Positron Age-Momentum Correlation with two detectors

B.Y. Wang, Z. X Li

Key Laboratory of Nuclear Analysis Techniques (LNAT)

Institute of High Energy Physics (IHEP)

Chinese Academy of Sciences (CAS)

Beijing 100049, China

Key Laboratory of Nuclear Analytical Techniques (LNAT)

-Chinese Academy of Sciences

Introduction of LNAT

•Development of New techniques in field of nuclear analysis•Application of nuclear techniques

Collectivity orientationCollectivity orientation

The Positron Group in IHEP

Methodology study of positron annihilation techniques

Construction of Positron beam & positron annihilation measurements

Application research in material scienceTechnicology support on Gama-ray

detection for nuclear imaging

Positron Annihilation in IHEP

Linac-based beam

22Na-based beam Doppler Broadening,, o-Ps self-decay intensity

High-resolution positron lifetime spectrometer

AMOC

Coincidence Doppler Broadening

Positron lifetime spectrometer

Doppler Broadening, Lifetime measurement, positron scattering, CDB, AMOC, Ps-TOF

Conventional positron annihilation spectroscopy

High performance

Multi-parameter measurement

Basic measurement

Multi-parameter techniques

CDB, Coincidence Doppler broadening SpectroscopyAMOC, Positron Age-Momentum Correlation2D-PALS, Positron Age-Pulse Height Correlation

2D-PALS

K. Sato, et al, Materials Sci. Forum. 607(2009) 53-57K. Sato, et al, Materials Sci. Forum. 607(2009) 53-57

The momentum distribution of o-Ps pick The momentum distribution of o-Ps pick off annihilation sensitively depends on off annihilation sensitively depends on the electronic states. the electronic states.

Chemical environmentChemical environment

0 5 10 15 20 250.47

0.48

0.49

0.50

0.51

0.52

0.53

0.54

0.55

0.56

0.57

S p

aram

eter

Positron Age (ns)

before after defect-free Si bulk

Oxidation-water vapor annealing for porous Si

AMOC: Powerful tool for study positronium

Physical for multi-parameter measurement

• Reducing the background - Separate the real events in a “noisy” environment

• Increasing the amount of valid information - improve the resolution

Positron annihilation ==Positron annihilation ==> Size of open volume + intensity Size of open volume + intensity + element species+ element species

AMOC

Triplex coincidence & Counting RateTriplex coincidence & Counting Rate

Start

Doppler spectrum

HPGe PMT

PMT Lifetime

AMOC

Sample

22Na

e+

??

Stop

AMOC

673

TAC(567)DoubleADC unit

PC

CFDD

Fast-Coincidence 414A

LinearGate426

HpGe

2mm Pb 片

863

CFD

Enable

Input

DelayCFDD

BaF2

(Stop)

BaF2

(Start)

22Na&Sample

Ext trig

energy window + energy window + detector shape & detector shape & geometrygeometry + + Pile-up reject Pile-up reject =>=> high Counting Ratehigh Counting Rate

AMOC

Coin. Cout. rate ： ~200 cps/40Ci Res. LT ～ 218 ps Ener. Res. Doppler ～ 1.2 keV

A

B

C

Why? two detector AMOC

•Good time resolution •High intensity of 22Na •PMT decline need to consider

• Much hiMuch high counting rate • Simple electronicsSimple electronics• Feasible time resolution for Long

lifetime measurements (o-Ps)• ~Slow positron beamline

startstartStop & energyStop & energy

Two detector AMOC

Two detector AMOC

400 600 800 1000 1200 1400 1600 1800 20001

10

100

1000

10000

C

ou

nts

/log

Channel(25.88ps/chn)

FWHM:85.41chn(2.21ns)

16ns16ns

Two detector AMOC

-10 0 10 20 30 40 501

10

100

1000

10000

Co

un

ts/lo

g

Lifetime(ns)

Ni PTFE SiO2

Two detector AMOC

Function of home made 2D-MCA

Two detector AMOC

PTFE PTFE NiNi

FWHM=2.21nsFWHM=2.21ns

Count rate= 200cps (10μCi)Count rate= 200cps (10μCi)

Two detector AMOC

0 200 400 600 800 10000

200

400

600

800

1000

1200

24

32

40

48

56

Co

un

t ra

te /

cp

s

CFD lower level / mV

Lifetime count rate Lifetime time resolution

FW

HM

/ c

hn

(5

1.7

6p

s/ch

n)

Φ44 ×30 mm

Larger BaF2 scintillator Larger BaF2 scintillator

detect efficiency increase ~75% Counting rate ~28 cps/μCi. Time resolution ~ 2.2ns.

Φ30×20 mm Volume increase to 3.06 times

Counting rate ~20 cps/μCi. Time resolution ~ 2.2ns.

Start detector scintillator

multi-parameter unit (2D-MCA)

RJ45 PHY FPGA

ADC14bit 50MHz

ADC14bit 50MHz

A 通道模拟信号

B通道模拟信号

3.3V触发信号

10V触发信号

PC

ADdriver

ADdriver

滤波

甄别

符合

触发

输出控制 网络传输

Double-ADC hardware design schematics Schematic diagram of FPGA data processing

multi-parameter unit

Time relation of the signalsDiscriminate level setting

峰宽过大，坏事例被滤除峰宽过大，坏事例被滤除 无法由峰宽条件滤除坏事例无法由峰宽条件滤除坏事例

触发电平

触发电平

最小峰宽最大峰宽

有效事例有效事例

无效事例无效事例

无效事例无效事例

触发电平

触发电平

触发电平

Specification of the 2D-MCA

1, waveform test mode (oscillograph) display A, B signals waveforms. 2, multichannel analyzer (MCA) (16000 channel)

A or B channel, respectively. equivalent to conventional multi-channel analyzer. Gaussian or square wave waveform (lifetime spectrum or energy spectrum). 3, CDB mode (4096 ch x 4096 ch) Inner trigger or external trigger mode for positron annihilation coincidence Doppler broadening measurements. 4, AMOC mode (4096 ch x 4096 ch)

Inner trigger or external trigger mode for positron annihilation age-momentum corelation measurement. 5, playback mode Open the previously stored measurement data files, and data analysis or conversion.

Specification of the 2D-MCA

Simplified the electronics and adjusting of system PAL + DB = AMOC Counting rate ~ 300 cps/50Ci

673

TAC(567)DoubleADC unit

PC

CFDD

Fast-coincidence

HpGe

2mm Pb 片

DelayCFDD

BaF2

(Stop)

BaF2

(Start)

22Na&Sample

Gate or strobeGate or strobe

Ch ACh ACh BCh B

USB2.0USB2.0

Inner trigger AMOC mode (ch A)Use TAC output (ch A) selects the energy output (ch B)

CDB Measurement Block Diagram

样品和 22Na

HPGe HPGe

定时虑波放大器

恒比定时

延时

定时虑波放大器

恒比定时

时幅转换器

单道分析器

符合

主放大器放大器

单道分析器

放大器主放大器

单道分析器

计算机多道ADC ADC

Gate

Time select + energy window + coincidence + Pile-up rejectTime select + energy window + coincidence + Pile-up reject

Specification of the 2D-MCA

DB + DB = CDBHigh counting rate with better performance

Inner trigger CDB mode

Sample & 22Na

HPGe HPGe

AMP

Double ADC Unit

PC

AMP

Usb2.0Usb2.0

B A

Specification of the 2D-MCA

3000 3500 4000 4500 5000 55000.52

0.53

0.54

0.55

0.56

0.57

0.58

0.59

0.60

0.61

0.62

S p

aram

eter

Channel

wai nei

internal trigger external trigger

counting rate 206cps 72cps

CountsPeak Background Peak Background

6686 0.0452 7136 0.0410

Peak-background ratio 1.4792×105 1.7405×105

total counts 11,960,000 10,400,000

internal triggerexternal trigger

Monocrystal SiMonocrystal Si

No obvious difference observed

Three Three detector detector

AMOC AMOC systemsystem

Summary Summary 1.1. Increase the Increase the efficiency of start detectorefficiency of start detector is very important to is very important to

improve the coincidence count rate for an (three or two improve the coincidence count rate for an (three or two detectors) AMOC measurementdetectors) AMOC measurement

2.2. Two detector AMOC can increase the counting rate remarkable Two detector AMOC can increase the counting rate remarkable with about 2ns FWHM of lifetime resolution.with about 2ns FWHM of lifetime resolution.

3.3. FPGA data bus (2D-MCA) can simplify the NIM for multi-FPGA data bus (2D-MCA) can simplify the NIM for multi-parameter measurements (CDB, AMOC)parameter measurements (CDB, AMOC)

4.4. AMOC become easier on a slow positron beamline with high AMOC become easier on a slow positron beamline with high efficiency!? efficiency!?

AMOC

BaF2

(Start)

2mm Pb 22Na+sample

HPGe

B

aF2

(S

top

)

Counting rate of Stat detector is much more important for lifetime & energy triplex coincidence!

Get high Counting RateGet high Counting Rate ！！

0 5 10 15 20 250.47

0.48

0.49

0.50

0.51

0.52

0.53

0.54

0.55

0.56

0.57

S p

ara

me

ter

Positron Age (ns)

before after defect-free Si bulk

Oxidation-water vapor annealing for porous Si

sample τ1/ns τ2/ns τ3/ns τ4/ns I1/% I2/% I3/% I4/%

before 0.224 1.116 33.03 81.8 4.38 13.65

after 0.214 0.511 2.34 35.5 62.3 27.1 9.37 1.2

CDB

Work Mode Inner trigger External triggerPile-up reject Pile-up reject

Count rate~ 100 cps 3.5×105 2.7×106 1×106 3.6×106

Count rate > 200 cps 1.5×105 4×105 2.75×105 1.6×106

Ver 2Ver 2 Ver 1Ver 1

Coincidence Doppler broadening

ET=2m0C2-EB E=(E2-E1)CP Element species information at site of

annihilation resolution improved 2

E 1 - E

2 =

0

E1

E2

E1 + E

2 = 2m0 c 2- E

B

E 1 - E

2 =

P Lc

511 keV

511 k

eV

•LNAT

•Multi-parameter techniques

•AMOC two detectors

•Double ADC data unit

OUTLINE

0 5 10 15 20 250.47

0.48

0.49

0.50

0.51

0.52

0.53

0.54

0.55

0.56

0.57

S p

aram

eter

Positron Age (ns)

before after defect-free Si bulk

各种制备条件及处理条件下多孔硅的 AMOC 测量结果。

Matrix structure oxidation-water vapor annealing

sample τ1/ns τ2/ns τ3/ns τ4/ns I1/% I2/% I3/% I4/%

before 0.224 1.116 33.03 81.8 4.38 13.65

after 0.214 0.511 2.34 35.5 62.3 27.1 9.37 1.2