Lifetime measurement of o-Ps in NaI(Tl) scintillator Diana Seitova - - PowerPoint PPT Presentation

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Lifetime measurement of o-Ps in NaI(Tl) scintillator Diana Seitova - - PowerPoint PPT Presentation

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Lifetime measurement of o-Ps in NaI(Tl) scintillator Diana Seitova Hayato Nishimiya Yasunori Sawada Yuta Sato Friday, December 25, 2015 Fourth-year students in the Department of Physics Osaka Univ. Overview 1 . Introduction 2 .

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Lifetime measurement of

  • -Ps in NaI(Tl) scintillator

Diana Seitova Hayato Nishimiya Yasunori Sawada Yuta Sato

Friday, December 25, 2015 Fourth-year students in the Department of Physics Osaka Univ.

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Overview 1 . Introduction 2 . Experimental setup 3 . Results 4 . Analysis 5 . Conclusion 6 . Future

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1.INTRODUCTION

①What is ortho-positronium? ②Theoretical Story ③Motivation

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①What is ortho-Positronium?

Bound state of e and e

+

  • -Ps → ３γ

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  • rtho

para

Spin parallel state (S = 1) Spin antiparallel state (S = 0)

p-Ps → 2γ

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②Theoretical Story

QED prediction :

N(t) = N(0) exp(−t/τ)

Definition of the lifetime τ:

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②Theoretical Story

・Pick-off 2γ ・Spin-flip ・Chemical reaction

Reactions of Positronium with materials

←Silica aerogels with hydroxyl surface are extremely hygroscopic

by Y.S. by Y.S.

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To reduce these reaction, We use SiO2 aerogel

(low density of electron)

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SLIDE 7

③Motivation of our research

・In order to test QED for the bound system.

Purely leptonic, no contamination in low energy !

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2.EXPERIMENTAL SETUP

① Systematic diagram of apparatus ② HV Setup ③ TDC Calibration ④ ADC Calibration ⑤ Testing

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①Systematic diagram of apparatus

Experimental Apparatuses

  • ・Positron Source 22Na

・Silica aerogel ・Plastic scintillator ・NaI(Tl) scintillator ・CAMAC modules

(Density and grain size are unknown.) (thickness = 350μm)

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Experimental Scheme

by Y.S.

Trigger (Start) TDC Stop ~50mm

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Arrangement

by Y.S.

Silica aerogel sensitive volume PMT NaI(Tl)

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22Na Source

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②HV Setup

  • Determination of applied voltage for each PMT by

measuring the plateau curve.

0.2 0.4 0.6 0.8 1000 1400 1800 2200 2600

Voltage [V] SCA[012]/SCA[12] Gain Adjustment of NaI(Tl) #0

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SLIDE 16

・The threshold voltage for discriminator is the minimum value of the specification.

HV (V)

  • Trig. Plastic

1200 NaI #0 1600 NaI #1 1600 NaI #2 1450 V_TH (mV)

  • Trig. Plastic

60 NaI #0 30 NaI #1 30 NaI #2 30

・We determined the voltages to apply to PMTs, seen from plateau curve.

※For trig plastic, chosen voltages signal being visible. ※For trig plastic, chosen the level to remove noise.

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③TDC Calibration

Block diagram for TDC calibration

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③TDC Calibration

TDC value [ch]

20 40 60 80 100 120 140

delay time [nsec]

10 20 30 40 50 y = 3.7862x - 60.319

Time[nsec] = TDC[ch] + 60.319 3.7862

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④ADC Calibration

Block diagram for ADC calibration.

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ADC Calibration with energy

ADC

Counts

NaI #0

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④ADC Calibration

Energy [keV] NaI #0 [ch] NaI #1 [ch] NaI #2 [ch] 106.8±0.0 53.82±0.01 109.5±0.0 511.0 1167±0.3 1035±0.3 1221±0.3 661.7 1498±0.4 1302±0.4 1579±0.5

E0[keV ] = (0.477 ± 0.005) × ADC[ch] − 50 ± 6 E1[keV ] = (0.528 ± 0.008) × ADC[ch] − 30 ± 7 E2[keV ] = (0.453 ± 0.008) × ADC[ch] − 48 ± 9

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⑤Testing

First, ・We must check whether ortho-positronium is really formed in Silica aerogel. We collected 3 million events in 12/18 ~ 20 using Aerogel, And for comparison, collected 1 million events in 12/21 without aerogel.

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Block diagram

  • f the data-acquisition electronics

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3.RESULTs

  • TDC Histogram (Time distribution)
  • ADC Histogram (Energy spectrum)
  • Correlation plot

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Time distribution

with aerogel

NaI #0 NaI #1 NaI #2

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Time[ns]

Counts

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Energy spectrum

NaI #0 NaI #1 NaI #2

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with aerogel

Energy[keV]

Counts

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Correlation plot

NaI #0 NaI #1 NaI #2

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with aerogel

Energy[keV]

Time[ns]

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Time distribution

without aerogel

NaI #0 NaI #2 NaI #1

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Time[ns]

Counts

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Energy spectrum

without aerogel

NaI #0 NaI #2 NaI #1

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Energy[keV]

Counts

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Correlation plot

without aerogel

NaI #2 NaI #0 NaI #1

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Energy[keV]

Time[ns]

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4.ANALYSIS

  • Time Walk Correction
  • Lifetime
  • Effect of Aerogel

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Time Walk Correction

h ∝ Energy Time = A Energy + B

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Time Walk Correction

  • aerogel

NaI#0 NaI#1 NaI#2 Fitting range : 200~500keV

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Energy[keV] Time[ns]

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Time Walk Correction

  • aerogel

NaI#0 NaI#1 NaI#2

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Time[ns] Energy[keV]

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Time Walk Correction

  • without aerogel

NaI#0 NaI#1 NaI#2

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Time[ns] Energy[keV]

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Lifetime

Blue : aerogel Red : without aerogel NaI#0 NaI#1 NaI#2

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Time[ns] Counts

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Lifetime (30~200keV)

Blue : aerogel Red : without aerogel NaI#0 NaI#1 NaI#2

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Counts Time[ns]

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Lifetime (200~450keV)

Blue : aerogel Red : without aerogel NaI#0 NaI#1 NaI#2

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Counts Time[ns] : Fitting range

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Lifetime (200~450keV)

・NaI#0 (Fit : 130~210ns)

  • ・NaI#1 (Fit : 140~220ns)
  • ・NaI#2 (Fit : 130~210ns)

aerogel : 141±16 [ns] without aerogel : 132±28 [ns] aerogel : 146±17 [ns] without aerogel : 118±26 [ns] aerogel : 140±15 [ns] without aerogel : 160±38 [ns]

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Lifetime (450~900keV)

Blue : aerogel Red : without aerogel NaI#0 NaI#1 NaI#2

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Counts Time[ns]

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The Energy Sum

・Peak Energy aerogel : 919.5±6.0keV Blue : aerogel Red : without aerogel without aerogel: 917±17keV

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cut:200～450keV for each channel

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5.CONCLUSION

  • Peak of energy sum event is not so different

between with aerogel and without aerogel.

  • On the energy sum plot, We couldn’t get

expected peak(around 1MeV)

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6.FOR FUTURE

  • To reduce 2γ events.
  • To understand strange peak in TDC.
  • Difference between “with aerogel” and

“without aerogel.

  • To change the condition of aerogel.
  • Trying to set a vacuum condition.

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2γ Events

So many events around 500keV

NaI#2 NaI#1 NaI#0

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counts Energy(keV)

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2γ Events

There are many gap around scintillator →We will change the position of leads block

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Strange peak

strange peak around 350ns NaI#0 NaI#2 NaI#1

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Time(ns) counts

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Strange peak

strange peak around 250ns NaI#0 NaI#1 NaI#2 Time walk version

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Time(ns) counts

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Time correlation

NaI#0:NaI#1 NaI#0:NaI#1(time walk) There is no correlation between two NaI’s

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NaI(1) Time(ns) NaI(0) Time(ns)

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Strange peak

The problem is caused by This part

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Energy Sum Events

Blue : aerogel Red : without aerogel

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We have little time for analysis. To get certain difference between with aerogel and without aerogel, We will analyze more than now

Energy[keV]

counts

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Any other for future

  • Aerogel is now wet, so we will dry it.
  • When we get good 3γ data, we will try to set

a vacuum condition.

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Thanks for your attention!

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References

[1]今坂俊博, 原口弘, 森哲平, “大気中でのオルソポジトロニウムの寿命測定” (2015) [2]宮崎康一, 山内洋子, 矢島和希, “大気中でのオルソポジトロニウムの寿命測定” (2014)

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Positron Deposition Energy in plastic

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Positron Deposition Energy in plastic

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③Theoretical Story

Disintegration of Positronium C-Parity of two spin-1/2 particles state:

C = (−1)L+S

L = 0

At ground state,

C = ⇢ 1 (S = 0) −1 (S = 1)

n photons have odd C-parity ; Conservation of C-parity

paraPs(S = 0) → 2γ, 4γ, 6γ, ...

  • rthoPs(S = 1) → 3γ, 5γ, 7γ, ...

Cγ = (−1)n