Studies involving discrete spectroscopy. Studies involving total absorption or calorimetry

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2 Two general themes Studies involving discrete spectroscopy Typically involving high resolution Ge detectors Ex. 8p/GRIFFIN at TRIUMF-ISAC Studies involving total absorption or calorimetry Typically involving large-volume, low-resolution detectors Ex. BELEN, 3HeN, MTAS 11/8/2016 2

3 The 8p spectrometer was a world unique device for b- decay studies. Simultaneous collection of g-singles, gg coincidences, b tagging, conversion electrons, and lifetime measurements 11/8/2016 3

4 20 HPGe detectors in truncated icosahedral arrangement Symmetry of arrangement enabled accurate extraction of g-ray intensities via coincidence analysis Angular correlation of emitted g-ray in cascade can affect extracted intensity Largest effect from cascade of ~7%, typical effect of a few % 11/8/2016 4

5 3.7 min 21 sec β + /EC β + /EC β + /EC γ Background subtracted gg matrix 250 million counts 20 h γ 11/8/2016 5

6 2366, , , , ? = 4.9(3) W.u. 0, Zr No evidence for transition might conclude no 11/8/2016 deformed coexisting band 6

7 2366, , , , = 4.9(3) W.u. 0, Zr Gate from below reveals 371-keV transition a 0.15% branch. 11/8/2016 7

8 Normalization factor related to total number of decays Intensity of feeding g Coincidence efficiency Angular correlation n g f Area of peak g d NI g f Efficiency of feeding g g f BR g d Branching ratio of draining g g d coinc Efficiency of draining g g f g d g 2 g f g d g 3 Peak area feeding intensity draining branching fraction Gating from above is limited by the draining fraction of 0.15% In case of the 371-keV transition, gating from below enhances peak by factor of 18 11/8/2016 8

9 5 unique opening angles between detector pairs (not analyzing sum peaks at 0 degrees) J3 γ1 γ1 W(θ)=1+A22P2(cosθ)+A44P4(cosθ)+ γ2 J2 J1 θ γ2 11/8/2016 9

10 Angular correlation of 1385-keV g-ray gated on 331-keV firmly establishes 0 + spin for 1716-keV level Previous spin /8/

11 Time-random background subtracted gg matrix events 0.79(9)% branch 54(12) W.u. 1978, , = 54(12) W.u : gate 354, 2 + 0, = 57.8(15) W.u. Intensity of 289-keV line is 10-5 of the Xe Studies on or near stability can take advantage of complementary information 11

12 Partial level scheme from 110 In b + /EC decay to 110 Cd In some cases, observe or place stringent limits on all possible decays from excited states allowing details tests of models 11/8/

13 gg-matrix projection prompt events, events random subtracted, events 180 suppressed 157-keV 112 In m internal transition Important to have sufficiently wide coincidence window to properly account for time-randoms 13

14 Beam implanted onto a moving tape at center of array Allows for movement of long-lived activity out of focus of spectrometer Tape speeds, dwell times, etc., variable Control of beam kicker tightly coupled beam collection time variable (down to ~ 100ms) Tape transport very flexible: can be motionless, or operated in continuous motion Deposition of source on tape can be internal to the array, as in the 8p, or external in other facilities and transported into array. 11/8/2016 Lead Shielding Tape Cassette 14

15 1 +, t ½ =30.9s 124 Cs? 1548, , , 2 + 0, Xe How does the 1 + parent populate the 6 + member of the daughter gsb? It doesn t! 11/8/

16 Counts observed in photopeak C(t) 124 Xe Cs b + /EC 0.11(2)% branch 124 Xe 6 +,7 +,8 + levels 124 Xe Beam on Beam off Usefulness of beam pulsing and tape cycling to determine half lives 16

17 Light Guides SCEPTAR Plastic Scintillators SCEPTAR divided into two hemispheres. Each half contains 10 thin (~1.6 mm) plastic scintillator panels. 10 panels arranged in two pentagonal rings. Photomultiplier Tubes 8p HPGe Detectors 1-to-1 correspondence between the SCEPTAR detectors and the Ge detectors allows to veto event that arises from high-energy b particles that reach Ge detector Rectangular Plastic Scintillators Photomultiplier Tubes Trapezoidal Plastic Scintillators Light Guides 11/8/

18 32 Na decay investigated as a means to study the excited nuclear states of 32 Mg (Z=12, N=20). Investigate the breakdown of shell closures far from stability. b-g coincidences measured with 8p and SCEPTAR. Reduce background and allow weak 32 Na decay spectrum to be measured. ( 32 Na beam rate at ~2 ions/s) kev peak 32 Na 32 Mg kev peak 40 K 40 Ar g-singles (without SCEPTAR) kev peak 208 Tl 208 Pb b-g Coincidences (with SCEPTAR) kev peak 32 Na 32 Mg 11/8/

19 b-g coincidences: Reduced background from room decays and induced reactions Increased signal to background ratio, better quality lineshape 1 st experiment: 10 3 s Li 2 nd experiment s Li Mattoon et al., PRC, (2009) 19

20 E. Zganjar, LSU 11/8/

21 Routinely observe electrons down to kev 11/8/2016 important for spectroscopy of odd-odd nuclei and actinides 21

22 Coincidences with 65-keV M2 transition 11/8/

23 gg coinc IT: 99.89% ge - coinc 11/8/2016 Previously unobserved transition 23

24 Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei Phase I completed ($8.9M) 16 large-volume unsegmented clover detectors (40% crystals 220% with addback) Support structure, new beam line, etc. Digital DAQ triggerless with aim to write 300 MB/s (~1 MHz event rate) Commissioned fall 2014 Phase II funded ($3.5M) BGO shields for clovers, LaBr 3 detectors Expected completion /8/

25 Operate in 2 modes maximum efficiency mode (detectors fully forward, source-to-detector distance 11 cm) full-suppression mode (allow for future BGO shields) Maximum efficiency Full suppression Former 8p 11/8/

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27 g coincidences with 885-keV in 32 Mg 8p: 2-3 pps, 5 days GRIFFIN: ~9 pps, ~2 days C. Mattoon et al., PRC75, (2007) Note scale! 11/8/

28 Ge X ray in g-g trigger Ge X ray Moving average filter algorithm Injected pulse: 5 kev Real photons: 10 kev 57 Co 241 Am g singles 11/8/

29 GRIFFIN Clovers at 11cm Eight 8π HPGe Low-Energy Efficiency Source-detector distance: 13.5 cm unsuppressed 16.5 cm suppressed Eight LaBr 3 (Ce) Fast timing Source-detector distance: 12.5 cm unsuppressed 16.5 cm suppressed 11/8/

30 5cm 5cm LaBr 3 (Ce) detectors with 8p BGO suppression shields Timing with two LaBr 3 detectors 11/8/

31 Commission the LaBr 3 detectors t ½ =840±20 ps (NNDC: 860±30 ps) GRIFFIN configuration 12 HPGE detectors 10 plastic scintillator paddles for b tagging 1 very-fast plastic scintillator for fast timing 4 LaBr 3 detectors for fast timing 68 DESCANT detectors for neutrons 11/8/

32 b-delayed neutron spectroscopy Total absorption spectroscopy 11/8/

33 β-strength distribution and β1n - β2n competition P β1n P β2n Nuclear Chemistry Gordon Conference, 2013 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 en 11/8/

34 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% More data points than just one single value are needed to guide/develop reliable theoretical descriptions of β1n/β2n rates.

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41 Detectors built by St. Gobain, filled with C 6 D 6. 11/8/

42 Show peak-like structure n-d scattering asymmetric in cm frame Lower threshold on order of 50 kev E n =100 kev 11/8/

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45 Modular Total Absorption Spectrometer at ORNL 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. March C. Goetz, R Grzywacz (UTK) Data acquisition based on digital pulse processing and using XIA Pixie16 modules (100 MHz) 11/8/

46 90 Br 90 Kr β-decay (Q β =11 MeV) measured with Tandem-OLTF-MTA outer 90 Br is an example of beta-delayed neutron (βn) 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 90 Br are again pointing to the large β-feeding I β to the highly excited states up to neutron separation energy of 6.5 MeV in 90 Kr, much larger I β than listed in ENSDF data. High energy tail in MTAS central and total spectra indicates the presence β-transitions of large energy, e.g., to the gs or 2 + state in 90 Kr. 11/8/2016 MTAS Central Inner Middle Outer middle MTAS experimental spectrum 03/05/2015 Total MTAS simulated spectrum following ENSDF A. Fijalkowska (Warsaw) Energy (kev) total MTAS S n ~ 6.5MeV central inner B.C. Rasco (LSU) Neutron induced MeV peaks from (n,γ) reactions on Na and I in NaI(Tl) crystals of outer, middle and inner rings of MTAS. 90 Br βn~25% 46

47 Clean beams or sources nearly as important for b decay as inbeam studies Statistics, statistics, statistics, With the 8p at TRIUMF, we aimed for events in our gg matrices for near-stability experiments GRIFFIN will move us into the realm of events for gg, and ggg cubes Tape collector with variable beam-spill control is vital High-throughput DAQ Measurement of angular correlations Complements e - for multipolarities, spin sequences Many ( perhaps most? ) previous g branching ratios wrong Singles problematic, coincidences affected by angular correlations 11/8/

48 Auxiliary detectors to increase range of physics Si for conversion e - for multipolarities, E0 transitions Introduction of fast-timing detectors like LaBr 3 Neutron detectors for b-delayed n emission Decay spectroscopy programme at modern RIB facilities can rapidly become the most successful 11/8/