MITKO G.G

for ″Thunderstorm″ Collaboration

ECRS-2012

Bursts of gamma-rays, electrons and Bursts of gamma-rays, electrons and low-energy neutrons during thunderstorms low-energy neutrons during thunderstorms

at the Tien-Shanat the Tien-Shan

″″Thunderstorm″ CollaborationThunderstorm″ Collaboration

V.P. AntonovaV.P. Antonova11, A.P. Chubenko, A.P. Chubenko22, A.N. Karashtin, A.N. Karashtin33, , G.G. MitkoG.G. Mitko22, M.O. Ptitsyn, M.O. Ptitsyn22, V.A. Ryabov, V.A. Ryabov22, ,

A.L. ShepetovA.L. Shepetov22, Yu.V. Shlyugaev, Yu.V. Shlyugaev44, L.I. Vildanova, L.I. Vildanova22, K.P. Zybin, K.P. Zybin22, , and A.V. Gurevichand A.V. Gurevich22

1 Institute of Ionosphere, National Center for Space Reaearch and Technology, Almaty, Kazakhstan

22 P.N. Lebedev Physical Institute of RAS, Moscow, RussiaP.N. Lebedev Physical Institute of RAS, Moscow, Russia 3 3 Research Radiophysics Institute, Nizhny Novgorod, RussiaResearch Radiophysics Institute, Nizhny Novgorod, Russia 44 Institute of Applied Physics of RAS, Nizhny Novgorod, RussiaInstitute of Applied Physics of RAS, Nizhny Novgorod, Russia

INTRODUCTIONINTRODUCTION New data of the last New data of the last

measurement season measurement season held at the Tien-Shan held at the Tien-Shan complex for complex for investigation gamma-investigation gamma-radiation, accelerated radiation, accelerated electrons and low-electrons and low-energy neutrons energy neutrons during thunderstorms during thunderstorms are presentedare presented

The experimental complex The experimental complex "Thunderstorm""Thunderstorm"

At present time, ”Thunderstorm” At present time, ”Thunderstorm” complexcomplex comprises the following comprises the following facilities: facilities:

an EAS registering system, an EAS registering system, the system of NaI scintillation the system of NaI scintillation

detectors for registration of the gamma- detectors for registration of the gamma- and X-ray emission in atmosphere, and X-ray emission in atmosphere,

the multi-layer ionization detectors of the multi-layer ionization detectors of energetic charged particles, energetic charged particles,

the neutron supermonitor for the neutron supermonitor for registration of the high-energy hadronic registration of the high-energy hadronic component of cosmic rays, component of cosmic rays,

a set of the detectors of low-energy a set of the detectors of low-energy (thermal) neutron background, (thermal) neutron background,

two independent radio systems, two independent radio systems, and electrostatic detectors of the local and electrostatic detectors of the local

electric field and its high frequency electric field and its high frequency component.component.

Extensive Air Extensive Air ShowersShowers Trigger System Trigger System

Four separate systems of Four separate systems of coincidence constructed on coincidence constructed on base of counters SI5G and use base of counters SI5G and use for development of a trigger for development of a trigger pulse at the moment of pulse at the moment of passage EAS through passage EAS through installation.installation.

The systems are in the The systems are in the vertexes of triangles with vertexes of triangles with length of an edge of 60-65 m.length of an edge of 60-65 m.

Configuration of the EAS Configuration of the EAS trigger system gives the trigger system gives the possibility to single out the possibility to single out the EAS generated with the EAS generated with the frequency about 10frequency about 10−2−2 s s−1 −1 by by cosmic ray particles having the cosmic ray particles having the energy 10energy 1015 15 eV or higher.eV or higher.

NaI-Scintillation SpectrometerNaI-Scintillation Spectrometer

To register soft To register soft gamma and hard X-gamma and hard X-ray radiation of the ray radiation of the electrons accelerated electrons accelerated in the electric fields in the electric fields of a thunderstorm of a thunderstorm cloud, 14 scintillation cloud, 14 scintillation detectors based on detectors based on NaI crystals were NaI crystals were used. used.

NaI-Scintillation SpectrometerNaI-Scintillation Spectrometer Seven registration points are Seven registration points are

situated as a chain on the situated as a chain on the slopes of the surrounding slopes of the surrounding mountains, across the usual mountains, across the usual direction of motion of direction of motion of thunderstorm clouds. thunderstorm clouds.

The distance between the The distance between the ends of this chain is about 2 ends of this chain is about 2 km, and the maximum km, and the maximum spacing of the detectors in spacing of the detectors in the vertical direction reaches the vertical direction reaches 600 m. 600 m.

The scintillation system The scintillation system designed in such a way designed in such a way allows one to study spatial allows one to study spatial distribution of the radiation distribution of the radiation inside thunderstorm clouds inside thunderstorm clouds in both horizontal and in both horizontal and vertical directions. vertical directions.

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Ionization charged particle detectorsIonization charged particle detectors

The detector is builThe detector is builtt on the basis of a on the basis of a SI5G type ionization counters which SI5G type ionization counters which are installed inside a box, 20 are installed inside a box, 20 counters per each box. counters per each box.

Counter boxes are grouped into Counter boxes are grouped into three layers, one under another.three layers, one under another.

The total sensitive area of a 20-The total sensitive area of a 20-counter box is about 2 mcounter box is about 2 m22 while that while that of a whole counter layer in a detector of a whole counter layer in a detector point is 6 mpoint is 6 m22..

The SI5G countres operate in a The SI5G countres operate in a proportional mode, when they have a proportional mode, when they have a 95−99% registration efficiency 95−99% registration efficiency concerning the relativistic charged concerning the relativistic charged particles, and a 0.05 − 1% efficiency, particles, and a 0.05 − 1% efficiency, in dependence on its energy, for in dependence on its energy, for gamma-radiation.gamma-radiation.

Neutron detectorsNeutron detectors

MMutual disposition of utual disposition of the Tien-Shan Station’s the Tien-Shan Station’s neutron detectors:neutron detectors:

A,B,C, and D — the A,B,C, and D — the units of 18NM64 units of 18NM64 neutron supermonitor; neutron supermonitor;

In, Ex, and U — the In, Ex, and U — the internal, external,internal, external,

and underfloor thermal and underfloor thermal neutron detectorsneutron detectors..

Thermal neutron detectorsThermal neutron detectors

FFor monitoringor monitoring of the low-energy (about and of the low-energy (about and below 1 eV) neutron fluxbelow 1 eV) neutron flux we use a set of special we use a set of special detectors based on the proportional neutron detectors based on the proportional neutron counterscounters..

The counters are filled with the gas The counters are filled with the gas 33He under the He under the pressure of 2 atmospheres, so the neutron pressure of 2 atmospheres, so the neutron registrationregistration in the thermal energy range in the thermal energy range succeeds due to reaction succeeds due to reaction 33He(n, p)t with an He(n, p)t with an efficiency of about 8efficiency of about 855%.%.

BecauseBecause of the absence of any neutron of the absence of any neutron moderating material around the counters, the moderating material around the counters, the considered detectors canconsidered detectors can register only the slow register only the slow neutrons which have just been moderated down neutrons which have just been moderated down to thermal energies (about 10to thermal energies (about 10−2−2eV )eV ) in in surrounding environment, but are fully surrounding environment, but are fully insensitive to the high-energy hadron flux of a insensitive to the high-energy hadron flux of a cosmic ray origin.cosmic ray origin.

Electrostatic fluxmeterElectrostatic fluxmeter

This setup comprises This setup comprises the detectors the detectors measuring changes in measuring changes in the electric field under the electric field under thunderstorm thunderstorm conditions: the quasi-conditions: the quasi-static (“slow”) electric static (“slow”) electric field is measured by an field is measured by an electrostatic fluxmeter electrostatic fluxmeter of the “field-mill” type, of the “field-mill” type, and variations in the and variations in the electric field in the electric field in the frequency range 0frequency range 0..5 – 5 – 25 kHz (“fast” field), by 25 kHz (“fast” field), by a capacitor-type a capacitor-type sensor.sensor.

Radio SystemRadio System

Two radiosystems are Two radiosystems are designed for short designed for short electromagnetic pulse electromagnetic pulse observations in the observations in the frequency range from frequency range from 0.1 to 30 MHz. Their 0.1 to 30 MHz. Their time resolution is 16 ns. time resolution is 16 ns. Also, the systems Also, the systems determined the determined the direction to radiation direction to radiation sources from the sources from the relative time delays of relative time delays of radio signals. radio signals.

The radiosystems The radiosystems operate in the external operate in the external trigger mode. trigger mode.

Atmospheric discharges and bursts Atmospheric discharges and bursts of gamma-rays of gamma-rays

WWe will consider the e will consider the identification of gammaidentification of gamma--radiationradiation bursts with the bursts with the moments of atmospheric moments of atmospheric discharges ondischarges on the the example example of one of the of one of the thunderstormsthunderstorms..

Atmospheric discharges Atmospheric discharges have been identified by the have been identified by the fast changes of the quasi-fast changes of the quasi-static electric field. static electric field.

There are negative and There are negative and positive discharges.positive discharges.

Record of the quasi-static electric field as measured by “field-mill” fluxmeter and its variations from a capacitor-type sensor. A – an active period of the thunderstorm 07:27–07:46, the electric field is significantly lowered. B – relaxation period of the thunderstorm 07:50–08:00 with an enlarged scale of electric field axis. Discharges marked by arrows.

Temporal scans of gamma-ray burstsTemporal scans of gamma-ray bursts

Temporal scans of gamma-ray bursts from negative 07:37:38 (left) and positive 07:40:00 (right) atmospheric discharges. From top to bottom: 1) scans of gamma-ray emission – numbers of gamma-quanta in 200 μs time interval, 2) quasi-static electric field, measured by “field-mill”, 3) electric field variations measured by the capacity sensor. The 0-th point corresponds to the trigger signal.

Temporal scans of gamma-ray burstsTemporal scans of gamma-ray bursts

Thou the mostly energetic gamma-ray bursts occur in the activeperiod of the thunderstorm (07:27–07:46 UT) in, sufficiently intensive bursts can be distinctly seen as well in the relaxation time, 07:50-08:00 UT.Two examples of gamma-ray bursts observed in the thunderstorm relaxation period corresponding to a small electric field jump. At the left – negative discharge (−0.8 kV/m ), at the right – positive discharge (+0.9 kV/m).

Duration of the gamma-radiation burstsDuration of the gamma-radiation bursts

Dependence of duration of gamma-ray bursts upon the duration of the positive (left) and negative (right) atmospheric discharges.

Duration of gamma-radiation bursts is generally proportional to the duration of atmospheric discharges

Intensity of gammaIntensity of gamma--radiation burstsradiation burstsDependence of gamma-radiation intensity upon the electric field change for positive (left) and negative (right) atmospheric discharges.

Total flux of gamma radiation effectively grows with an increase of the jump amplitude of electric field

Altitude dependenceAltitude dependence

Four temporal scans of the gamma-ray burst intensity obtained at the heights above the mean Tien-Shan Station’s level. From top to bottom: at 540 m (registration point 4), at 310 m (point 3), at 180 m (point 2) and at 60 m (point 1). Two lowest panels – quasi-static electric field measured by the “field-mill” and it’s variation measured by the capacity sensor.

An altitude dependence is really dramatic!

Registration bursts of the accelerated Registration bursts of the accelerated electronselectrons

Signals from the fast avalanche of Signals from the fast avalanche of energetic charged particles energetic charged particles (accelerated electrons), being (accelerated electrons), being observed in the moments of the close observed in the moments of the close electric discharge.electric discharge.

The bursts of counting rate are seen The bursts of counting rate are seen not only in records of the separate not only in records of the separate counter layers, but also in the counter layers, but also in the intensity of coincidences both intensity of coincidences both between the upper and middle, and between the upper and middle, and between the upper, middle and lower between the upper, middle and lower layers.layers.

Because of the total absorber Because of the total absorber thickness between the counter layers thickness between the counter layers being about 1being about 1..5−2 g/cm5−2 g/cm22, the , the observation of the signal coincidences observation of the signal coincidences means, that the energy of accelerated means, that the energy of accelerated electrons being registered inside a electrons being registered inside a thundercloud should be above 3 − 6 thundercloud should be above 3 − 6 MeV. MeV.

Transient enhancements of the thermal Transient enhancements of the thermal neutron flux in thunderstorm periodneutron flux in thunderstorm period

We observe at the moment of discharge minutely thermal neutron pulse counts, both in external and in internal detector, exceed mean background levels up to 2.5 − 3 times. The short-time intensity enhancements in same moments of time are also visible in the underfloor detector, thou their amplitude here is only about 20 − 30%; and even in the neutron supermonitor, where the typical enhancement amplitude of 2.5 − 5% is noticeable due to the high counting statistics.

Transient enhancements of the thermal Transient enhancements of the thermal neutron flux in thunderstorm periodneutron flux in thunderstorm period

Statistically, the observed excesses in Statistically, the observed excesses in neutron intensity are quite satisfied. neutron intensity are quite satisfied. Thermal neutron intensity over Thermal neutron intensity over background level exceeds more then 50 σ. background level exceeds more then 50 σ.

The low-energy neutron fluxes registered The low-energy neutron fluxes registered during thunderstorms reach the values of during thunderstorms reach the values of (20–40)·10(20–40)·1033 neutrons per m neutrons per m22 per minute. per minute.

Transient enhancements of the thermal Transient enhancements of the thermal neutron flux in thunderstorm periodneutron flux in thunderstorm period

Beginning summer 2011 we have thermal neutron observation in high resolution mode – during 200 μs time interval.

Transient enhancements of the thermal Transient enhancements of the thermal neutron flux in thunderstorm periodneutron flux in thunderstorm period

For the first time we For the first time we have observed have observed neutron bursts within neutron bursts within 200 200 μμs intervals s intervals during thunderstorm during thunderstorm activityactivity

ConclusionConclusion

The prolonged (100–600 ms) gamma-radiation bursts are found and The prolonged (100–600 ms) gamma-radiation bursts are found and for the first time identified with electric atmospheric discharges for the first time identified with electric atmospheric discharges during a thunderstorm. For the first time shown that the intensive during a thunderstorm. For the first time shown that the intensive gamma radiation is generated at the all stages of an atmospheric gamma radiation is generated at the all stages of an atmospheric discharge. The intensity of gamma radiation of the short flashes is by discharge. The intensity of gamma radiation of the short flashes is by two orders of magnitude higher than that of the background. two orders of magnitude higher than that of the background.

We have detected the short-time outbursts of the counting intensity We have detected the short-time outbursts of the counting intensity which may be interpreted as signal from the fast electrons which may be interpreted as signal from the fast electrons accelerated inside the strong electric fields of a thundercloud. Typical accelerated inside the strong electric fields of a thundercloud. Typical duration of the registered electron flows is of the order of some duration of the registered electron flows is of the order of some hundreds of microseconds, and the presence of the particles hundreds of microseconds, and the presence of the particles accelerated up to some MeV is immediately estimated in the accelerated up to some MeV is immediately estimated in the avalanche. These values are in an agreement with the mechanism of avalanche. These values are in an agreement with the mechanism of runaway breakdown effect.runaway breakdown effect.

ConclusionConclusion

A series of events was found, in which temporal correlation of the A series of events was found, in which temporal correlation of the flashes of thermal neutrons with atmospheric discharges is observed. flashes of thermal neutrons with atmospheric discharges is observed. Statistical confidence of observable excesses in thermal neutron Statistical confidence of observable excesses in thermal neutron intensity over background level exceeds more then 50 σ. The low-intensity over background level exceeds more then 50 σ. The low-energy neutron fluxes registered during thunderstorms reach the energy neutron fluxes registered during thunderstorms reach the values of (20–40)·10values of (20–40)·1033 neutrons per m neutrons per m22 per minute. These firstly per minute. These firstly observed extremely high neutron fluxes are a challenge for the theory. observed extremely high neutron fluxes are a challenge for the theory.

For the first time we have observed neutron bursts within 200 For the first time we have observed neutron bursts within 200 μμs s intervals during thunderstorm activityintervals during thunderstorm activity

We have shown that the complex observation of gamma radiation, We have shown that the complex observation of gamma radiation, accelerated electrons and neutrons at the mountain height (more than accelerated electrons and neutrons at the mountain height (more than 4 km) could serve as a new important method of the investigation of 4 km) could serve as a new important method of the investigation of physical processes occurring in atmospheric discharges.physical processes occurring in atmospheric discharges.