the b -delayed deuteron-decay of 6 he

The -delayed deuteron-decayof 6He

J. Ponsaers, R. Raabe, F. Aksouh, D. Smirnov, I. Mukha, A. Sanchez, M. Huyse, P. Van Duppen, C.

Angulo, O. Ivanov, J.C. Thomas

1. Introduction2. Experiment3. Analysis4. Conclusion

Discovered in 1985: high interaction cross section.[1]Extended matter distribution.6He is a Borromean system of + n + n

6He

E

r

Usual probability density of a neutron

E

r

Probability density of a halo neutron

6He = 2n-halo-nucleus

[1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)

II

I

Discovered in 1985: high interaction cross section.[1]Extended matter distribution.6He is a Borromean system of + n + n

6He

E

r

Usual probability density of a neutron

E

r

Probability density of a halo neutron

6He = 2n-halo-nucleus

[1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)

II

I

Discovered in 1985: high interaction cross section.[1]Extended matter distribution.6He is a Borromean system of + n + n

6He

E

r

Usual probability density of a neutron

E

r

Probability density of a halo neutron

6He = 2n-halo-nucleus

[1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)

We want to measure: • Branching ratio of the decay channel II: very small (~10-6) very difficult• Energy spectrum of the decay particles E+d

Information provided by the deuteron-branch of 6He

1. High branching ratio dineutron correlation

Information provided by the deuteron-branch of 6He

1. High branching ratio dineutron correlation2. Low branching ratio cigar correlation

Information provided by the deuteron-branch of 6He

Reference Branching ratio (10-6)

E d >E 0

Cutoff energy E 0 (lab), keV

[1] Isolde (1990) [2] Isolde (1993) Triumf (1994) [3] Triumf (2002) [4] Two Center Cluster Model [5] Three-Body (,n,n) Model (hypersph. co.) [6] Dynamical Microscopic Cluster Model

2.8(5) 7.6(6) 1.8(9)

2.6(1.3)

200

30-40 3.1

250 350 350

0

250

350

[1] K. Riisager et al., Phys. Lett. B 235(1990)30[2] M. J. G. Borge et al., Nucl. Phys. A 560(1993)664[3] D. Anthony et al. Phys., Rev. C 65(2002)034310

[ 4] P. Descouvement and C. Leclercq- Willain, J. Phys. G 18(1992)L99[5] M. V. Zhukov et al., Phys. Rev. C 47(1993)2937[6] A. Csoto and D. Baye, Phys. Rev. C 49(1994)818

[6] suggests that we need a detailed description of thewave functions to explain the decay.

1. High branching ratio dineutron correlation 2. Low branching ratio cigar correlation

The methodProblems in previous experiments:•High threshold energies for deuterons •Large uncertainties (difficult to normalize)

The methodProblems in previous experiments:•High threshold energies for deuterons•Large uncertainties (difficult to normalize)

New method: 6He implantation in DSSSD(Double Sided Silicon Strip Detector)This can count implantations AND + d decays

The method

DSSSD divided into 48 strips x 48 strips = 2304 pixelsSmall pixel size (300m)

•Get the energy drop of -particles below the spectrum of the br.ratio•No problem for + d detection

Problems in previous experiments:•High threshold energies for deuterons•Large uncertainties (difficult to normalize)

New method: 6He implantation in DSSSD(Double Sided Silicon Strip Detector)This can count implantations AND + d decays

The experiment

Beam on (1s): implantation and detection of 6He nuclei number of implantations counted absolute normalization for br.rat. very accurate

Beam off (2s): detection of decay of 6He nuclei caught inside the detector

6He nuclei at 8 MeV periodically implanted into DSSSD detector.

Experiment: performed at CRC, Louvain-la-Neuve, Belgium

Analysis

1. -peak2. 6He implants3. partial E-collection

Beam on + off E (keV)

21

(Num

ber

of e

vent

s)/(

10ke

V)

3

Beam off E (keV)

(Num

ber

of e

vent

s)/(

10ke

V)

1

Analysis

1

Time spectrum exp. fit 1: T1/2 = 806.0ms

1. -peak2. 6He implants3. partial E-collection4. + d events

Beam on + off E (keV)

21

(Num

ber

of e

vent

s)/(

10ke

V)

3

4

Beam off E (keV)

(Num

ber

of e

vent

s)/(

10ke

V)

1

Analysis

1

Time spectrum exp. fit 1: T1/2 = 806.0ms

1. -peak2. 6He implants3. partial E-collection4. + d events

Beam on + off E (keV)

21

(Num

ber

of e

vent

s)/(

10ke

V)

3

4

Suspicious: background much higher than expected!

Beam off E (keV)

(Num

ber

of e

vent

s)/(

10ke

V)

1

Analysis

Beam off E (keV)

1

4

1

4

Time spectrum exp. fit 1: T1/2 = 806.0ms2: T1/2 = 1102ms

1. -peak2. 6He implants3. partial E-collection4. + d events

Beam on + off E (keV)

21

(Num

ber

of e

vent

s)/(

10ke

V)

(Num

ber

of e

vent

s)/(

10ke

V)

Suspicious: background much higher than expected!

3

4

Beam off E (keV)

(Num

ber

of e

vent

s)/(

10ke

V)

1

Beam off E (keV)

1

4

1

4

Time spectrum exp. fit 1: T1/2 = 806.0ms2: T1/2 = 1102ms

1. -peak2. 6He implants3. partial E-collection4. + d events

Beam on + off E (keV)

21

(Num

ber

of e

vent

s)/(

10ke

V)

(Num

ber

of e

vent

s)/(

10ke

V)

Suspicious: background much higher than expected!

2.New fit:

162 ± 69 background events 425 + d events

3

4

Analysis

•Total branching ratio: W = (2.03 ± 0.35) x 10-6

•Corresponds with the value from microscopic description

•Large uncertainty from background events.

•No reliable energy spectrum of + d because we don’t know the energy spectrum of the background.

Conclusion and outlook

•New measurement on 6He in Louvain-la-Neuve

•Same experiment on 11Li at TRIUMF