Charged-particle spectroscopy with the Optical TPC

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1 Charged-particle spectroscopy with the Optical TPC Marek Pfützner 1

2 Outline Nuclei at the proton drip-line and beyond Two-proton radioactivity Optical TPC Decay study of 45 Fe (and 43 Cr) Decay study of 48 Ni (and 46 Fe, 44 Cr) Beta-delayed 3p emission from 31 Ar Rare decay of 6 He Beta decay of 8 He New TPC for ELI-NP 2

Beyond the proton drip-line Competition between two decay modes The b + decay V(r) The emission of particles Probability of transition: Decay energy may be large, but the weak interaction is really

3 Beyond the proton drip-line Competition between two decay modes The b + decay V(r) The emission of particles Probability of transition: Decay energy may be large, but the weak interaction is really weak 5 Q T12 1 ms There is a potential barrier which hampers emission of an unbound proton (a, 2p, 14 C,..) 2 rout exp 2 [ V ( r) Qp] dr r in r To find where the drip-line actually is and to predict which decay will happen, precise estimates of atomic masses are required! To study particle radioactivity fast techniques are needed! 3

4 b-delayed particle emission When the b decay energy is large, many exotic channels are available Blank and Borge, Progress in Part. Nucl. Phys. 60 (2008) 403 4

5 Separation energy [MeV] Separation energy [MeV] p and 2p emission The limit of existence beyond the proton drip-line is determined by emission of protons Q p < 0 (Z,N) 2p true simultaneous Z = 27 Q 2p > Single p emission S 1p S 2 p (Z-2,N) Neutron number Q p > 0 sequential 4 3 Z = 26 2 (Z,N) 1 0 pp -1-2 S 1p Q 2p > 0 (Z-2,N) V.I. Goldanskii, Nucl. Phys. 19 (60) Neutron number, N S 2 p 5

6 simultaneous sequential Full 2p landscape Global prediction based on EDF theory with 6 Skyrme forces and simple models of 2p emission New terra incognita Model averaged path of 2p/pp emission Erler et al., Nature 486 (2012) 509 Olsen et al., PRL 110 (2013) ; PRL 111 (2013) (E) 6

gating electrode Trigger charge amplification light PMT CCD PMT Recording system Combination

7 TPC detector Time projection chamber with optical readout (OTPC) counting gas at atmospheric pressure a particle CCD incoming identified ion ionization electrons e p E HV electrodes gating electrode Trigger charge amplification light PMT CCD PMT Recording system Combination of the CCD image with the PMT waveform allows to fully reconstruct the track in three dimensions 7

8 Raw data and ion ID CCD ID data PMT 8

9 Track reconstruction A track is reconstructed by comparing the data with the SRIM simulation E p = 1393 (50)(6) kev Q = 28 (4)(1) Pomorski et al., PRC 90 (14)

10 OTPC 10

11 OTPC 11

12 Study of 45 Fe NSCL/MSU, February 2007: 58 Ni at 161 MeV/u + nat Ni 45 Fe 2p decay of 45 Fe trigger 45 Fe 12

with the 3-body model of Grigorenko et al. Miernik et al.

13 p-p momentum correlations for 45 Fe Proton-proton momentum correlations measured for 45 Fe are complex and indicate a genuine 3-body phenomenon Good agreement with the 3-body model of Grigorenko et al. Miernik et al., PRL 99 (07) Grigorenko et al., PLB 677 (2009) 30 MP, Karny, Grigorenko, Riisager, RMP 84 (12)

14 Decays of 45 Fe and 43 Cr NSCL/MSU, p b3p 11% 44 Mn+p 45 Fe Q EC = 18.7 MeV T 1/2 = 7 ms b2p b3p 0.08% b + 43 Cr+2p 70% 2p b + 30% b2p b3p IAS IAS bp 40 Ca+3p b2p 41 Sc+2p bp b4p bp b2p b3p bpa 41 Sc+4p 40 Ti+pa bp Pomorski et al., Phys. Rev. 83 (2011) Ti+p 43 V Mn 44 Cr+p Miernik et al., PRL 99 (07) V+2p 42 Ti+3p

15 Study of 48 Ni NSCL/MSU, March 2011: 58 Ni at 160 MeV/u + nat Ni 48 Ni 10 events of 48 Ni in 10 days Cross section: s = 150(50) fb! 46 Fe 48 Ni 44 Cr 46 Fe 44 Cr Pomorski et al., PRC 90 (14)

16 2p decay of 48 Ni PMT 2p βp CCD Ion 48 Ni Four 2p events of 48 Ni Q 2p = 1.29 (4) MeV Pomorski et al., PRC 90 (14)

Number of events/50 kev b-delayed protons from 44 Cr 5542 identified ions of 44 Cr 4098 properly stopped 183 decays observed b 10 1 % p Dossat : b 14.0 9 % p Dossat et al., Nucl. Phys.

17 Number of events/50 kev b-delayed protons from 44 Cr 5542 identified ions of 44 Cr 4098 properly stopped 183 decays observed b 10 1 % p Dossat : b % p Dossat et al., Nucl. Phys. A 792 (2007) 18 A clear new line at 740(20) kev I % p reconstructed protons No beta background! Dossat et al. This work (5)% 1.4(3)% 0.5(2)% 44 Cr Energy [kev] Pomorski et al., PRC 90 (14)

18 Counts of 46Fe b-delayed protons from 46 Fe 471 identified ions of 46 Fe 269 properly stopped 148 decays observed Dossat : b p 66 4 % b 79 4 % p Dossat et al., Nucl. Phys. A 792 (2007) reconstructed protons 1 46 Fe Energy [kev] Pomorski et al., PRC 90 (14)

19 b2p channel in 46 Fe One good event! CCD 46 Fe PMT 46 Fe 19

20 b2p channel in 46 Fe Both protons escaped the detector. From the length of tracks we know only that: E MeV This cannot go through the IAS! E MeV E1 E MeV 3090 Pomorski et al., PRC 90 (14) Dossat et al., Nucl. Phys. A 792 (2007) 18 20

21 Decay scheme of 48 Ni Q T 2 p MeV 2.1 ms 21

22 b3p in 31 Ar b3p? b3 p 2.1% expected b3 p 0.1% 22

23 b3p in 31 Ar Experiment at FRS, August 2012 Confirmed at ISOLDE 31 Ar Lis et al., to be published Koldste et al., PRC 89 (2014)

Decay of 6 He into a + d 6 He has a very weak decay branch

succeeded in satisfactory description of both the shape

100% a d Due to b-background, it was not possible to

24 Decay of 6 He into a + d 6 He has a very weak decay branch to a + d Raabe Anthony b d 10 6 Tursunov No model has succeeded in satisfactory description of both the shape and the intensity of the a+d spectrum! 100% a d Due to b-background, it was not possible to determine the spectrum below E CM 400 kev! R. Raabe et al., Phys. Rev. C80 (2009)

6 He into OTPC at ISOLDE Experiment at CERN-ISOLDE, August 2012 A bunch of 10 3-10 4 6 He ions,

Light from many beta decays is seen as a smeared cloud around the implantation points 13 cm The

25 6 He into OTPC at ISOLDE Experiment at CERN-ISOLDE, August 2012 A bunch of He ions, accelerated to 3 MeV/u by REX-Isolde, is implanted into the OTPC Data are taken for 650 ms exposure. Light from many beta decays is seen as a smeared cloud around the implantation points 13 cm The difference in the depth of implantation corresponds to the energy loss of 6 He in a layer of 5 m of Cu + 2 m of Au 25

fast sampling, 100 MHz (fine details of events) Bunch of 10

26 Decay of 6 He with OTPC at ISOLDE CCD image, 650 ms exposure PMT slow sampling, 1 MHz (rough history of what happened) PMT fast sampling, 100 MHz (fine details of events) Bunch of He ions Practically no background in the PMT traces 26

27 Event reconstruction L = 23 mm Horizontal length: 23 mm Vertical length : 62 mm Total length = 66 mm Angle = 69 Energy = 1000 ± 30 kev 27

28 Event reconstruction L < 3 mm Horizontal length: 3 mm Vertical length : 16 mm Total length = 16 mm Angle = 80 Energy = 150 ± 10 kev 28

29 The spectrum 317 events collected in 12 h Full statistics should be up to 6 times larger? 29

30 ? Tillley et al., NP A 747 (2004) 155 b decay of 8 He The previous experiment on 8 He b decay : ISOLDE (1992) M. Borge et al., NP A 560 (1993) 664 Observation of strong b-delayed triton channel He Li a t n 8 8 * The branching: B GT 5.2, log ft = 2.9! 2a Essentially, this is the tetra-neutron decay to a triton and a neutron! (If the clustering approximation is the good one). 30

Amplitude [a.u.] Energy (MeV) Decays to particle bound states of 8 Li Dubna, Acculinna, 2009/2012 CCD a 12 10 10.65 8 He ~9.

31 Amplitude [a.u.] Energy (MeV) Decays to particle bound states of 8 Li Dubna, Acculinna, 2009/2012 CCD a He ~9.67 (9) a % He PMT Li 2a Be L z [mm] 31

32 Counts / 400 kev Final-state continuum in 8 Li 2a decay Excitation energy of 8 Be (kev) Mianowski, PhD thesis Bhattacharya et al. PRC73(2006) OTPC Si det. 32

Amplitude [a.u.] Energy (MeV) Reconstruction of a-t-n decay event CCD 4 He 12 3 H 10 10.65 8 He 0.9% ~9.67 (9) 8 Q = 4.3 MeV 8 He 7.10 0.6 0.5 0.4 0.3 0.

33 Amplitude [a.u.] Energy (MeV) Reconstruction of a-t-n decay event CCD 4 He 12 3 H He 0.9% ~9.67 (9) 8 Q = 4.3 MeV 8 He PMT E a = 1150 kev E t = 2570 kev E n = 610 kev We see about triton events. The branching for the bt is 0.9 % He+t 4He+t+n L z [mm] 0 8 Li 33

Energy (MeV) Feeding of a-t-n decaying states 12 10 10.65 8 He 0.9% ~9.67 (9) 8 7.10 6 4 6.53 6.10 5.40 5.39 4.

34 Energy (MeV) Feeding of a-t-n decaying states He 0.9% ~9.67 (9) He+t 4He+t+n B GT evaluation is in progress Li Mianowski, Janas, to be published Mianowski, PhD thesis 34

35 Helium burning problem Understanding the C a, O reaction is still one of the key open questions in nuclear astrophysics. It determines the carbon/oxygen ration which determines the fate of massive stars and the light curve of SN I a ( standard candles ) M. Gai, Phys. Rev. C88 (2013) (R) 35

36 e-tpc The proposed solution is to measure the reverse reaction: using photon beams at ELI-NP O C a Advantages: very clean signal, no background issues, angular correlations alows E1/E2 decomposition gas containing 16 O a photon 12 C E To have the full freedom of gas selection, a new detector with electronic readout is developed at University of Warsaw Other reactions planned: F, p O, Mg a, Ne, Ne a, O, See a talk by Jan Bihałowicz on Thursday! 36

37 Summary The OTPC detector is a very efficient tool to search for very rare multiparticle decays or to investigate particle decays obscured by beta background. Can provide precise branching ratios for b-delayed particle channels. Although the energy resolution is worse than for Si detectors, yields complementary data for low-energy particles. Non-trivial 3-body character of 2p decay of 45 Fe discovered. 2p decay of 48 Ni discovered. New decay channels, like b3p ( 45 Fe, 43 Cr, 31 Ar), observed for the first time. b2p emission discovered in 46 Fe based on one atom decay! Low-energy part of d-spectrum will shed light on the halo structure of 6 He Strong b-delayed triton emission confirmed for 8 He. Will provide the B GT strength for the t-emitting states. A new TPC with electronic read-out being developed for ELI-NP to solve the helim burning problem. 37

38 Thank you! 38

39 Additional slides 39

40 Study of 29 P(p, ) via 31 Ar b2p There is astrophysical interest in the reaction rate of 29 P(p, ) 30 Si. The proton width of the relevant states above 29 P+p threshold can be studied by b2p decay of 31 Ar Koldste et al., PRC 87 (2013) Ep 294 kev Very hard to identify 300 kev line because of b-background and noise. OTPC offers a straightforward and clean method to detect such a transition Proton ranges in pure helium: 300 kev R = 20 mm 830 kev R = 100 mm 40

41 Search for 19 Ne(p, ) via 20 Mg bp The key reaction for the breakout from the hot CNO cycle into the rp-process is 19 Ne(p, ) 20 Na. It is expected to be dominated by a single resonance at 457 kev. Piechaczek et al., NPA 584 (1995) 509 Wallace et al., Phys. Lett. B712 (2012) 59 Ep 457 kev Search for the 457 kev line in the 20 Mg bp spectrum failed. The present limit for the feeding of the state is 0.02% OTPC could be used to verify/improve this limit in the background free measurement 41

42 Simultaneous vs. sequential In all cases investigated, the b2p emission proceeds sequentially. In principle, however, both protons can go simultaneously. A simple direct model of 2p emission describes both mechanisms. Q 1.15 MeV, Q 0.23 MeV Both sequential and simultaneous modes visible. 2p 1p According to this model, as long as Q 0.2Q 1p 2p the simultaneous emission dominates. 42

43 The current status of 2p emission Ground-state 2p radioactivity first observed in 45 Fe. Later also in 54 Zn, 48 Ni and 19 Mg 58,59 Ge 62,63 Se 66,67 Kr In lighter nuclei due to small Coulomb barrier 2p emission is fast, T 1/2 ( 19 Mg) = 4 ps! 48 Ni 45 Fe 54 Zn Below 19 Mg 2p are emitted from broad resonances, like 6 Be 30 Ar 26 S 34 Ca 19 Mg 15,16 Ne 12 O 6 Be True 2p emitters - expected/discussed - established - p-p correlations determined 43

44 Up to tellurium Predictions of the direct model simultaneous 2p emission Q 0, Q 0.2 Q 2p p 2p 100 ns T 100 ms 2 p Pd 92,93 Sn 89 Cd 103 Te Z=50 77,78 Mo 73 Zr 81,82 Ru 65,66 Kr 69,70 Sr 62 Se 57 Ge 52,53 Zn 54 Zn 48 Ni Z=28 45 Fe N=50 44

45 Between tellurium and lead Predictions of the direct model N=Z Z=82 sequential pp emission Q 0, Q 0.2 Q 2p p 2p 100 ns T 100 ms Tpp 10 pp 12 T a 145 Hf T 10 T 10 T pp a pp 110 Ba 103 Te Z=50 N=50 N=82 45

Particle emission at the proton drip-line

Particle emission at the proton drip-line Marek Pfützner M. Pfützner@PROCON 2015, Lanzhou, China, 6-10 July, 2015 1 Outline Nuclei at the proton drip-line and beyond Optical TPC Reminder of 45 Fe Decay