1 Sources of systematic errors of 214 Po half-life measurements. P&C - 2014 E.N.Alekseev 1, Yu.M.Gavrilyuk 1, A.M.Gangapshev 1, V.V.Kazalov 1, V.V.Kuzminov

1

Sources of systematic errors of 214Po

half-life measurements.

P&C - 2014

E.N.Alekseev1, Yu.M.Gavrilyuk1, A.M.Gangapshev1,

V.V.Kazalov1, V.V.Kuzminov1, S.I.Panasenko2,

S.S.Ratkevich2

1. Baksan Neutrino Observatory of INR RAS, Russia 2. Kharkov National University, Kharkov, Ukraine

2

Sources of systematic errors of 214Po half-life

Decay rates data1. 32Si/36Cl (half-life of 32Si →(172y)/(3∙105y))D.E. Alburger, G. Harbottle, E.F. Norton, Earth Planet Sci. Lett. 78 (1986) 168. (Brookhaven National Laboratory (BNL)) 2. 226Ra (long-lived comparison standard)H. Siegert, H. Schrader, U. Schötzig, Appl. Radiat. Isot. 49 (1998) 1397.Physikalisch-Technische Bundesanstalt (PTB) in Germany

J.H. Jenkins et al. / Astroparticle Physics 32 (2010) 42–46Evidence of correlations between nuclear decay rates and Earth–Sun distance

Correlation between the raw decay rates of 32Si/36Cl at BNL and 226Ra at PTB.

A365d ≈ 8∙10-4

“We have presented evidence for an annual variation of nuclear decay rates seen in overlapping data sets from BNL and PTB whose origin is at present unknown. Since the observed BNL and PTB correlations of each data set with 1/R2, as well as with each other, could arise from a variety of conventional and unconventional sources, further experiments on a number of different nuclides will be required to determine the origin of these correlations.”

P&C - 2014

3

P&C - 2014Sources of systematic errors of 214Po half-life

198Au (T1/2 = 2.695 d), A365d ≤ 2∙10-4 (95 % C.L.) J.C. Hardy*, J.R. Goodwin and V.E. Iacob“DO RADIOACTIVE HALF-LIVES VARY WITH THE EARTH-TO-SUN DISTANCE?” arXive: 1108.5326v1, 2011 y.

137Cs (Т1/2=10942 d), A365d ≤ 8.5∙10-5 (95 % C.L.)E.Bellotti ,C.Broggini ,G. Di Carlo ,M.Laubenstein ,R. Menegazzo“Search for time dependence of the 137Cs decay constant”arXive: 1202.3662, 2012 y

40K (Т1/2= 1.28∙109 y), A365d ≤ 6.1∙10-5 (95 % C.L.)232Th (Т1/2= 1.40∙1010 y), A365d ≤ 4.0∙10-5 (95 % C.L.)E.Bellotti, C.Broggini, G.Di Carlo, M.Laubenstein, R. Menegazzo, M.Pietroni“Search for time modulations in the decay rate of 40K and 232Th and influence of a scalar field from the Sun”arXive: 1311.7043, 2013 y

Decay rates data

4


1. Count rate instability (background; electric and

Decay rate variations = F{ magnetic fields; temperature; pressure; humidity; } aging; source-detector characteristics …)

2. Half-life variations

Decay rate measurements → Life time measurements

214Po (Т1/2= 162.73±0.10 μs), TAU-1 – 1038 d, “KAPRIZ”, 1000 m w.e. (Т1/2= 164.25±0.12 μs), TAU-2 - 562 d, “DULB-4900”, 4900 m w.e.

A365d ≤ 3.3∙10-3 (90% C.L.)

E.N. Alexeyev, V.V. Alekseenko, Ju.M. Gavriljuk, A.M. Gangapshev, A.M. Gezhaev, V.V. Kazalov, V.V. Kuzminov, S.I. Panasenko, S.S. Ratkevich, S.P. Yakimenko. “Experimental test of the time stability of the half-life of alpha-decay 214Po nuclei” Astroparticle Physics, 46 (2013) 23-28.

→214Bi→(β, Т1/2= 19.9 m)→214Po*→γ→ 214Po (α,Т1/2= 164.3±2.0 μs)→

5


Test1. TAU1 and TAU2 DO-scales comparison – δ≤ 3∙10-4

TAU1 and TAU2 improvements:1. New Ra-226 radioactive sources;2. TAU1 γ-detector exchange; α-detector exchange.

6

P&C - 2014

2

2222

14

1/ 2

2101/

2181/ 2

261/ 2 1/ 2

2

4.78 5.49

6.00

( 1600 ) ( 3.8

( 26.8 )

( 2

( 3.05 )

25

2

)

.3 )

E MeV E MeV

E MeV Pb T m

Pb

Ra T y

Po T

T

y

n

T

R

m

d

-214

1

214

2-4

1/ /2β α

E=7.69MeVPo(T = 1.6Bi(T = 1 109.9 s)m)210

1/ 2

202101/

6

2 5.31

( 5.01

( 138

)

).) (E MeVP

Bi T d

Pb stablT eo d

Scheme of Scheme of 222266RRaa decaydecay


7

P&C - 2014

Scheme of Scheme of Bi-PoBi-Po decay levelsdecay levels

214Bi→214Po (19.9% - ground level; 80.1% - exited levels)

Eγ ≥ 609 keV – 1.187 γ/decay

γ-β-(delayed α) – coincidence


8

P&C - 2014

Plastic PETP 2.5 μm film “Goodfellow”

Glue

226Ra

226Ra-source


d=3 mm

d=14 mm

0.05 mm

9

P&C - 2014

TAU-1 4900 m w.e. →1000 m w.e. NaI(Tl)×2 - 150×150 mm 15 cm Pb+8 cm Cu

Schematic view of TAU-1 installation

TAU-2 4900 m w.e. NaI(Tl)×2 - 150×150 mm25 cm PE+1mm Cd+(15 cm+15 cm Pb)

Schematic view of TAU-2 installation

ADC Digital Oscilloscope ЛА-н20-12PCI, F = 6.25 MHz (time channel = 0.16 µs). A Amplifier.


10

P&C - 2014

TAU-1, (L=620 m, T=(20±1)oC), g1 ≈ 980.6000 cm∙s-2.

TAU-2, (L=3670 m, T=(26.5±0.2)oC), g2 ≈ 980.5050 cm∙s-2; Δg = 9.7∙10-5.

Schematic view of BNO underground laboratories

B – Gallium Germanium SN-Telescope


11

P&C - 2014

Example of coinciding event at TAU-2: Delayed α-pulse in the “history” follows atprompt coinciding γ- and β-pulses.

NaI(Tl)-γ-pulse α-det., β-pulsePrompt coins.

α-detector, α-pulseDelayed coinc.


12

P&C - 2014

Data registration

1. NaI(Tl)-signal triggers the data record.

Time interval duration - 655.36 µs (4096×160ns),

81.92 µs –“prehistory”, 573.44 µs –“history” >3τ

2. TAU-1 ~6 s-1 ~10 Gb∙d-1.

TAU-2 ~12 s-1 “On line” program selection of

useful events, data-compression – writing amplitudes

and time of pulse appearing: 25 Mb∙d-1.

3. NaI(Tl)-background (E>400 keV):

TAU-1, TAU-2 – ~2.3×2 ≈ 4.6 s-1


13

P&C - 2014

Amplitude spectra of γ-quanta (a) and α-particles pulses (b) for coinciding events at TAU-1.


0 200 400 600 800 100012001400160018002000220024002600280030000

4000

8000

12000

16000 0 200 400 600 800 100012001400160018002000220024002600280030000

3000

6000

9000

12000

Gamma-Spectrum, TAU1

Cou

nts

/ (ch

anne

l*270

h )

Channel

Alpha-Spectrum, TAU17.69 MeV

609 keV

1765 keV

(a)

(b)

14

P&C - 2014

Amplitude spectra of γ-quanta (a), α-particles (b) and β-particles (c)pulses of the prompt- delayed coinciding events at TAU-2.


0 200 400 600 800 100012001400160018002000220024002600280030000

10000

20000

30000

40000

0 200 400 600 800 100012001400160018002000220024002600280030000

10000

20000

30000

40000

0 200 400 600 800 100012001400160018002000220024002600280030000

10000

20000

30000

Gamma-Spectrum, TAU2

Alpha-Spectrum, TAU2

Cou

nts

/ (ch

anne

l*453

h )

Beta-Spectrum, TAU2

Channel

609 keV

1765 keV

7.69 MeV

(a)

(b)

(c)

15

P&C - 2014

Distribution of lifetime of 214Po nuclei for a total data set of TAU-1 τ = 163.9±0.2 μs

Dependence of 214Po half-life on low threshold of the decay curve of TAU-1

Results

New measured half-life value for 214Po – 163.58±0.29(stat.)±0.10(syst.) µs[G. Bellini, J.Benziger, D.Bick et al. “Lifetime measurements of 214Po and 212Po with the CTF liquid scintillator detector at LNGS”. Eur. Phys. J. A (2013) 49:92]


y=a∙exp(-ln(2)∙t/)+b

0 100 200 300 400 500 6000

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

# o

f ev

ents

per

0.1

6 s

Time (s)

Detector TAU-1, depth = 4900 m.w.e.Total time = 116 days

half-life = 163.85 0.19 s

0 20 40 60 80 100 120 140 160 180163,0

163,2

163,4

163,6

163,8

164,0

164,2

164,4

164,6

164,8

0 20 40 60 80 100 120 140 160 180

210

215

220

225

230

235

240

245

250

Hal

f-li

fe o

f th

e P

o-2

14 (s

)

Low threshold of the decay curve (s)

B

ackg

rou

nd

per

ch

ann

el

Detector TAU-1, depth = 4900 m.w.e.

16

P&C - 2014

Results

Dependence of 214Po half-life on low threshold of the decay curve of TAU-1 τ = 164.4±0.2 μs

Dependence of 214Po half-life on low threshold of the decay curve of TAU-1 τ = 163.9±0.2 μs - 4900 m w.e.τ = 164.4±0.2 μs - 1000 m w.e.


0 20 40 60 80 100 120 140 160 180163,0

163,2

163,4

163,6

163,8

164,0

164,2

164,4

164,6

164,8

0 20 40 60 80 100 120 140 160 180190

200

210

220

230

240

250

260

Hal

f-li

fe o

f th

e P

o-2

14 (s

)


Bac

kgro

un

d p

er c

han

nel

TAU-1 detector, depth = 1000 m.w.e.Total time = 88 days

0 20 40 60 80 100 120 140 160 180163,0

163,2

163,4

163,6

163,8

164,0

164,2

164,4

164,6

164,8


Hal

f-li

fe o

f th

e P

o-2

14 (s

)

Depth = 4900 m.w.e. Depth = 1000 m.w.e.

Detector TAU-1

17

P&C - 2014

Distribution of lifetime of 214Po nuclei for a total data set of TAU-2 τ = 163.42±0.06 μs

Dependence of 214Po half-life on low threshold of the decay curve of TAU-2

Results

New measured half-life value for 214Po – 163.58±0.29(stat.)±0.10(syst.) µs[G. Bellini, J.Benziger, D.Bick et al. “Lifetime measurements of 214Po and 212Po with the CTF liquid scintillator detector at LNGS”. Eur. Phys. J. A (2013) 49:92]


y=a∙exp(-ln(2)∙t/)+b

0 100 200 300 400 500 6000

50000

100000

150000

200000

250000

# o

f th

e ev

ents

per

0.1

6 s

Time (s)

TAU-2 detector, depth = 4900 m.w.e.Total time = 350 days.

Half-life = 163.416 0.056 s

0 20 40 60 80 100 120 140 160 180163,0

163,2

163,4

163,6

163,8

164,0

0 20 40 60 80 100 120 140 160 180900

950

1000

1050

1100

1150

1200

1250

1300

Hal

f-li

fe o

f th

e P

o-2

14 n

ucl

eus

(s)

Low threshold of the decay curve of TAU-2(s)


B

ackg

rou

nd

per

ch

ann

el

18

P&C - 2014

Results


0 10 20 30 40 50161,0

161,5

162,0

162,5

163,0

163,5

164,0

164,5

165,0

165,5

166,0

Hal

f-ti

me

of

the

Po

-214

nu

cleu

s p

er w

eek

Time (week)


30 september 2012 y.

y(t,Δti)= ai∙exp(-ln(2)∙t/i)+bi

Δti = week, i = 1-50y(t,Δti)= ai∙exp(-ln(2)∙t/i)+btot∙Ni/Ntot

Δti = week, i = 1-50

Distribution in time of half-life of 214Po for ‘a week data’ sets of TAU-2 for the ORIGIN fitting

Distribution in time of half- life of 214Pofor ‘a week data’ sets of TAU-2 for the MLM fitting

0 10 20 30 40 50161,0

161,5

162,0

162,5

163,0

163,5

164,0

164,5

165,0

165,5

166,0

Hal

f-li

fe o

f th

e P

o-2

14

per

wee

k (

s)

Time (week)


Analysis by Maximum likelihood method

30 september 2012 y.

19

P&C - 2014

Results

Distribution in time of normalized values of half- life of 214Po for ‘a week data’ sets of TAU-2 . A365 ≤ 7∙10-4 (90% C.L.)


0 10 20 30 40 50 600,996

0,997

0,998

0,999

1,000

1,001

1,002

1,003

1,004

0 10 20 30 40 50 600,96

0,97

0,98

0,99

1,00

1,01

1,02

1,03

1,04

Hal

f-li

fe o

f th

e P

o-2

14 (

rela

tive

un

its)

Time (week)

Detector TAU-2, depth = 4900 m.v.eTotal time = 350 days.

Maximum likelyhood method

1/

R2 (

a.u

.)-2

Dependence of 214Po τ for “26 weeks data” sets of TAU-2 on the set shift with 1 week step. Amplitude of a “season” variation τ: A winter/summer ≈± 6∙10-4

0 10 20 30 40 50 60163,0

163,1

163,2

163,3

163,4

163,5

163,6

163,7

163,8

163,9

Hal

f-li

fe o

f th

e P

o-2

14 n

ucl

eus

(s)

Time (week) 0-25 w., 1-26 w., ... etc.

Detector TAU-2, depth = 4900 m.w.e.

Half-life at 0.5 year shifted in sequence with 1 week stepStart time 30 september 2012 y.

20

P&C - 2014

Results


Dependence of half-life of 214Po for “a 12 hours data” sets of TAU-2 on the set shift with 1 h step for the averaged Sun day, Star day and Moon day. Day-Night variation A24h/12h ≈± 9∙10-4

0 5 10 15 20 25163,0

163,1

163,2

163,3

163,4

163,5

163,6

163,7

163,8

163,9

164,0

Hal

f-li

fe o

f th

e P

o-2

14 n

ucl

eus

(s)

Observation time 0-12 m.h., 1-13 m.h., ... etc


Moon day = 24 h. 50 min. 28.2 sec.=24 moon hours0 5 10 15 20 25

163,0

163,1

163,2

163,3

163,4

163,5

163,6

163,7

163,8

163,9

164,0

Hal

f-li

fe o

f th

e P

o-2

14 n

ucl

eus

(s)

Observation time 0-12 h, 1-13 h, ... and so on.


Sun day

0 5 10 15 20 25163,0

163,1

163,2

163,3

163,4

163,5

163,6

163,7

163,8

163,9

164,0

Hal

f-li

fe o

f th

e P

o-2

14 n

ucl

eus

(s)

Observation time 0-11 s.h., 1-12 s.h., ... etc

Detector TAU-2, depth = 4900 m. w. e.Total time = 350 days

Star day = 23 h. 56 min. 56.55537 sec. = 24 star hours

21

P&C - 2014

Conclusions1. A sensitivity of two underground installations aimed at monitoring the time stability of 214Po half-life have been improved by using of the new Ra-226 source construction and the MLM data processing.

2. Values of τ measured by TAU-1 equal to 163.8±0.2 μs at 4900 m w. e. and 164.4±0.2 μs at 1000 m w. e. Magnitudes of the values depend on low thresholds of the decay curve of TAU-1.

3. Averaged value of τ measured by TAU-2 at 350 days equal to 163.42±0.06 μs at 4900 m w. e. Magnitude of the value does not depend on low thresholds of the decay curve of TAU-2.

4. Amplitude of possible annual variation of 214Po half-life does not exceed A365 ≤ 7∙10-4 (90% C.L.) of the τ mean value on TAU-2.

5. The winter-summer variation of τ with amplitude of Awinter/summer≈ 6∙10-4 was found in the summed at 26 weeks shifted data set of TAU-2.

6. The day-night variation of τ with amplitude of A24h/12h ≈ 9∙10-4 was found in the summed at 350 days averaged 24 hours data set of TAU-2.

Plans:1. To recognize the reasons of the winter-summer and day-night variations of the τ.2. To improve a sensitivity to a possible annual variation of the τ


22


Documents

1 Sources of systematic errors of 214 Po half-life measurements. P&C - 2014 E.N.Alekseev 1, Yu.M.Gavrilyuk 1, A.M.Gangapshev 1, V.V.Kazalov 1, V.V.Kuzminov