Updates on Beta-Delayed Neutron Emission Experiments and Data Evaluation
Recent experiments and evaluated data concerning beta-delayed neutron emission, specifically focusing on proposals, measurements, collaborations, and motivations within the field of nuclear physics.
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Update on relevant proposals on beta-delayed neutron emission, recent experiments and evaluated data K.P. Rykaczewski Physics Division, ORNL Oak Ridge - BRIKEN experiment Around 78Ni - ORNL MTAS experiment, March 2015 - New evaluated data north-east of 78Ni IAEA, 2nd CRP dn meeting, 23-27th March 2015
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 2 NP Comparative Review 2013
BRIKEN status - C. Domingo-Pardo (IFIC Valencia, Spain) as a project speaker - Proposal to measure n-emission around mass A=130 accepted in June 2014 (A, 6.5 days) - (G. Lorusso, F. Montez, A. Estrade, S. Nishimura) - Proposal to measure 1n/ 2n 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) Large collaboration formed in 2012-2013, construction proposal accepted at RIKEN in December 2013 Our motivation: 1. Provide new data important for understanding and predicting 1n and 2n ( xn) emission rates 2. Provide new data important for understanding and modeling r-process nucleosynthesis 3 NP Comparative Review 2013
Important physics case: -strength (Gamow-Teller vs first forbidden -decays) and 1n - 2n competition P 1n and P 2n values as input for the r-process path analysis This 78Ni and beyond project is aiming in a determination of 20 new P 1n and 14 new P 2n values i.e., the discovery of 14 2n 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. 4 NP Comparative Review 2013 Nuclear Chemistry Gordon Conference, 2013
-strength distribution and 1n - 2n competition P 1n P 2n Nuclear Chemistry Gordon Conference, 2013 First forbidden transitions compete for a beta-feeding with Gamow-Teller ones and reduce xn branching ratios 1n emission competes with 2n emission in full one-neutron emission window, ( 1n is not occurring ONLY in the excitation energy window between 1n and 2n separation energies) Nuclear Chemistry Gordon Conference, 2013
P1n and P2nvalues 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 6 NP Comparative Review 2013
7 NP Comparative Review 2013 K. Miernik, PR C 90, 054306,2014
K. Miernik, PR C 90, 054306,2014 8 NP Comparative Review 2013
K. Miernik, PR C 90, 054306,2014 9 NP Comparative Review 2013
1n and 2n emitter 86Ga Miernik et al., PRL 111,132502,2013 post-dictions pre-dictions exp Moeller 2003 Borzov 2013 Kawano (ENDF VII) Miernik n - PR C88, 2013 FRDM+QRPA DF3a+CQRPA (Moeller + CGM) xn PR C90, 2014 1n 60(10)% 21% 20% 71% 53% 2n 20(10)% 44% 12% 5% 22% R. Grzywacz + I. Borzov More data points than just one single value are needed to guide/develop reliable theoretical descriptions of 1n/ 2n rates. 14 new values of 1n/ 2n should result from proposed experiment. 10 NP Comparative Review 2013
-delayed neutron emission during supernova type cold r-process -delayed neutron emission in a cold r-process cold r-process: equilibrium between (n, ) and decay with -delayed neutrons post r-process abundances Y(A) R. Surman neutron density without beta-delayed neutrons mass in r-process R. Surman, at Gordon conf., June 2013, at ARIS conf., June 2014
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, =50 ms, (t) = 0 x exp(-3t/ ) Pxn Moeller P1n = 0 P1n maximized The effect of n-emission in the 78 < A < 100 nuclei is seen in Y(A) at higher masses P1n(max) = P0n + P1n + (P2n+P3n), P0n, P2n and P3n at 50% of Moeller s values 12 NP Comparative Review 2013
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 13 NP Comparative Review 2013
Region of interest (2 Big RIPS settings) Experimental P 1nvalues are given in black Predicted P 1n and P 2n values listed according to Moeller 2003 Present reach of 3 days exp at RIKEN with 238U 25 pnA/345 MeV/u and BRIKEN n-array 14 NP Comparative Review 2013
78Ni/79Ni/81Cu 82Cu/84Zn/86Ga 85Zn/87Ga/89Ge 0.8% ~21% 3.2% 10% 8% 1% Se 0.01% 0% 28% 2.6% 89% 3.2% 76% 1.3% 63% 36% 15% 32% 45% 39% As 2.2% 10% 17% 45%31% 49% 0.5% 9.9% 1.2% 74% 3.2% 0n 0n 43% 19% Ge 4.6% 31% 4.6% 61% 10% 74% 15% 70% 19% 9% 20% 47% 10% 60% 20% 35% 41% 12% 20% 63% 0.9% Ga 28% 9% 1.0% 12% 58% 29% 49% 13% 1.3% 46% 27% 5% 64% 5% 65% 10% 8% Zn 21% 46% 31% 18% 13% 64% 18% 24% 43% 31% 66% 72% 44% 62% 21% 29% 57% Cu 13% Expected reach of FRIB and BRIKEN-like n-array in 2022 ~30% 39% 20% 57% 6% 37% 22% 29% 35% 22% 29% 62% 5% 64% 14% Ni Z=28 0% 26% 6% 67% 16% 15% 1% 73% 25% 69% 7% 41% 25% Co N=50 52 54 56 58 Predicted P 1n ,P 2n and P 3nvalues listed according to Moeller 2003 15 NP Comparative Review 2013
SUMMARY for Around 78Ni BRIKEN proposal BRIKEN collaboration is intending to measure -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 P 1n (20 ) and P 2n (14) experimental values allowing us to analyze and understand better the GT vs ff -strength distribution and 1n 2n competition. from spherical (78Ni) to deformed (91As) emitters 85Ga,86Ga and 87Ga predicted by Moeller to exhibit 3n emission are within our settings (but let first understand the 1n 2n 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
New (and earlier) experiments with Modular Total Absorption Spectrometer MTAS and pure beams at ORNL (March 2nd-20th, 2015) M/ M~600 17 NP Comparative Review 2013
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 18 new s and 11 new -fed levels added to 139Xe decay scheme 240 -lines populating 63 levels known from 139Xe decay 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 keV 13% decrease Aleksandra Fija kowskaet al., Nuclear Data Sheets 120, 26 (2014) 18 NP Comparative Review 2013
Measured and modified 139Xe decay in central and inner rings of MTAS Modular construction of MTAS helps to validate results ! see also Rasco et al., ARIS 2014 proceedings 19 NP Comparative Review 2013
Electron and anti-neutrino energy spectra in 139Xe decay Energy spectrum of electrons Energy spectrum of anti-neutrinos ENSDF MTAS ENSDF MTAS In 139Xe decay, the average anti-neutrino energy is shifted down from 2240 keV (ENSDF) to 2014 keV (MTAS), i.e., by 226 keV Fija kowska, Karny, et al., 2015 20 NP Comparative Review 2013
Anti-neutrino interactions with protons High energy anti-neutrinos have higher cross section for the interactions with protons, i.e., have higher probability to be removed from beam. cross section (10-41 cm2) + p n + e+ energy threshold 1.8 MeV For anti-neutrinos with energies below 1.8 MeV energy threshold: no interactions on protons. ( + p) ~ (E )2 anti-neutrino energy (MeV) A. Strumia and F. Vissani, PL B 564, 42, 2003 21 NP Comparative Review 2013
Interacting anti-neutrinos emitted in 89Kr and 139Xe decay Number of interactions of 89Kr and 139Xe anti-neutrinos per 10 keV energy bin (in % x 10-43 cm2 units). 139Xe 89Kr ENSDF MTAS ENSDF MTAS 21 % 41 % reactor antineutrino anomaly 94.3(23) % ~ 6 % missing MTAS results for 89Kr and 139Xe decays account for 2.9 of the missing 6% difference in the reactor anti-neutrino anomaly for a fresh nuclear fuel load, and for 1.8and1.5 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. 22 NP Comparative Review 2013
40 MeV, 50 enA proton beam on 238U MTAS on-line to the ORNL mass separator OLTF (On-line Test Facility = ISOL, m/ m~600) Pixie16 Ge detector for monitoring collection point MTC Reference NaI(Tl) crystal with pulsed blue laser light for monitoring amplification changes. Laser light was split between reference and central/inner ring detectors. K. C. Goetz, R Grzywacz (UTK) March 2015 Data acquisition based on digital pulse processing and using XIA Pixie16 modules (100 MHz) 23 NP Comparative Review 2013
New experiments with Modular Total Absorption Spectrometer MTAS and pure beams at ORNL (March 2nd-20th, 2015) n emitters Green MTAS measurements with pure Bromine beams from LaB6 source Blue MTAS measurements with Rb/Sr beams from surface ionized ion source ORNL s Tandem-mass separator OLTF MTAS 24 NP Comparative Review 2013
New experiments with Modular Total Absorption Spectrometer MTAS and pure beams at ORNL (March 2nd-20th, 2015) n emitters Green MTAS measurements with pure Bromine beams from LaB6 source Blue MTAS measurements with Cs beams from surface ionized ion source ORNL s Tandem-mass separator OLTF MTAS 25 NP Comparative Review 2013
85Br85Kr decay (Q=2.9MeV) measured with Tandem-OLTF-MTAS New levels fed in -decay These new high energy levels in 85Kr fed by 85Br -decay were identified to de-excite to the 0.3 MeV isomeric level through the analysis profiting from MTAS segmentation. MTAS experimental spectrum 03/02/2015 MTAS Central Inner Middle Outer MTAS simulated spectrum following ENSDF data Energy ( keV) 26 NP Comparative Review 2013
MTAS results for 85Br -energy in single outer/middle modules B.C. Rasco LSU - Total MTAS energy (keV) New levels fed in -decay MTAS Central Inner Middle Outer counts MTAS experimental spectrum 03/02/2015 Total MTAS energy (keV) 27 NP Comparative Review 2013
Priority 1 88Br88Kr -decay (Q= 9 MeV) measured at Tandem-OLTF-MTAS 775 keV Much larger -feeding to high energy states in 88Kr From the comparison of experimental and simulated MTAS energy spectra one can see that the intensity of beta feeding to the first excited 2+ state at 775 keV is much lower than the ENSDF value (note log scales in figures). MTAS experimental spectrum 03/03/2015 It means there are much less of high energy anti-neutrinos emitted in this decay and -decay heat value will be higher. 775 keV 7 MeV MTAS simulated spectrum following ENSDF data Energy ( keV) 28 NP Comparative Review 2013
90Br90Kr -decay (Q=11 MeV) measured with Tandem-OLTF-MTAS MTAS total MTAS B.C. Rasco (LSU) Central central Inner Middle inner Outer middle outer 90Br is an example of beta-delayed neutron ( n) precursor studied with MTAS. Neutron induced peaks occur in 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 -feeding I to the highly excited states up to neutron separation energy of 6.5 MeV in 90Kr, much larger I than listed in ENSDF data. High energy tail in MTAS central and total spectra indicates the presence -transitions of large energy, e.g., to the gs or 2+ state in 90Kr. MTAS experimental spectrum 03/05/2015 Neutron induced 6.8-6.9 MeV peaks from (n, ) reactions on Na and I in NaI(Tl) crystals of outer, middle and inner rings of MTAS. 90Br n~25% Sn~ 6.5MeV Total MTAS simulated spectrum following ENSDF A. Fijalkowska (Warsaw) Energy (keV) 29 NP Comparative Review 2013
91Br91Kr -decay (Q=9.9 MeV) and 91Br90Kr ~ 20% n-decay (Q-Sn= 5.8 MeV) measured with Tandem-OLTF-MTAS MTAS Central total MTAS Inner Middle B.C. Rasco (LSU) Outer 707 keV 2+ 0+ in 90Kr note color code change vs previous slides 1362 keV (4+) 2+ in 90Kr Energy spectrum of central crystal gated by neutron peaks in outer and middle detectors Neutron induced (6.8-6.9) MeV and (6.8-6.9 + 0.707) MeV peaks from (n, ) and (n, +0.707 MeV) reactions in NaI(Tl) crystals of outer and middle MTAS rings n 91Br 1362keV 707 keV 0 keV 90Kr 30 NP Comparative Review 2013
New evaluated data from HRIBF LeRIBSS exp with molecular GeS and AsS beams 86Ge and its decay products C. Mazzocchi et al., 2015 31 NP Comparative Review 2013
Decay of 86Ge C. Mazzocchi et al., 2015 Miernik et al., PRL 2013 32 NP Comparative Review 2013
86As decay 33 NP Comparative Review 2013
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 n 34 NP Comparative Review 2013
Structure of N=53 isotones All GT decay of 83Cu 83Zn will go through n High-energy GT-states A. Korgul et al., Phys. Rev. C 88, 044330 (2013). 35 NP Comparative Review 2013
Summary - BRIKEN experiment Around 78Ni two BRIKEN experiments are accepted at RIKEN, impressive set of new data on 1n- and 2n-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 2015 New data on true -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 1n-emitters were measured with MTAS, segmentation allows for the analysis of the effects of n-interaction with MTAS crystals, n-capture + energy deposition observed. - New evaluated data north-east of 78Ni Decays of n-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. 36 NP Comparative Review 2013