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.”
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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
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P&C - 2014Sources of systematic errors of 214Po half-life
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)→
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P&C - 2014Sources of systematic errors of 214Po half-life
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.
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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
Sources of systematic errors of 214Po half-life
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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
Sources of systematic errors of 214Po half-life
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Plastic PETP 2.5 μm film “Goodfellow”
Glue
226Ra
226Ra-source
Sources of systematic errors of 214Po half-life
d=3 mm
d=14 mm
0.05 mm
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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.
Sources of systematic errors of 214Po half-life
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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
Sources of systematic errors of 214Po half-life
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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.
Sources of systematic errors of 214Po half-life
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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
Sources of systematic errors of 214Po half-life
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Amplitude spectra of γ-quanta (a) and α-particles pulses (b) for coinciding events at TAU-1.
Sources of systematic errors of 214Po half-life
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)
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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.
Sources of systematic errors of 214Po half-life
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)
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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]
Sources of systematic errors of 214Po half-life
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.
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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.
Sources of systematic errors of 214Po half-life
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
)
Low threshold of the decay curve (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
Low threshold of the decay curve (s)
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
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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]
Sources of systematic errors of 214Po half-life
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)
Detector TAU-2, depth = 4900 m.w.e.Total time = 350 days
B
ackg
rou
nd
per
ch
ann
el
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Results
Sources of systematic errors of 214Po half-life
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)
Detector TAU-2, depth = 4900 m.w.e.Total time = 350 days
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)
Detector TAU-2, depth = 4900 m.w.e.Total time = 350 days
Analysis by Maximum likelihood method
30 september 2012 y.
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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.)
Sources of systematic errors of 214Po half-life
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.
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Results
Sources of systematic errors of 214Po half-life
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
Detector TAU-2, depth = 4900 m.w.e.Total time = 350 days
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.
Detector TAU-2, depth = 4900 m.w.e.Total time = 350 days
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
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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
Sources of systematic errors of 214Po half-life
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P&C - 2014Sources of systematic errors of 214Po half-life