Update on relevant proposals on beta-delayed neutron emission, recent experiments and evaluated data...

Update on relevant proposals on beta-delayed neutron emission, recent experiments and evaluated

data

K.P. Rykaczewski Physics Division, ORNL

Oak Ridge

IAEA, 2nd CRP βdn meeting, 23-27th March 2015

- BRIKEN experiment “Around 78Ni” - ORNL MTAS experiment, March 2015- New evaluated data “north-east” of 78Ni

2 NP Comparative Review 2013

Beta-delayed neutrons - BRIKEN at RIKEN

BRIKEN:- 20 pnA of 345 MeV/A of 238U beam and BigRIPS at RIKEN- nearly all 3He gas available for nuclear spectroscopy (~ 70% ORNL)

- the most powerful ion implantation/decay Si-array AIDA


BRIKEN status- Large collaboration formed in 2012-2013, construction proposal accepted at RIKEN in December 2013 C. Domingo-Pardo (IFIC Valencia, Spain) as a project speaker- Proposal to measure βn-emission around mass A=130 accepted in June 2014 (A, 6.5 days)- (G. Lorusso, F. Montez, A. Estrade, S. Nishimura)- Proposal to measure β1n/β2n emission between 76Co and 92Se accepted in Dec. 2014 (A, 4 days) (KR, J. L. Tain, R. Grzywacz, I. Dillmann, S. Nishimura)- First batch of 3He tubes from Oak Ridge received at RIKEN on 16th March 2015- Test run planned for the end of April 2015 (Jose L. Tain)

Our motivation:

1. Provide new data important for understanding and predicting β1n and β2n (βxn) emission rates 2. Provide new data important for understanding and modeling r-process nucleosynthesis

4 NP Comparative Review 2013Nuclear Chemistry Gordon Conference, 2013

Important physics case: β-strength (Gamow-Teller vs first forbidden β-decays) and β1n - β2n competition

Pβ1n and Pβ2n values as input for the r-process path analysis

This “78Ni and beyond” project is aiming in a determination of 20 new Pβ1n and 14 new Pβ2n values i.e., the discovery of 14 β2n emitters at the r-process path.

The examples of the effects of GT to ff competition on Pn values in Cu and Zn isotopes [Borzov 2005] .Blue arrows indicate the range of Cu and Zn isotopes to be measured in our project.

Nuclear Chemistry Gordon Conference, 2013

β-strength distribution and β1n - β2n competition

Nuclear Chemistry Gordon Conference, 2013

Pβ1n Pβ2n

First forbidden transitions compete for a beta-feeding with Gamow-Teller ones and reduce βxn branching ratios

β1n emission competes with β2n emission in full one-neutron emission window, (β1n is not occurring ONLY in the excitation energy window between 1n and 2n separation energies)


P1n and P2n values predicted for “our” new nuclei

comparison of Miernik’s EDM 2014*) vs Moeller’s QRPA 2003

Larger P1n

Lower P2n

*) K. Miernik, PR C 90, 054306,2014

7 NP Comparative Review 2013 K. Miernik, PR C 90, 054306,2014


K. Miernik, PR C 90, 054306,2014


β1n and β2n emitter 86Ga Miernik et al., PRL 111,132502,2013

exp Moeller 2003 Borzov 2013 Kawano (ENDF VII) Miernik βn - PR C88, 2013 FRDM+QRPA DF3a+CQRPA (Moeller + CGM) βxn – PR C90, 2014

β1n 60(10)% 21% 20% 71% 53% β2n 20(10)% 44% 12% 5% 22%

pre-dictions “post-dictions”

More data points than just one single value are needed to guide/develop

reliable theoretical descriptions of β1n/β2n rates.

14 new values of β1n/β2n should result from proposed experiment.

R. Grzywacz + I. Borzov

β-delayed neutron emission in a cold r-processR. Surman cold r-process: equilibrium between (n,γ) and β decay

β-delayed neutron emission during supernova type cold r-process

R. Surman, at Gordon conf., June 2013, at ARIS conf., June 2014

mass

post

r-pr

oces

s ab

unda

nces

Y(A

)

without beta-delayed neutrons

with β-delayed neutrons

in r-process

neut

ron

dens

ity


Sensitivity of isobaric post r-process abundances to Pn values in the region of 78 < A < 100 nuclei (R. Surman 2014)

Weak r-process trajectory [Panov&Janka2009], found in ejecta of NS-NS merger, with low entropy per baryon s/k=20 [Wanajo2014], low electron fraction Ye=0.35, and fast dynamic timescale, τ=50 ms, ρ(t) = ρ0 x exp(-3t/τ)

P1n(max) = ½ P0n + P1n + ½(P2n+P3n), P0n, P2n and P3n at 50% of Moeller’s values

Pxn – MoellerP1n = 0P1n maximized

The effect of βn-emissionin the 78 < A < 100 nuclei is seen in Y(A) at higher masses


Sensitivity measure F to the changes in P1n branching ratio [Surman2014].

The squares in different colors indicate the total change in ALL r-process abundances X(A), obtained by maximizing ONE P1n value for a given nucleus, with respect to the calculations using baseline P1n


Predicted Pβ1n and Pβ2n values listed according to Moeller 2003

Region of interest (2 Big RIPS settings)

Experimental Pβ1n valuesare given in black

Present reachof 3 days exp

at RIKEN with 238U 25 pnA/345 MeV/u

andBRIKEN βn-array


N=50

NiZ=28

52 54 56 58

Co

Cu

Zn

Ga

Ge

As

Se

26% 6%

69% 7%

41%25%

67%16%15%

1%73%25%

~30% 39% 0%

62% 5%

64%14%

20%57%6%

37%22%29%

66% 72% 44%13%

62%21%

13%64%18%

24%43%31%

1.0% 12% 58% 29%21%

49%13%

28% 9%

64% 5%

46%27%5%

12% 20% 63% 74%15%

61%10%

60%20%

31%4.6%

35%41%

70%19% 9%

20%47%10%

10% 17% 45% 31%4.6%

49%0.5%

9.9%1.2%

74%3.2%

43%19%

29%57%

46%31%18%

63% 36% 15% 32%2.2%

76%1.3%

28%2.6%

89%3.2%

45%39%

8%0.8% ~21%

0.01%3.2% 10%

0%

1.3%

0.9%

β0n β0n

1%

78Ni/79Ni/81Cu 82Cu/84Zn/86Ga 85Zn/87Ga/89Ge

Predicted Pβ1n , Pβ2n and Pβ3n values listed according to Moeller 2003

Expected reach of FRIBand

BRIKEN-like βn-arrayin 2022

35%22%29%

65%10%8%

SUMMARY for “Around 78Ni” BRIKEN proposalBRIKEN collaboration is intending to measure β-delayed neutron emission

in the ”78Ni and beyond“ part of nuclear chart, which is a starting region of the r-process.

We will get a large set of new Pβ1n (20 ) and Pβ2n (14) experimental values allowing us to analyze and understand better the GT vs ff β-strength distribution and β1n – β2n competition. from spherical (78Ni) to deformed (91As) emitters

85Ga,86Ga and 87Ga predicted by Moeller to exhibit β3n emission are within our settings (but let first understand the β1n – β2n competition)

Much more reliable input data for the r-process analysis affecting the abundances of nuclei created in the weak- r-process

and affecting the later stages of main r-process.

SUMMARY for “hybrid-3Hen + ranging-out” proposal at TRIUMF

- Proposal to study bn-emitters accepted in 2013, but a Canadian’s permit to transfer 3He tubes for about 10 km on Canadian soil (Vancouver airport to TRIUMF laboratory) was not granted- Proposal status changed to “Letter of Intent” at the end of 2014


M/ΔM~600

New (and earlier) experiments with Modular Total Absorption Spectrometer MTAS

and pure beams at ORNL (March 2nd-20th, 2015)


Priority “1” 139Xe →139Cs decay (T1/2= 39.7 s)cumulative yield of 139Xe in nth + 235U fission is about 5% (ENDF/B-

VII.1)

MTAS result: average gamma energy release per 139Xe decay increased from 935 keV to 1370 keV

46.5 % increase

average beta energy release per 139Xe decay decreased from1774 keV to 1573 keV13% decrease

18 new ’s and 11 new β-fed levels added to

139Xe decay scheme

240 -lines populating 63 levels

known from 139Xe decay

MTAS

Aleksandra Fijałkowska et al., Nuclear Data Sheets 120, 26 (2014)


Modular construction of MTAS helps to validate results !

Measured and modified 139Xe decay in central and inner rings of MTAS

see also Rasco et al., ARIS 2014 proceedings


In 139Xe decay, the average anti-neutrino energy is shifted down from 2240 keV (ENSDF) to 2014 keV (MTAS),

i.e., by 226 keV

Electron and anti-neutrino energy spectra in 139Xe decay

Energy spectrum of electrons

ENSDFMTAS

ENSDFMTAS

Energy spectrum of anti-neutrinos

Fijałkowska, Karny, et al., 2015


Anti-neutrino interactions with protons

ν+ p →n + e+

High energy anti-neutrinos have higher cross section for the interactions with protons,i.e., have higher probability to be removed from ν beam.

For anti-neutrinos with energiesbelow 1.8 MeV energy threshold: no interactions on protons.

anti-neutrino energy (MeV)

cros

s se

ctio

n (1

0-41

cm2 )

energy threshold1.8 MeV

A. Strumia and F. Vissani, PL B 564, 42, 2003

σ(ν+ p) ~ (Eν)2


Number of interactions of 89Kr and 139Xe anti-neutrinos per 10 keV energy bin (in % x 10-43 cm2 units).

Interacting anti-neutrinos emitted in 89Kr and 139Xe decay

89Kr 139XeENSDFMTAS

ENSDFMTAS

MTAS results for 89Kr and 139Xe decays account for 2.9 of the “missing 6%” differencein the reactor anti-neutrino anomaly for a fresh nuclear fuel load, and for 1.8 and 1.5 out of the missing 6% for the burn-up phases corresponding to 2% FIMA and 3% FIMA, respectively, if applied to the anti-neutrino anomaly as calculated from all data contained in ENSDF.

41 % ↓ 21 % ↓

reactor antineutrino anomaly 94.3(23) % ~ 6 % missing


40 MeV, 50 enA proton beam on 238UMTAS on-line to the ORNL mass separator OLTF

(On-line Test Facility = ISOL, m/Δm~600)

Data acquisition based on digital pulse processing and using XIA Pixie16 modules (100 MHz)

March 2015

Ge detectorfor monitoring collection point

MTC

Pixie16

Reference NaI(Tl) crystal with pulsed blue laser light for monitoring

amplification changes.Laser light was split

between reference andcentral/inner ring

detectors.K. C. Goetz, R Grzywacz

(UTK)


New experiments with Modular Total Absorption Spectrometer

MTAS and pure beams at ORNL (March 2nd-20th, 2015)

Green – MTAS measurements with pure Bromine beams from LaB6 sourceBlue – MTAS measurements with Rb/Sr beams from surface ionized ion source

ORNL’s Tandem-mass separator OLTF –MTAS

βnemitters


New experiments with Modular Total Absorption Spectrometer MTAS and pure beams at ORNL (March 2nd-20th, 2015)

βnemitters

Green – MTAS measurements with pure Bromine beams from LaB6 sourceBlue – MTAS measurements with Cs beams from surface ionized ion source

ORNL’s Tandem-mass separator OLTF –MTAS


85Br→85Kr decay (Qβ=2.9MeV) measured with Tandem-OLTF-MTAS

MTAS simulated spectrum

following ENSDF data

New levels fed in β-decay

MTAS experimental spectrum

03/02/2015

Energy ( keV)

These new high energy levels in 85Kr fed by 85Br β-decay were identified to de-exciteto the 0.3 MeV isomeric levelthrough the analysis profiting from MTAS segmentation.

Central

Inner

Middle

Outer

MTAS


MTAS results for 85Br

New levels fed in β-decay


03/02/2015

γ-en

ergy

in s

ingl

e ou

ter/m

iddl

e m

odul

es

Total MTAS energy (keV)

Total MTAS energy (keV)

coun

ts

-

Central

Inner

Middle

Outer

MTAS

B.C. RascoLSU


Priority 1 88Br→88Kr β-decay (Qβ= 9 MeV) measured at Tandem-OLTF-MTAS

Energy ( keV)

MTAS simulated spectrum

following ENSDF data


03/03/2015

From the comparison ofexperimental and simulatedMTAS energy spectra one can see that the intensity of betafeeding to the first excited 2+ state at 775 keV is much lower than the ENSDF value (note log scales in figures).

It means there are much less of high energy anti-neutrinos emitted in this decay and γ-decay heat value will be higher.

775 keV

775 keV

Much largerβ-feeding tohigh energystates in 88Kr

7 MeV

29 NP Comparative Review 2013Energy (keV)

90Br→90Kr β-decay (Qβ=11 MeV) measured with Tandem-OLTF-MTAS

Total MTAS simulated spectrum

following ENSDF A. Fijalkowska (Warsaw)


03/05/2015

Neutron induced 6.8-6.9 MeV peaksfrom (n,γ) reactions

on Na and I in NaI(Tl) crystalsof outer, middleand inner rings

of MTAS.90Br βn~25%

total MTAScentral

inner

middle

outer90Br is an example ofbeta-delayed neutron (βn)precursor studied with MTAS.Neutron induced peaks occurin outer, middle and inner ring crystals. Neutrons are slowing down in central detector, but are rarely captured there (smaller volume and fast neutrons).MTAS spectra for 90Br are again pointing to the large β-feeding Iβ to the highly excited states up to neutron separation energy of 6.5 MeV in 90Kr, much larger Iβ than listed inENSDF data. High energy tail in MTAS central and total spectra indicates the presence β-transitionsof large energy, e.g., to the gs or 2+ state in 90Kr.

Sn~ 6.5MeV

B.C. Rasco(LSU)

Central

Inner

Middle

Outer

MTAS


91Br→91Kr β-decay (Qβ=9.9 MeV) and 91Br→90Kr ~ 20% βn-decay (Qβ-Sn= 5.8 MeV) measured with Tandem-OLTF-MTAS

Central

Inner

Middle

Outer

MTAS

note color code changevs previous slides

total MTAS

707 keV2+→0+ in 90Kr

1362 keV(4+) →2+ in 90Kr

Neutron induced (6.8-6.9) MeV and (6.8-6.9 + 0.707) MeV peaksfrom (n,γ) and (n,γ+0.707 MeV) reactions

in NaI(Tl) crystals of outer and middle MTAS rings

Energy spectrum of central crystalgated by neutron peaks in outer and middle detectors

91Br

0 keV707 keV1362keV

90Kr

βn

B.C. Rasco(LSU)


86Ge and its decay products

C. Mazzocchi et al., 2015

New evaluated data from HRIBF LeRIBSS exp with molecular GeS and AsS beams


Decay of 86Ge

Miernik et al., PRL 2013

C. Mazzocchi et al., 2015


86As decay


New evaluated data from HRIBF LeRIBSS exp with molecular GeS and AsS beams

A. Korgul et al., 2015 , beta-gamma and beta-delayed neutron – gamma emission after 87As decay

βn


Structure of N=53 isotones

A. Korgul et al., Phys. Rev. C 88, 044330 (2013).

High-energyGT-states

All GT decay of 83Cu →83Znwill go through βn


Summary- BRIKEN experiment “Around 78Ni” two BRIKEN experiments are accepted at RIKEN, impressive set of new dataon β1n- and β2n-emitters is expected, it looks like this time we can ship 3He detectors from ORNL to RIKEN (not yet for TRIUMF).- ORNL MTAS experiment, March 2015New data on true β-strength function distribution for several Br/Kr , I/Xe and Rb/Sr decays were obtained with pure beams, including 88Br, 136m,gsI and 140Xe having priority 1 for decay heat simulation (NEA 2007), again showing the presence of “gaps in nuclear data”. Several β1n-emitters were measured with MTAS, segmentation allows for the analysis of the effects of βn-interaction with MTAS crystals, n-capture + γ energy deposition observed.- New evaluated data “north-east” of 78NiDecays of βn-emitters in A=86 and A=87 were studied at the HRIBF and evaluated, mixed message about shell model applicability to these n-rich nuclei.

Update on relevant proposals on beta-delayed neutron emission, recent experiments and evaluated data...

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