new new measurements with the bege detector · 2008. 11. 24. · 2 bege: promising new detector for...

New measurements withNew measurements withthe the BEGeBEGe detectordetector

MarikMarik BarnabBarnabéé HeiderHeider •• DuDuššanan BudjBudjášáš •• Oleg ChkvoretsOleg ChkvoretsStefan Stefan SchSchöönert nert •• Nikita Nikita Xanbekov*Xanbekov*

MPI fMPI füür Kernphysik r Kernphysik •• HeidelbergHeidelberg* also: ITEP * also: ITEP •• MoscowMoscow

MMAXAX--PPLANCKLANCK--IINSTITUTNSTITUTFFÜÜR R KKERNPHYSIKERNPHYSIK

2

BEGeBEGe: promising new detector for : promising new detector for 0νββ0νββ searchsearchMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan Budjášášáš

studied at MPIK since April, motivaded by Majorana p-pcvery good PSA perfomance, minimal amount of signal contacts (potential background), excelent energy resolution, o(kg) mass⇒ ideal for ultra-low background experiments

p+ contact

p-type germanium

n+contact

φ 81 mm

32 m

m 878 gFWHM

0.49 keV

241Am FWHM1.6 keV

60Co

coun

ts

DEP90.9%

1.62 MeV12.5%

3

Questions remaining after June GERDA meeting:Questions remaining after June GERDA meeting:

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan Budjášášáš

do we have signal losses due to "inconventional" field distribution in the BEGe crystal?

how reliable is our pulse-shape analysis?

does DEP represent the 0νββ events well enough?

Work performed since then:Work performed since then:

characterisation of charge collection losses

single Compton-scattering measurements to obtain pure samples of electron-induced events

comparison of SCS events at DEP and Qββ energies

4

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCollimator scanningCollimator scanning

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MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCollimator scanning: side scanCollimator scanning: side scan

collimated 59.5 keV

γ-ray beam

d

Gain variation: ≤ 0.055%

Majorana PPC detector:Gain variation: ≤ 0.15%

P.S. Barbeau, J.I. Collar and O. TenchJCAP 0709:009,2007

collimated 241Am scan

59.3

59.35

59.4

59.45

59.5

59.55

59.6

0 5 10 15 20 25 30 35distance from the top of crystal, d [mm]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

FWH

M [k

eV]

peak positionFWHM

peak

pos

ition

[keV

]

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30 35 40 45position d [mm] (0 mm = top of housing)

coun

t rat

e [c

ps]

Monte Carlo

241Am scan

detector extent

6

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCollimator scanning : side scanCollimator scanning : side scan

d

7

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCollimator scanning: top scanCollimator scanning: top scan

59.4

59.42

59.44

59.46

59.48

59.5

59.52

59.54

-50 -40 -30 -20 -10 0 10 20 30 40 50distance from center [mm]

peak

pos

ition

[keV

]

0.4

0.5

0.6

0.7

0.8

0.9

1

FWH

M [k

eV]

peak position

FWHM

d

3

3.5

4

4.5

5

-50 -40 -30 -20 -10 0 10 20 30 40 50distance from center, d [mm]

coun

t rat

e [c

ps]

241Am scanMonte Carlodetector extent

8

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCharge collection losses: peak tailsCharge collection losses: peak tails

Energy [keV]

norm

alis

ed c

ount

rate

uncollimated 241Am sourcecollimated beam near bottom edge

9

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCharge collection losses: peak tailsCharge collection losses: peak tails

Energy [keV]

coun

ts /

0.5

keV

60Co source

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

dead layer thic knes s [mm]

⎝‐line ratio

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MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCharge collection losses: dead layerCharge collection losses: dead layer

inte

nsity

-cor

rect

ed γ-

line

ratio

: ε 5

9/

(ε99

+ ε 1

03)

241Am source

0.42 mm dead layer(Canberra specification: 0.5 mm)

simulated data points

measured ratio

0.31

0.315

0.32

0.325

0.33

0.335

0.34

0.345

148 150 152 154 156 158 160

ac tive volume [cm 3]

1332

.5 keV

line efficien

cy [%]

11

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCharge collection losses: active volumeCharge collection losses: active volume

60Co source

157 cm3 active volume

simulated data points

measured efficiency

active mass: 836 g (95 % of total mass of 878 g)corresponds to 0.44 mm dead layer(assuming uniform around the crystal)

12

Summary of charge collectionSummary of charge collectionMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan Budjášášáš

no inhomogeneity of charge collection

no incomplete charge collection at all

BEGe dead layer as thin as in any good quality p-type detector

active mass is 95 % of the total mass⇒ only the Li-drifted n+ contact inactive

ComptonCompton--scattering coincidence measurementsscattering coincidence measurementsMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan Budjášášáš

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14

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCoincident recordingCoincident recording

Struck SIS 3301 flash-ADC

14-bit, 100 MHz

pulse recording, digital shaping (τshaping = 10 μs)

1.6 μs coincidence

window

software gate

Amplified raw signal

Canberra2002CSL

MPIKno shaping

TFACanberra2111

Time-filtered signal (10 ns differentiation and

10 ns integration time)

Amplified raw signal

Preamp

no shapingMPIK

228Th source(no collimator)

Pb/Cu shield solid angle:~ 10°

25 c

m -

80 c

m

23.6 cm

Energy BEGe [channels]

Ener

gy D

ario

[cha

nnel

s]

~69° scattering (E ≈ 2 MeV)

15



Ener

gy D

ario

[cha

nnel

s]

~43° scattering (E ≈ 1.5 MeV)

DEP

SEP

Etotal = 2.6 MeV2.6 MeV

1.46 MeV

511 keV

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2.6 MeV

true coincidencerandom coincidence

(same window, asynchronous time offset)


Rate

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCoincident backgroundsCoincident backgrounds

1.6 μs coincidence window

Etotal = 2614.5 keV ± 6 keV

40° scattering

17

50° scattering 228Th70° scattering 228Th

random coincidencebackground without source


Rate

[cpd

/ 0.

14 k

eV]




18


Ener

gy D

ario

[cha

nnel

s]

860 KeV

possible true coincident backgrounds from 208Tl:

cascades with 2.6 MeV line

19


583 KeV

20


Energy [keV]

coun

ts /

keV

Etotal = EDario + EBEGe spectrum

Compton scattering

events

cascade and random events

scattering with energy loss outside

detectors, etc.

21

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCompton scattering eventsCompton scattering events

Energy in BEGe [keV]

coun

ts /

0.5

keV

(unn

orm

alise

d)

70° scattering40° scattering



22


equivalent scattering angle α [°]

coun

ts /

0.5

keV

(unn

orm

alise

d)


~43° ± 7°

~69° ± 8° 1.6 μs coincidence window


⎟⎠⎞

⎜⎝⎛ +

−−

=52614

51152614

5111..

cosE

arα

23


Energy in BEGe [keV]




SCS around Qββ

SCS around DEP energy

coun

ts /

0.5

keV

(unn

orm

alise

d)

24


Pulse shape analysisPulse shape analysis

typical electron event typical gamma-ray event

char

ge p

ulse

curre

nt p

ulse

after differentiation:

raw preamplifier output:

Time [10 ns]

Time [10 ns] Time [10 ns]

Time [10 ns]

25


Single compton scattering~43° ± 7°

1.35 - 1.7 MeV

Current pulse amplitude [arbitrary units]

Current pulse amplitude [arbitrary units]26


MCS around 2.3 MeV



SCS around 1.4 MeV

SCS around 1.55 MeV



SCS around 1.59 MeV

DEP (coincidence with 511 keV line in Dario)

29

Summary of PSASummary of PSAMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan Budjášášáš

electron and gamma-induced events can be distinguished with the help of current-pulse amplitude

DEP and SCS data with different volume distribution have similar distribution of the current-pulse amplitude

SCS measurements can be used to calibrate cut parameters at different energies

cut function stability needs to be investigated

30


OutlookOutlook

Understand how to generalise our pulse shape discrimination to 0νββ events and expected background events:

measurements with different spatial distributions of electron events to experimentally check how the efficiency of pulse-shape discrimination varies?

pulse-shape simulation of the BEGe detector?

31


Backup slidesBackup slides

0

200

400

600

800

1000

1200

1400

1600

1800

-400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300pulse arrival difference [10 ns]

coun

ts

pulse arrival time difference [10 ns]32

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCoincident recordingCoincident recording

33

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášCoincident dataCoincident data


Diff

eren

tiate

d si

gnal

am

plitu

de

50° scattering

CurrentCurrent--maximum distributionmaximum distributionMPIK HeidelbergMPIK HeidelbergMPIK Heidelberg

35

DuDuDušššan Budjan Budjan Budjášášáš

SEPDEP γ 1.62 MeVγ 2.61 MeV

Energy [keV]

Cur

rent

-ma

ximum

/ e

nerg

yC

ount

s

CurrentCurrent--maximum discriminationmaximum discriminationMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan Budjášášáš

36

• cut-profile determination from SSE dominated regions:

DEP

γ-line 1.62 MeV

Compton near DEP

SEP

SSE dominated

SSE dominated

MSE dominated

MSE dominated

Current-maximum / energy

cut at3 st. dev. fit with gaussian

distribution function




CurrentCurrent--maximum discriminationmaximum discriminationMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan Budjášášáš

Energy [channels]

Cur

rent

-ma

ximum

/ e

nerg

y

SEP

DEPγ 1.62 MeV

γ 2.61 MeV

37

Compton continuum

Cut function interpolated from cut-values at several points

38

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášTable of results (June 08)Table of results (June 08)

E [keV] reduction ± bck. red. ± suppresion ±351.9 38.74% 0.33% 46.68% 1.29% 2.58 0.24609.3 22.20% 0.18% 35.80% 1.81% 4.51 0.41

1120.3 13.29% 0.20% 35.91% 1.23% 7.52 0.931764.5 13.29% 0.13% 25.91% 1.51% 7.52 0.741847.4 12.88% 0.39% 43.92% 1.65% 7.76 1.352118.6 14.75% 0.42% 33.27% 1.51% 6.78 1.142204.2 15.28% 0.21% 28.86% 1.99% 6.54 0.772447.9 14.55% 0.21% 18.25% 2.27% 6.87 0.83

1173.2 11.96% 0.05% 12.97% 0.59% 8.36 0.551332.5 11.45% 0.05% 7.76% 0.80% 8.74 0.582505.7 0.49% 0.01% 0.57% 0.15% 205.74 26.48

510.77 27.64% 0.25% 41.84% 1.23% 3.62 0.34583.19 24.41% 0.06% 39.43% 1.63% 4.10 0.20860.56 17.14% 0.15% 50.19% 1.14% 5.84 0.541592.5 91.01% 0.62% 58.30% 1.34% 1.10 0.091620.5 13.20% 0.45% 56.42% 0.90% 7.57 1.402103.5 9.10% 0.29% 46.86% 0.61% 10.99 1.942614.5 13.19% 0.06% 8.97% 3.51% 7.58 0.49

60Co

226Ra

228Th

39


DEP from 70° run

DEP from 40° run

Setup modified between the two runs!

40

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDuDuDušššan Budjan Budjan BudjášášášSingle Compton scatteringSingle Compton scattering

DEP noncoincident, source on top vs DEP coincident, source on side

41


DEP vs SEP

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

40 50 60 70 80 90 100 110

Energy [keV]

Cou

nts

42


Dead layer determinationDead layer determinationTwo methods considered:1. using absolute countrate in low-energy γ-lines (133Ba: 81 keV, 241Am: 59.5 keV) 2. using ratio of γ-line countrates → must use γ-lines with low energy

because the size of inner borehole was not known beforehand ⇒ 241Am: 59.5 keV, 99 keV, 103 keV

measured 241Am spectrum

calculated with the sum of the two γ-lines

43


Dead layer determinationDead layer determination

Example of front dead-layer determination using ratio of 241Am γ-lines:MC simulations performed with different dead-layer thickness valuesexponential dependancy of line ratio derived from MC datainterpolated the dependancy to the measured γ-line ratio

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

40 50 60 70 80 90 100 110

Energy [keV]

Cou

nts

Dead layer determination from 241Am γ-lines ratio

0.2%

0.3%

0.4%

0.5%

0.6%

0.7%

0.8%

0.9%

0.5 1 1.5 2 2.5Dead layer thickness [mm]

Effic

ienc

y ra

tio

2 /

1

measured ratio / interpolated thicknessMC dataExponential fit of MC data

Dead layer thicknesses obtained by all methods

1

1.2

1.4

1.6

1.8

2

2.2

0 25 50 75 100 125 150 175 200

Distance [mm]

Dea

d la

yer [

mm

]

59keV81keV99keV&103keV241Am relative133Ba relative

44


Dead layer determinationDead layer determinationSimilar interpolation also with single-line / absolute-countrate method.

Only the result obtained from 241Am with the ratio method was used: does not depend on activity of the sourcedoes depend only little on source distance and other factors (dead time...)does not depend on the unknown borehole-dimensions

⇒ fewer uncertainties

in function of the distance from detector

45


New measurements with�the BEGe detectorQuestions remaining after June GERDA meeting:Summary of charge collectionSummary of PSA

new new measurements with the bege detector · 2008. 11. 24. · 2 bege: promising new detector for...

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