LIFETIME MEASUREMENT

Advanced experiment group: Le Cong HaoTran Hoai NamTran Duy TapTran Thien ThanhDang Ngoc ThangGuo WeiHu JunZhao Pengwei

The primer course of experimental particle and nuclear physicsOsaka University – 2009

Outline

Introduction Principle of lifetime measurement Procedure Results

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Introduction

Lifetime is an important parameter in nuclear structure. 1st excited state of 57Fe:

1 = 122 keV

2 = 14.4 keV

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Principle of lifetime measurement (1)

Impossible to predict the lifetime of an nucleus, but mean lifetime can be determined

Lifetime of unstable nucleus follows the decay law:

( ) tN t e

0 0

1( ) tt tf t dt te dt

1/2

ln 2T

( ) tf t e

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Principle of lifetime measurement (2)

Using TAC (Time to Amplitude Converter)

1

2

DET 1

DET 2

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Procedure (1)

Setup:

NEG.

DISCR.AMP SCA

DET A AMP SCA DISCR.

TAC MCAStart

StopNEG.

DET B

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Procedure (2)

Select two gamma rays: same method as experiment 1

coinc.

AMP DELAY

SCA(NORM)

MCADETBiPol signal

POS.

Det A: •HV = -900V•Gain: coarse 40, fine 3.5•Window: - upper level = 9V

- lower level = 7VDet B: •HV = +1000V•Gain: coarse 40, fine 6•Window: - upper level = 1.4V

- lower level = 0.8V

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Procedure (3)

Time to channel calibration:

Delay unit: 0 ÷ 500 ns

DET AMP SCA

Delay DISCR.

DISCR.

TAC MCA

NEG.

Start

Stop

0.27218 0.04545y x

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Procedure (4)

Adjust delay time of SCA:

DET A AMP SCA

DISCR.

DISCR.

TAC MCA

NEG.

Start

StopSCANEG.

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Procedure (5)

Time spectrum measurement:

NEG.

DISCR.AMP SCA

DET A AMP SCA DISCR.

TAC MCAStart

StopNEG.

DET B

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Result (1)

Time spectrum:

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Result (2)

Calculating: Estimate background NBG

Subtract BG:

Convert to logarithmic scale

Linear fit using least square method

Estimate error

,i m i BGN N N

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Result (3)13

Result (4)

Another method to calculate:

Result (5)

Half life time: Measured value:

1st method: 2nd method:

Reference value: Other groups’ results:

1/2 100.65 2.46 nsT

98 ns

96.01 2.61 ns

116.47 16.25 ns

96.525 0.825 ns

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95.00 ± 3.79

Summary

In this experiment, we have measured the lifetime of 1st excited state of 57Fe by using TAC.

Lifetime can be measured by other methods: delayed coincidence, …

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Summary

In this experiment, we have measured the lifetime of 1st excited state of 57Fe by using TAC.

Lifetime can be measured by other methods: delayed coincidence …

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Acknowledgement

Osaka University JICA Professors and TAs My partner and coincidence group

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Thanks for your attention!

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