Transcript Slide 1
Unbound Nuclei Workshop
Pisa, 3-5 November 2008
Unbound states of 8-10He obtained in (d,p) and (t,p) reactions
M.S.Golovkov, L.V.Grigorenko, A.S.Fomichev, A.V.Gorshkov, V.A.Gorshkov, S.A.Krupko,
Yu.Ts.Oganessian, A.M.Rodin, S.I.Sidorchuk, R.S.Slepnev, S.V.Stepantsov, G.M.Ter-Akopian
JINR, Dubna, Russia
R. Wolski
JINR, Dubna, Russia; The Henryk Niewodniczański INP, Kraków, Poland
A.A. Korsheninnikov, V.A. Kuzmin, B.G. Novatskii, D.N. Stepanov
“The Kurchatov Institute”, Moscow, Russia
P. Roussel-Chomaz, W. Mittig
GANIL, Caen, France
E.Yu. Nikolskii
RIKEN, Saitama, Japan
F. Hanappe, A. Ninanne
Universite Libre de Bruxelles, Brussels, Belgium
O. Dorvaux, L. Stuttge
IPHC/DRS Strasbourg, France
A.A. Yukhimchuk, V.V. Perevozchikov, Yu.I. Vinogradov, S.K. Grishechkin
RNFC, Sarov, Russia
The ACCULINNA separator and in-flight beams
provided at the U-400M cyclotron in Dubna.
Specifics inherent to the (d,p) and (t,p) reactions carried
out in inverse kinematics. The cryogenic tritium target.
Messages from the new data on 9He acquired from the
2H(8He,p)9He reaction.
10He and 8He studied by means of the 3H(8He,p)10He
and 3H(6He,p)9He reactions.
Separator ACCULINNA at the U-400M cyclotron
ACCULINNA
Primary beam
beam
dump
Production
target (Be)
Reaction
chamber
Wedge
(Be)
0
5
10 m
Secondary RIBs from separator ACCULINNA
Beam
EnergyMeV/amu
Intensity, pps
Purity, %
6Не
20 - 45
3105
99
8Не
15 - 30
2104
98
9Li
15 - 45
2105
98
11Li
15 - 35
2103
95
12Be
15 - 40
3105
90
14Be
15 - 35
1103
80
16C
15 - 45
3105
80
18C
15 - 40
2103
80
12N
30 - 40
2x104
25
14O
30 - 45
2x105
50
15O
20 - 45
5x105
60
The (d,p) and (t,p) reactions for the study of light nuclei beyond
the neutron drip line.
These are single-step reactions favoring the occupation of valence states.
Zero spin 2n transfer dominates.
Transfer reactions seem to be suitable to reproduce a broad resonance state.
Background conditions are favorable at small CM angles.
9He
Reaction
8He+2H
9He+p
8He+n+p
Deuterium
gas target
8He
8He
9He
q8He
n
p
The “zero geometry” approach:
The recoil particle (here proton) is detected at the backward angles corresponding to
small CM angle (3≤qp≤7).
Hence, the angular momentum transferred to the studied system should have zero
projection on the momentum transfer axis.
For the states with J > 1/2 in 9He only the states with M =1/2 should be populated
for J = 5/2+, 3/2-, and 3/2+ states.
ACCULINNA, 2006
Reaction 8He(2H,p)9He
Golovkov et al., Phys. Rev. C 76, 021605(R) (2007)
Telescope
60 60 mm2
TOF
base 8 m
Target
~
~
8He
beam
+
Detector
=84 mm
MWPC1 MWPC2
10 cm
Deuterium gas target:
30K, 2.2 1020 cm-2
50 cm
8He
beam energy Elab=200 MeV
Beam dose: 2 1010
definite conclusions :
s–p interference at E9He = 0 – 3 MeV
p-d interference at E9He = 3 – 5 MeV.
no room for a narrow 9He resonance.
Counts per 333 keV
1/2-
5/2+
1/2+,
a=-4 fm
-1 0
2
E9He,
4
MeV
6
R e s o n a n c e s t a t e s o f 9H e :
E (MeV) 1.13(10)
2.3
published experimental data
4.9
8.1
K.K. Seth, et al.
0.50(10)
0.55(10)
(1987)
(5/2+, 3/2-)
(3/2-, 5/2+)
G (MeV)
0.40(10)
0.42(10)
jπ
1/2-
1/2+
E (MeV)
1.27(10)
2.42(10)
4.30(10)
5.25(12)
G (MeV)
0.10(6)
0.7(2)
narrow
narrow
jπ
1/2-
(3/2-, 1/2+)
5/2+
E (MeV)
1.1
2.2
4.0
G (MeV)
<0.1
0.8(3)
0.24(10)
jπ
1/2- (3/2-)
3/2- (1/2-, 1/2+)
5/2+ (3/2+)
E (MeV)
2.0(2)
G (MeV)
~2
jπ
1/2-
a > -20 fm
(a relaxed limit)
G.V. Rogachev,
at al. (2003)
≥4.2
5/2+
Data reported on a 2s state in the 8He+n system
a < -10 fm
H.G. Bohlen, et
al.
(1993)
L. Chen et al., Phys. Lett. B505 (2001)21.
M.S. Golovkov, at al. (2007)
M.S. Golovkov,
at al., (2007)
If indeed the s-wave scattering length is about -10 fm for 9He
the problem of 10He should be scrutinized.
S. Aoyama, 2003 (after the paper by L. Chen et al., 2002):
“Where is the ground state of 10He?”
Only two experimental papers are published on the ground (first) resonance state of 10He:
A.A. Korsheninnikov et al., 1994
Er=1.2(3) MeV, G<1.2 MeV.
A.N. Ostrowski et al., 1994
Er=1.07(7) MeV, G=0.3(2) MeV.
Both the presence of a 2s state and the obtained true energy for the p1/2 resonance
in 9He are in conflict with the energy and width reported for the 10He ground state
resonance.
We decided to explore the (t,p) type reaction 3H(8He,p)10He.
Reaction: 6Не+3Н
8He
р+8Не(g.s.)
р+6Не+2n
Target, tritium (1000 Ci)
cooled to 25 K
2×1020 at./cm2
6Не
48 modules of the neutron
spectrometer DEMON
6He
25 AMeV
Beam dose
2×1010
8He
n
p
n
Si detectors
Annular
Si detectors
Angular range measured for the 3H(6He,p)8He reaction:
θ = 6 ÷ 11 degrees in CM system
8He:
Experimental missing mass spectra
He
0
+
2 (1 )
Coincidence with He
+
(0 )
1,0
15
5
8
0,5
with He
(a)
6
He+n+n threshold
Coincidence with He
and neutrons
5
(b)
0
-5
0
0,2
0,1
5
10
0,0
15
Good agreement with other
experimental data
2+ state at about 3.6-3.9 MeV
and clear observation of (1+)
state at about 5.4 MeV
Cross sections for 0+, 2+, (1+):
200, < 250, < 125 b/sr
0,0
0
10
Efficiency
10
Coincidence
Efficiency
8
20
+
6
Counts / (400 keV) Counts / (400 keV)
6
+
Level ordering 0+, 2+, 1+, 0+, 2+
is stable through literature
Rise of the spectrum straight
from the 6He+n+n threshold
E (MeV)
Work
Method
2+
1+
0 2+
2 2+
A. Adahchour, P. Descouvemont, Phys. Lett. B 639 (2006) 447
RGM
5
S.C. Pieper, Nucl. Phys. A 751 (2005) 516c
QMC
4.7
6
7
8
A. Volya and V. Zelevinsky, Phys. Rev. C 74, 064314 (2006)
CSM
3.8
6
9.6
10.4
threshold behaviour in the 8He spectrum
“Standard”
R-matrix parameterization
for sequential decay via 7He (3/2-)
g.s. resonance
Energy ~3.6 MeV and width ~0.6
MeV
Low-energy events are not
reproduced in any of the cases
Possible explanation is a soft
dipole mode in 8He (E1 transitions)
We have shown /Golovkov et al.
2008arXiv0804.0310G/ that the
peak in the 1ˉ continuum of 8He
can be at ~1 MeV
(mb/MeV)
(a)
Markemroth et al.
10
6
He+n+n
threshold
5
0
(mb/MeV)
!!! Large uncertainty in the
state
energy E(2+) = 2.7 - 3.6 MeV
D.R. Tilley et al. NPA 745 (2004) 155
15
100
(b)
Meister et al.
50
0
Number of events
2+ 8He
60
Number of events
8He:
15
polynomial "background"
(c)
40
20
Bohlen et al.
0
2+, no E1
12+, with E1
1- + 2+
10
5
(d)
0
0
2
4
*
E (MeV)
6
8
8He:
Conclusions
Cross sections for population of resonant states 0+, 2+,
(1+) in 8He are determined to be : 200, < 250, < 125 b/sr
Possibility of a more consistent explanation of the near
threshold 8He spectra.
We expect location of E1 peak below 2+ state in 8He.
It is a simple explanation of the earlier experimental
observations.
Data not 100% conclusive. Angular correlations are
required to fix the problem. Statistics at the moment is
not sufficient.
Reaction: 8Не+3Н
10He
р+10Не
р+8Не+2n
Target, tritium (1000 Ci)
cooled to 25 K
2×1020 at./cm2
48 modules of the neutron
spectrometer DEMON
8Не
27.4 AMeV
Beam dose
5×109
beam energy 219 MeV
beam dose 5·109
8He
p10He
n
p
n
Si detectors
Annular
Si detectors
Angular range measured for the 3H(8He,p)10He reaction:
θ = 6 ÷ 11 degrees in CM system
3
Experimental missing mass spectrum
Low statistics, however low
background.
10
He
Lowest group of events is
observed at about 3 MeV.
2
Specific energy correlation can
be seen for this group of
events.
1
(a)
14 b/sr for one event is
imposed for population of
continuum above threshold.
0
1.0
4
0.5
2
(b)
0
-5
0
5
E10He (MeV)
10
15
0.0
Efficiency
Counts / (500 keV) E(8He) in 10He cms (MeV)
10He:
Estimated cross section is
larger than 120 b/sr for the
population of either the [p1/2]2
and [s1/2]2 states.
At least 8 events below 2.5
MeV were expected. Poisson
distribution provides statistical
probability 3x10-4 for the “zero
event s” result.
10He:
Spectroscopic properties of 8He and 10He
Theoretical model analogous to COSMA
model of M.V. Zhukov, A.A. Korsheninnikov, M.H.Smedberg, PRC 50 (1994)
R1:
-particle + valence nucleons
Weight of the 6He g.s. configuration is stable in 8He: 1-2
Realistic values of parameter :
- ≤
Spectroscopic factor for the two-neutron configuration is stable in 8He: 1-12
Cross sections for the population of 10He states are sensitive to the 8He
structure
Expected cross sections for the population of [p1/2]2 state in 10He is not
small:
1-1
Expected cross sections for the population of [s1/2]2 state in 10He is higher
than for [p1/2]2 state: 11-
10He:
Comparison with theory
L. Grigorenko and M. Zhukov, PRC 77, 034611 (2008).
d /dE (arb. units)
6
Exp. Korsheninnikov et al.
Pure [p1/2]2 structure state
4
2
0
0
1
2
3
4
5
E (MeV)
The same three-body Hamiltonian is used in both cases.
Different reaction mechanisms: in the case of the proton removal from 11Li the extreme
size of the neutron halo in 11Li causes the enhancement of the low-energy side of the
observed spectrum.
S-matrix pole position at about 2.5 MeV: reactions with “ordinary” nuclei seem to be
more suitable to access the 10He properties.
6
3 10
He
2
1
(a)
0
1.0
4
0.5
2
(b)
0
-5
0
5
E10He (MeV)
e
10
15
0.0
Efficiency
He cms (MeV)
10
d/de
1.8
-1.4
-5
-10
Counts / (500 keV) E( 8He) in
2.9
10He:
Conclusions
The population cross section of the 3 MeV peak in 10He 10 = 140(30) b/sr
is consistent with the estimated resonance cross section for the population
of the 10He 0+ state with the [p1/2]2 structure.
The 3 MeV peak position obtained here for the 10He ground state seems to be
in agreement with the 1.2 MeV position found in the case of the proton removal
from 11Li.
There is NO ATRACTION in s-wave state for 9He.
Limits reported for the scattering length