University of Brighton

Isospin purity in the A=38, T=1 nuclei tested via lifetime

measurements in 38K.F. M. Prados Estevez, A.M.Bruce, M.J.Taylor1

University of Brighton

H.Amro, C.W.Beausang2, R.F.Casten, J.J.Ressler3

Yale University

C.J.Barton1

Daresbury Laboratory

C.Chandler, G.Hammond1

University of Keele

Current address: 1 University of York 2: University of Richmond 3: Simon Fraser University

University of Brighton

Systematics of B(E2) values and matrix elements between 2+ (T=1) and 0+ (T=1) states in T=1

isospin triplets.

0+ (T=1)

2+1(T=1)

2+2(T=1)

A=22: Ne, Na, Mg

A=26: Mg, Al, Si

A=30: Si, P, S

A=34: S, Cl, Ar

A=38: Ar, K, Ca

A=42: Ca, Sc, Ti

University of Brighton

Systematics of N=Z=odd nuclei

2+1 -> 0+

2+2 -> 0+

University of Brighton

Is it the right 2+ state?

The energy agrees with the neighbours.

2+ T=1

1+ T=0

38K

38Ca

1+ T=0

0+ T=1

3+ T=0

2206 keV 2167 keV 2403 keV

38Ar

University of Brighton

Comparison across the T=1 triplet

2 * M (Tz=0)

M (Tz=1) + M(Tz=-1)

Data suggests all three values are low but, in fact, it’s hiding something:

(for Tz=0 nucleus)

University of Brighton

The variation of M against Tz Tz defined as (N-Z)/2

38K

38Ca38Ar

University of Brighton

Clearly something of interest in 38K:

7+ T=0 22s

2+ T=1

1+ T=0

1+ T=0

0+ T=1

3+ T=0 38K

Fusion-evap not possible:

3 previous measurements

40Ca(d,) 76 (50) fs

39K (3He,) 54 (25) fs

40Ca(d,) 90 (25) fs

Weighted average = 72 (16) fs

2403 keV

2272 keV 1944 keV

University of Brighton

Experimentalset-up.

Target:220 g/cm2 Ca on aNi backing of 1mg/cm2 . Flash of gold on front face.

d

-particles

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Experimental set up, 8 solar cells ~ 2cm from the target.Angles subtended 1430-1660.

8 clovers (900, 1400) and 2 LEPS (900).

University of Brighton

Angular behaviour of the 1944 keV transition.

University of Brighton

F() value from the 1944 keV transition 0.868 (36)

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Data fitted with a modified version of Dechist.

114 (26) fs

159 (30) fs

Fitted values for the 2403 keV level:

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The variation of M against Tz Provisional data point added for 38K

38Ca38Ar

University of Brighton

Branching ratio of the 2+ state is also important:

1+ T=0

0+ T=1

3+ T=0

2+ T=1

1+ T=0

38K

2403 keV

2272 keV 1944 keV

Ratio from previous work is:

2272 keV: 6.41944 keV: 100

but 1944 is clearly a doublet which we are currently trying tosort out, this will increase the relative strength of the 2272 keV transition. A factor of 2 would take the matrix element to 7.5.

University of Brighton

Shell model calculations

0

5

10

15

20

-1.5 -0.5 0.5 1.5

Tz=(N-Z)/2

M (

efm

^2)

22

26

30

34

38

B.A.Brown et al

Phys Rev C26(1982)2247

sd model space

Chung-Wildenthal

wave functions

University of Brighton

Thanks to all Yale staff for their efforts during the experiment.

University of Brighton

University of Brighton

Dedication

Dave Warner1950-2005