New detection systems and prospects for TOF measurements of s-process branching nuclei at CERN n_TOF

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• Introduction:
• Time-of-Flight
• Pulse Weight Height Technique

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• State-of-the-art (n,ɣ) detection systems:
• i-TED
• sTED
• Recent astrophysical highlights:
• ⁷⁹Se(n,ɣ)
• ⁹⁴Nb(n,ɣ)
• Ongoing detector development: Stilbene-d12 deTector ARray (STAR)
• Next measurements (2024):
• ¹⁴⁶Nd(n,ɣ) & ²⁰⁹Bi(n,ɣ)
• Summary and conclusions

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Asymptotic Giant Branch stars are the crib for s-process:

• It take place during thermal pulses.
• It it seed seed by ¹³C(⍺,n) [²²Ne(⍺,n)].

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Describe accurately the chemical isotope evolution

(A>57) require complex stellar models:

• T, ⍴ ,metallicity, B…

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Nuclear data plays a crucial role in the process:

• “Production” 𝜎_ɣ:
• Pointwise 𝜎_ɣ for stellar T dependence. ←ToF!
• 𝜎_ɣ Uncertainties below <5%. ←Developments!
• “Destruction” 𝛽^-:
• t_1/2(T)

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Both nuclear data helps to constraints stellar models and help to make predictions!

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T =10⁸ -10⁹ K

N_n = 10⁶-10¹² cm^-3

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Start: p-beam time impact Stop: (n,ɣ) time detection

Start

Stop

Stop

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Efficiency for (n,ɣ) cascade is quite complex to calculate because of the “infinite” paths:

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Solution: TED detectors (ε↓↓)

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How do we get a TED detector?

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F. Kaeppeler et al.,

Rev. Mod. Phys 83, 157 (2011)

More than than 100 isotopes interesting both for s-process and nuclear technology have been measured @ nTOF!

https://twiki.cern.ch/twiki/bin/view/NTOFPublic/DataDissemination

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There are several isotopes acting as branching points and other many as a bottlenecks conditioning the isotopic global production to be measured!

Very challenging cross section measurements:

• Small cross-sections
• Highly radioactive
• Low mass/Non existing in nature →Need to be produced in nuclear reactors or other facilities.

ToF measurements requires further developments to adapt for those cases:

• High luminosity luminosity facilities with good time resolution. → EAR2
• High sensitivity (n,ɣ) detection setups. →sTED array
• Background suppression techniques. →iTED array

C. Domingo et al.,

Eur. Phys. J. A (2023) 59:8(2023)

Our main partners for radioactive sample production:

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P. Zugec, et al., Nucl. Instrum. Methods A 760, 57 (2014);

Background level

Background level

MC simul.

⁹³Zr(n,γ)

Limitation:

Poor background rejection capabilities.

In particular, background originated from neutron scattered in the sample

C₆D₆ TED: Most extensively used detectors for (n,ɣ)

• Fast response (10 ns width signals)
• Low neutron sensitivity

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protons

neutrons

collimated neutron beam

Flightpath L

γ

New detector for (n,ɣ)

• Based on position sensitive detectors
• Imaging capabilities

Solution: Exploit the Compton Imaging technique to reduce the neutron background and enhance the detection sensitivity

nucleosynthesis & MS evolution

COMPTON

IMAGING

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⁵⁶Fe(n,ɣ):

(n,n)>>(n,ɣ)

3.5

Babiano-Suárez, V., et al. Eur. Phys. J. A 57, 197 (2021)

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protons

neutrons

collimated neutron beam

Flightpath L

New detector for (n,ɣ)

• Based on position sensitive detectors
• Imaging capabilities

Solution: Exploit the Compton Imaging technique to reduce the neutron background and enhance the detection sensitivity

nucleosynthesis & MS evolution

COMPTON

IMAGING

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⁵⁶Fe(n,ɣ):

(n,n)>>(n,ɣ)

3.5

Babiano-Suárez, V., Lerendegui-Marco, J. et al. Eur. Phys. J. A 57, 197 (2021).

Neutron induced background

Babiano-Suárez, V., et al. Eur. Phys. J. A 57, 197 (2021)

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State-of-the-art high sensitivity sTED array (9) in compact configuration @ n_TOF EAR2:

• Individual cells only 49 ml of C₆D₆:
• Deal with large (n,ɣ) rate free of DT.

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• Geometrical optimization (ring+4.5 cm):
• High sensitivity (s/b) for (n,ɣ).

ɣ-rays from target position

V_sTED/V_C6D6~0.44

C₆D₆

J. Balibrea, EPJ Web of Conferences 279, 06004 (2023)

V. Alcayne , EPJ Web of Conferences 284, 01043 (2023)

Lerendegui-Marco, J. et al., EPJ Web Conf. 279, 13001 (2023).

x4.4

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Strong competing (n,ɣ) and 𝛽 decay!

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Large influence on local (global) isotopes abundances!

They can be used as thermometer for stellar environments!

Highly Challenging (n,ɣ) cross-section measurements:

• High radioactive samples.
• Highly difficult sample production.
• Others difficulties (↑↑ (n,n), impurities...)

Never measured before!

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Only 3mg of ⁷⁹Se in a 3.9g sample �of ²⁰⁸Pb⁷⁸Se!!

i-TED+EAR1

sTED+EAR2

t_1/2~3.27 x 10⁵ years

~10 MBq of Activity!

Lerendegui-Marco, J. et al., EPJ Web Conf. 279, 13001 (2023).

(2022)

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⁷⁹Se

⁷⁹Se

⁷⁹Se

⁷⁹Se(n,ɣ):

10-15 observed resonances up to En~1keV

never measured before!

Lerendegui-Marco, J. et al., EPJ Web Conf. 279, 13001 (2023).

PRELIMINARY

PRELIMINARY

PRELIMINARY

⁷⁹Se

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• Explain anomalies on Mo isotopes found in presolar grains.

Earth and planetary science letters, Vol473, 215-226 (2017)

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• Super Nova type-Ia heavy elements production.

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• Constrain temperature in helium flashes for AGB stars.

Nature Vol 517, 174 (2015)

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Never measured before!

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304 mg hyper-pure ⁹³Nb+⁹⁴Nb material (47+45 mm wires).

⁹⁴Nb/⁹³Nb ~ 1% (9.24×10¹⁸ ⁹⁴Nb atoms).

10.1 MBq (only ⁹⁴Nb) (e^- (200 keV) + ɣ(702+871) keV)

sTED+EAR2

J. Balibrea, EPJ Web of Conferences 279, 06004 (2023)

(2022)

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⁹⁴Nb resonances →⁹⁴Nb

⁹³Nb resonances →⁹³Nb

Contaminant resonances →C

J. Balibrea, EPJ Web of Conferences 279, 06004 (2023)

⁹⁴Nb(n,ɣ):

12-15 observed resonances En~1keV

never measured before!

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“Big” C₆D₆ Liquid scintillators

Large & segmented C₆D₆

“High” TED efficiency

Strong limitation in Count rate

Chemical hazard

High S/B & (n,ɣ) efficiency

High counting rates capabilities

Chemical hazard

Solid organic scintillators

Read-outs/Power supplies

High S/B & (n,ɣ) efficiency

High counting rates capabilities

No Chemical hazard

Further S/B improvement?

Compact array of small C₆D₆

The new frontier

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PSD stilbene-H(D)/C6D6 ~3

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J. Lerendegui INTC-P-671

J. Balibrea INTC-P-675

EURATOM-APRENDE

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• The s-process is responsible of half of the abundances beyond Fe:
• ToF measurements offer pointwise neutron capture cross sections important for stellar models

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• The gamma and neutron spectroscopy group has a leading role in CERN n_TOF in the framework of the nuclear astrophysics s-process:
• 4 Ph.D thesis (Victor Babiano, Adrià Casanovas, Giuseppe Giubrone, César Domingo) + 2 PhD thesis ongoing (Bernardo Gameiro, Gabriel de la Fuente).
• First author in 20+ peer review articles & conferences related to s-process or instrumentation and techniques associated.
• 5 spokespersons/leading role in n_TOF measurements for s-process branching points.

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• Our group push continuously innovative developments to tackle new measurements:
• i-TED → ERC HYMNS →⁷⁹Se @ EAR1.
• sTED array →PID2019/AEI →⁹⁴Nb, ⁷⁹Se @ EAR2.
• STAR →ASFAE/2022/027+MRR-CERN →WW-Unique stilbene-d12 based high sensitivity detector array for very high count-rate conditions (radioactive samples / s-process branchings / i-process).
• We are very active within the n_TOF collaboration for new cross section measurements:
• ¹⁴⁶Nd →First ever measurement!, PhD Thesis topic of Bernardo Gameiro (IFIC)
• ²⁰⁹Bi →High precision measurement with implications in astrophysics and GenIV reactors → PhD thesis of Gabriel de la Fuente (IFIC)

Thank you very much for your attention!

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