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

Tennessee3 Physics Division, Oak Ridge National Laboratory

4 Department of Physics, University of Liverpool5 Department of Physics and Astronomy, Vanderbilt University

6 Department of Physics, University of Maryland7 Department of Physics, Mississippi State University

8 Institute of Experimental Physics, Warsaw University9 Joint Institute for Heavy-Ion Reactions, Oak Ridge

10 Institute of Nuclear Physics, Polish Academy of Sciences11 East Tennessee Technical University

an island of -radioactivity above proton-rich Sn isotopes due to the Z=50 and N=50 shell closures

N=82

N=50

Z=50

Z=82

N=126

-decaynear proton and neutron

shell closures

Z

N

Z=

50

Z=

50

N=50N=50

109I

109Xe CN112Xe*

105Te

N=Z

101Sn

109I

105Sb

Search for new alpha emitters above Search for new alpha emitters above 100100Sn: Sn: 109109Xe, Xe, 105105Te, Te, 109109II

• 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]

109I decay and 105Sb

Z=

50

Z=

50

N=50N=50

109I109I

104Sn

105Sb

108Te

Q = 3445 keV

b ~50%[Schardt et al., NPA326 (1979)]

p

109I

108Te

105Sb

104Sn

100 s

1.12 s p

b < 0.5 %

[Page et al., PRL49 (1994)]

Qp=483 keV< 1%[Tighe et al, PRC49 (1994)]

Qp=820 keV bp=100%

[Faestermann et al., PLB137 (1984)]

Termination of the astrophysical rp-process

Z=

50

Z=

50

N=50N=50

109I

• 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.

105Sb

Schatz et al, PRL 86, 3471 (2001)

HRIBF

• Fusion-evaporation reactions 54Fe(58Ni,3n)109Xe ~8 part.nA

• Recoil Mass Spectrometer used to separated out reaction products based on A/Q.

Excitation function of Excitation function of 110110Xe and Xe and 109109Xe:Xe:

HIVAP vs experiment

Test run (RIB000)preliminary

LARGEMCP

SMALLMCP

DSSD

109/29+

109/28+

40 x 40 strips

1600 pixels

109/29+109/28+

109

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.

(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.

Thick Si(Li) and Four Si detectors around the DSSD

Digital ElectronicsDigital Electronics• DSP-based data acquisition system (UT/ORNL/UNIRIB):

→ recording pulse shapespulse shapes (traces) for single and pile-up -

decay events (109Xe 105Te 101Sn)

→ method very selective selective (identify 100 events among 4.4*10(identify 100 events among 4.4*1088

implanted ions and 1.7*10implanted ions and 1.7*1077 decays). decays).,

→ very sensitivesensitive (T between two pile-up traces covers wide

range) very small dead time small dead time (<15% at ~3 kHz

ions and ~150 Hz traces)

109Xe

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 s obtained for offline analysis.

109Xe milliseconds ns

700ns

109Xe

105Te

Information recorded

EnergyTime

implantationevent

> 9.2 MeV

decay event< 9.2 MeV

Time (not to scale)

400

600

800

Am

plitu

de

(23

keV

/ch

) 35 55 75Time (25 ns/ch)

Energy deposited in DSSD

109Xe → 105Te → 101SnExample of pile-up traces

Back Strip

Front Strip

105Te

109Xe

0.275s

50003500 45004000

10

20

0

0

109Xe 105Te

105Te 101Sn

Energy (keV)

10

20

Alpha energy spectra

3.918 MeV

4.062 MeV

4.703 MeV

• 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.

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.

[1] K.-H. Schmidt et al., Z. Phys A, 316, 19 (1984)

620

109Xe → 105Te → 101Sn

l=2l=0

(7/2+)

(5/2+)

(5/2+)

(7/2+)Ea = 4.062 MeV

ba = 70%

Ea = 3.918 MeV

ba = 30%

Ea = 4.703 keV

ba = 100%

0.15 MeV

13132 ms2 ms

620 620 70 ns70 ns

1.9 s

l=0

109Xe5554

105Te5352

101Sn5150

Ratio of half-lives:1:20000

Systematics of 7/2+ and 5/2+

levels

• In a simple single-particle shell model, energy separation between d5/2 and g7/2 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.

109I

SummarySummary

• 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 forwardLooking forward• Search for fine structure in 105Te alpha

decay to 101Sn and identification of d5/2 and g7/2 energy separation in 101Sn.

• Discover 108Xe →104Te →100Sn alpha decay chain: best case for superallowed alpha decay.