Investigating the nuclear molecule structure of states in 18 O *

Transcription

1 Investigating the nuclear molecule structure of states in 18 O * STUART PIRRIE, UNIVERSITY OF BIRMINGHAM SOTANCP4, 05/17/2018 GALVESTON, TEXAS

2 Overview Aims and motivations Clustering models and rotational bands Experimental set-up Observed 18 O states Catania plots Preliminary results Future work

3 Aims and Motivations Aims: Determine branching ratios in high-energy excited states of 18 O. Extract the structure of certain rotational bands through their partial α-decay widths. Motivations: A measurement performed by W. von Oertzen et. al identified 30 new states in 18 O (Munich). 18 O is an excellent contender for observing cluster structure. Nuclear clustering provides a good test of theoretical models.

4 W. von Oerzten 2001 Eur. Phys. J. A Edited by C. Beck, (2016). JPCS Cluster16 - Recent Experimental Results on Nuclear Cluster Physics

5 Excitation energy (MeV) α 2n 2α α 2n 12 C α 14 C W. von Oerzten 2001 Eur. Phys. J. A Edited by C. Beck, (2016). JPCS Cluster16 - Recent Experimental Results on Nuclear Cluster Physics

6 12 C 2n α K π = 0 4 +/- 14 C α K π = 0 2 +/-

7 Rotational bands W. von Oertzen et al. Eur. Phys. J. A 43, (2010) The energy of an excited state in a nucleus can be related to its total angular momentum as follows: E x J = ħ2 2Θ J J E 0. Members of the same rotational band have an identical structure. Broken intrinsic reflection symmetry causes signature splitting. The rotational bands of interest (non-shell model) are the K π = 0 2 +/- and K π = 0 4 +/-

8 Experimental set-up 12 C( 7 Li,p) 18 O * 1 3 1: 31.0, +14.2, 86 mm 2: 31.0, 13.5, 80 mm 3: 71.0, +23.7, 70 mm 4: 71.0, 16.1, 64 mm 12 C target (110 μg/cm 2 ) 2 4 Total angular range: ϑ x 14 to 92 ϑ y 36 to 40

9 Q3D spectrometer Angular acceptances of ±3 (x) and ±2 (y) when slits fully open. Position of particle detection at focal plane detector determines energy of incident particle.

10 Q3D spectrometer d p

11 W. von Oertzen et al. Eur. Phys. J. A 43, (2010)

12 1.980, 2 + g.s., 0 + W. von Oertzen et al. Eur. Phys. J. A 43, (2010)

13 7.112, , , W. von Oertzen et al. Eur. Phys. J. A 43, (2010)

14 10.297, , , W. von Oertzen et al. Eur. Phys. J. A 43, (2010)

15 Catania plots DSSD 12 C( p 7 Li,p) 4 He+ 14 C beam

16 Catania plots DSSD The Q-value equation for the 12 C( 7 Li,p) 4 He+ 14 C reaction is as follows: Q = MeV = E 14c + E α + E p E beam. 12 C( p 7 Li,p) 4 He+ 14 C beam

17 Catania plots DSSD The Q-value equation for the 12 C( 7 Li,p) 4 He+ 14 C reaction is as follows: Q = MeV = E 14c + E α + E p E beam. Also, E α = p α 2 2m α. 12 C( p 7 Li,p) 4 He+ 14 C beam

18 Catania plots DSSD The Q-value equation for the 12 C( 7 Li,p) 4 He+ 14 C reaction is as follows: Q = MeV = E 14c + E α + E p E beam. Also, E α = p α 2 2m α. Through rearranging we see that E beam E 14c E p = 1 2 p α m α 2 Q. 12 C( p 7 Li,p) 4 He+ 14 C beam

19 Catania plots DSSD The Q-value equation for the 12 C( 7 Li,p) 4 He+ 14 C reaction is as follows: Q = MeV = E 14c + E α + E p E beam. Also, E α = p α 2 2m α. Through rearranging we see that E beam E 14c E p = 1 2 p α m α 2 Q. 12 C( 7 Li,p) 4 He+ 14 C p beam y = m x + c

20 Catania plots Gradient = ¼ = 1/m α , , , y-intercept = MeV = -Q

21 Gradient = 1/4 y-intercept =

22 Gradient = 1/14 y-intercept =

23 Gradient = 1/1 y-intercept =

24 Efficiency corrections (Monte Carlo)

25 Total excitation spectrum

26 Total excitation spectrum Detected 14 C gate

27 Total excitation spectrum Detected 14 C gate Detected α gate 17

28 Total excitation spectrum Detected 17 O gate Detected 14 C gate Detected α gate 17

29 But what about other decay paths? Photon decay is possible, especially for states close to or below threshold for appropriate decay paths , , , 2+ How do we know whether or not we are observing photon decay? Alpha threshold: MeV Neutron threshold: MeV

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31 18 O

32 7.112, , ,

33 7.112, , ,

34

35

36

37 Total Q3D spectrum γ-gated Q3D spectrum 7.112, , , , , , , 3 + / , 3 + / , 2 + α-gated Q3D spectrum 8.214, , , , , , , , 3 + / , 2 + n-gated Q3D spectrum 7.969, 3 + / , 2 +

38 Preliminary branching ratios Energy (MeV) α B.R. n B.R (2)% >80% (3)% (9)% >1% (3)% 8(1)% (2)% 50(4)%

39 Future work Correct efficiencies and angular distributions from simulation. Energy-loss corrections. Analyse higher excitation ranges (with more decay paths). Establish branching ratios for all measured states. Calculate partial α-decay widths to infer tendency towards cluster structure.

40 References K. Ikeda, N. Tagikawa and H. Horiuchi, 1968 Prog. Theor. Phys. (Suppl.) extra number, 464 W. von Oertzen, M. Freer and Y. Kanada-En yo, 2006 Physics Reports 432, 43 W. von Oerzten 2001 Eur. Phys. J. A C. Beck, (2016). JPCS Cluster16 - Recent Experimental Results on Nuclear Cluster Physics W. von Oertzen et al. Eur. Phys. J. A 43, (2010) - Molecular and cluster structures in 18O C. Wheldon et al. Phys. Rev. C 83, Published 28 June 2011-High-resolution measurement of absolute α-decay widths in 16O

41 Collaborators S. Pirrie, Tz. Kokalova, C. Wheldon, S. Bailey, J. Bishop, N. Curtis, R. Smith, D. Torresi, A. Turner R. Hertenberger, H.-F. Wirth Th. Faestermann D. Mengoni D. Dell Aquila University of Birmingham Ludwig-Maximilians Universität München Technische Universität München Università degli Studi di Padova Università degli Studi di Napoli Fedorico II