contents breakup reactions of 14 be on a proton target inelastic scattering ( 14 be) one-neutron...
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Invariant-mass spectroscopy of neutron-rich Be isotopes
ContentsBreakup reactions of 14Be on a proton target
Inelastic scattering (14Be)One-neutron removal reaction (13Be)
Y. KondoRIKEN Nishina Center
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CollaboratorsY. Kondo, T. Nakamura, Y. Satou, T. Matsumoto, N. Aoi, N. Endo, N. Fukuda, T. Gomi,
Y. Hashimoto, M. Ishihara, S. Kawai, M. Kitayama, T. Kobayashi, Y. Matsuda, N. Matsui,
T. Motobayashi, T. Nakabayashi, K. Ogata, T. Okumura, H. J. Ong, T. K. Onishi, H. Otsu,
H. Sakurai, S. Shimoura, M. Shinohara, T. Sugimoto, S. Takeuchi, M. Tamaki, Y. Togano,
Y. Yanagisawa
Tokyo Institute of Technology RIKEN Nishina Center Tohoku University Rikkyo University Kyushu University University of Tokyo Center for Nuclear Study (CNS), University of Tokyo
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Nuclear Chart
Exotic structures▷Neutron halo▷Magicity loss (12Be, 32Mg)▷Di-neutron correlation? (6He, 11Li)▷Different deformation of proton/neutron density(16C)
Neutron halo
Magicity loss
Different deformations of Protons and neutronsDi-neutron?
13Be, 14Be
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14Be▷Drip-line nucleus▷Two neutron halo▷Borromean (12Be+n, n+n systems are unbound)▷No bound excited states
excited states locate above the neutron separation energy (S2n=1.26MeV)
13Be▷Unbound nucleus▷Low-lying levels are not clarified
Several experimental results are not consistent
Breakup of 14Be on proton
14Be and 13Be
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Inelastic scattering
One-neutron removal reaction
14Be▷Angular distribution Jp assignment▷cross section collectivity
13Be▷Momentum distribution
of 13Be system Jp assignment
Breakup Reactions on a low-Z target
p
12Ben
n
14Be
1np
12Be
n
n2np
Be12p
q 12Ben
n
14Be*
~ 70 MeV/u
1np
p
12Ben
n
14Be12Be
n
Be12p
q 12Ben
13Be
n~ 70 MeV/u• Coulomb breakup cross section is small
Invariant mass 22 ii pEM
Momentum Distribution of 13Be (transverse)
2/513
22/113
12/113
014 05/2Be01/2Be11/2Be0Be dps
l=0 l=1 l=2
Momentum distribution spin-parity assignment of 13Be
l=2
l=1
l=0
Example of momentum distribution width of P distribution▷depends on the orbital
angular momentum of a knocked-out neutron
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Experiment
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Experimental Setup
Primary beam18O 100 MeV/u
Production targetBe 6 mm
Plastic scintillator1 mm
14BeEnergy : ~ 70MeV/uIntensity : ~8,000 counts/sPurity : 90%
RIPS ( RIKEN Projectile-fragment Separator)
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Experimental Setup
14Be
PPACAngle of 14Be
Dipole magnet
Drift chamber (FDC)Particle Identification
Drift chamber (MDC)Angle of 12Be
NaI(Tl) scintillator g ray from 12Be
Reaction TargetLiquid H2 (227 mg/cm2)
charged particle Hodoscope(plastic scintillator)
Velocity of 12Be
Neutron counter(plastic scintillator)
Veto counter
12Be
n
Detect 12Be and (a) neutron(s) in coincidence
~ 70 MeV/u
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Experimental Setup (photo)
Dipole MagnetTarget
Drift Chamber
He bag
Hodoscope
Neutron Detector
RIPSBeam
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Neutron counter
Charged particle VETO(thin plastic scintillators)
Neutron counter
Beam direction
~2m%5.21
Efficiency
For 1n detection
Neutron Counter54bars6x6x214cm3
Relative energy spectrum (12Be+n+n)Angular distribution
Results (Inelastic scattering)
p
12Ben
n
14Be
1np
12Be
n
n2np
Be12p
q12Be
n
n
14Be(2+)
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Inelastic scattering14Be+p 14Be* 12Be+n+n
▷Select Mn=2 (detection multiplicity) crosstalk rejection (position, timing)
Neutron Crosstalk Analysis
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2
Two neutron event
CrosstalkOne neutron is detected by two (or more) detectors
Crosstalk events
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1
NEUT-BNEUT-A
Same Wall event
Different Wall event
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Comparison with 14Be+C data (previous experiment)
p(14Be,12Be+n+n)69 MeV/nucleon
neutron crosstalk events are eliminatedefficiency and acceptance are corrected
Similar peak at around 0.3MeV was observed
C(14Be,12Be+n+n)68 MeV/nucleon(previous exp.)
T. Sugimoto, T. Nakamura, Y. Kondo et alPLB 654,160 (2007)
14Be(2+)
Er=0.28(1)MeV
DL=2
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14Be+p experiment
DWBA analysisTwo optical potentials
(A) A.A. Korsheninnikov et al. PLB343, 53 (1995)(B) R.L. Varner et al.
Phys. Rep. 201, 57 (1991) (CH89)
d =1.40(19) fm (14Be+p)
p(14Be,12Be+n+n)69 MeV/nucleon
14Be(2+)
Erel(12Be+n+n) (MeV)
Erel=0.25(1) MeVs =12.5±0.2±1.6 mb
(A)
(B)p(14Be,14Be(2+) )69 MeV/nucleon
Y. Kondo, T. Nakamura, Y. Satou et al.: to be submitted
Width is dominated by the experimental resolution
(~100keV (1 )s @ 0.25MeV)
relrel 19.0~ EE (1s)
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2+ energy & deformation length
2+ energyLower than 12Be
Deformation lengthSmaller than 12Be
Proton/neutron collectivities can be deduced (now in progress)
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Phase space decay▷ 14Be(21
+) 12Be+n+nSequential Decay▷ 14Be(21
+) 13Be+n
(Erel=0.1MeV) 12Be+n+n
(Erel=0.15MeV)
Decay of 14Be(21+)
sequential
phase space
12Ben
n
Ec-n1
En-n
Ec-n2
Ec-(nn)
Relative energy spectrum (12Be+n)Transverse momentum distributions
Results(One-neutron removal)
1np
p
12Ben
n
14Be12Be
n
Be12p
q 12Ben
13Be
n
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Mn=1 events
Subtraction of Inelastic Component
Mn=1 events
Inelastic channelEstimated from Mn=2 events
One-neutron removal channel
Corresponds to 14Be(2+)
One-neutron removal channel(one neutron is emitted)
knocked out
Inelastic channel(two neutrons are emitted)
not detected
two cases in Mn=1 events▷ inelastic component should be subtracted
p(14Be,12Be+n+n)69 MeV/nucleon
14Be(2+)
Erel(12Be+n+n) (MeV)
Erel=0.25(1) MeVs =12.5±0.2±1.6 mb
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13Be12Be+n+g
13Be12Be(1-)+n(Eg=2.7MeV)
13Be12Be(2+)+n(Eg=2.1MeV)
s=11(2)mb(Erel=0~4MeV)
s=5.3(7)mb(Erel=0~4MeV)
12Be+n s=89(6)mbs for 12Be+n+g is small
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Two peaks at 0.5MeV, 2MeV
Transverse momentum distribution
(not longitudinal)▷Width of momentum distributions
are different between peak regions
Relative Energy Spectrum
Erel(12Be+n) (MeV)
p(14Be,12Be+n)
s=89(6)mb(Erel=0-4MeV)
0.25-0.75MeV 2.0-2.5MeV
Px resolution~30MeV/c
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Relative energy spectrum▷ p- and d-wave components Breit-Wigner shape
▷ s-wave component G.F. Bertsch et al: PRC 57, 1366 (1998)
Momentum distribution CDCC calculation (by T. Matsumoto)13Be is assumed to be a core in 14Be
▷ 13Be-p interaction JLM interaction J. Jeukenne et al.: PRC16, 80 (1977)
▷ n-p interaction R.A. Malfliet and J.A.Tjon NPA127, 161 (1969)
▷ 13Be-n potential Wood-Saxon form
Depth is adjusted to reproduce the separation energy
Fitting of Erel spectrum and momentum distributions
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22)sin()cos(
1
relrelrel
relrel
akk
akk
kdE
d
/2 BE /2 relrel Ek
a : Scattering length
4/22rrelrel
EEdE
d
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0.5 MeV peak p-wave resonance
2 MeV peak d-wave resonance
Relative Energy Spectrum
p
s
d
ps
d
Erel(12Be+n) (MeV)
p(14Be,12Be+n)
s=89(6)mb(Erel=0-4MeV)
0.25-0.75MeV 2.0-2.5MeV
p
ds
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p-wave component▷ Er=0.50(1) MeV▷ G=0.36(2) MeV
consistent with Gsp (l=1)▷ Jp=1/2-
d-wave component▷ Er=2.48(7) MeV▷ G=2.4(2) MeV
larger than Gsp (l=2)other state @ 2MeV?
Relative energy spectrum
s component as~ -3fm
d state Er=2.48(7) MeV Γ=2.4(2)MeV
p state Er=0.50(1) MeV Γ=0.36(2)MeV
single particle width
p-wave @0.50MeV Gsp~0.5MeV
d-wave @2.48MeV Gsp~1.4MeV
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Summary of the observed levels
The 2+ state in 14Be locates lower than the g.s. of 13BeSequential decay process is energetically forbidden
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The low-lying negative parity state Intruder state
Low-lying state of 13Be
Thiswork
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Shell model calculation
▷ PSDMK D.J. Millener et al.: NPA255, 315 (1975)
Provides the shell closure at 12Be
▷ SFO (spin-flip p-n monopole interaction) T. Suzuki et al.: PRC67, 044302 (2003)
resonably reproduce the magicity loss at 12Be
Energy Levels of 12Be and 13Be
13Be
PSDMKHigher excitation energy of 1/2-
SFOGround state of 1/2- good!several states at ~2MeV
Intruder 1/2- statedisappearance of N=8 magicity
explained by spin-flip p-n monopole interaction
12Be
13Be
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▷energy gap between [220 ½] and [101 ½] orbitals disappears with large prolate deformation
▷Large quadrupole deformation (b~0.6) of 12Be H. Iwasaki et al. PLB481, 7
(2000)
intruder 1/2- state of 13Be indicate large deformation?
Deformation?Ref) A. Bohr and B.R. Mottelson Nuclear structure Vol.1
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Breakup reactions (14Be+p)
Inelastic scattering▷2+ state of 14Be▷Phase space decay of 2+ state
One-neutron removal reaction▷Low-lying p-wave (intruder) resonance of 13Be
Summary