Sources of systematic errors of 214 Po half-life measurements.

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

2. J.H. Jenkins et al. / Astroparticle Physics 32 (2010) 42–46 Evidence of correlations between nuclear decay rates and Earth–Sun distance Decay rates data 1. 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 Sources of systematic errors of 214Po half-life P&C - 2014 “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.” Correlation between the raw decay rates of 32Si/36Cl at BNL and 226Ra at PTB. A365d ≈ 8∙10-4

3. Sources of systematic errors of 214Po half-life Decay rates data 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 P&C - 2014

4. Sources 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 →214Bi→(β, Т1/2= 19.9 m)→214Po*→γ→ 214Po (α,Т1/2=164.3±2.0 μs)→ 214Po (Т1/2=162.73±0.10 μs), TAU-1 – 1038 d, “KAPRIZ”, 1000 m w.e. (Т1/2=164.25±0.12μs), 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. P&C - 2014

5. Sources of systematic errors of 214Po half-life Test 1. 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. P&C - 2014

6. Sources of systematic errors of 214Po half-life Scheme of 226Radecay P&C - 2014

7. Sources of systematic errors of 214Po half-life Scheme of Bi-Podecay levels P&C - 2014 214Bi→214Po (19.9% - ground level; 80.1% - exited levels) Eγ≥ 609 keV – 1.187 γ/decay γ-β-(delayed α) – coincidence

8. Sources of systematic errors of 214Po half-life d=14 mm Plastic PETP 2.5 μmfilm “Goodfellow” Glue 0.05 mm d=3 mm 226Ra P&C - 2014 226Ra-source

9. Sources of systematic errors of 214Po half-life P&C - 2014 Schematic view of TAU-2 installation Schematic view of TAU-1 installation TAU-1  4900 m w.e. →1000 m w.e. NaI(Tl)×2 - 150×150 mm 15 cm Pb+8 cm Cu TAU-2  4900 m w.e. NaI(Tl)×2 - 150×150 mm 25 cm PE+1mm Cd+(15 cm+15 cm Pb) ADC  Digital Oscilloscope ЛА-н20-12PCI, F = 6.25 MHz (time channel = 0.16 µs). A  Amplifier.

10. Sources of systematic errors of 214Po half-life B – Gallium Germanium SN-Telescope 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

11. Sources of systematic errors of 214Po half-life α-detector, α-pulse Delayed coinc. NaI(Tl)-γ-pulse α-det., β-pulse Prompt coins. P&C - 2014 Example of coinciding event at TAU-2: Delayed α-pulse in the “history” follows at prompt coinciding γ- and β-pulses.

12. Sources of systematic errors of 214Po half-life Data registration 1.NaI(Tl)-signal triggers the data record. Time interval duration - 655.36 µs (4096×160ns), 81.92µs –“prehistory”, 573.44µs –“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 P&C - 2014

13. Sources of systematic errors of 214Po half-life 7.69 MeV (b) 609 keV 1765 keV P&C - 2014 (a) Amplitude spectra of γ-quanta (a) and α-particles pulses (b) for coinciding events at TAU-1.

14. Sources of systematic errors of 214Po half-life 609 keV 1765 keV (a) 7.69 MeV (b) P&C - 2014 (c) Amplitude spectra of γ-quanta (a), α-particles (b) and β-particles (c) pulses of the prompt- delayed coinciding events at TAU-2.

15. Sources of systematic errors of 214Po half-life Results y=a∙exp(-ln(2)∙t/)+b 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 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]

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

17. Sources of systematic errors of 214Po half-life Results y=a∙exp(-ln(2)∙t/)+b 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 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]

18. Sources of systematic errors of 214Po half-life Results y(t,Δti)=ai∙exp(-ln(2)∙t/i)+bi Δti = week, i = 1-50 y(t,Δti)=ai∙exp(-ln(2)∙t/i)+btot∙Ni/Ntot Δti = week, i = 1-50 P&C - 2014 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 214Po for ‘a week data’ sets of TAU-2 for the MLM fitting

19. Results Sources of systematic errors of 214Po half-life P&C - 2014 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.) Dependence of 214Po τfor “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

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

21. Sources of systematic errors of 214Po half-life Conclusions 1. 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 τmeasured by TAU-1equal to 163.8±0.2μs at 4900 m w. e. and 164.4±0.2μs at 1000 m w. e. Magnitudes of the values depend on low thresholds of the decay curve of TAU-1. 3. Averaged value of τmeasured by TAU-2 at 350 days equal to 163.42±0.06μs 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 τmean 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. P&C - 2014 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. Sources of systematic errors of 214Po half-life P&C - 2014