EGAF Status 2015Richard B. Firestone

Lawrence Berkeley National Laboratory and the University of California, Berkeley, 94720, USA

21st Technical Meeting of the NSDDIAEA Headquarters, Vienna, Austria

20-24 April 2015

Outline1. Published results 2013-2015 (9 journal publications) – 23Na, 39,40,41K,

152,154Eu, 156,158Gd, 180,182,183,184,186W, 237Np, 241Am, 242Pu(n,g)

2. Evaluations in progress – 2H, 16,17,18O, 54,56,57,58Fe, 90Y, 94Nb, 140La, 186Re(n,g)

3. 57Fe photon strength function

a) Primary g-ray strengthsb) Secondary g-ray strengthsc) Comparison to Porter-Thomas distribution

4. Future plans

Published Results 2013-2015

Isotope s0 (b) Atlas* s0 (b) This work23Na 0.517(4) 0.541(3)

39K 2.1(2) 2.28(4)40K 30(8) 90(7)41K 1.46(3) 1.62(3)

Eg 42K(b-) Pg ENSDF Pg This work

1524.7 0.1808(9) 0.164(4)

New Potassium Nuclear Structure DataIsotope 23Na 40K 41K 42K# levels below Ecrit (RIPL)† 4 15 11 4# levels below Ecrit (This work) † 13 21 16 17

New Jp assignments 21 3 2 8

New levels placed 0 18 0 0

Previous levels removed 0 1 0 0

New g-rays placed 27 2 0 0

23Na: R.B. Firestone et al, submitted to Phys. Rev. C 89, 014617 (2014)39,40,41K: R.B. Firestone et al, Phys. Rev. C 87, 024605 (2013)

*Atlas of Neutron Resonances, S.F. Mughabghab, Elsevier (2006).

† Ecrit is the excitation energy where the level scheme is complete.

Sn (keV)

Isotope This work AME24Na 6959.352(18) 6959.42(4)

40K 7799.57(12) 7799.62(6)41K 10095.243(15) 10095.37(6)42K 7533.829(10) 7533.80(11)

Published Results 2013-2015

Tungsten Thermal (n,g) Cross Sections

IsotopeCross section (b)

This work Atlas182W(n,g)183W 20.5(14) 19.9(3)182W(n,g)183Wm 0.177(18) ---183W(n,g)184W 9.4(4) 10.4(2)183W(n,g)184Wm 0.025(6) ---184W(n,g)185W 1.43(10) 1.7(1)184W(n,g)185Wm 0.0062(16) ---186W(n,g)187W 33.3(6) 38.1(5)*186W(n,g)187Wm 0.400(16) ---

Tungsten Neutron Separation Energy Isotope Sn (keV)

This Work AME183W 6190.88(6) 6190.81(5)184W 7411.11(13) 7411.66(25)185W 5753.74(5) 5753.71(30)187W 5466.62(7) 5466.79(5)

182,183,184,186W: A.M. Hurst, et al, Phys. Rev. C 89, 014606 (2014).187W b- decay Pg(686 keV)

This work 0.352(9)

ENSDF 0.332(5)

* Based on old ENSDF decay scheme normalization.

Published Results 2013-2015New Tungsten Nuclear Structure Data

Isotope 183W 184W 185W 187W# levels below Ecrit (RIPL) 11 12 8 3# levels below Ecrit (This work) 12 18 11 40

New Jp assignments 1 1 3 16

New levels placed 0 0 0 1

Previous levels removed 1 1 0 0

New g-rays placed 1 2 2 5

Jp of -26.6 eV 184W bound resonanceENSDF (0,1)-

This work 1-

ENSDF This work

Published Results 2013-2015180W(n,g): A. Hurst et al, Nucl. Data Sheets 119, 91, 2014

180W(0.12% nat) target enriched to 11.35%

Reference s0 (b)Pomerance (1952) <15 0Kang (2007) 22.6±1.7Vorona (200*) 36.3±2.4This work 24.7±0.8181mW(14.6 ms) 6.8±0.9

Sn=6686±5 keV AMESn=6668.79±20 keV This work

Published Results 2013-2015

IsotopeCross section (b)

This work Atlas152Eu(n,g)153Eug 7060(400) 5900(200)

152Eu(n,g)153Eum1 2345(220) 3300(200)152Eu(n,g)184Eug+m1 9405(460) 9200(100)

154Eu(n,g)155Eum 335(10) 310(7)155Gd(n,g)156Gd 56,700(2100) 60,900(500)157Gd(n,g)158Gd 239,000(6000) 254,000(815)

The discrepancy in the 153Eum1 cross section due to decay scheme normalization.

152,154Eu: Basunia et al, Nucl. Data Sheets 119, 88 (2014).155,157Gd: Choi et al, Nucl. Sci. Eng. 177, 219 (2014)

Published Results 2013-2015241Am: Genreith et al, Nucl. Data Sheets 119, 69 (2014)

Sn (tentative)

This work AME

5534.87(15) 5537.64(10)

Published Results 2013-2015237Np, 242Pu: Genreith et al, J. Radioanal. Nucl. Chem. 296, 699 (2013).

Sn (tentative)

Isotope This work AME238Np 5039.0(4) 5033.9(26)243Pu 5490.44(5) 5488.32(20)

2H16,17,18O(n,g)

Multiple internal standards

EGAF Evaluations in Progress

16O(n,g)

17O(n,g)

EGAF Evaluations in Progress Reference s0(mb)Jurney (1963) 0.178(25)McDonald (1973) 0.185(26)*Wuest(1977) 0.187(10)This work 0.167(3)*Recalibrated to new standard

Reference s0(mb)Lone (1978) 0.54(6)This work 0.66(6)

EGAF Evaluations in Progress Reference s0(mb)Seren (1947) 0.22(4)Blaser (1971) 0.16(1)Ohsaki(2002) 0.156(16)Nagai(2007) 0.153(10)This work (prompt) 0.139(3)This work (Activation) 0.139(5)

Sn=3955.6(26) keV (AME)Sn=3963.18(19) keV (This work)

18O(n,g)

2H(n,g)

Enriched 2H17,18O data1. s0(2H)=0.478(18) mb2. s0(2H)=0.477(17) mb

2HnatO data s0(2H)=0.535(13) mb

This discrepancy appears to be repeatable in our measurements and is not yet understood!

EGAF Evaluations in Progress

Isotope CS composition s0(this work) s0(Atlas) Lead researcher 90Y(2-) 99.75%-1-, 0.25%-0- 1.34±0.03 b 1.28±0.02 b Abusaleem (Jordan) 90Y (7+) 7+ 1.9±0.3 mb 1.0±0.2 mb Abusaleem (Jordan) 94Nb(6+) 85%-4+, 15%-5+ 1.27±0.08 b 1.15±0.05 b Turkoghu (Ohio State)140La(3-) 0.9%-3+, 99.1% 4+ 8.5±0.4 b 9.04±0.04 b Ureche (UC Berkeley)186Re(1-) 47.4%-2+, 52.6% 3+ 84±6 b 112±2 b Lerch (US Army)

Level scheme intensity balance

56Fe(n,g)A nearly complete (n,g) decay scheme has been constructed from a Budapest cold neutron measurement on a 56Fe, target enriched to 99.94%, and gg coincidence data from the Rez Reactor, Prague. 449 g-rays and 99 levels were placed in this work, including 37 new levels, and 38 previous levels not confirmed.

Reference s0 (b)

Pomerance (1952) 2.65(8)

Shcherbokov (1977) 2.57(14)

This work 2.71(4)

Intensity balance through the level scheme is >99% complete.

Low-energy photon strength enhancement in 57Fe

56Fe(3He,ag)Substantial enhancement in the reduced photon strength is seen in 57Fe below 2 MeV.E. Tavukcu, et al, Proceedings of the Eleventh International Capture Gamma Ray Symposium, Pruhonice, Prague, Czech Republic, 2–6 September 2002.

Primary g-ray strength fg definition

Gg=0.9 eV – capture state (CS) width*D0=22 keV – level spacing at CS*Pg – transition probability per decay of CSEg – g-ray energy

*Mughabghab Atlas

𝑓 𝛾=Γ𝛾 𝑃𝛾 /𝐷0𝐸𝛾3

57Fe primary g-ray strengthThe 57Fe primary g-ray strength can be investigated microscopically with these data.

Increased strength at low energies appears to be M1

57Fe secondary g-ray strengthPhoton strengths can also be determined for secondary g-rays from levels with known widths. Here we define individual transition strengths fg’=Gg/Eg

2l+1 ignoring level spacing. Here f’BA=fBAD0

M1 strength greater than E1 or E2 strength

57Fe g-ray strength level energy dependency

No significant dependency of the photon strength on level energy is observed. Notice that the strengths vary over two orders of magnitude at each level.

Test of Porter-Thomas photon strength distribution

Transition strengths are assumed to follow a P-T distribution (chi square, n=1). Only the 57Fe E1 are found to follow P-T.

Summary1. Evaluation of (n,g) data for 16 isotopes published 2013-2015.

2. Evaluation of 12 isotopes in progress.

3. 5 Sn measurement found to have large discrepancies wrt AME.

4. 3 decay scheme normalizations found to be discrepant.

5. Inconsistent cross section measurements for 2H not yet resolved.

6. Low energy photon strength enhancement in 57Fe ascribed to M1 transition strength.

7. M1 and E2 transition probabilities were found to be inconsistent with Porter-Thomas distribution.

Future EGAF Plans1. Complete ENSDF format evaluations of (n,g) nuclei

a. Thermal (n,g) data sets1) Pg and sg normalizations2) Adopted s0 values plus summary of all measurements3) Photon strengths4) Fitted Sn values

b. ARC, Resonance datac. Adopted Levels, Gammas

1) All relevant datasets2) Recommended RIPL data

d. (n,g) activation decay data sets2. (n,n’x) data

a. Baghdad (n,n’g) databaseb. Data from the literaturec. New measurements from FRM-II and LBNLd. Pg and sg normalizationse. Adopted Levels, Gammas as discussed above