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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
Introduction
Lifetime is an important parameter in nuclear structure. 1st excited state of 57Fe:
1 = 122 keV
2 = 14.4 keV
3
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
4
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
7
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
8
Procedure (4)
Adjust delay time of SCA:
DET A AMP SCA
DISCR.
DISCR.
TAC MCA
NEG.
Start
StopSCANEG.
9
Procedure (5)
Time spectrum measurement:
NEG.
DISCR.AMP SCA
DET A AMP SCA DISCR.
TAC MCAStart
StopNEG.
DET B
10
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
12
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
15
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, …
16
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 …
17