Transcript ecrs2012.sinp.msu.ru

Bursts of gamma-rays, electrons and
low-energy neutrons during thunderstorms
at the Tien-Shan
MITKO G.G
for ″Thunderstorm″
Collaboration
ECRS-2012
″Thunderstorm″ Collaboration
V.P. Antonova1, A.P. Chubenko2, A.N. Karashtin3,
G.G. Mitko2, M.O. Ptitsyn2, V.A. Ryabov2,
A.L. Shepetov2, Yu.V. Shlyugaev4, L.I. Vildanova2, K.P. Zybin2,
and A.V. Gurevich2
 1



Institute of Ionosphere, National Center for Space Reaearch
and Technology, Almaty, Kazakhstan
2 P.N. Lebedev Physical Institute of RAS, Moscow, Russia
3 Research Radiophysics Institute, Nizhny Novgorod, Russia
4 Institute of Applied Physics of RAS, Nizhny Novgorod, Russia
INTRODUCTION

New data of the last
measurement season
held at the Tien-Shan
complex for
investigation gammaradiation, accelerated
electrons and lowenergy neutrons
during thunderstorms
are presented
The experimental complex
"Thunderstorm"
At present time, ”Thunderstorm”
complex comprises the following
facilities:
an EAS registering system,
the system of NaI scintillation
detectors for registration of the
gamma- and X-ray emission in
atmosphere,
the multi-layer ionization detectors
of energetic charged particles,
the neutron supermonitor for
registration of the high-energy
hadronic component of cosmic rays,
a set of the detectors of low-energy
(thermal) neutron background,
two independent radio systems,
and electrostatic detectors of the
local electric field and its high
frequency component.
Extensive Air Showers Trigger System



Four separate systems of
coincidence constructed on
base of counters SI5G and use
for development of a trigger
pulse at the moment of
passage EAS through
installation.
The systems are in the
vertexes of triangles with
length of an edge of 60-65 m.
Configuration of the EAS
trigger system gives the
possibility to single out the
EAS generated with the
frequency about 10−2 s−1 by
cosmic ray particles having the
energy 1015 eV or higher.
NaI-Scintillation Spectrometer

To register soft
gamma and hard Xray radiation of the
electrons accelerated
in the electric fields
of a thunderstorm
cloud, 14 scintillation
detectors based on
NaI crystals were
used.
NaI-Scintillation Spectrometer
Seven registration points are
situated as a chain on the
slopes of the surrounding
mountains, across the usual
direction of motion of
thunderstorm clouds.
The distance between the
ends of this chain is about 2
km, and the maximum
spacing of the detectors in
the vertical direction reaches
600 m.
The scintillation system
designed in such a way
allows one to study spatial
distribution of the radiation
inside thunderstorm clouds
in both horizontal and
vertical directions.
7
6
5
4
Ionization charged particle detectors




The detector is built on the basis of a
SI5G type ionization counters which
are installed inside a box, 20
counters per each box.
Counter boxes are grouped into three
layers, one under another.
The total sensitive area of a 20counter box is about 2 m2 while that
of a whole counter layer in a detector
point is 6 m2.
The SI5G countres operate in a
proportional mode, when they have a
95−99% registration efficiency
concerning the relativistic charged
particles, and a 0.05 − 1% efficiency,
in dependence on its energy, for
gamma-radiation.
Neutron detectors



Mutual disposition of
the Tien-Shan Station’s
neutron detectors:
A,B,C, and D — the
units of 18NM64
neutron supermonitor;
In, Ex, and U — the
internal, external,
and underfloor thermal
neutron detectors.
Thermal neutron detectors



For monitoring of the low-energy (about and
below 1 eV) neutron flux we use a set of
special detectors based on the proportional
neutron counters.
The counters are filled with the gas 3He under
the pressure of 2 atmospheres, so the
neutron registration in the thermal energy
range succeeds due to reaction 3He(n, p)t
with an efficiency of about 85%.
Because of the absence of any neutron
moderating material around the counters, the
considered detectors can register only the
slow neutrons which have just been
moderated down to thermal energies (about
10−2eV ) in surrounding environment, but are
fully insensitive to the high-energy hadron
flux of a cosmic ray origin.
Electrostatic fluxmeter

This setup comprises
the detectors
measuring changes in
the electric field under
thunderstorm
conditions: the quasistatic (“slow”) electric
field is measured by an
electrostatic fluxmeter
of the “field-mill” type,
and variations in the
electric field in the
frequency range 0.5 –
25 kHz (“fast” field), by
a capacitor-type
sensor.
Radio System

Two radiosystems are
designed for short
electromagnetic pulse
observations in the
frequency range from
0.1 to 30 MHz. Their
time resolution is 16 ns.
Also, the systems
determined the
direction to radiation
sources from the
relative time delays of
radio signals.

The radiosystems
operate in the external
trigger mode.
Atmospheric discharges and bursts
of gamma-rays



We will consider the
identification of gammaradiation bursts with the
moments of atmospheric
discharges on the example
of one of the
thunderstorms.
Atmospheric discharges
have been identified by the
fast changes of the quasistatic electric field.
There are negative and
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 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 bursts
Thou the mostly energetic gamma-ray bursts occur in the active
period 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 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 gamma-radiation bursts
Dependence 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 dependence
Four temporal scans of the gamma-ray burst intensity obtained at the heights above the mean TienShan 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 “fieldmill” and it’s variation measured by the capacity sensor.
An altitude dependence is really dramatic!
Registration bursts of the accelerated
electrons



Signals from the fast avalanche of
energetic charged particles
(accelerated electrons), being
observed in the moments of the
close electric discharge.
The bursts of counting rate are seen
not only in records of the separate
counter layers, but also in the
intensity of coincidences both
between the upper and middle, and
between the upper, middle and
lower layers.
Because of the total absorber
thickness between the counter
layers being about 1.5−2 g/cm2, the
observation of the signal
coincidences means, that the
energy of accelerated electrons
being registered inside a
thundercloud should be above 3 − 6
MeV.
Transient enhancements of the thermal
neutron 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
neutron flux in thunderstorm period
Statistically, the observed excesses in
neutron intensity are quite satisfied.
Thermal neutron intensity over
background level exceeds more then 50 σ.
 The low-energy neutron fluxes registered
during thunderstorms reach the values of
(20–40)·103 neutrons per m2 per minute.

Transient enhancements of the thermal
neutron 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
neutron flux in thunderstorm period

For the first time we
have observed
neutron bursts within
200 μs intervals
during thunderstorm
activity
Conclusion

The prolonged (100–600 ms) gamma-radiation bursts are found and
for the first time identified with electric atmospheric discharges during
a thunderstorm. For the first time shown that the intensive gamma
radiation is generated at the all stages of an atmospheric discharge.
The intensity of gamma radiation of the short flashes is by two orders
of magnitude higher than that of the background.

We have detected the short-time outbursts of the counting intensity
which may be interpreted as signal from the fast electrons accelerated
inside the strong electric fields of a thundercloud. Typical duration of
the registered electron flows is of the order of some hundreds of
microseconds, and the presence of the particles accelerated up to
some MeV is immediately estimated in the avalanche. These values
are in an agreement with the mechanism of runaway breakdown
effect.
Conclusion

A series of events was found, in which temporal correlation of the
flashes of thermal neutrons with atmospheric discharges is
observed. Statistical confidence of observable excesses in thermal
neutron intensity over background level exceeds more then 50 σ.
The low-energy neutron fluxes registered during thunderstorms
reach the values of (20–40)·103 neutrons per m2 per minute. These
firstly observed extremely high neutron fluxes are a challenge for the
theory.

For the first time we have observed neutron bursts within 200 μs
intervals during thunderstorm activity

We have shown that the complex observation of gamma radiation,
accelerated electrons and neutrons at the mountain height (more
than 4 km) could serve as a new important method of the
investigation of physical processes occurring in atmospheric
discharges.