2026)

Photodisintegration of p-nuclei in nuclear astrophysics (ground and excited states)

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Possible impact of ^93mMo on p-isotope ⁹²Mo production

W. R. Fan, W. Luo* et al., Physical Review Research 5, 043120 (2023)

Photodisintegration of p-nuclei in nuclear astrophysics (isometric states)

• The ⁴He(⁹¹Zr, 2n)^93mMo reaction channel is recommended, since it can achieve a high depletion yield of 4.29*10^-1 events/shot under 800 MeV ⁹¹Zr ion irradiation with a 5 mg/cm² target.

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Does the isomeric state ¹¹³ᵐSn affect the nucleosynthesis of the p-nuclide ¹¹²Sn?

• ¹¹²Sn is a typical proton-magic p-nuclide, and current theoretical models cannot fully explain its astrophysical nucleosynthesis process. Does the ¹¹³ᵐSn–¹¹²Sn reaction flow participate in the nucleosynthesis of ¹¹²Sn?

Energy levels and half-life of ^113mSn: E_x = 77.4 keV , T_1/2=21.4 min

Half-life of ^113gSn: T_1/2=115.1 day

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H. C. Liu, W. Luo* et al., The Astrophysical Journal 1007:74 (2026).

Does the isomeric state ¹¹³ᵐSn affect the nucleosynthesis of the p-nuclide ¹¹²Sn?

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Y. Guo, Z. C. Li*, W. Luo* et al., (In preparation).

Does the isomeric state ^99mRh affect the nucleosynthesis of the p-nuclide ⁹⁸Ru?

An increase of up to 606%

Preliminary result

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• Background and motivation
• (γ, n) reaction experiments and (γ, f) reaction simulations
• Astrophysical reaction rates and nucleosynthesis calculations
• (n, γ) cross section inferences for unstable nuclei
• Summary and Outlook

Outline

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²³³Pa：C.X.Tan, W. Luo^* et al., Phys. Rev. C 109, 044615 (2024)

⁸⁸Y：S.T.Zhang, W. Luo^* et al., Commun. Phys. under review

²³⁸U：W. H. Liu, W. Luo^* et al., In preparation

¹⁷²Yb：W. H. Liu, W. Luo^* et al., In preparation

(n, γ) cross section inferences for unstable nuclei

²³³Pa ⁸⁸Y ²³⁸U ¹⁷²Yb

⁶²Cu ⁶⁴Cu ¹⁷⁴Lu ^153,159Gd ^{111,113,121,123}Sn ^141,147,149Nd

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2

2024

2025

2026

⁶²Cu：Z. C. Li, W. Luo^* et al., Nucl. Sci. Tech. 36, 27 (2025)

⁶⁴Cu：Y. L. Shen, W. Luo^* et al., CPC 50, 064002 (2026)

¹⁷⁴Lu：Z. C. Li, W. Luo^* et al., Eur. Phys. J. A 62, 63 (2026)

^153,159Gd：S.T.Zhang, W. Luo^* et al., Front. Phys. 21, 096201 (2026)

^{111,113,121,123}Sn：J. M. Chen, Z. C. Li, W. Luo^* et al., In preparation

^141,147,149Nd：X. Y. Zhang, Z. C. Li, W. Luo^* et al., In preparation

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Surrogate reaction-based (n, γ) cross section extraction

(accounting for spin-parity distribution)

(n, γ) cross section inferences via surrogate reactions

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Simultaneous fitting P_γ and γSF for ⁸⁹Y^* and extracting the ⁸⁸Y(n, γ) cross section

S.T. Zhang, W. Luo* et al., Communications Physics (under review)

Different OMPs

Spin-parity distribution ±1ћ

⁸⁸Y cases

Preliminary result

The P_γ measurement was perfomred by Prof. Jing Feng from CIAE, China.

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• The extracted neutron capture cross sections for ¹⁷²Yb are in line with experimental ones.
• The astrophysical rates of ¹⁷³Yb(γ, n) and ¹⁷³Yb(γ, p) reactions are derived for the first time.

Fitting the ¹⁷³Yb^* decay probability P_γ(E^*) and extracting the ¹⁷²Yb(n, γ) cross section

¹⁷³Yb(γ, n) rate

¹⁷³Yb(γ, p) rate

W. H. Liu, W. Luo* et al., (In preparation)

¹⁷²Tb cases

Preliminary result

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• At E_n = 0.1–1 MeV, the extracted cross sections agree well with existing experimental measurements.
• At E_n = 1–10 MeV, both the evaluated and measured data deviate significantly, our data reproduce the pattern “first decreasing and then increasing”, which is also shown in the ENDF/B-VIII.1.

W. H. Liu, W. Luo* et al., (In preparation)

²³⁸U cases

Preliminary result

C.X. Tan, W. Luo* et al., Phys. Rev. C. 109.044615 (2024)

• ²³³Pa(n, γ) cross sections directly impact on the final yield of ²³³U. We extracted them by using the surrogate reaction of ²³²Th(³He, p)²³⁴Pa^∗involving spin-parity (SP) distribution.
• The extracted data are in accordance with the ENDF/B-VIII.0 and JENDL-5 evaluations at E_n < 0.3 MeV, above which they start to deviate from the latter by a factor of less than 0.5.

Fitting the ²³⁴Pa^* decay probability P_γ(E^*) and inferring the ²³³Pa(n, γ) cross section

(w/t introduction of machine learning)

²³³Pa cases

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Physical Review C 72, 044311 (2005).

Physical Review C 80, 054310 (2009).

Brink hypothesis-based (n, γ) cross section extraction

(n, γ) cross section inferences via Brink hypothesis

(γ, n) data

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(n, γ) cross section for the unstable nuclides ⁶²^,⁶⁴Cu and ¹⁷⁴Lu

(Use: medical isotope production; advancing nuclear data development)

• Using the (γ, n) cross sections of ⁶³^,⁶⁵Cu and ¹⁷⁵Lu from SLEGS, we obtain experimentally constrained neutron capture cross sections for ⁶²^,⁶⁴Cu and ¹⁷⁴Lu.

^62,64Cu, ¹⁷⁴Lu cases

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(n, γ) cross section for the unstable nuclides ^{111,113,121,123}Sn

(Use: s-process branching explanation; s-only abundances)

• The uncertainty of the cross sections derived is about 50%, which is reduced by a factor of about 1.8 compared to the TALYS calculatoins with different nuclear models.

J.M. Chen, Z.C. Li*, W. Luo* et al., In preparation

^{111,113,121,123}Sn cases

Preliminary result

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(n, γ) cross section for the unstable nuclides ^141,147,149Nd

(Use: s-process and p-process nucleosynthesis)

X.Y. Zhang, Z.C. Li*, W. Luo* et al., In preparation

• The uncertainty of the cross sections derived is about 29%, which is reduced by a factor of 6 compared to the TALYS calculatoins with different nuclear models.

^141,147,149Nd cases

Preliminary result

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S.T. Zhang, Z.C. Li*, W. Luo* et al., FOP 21 (2026) 096201.

(n, γ) cross section for the unstable nuclides ^153,159Gd

(Use: s-process nucleosynthesis; reactor designs; medical applications)

• The uncertainty of the cross sections obtained in this work is about 30%, which is reduced by a factor of 5.5 compared to the TALYS calculatoins with different nuclear models.

^153,159Gd cases

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• Background and motivation
• (γ, n) reaction experiments and (γ, f) reaction simulations
• Astrophysical reaction rates and nucleosynthesis calculations
• (n, γ) cross section inferences for unstable nuclei
• Summary and Outlook

Outline

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• Photoneutron cross sections of ^{63, 65}Cu, ⁷⁶Ge and ^natLu are measured. The FACSs of ²⁷Al photodisintegration and the isomeric ratio of ^152mEu are extracted. Photofission of actinide nuclides are studied, as well as vortex photon-induced photofissions.
• Photodisintegration reaction rates involving p-nuclide nucleosynthesis are computed. The effects of ^113mSn (and ^99mRh) on the abundances of ¹¹²Sn (and ⁹⁸Ru) are clarified.
• Two approaches on inferring neutron capture cross sections for unstable nuclei are developed. Neutron capture cross sections for unstable ^{62, 64}Cu, ¹⁷⁴Lu, ^{111,113,121,123}Sn, ^141,147,149Nd, ^{153, 159}Gd, and ⁸⁸Y, ¹⁷²Tb, ^141,147,149Nd, ²³⁸U and ²³³Pa are then inferred successfully.
• We warmly welcome possible collaborations from you in terms of photonuclear measurements, neutron capture cross section inferences and astrophysical nucleosynthesis calculations.

Summary and outlook

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Main collaborators

• Shanghai Institute of Applied Physics, Chinese Academy of Sciences (SINAP)

XU Wang, CAI Xiangzhou, CHEN Jingen, et al.

• Shanghai Advanced Research Institute, Chinese Academy of Sciences (SARI)

WANG Hongwei, FAN Gongtao, et al.

• China Academy of Engineering Physics (CAEP)

GU Yuqiu, ZHOU Weimin, DENG Zhigang, QI Wei, et al.

• China Institute of Atomic Energy (CIAE)

XU Ruirui, RUAN Xichao, FENG Jing, LI Zhihong, et al.

• Peking University

YAN Xueqing, WU Di, LAN Haoyang, WANG Meizhi, et al.

• Fudan University / East China Normal University

MA Yugang

• Beihang University

PANG Danyang, SUN Baohua, et al.

• Extreme Light Infrastructure - Nuclear Physics (ELI-NP)

Y. Xu, D. L. Balabanski

• Konan University

H. Utsunomiya

Thanks for your attention！

The 8^th International Workshop on Nuclear Dynamics in Heavy-ion Reactions (IWND2026), Aug. 21-25, Taiyuan, China