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

β decay of 69Kr and 73Srand the rp process

Bertram BlankCEN Bordeaux-Gradignan

Bertram Blank PRESPEC meeting, Brighton, 12-13 January 2011

MotivationMotivation

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”.


6969Br and the Br and the rprp process 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


Previous measurementsPrevious measurements

Non-observation: Upper limit on the 69Br lifetime estimated from 78Kr fragmentation cross sections

T1/2<100 ns Sp < -450 keV (Blank et al., 1995)

T1/2<24 ns Sp < -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 = -785+35-40 keV

(A.M. Rogers et al., 2011)

P. Schury et. alA. M. Rogers et al.


Populating Populating 6969Br via Br via 6969Kr β decay Kr β decay Method: Populate the 69Br g.s. in

the β decay of 69Kr and look at β-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.


SetupSetup Fragmentation of 78Kr

primary beam. E=70 MeV/A

Intensity ~ 3-4 eμA. Utilized the LISE3

spectrometer with an Al (100μm) degrader and a Wien filter.

CSS1CSS2

LISE3

DSSSD

MCP

EXOGAMClovers

Implant-decay experiment using β-p and β-γ 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).γ's are measured using four germanium

clover detectors. ΔE

E

ToF

LISE Target: natNi 200 mg/cm2

CENBG, GANIL, ANL


Identified 211 69Kr implantation events →87 69Kr/day.

Clean PID based on redundant identification parameters.

Fragmentation of 78Kr primary beam.

E=70 MeV/A Intensity ~ 3-4 eμA.

Utilized the LISE3 spectrometer with an Al (100μm) degrader and the Wien filter.

SetupSetup


Measurements of known half-livesMeasurements of known half-lives

Known T1/2(62Ga) = 116.12 (23) ms.

Negligible additional decay components.

Known T1/2(67Se) = 136 (12) ms

So far there is good agreement with most easily measured half-lives.


6565Se β decay preliminary resultsSe β 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.


6969Kr β decay preliminary resultsKr β decay preliminary results



Half-life previously measured by X.J. Xu et al, Phys. Rev. C R533, 1997 of T1/2=32 (10) ms.

Also claimed to observe a single proton group at 4.07 (0.05) MeV.

X. J. Xu et al, Phys. Rev. C 533, 1997


6969Kr β decay proton spectrumKr β decay proton spectrum



We observe proton decays to excited states.

However, IAS is observed at E=2.97 MeV.

We do not observe 69Br ground-state proton decays.





We observe proton decays to excited states.

However, IAS is observed at E=2.97 MeV.

We do not observe 69Br ground-state proton decays.


Level SchemeLevel Scheme


69Kr

73Sr

73Rb

72Kr

69Br

68Se

Measurement aims: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 < 30ns

(Janas et al., PRL82 (1999) 295)


Production: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.


Correlation methodCorrelation 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.

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

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