1

• ß decay of 69Kr and 73Sr
• and the rp process
• Bertram Blank
• CEN Bordeaux-Gradignan

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Motivation

• 69Kr rp-Process Drip-Line Nucleus 69Br
• Measurement of the 69Br ground state.
• Constraints on the 68Se rp-process waiting
  point.
• 73Sr rp-Process Drip-Line Nucleus 73Rb
• Measurement of the 73Rb ground state.
• Constraints on the 72Kr rp-process waiting
  point.

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69Br and the rp process

• The rapid proton, or rp process, is thought to
  mainly occur during Type I X-ray bursts
  (timescale of 10-100 s).
• Burst properties and nucleosynthesis of heavy
  nuclei is significantly influenced by
  waiting-point nuclei.

• T1/2(68Se)35.5s and 69Br is proton unbound.
• How strongly can the 68Se waiting point be
  bypassed via 2p captures?
• 2p-capture rate depends exponentially on Sp.
• ?Need spectroscopy beyond the drip line.

A. Rogers, ANL
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Previous measurements
A. M. Rogers et al.
P. Schury et. al

• Non-observation Upper limit on the 69Br
  lifetime estimated from 78Kr fragmentation cross
  sections
• ? T1/2lt100 ns ? Sp lt -450 keV
  (Blank et al., 1995)
• ? T1/2lt24 ns ? Sp lt -500 keV
  (Pfaff et al., 1996)
• Indirect High-precision penning trap mass
  measurements of 68Se and 69Se CDE
• (Coulomb Displacement Energy) ? Sp -636 ?105
  keV
• (Brown et al., 2002 Schury et al., 2007
  Savory et al., 2009)
• Direct Kinematic reconstruction of the 69Br
  proton decay ? Sp -78535-40 keV
• (A.M. Rogers et al., 2011)

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Populating 69Br via 69Kr ß decay

• Method Populate the 69Br g.s. in the ß decay of
  69Kr and look at ß-p correlations
• Monoenergetic protons.
• Clean and selective technique.
• Problem Decay to the Isobaric Analog State is
  favored over the g.s. -- X.J. Xu et al. Phys.
  Rev C 55, R533 (1997)
• However, a few percent of the decay flux may go
  to the g.s.

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Setup

• Fragmentation of 78Kr primary beam.
• E70 MeV/A Intensity 3-4 eµA.
• Utilized the LISE3 spectrometer with an Al
  (100µm) degrader and a Wien filter.

CSS2
CSS1
LISE3
LISE Target natNi 200 mg/cm2
EXOGAM Clovers

• Implant-decay experiment using ß-p and ß-?
  event tagging.
• ToF from RF and MCP's.
• Si detector for energy loss of heavy ions.
• Heavy ions are implanted into a 16x16 strip DSSD
  (3 mm pitch, 500 µm thick).
• ?'s are measured using four germanium clover
  detectors.

DSSSD
E
ToF
?E
MCP
CENBG, GANIL, ANL
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Setup

• Fragmentation of 78Kr primary beam.
• E70 MeV/A Intensity 3-4 eµA.
• Utilized the LISE3 spectrometer with an Al
  (100µm) degrader and the Wien filter.

• Identified 211 69Kr implantation events ?87
  69Kr/day.
• Clean PID based on redundant identification
  parameters.

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Measurements of known half-lives

• Known T1/2(67Se) 136 (12) ms
• So far there is good agreement with most easily
  measured half-lives.

• Known T1/2(62Ga) 116.12 (23) ms.
• Negligible additional decay components.

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65Se ß decay preliminary results

• Batchelder et al (Phys. Rev. C 47, 2038 1996)
  identified a single proton group at 3.55 (0.03)
  MeV.
• We also observe a proton peak at an energy of
  3.51 MeV.

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69Kr ß decay preliminary results
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69Kr ß decay preliminary results
X. J. Xu et al, Phys. Rev. C 533, 1997

• Half-life previously measured by X.J. Xu et al,
  Phys. Rev. C R533, 1997 of T1/232 (10) ms.
• Also claimed to observe a single proton group at
  4.07 (0.05) MeV.

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69Kr ß decay proton spectrum

• We observe proton decays to excited states.
• However, IAS is observed at E2.97 MeV.
• We do not observe 69Br ground-state proton decays.

• Half-life previously measured by X.J. Xu et al,
  Phys. Rev. C R533, 1997 of T1/232 (10) ms.
• Also claimed to observe a single proton group at
  4.07 (0.05) MeV.

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69Kr ß decay preliminary results

• We observe proton decays to excited states.
• However, IAS is observed at E2.97 MeV.
• We do not observe 69Br ground-state proton decays.

• Half-life previously measured by X.J. Xu et al,
  Phys. Rev. C R533, 1997 of T1/232 (10) ms.
• Also claimed to observe a single proton group at
  4.07 (0.05) MeV.

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Level Scheme
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Measurement aims

• Study of decay of 73Sr to 73Rb and 72Kr
• Study of decay of 69Kr to 69Br and 68Se

• Known Properties
• 73Sr decay
• - Proton line at 3.75(4) MeV
• assumed to be IAS
• (Batchelder et al.,
• PRC48 (1993) 2593)
• 73Rb
• - half-life T1/2 lt 30ns
• (Janas et al., PRL82 (1999) 295)

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Production

• 92Mo fragmentation at the FRS at 500 MeV/u,
  4g/cm2, 9Be target, 5e9pps
• expected rates
• 73Sr 250 per day
• 69Kr 200 per day
• in same setting
• ? 5-7 days experiment
• ? Factor of 5 more statistics
• than at GANIL for 69Kr
• ? First data for 73Sr decay
• (beyond IAS)
• setup
• DSSSD setup
• Gamma-ray detection

B. Fernandez-Dominguez et al.
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Correlation method

• For any given implant there are uncorrelated
  decay events that follow implantation.
• One of the events will be a true correlation
  while the others are false/uncorrelated.
• SPATIAL CORRELATION Requirement that the implant
  and decay occurs in the same DSSD pixel.
• TIME CORRELATION Requirement that the decay
  occurs within an adjustable time correlation
  window.
• False correlations add to a randomly distributed
  continuous background.