β-delayed neutron emission probability measurements at RIKEN RIBF

Transcription

1 β-delayed neutron emission probability measurements at RIKEN RIBF G. G. Kiss RIKEN Nishina Center for Accelerator-Based Science Radioactive Isotope Physics Laboratory (in behalf of the BRIKEN collaboration)

2 r process nucleosynthesis Produces ~50% of the stable isotopes heavier than Iron Site unknown: Core collapse Supernovae or Neutron Star Merger? (G. Martínez Pinedo, T. Kajino, S. Goriely) Nuclear Physics input: Masses r process path (R. Surman) Shell structure peak location T 1/2, fission parameters, Pn values abundance distribution J. Covan, Nature , S. Goriely, PRL

3 The role of β-delayed neutrons Location of the peaks Smoothing the abundance distribution Forming the Rare Earth Peak A. Arcones, PRC , A. Farouqi, APJ , R Surman, JPS conf. Proc M. Mumpower, PRC

4 β-delayed neutrons The Pn value is the % that the β- decay is followed by at least one neutron emission. The P1n value is the % that the β- decay is followed by one neutron emission. Pn= P1n+P2n+P3n+ P0n=100%-Pn P n = Q β S n S β E x f(q β E x ) Q β 0 Γ n Γ n + Γ γ de x S β E x f Q β E x de x The neutron emission probability Pn measures the fraction of β-strength above the neutron separation energy S n For n-rich nuclei very far from stability T 1/2 and Pn will provide (the only) access to nuclear structure information

5 Pn[%] Pn[%] Pn [%] Pn[%] Pn[%] Available information for r process simulations Lack of available data: (Jeff 3.1 vs number of isotopes with Q βn >0 (using known masses from AME12) Energetically possible Experimental information Fraction measured Mass region β1n 606 ~ % 8 He- 150 La & 213,214 Tl β2n 295 ~ % 11 Li- 52 K & 98,100 Rb 80 HFD-EDM β3n 104 ~ 4 3.8% 11 Li, 17,19 B, 23 N β4n % 17 B Distribution of the data: Large differences: QRPA-FRDM KTUY-GT neutron ~ 40% number in the [N] non-fission region (A < 75) ~ 33% for nuclear industry (Br, Kr, Rb, I, Cs, Xe) No data above 150 La except 213,214 Tl QRPA-FRDM KTUY-GT2 HFD-EDM 25 Mn neutron number [N] Mn Ga P1n - exp. P2n - exp. P1n - theo. P2n - theo. P3n - theo QRPA-FRDM KTUY-GT2 HFD-EDM PRL PRC Z.Phys Cu neutron number [N] neutron number [N] P. Möller et el., PRC 67 (2003) K. Miernik et al., PRC88 (2013)

6 What is BRIKEN? β-delayed neutron emission probability measurements at RIKEN 238 U primary beam 345 MeV / nucleon & ~50μA RI separation RI identification BRIKEN aims for a large scale survey of β decay parameters: Most exotic nuclei RNC SRC + BiGRIPS (largest acceptance) spectrometer Largest detection efficiency (most) Advanced Implantation Detector Array AIDA The largest β-delayed neutron detector

7 Decay setup AIDA: most advanced implantation array Accept 1 khz implantation rate Several (6-7) highly (128 x 128) segmented DSSD detectors BRIKEN: highest efficiency counter setup ever built (~68%-76%)! 3 He filled proportional counters from embedded in a ~ 1m 3 polyethylene moderator ORNL (84), UPC (42), RIKEN (26), GSI (10) Flat efficiency curve led to minimalized systematical uncertainty Hybrid geometry (148 tubes + 2 clovers) Compact geometry (166 tubes) More details: A. Tolose talk (Tuesday 12:50-13:10) C. Griffin et al., Pos (NIC XIII) 097 (2014) A. Tarifeño-Saldivia et al., JINST 12 P04006 (2017)

8 Title Measurements of new beta-delayed neutron emission properties around doubly-magic 78 Ni Decay properties of r-process nuclei in deformed region around A = 100 ~ 125 Measurement of β-delayed neutron emission probabilities relevant to the A = 130 r-process abundance peak Half-lives and beta delayed neutron emission probabilities relevant to understand the formation of the rare earth r process peak Scientific cases Approved Length [days] Aims 3.5 ~ 20 new P1n & ~ 14 new P2n 6.5 ~ 60 new P1n & ~ 30 new P2n To be submitted newt PAC meeting (2017 December) Study of the multiple delayed neutron emission Spokespersons K.P. Rykaczewski, J. L. Tain, R. Grzywacz, I. Dillmann S. Nishimura, A. Algora 6.5 ~33 new P1n & A. Estrade, ~ 6 new Half-lives P2n & and beta delayed G. Lorusso, neutron emission probabilities F. Montes relevant to 10 ~ 36 new understand P1n the formation G. G. Kiss, of the rare earth r process peak A. Morales, Measurement of β-delayed neutron A. Tarifeño-Saldivia, emission probabilities relevant to the A A. = Estrade 130 r-process abundance peak Decay properties of r-process nuclei in deformed region around? A = 100 ~ new P1n & I. Dillmann Measurements of new 21 beta-delayed new P2n & neutron emission properties around 21 new doubly-magic P3n 78 Ni

9 Measurement of β-delayed neutron emission probabilities relevant to the A = 130 r-process abundance peak Low entropy hot wind Different T, ρ n shifts the A ~ 130 peak! High entropy hot wind cold wind 6.5 days beamtime, settings were centered on 130 Ag (~4.5 d) and 149 Xe (~1.5 d). More than 25 P1n were measured for the first time, data analysis is in progress ( 127 Pd, 131 Ag, 133 Cd ). Neutron star merger Roederer, APJ. Lett. 747 L8, Mumpower, Prog. Part. Nucl. Phys

10 The Origin of the Rare Earth Peak Located far from closed shells, new production mechanism is needed! 213,214 Tl (Z=81) No Pn data! 150 La (Z=57) 1. Slower neutron capture in the peak region? 2. Kink in the separation energies? 3. Prompt / β-delayed fission? R. Surman, PRL ; PRC M. Mumpower, PRC , PRC ; S. Goriely, PRL A. Arcones, PRC ; T. Scafer, PRC C. Freiburghaus, Astrophys. J and further references therein. 2.5 days beamtime, setting was centered on 167 Sm. Several new P1n values and T 1/2 were measured

11 Summary β-delayed neutron emission probabilities are important for r process nucleosynthesis calculations There is lack of experimental data The BRIKEN collaboration aims a large scale survey of β decay parameters for isotopes located far from the valley of stability Measurements and data analysis are in progress

12 Thank you for your attention! ご清聴ありがとうございました (Go seichō arigatōgozaimashita) Grazie per la vostra attenzione! Köszönöm a figyelmet!