Neutron capture cross section measurements on short-lived isotopes

PI: Sean LiddickCoPI: Artemis Spyrou

Presenter: Andrea RichardSSAP Symposium, Feb. 26-27, 2020

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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– Constrain neutron-capture cross sections for influential

reactions in r-process scenarios in the Co-Cu region.– Constrain neutron-capture cross

sections of interest for stockpile stewardship approaching 95Zr

– Train graduate students and postdoctoral researchers in nuclear science techniques and connect them with staff at the national laboratories.

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- A. Spyrou, Annals of Physics 412, 168017 (2020)- S.N. Liddick, et al., Phys. Rev. C 100, 024624 (2019)- A. Voinov, et. Al., Phys. Rev. C 99, 054609 (2019) - R. Lewis et. al., Phys. Rev. C 99, 034601 (2019)

- A.C Dombos et. al. Phys. Rev. C 99, 015802 (2019)- A.C. Larsen et al., Phys. Rev. C 97, 054329 (2018)- A.Spyrou, A.C. Larsen, S.N. Liddick et al., J. Phys. G 44, 044002 (2017)

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 SpyrouProfessor National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy

• Two graduate students and one postdoc supported:– Rebecca Lewis (MSU, graduate student NNSA GFP Summer 2019)– Debra Richman (MSU, graduate student)– Benjamin Crider (postdoctoral researcher MissSU Assistant Professor)– Mallory Smith (MSU, postdoctoral researcher staff National Superconducting

Cyclotron Laboratory)– Andrea Richard (MSU, postdoctoral researcher)

• Peer-reviewed papers

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Significant laboratory engagement bysupported graduate students

• Rebecca Lewis– 3-month placement at LANL in 2017.– Performed work with neutron science

experimenters and theorists at LANL including A. Couture and T. Kawano

– Manuscript on 73Zn(n,γ) PRC 2019.– Completed thesis in 2019– NNSA GFP Summer 2019!

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Significant laboratory engagement bysupported 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.

– Analysis in progress– First results presented at Nuclear

Astrophysics winter school Russbach 2017, NASA Laboratory Astrophysics 2018, DNP 2019

60Fe

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Scientific program focused on rapid-neutron capture process, slow-neutron capture process, and stewardship science.

• Inferring neutron capture cross sections on short-lived nuclei receiving strong support from NSCL and ANL Program Advisory Committee.

A. Spyrou (MSU): Study of Kr isotopes

for astrophysical applications.

N. Scielzo (LLNL):Determination of the

92Sr neutron-capture cross

section and fission product burn up.

Approved

Completed

A. Spyrou (MSU):Constraints on

nucleosynthesis in the iron region

S. Liddick (MSU):New technique for neutron capture

cross section measurements on short-lived nuclei

Approved

Completed

A. Spyrou (MSU) / S. Liddick (MSU):

Constraining supernova models

with SuN

S. Liddick (MSU): Neutron-capture cross section constraints in neutron-rich Sn and Sb isotopes

A. Spyrou (MSU): Constraints on neutron-capture reactions around N=82

A. C. Larsen (Oslo): The rare-earth r-process peak: 156-159Sm(n,γ) reaction rates constrained with the beta-Oslo method

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Nuclear level densities and γ-ray strength functions are the dominate uncertainties in (n,γ) calculations

Hauser – Feshbach• Nuclear Level DensityConstant T+Fermi gas, back-shifted Fermi gas, superfluid, microscopic

• γ-ray strength functionGeneralized Lorentzian, Brink-Axel, various tables

• Optical model potentialPhenomenological, Semi-microscopic

Level density

γ-strength function

ALLOMP

TALYS

95Sr(n,γ)96Sr

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

S.N. Liddick, A. Spyrou, et al., Phys. Rev. Lett. 116, 242502 (2016)R. Surman and J. Engel, Phys. Rev. C, 64, 035801 (2001)

Monte-Carlo variations of (n,γ) rates within a factor 100 – 10 – 2 (light –darker – dark bands)

(n,γ) uncertainties

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Sensitive (n,γ) rates in the neutron-rich Ni region

• Inferred neutron capture rates of 68,69Ni and 73Zn have already been performed.

• Extract neutron capture rates of 71,72,73Ni

• Strong local impact on astrophysical abundance predictions.

• Covers a number of high sensitivity reactions

• Provides systematics across a chain of five Ni isotopes.

72Co

71Ni

(n,γ)

72Ni64Ni 70Ni

71Co

S.N. Liddick, A. Spyrou, et al., Phys. Rev. Lett. 116, 242502 (2016)R. Surman and J. Engel, Phys. Rev. C, 64, 035801 (2001)

(n,γ)

73Co

(n,γ)

(β)73Ni

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Nuclear level densities and gamma-ray strength functions in the neutron-rich Ni region

• Constrained nuclear levels densities, gSF, and neutron capture cross sections on 71,72,73Ni

• Combined with prior results provides systematics across a chain of five Ni isotopes.

• Impact on astrophysical abundance predictions underway.

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Neutron capture needs for diagnostics: 95Zr

• 95Zr can be used as a yield indicator.

• However, 95Sr is short lived and can’t be made into a target.

(n,p)

(n,γ)

(n,2n)

(n,γ)(n,γ)

(n,2n)

(n,γ)93Zr1.5E6 y

94ZrStable

95Zr64.02 d

96ZrStable

97Zr16.8 h

93Y0.9s/10.2h

93Sr7.41 m

93Rb5.85 s

93Kr1.29 s

94Y18.7 m

95Y10.3 m

96Y9.6s/5.3s

97Y1.2s/3.8s

94Sr1.25 m

95Sr25.1 s

96Sr1.07 s

97Sr0.43 s

94Rb2.71 s

95Rb377 ms

96Rb199 ms

97Rb169 ms

94Kr0.21 s

95Kr0.78 s

96KrUK

97Kr<0.1 s

β β β β β

β

β

β

β β β β

β β β β

β β β β

(n,2n) (n,2n)

(n,2n)

(n,2n)

(n,2n)

(n,2n)

(n,2n) (n,2n) (n,2n)

(n,2n) (n,2n) (n,2n)

(n,2n) (n,2n) (n,2n)

(n,2n) (n,2n) (n,2n)

(n,γ)

(n,γ)

(n,γ)

(n,γ)

(n,γ) (n,γ) (n,γ)

(n,γ) (n,γ) (n,γ)

(n,γ) (n,γ) (n,γ)

(n,γ) (n,γ) (n,γ)

Known cross-sectionsMeasured

Importance Factor IF = IY * ADTIY is maximum independent yieldADT = 2 (A=95), 1 (A=94,96),

0.5 (A=93,97)

>5IF

1-50.5-10.1-0.5< 0.1

(n,p)

(n,p)

(n,p)(n,p)(n,p) (n,p) (n,p)

(n,p)

(n,p)

(n,p)(n,p)

(n,p)

(n,p)(n,p)(n,p)

(n,p)

(n,p) (n,p)

(n,p)

Courtesy M. Stoyer (LLNL)• UCB, LLNL, MSU, Oslo

collaboration.Meeting Isotope Needs and Capturing Opportunities for theFuture: The 2015 Long Range Plan for the DOE-NP IsotopeProgram, NSAC Isotopes Subcommittee, July 20, 2015

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Decay of 93Rb: Providing (n,γ) for 92Sr

• Experiment to deliver thermal 93Rb within last year to perform stopped beam β-decay with 93Rb.

• Moving tape collector and interior plastic scintillator completed previously.

SuN

93Rb93Sr

93Y

𝛽𝛽 −

𝛽𝛽 −

𝜷𝜷 𝜸𝜸93Rb

(thermal)

t1/2 =5.84(2) s

t1/2 =7.43(3) m

t1/2 =10.18(8) h

E (keV)

Total Absorption Spectra

Production Runs93Rb

Daughter RunsOnly levels in 93Y

coun

ts

• Analysis in progress; working on response function of plastic scintillator within SuN.

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Testing Spin Independence of γSF: Preliminary beam test with 70Cu isomeric states

• Test the independence of the γSF from different initial spin distributions.

• 70Cu has three different isomeric states.

• Experiment completed summer 2019, analysis is ongoing. 0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 2 4 6 8 10 12 14

Perc

enta

ge

Spin

-8 -6 -4 -2 0 2 4 6

31

32

33

34

351+

16%3-

26%

TOF

[µs]

νrf - 2,055,181.5 [Hz]

g.s. (6-)58% ─ g.s. 6-

─ 1+

-8 -6 -4 -2 0 2 4 6

2829303132333435 g.s. 6-

TOF

[µs]

νrf - 2,055,181.5 [Hz]

1+

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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, slow-neutron capture process, and stewardship science.

– Cross section constrained for a range of neutron-rich Ni isotopes.– Neutron-rich 59Fe analysis in progress– 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.

• One graduate student has taken a position with the NNSA GFP.

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ThanksMichigan State University• A. Spyrou• S.N. Liddick• B.P. Crider• K. Childers• A.C. Dombos• R. Lewis• F. Naqvi• C.J. Prokop• S.J. Quinn• A. L. Richard• A. Rodriguez• C.S. Sumithrarachchi• R.G.T. Zegers

University of Oslo• A.C. Larsen• M. Guttormsen• L. Crespo Campo• S. Siem• T. Renstrøm

Central Michigan University• G. Perdikakis• S. Nikas

Notre Dame• A. Simon• R. Surman

LLNL• D.L. Bluel• N. Scielzo

LANL• A. Couture• S. Mosby• M. Mumpower

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Questions?