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ISSN 0016-7932, Geomagnetism and Aeronomy, 2007, Vol. 47, No. 6, pp. 776–780. © Pleiades Publishing, Ltd., 2007.Original Russian Text © B.M. Vladimirskii, A.V. Bruns, 2007, published in Geomagnetizm i Aeronomiya, 2007, Vol. 47, No. 6, pp. 819–824.

1. INTRODUCTION

The problem of variations in the intensity of solarneutrino remains complex and contradictory. One ofthe possible ways to solve this problem is the hypothe-sis that a special uncontrolled factor affects results ofcorresponding measurements [Vladimirskii and Bruns,2001, 2004]. It is assumed that the effectiveness of neu-trino registration (specifically, with radiochemicalfacilities) is affected by heliogeophysical electromag-netic disturbances at extremely low frequencies (thesedisturbances easily penetrate into underground labora-tories).

The above hypothesis is still justified by indirectarguments. It turned out that the measured neutrino fluxdepends on the value of cosmophysical indices duringthe last weeks of the exposure at all active radiochemi-cal facilities. On the other hand, the effect of very weakvariable magnetic fields on the parameters of aqueoussolutions has been found out in laboratory experiments.For example, the magnetic field at a frequency of 10 Hzreliably changes the crystallization dynamics in anaqueous solution at an amplitude of only 0.6 nT [Led-nev et al., 2003]. A change in electric conductivitycauses changes in the values of other parameters,including the ability to irreversibly bind neutrino reac-tion products in solution. False variations in the inten-sity of solar neutrino in Cherenkov detectors can beobserved at a change, e.g., in refraction coefficient[Vladimirskii and Konradov, 2005].

It has been discovered that the flux of neutrino ficti-tiously increases during all three radiochemical experi-

ments (Brookheaven, SAGE, and GALLEX) if a globalmagnetic storm is observed during the last weak of theexposure [Vladimirskii and Bruns, 2004]. It is interest-ing whether any similar variations in the intensity orig-inate during the development of smaller-scale but par-tially similar disturbances related to chromosphericflares, i.e., sudden ionospheric disturbances. The flareindex was not used in the cited work as a heliogeophys-ical indicator to analyze false variations. Therefore, theresults of searching for the flare effect in radiochemicalmeasurements could be a certain additional verificationof the considered hypothesis.

Studying the effect of flare activity on the results ofsolar neutrino flux measurements is additionally stimu-lated by certain other considerations. The cycle ofabout five months has recently been found out in themeasured neutrino intensity variations [Raychandhuri,2003]. This period (~155 days), well-known in geo-physics, was finally discovered precisely in the flarerecurrence rate.

It is known that the first indications that the flareeffect is present in neutrino measurements wereobtained more than 10 years ago [Bazilevskaya et al.,1984]. Subsequently, many researchers studied thisproblem (the problem is reviewed and the bibliographyis presented in the monograph [Bahcall, 1989]). It wasconvincingly indicated, using the data of direct count-ing detectors, that flares cannot perceptibly contributeto the neutrino intensity measured with radiochemicalfacilities. However, this conclusion was mainly relatedto the data interpretation by Bazilevskaya et al. [1984]

Effect of Solar Flares in Radiochemical Measurements of Solar Neutrino Intensity

B. M. Vladimirskii and A. V. Bruns

Research Institute Crimean Astrophysical Observatory, National Academy of Sciences of Ukraine, p/o Nauchnyi, Crimea, 334413 Ukraine

Received February 21, 2006; in final form, January 29, 2007

Abstract

—The effect of chromospheric flares at the end of the exposure has been studied for all radiochemicalfacilities measuring the flux of solar neutrino. For chlorine-argon measurements (Brookheaven), it has beenfound that the development of flared results in the count rate acceleration to

4.7

±

1.2

SNU. The effect of thisgrowth is fictitious; this is an increase in the effectiveness of reaction product extraction from the target matterunder the action of the ULF electromagnetic disturbance induced by the flare X-rays rather than an increase inthe flux. The indications that a similar effect is present in the SAGE gallium–germanium measurement havebeen obtained. For the GALLEX gallium–germanium experiment, the effect of flares has not been found; thesign of this effect possibly differs from that of the Brookheaven and SAGE measurements. The found differenceagrees with the conclusion that the results of the SAGE and GALLEX measurements anticorrelate for the expo-sures that end simultaneously.

PACS numbers:

9

5.85.Ry

DOI:

10.1134/S0016793207060114

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EFFECT OF SOLAR FLARES IN RADIOCHEMICAL MEASUREMENTS 777

rather than to the observational, purely empirical, partof the situation. The problem of the effect of flares onthe results of radiochemical measurements remainedreally open.

The aforesaid explains why it would be reasonableto consider again the results of these studies. Below, wepresent the results of an analysis for all operating radi-ochemical facilities.

2. INITIAL DATA AND METHOD OF ANALYSIS

As an initial material we used all data collected in[Vladimirskii and Bruns, 2004]: the chlorine–argonmeasurements performed in 1970–1994 (108 expo-sures) [Clevelend et al., 1998]; GALLEX data for1991–1997 (65 exposures) and GNO data for 1998–1999 (19 exposures) [GALLEX, 1992–1999]; theresults of the SAGE measurements performed in 1989–2000 (80 exposures, presented by the authors of theexperiment). Since all cosmic indices, including flareactivity, reflect the situation at the end of the exposure,when the reaction products have been accumulated, alldigital data are used as an indicator of the completenessof product extraction from a target matter. Possiblevariations in the extraction completeness are masked byconsiderable statistical fluctuations.

The procedure of a search for flare effects as a resultof these measurements unambiguously depends on thephenomenological pattern of sudden ionospheric dis-turbance and on the hypothetical model of the effect ofthe corresponding magnetic complex of phenomena ona fluid, i.e., a target matter. Ionospheric disturbance iscaused by absorption of the flare X rays (pulses lastingabout an hour for a sufficiently powerful event). A sharpincrease in ionization results in a sudden intensificationof LF atmospheric radiowaves and in the appearance ofexcess geomagnetic pulsations. The latter belong toordinary daytime pulsations according to the mostimportant their properties but have the larger amplitude(see e.g., [Dovbnya et al., 1994]). The described picturedevelops at the sunlit hemisphere, is pronounced nearthe subsolar point, and depends on the X-ray flareparameters.

It is assumed that an LF electromagnetic distur-bance substantially affects the dynamics of structuraltransitions in a fluid target. For example, two classes ofstates can exist in a target. In one such state, the abilityto irreversibly bind reaction products with neutrino—molecular complexes that originated around Ar

37

and

Ge

71

ions—is relatively high. If the exposure end fallson precisely such situation, the measured intensity willbe decreased. In the case of transition into the otherstructural state (the ability of combination of the molec-ular ensemble with the above ions is lower), the inten-sity can become higher in the corresponding exposure.The characteristic lifetimes of such states are appar-ently several days (certainly, these lifetimes are reallyunknown). By analogy with the effect of magnetic

storms, we can assume that the effect of a flare inducesthe transition into the state of weak retention of neu-trino reaction products. In such a case, the appearanceof flares at the very end of an exposure will be accom-panied by an imaginary intensification for events nearthe subsolar point, which will be absent in the localnighttime.

To verify the considered scenario, we compiled aspecial catalog of chromospheric flares for the last 14days of each exposure during each experiment. Allflares of optic importance

≥

2F

were included in the cat-alog.

If a given flare produced accelerated protons, thisflare was included in the catalog even if its importancewas lower. International summaries [Quat. Bull. Sol.Act.] and standardized lists of proton events[www.ngdc.noaa.gov] gave materials for the catalog.The local time of a flare beginning for a given facilitywas determined from the explicit relationship

T

1

=

T

u

+

λ

/15 (

λ

is the geographic longitude of a facility). If nec-essary, a flare heliolongitude was taken into account.Additional data on the integral indices of solar activity(Wolf numbers

R

) and geomagnetic activity

Ap

weretaken from the bulletin

Solar–Geophysical Data

or itselectronic analog. The above cases of a fictitiousincrease in the neutrino flux, related to magnetic storms(the average

Ap

value during the last week of the expo-sure were

≥

25.0

) were not considered from the verybeginning. Below, we present the spread of averages,i.e., standard deviations. The statistical significance ofa difference in the averages was everywhere calculatedaccording to the Mann–Whittney criterion

P

(

U

) (a non-parametric analog of the Student criterion).

3. RESULTS

3.1. Brookheaven–SAGE Experiment

It is reasonable to jointly consider the experimentswhich showed a similar behavior under the action ofdisturbances, although the technology of measurementwas different for these experiments. It was found thatfictitious changes in the neutrino intensities for simul-taneously ending exposures are synchronous in thechlorine–argon measurements and in the SAGE exper-iment [Vladimirskii and Bruns, 2004]. For evident rea-sons, it is possible to study the data of chlorine–argonmeasurements in more detail. Therefore, the data onthis experiment are presented below most thoroughly.

On the basis of flare presence–absence for the last14 days of exposure, the data for both facilities weredivided into two equal groups. Table 1 presents the datafor the Brookheaven facility. The count rate

Q

is givenin the units used by the authors:

Ä

r

37

day

–1

. Magneticactivity—the

Ap

index, Wolf number

R

, and exposureduration

∆

(days)—is represented by average values fora given sample.

The sample in the last line of Table 1 includes theresults corresponding to the absence of any sporadic

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disturbances at the end of exposure. This standard valuefor quiet conditions is slightly larger than the averagevalue for the entire set of measurements, probably, dueto weak anticorrelation between the count rate and Wolfnumbers (this anticorrelation is evident for odd cycles,see [Vladimirskii and Bruns, 2004]).

The next step is a search for the day–night effect.For this purpose, we divided the sample in the first lineof Table 1 into two parts based on the following criteria:

(1) The day situation: at least one flare with thezenith distance from the local noon meridian not morethan 6 h should be observed within the considered two-week interval.

(2) The night situation: only flares with the zenithdistance > 6 h (nighttime flares for a given facility)were registered within the above interval in the catalog.

The results for the Brookheaven and SAGE facilitiesare presented in Tables 2 and 3, respectively (in the lat-ter case, the count rate is expressed in SNU).

For the chlorine–argon measurements (Table 2), anincrease in the count rate

Q

for daytime events—a fac-tor of approximately 1.5 as compared to nighttimeevents (significant at a level of

P

(

U

*) =

2

×

10

–2

)—should be related to the effect of flares since all remain-ing parameters (

Ap

,

R

, and

∆

) are almost identical inTable 2. If only proton flares are considered in thisgroup, the effect remains valid: day—

0.541

±

0.430(

n

= 7)

: night—

0.323

±

0.237 (

n

=

13)

= 0.31. The firstresearchers of the effect of flares on the result of chlo-rine–argon measurements noted that this effect is more

contrasting if a flare is located closer to the expositionend [Bazilevskaya et al., 1984]. This tendency is con-firmed: it was found that the count rate

Q

for daytimeevents increases due to the cases that took place duringthe final week of the exposure. For this week,

Q

=

0.552

±

0.298 (

n

= 10)

; for the previous week,

0.450

±

0.264(

n

=

13)

; the difference is significant at

P

(

U

*) = 0.17. Itwas also found that, in the same situation of a daytimeflare, the effect is imperceptible (or absent) if flareactivity is extremely high: the flare recurrence rate is0.5 events per day or higher.

Finally, we can verify the effect reality, havingselected the events when the anticipated effect of flareson the result of measurements would be maximal.According to the above scenario and taking intoaccount the results considered previously [Vladimirskiiand Bruns, 2004], such cases should simultaneouslysatisfy the following three conditions: (i) a flare shouldnot take place more than eight days from the end ofexposure; (ii) the flare time should be close to localnoon for a given facility; i.e., the zenith distance shouldbe not more than 3.3 h; (iii) the exposure durationshould be not more than 70 days. Only six exposuressatisfy these conditions. However, the count rate forthese events is twice as high as this rate for nighttimeflares (0.83

±

0.212). A difference between the averages(a comparison with the low line in Table 2) is signifi-cant at a level of

P

(

U

*) =

5

×

10

–2

. In spite of a cata-strophic decrease in the number of cases, variancedecreased.

Table 1.

Brookheaven experiment: presence–absence of flares

Situations Numberof cases,

n

Parameters

Q Ap R

∆

Flares available 51 0.440

±

0.319 15.1

±

5.3 111.8

±

49.6 76.5

±

30.1

Flares absent 39 0.496 + 0.315 11.3

±

4.5 47.2

±

41.7 74.1

±

32.3

Table 2.

Brookheaven experiment: day–night effect

Situations Number of cases,

n

Parameters

Q Ap R

∆

Day 27 0.516

±

0.314 15.3

±

6.3 124.9

±

50.0 69.8

±

19.3

Night 24 0.353

±

0.302 14.9

±

4.0 97.0

±

44.8 84.0

±

37.5

Table 3.

SAGE experiment: day–night effect

Situations Number of cases,

n

Parameters

SNU

Ap R

∆

Day 33 73.6 + 59.6 11.4

±

4.6 106.7

±

149.7 34.1

±

16.7

Night 4 76.4 + 52.6 11.6

±

5.0 35.1

±

31.2 37.9 + 10.0

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EFFECT OF SOLAR FLARES IN RADIOCHEMICAL MEASUREMENTS 779

It is impossible to make a certain conclusion on theeffect of flares for the SAGE experiment based on adirect comparison (Table 3) because the number ofnighttime events is small. However, the regularitiesfound above for the Brookheaven measurements arealso traced (as tendencies) for this facility. The detec-tion of the flare effect is most favorable (the same threeconditions, but the critical value of the exposure dura-tion is not more than 32 days) when the value is largerthan the average:

115.6

±

82.1 (

n

= 7)

at a significanceof P(U*) = 0.26 for the difference from the nighttimeevents. On the whole, the effect of flares in the SAGEmeasurements, similar to the chlorine–argon measure-ments, probably exists, but data are insufficient for us toform a certain judgment.

3.2. GALLEX Gallium–Germanium Measurements

Additional difficulties in studying the flare effect atthe GALLEX facility arise since the count rate anticor-relates with the level of magnetic activity found in[Vladimirskii and Bruns, 2004]. The day–night effect isshown in Table 4 (the count rate is given in SNU, andthe exposure duration is almost the same, so that thecorresponding column is omitted).

For the daytime events, the count rate value is pre-sented in the second line and corresponds to the lowerlevel of magnetic activity for nighttime cases. It is clearthat the value obtained after correction is very close tothe average value for the entire set of measurements(76.1, if magnetic storms are eliminated). A small num-ber of nighttime events does not allow us to make a cer-tain conclusion, but we can assume that a flare effect isnot observed in this case.

Such an assumption is confirmed by both tests usedin the previous section.

(1) The count rate is compared for the last week ofthe exposure and for the preceding week. The following

results are obtained: the last week of the exposure—41.6 ± 35.7 (n = 7); previous week—78.6 ± 36.6 (n =16). A difference is significant at a level of P(U*) = 0.17but has an opposite sign as compared to theBrookheaven and SAGE facilities. This differenceremains valid for both high and low magnetic activity.

(2) For the group of events when the effect of flaresshould be revealed most evidently (the same condi-tions: the zenith distance of a flare is not more than3.3 h for this facility; the time interval between theoccurrence of a flare and the end of the exposure is notmore than eight days; the exposure duration is not morethan 22 days), the obtained value is smaller than theaverage value for the entire set of measurements: 56.2 ±27.3 (n = 5). This value almost coincides with such avalue for nighttime cases (the second line in Table 4).

On the whole, it turned out that flare activity duringGALLEX measurements suppresses the measuredcount rate. The effect of flares found for theBrookheaven and SAGE facilities is absent in this case.

4. DISCUSSION

The search for the effects of flares for all three radi-ochemical facilities is summarized in Table 5. To facil-itate a comparison, all results are normalized to theaverage count rates for the corresponding complete setsof measurements. The last line includes the effects ofmagnetic storms taken from [Vladimirskii and Bruns,2004]. The spread in values represents standard devia-tions.

For the chlorine–argon measurements, the effect offlares is detected unambiguously, which can be consid-ered as the confirmation of the early results [Bazi-levskaya et al., 1984]. A large body of data makes itpossible to found out the day–night effect and to inter-pret these effects differently (as variations independentof real variations in neutrino fluxes). A similar effect

Table 4. GALLEX experiment: day–night effect

Situations Number of cases, nParameters

SNU Ap R

Day 30 (13) 69.06 ± 43.3 (75.8 ± 30.2) 14.2 ± 5.1 90.7 ± 48.1

Night 6 51.2 ± 47.7 10.4 ± 4.9 73.6 ± 47.7

Table 5. Effect of flares for all facilities, normalized values

SituationsParameters

Brookheaven SAGE GALLEX

Flares near the noon meridian 1.72 ± 0.45 1.39 ± 1.08 0.84 ± 0.62

Flares at night 0.75 ± 0.65 0.77 ± 0.23 0.72 ± 0.67

High flare activity 0.51 ± 0.51 0.73 ± 0.84 1.05 ± 0.73

Magnetic storms 1.19 ± 0.58 1.77 ± 1.50 1.30 ± 1.08

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was apparently found for the SAGE gallium–germa-nium measurements. For the GALLEX measurements,a fictitious increase in the count rate caused by flares isundoubtedly absent. In this case the flare effect hasprobably the opposite sign: the presence of flares sup-presses the count rate. In all three cases, it seems thatvery high flare activity changes the sign of the effect.The effect is similar for all facilities only for globalmagnetic storms that occurred during the last week ofthe exposure period.

A change of the flare effect sign at the GALLEXfacility could cast doubt on the reality of the phenome-non itself during the Brookheaven and SAGE measure-ments (since the statistical significance of the data pre-sented above is marginal!). However, it was actuallynoted that the count rates of the SAGE and GALLEXfacilities anticorrelate with each other for synchro-nously terminating exposures [Vladimirskii and Bruns,2004]. Therefore, this result seems to be natural.

It is clear that the reality of the flare effect should beconfirmed. However, we can note that the consideredphenomenon roughly agrees with the general pattern ofvariations in the count rate during the radiochemicalmeasurements, where different electromagnetic phe-nomena (indices) affect the result independently anddifferently at different facilities. For the chlorine–argonmeasurements, the count rate increases with the appear-ance of flares to the extremely large average values(4.7 ± 1.2 1.2 SNU). Vladimirskii and Bruns [2004]obtained the value 4.5 ± 1.5 without using the flareindex. A similar effect apparently takes place for theSAGE facility. However, for the GALLEX measure-ments, the maximal count rate (110.2 ± 31.2) isobserved during the periods of “absolute calmness”(Ap < 12.5; R < 30).

The change of the flare effect sign in the situationwhen the recurrence rate of events becomes high shouldcertainly be confirmed. Within the scope of the consid-ered model of the effect of weal electromagnetic fieldson the fluid parameters, the result seems to be not par-adoxical. This result can be the manifestation of thewell-known regularity: the result of the effect of a cer-tain factor on a system depends on the initial state ofthis system. An analysis performed once more con-firmed that the flux of neutrino during radiochemicalmeasurements is underestimated. Such an underestima-tion does not have the character of a systematic errorbut is accumulated due to individual episodes, when thecount rate catastrophically decreases during someexposures.

5. CONCLUSIONS

(1) For the chlorine-argon measurements, chromo-spheric flares of importance ≥2F result in an increase inthe registered count rate, if these flares occur near thesubsolar point for a given facility and the time interval

between a flare and the exposure termination is notmore than a week. In this case the measured flux canreach 4.7 ± 1.2 SNU. If a flare occurs at night, the effectis absent. This unambiguously indicates that the char-acter of an increase is fictitious.

(2) The indications exist that a similar effect isobserved during the SAGE gallium–germanium mea-surements.

(3) During the GALLEX gallium–germanium mea-surements, the effect of an increase in the count rateduring the development of flares was not found. Duringthese measurements, moderate flare activity possiblysuppresses the count rate.

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