Fission 2017, Chamrousse, 20th-24th March 2017

J. Lerendegui-Marco, C. Guerrero, C. Domingo-Pardo, A. Casanovas, S. Halfon,

S. Heinitz, N. Kivel , U. Köster, M. Paul, R. Dressler , D. Schumann, M. Tesslerand The n_TOF Collaboration

Measuring neutron capture rates on ILL-produced unstable isotopes for

nucleosynthesis studiesJ. Lerendegui-Marco1, C. Guerrero1, C. Domingo-Pardo2, A. Casanovas3,

S. Halfon4, S. Heinitz5, N. Kivel5 , U. Köster6, M. Paul7, R. Dressler5 , D. Schumann5 , M. Tessler7 and The n_TOF Collaboration8

1) Universidad de Sevilla, Sevilla, Spain2) Instituto de Física Corpuscular, Paterna, Spain

3) Universitat Politècnica de Catalunya, Barcelona, Spain4) Soreq NRC, Yavne, Israel

5) Paul Scherrer Institut, Villigen, Switzerland6) Institut Laue-Langevin, Grenoble, France

7) Racah Institute of Physics, Hebrew University, Jerusalem, Israel8) European Center for Nuclear Research (CERN), Geneva, Switzerland

Interest for neutron capture measurements

Nuclear Astrophysics: s-process

2

Nucleosynthesis of elements A>60

• Site: He-intershell in AGB stars (red giant)

• Branching point: β- decay competes with (n,g)

(n,g)b-

(n,g)b-

(n,g) (n,g) (n,g)

(n,g) (n,g)

Suff. long t1/2 || Suff. High Fn

Branching point s-process

b- decay

StableZ

N

(n,γ) measurements onunstable isotopes

3

Main limitation of current facilities and techniques :Need for massive (~mg) and isotopically pure samples

Successful collaboration to produce relevant unstable isotopes (ILL) and prepare high quality targets (PSI)

After this big effort to produce the samples: Complementary (n,γ) measurements using different the

beams and techniques available (n_TOF, LILIT, TRIGA, BRR)

171Tm (n,γ): thermal, resonance and MACS

cross sections

--------------------------------------------------------------------------------171Tm: 170Er(n,g)171Er(b-, 7.5h)171Tm (enrichment 1.8%)

3.81 mg of 171Tm (1.9 y) [1.3 1019 atoms]

Production via (n, γ) or (n, γ )+b- at the ILL research reactor [Contact: Ulli Koester]Neutron flux: 1.5x1015 n/cm2/sIrradiation time: 55 days

171Tm(n,γ): Preparation of radioactive targets

Chemical separation and targets @ PSI [Stephan Heinitz´s Talk]

PCB frame (50 mm diameter)Mylar (5 mm)

147Pm deposit (20 mm diameter)Aluminum (7 mm) backing

Assemblymounted

6

Do not exist in nature Small masses producedActivity challenge to handle and measure

171Tm (n,γ): Energyranges and beams

7

Pulsed white n-beam(i.e. n_TOF@CERN, etc.)

“quasi-Mawellian” n-beam(i.e. FZK, LiLiT, FRANZ, etc.)

Time-of-flight→ pointwise s(n,g)

Activation→ MACS(single value)

Nuclear reactor(i.e TRIGA, BRR)

Activation→ σth

(single value)

MACS:MaxwellianAveraged Cross Section

MaxwellBoltzmanndistribution @ KB.T=30keV

7Li(p,n)7Beor D-T)

AX

Sn

En

A+1X

sg

Ec

+n

Ec

NEUTRON CROSS SECTION MEASUREMENTS:How to produce of neutrons in each energy range

How to measure neutron energy and detect the reaction products

8

171Tm(n,γ) MACS:LiLiT facility @ SARAF

197Au-frontmonitor

197Au-backmonitor

~1.935 MeV protons

1-2 mA

Precise beam intensity and energydistribution depend on distance and

angle coverage

Case1. 197Au(n,g)198Au -> b- decay with t1/2=2.69 d -> Eg = 412 keV

Case2. 171Tm(n,g)172Tm -> b- decay with t1/2=2.65 d -> Eg = 1093, 1387, 1529, 1608 keV

Liquid lithium: 7Li(p,n)

25

mm

22

mm~12 mm

NORMALIZATION

171Tm(n,γ) MACS:Results

sMACS (171Tm, kT=30 keV) = 198 (22) mb

This work(183±27 mb)

Significant reduction of the MACS at 30keV

JEFF 3.2 (x6) and also KADoNiS overestimate the MACS

Evolution of calculations also tends to lower the cross-section10

MACS @ 30 keV

KADoNiS: x 2.7

Reifarth: x 1.6

171Tm(n,γ) Thermal Cross-section

Thermal cross-section: Maxwellian spectra @ KT= 25meV

Prompt Gamma Activation Analysis using the n_TOF targets

Budapest Research Reactor

MACS and thermalprovide just two points:

TOF measurement needed for pointwise

cross-section

11

Flux (Φ) (neutrons/cm2)

nat (atoms/cm2)

Reaction products

Transmission

Scattering

γt0

tL= 184 m

PS Protonpulses

(20 GeV/c)σ = 7 ns

PbSpallationMeV-GeVNeutrons

CERN-n_TOF: Time-of-flight techniqueBEAM LINE EAR1

Time-of-Flight to En relation (non-rel.): nE

LttToF 05cm water moderator

Neutrons (meV to GeV)

12

C6D6

Scintillators

13

171Tm (n,γ) @n_TOF in brief

Counts -> Pointwise cross section

Efficiency to detect a cascade

Resonance analysis 1 - 700 eV

Counts vs En

Challenge:Sample activity

𝝈𝒏,𝜸(𝑬𝒏) =𝑪(𝑬𝒏) − 𝑩(𝑬𝒏)

𝒏𝒂𝒕𝜺𝒅𝒆𝒕𝜱𝒏(𝑬𝒏)

Resonance parameters: E, J, Γn, Γγ

14

171Tm (n,γ) at n_TOF: Resonance region

Neutron strenght:S0

RRR:Directlymeasured(27 new resonances!)

URR: Extrapolated withthese avg. parameters

Before: Just TENDL-2012 (TALYS calculation)n_TOF data: Overestimation of density and strength in TENDL

S0, D0, <Gg> significantly smaller than systematics (Mughabghab)

15

147Pm 204Tl

Branching at A= 147/148

146Nd(n,g)147Nd (b-, 10d)147Pm→ Final mass 83 ug!

n_TOF - EAR2 : First time ever (n, γ)Few resonances (smallest mass ever!)

MACS @ LiLiT: 1200 ± 120 mbSignificantly larger than previous measurement

205Pb/205Tl clock early universe

203Tl(n,g)204Tl → 6 mg of 204Tl (3.78 y) [3.25e19 atoms]

n_TOF - EAR1 : First time ever (n, γ)- 200 GBq + high Qβ decay-Pellet disaggregation during irradiation -Resonances (KeV) Direct MACSNo activation possible (205Tl stable)

Other s-processisotopes produced at ILL

16

79Se 163Ho

Upcoming measurements

Relevant branching A=80to constrain s-process T , densityand role of main/weak

78Se(n,g)79Se (327ky) → ~8mg-Difficulty in the past: Impurities in the Pb-Se alloy ( Melts @ 217 ºC)-This time: Pure 208Pb-78Se seed

Planned to be measured at n_TOF -EAR2 : First time ever (n, γ)Direct MACS from resonances

No activation possible (80Se stable)

Branching A=163, beta decay rate<-> mass density

HOLMES Project : neutrino mass with a calorimeter measuring the endpoint of the 163Ho β+ spectrum.

162Er(n, γ)163Er (b+)163Ho (4570 y) : ~6 mg

Proposed at n_TOF - EAR1+EAR2:First time ever (n, γ)Resonance parameters + MACS

Summary andconclusions

s-process: (n, γ) cross-section certain isotopes key input for stellar evolution models

171Tm, 147Pm, 204Tl, 79Se, 163Ho: s-process branching points:

Benefitted from the collaboration with ILL for the production + PSI for target preparation of radioactive targets, our main interest for both astrophysics and reactor physics.

171Tm (n,γ): different neutron beams & techniques in complementary energy ranges

n_TOF : White neutron beam + Time-of-flight technique Pointwise cross section Resonances and average parameters for the keV region

LiLiT @ SARAF : Quasi-stellar spectra ( 7Li(p,n)7Be reaction) MACS measurement via activation Decay of the produced 172Tm nuclei

TRIGA (analysis ongoing) and BRR (near future): Maxwellian spectra at thermal Measurement via activation and PGAA

n_TOF and SARAF indicate a significant reduction of x-section compared to models

17

THANKS FOR YOUR ATTENTION!

18

s-process branching points

17

Interest for neutron capture measurements

18

(n,g)b-

(n,g)b-

(n,g) (n,g) (n,g)

(n,g) (n,g)

Branching point s-process

b- decay

Stable

U. Sevilla

ILL

PSI

TRIGA Mainz

BRR

LiLiT

CERN

171Tm (n,γ): a European trip towards thethermal, resonance and MACS cross sections

1) Irradiation of stable seeds

Coordination and analysis

2) Separation and samples

3) Activation: thermal reactor

4) TOF + white n beam:Pointwise cross section

5) Activation:Quasi-stellar spectrum

6) PGAA: thermal reactor

Carlos GUERRERO “Neutron capture cross sections of the s-process branching points 147Pm, 171Tm and 204Tl” Nuclei in the Cosmos NIC-2016, Niigta, Japan (June 20th-24th 2016)

Nucleosynthesis through the s process

MASS NUMBER

AB

UN

DA

NC

Esolar abundance distribution

stellar burning

NSE

r-process

weak main s-process

p-process

Others ?

C. Guerrero and C. Domingo-Pardo @CERN/INTC February 2014

“Neutron capture at the s-process branching points 171Tm and 204Tl”

171Tm as part of branching at A=170/171

The A=170/171 branching point is one of the branchings that is independent ofstellar temperature, therefore suited for constraining the s-process neutrondensity in low-mass AGB stars (i.e. main s-process component).

In view of the difficulties related to production of 170Tm, experimental informationon 171Tm becomes important as part of the branching, but also as the moreimportant for improved HF predictions of the 170Tm cross section.

F. Kaeppeler et al., ApJ 354 (1990) 630-643 nn= 𝟎. 𝟕−𝟎.𝟓+𝟒.𝟗 ∙ 𝟏𝟎𝟖 𝒄𝒎−𝟑

171Tm (n,γ): Activatednuclei to MACS

𝜎𝑒𝑥𝑝 𝐴𝑢 =

𝜎𝑒𝑣𝑎𝑙𝑢𝑎𝑡𝑒𝑑 𝐸𝑛, 𝐴𝑢𝑑𝑛𝑠𝑖𝑚𝑑𝐸𝑛

𝑑𝐸𝑛

𝑑𝑛𝑠𝑖𝑚𝑑𝐸𝑛

𝑑𝐸𝑛,

Correction for

the shape of the

flux of the Au

ref. MACS

Measured quantity:

Activated nuclei𝐶𝐸𝑛 𝑇𝑚, 𝑘𝑇 = 30𝑘𝑒𝑉

=2

𝜋

0∞𝜎𝑙𝑖𝑏(𝑇𝑚, 𝐸𝑛)𝐸𝑛𝑒

− Τ𝐸𝑛 𝑘𝑇𝑑𝐸𝑛

0∞𝐸𝑛𝑒

− Τ𝐸𝑛 𝑘𝑇𝑑𝐸𝑛

0∞ 𝑑𝑛𝑠𝑖𝑚

𝑑𝐸𝑛𝑑𝐸𝑛

0∞𝜎𝑙𝑖𝑏 𝑇𝑚,𝐸𝑛

𝑑𝑛𝑠𝑖𝑚𝑑𝐸𝑛

𝑑𝐸𝑛

𝝈𝑴𝑨𝑪𝑺 𝑻𝒎, 𝒌𝑻 = 𝟑𝟎𝒌𝒆𝑽 =2

𝜋𝐶𝐸𝑛 𝑇𝑚, 𝑘𝑇 = 30𝑘𝑒𝑉 𝜎𝑒𝑥𝑝(𝐴𝑢)

Τ𝑁172𝑇𝑚 𝑁171𝑇𝑚Τ𝑁198𝐴𝑢 𝑁197𝐴𝑢

Correction for the

shapes of the flux

and the 171Tm

X-section

9

22

Neutron Energy Distribution @ EAR1 (v10.0.3)

Normalization factors of *_INCLXX_HPT physics lists are improved in v10.1.1 by about

15% w.r.t v10.0.3 of the Geant4 toolkit.

15

171Tm (n,γ) at n_TOF: Resonance region

<Gg>= 76(9) meV (sys: 100 meV)D0 =21(3) eV (sys: 7 eV) S0 0.90(26) (sys:1.6)

RRR:Directlymeasured(27 new resonances!)

URR: Extrapolated withthese avg. parameters

Average resonance parameters

Significant reduction of x-section wrt

systematic studies

Carlos GUERRERO “Neutron capture cross sections of the s-process branching points 147Pm, 171Tm and 204Tl” Nuclei in the Cosmos NIC-2016, Niigta, Japan (June 20th-24th 2016)

Branching points: example at A=147/148

s-only

s-only

Carlos GUERRERO “Neutron capture cross sections of the s-process branching points 147Pm, 171Tm and 204Tl” Nuclei in the Cosmos NIC-2016, Niigta, Japan (June 20th-24th 2016)

25

Results for 147Pm(n,g) @n_TOF-EAR2

• Activity background not a problem in EAR2• Statistics very limited, due to small mass • But still, 10-15 resonances observed (1st time!)

147Pm(n,g)148Pm -> b- decay witht1/2=5.4||41 d

26

1014 keV: from 147Pm(n,g)148mPm 1465 keV: from 147Pm(n,g)148gPm

Peliminary results indicate that the partial cross sections are quite different, whilethe only available (Reifarth:2003) data suggest only a difference of only 25%.

Ground state: cps/Ig/e=3,0(3) @12.2d → A0=34(2) Bq → 2,2x107 148Pm atomsMetastable state: cps/Ig/e=7,1(3) @12.2d → A0=8,7(4) Bq → 4,5x107 148Pm atoms (>>)

Hig

h b

ackg

. fro

msh

ort

live

dac

tiva

tio

np

rod

uct

s

Hig

h b

ackg

. fro

msh

ort

live

dac

tiva

tio

np

rod

uct

s

Carlos GUERRERO “Time-of-flight and activation experiments on 147Pm and 171Tm for astrophysics ” Int. Conf. Nuclear Data for Sc. and Tech, Bruges, Belgium (September 12th 2016)

MACS results for 147Pm

27

sMACS (147gPm, kT=30 keV) = 406(60*) mb

sMACS (147mPm, kT=30 keV) = 830(125*) mbsMACS (147Pm, kT=30 keV) = 1236 (185*) mb

*Preliminary 15% uncertainty

C. Guerrero and C. Domingo-Pardo @CERN/INTC February 2014

“Neutron capture at the s-process branching points 171Tm and 204Tl”

204Tl determines the 205Pb/205Tl clock for dating of early Solar System

205Pb (t1/2 = 1.5x107 a) is produced only by the s-process:The ratio 205Pb/205Tl provides highly interesting chronometric information aboutthe time span between the last nucleosynthetic events that were able to modifythe composition of the solar nebula and the formation of solar system solid bodies.

(At present, there is an upper limit for the 205Pb/205Tl abundance ratio of 9x10-5 from meteorites)

Anders & Stevens, J. Geoph. Res., 1961Huey & Kohman, Earth Plan. Sci. Lett., 1972Blake et al., Nature, 1973Blake and Schramm, ApJ, 1975

K. Yokoi et al., Astronomy and Astrophysics 145, 339-346 (1985)

J. Lerendegui-Marco, S. Heinitz and C. Guerrero @n_TOF Coll. Meeting, November 2016

“Neutron capture on the unstable 163Ho for the study of the branching at A=163…”

The ERC-Advanced Grant “HOLMES” project

HOLMES: The Electron Capture Decay of 163Ho to Measure the Electron Neutrino Mass with sub-eV sensitivityThe determination of the absolute neutrino mass mn is still an open question in particle physics.Currently, the most stringent limit of mne < 2 eV was achieved for the electron anti–neutrinomass from the measurement of the endpoint of the decay of 3H. Novel experimental approachesexploring the endpoint of the b--decay of 3H or the electron capture of 163Ho offer greatpotential to reach a sub–eV sensitivity on mne.The HOLMES experiment is going to investigate the neutrino mass with a calorimeter measuring the endpoint of the 163Ho spectrum.

J. Lerendegui-Marco, S. Heinitz and C. Guerrero @n_TOF Coll. Meeting, November 2016

“Neutron capture on the unstable 163Ho for the study of the branching at A=163…”

163Ho as part of branching at A=163163Dy is stable, but b- (47 d) to 163Ho when fully ionized (stellar plasma)Equilibrium abundance of 163Ho from decay of 163Dy and decay back from 163Homakes it possible to produce 164Ho via (n,g). The equilibrium abundance of 163Ho isdetermined by the temperature and electron density in the star, which is directlyrelated to the mass density.

S. Jaag and F. Käppeler, ApJ 464 (1996) → 163Ho MACS30keV = 2125(95) mb (0,2mg target)

Time of Flight experiments with white neutron beams

Outcome: (point-wise) capture cross sections as function of En

Measuring s(n,g): activation & ToF

32

Activation with a Maxwellian (kT=tens of keV) neutron beam from 7Li(p,n) reactions

Outcome: capture cross sections at a given kT=tens of keV (ONE POINT!)

HPGedetector

Lead shield

g

g

g

Pulsedp+ beam (20 GeV)

Neutrons (meV-GeV)→diff. ToF

tof

Stellar

Experimental

Offline!

A+1Z unstable

This project:

Highest intensity 7Li(p,n) beam worldwide: LiLiT @ SARAF (Israel)

This project:

Highest inst. intensity pulsed white beam worldwide: n_TOF@CERN(we need to measure (n,g) g-rays from GBq targets)

7

171Tm (n,γ): MACS measurement @ LiLiT

2

Stellar

Experimental

2x1010 n/s/mA1-2 mA~2 kW

Liquid Lithium Target

(@SARAF, Israel)

13

171Tm (n,γ) measurement@ n_TOF

EAR1 using Total Energy Detectors

PULSE HEIGHT WEIGHTING TECHNIQUE:Accurate simulations requiredNov-Dec 2014

C6D6 Scintillators

Geant4 model of the setup

Total Energy Detectiontechnique

35

Two conditions must be fulfilled:

I.) Low Efficiency Detectors:

II.) Efficiency to detect a γ-ray is proportional to

its energy: egi∝Egi

First idea: Moxon-Rae detectors:• Using a converter: maximum depth of escaping electrons increases with Eg …• Proportionality not really fulfilled• Sensitive to neutrons

egi ≪1, i

eC = 1 - (1 - egi)i=1

mg

𝜺𝒄 ≈

𝒊=𝟏

egi

Bi/C-converter

e g/

Eg

Eg

(g,e-) converter

thin scintillator

PM tube

𝜺𝒄 = 𝒌

𝒊=𝟏

Egi = 𝒌𝑬𝒄

AX

-

Sn

En

A+1X

sg

Ec

+n

Ec

Total efficiency depends on Ec

and not on the decay path

TED with C6D6

detectors

36

C6D6 Detectors : Low neutron sensitivity (104. eg )

• Benzene: Organic scintillator

• H replaced by D Avoid H(n,γ)D + 2.2MeV γ-ray

Fulfill condition I : Low efficiency detectors egi<<1

Detecting a cascade: ec=1-(1- egi) ≈ σ egi

The efficiency is NOT proportional to γ-ray energy:

egi∝Egi

Proportionality fulfilled with Weighting factors Wj dependent on the Energy deposited Egj :

Wj=W(Egj) : σ𝒋 WjRij=Egi, 𝜺𝒊 ≈ σ𝒋Rij

The proportionality between efficiency

and g-ray energy is obtained by

software manipulation of the detector

response (Rij)

Pulse Height Weighting

Technique (PHWT)

k=1