1. 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, S.I.Panasenko 2, S.S.Ratkevich 2 1. Baksan Neutrino Observatory of INR RAS, Russia 2. Kharkov National University, Kharkov, Ukraine

2. 2 Sources of systematic errors of 214 Po half-life Decay rates data 1. 32 Si/ 36 Cl (half-life of 32 Si → (172y)/(3∙10 5 y) ) D.E. Alburger, G. Harbottle, E.F. Norton, Earth Planet Sci. Lett. 78 (1986) 168. (Brookhaven National Laboratory (BNL)) 2. 226 Ra (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) 42–46 Evidence of correlations between nuclear decay rates and Earth–Sun distance Correlation between the raw decay rates of 32 Si/ 36 Cl at BNL and 226 Ra at PTB. A 365d ≈ 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/R 2, 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. 3 Sources of systematic errors of 214 Po half-life 198 Au (T 1/2 = 2.695 d), A 365d ≤ 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. 137 Cs (Т 1/2 =10942 d), A 365d ≤ 8.5∙10 -5 (95 % C.L.) E.Bellotti,C.Broggini,G. Di Carlo,M.Laubenstein,R. Menegazzo “Search for time dependence of the 137 Cs decay constant” arXive: 1202.3662, 2012 y 40 K (Т 1/2 = 1.28∙10 9 y), A 365d ≤ 6.1∙10 -5 (95 % C.L.) 232 Th (Т 1/2 = 1.40∙10 10 y), A 365d ≤ 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 40 K and 232 Th and influence of a scalar field from the Sun” arXive: 1311.7043, 2013 y Decay rates data

4. 4 P&C - 2014 Sources of systematic errors of 214 Po 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 214 Po (Т 1/2 = 162.73±0.10 μs), TAU-1 – 1038 d, “KAPRIZ”, 1000 m w.e. (Т 1/2 = 164.25±0.12 μs), TAU-2 - 562 d, “DULB-4900”, 4900 m w.e. A 365d ≤ 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 214 Po nuclei” Astroparticle Physics, 46 (2013) 23-28. → 214 Bi→(β, Т 1/2 = 19.9 m)→ 214 Po * →γ→ 214 Po (α,Т 1/2 = 164.3±2.0 μs)→

5. 5 P&C - 2014 Sources of systematic errors of 214 Po 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.

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

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

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

9. 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 mm 25 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 214 Po half-life

10. 10 P&C - 2014 TAU-1, (L=620 m, T=(20±1) o C), g 1 ≈ 980.6000 cm∙s -2. TAU-2, (L=3670 m, T=(26.5±0.2) o C), g 2 ≈ 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 214 Po half-life

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

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

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

14. 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. Sources of systematic errors of 214 Po half-life 609 keV 1765 keV 7.69 MeV (a) (b) (c)

15. 15 P&C - 2014 Distribution of lifetime of 214 Po nuclei for a total data set of TAU-1 τ = 163.9±0.2 μs Dependence of 214 Po half-life on low threshold of the decay curve of TAU-1 Results New measured half-life value for 214 Po – 163.58±0.29(stat.)±0.10(syst.) µs [G. Bellini, J.Benziger, D.Bick et al. “Lifetime measurements of 214 Po and 212 Po with the CTF liquid scintillator detector at LNGS”. Eur. Phys. J. A (2013) 49:92] Sources of systematic errors of 214 Po half-life y=a∙exp(-ln(2)∙t/  )+b

16. 16 P&C - 2014 Results Dependence of 214 Po half-life on low threshold of the decay curve of TAU-1 τ = 164.4±0.2 μs Dependence of 214 Po 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 214 Po half-life

17. 17 P&C - 2014 Distribution of lifetime of 214 Po nuclei for a total data set of TAU-2 τ = 163.42±0.06 μs Dependence of 214 Po half-life on low threshold of the decay curve of TAU-2 Results New measured half-life value for 214 Po – 163.58±0.29(stat.)±0.10(syst.) µs [G. Bellini, J.Benziger, D.Bick et al. “Lifetime measurements of 214 Po and 212 Po with the CTF liquid scintillator detector at LNGS”. Eur. Phys. J. A (2013) 49:92] Sources of systematic errors of 214 Po half-life y=a∙exp(-ln(2)∙t/  )+b

18. 18 P&C - 2014 Results Sources of systematic errors of 214 Po half-life y(t,Δt i )= a i ∙exp(-ln(2)∙t/  i )+b i Δt i = week, i = 1-50 y(t,Δt i )= a i ∙exp(-ln(2)∙t/  i )+b tot ∙N i /N tot Δt i = week, i = 1-50 Distribution in time of half-life of 214 Po for ‘a week data’ sets of TAU-2 for the ORIGIN fitting Distribution in time of half- life of 214 Po for ‘a week data’ sets of TAU-2 for the MLM fitting

19. 19 P&C - 2014 Results Distribution in time of normalized values of half- life of 214 Po for ‘a week data’ sets of TAU-2. A 365 ≤ 7∙10 -4 (90% C.L.) Sources of systematic errors of 214 Po half-life Dependence of 214 Po 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

20. 20 P&C - 2014 Results Sources of systematic errors of 214 Po half-life Dependence of half-life of 214 Po 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 A 24h/12h ≈± 9∙10 -4

21. 21 P&C - 2014 Conclusions 1. A sensitivity of two underground installations aimed at monitoring the time stability of 214 Po 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 214 Po half-life does not exceed A 365 ≤ 7∙10 -4 (90% C.L.) of the τ mean value on TAU-2. 5. The winter-summer variation of τ with amplitude of A winter/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 A 24h/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 214 Po half-life

22. 22 P&C - 2014 Sources of systematic errors of 214 Po half-life