Solar influence on nuclear decay rates: constraints from the MESSENGER mission

We have analyzed ¹³⁷Cs decay data, obtained from a small sample onboard the MESSENGER spacecraft en route to Mercury, with the aim of setting limits on a possible correlation between nuclear decay rates and solar activity. Such a correlation has been suggested recently on the basis of data from ⁵⁴Mn decay during the solar flare of 13 December 2006, and by indications of an annual and other periodic variations in the decay rates of ³²Si, ³⁶Cl, and ²²⁶Ra. Data from five measurements of the ¹³⁷Cs count rate over a period of approximately 5.4 years have been fit to a formula which accounts for the usual exponential decrease in count rate over time, along with the addition of a theoretical solar contribution varying with MESSENGER-Sun separation. The indication of solar influence is then characterized by a non-zero value of the calculated parameter ξ, and we find ξ=(2.8±8.1)×10⁻³ for ¹³⁷Cs. A simulation of the increased data that can hypothetically be expected following Mercury orbit insertion on 18 March 2011 suggests that the anticipated improvement in the determination of ξ could reveal a non-zero value of ξ if present at a level consistent with other data.     

Power Spectrum Analysis of Physikalisch-Technische Bundesanstalt Decay-Rate Data: Evidence for Solar Rotational Modulation

Evidence for an anomalous annual periodicity in certain nuclear-decay data has led to speculation on a possible solar influence on nuclear processes. We have recently analyzed data concerning the decay rates of ³⁶Cl and ³²Si, acquired at the Brookhaven National Laboratory (BNL), to search for evidence that might be indicative of a process involving solar rotation. Smoothing of the power spectrum by weighted-running-mean analysis leads to a significant peak at frequency 11.18 year⁻¹, which is lower than the equatorial synodic rotation rates of the convection and radiative zones. This article concerns measurements of the decay rates of ²²⁶Ra acquired at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. We find that a similar (but not identical) analysis yields a significant peak in the PTB dataset at frequency 11.21 year⁻¹, and a peak in the BNL dataset at 11.25 year⁻¹. The change in the BNL result is not significant, since the uncertainties in the BNL and PTB analyses are estimated to be 0.13 year⁻¹ and 0.07 year⁻¹, respectively. Combining the two running means by forming the joint power statistic leads to a highly significant peak at frequency 11.23 year⁻¹. We will briefly comment on the possible implications of these results for solar physics and for particle physics.     

Long-term measurements of 36Cl to investigate potential solar influence on the decay rate

Recently, Jenkins et al. [6] reported on fluctuations in the detected decay events of ³⁶Cl which were measured with a Geiger–Müller counter. Experimental data of ³²Si measured by means of an end-window gas-flow proportional counter at the Brookhaven National Laboratory show similar periodicity, albeit a different amplitude. Jenkins et al. interpret the fluctuations as evidence of solar influence on the decay rates of beta-decaying radionuclides.In this work, liquid scintillation counting was used to check for potential variations in the ³⁶Cl decay rates. A custom-built counter with three photomultiplier tubes was used. In contrast to commercial counters, the relevant parameters of our system are well controlled and the discrimination threshold and HV setting can be adjusted and checked. The experimental data were analyzed by means of the triple-to-double coincidence ratio (TDCR) method which is a primary method for activity determination. Thus, our results do not depend on any other standard or reference source.Our data show fluctuations which are by more than one order of magnitude lower than those seen in the experiment using a Geiger–Müller counter. More importantly, no oscillation could be identified. Interestingly, our data overlap in time with those from Jenkins et al. [6]. We do not observe the phase and amplitude as seen by Jenkins and conclude that the fluctuations are not due to solar influence. This also implies that the interpretation by Jenkins et al. is false.     

Perturbation of nuclear decay rates during the solar flare of 2006 December 13

Recently, correlations have been reported between fluctuations in nuclear decay rates and Earth–Sun distance, which suggest that nuclear decay rates may be affected by solar activity. In this paper, we report the detection of a significant decrease in the decay of ⁵⁴Mn during the solar flare of 2006 December 13, whose X-rays were first recorded at 02:37 UT (21:37 EST on 2006 December 12). Our detector was a 1 μCi sample of ⁵⁴Mn, whose decay rate exhibited a dip coincident in time with spikes in both the X-ray and subsequent charged particle fluxes recorded by the Geostationary Operational Environmental Satellites (GOES). A secondary peak in the X-ray and proton fluxes on December 17 at 12:40 EST was also accompanied by a coincident dip in the ⁵⁴Mn decay rate. These observations support the claim by Jenkins et al. that nuclear decay rates may vary with Earth–Sun distance.     

Stochastic wave growth, power balance, and beam evolution in type III solar radio sources

Energy-balance arguments are combined with the stochastic-growth theory of type III radio sources to determine the properties of the source in average dynamical equilibrium with the beam, and the beam's long-term evolution. Purely linear stochastic-growth theory has previously emphasized that the beam evolves to a state close to marginal stability. Small mean residual deviations from marginal stability are present at dynamical equilibrium and these lead to residual energy flows that feed the waves observed in situ and by remote receivers; consequently the beam energy is depleted. Here, dynamical equilibrium beam and wave levels are estimated for the first time and it is found that the main sink of beam-driven Langmuir waves is either via electrostatic decay into product Langmuir and ion-sound waves or via scattering by short-wavelength density fluctuations, depending on the conditions. Improved estimates of energy branching ratios imply that, at 1 AU from the Sun, typically 20% of the beam energy is converted to Langmuir waves that are scattered off low-frequency density fluctuations and then dissipated, with almost all the remaining waves undergoing electrostatic decay, although as little as one-third of the Langmuir waves may decay in atypical circumstances. Of order 10^–3 of the beam energy is converted into sound waves, which are mostly dissipated, and of order 10^–5 is converted into potentially observable electromagnetic waves. The mean lifetime of the Langmuir waves at 1 AU is 1–40 s, while that of the beam is of order 1000 s. The beam density decreases relative to that of the background as the beam propagates. For most parameters, analysis of energy losses from the beam to the waves shows that the beam velocity decreases at roughly the same rate as the thermal velocity of the background plasma. It is argued from these considerations, and from in situ observations at 1 AU, that these trends imply that only the densest and fastest type III beams will be able to penetrate much past 1 AU from the Sun. This implies a low-frequency cutoff to type III emission at roughly 10 kHz, in good agreement with recent Ulysses remote observations, showing their consistency with in situ measurements.     

Evidence of redshifts in the average solar line profiles of C iv and Si iv from OSO-8 observations

Measurements of the C iv 1548 Å and Si iv 1393 Å lines made with the University of Colorado Ultraviolet Spectrometer on board OSO-8 show that the mean profiles are redshifted at disk center. Assuming these lines to be optically thin, we measure an apparent average downflow of material in the 50 000 to 100 000 K temperature range which is weighted by the emission measure in these lines. The magnitude of the redshift varies from 6–17 km s^–1 with a mean of 12 km s^–1 and is persistent at least on the order of months, which is the time covered by the observations presented in this paper. Pneuman and Kopp (1978) have demonstrated that the flux of material associated with this downflow is of the same order of magnitude as the flux of material being carried upward in spicules. Thus, it is possible that material observed to be downflowing in C iv and Si iv has its origins in the upward moving spicule material.     

The decay of the mean solar magnetic field

We have analyzed the effects that differential rotation and a hypothetical meridional flow would have on the evolution of the Sun's mean line-of-sight magnetic field as seen from Earth. By winding the large-scale field into strips of alternating positive and negative polarity, differential rotation causes the mean-field amplitude to decay and the mean-field rotation period to acquire the value corresponding to the latitude of the surviving unwound magnetic flux. For a latitudinally broad two-sector initial field such as a horizontal dipole, the decay is rapid for about 5 rotations and slow with a t ^–1/2 dependence thereafter. If a poleward meridional flow is present, it will accelerate the decay by carrying the residual flux to high latitudes where the line-of-sight components are small. The resulting decay is exponential with an e-folding time of 0.75 yr (10 rotations) for an assumed 15 m s^–1 peak meridional flow speed.E.O. Hulburt Center for Space Research.Laboratory for Computational Physics.     

Energetic protons from the solar flare of March 24, 1966

Ten to 100 meV protons from the solar flare of March 24, 1966 were observed on the University of California scintillation counter on OGO-I. The short rise and decay times observed in the count rates of the 32 channels of pulse-height analysis show that scattering of the protons by the interplanetary field was much less important in this event than in previously observed proton flares. A diffusion theory in which D = M _r is found to be inadequate to account for the time behavior of the count rates of this event. Small fluctuations of the otherwise smooth decay phase may be due to flare protons reflected from the back of a shock front, which passed the earth on March 23.     

The evolution of nonlinear hydrodynamical density fluctuations of the photon-plasma gas during the recombination era of the Universe

On the basis of the hydrodynamical equations of a two-component gas (photons and hydrogen with coupling via Thomson scattering) in the recombination era of the Universe (standard model), the evolution of the density perturbations up to second order are calculated. It is shown, that the generated second-order amplitudes of the density fluctuations of the matter reach values of the same order as the first-order amplitudes within only one tenth of the expansion time for fluctuations with wavelengths corresponding to 10⁷ M . Upper limits in the density fluctuations (for the gravitationally instable modes) up to which first-order calculations are valid, are given. This calculation indicates that the linear perturbation analysis is very restricted, especially at wavelengths near the lower limit of the Jeans length.The linear analysis would be a good approximation only for density fluctuations of the matter with the density contrast less than 10^–5–10^–4 at the recombination era. Therefore, a nonlinear analysis which is not based on a perturbation series is required for studying the evolution of the density perturbations, because for this we need a density contrast of 10^–2–10^–3 at the end of the recombination era.     

Wave propagation in the photosphere

Using a 32 minutes sequence of observation, brightness and velocity fluctuations in the wings of the Mgi line at 5172.7 Å and Fe ii line at 5197.578 Å are analysed. The analysis of phase shifts and amplitude ratios leads to the following conclusions:

Characteristics of soft solar X-ray bursts

The burst component of the solar X-ray flux in the soft wavelength range 2 < < 12 Å observed from Explorer 33 and Explorer 35 from July 1966 to September 1968 was analyzed. In this period 4028 burst peaks were identified.The differential distributions of the temporal and intensity parameters of the bursts revealed no separation into more than one class of bursts. The most frequently observed value for rise time was 4 min and for decay time was 12 min. The distribution of the ratio of rise to decay time can be represented by an exponential with exponent -2.31 from a ratio of 0.3 to 2.7; the maximum in this distribution occurred at a ratio of 0.3. The values of the total observed flux, divided by the background flux at burst maximum, can be represented by a power law with exponent -2.62 for ratios between 1.5 and 32. The distribution of peak burst fluxes can be represented by a power law with exponent - 1.75 over the range 1–100 milli-erg (cm² sec)^–1. The flux time integral values are given by a power law with exponent -1.44 over the range 1–50 erg cm^–2.The distribution of peak burst flux as a function of H importance revealed a general tendency for larger peak X-ray fluxes to occur with both larger H flare areas and with brighter H flares. There is no significant dependence of X-ray burst occurrence on heliographic longitude; the emission thus lacks directivity.The theory of free-free emission by a thermal electron distribution was applied to a composite quantitative discussion of hard X-ray fluxes (data from Arnoldy et al., 1968; Kane and Winckler, 1969; and Hudson et al., 1969) and soft X-ray fluxes during solar X-ray bursts. Using bursts yielding measured X-ray intensities in three different energy intervals, covering a total range of 1–50 keV, temperatures and emission measures were derived. The emission measure was found to vary from event to event. The peak time of hard X-ray events was found to occur an average of 3 min before the peak time of the corresponding soft X-ray bursts. Thus a changing emission measure during the event is also required. A free-free emission process with temperatures of 12–39 × 10⁶K and with an emission measure in the range 3.6 × 10⁴⁷ to 2.1 × 10⁵⁰ cm^–3 which varies both from event to event and within an individual event is required by the data examined.Now at Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey.     

Densities and mass motions in transition-zone plasmas in solar flares observed from Skylab

We studied the EUV line spectra of three flare observed with the NRL slit spectrograph on Skylab. The electron densities in the flare transition-zone plasmas are determined from density-sensitive lines of Si iii and O iv. The electron densities in all three flares studied were greatest during the flare maximum with values of the order of 10¹² cm^–3. The density decreases by a factor of 2 to 3 in the decay phase of the flares. The intensities of EUV lines from the flare chromospheric and transition-zone plasmas all are greatly enhanced. In contrast to lines for Oi, Ci, Feii and other chromospheric ions, the lines of Oiv and Nv and other transition-zone lines are not only enhanced but also very much broadened.Fitting of the N v 1242 Å line with a two-gaussian model shows that for two of the flares studied, there is a red-shifted component in addition to an unshifted component. The shifted component in the N v line profiles is interpreted as due to a dynamic and moving plasma with a bulk motion velocity of 12 km s^–1 for one flare and more than 70 km s^–1 for the other. The broadened line profiles indicate that there are large turbulent mass motions with random velocities ranging from 30 to 80 km s^–1.Ball Corporation. Now with NASA/Marshall Space Flight Center.     

Analysis of 2-d flare spectra: Velocity fields derived from Hα line asymmetries

We derive a time series of two-dimensional velocity fields for a flare region on 1992 December 16, based on the asymmetries of the H line. The H spectra were obtained by an imaging spectrograph at the Solar Tower Telescope of Nanjing University. Four sites with evident chromospheric downflows are found to appear and decay consecutively in the studied region. The value of maximum velocities is 30–40 km s^–1 and the lifetime of downflows is 2–3 min at these sites. It is also shown that the asymmetries only exist at the line wing, while the line center has nearly no shifts for this flare. Finally, we make a discussion on the characteristics of the velocity distribution and its correlations with the intensity distribution, as well as with the hard X-ray emission.     

Interpretation of time characteristics of solar X-ray bursts referring to associated microwave bursts

It has been controversial whether the flare-associated hard X-ray bursts are thermal emission or non-thermal emission. Another controversial point is whether or not the associated microwave impulsive burst originates from the common electrons emitting the hard X-ray burst.It is shown in this paper that both the thermal and non-thermal bremsstrahlung should be taken into account in the quantitative explanation of the time characteristics of the hard X-ray bursts observed so far in the photon energy range of 10–150 keV. It is emphasized that the non-thermal electrons emitting the hard X-rays and those emitting the microwave impulsive burst are not common. The model is as follows, which is also consistent with the radio observations.At the explosive phase of the flare a hot coronal condensation is made, its temperature is generally 10⁷ to 10⁸K, the number density is about 10¹⁰ cm^–3 and the total volume is of the order of 10²⁹ cm³. A small fraction, 10^–3–10^–4, of the thermal electrons is accelerated to have power law distribution. Both the non-thermal and thermal electrons in the sporadic condensation contribute to the X-ray bursts above 10 keV as the bremsstrahlung. Fast decay of the harder X-rays (say, above 20 keV) for a few minutes is attributed to the decay of non-thermal electrons due to collisions with thermal electrons in the hot condensation. Slower decay of the softer X-rays including around 10 keV is attributed to the contribution of thermal component.The summary of this paper was presented at the Symposium on Solar Flares and Space Research, COSPAR, Tokyo, May, 1968.     

The Hard X-ray Telescope (HXT) for the SOLAR-A mission

The Hard X-ray Telescope (HXT) is a Fourier-synthesis imager; a set of spatially-modulated photon count data are taken from 64 independent subcollimators and are Fourier-transformed into an image by using procedures such as the maximum entropy method (MEM) or CLEAN. The HXT takes images of solar flares simultaneously in four energy bands, nominally 15 (or 19)–24, 24–35, 35–57, and 57–100 keV, with an ultimate angular resolution as fine as 5 arc sec and a time resolution 0.5 s. Each subcollimator has a field of view wider than the solar disk. The total effective area of the collimator/detector system reaches 70 cm², about one order of magnitude larger than that of the HINOTORI hard X-ray imager. Thanks to these improvements, HXT will for the first time enable us to take images of flares at photon energies above 30 keV. These higher-energy images will be compared with lower-energy ones, giving clues to the understanding of nonthermal processes in solar flares, i.e., the acceleration and confinement of energetic electrons. It is of particular importance to specify the acceleration site with regard to the magnetic field figuration in a flaring region, which will be achieved by collaborative observations between HXT and the Soft X-ray Telescope on board the same mission.After the launch the name of SOLAR-A has been changed to YOHKOH.     

Evidence for correlations between fluctuations in 54Mn decay rates and solar storms

Following recent indications that several radioactive isotopes show fluctuating decay rates which may be influenced by solar activity, we present findings from a 2 year period of data collection on ⁵⁴Mn. Measurements were recorded hourly from a 1 μCi sample of ⁵⁴Mn monitored from January 2010–December 2011. A series of signal-detection algorithms determine regions of statistically significant fluctuations in decay behaviour from the expected exponential form. The 239 decay flags identified during this interval were compared to daily distributions of multiple solar indices, generated by noaa, which are associated with heightened solar activity. The indices were filtered to provide a list of the 413 strongest events during a coincident period. We find that 49% of the strongest solar events are preceded by at least 1 decay flag within a 48 h interval, and 37% of decay flags are followed by a reported solar event within 48 h. These results are significant at the 0.9σ and 2.8σ levels respectively, based on a comparison to results obtained from a shuffle test, in which the decay measurements were randomly shuffled in time 10,000 times. We also present results from a simulation combining constructed data reflecting 10 sites which compared and filtered decay flags generated from all sites. The results indicate a potential 35% reduction in the false positive rate in going from 1 to 10 sites. By implication, the improved statistics attest to the benefit of analysing data from a larger number of geographically distributed sites in parallel.     

The ionization state of oxygen ions in anomalous cosmic rays: Results from the ANURADHA experiment in Spacelab-3

We report the first results on the determination of the ionization states of oxygen ions in the anomalous cosmic rays (ACR) from the measurements of their flux in the cosmic-ray experiment in Spacelab-3 (SL-3) mission of NASA flown at 350 km altitude during 29 April–6 May, 1985. The detectors used were specially prepared CR-39 plastics of very high sensitivity for recording tracks of ions withZ>2. The measured orbit averaged flux of ACR oxygen is (2.9±1.3)×10^–4 particles m^–2sr^–1s^–1 (MeV N^–1) at an energy of 23 MeV N^–1. We made an independent estimate of the expected ACR oxygen flux at SL-3 orbit from interplanetary data and compared this with the measured flux to infer the ionization states of ACR oxygen ions. The flux and energy spectra of ACR oxygen at 1 AU outside the magnetosphere is obtained from the data of Voyager-2, during the same epoch as the SL-3 flight, and using the measured radial intensity gradient of 15%/AU for ACR oxygen between 1–17 AU. We calculate the geomagnetic transmission factors for ACR oxygen ions of charge states O⁺¹, O⁺², etc., from the known cut-off rigidities in the world grid and using the SL-3 trajectories for 116 orbits in the 6-day mission to obtain the expected flux at SL-3 for different charge states. When these flux values are compared with our measured flux, the averge ionization state of ACR oxygen ions in the energy interval of 20–26 MeV N^–1 is obtained as O⁺¹.     

Characteristic size and diffusion of quiet sun magnetic patterns

We have previously studied large-scale motions using high-resolution magnetograms taken from 1978 to 1990 with the NSO Vacuum Telescope on Kitt Peak. Latitudinal and longitudinal motions were determined by a two-dimensional crosscorrelation analysis of pairs of consecutive daily observations using small magnetic features as tracers. Here we examine the shape and amplitude of the crosscorrelation functions. We find a characteristic length scale as indicated by the FWHM of the crosscorrelation functions of 16.6 ± 0.2 Mm. The length scale is constant within ±45° latitude and decreases by about 5% at 52.5° latitude; i.e., the characteristic size is almost latitude independent. The characteristic scale is within 3% of the average value during most times of the solar cycle, but it increases during cycle maximum at latitudes where active regions are present. For the time period 1978–1981 (solar cycle maximum), the length scale increases up to 1.7 Mm or 10% at 30° latitude. In addition, we derive the average amplitude of the crosscorrelation functions, which reflects the diffusion of magnetic elements and their evolutionary changes (including formation and decay). We find an average value of 0.091 ± 0.003 for the crosscorrelation amplitude at a time lag of one day, which we interpret as being caused by the combined effect of the lifetime of magnetic features and a diffusion process. Assuming a lifetime of one day, we find a value of 120 km² s^–1 for the diffusion constant, while a lifetime of two days leads to 230 km² s^–1.Operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation.     

New period and period variations of DX Aquarii

The new period (P=0 _. ^d 461700) of the eclipsing binary system DX Aqr has been presented, which is based on available times of minima. O–C diagram of DX Aqr has been presented for the first time, and the period variations present in the system have been analysed. In all five period increases and five period decreases are nothed, and four period increases and five period decreases have been discussed. The strongest period increase occurs between 1975 and 1976. The total period change in different portions of the O–C diagram ranges from 1.40×10^–4 d to 3.61×10^–6 d. Appreciable period fluctuations have been noted to have occurred in the time intervals, 1964–1965 and 1974–1975.     

The quantitative properties of three soft X-ray flare kernels observed with the AS&E X-ray telescope on Skylab

The physical parameters for the kernels of three solar X-ray flare events have been deduced using photographic data from the S-054 X-ray telescope on Skylab as the primary data source and 1–8 and 8–20 Å fluxes from Solrad 9 as the secondary data source. The kernels had diameters of 5–7 and in two cases electron densities at least as high as 3 × 10¹¹ cm^–3. The lifetimes of the kernels were 5–10 min. The presence of thermal conduction during the decay phases is used to argue: (1) that kernels are entire, not small portions of, coronal loop structures, and (2) that flare heating must continue during the decay phase.We suggest a simple geometric model to explain the role of kernels in flares in which kernels are identified with emerging flux regions. The flare is triggered at the neutral sheet between the EFR and a larger loop structure. We associate the X-ray kernels with H kernels, which previously associated (incorrectly, we believe) with the nonthermal impulsive phases of flares.Most of this work was completed while the author was a Visiting Scientist at the Center for Astrophysics, Cambridge, Massachusetts 02138.