NEUTRON CAPTURE CROSS SECTION MEASUREMENTS ON SHORT-LIVED ISOTOPES - PI: SEAN LIDDICK COPI: ARTEMIS SPYROU SSAP SYMPOSIUM, FEB. 16-18, 2021

Neutron capture cross section
measurements on short-lived isotopes

 PI: Sean Liddick
 CoPI: Artemis Spyrou
 SSAP Symposium, Feb. 16-18, 2021

Neutron capture cross section measurements on
 short-lived isotopes
• Scientific Challenge
 – Constrain neutron capture cross sections of short-lived nuclei for
 stewardship science and astrophysical production of heavy
 elements.
• Goals
 – Investigate the spin dependence of the γ-ray strength
 function using the β decay of isomeric states.
 – Constrain neutron capture cross
 sections of interest for stockpile
 stewardship approaching 95Zr and i-
 process nuclei
 – Train graduate students and
 postdoctoral researchers in nuclear
 science techniques and connect
 them with staff at the national
 laboratories.
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 SSAP 2021

Neutron capture cross section measurements on
 short-lived isotopes
• PI: Sean Liddick
 Associate Prof. National Superconducting Cyclotron Laboratory and
 Department of Chemistry
• Co-PI: Artemis Spyrou
 Professor National Superconducting Cyclotron Laboratory and Department of
 Physics and Astronomy
• Two graduate students and one postdoc supported:
 – Debra Richman (MSU, graduate student)
 – Andrea Richard (MSU, postdoctoral researcher)
 – Katherine Childers (MSU, graduate student  Texas A&M University 2021)
 – Rebecca Lewis (graduated MSU, graduate student  NNSA GFP Summer 2019)
 – Benjamin Crider (postdoctoral researcher  MissSU Assistant Professor)
 – Mallory Smith (MSU, postdoctoral researcher  staff NSCL)
• Peer-reviewed papers
- M. Guttormsen et. al., Acta. Phys. Pol. B51, 667 (2020) - R. Lewis et. al., Phys. Rev. C 99, 034601 (2019)
- A. Spyrou, Annals of Physics 412, 168017 (2020) - A.C Dombos et. al. Phys. Rev. C 99, 015802 (2019)
- Ong et al, PRL (2021) - A.C. Larsen et al., Phys. Rev. C 97, 054329 (2018)
- S.N. Liddick, et al., Phys. Rev. C 100, 024624 (2019) - A.Spyrou, A.C. Larsen, S.N. Liddick et al., J. Phys. G 44,
- A. Voinov, et. Al., Phys. Rev. C 99, 054609 (2019) 044002 (2017)
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 SSAP 2021

Significant laboratory engagement by supported
 graduate students
• Katherine Childers
 – β-Oslo on 83Se for 82Se (n,γ)
 – Direct (n,γ) at LANL with DANCE
 – 2-month placement at LANL.
 – Performed work with neutron science
 experimenters and theorists at LANL
 including A. Couture and C. Prokop
 – Manuscript in preparation.
 – Completed thesis in 2020. β-Oslo matrix for 83Se
 Direct (n,γ) on 82Se target

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 SSAP 2021

Significant laboratory engagement by supported
 graduate students
• Debra Richman
 – Permanently placed at Los
 Alamos National Laboratory
 working within the P-27 group
 with A. Couture and S. Mosby.
 – Performing analysis to extract
 neutron capture cross section
 of 59Fe, a key reaction rate in
 the astrophysical s-process.
 – First results presented at 60Fe

 Nuclear Astrophysics winter
 school Russbach 2017, NASA
 Laboratory Astrophysics 2018,
 DNP 2019
 – Expected graduation in 2021

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 SSAP 2021

Scientific program focused on rapid-neutron capture process,
 slow neutron capture process, and stewardship science.
 Completed
• Inferring neutron capture cross sections on S.Liddick (MSU):
 short-lived nuclei receiving strong support New technique for
 neutron capture
 from NSCL and ANL Program Advisory Approved cross section
 Committee. measurements on
 short-lived nuclei
 S. Liddick (MSU):
 Neutron-capture cross
 section constraints in A. Spyrou (MSU):
 neutron-rich Sn and Constraints on
 Sb isotopes nucleosynthesis in
 Completed the iron region
 A. Spyrou (MSU):
 Approved Constraints on A. Spyrou (MSU) /
 neutron-capture S. Liddick (MSU):
 reactions around Constraining
 N=82 supernova models
 with SuN
 A.C. Larsen (Oslo):
 The rare-earth r- N. Scielzo (LLNL):
 process peak: 156- Determination of the 92Sr
 159Sm(n,g) reaction neutron-capture cross
 rates constrained with section and fission
 the beta-Oslo method product burn up. –

 A. Spyrou (MSU):
 Study of Kr isotopes
 for astrophysical
 applications.
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 SSAP 2021

Nuclear level densities and γ-ray strength functions are
 the dominate uncertainties in (n,γ) calculations
 Hauser – Feshbach
 • Nuclear Level Density
 Constant T+Fermi gas, back-shifted Fermi
 gas, superfluid, microscopic
 Level density
 • γ-ray strength function
 Generalized Lorentzian, Brink-Axel,
 various tables

 • Optical model potential
 Phenomenological, Semi-microscopic

 γ-strength function

 OMP
 ALL
 95Sr(n,γ)96Sr

 TALYS
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 SSAP 2021

Extrapolation of nuclear level densities and γ-ray
 strength functions to exotic nuclei are uncertain
γ-ray strength functions Level densities
• Unexpected structural • What is N,Z dependence
 features. of a?

 8
 A.C. Larsen et al., Phys. Rev. C, 82, 014318 (2010) SSAP 2021
 Al-Quraishi et al., Phys. Rev. C 63, 065803 (2001)

Using beta decay total absorption spectroscopy to
 infer neutron capture cross sections
• Measure beta decay of nucleus.
 – Extract level densities and gamma-ray strength function
• Need total excitation energy of the daughter isotope.
 – Can’t use beta-decay electron (three body process)
• Instead, measure total emitted photon energy.

 • Require high detection efficiency.
 • Extract nuclear level density and γ-ray
 strength function.
 • Insert both quantities into a statistical
 reaction model to constrain (n,γ) rate.
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 SSAP 2021

Testing Spin Independence of γSF: Decay of 70Cu
 isomeric states over a wide spin range

• Test the independence of the γSF from 1+ 243
 93%
 different initial spin distributions. 3- 101
• 70Cu has three different isomeric states. 52%
• Experiment completed summer 2019, 6- 0
 analysis is ongoing. 70Cu 100%

 0.16

 0.14

 0.12

 0.1
 Percentage

 0.08

 0.06

 0.04

 0.02

 0
 0 2 4 6 8 10 12 14
 Spin

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 SSAP 2021

70Cu beta decay as a probe of the spin independence of the γSF
 1+ 3- g.s. (6-)
• Multiple isomeric states 35 16% 26% 58%
 produced.
 34
• Ran beam on/beam off cycle of

 TOF [µs]
 10/10 minutes 33

• Analysis in progress. 32

 31

 -8 -6 -4 -2 0 2 4 6
 νrf - 2,055,181.5 [Hz]

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 SSAP 2021

(n,γ) uncertainties impact the intermediate-neutron
 capture process for heavy element creation

•Neutron density: 1015 cm-3, intermediate between s process, and r
process
•Proposed in the 1970s and revived recently to explain observations of
“strange” abundance distributions (post-AGB, CEMP stars, and RAWDs)
•Requires mixing between H and He layers of the star
•Neutron production:
13C( ,n)16O reaction, like

s-process
•13C replenished via
12C(p, )13N, then
13N(e+)13C, T (13N) ~ 10
 1/2
minutes

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 SSAP 2021

(n,γ) uncertainties impact the intermediate neutron-
 capture process for heavy element creation
 • Neutron-capture (n,γ) uncertainties
 reactions affect the final
 abundance distribution.
 • Varying the reactions
 within their
 uncertainties shows
 which reactions have a
 larger impact
Y /Zr

 87-89Kr(n,γ)88-90Kr
 reactions
 can affect the abundances
 Sr
 of Rb, Sr, Y and Zr
 /Y 13
 Denissenkov et al. JPG 2018 SSAP 2021

135I (n,γ) rates studied indirectly from the decay of Te isotopes
 inform the i-process
La /Eu

 Ba/La
• 135I(n,γ)136I
 – bottleneck affecting

 Ex (keV)
 the production of heavier elements
• Experiment performed at ANL to
 constrain this reaction indirectly
• β- decay of
 136Te -> 136I
 Eγ (keV)
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 SSAP 2021

Neutron capture needs for diagnostics: 95Zr
 Importance Factor IF = IY * ADT
 Measured IY is maximum independent yield
 Known cross-sections ADT = 2 (A=95), 1 (A=94,96),
 (n,γ)
 0.5 (A=93,97)
 93Zr 94Zr (n,γ) 95Zr (n,γ) 96Zr (n,γ) 97Zr
 1.5E6 y (n,2n) Stable (n,2n) 64.02 d (n,2n) Stable 16.8 h
 (n,2n)
 (n,p) (n,p)
 IF
 (n,p) (n,p) (n,p)
 β β β β β >5
 (n,γ) 94Y (n,γ) 95Y
 93Y (n,γ) 96Y (n,γ) 97Y 1-5
• 95Zr
 can be 0.9s/10.2h (n,2n) 18.7 m (n,2n) 10.3 m (n,2n) 9.6s/5.3s (n,2n) 1.2s/3.8s
 0.5-1
 (n,p) (n,p) (n,p)
 (n,p)
 used as a yield β β β
 (n,p)
 β β
 (n,γ) 0.1-0.5
 (n,γ) (n,γ) (n,γ)
 indicator. 93Sr 94Sr 95Sr 96Sr 97Sr
 < 0.1
 7.41 m (n,2n) 1.25 m (n,2n) 25.1 s (n,2n) 1.07 s (n,2n) 0.43 s
• However, 95Sr (n,p) (n,p) (n,p) (n,p) (n,p)
 β β β β β
 is short lived 93Rb
 (n,γ)
 94Rb (n,γ) 95Rb (n,γ) 96Rb (n,γ) 97Rb
 and can’t be 5.85 s (n,2n) 2.71 s (n,2n) 377 ms (n,2n) 199 ms (n,2n) 169 ms

 made into a β
 (n,p)
 β
 (n,p)
 β
 (n,p)
 β
 (n,p)
 β
 (n,p)

 target. 93Kr
 (n,γ)
 94Kr (n,γ) 95Kr (n,γ) 96Kr (n,γ) 97Kr

• UCB, LLNL, MSU, Oslo 1.29 s (n,2n) 0.21 s (n,2n) 0.78 s (n,2n) UK (n,2n)

Decay of 93Rb: Providing (n,γ) for 92Sr
 • Experiment to deliver thermal 93Rb
 93Rb − within last year to perform stopped
 t1/2 =5.84(2) s 93Sr beam β-decay with 93Rb.
 −
 • Moving tape collector and interior plastic
 t1/2 =7.43(3) m 93Y
 scintillator completed previously.
 t1/2 =10.18(8) h
 Total Absorption Spectra

 93Rb
 counts Production Runs
 (thermal)

 SuN Daughter Runs
 Only levels in
• Analysis in progress; working 93Y

 on response function of plastic
 scintillator within SuN. E (keV)
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 SSAP 2021

Conclusions
• Application of technique to infer neutron capture cross sections on
 short-lived neutron-rich nuclei ongoing.
• Applicable to studies of rapid-neutron capture process, intermediate
 neutron capture process, slow-neutron capture process, and
 stewardship science.
 – Studies of sensitive i-process nuclei.
 – Neutron-rich 59Fe analysis nearing completion
 – Stockpile stewardship analysis on neutron-rich Sr isotopes in progress
• Investigation of spin dependence of strength function using isomeric
 states in 70Cu – analysis in progress
• Funding supports two graduate students and one postdoctoral
 researcher strongly connected to the national laboratories.

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 SSAP 2021

Thanks
Michigan State University University of Oslo LLNL
• A. Spyrou • A.C. Larsen • D.L. Bluel
• S.N. Liddick • M. Guttormsen • N. Scielzo
• B.P. Crider • L. Crespo Campo
• K. Childers • S. Siem LANL
• A.C. Dombos • T. Renstrøm • A. Couture
• R. Lewis • S. Mosby
• F. Naqvi Central Michigan University • M. Mumpower
• C.J. Prokop • G. Perdikakis
• S.J. Quinn • S. Nikas
• A. Rodriguez
• C.S. Sumithrarachchi Notre Dame
• R.G.T. Zegers • A. Simon
 • R. Surman

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 SSAP 2021

Questions?

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 SSAP 2021