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Charged-particle spectroscopy of exotic nuclei with the Optical TPC. Marek Pf ü tzner Faculty of Physics, University of Warsaw. b -delayed particle emission.  When the b decay energy is large, many exotic channels are available.

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Charged-particle spectroscopy of exotic nuclei with the Optical TPC

MarekPfütznerFaculty of Physics, University of Warsaw

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

b delayed particle emission
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

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

tpc with optical readout

counting gas at atmospheric pressure

p

HV electrodes

incomingidentified

ion

p

ionizationelectrons

e

gating electrode

charge

amplification

Trigger

light

PMT

CCD

Recordingsystem

TPC with optical readout

b2a decay of 8Li

b3adecay of 12N

 Decay event 6He  a + d seen on the background of about 104 beta rays

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

slide4
OTPC

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

decays of 45 fe and 43 cr

b3p 11%

b3p 0.08%

b2p

b2p

b3p

b3p

bp

bp

Decays of 45Fe and 43Cr

2p

NSCL/MSU, 2007

QEC = 18.7 MeV

T1/2 = 7 ms

45Fe

44Mn+p

2p

b+

b+

43

Cr+2p

 70%

 30%

IAS

IAS

bpa

b2p

b4p

40Ca+3p

bp

40Ti+pa

41Sc+4p

41Sc+2p

b2p

bp

43V+2p

42Ti+3p

43V

42Ti+p

45Mn

Pomorski et al., Phys. Rev. 83 (2011) 014306

44Cr+p

Miernik et al., Eur. Phys. J. A 42 (2009) 431

Miernik et al., PRL 99 (07) 192501

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

decay channels of 43 cr
Decay channels of 43Cr

Dossat et al., Nucl. Phys. A 792 (2007) 18

11660

81%

12

0.08%

1020

7%

Dossat et al.

no protons

12%

Pomorski et al., Phys. Rev. C 83 (2011) 014306

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

43 cr puzzle
43Cr puzzle

 12% for the b-no-proton branch of in 43Cr is surprizingly large!

3/2+

43Cr

T1/2 = 211 msQEC=16.100.23 MeV

From mirror symmetry

0.57 %

2 %

< 3 %

0.03 %

0.003 %

Sp=190(230) keV

7/2

0.12 %

43V

Pomorski et al., Phys. Rev. C 83 (2011) 014306

Warburton & Alburger, Phys. Rev. C 38 (1988) 2822

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

study of 48 ni
Study of 48Ni

NSCL/MSU, 2011

58Ni @ 160 MeV/u + natNi  48Ni

46Fe

44Cr

46Fe

44Cr

Pomorski et al., PRC 83 (11) 061303(R)

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

track reconstruction
Track reconstruction

 Example reconstruction of b-delayed proton from 44Cr

PMT

CCD

Pomorski et al., to be published

Ep = 1280 (30) keVQ = 24(4)°

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

b delayed protons from 44 cr
b-delayed protons from 44Cr

Dossat et al., Nucl. Phys. A 792 (2007) 18

5542 identified ions of 44Cr

4098 properly stopped 210 decays observed

Dossat :

A clear new line at 730(20) keV

97 reconstructed protons

No beta background!

This work

Dossat et al.

2.6(4)%

1.3(3)%

0.3(1)%

Pomorski et al., to be published

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

b delayed protons from 46 fe
b-delayed protons from 46Fe

471 identified ions of 46Fe 269 properly stopped 148 decays observed

Dossat et al., Nucl. Phys. A 792 (2007) 18

Dossat :

19 reconstructed protons

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

b 2p channel in 46 fe
b2p channel in 46Fe

 One good event!

PMT

CCD

46Fe

46Fe

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

b 2p channel in 46 fe1
b2p channel in 46Fe

 Both protons escaped the detector. From the length of tracks we know only that:

This cannot go through the IAS!

3090

Dossat et al., Nucl. Phys. A 792 (2007) 18

Pomorski et al., to be published

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

simultaneous vs sequential
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.

Both sequential and simultaneous modes visible.

 According to this model, as long as the simultaneous emission dominates.

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

b 3p in 31 ar
b3p in 31Ar

 Experiment at FRS, August 2012

expected

b3p ?

31Ar

b decay of 8 he

Tillley et al., NP A 747 (2004) 155

b decay of 8He

?

 The previous experiment on 8He b decay :

ISOLDE (1992) M. Borge et al., NP A 560 (1993) 664

Observation of strong b-delayed triton channel

The branching:

BGT 5.2, log ft = 2.9 !

 Essentially, this is the tetra-neutron decay to a triton and a neutron! (If the clustering approximation is the good one).

2a

decays to particle bound states of 8 li
Decays to particle bound states of 8Li

Dubna, Acculinna, 2009/2012

CCD

a

a

8He

PMT

2a

final state continuum in 8 li 2 decay
Final-state continuum in 8Li  2 decay

Mianowski, PhD thesis

Bhattacharya et al. PRC73(2006) 055802

reconstruction of a t n decay event
Reconstruction of a-t-n decay event

CCD

4He

3H

Q = 4.3 MeV

8He

PMT

Ea = 1150 keVEt = 2570 keVEn = 610 keV

We see about 400 triton events.The branching for the bt is 0.9 %

feeding of a t n decaying states1
Feeding of a-t-n decaying states

0.9%

BGT evaluation is in progress

Mianowski, Janas, to be published

Mianowski, PhD thesis

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

study of 29 p p g via 31 ar b 2p
Study of 29P(p,g) via 31Ar b2p

 There is astrophysical interest in the reaction rate of 29P(p,g)30Si. The proton width of the relevant states above 29P+p threshold can be studied by b2p decay of 31Ar

Koldste et al., PRC 87 (2013) 055808

 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

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

search for 19 ne p g via 20 mg b p
Search for 19Ne(p,g) via 20Mg bp

 The key reaction for the breakout from the hot CNO cycle into the rp-process is 19Ne(p,g)20Na. It is expected to be dominated by a single resonance at 457 keV.

Wallace et al., Phys. Lett. B712 (2012) 59

Piechaczek et al., NPA 584 (1995) 509

 Search for the 457 keV line in the 20Mg 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

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

summary
Summary
  • The OTPC detector is an 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.
  • b2p emission discovered in 46Fe. Decay of one atom observed!
  • b3p emission finally observed in 31Ar. See the Gunvor’s talk later this session!
  • Strong b-delayed triton emission confirmed for 8He. By recording tracks of both a and t, the decay energies were reconstructed in the model independent way. Will shed light on the mechanism of the decay and provide the BGT strength for the t-emitting states.
  • Possible applications include search for low-energy b-delayed proton channels of astrophysical interest, like 31Ar b2p  29P or 20Mgbp  19Ne .

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013

thank you
Thank you!

The main work was done by two PhD students:Sławek Mianowski and Marcin Pomorski

M. Pfützner, Isolde Workshop, CERN, November 25-27, 2013