a decay above 100Sn: 109Xe, 105Te and 109I

1
a decay above 100Sn 109Xe, 105Te and 109I
S.N. Liddick1,2, R.Grzywacz2,3, C.Mazzocchi3,
R.D.Page4, K.P.Rykaczewski3, J.C.Batchelder1,
C.R.Bingham2,3, I.G.Darby4, G.Drafta2, C.Goodin5,
C.J.Gross3, J.H. Hamilton5, A.A.Hecht6,
J.K.Hwang5, S.Ilyushkin7, D.T.Joss4,
A.Korgul2,5,8,9, W.Krolas9,10, K.Lagergren9,
K.Li5, D.Simpson2,11, M.N.Tantawy2, J.Thompson4,
J.A.Winger1,7,9 1 UNIversity Radioactive Ion
Beam Consortium 2 Department of Physics and
Astronomy, University of Tennessee 3 Physics
Division, Oak Ridge National Laboratory 4
Department of Physics, University of Liverpool 5
Department of Physics and Astronomy, Vanderbilt
University 6 Department of Physics, University of
Maryland 7 Department of Physics, Mississippi
State University 8 Institute of Experimental
Physics, Warsaw University 9 Joint Institute for
Heavy-Ion Reactions, Oak Ridge 10 Institute of
Nuclear Physics, Polish Academy of Sciences 11
East Tennessee Technical University
2
a-decay near proton and neutron shell closures
N126
N82
Z82
N50
Z
Z50
N
an island of a-radioactivity above proton-rich
Sn isotopes due to the Z50 and N50 shell
closures
3
Search for new alpha emitters above 100Sn 109Xe,
105Te, 109I

• fine structure in alpha decay ? single particle
  levels
• mass measurements
• rp-process termination
• nucleons (both protons and neutrons) in d5/2 and
  g7/2 orbitals ? proton-neutron correlations ?
  superallowed alpha decay Macfarlane65

109Xe
CN 112Xe
109I
109I
105Te
105Sb
Z50
101Sn
N50
4
Single-particle orbitals above a doubly-magic
core 100Sn
5
109I a decay and 105Sb
100 ms
ba lt 0.5 Page et al., PRL49 (1994)
109I
Qp820 keV bp100
p
1.12 s
Faestermann et al., PLB137 (1984)
p
105Sb
Qp483 keV lt 1
108Te
Tighe et al, PRC49 (1994)
Qa 3445 keV ba 50Schardt et al., NPA326
(1979)
109I
109I
104Sn
108Te
105Sb
Z50
104Sn
N50
6
Termination of the astrophysical rp-process

• Alpha decay above 100Sn leads to the termination
  of the rp-process.
• Shifting masses / proton separation energies
  could affect the direction of the rp-process to
  more exotic nuclei.

109I
105Sb
Z50
N50
Schatz et al, PRL 86, 3471 (2001)
7
HRIBF
8

• Fusion-evaporation reactions 54Fe(58Ni,3n)109Xe
  8 part.nA
• Recoil Mass Spectrometer used to separated out
  reaction products based on A/Q.

9
Excitation function of 110Xe and 109Xe HIVAP vs
experiment
Test run (RIB000)
preliminary
10
109
109/28
109/29
LARGEMCP
SMALLMCP
DSSD
40 x 40 strips
109/29
109/28
1600 pixels
11
Double-sided Silicon Strip Detector

• DSSD implantation detector SiBox and SiLi.
• Centerpiece of system is DSSD.
• 4 cm x 4 cm segmented into 40 1-mm strips on
  front and back for a total of 1600 pixels.
• 60 um thick.
• Implanted ions and subsequent decay events are
  recorded on an event-by-event basis.

12
Thick Si(Li) and Four Si detectors around the DSSD
(UTK,Mississippi,Vanderbilt contributed)
5 cm

• DSSD surrounded by four Si detectors used to
  reduce background from decay events that are not
  fully stopped in the DSSD.
• Behind DSSD is a thick SiLi detector also for use
  as a veto.

13
Digital Electronics

• DSP-based data acquisition system
  (UT/ORNL/UNIRIB)? recording pulse shapes
  (traces) for single ? and pile-up ?- ? decay
  events (109Xe ? 105Te ? 101Sn)? method very
  selective (identify 100 events among 4.4108
  implanted ions and 1.7107 decays)., ? very
  sensitive (DT between two pile-up traces covers
  wide range) very small dead time (lt15 at 3
  kHz ions and 150 Hz traces)

14
109Xe
15
New Acquisition Mode

• New acquisition mode developed in order to record
  microsecond 105Te activity after millisecond
  109Xe activity.
• For signals greater than a predetermined
  threshold, only energy and time recorded.
• All others, trace with a length of 25 ms obtained
  for offline analysis.

16
109Xe ? 105Te ? 101Sn
Example of a-a pile-up traces
Back Strip
Front Strip
105Te
109Xe
0.275ms
17
Alpha energy spectra

• A energy spectra for those events identified
  after a 109Xe or 105Te decay.
• Fine structure observed in the a decay of 109Xe.
• Place excited state in 105Te at an energy of 150
  keV.
• Only one transition observed in 105Te.

3.918 MeV
4.062 MeV
4.703 MeV
18
109Xe,105Te time distributions

• Time distributions for 105Te and 109Xe on a
  logarithmic time axis.
• Half-lives fit using the method of Schmidt et al.
  1 and result in 620 ? 70 ns and 13 ? 2 ms for
  decay of 105Te and 109Xe, respectively.
• Time distribution cut off at low times in 105Te
  decay due to software limitations on the
  identification of an event as a double pulse.

620
1 K.-H. Schmidt et al., Z. Phys A, 316, 19
(1984)
19
109Xe ? 105Te ? 101Sn
(7/2)
Ea 3.918 MeV ba 30
13?2 ms
109Xe55
54
l0
l2
(7/2)
0.15 MeV
Ea 4.062 MeV ba 70
(5/2)
620 ? 70 ns
105Te53
52
l0
Ratio of half-lives 120000
Ea 4.703 keV ba 100
(5/2)
1.9 s
101Sn51
50
20
Systematics of 7/2 and 5/2 levels

• In a simple single-particle shell model, energy
  separation between nd5/2 and ng7/2 can be
  estimated from levels in 101Sn to be 160 keV.
• Systematics of 7/2 level break at N 53.
• 7/2 level in 101Sn can be speculated to be 160
  keV.

21
109I
22
Summary

• Observation of 109Xe fine structure with first
  excited state at 150 keV.
• Measurement of 109I alpha decay branch and infer
  the proton separation energy in 105Sb.

Looking forward

• Search for fine structure in 105Te alpha decay to
  101Sn and identification of nd5/2 and ng7/2
  energy separation in 101Sn.
• Discover 108Xe ?104Te ?100Sn alpha decay chain
  best case for superallowed alpha decay.