2 Decay of 150 Nd, Preliminary Results (PhaseI data)

Nasim Fatemi-Ghomi, Dubna meeting 17-20 September 2006

2 Decay of 150Nd, Preliminary Results

(PhaseI data)

Nasim Fatemi-Ghomi


Introduction

Background study of 150Nd2• A study of the 207Bi and 214Bi background in the e-channel.• A study of the 210Bi, 207Tl+211Pb and 234mPa background in the e-channel.• Cross check external background with Cu foil.

Extraction of half-life of 150Nd2

Data Selection

• Good betbeta runs between 2019-3395 (phase I).• Data taking time =2.8836 x 107s = 0.91 yrs.• Events should come from Nd2O3. The foil has 57g mass (37gr pure 150Nd).


Internal BackgroundInternal Background

Bg Act(mBq/kg) Ge measurement

Modane-Baksan

Found from 1e channel slide 8

210Bi 368.42 -

207Tl 163.0 -

211Pb 163.0 -

234mPa 84.4 -

Found from eChannel slide 6

207Bi 235 128 - 120

Fround from e + Slide 7

214Bi 15.3 < 3 - 20

V.Tretyak(Aussois 2005)

40K 66.7 < 6.6 - 9.6

V.Vasiliev (Dubna 2004)

208Tl 7.95 9.6 - 5

228Ac 22.1 20 - 15

212Bi 22.1 -

Ge measurement

152Eu 38.3(modane) 21.6(Baksan)

External Background &External Background & Background on the SurfaceBackground on the Surface of the Wires and Foils.of the Wires and Foils.

Bg Act(Bq)

SW 214Bi 0.623

SW 214Pb 0.623

SF 214Bi 0.0185

SF 214Pb 0.0185

PM 214Bi 374

PM 214Pb 374

PM 228Ac 515

PM 60Co 50.7

PM 40K 954

Air 214Pb 702

Air 214Bi 702

Found byFound byV.Vasilev V.Vasilev checkedcheckedwith Cu foilwith Cu foilSlide 9Slide 9


207Bi and 214Bi Background Studies

Pre-Selection Cuts for e-channel:• One negatively charged track associated with an isolated PMT (E(e)> 0.2MeV).• Only one cluster with E()> 0.2MeV. No other with E()> 0.15MeV.• Internal TOF hypothesis for e events > 5% & external hypothesis < 1%.• Tracks must have one hit in one of the two first layers of GG.

Cos(e) < 0.9


Fit Fit 207207Bi with the data minus backgroundBi with the data minus background

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Activity ofActivity of 207 207BiBi

In addtion to the pre-selection criteria described there should not be any single or In addtion to the pre-selection criteria described there should not be any single or group delayed hit(s) in the tracker. group delayed hit(s) in the tracker.


Look at the energy region 0.7 MeV< Ee <1.1 MeV and 0.25 MeV< ELook at the energy region 0.7 MeV< Ee <1.1 MeV and 0.25 MeV< E <0.6 MeV <0.6 MeV where where 207207Bi dominated over all other backgrounds.Bi dominated over all other backgrounds.

AA207Bi207Bi=13.4 ± 0.3 mBq ~ 235 ± 5 mBq/kg =13.4 ± 0.3 mBq ~ 235 ± 5 mBq/kg


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Activity of Activity of 214214Bi Bi

Events should accompany with an alpha particle (delayed or single hits.) Events should accompany with an alpha particle (delayed or single hits.)

AA214Bi 214Bi = 0.87 = 0.87 0.17 mBq ~ 15.26 0.17 mBq ~ 15.26 2.98 mBq/kg 2.98 mBq/kg






1e Channel1e Channel

Selection cuts:Selection cuts:• One track with negative charge associated with isolated PMT.One track with negative charge associated with isolated PMT.• Track has to have a reconstructed vertex.Track has to have a reconstructed vertex.• E(e) > 0.5 MeV. E(e) > 0.5 MeV. • Track has to have a hit in one of the first two layers of GG.Track has to have a hit in one of the first two layers of GG.





mBq

210Bi 21.0 0.3 0.3

207Tl 9.29 0.15 0.15

211Pb 9.29 0.15 0.15

234mPa 4.81 0.050.05


External backgroundExternal background

The external background activity found by V.Vasiliev is checked with The external background activity found by V.Vasiliev is checked with looking at the energy distribution of the energy of e- looking at the energy distribution of the energy of e- events coming from events coming from the Cu foil. the Cu foil.

Data = 35524±188, Total Background=34251± 382Data = 35524±188, Total Background=34251± 382Data-Background= 1273 ± 425 -> has to be added to the Data-Background= 1273 ± 425 -> has to be added to the systematic uncertainty.systematic uncertainty.






150150Nd Half-lifeNd Half-life

Pre-selection for Pre-selection for 150150Nd to 2Nd to 2 events: events:• Two negatively charged tracks associated with isolated PMTs and E1 ,E2 > 0.2 MeV.• Both electrons originate from a common vertex with |∆r| < 2 cm & |∆z| < 4 cm.• Internal TOF hypothesis > 4% & external TOF hypothesis < 1%.• Track starts from layers 1 & 2 of GG.• No delayed alpha decay with refiring time > 70 s.• No single or group delayed hit(s).










ResultsResults

Number of data events: 1011

Number of total background: 315

Efficiency =133643/2000000 6.68%

T12= (9.04 -0.57+0.63(stat) +- 0.40 (Act)+- 0.78 (syst)) x 1018 y

Documents

2 Decay of 150 Nd, Preliminary Results (PhaseI data)