Neutron capture cross section measurements

for nuclear astrophysics at n_TOF

Michael Heil

on behalf of the n_TOF collaboration

Outline The CERN n_TOF Facility

MotivationBasic parametersExperimental Setup

Experimental campaigns in 2002-2004Neutron capture measurements

for astrophysics Perspectives

Michael Heil NIC IX, June 2006, Geneva

The n_TOF collaborationThe n_TOF collaboration

U. Abbondanno20, G. Aerts7, H. Álvarez35, F. Alvarez-Velarde31, S. Andriamonje7, J. Andrzejewski26, P. Assimakopoulos16, L. Audouin12, G. Badurek1, P. Baumann10, F. Bečvář 6, E. Berthoumieux7, F. Calviño34, D. Cano-Ott31, R. Capote3,36, A. Carrillo de Albornoz27, P. Cennini37, V. Chepel128, E. Chiaveri37, N. Colonna19, G. Cortes33, A. Couture41, J. Cox41, M. Dahlfors37, S. David9, I. Dillmann12, R. Dolfini23, C. Domingo-Pardo32, W. Dridi7, I. Duran35, C. Eleftheriadis13, M. Embid-Segura31, L. Ferrant9, A. Ferrari37, R. Ferreira-Marques28, L. Fitzpatrick37, H. Frais-Koelbl3, K. Fujii20, W. Furman30, C. Guerrero31, I. Goncalves28, R. Gallino22, E. Gonzalez-Romero31, A. Goverdovski29, F. Gramegna18, E. Griesmayer3, F. Gunsing7, B. Haas8, R. Haight39, M. Heil12, A. Herrera-Martinez37, M. Igashira25, S. Isaev9, E. Jericha1, Y. Kadi37, F. Käppeler12, D. Karamanis16, D. Karadimos16, M. Kerveno10, V. Ketlerov29,37, P. Koehler40, V. Konovalov30,37, E. Kossionides15, M. Krtička6, C. Lamboudis13, H. Leeb1, A. Lindote28, I. Lopes28, M. Lozano36, S. Lukic10, J. Marganiec26, L. Marques27, S. Marrone19, P. Mastinu18, A.Mengoni3,37, P.M. Milazzo20, C. Moreau20, M. Mosconi12, F. Neves28, H. Oberhummer1, S. O'Brien41, M. Oshima24, J. Pancin7, C. Papachristodoulou16, C. Papadopoulos14, C. Paradela35, N. Patronis16, A. Pavlik2, P. Pavlopoulos11, L. Perrot7, R. Plag12, A. Plompen5, A. Plukis7, A. Poch33, C. Pretel33, J. Quesada36, T. Rauscher38, R. Reifarth39, M. Rosetti17, C. Rubbia23, G. Rudolf10, P. Rullhusen5, J. Salgado27, L. Sarchiapone37, I. Savvidis13, C. Stephan9, G. Tagliente19, J.L. Tain32, L. Tassan-Got9, L. Tavora27, R. Terlizzi19, G. Vannini21, P. Vaz27, A. Ventura17, D. Villamarin31, M.C. Vincente31, V. Vlachoudis37, R. Vlastou14, F. Voss12, S. Walter12, H. Wendler37, M. Wiescher41,and K.Wisshak12

Michael Heil NIC IX, June 2006, Geneva

41 Research Groups41 Research Groups120 researchers 120 researchers

Neutron physics at n_TOFNeutron physics at n_TOF

• Nuclear Data for ADSn_TOF idea (C. Rubbia et al., 1998):

Measurements of neutron cross sections relevant for Nuclear Waste Transmutation and related Nuclear Technologies

n_TOF-ND-ADS: EC FP5 project running from November 2000 to December 2004 coordinated by CERN

spokespersons: Noulis Pavlopoulos, Alberto Mengoni

• Basic nuclear Physics with neutrons

• Nuclear AstrophysicsNeutron capture cross section measurements

relevant for Nuclear Astrophysics

Michael Heil NIC IX, June 2006, Geneva

The n_TOF facility at CERNThe n_TOF facility at CERN

Basic parameters of n_TOFBasic parameters of n_TOF

proton beam momentum 20 GeV/c

intensity (dedicated mode) 7 x 1012 protons/pulse

repetition frequency 1 pulse/2.4s

pulse width 6 ns (rms)

n/p 300

lead target dimensions 80x80x60 cm3

cooling & moderation material H2O

moderator thickness in the exit face 5 cm

Michael Heil NIC IX, June 2006, Geneva

Characteristics of the neutron beamCharacteristics of the neutron beam

neutron spectrum

thermal – GeV

neutron flux

10-100 keV

7·104 n/pulse

flight path 187.5 m

Ø 2nd collimator

beam size

1.8 cm

< 4 cm

E/E @ 30 keV 1·10-3

• 40 BaF2 crystals• High detection efficiency ≈100%• Good energy resolution• so far, only used for (n,) measurements of actinides

Experimental setup and detectorsExperimental setup and detectors

C6D6

C6D6

Neutron beam

Sample changer

-ray detection via C6D6

scintillators

Neutron flux monitor

4 BaF2 detector array

Pulse height weighting technique:Correction of the -response by weighting function to make the detector efficiency proportional to -ray energy

Silicon detectors viewing a thin 6LiF foilSince 2004 BaF2 detector is operational

Michael Heil NIC IX, June 2006, Geneva

Sample changer and beam pipe made out of carbon fibre

sample

Astrophysics at n_TOFAstrophysics at n_TOF

Michael Heil NIC IX, June 2006, Geneva

n_TOF features Use in astrophysics

broad neutron energy rangeneutron capture cross sections for

s-process studies (0.1 – 500 keV)

high instantaneous flux

small capture cross sections

small sample quantities (isotopically enriched samples)

radioactive samples (low intrinsic background)

excellent energy resolution resonance dominated cross sections

low neutron sensitivity

low backgrounds

accurate cross section measurements

even for large el/capture

Reaction Motivation24,25,26Mg(n,) Abundance anomalies in grains,

Strength of neutron source 22Ne(,n)25Mg90,91,92,93,94,96Zr(n,) Neighborhood of s-process branching at

A=95,

Sensitivity to neutron flux139La(n,) Bottleneck at N=82 and s-process indicator for

spectroscopic observations151Sm(n,) s-process branch point186,187,188Os(n,) Nuclear Cosmochronology (Re/Os clock)204,206,207,208Pb(n,)209Bi(n,)

Termination of the s-process pathsee talk by Marita Mosconi today at 9 am

see poster 22.03 by Giuseppe Tagliente

Neutron capture measurementsNeutron capture measurements

Mg

Zr

La

Sm

Os

Pb

Bisee talk by C. Domingo Pardo today at 10:15 am

see poster 20.38 by Stefano Marrone

Michael Heil NIC IX, June 2006, Geneva

90,91,92,90,91,92,9393,94,96,94,96Zr(n,Zr(n,) measurements) measurements

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

• 90Zr is neutron magic (N=50)small x-section (resonance dominated)

bottleneck in the s-process flow• Zr abundances are sensitive to neutron flux in AGB models• s-process branching at 95Zr

90,91,92,90,91,92,9393,94,96,94,96Zr(n,Zr(n,) measurements) measurements

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

Samples• Isotopically enriched samples• diameter 2.2 cm• mass: 1.3 – 3.4 g• Al can

90,91,92,90,91,92,9393,94,96,94,96Zr(n,Zr(n,) measurements) measurements

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

The extracted resonance parameters were compared witha previous measurement (Boldeman et al., 1976)

L Marques, et al. - The n_TOF Collaboration

90,91,92,90,91,92,9393,94,96,94,96Zr(n,Zr(n,) measurements) measurements

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

≈ 20% lowerthan previous data

C Moreau, et al. - The n_TOF CollaborationND2004 Conference, Santa Fe, NM – Sept. 2004

96ZrZr

90,91,92,90,91,92,9393,94,96,94,96Zr(n,Zr(n,) measurements) measurements

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

Preliminary Maxwellian averaged cross sections @ kT=30 keV

n_TOF Bao et al.90Zr 20 ± 1 21 ± 291Zr 58 ± 3 60 ± 892Zr 30 ± 2 33 ± 494Zr 36 ± 2 26 ± 196Zr 7.5 ± 0.4 10.7 ± 0.5

Analysis 93Zr in progress!

139139La(n,La(n,) measurement) measurement

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

139La

• Neutron magic N=82small x-section (resonance dominated)

bottleneck in the s-process flow• 139La is mono-isotopic and easier to detect in stellar spectroscopy than Ba• On the basis of accurate neutron capture cross sections 139La can be used as s-process indicator (complement to Eu as r-process indicator)

139139La(n,La(n,) measurement) measurement

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

Remarkable energy resolution and background conditions have allowed to determine the resonance parameters up to 9 keVIn the past, the best experimental data did not exceed 2.7 keV.

R. Terlizzi et al. (INFN)

Up to 2.7 KeV:<capture strength> n_TOF < 10% of Nakajima + Musgrove

< 20% of databasesMACS-30 in agreement with the FZK activation measurement(s)

151151Sm(n,Sm(n,) measurement) measurement

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

Sm

Eu

Gd

150Sm

151Sm 93 a

152Sm

153Sm

154Sm

151Eu

152Eu

153Eu

154Eu

155Eu

156Eu

152Gd

153Gd

154Gd

155Gd

156Gd

157Gd

First s-process branch point which was directly measured via TOF

Sample:• 206 mg 151Sm2O3 (Oak Ridge)• 90 % enrichment• t1/2 = 93a, activity: 156 GBq• encapsulated in Ti-can

Branchings can be used to determine • neutron density• temperature• mass density• convection time scales

in the interior of stars

151151Sm(n,Sm(n,) measurement) measurement

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

151151Sm(n,Sm(n,) measurement) measurement

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

U Abbondanno et al. Phys. Rev. Lett. 93 (2004), 161103

MACS-30 = 3100 ± 160 mb

<D0> = 1.48 ± 0.04 eV, S0 = (3.87 ± 0.20)×10-4

n_TOF

S. Marrone et al. Phys. Rev. C 73 (2006) 03604

24,25,2624,25,26Mg(n,Mg(n,) measurements) measurements

Motivation:• Neutron poison for s process• Strength of 22Ne(,n)25Mg neutron source• Magnesium anomalies in presolar grains• 26Mg excess from in situ decay of radioactive 26Al

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

Mg

Zr

La

Sm

Os

Pb

Bi

Michael Heil NIC IX, June 2006, Geneva

Fitting of resonance parameter in progress!

24,25,2624,25,26Mg(n,Mg(n,) measurements) measurements

first known Mg resonance at 24 keV

ImpuritiesIn, Sb

Outlook - Plan for measurements in Phase-2

Michael Heil NIC IX, June 2006, Geneva

Capture measurements

Mo, Ru, Pd stable isotopes

Fe, Ni, Zn, and Se (stable isotopes)63Ni, 79Se

A≈150 (isotopes varii)

147Sm(n,), 67Zn(n,), 99Ru(n,),58Ni(n,p)

r-process residuals calculationisotopic patterns in SiC grains

s-process nucleosynthesis in massive stars

accurate nuclear data needs for structural materials

s-process branching pointslong-lived fission products

p-process studies

n_TOF will continue:Letter of Intent signed by 24 research labs of the n_TOF Collaboration + 4 newcomers (January 2005)

n_TOF target

NewExperimentalArea (EAR-2)

EAR-1 (at 185 m)

~ 20 m

Flight-path length : ~20 m at 90° with respect to p-beam expected neutron flux enhancement: ~ 100 drastic reduction of the t0 flash duty factor improved by factor of 10

Michael Heil NIC IX, June 2006, Geneva

Second n_TOF beam line & EAR-2Second n_TOF beam line & EAR-2

Use of DUse of D22O moderatorO moderator

Michael Heil NIC IX, June 2006, Geneva

Photon time distribution (E>1MeV)

EAR-2: Optimized sensitivityEAR-2: Optimized sensitivity

Michael Heil NIC IX, June 2006, Geneva

Improvements (ex: 151Sm case)

• sample mass / 3 s/bkgd=1

• use BaF2 TAC x 10

• use D2O 30 x 5

• use 20 m flight path 30 x 100

consequences for sample mass

50 mg

5 mg

1 mg

10 g

boosts sensitivity by a factor of 5000 !(a factor of 100 ONLY from higher flux)

problems of sample production and safety issues relaxed