Photonuclear reactions
triggered by lightning discharges
in a Japanese winter thunderstorm
Teruaki Enoto, Yuki Wada, Yoshihiro Furuta, Kazuhiro Nakazawa, Takayuki Yuasa,Kazufumi Okuda, Kazuo Makishima, Mitsuteru Sato, Yousuke Sato, Toshio Nakano, Daigo
Umemoto, Harufumi Tsuchiya, and GROWTH collaboration (Kyoto Univeristy,
The University of Tokyo, RIKEN, Nagoya University, Hokkaido University, and JAEA)

Enoto et al., Nature 551, 481 (2017)

Photo at Fukui, Japan by Otowa Electric Co., Ltd. / Masako Tanaka
EGU2018-3798, 14:00-14:15, April 10, 2018, Vienna, Austria, “Atmospheric Electricity, Thunderstorms, Lightning and there effects” (NH1.2/AS1.14/SSS13.43)

5606000

Winter thunderstorm and lightning in Japan
23:50

00:00

23:50

00:10
00:20
Date (JST)

00:10

00:30
00:30

00:40

23:50
23:50

00:00

00:10
00:20
00:30
00:10
00:30
Date (JST)00:40

50 frequent positive discharge
low altitude(<1km),powerfullightning,
TRB161208b (fy2016c)
中心時刻 02:56:26
Ideal forthe high-energy atmospheric phenomena
180observing
5045

180
1604040

小松高校

2017/2/6 15:00 JST
Himawari-8 / NICT
http://himawari8.nict.go.jp

140140Siberian
airmass

3530

120

30

−

2520

100
100

Wind

2080++−+

151010+5200

Count Rate (count/sec)

180
180
160

140

140

02:40

02:40

02:50

03:10

03:20

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island“Long”-duration
4040 event (Tsuchiya+07)

GROWTH (Gamma-Ray Observationof Winter Thundercloud) project
100in 2006, and expanded
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since 2015
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60
120
100

80

02:40

02:40

02:50

03:00
Date (JST)

03:00

03:10

03:20
03:20

03:10

03:20

03:20

Japan island

5050

TRB161208c(fy2016d)
中心時刻 02:58:19
サイエンスヒルズこまつ

60
02:30

00 02:30 Japan
02:40
02:50
03:00
02:40 SeaDate03:00(JST)

Japan03:20
03:00

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Date (JST)Count rate(cnt/s) [>3 MeV]Count Rate (count/sec)

6060 02:30

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Count Rate (count/sec)

Count Rate (count s-1)

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gamma-rays
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electrons inthunderstorms

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background50002:30

02:40
02:40

02:50

03:00
03:00
Date (JST)

03:10

03:20
03:20
Time (JST)Radiation detectors for mapping observations

BoardA new stand-alone, low cost, and high-performance data acquisition (DAQ)

system was developed; e.g., FPGA board of 4 channel 50 MHz, 12 bit ADC

data acquisitiondADC board

DC 4
ht and detection timeth FPGAquisition withRaspberry Pill-sized linux)
ion possible
95 mm
95 mm
W
95,000JPY (~$1k)(Shimafuji Elec.)
Yuasa & Shimafuji Elec.

• Gamma-rays detected with BGO scintillators• Recorded with energy and GPS time tag• Environmental sensors (temperature, pressure, etc)
• Mobile data transfer & remote control• Deployed at local high schools, universities• Supported by academic crowdfunding, andaiming at distributing to citizen scientists

Front-end
Board
BGO scintillator

web camera(25x8x2.5 cm3)

PMTDAQelectronics

cm20 cm

ADC board

45c35mRaspberry Pi

DAQ

water proof box(Detector FY2016)

Wada, Master thesis of the University of Tokyo, “Construction of the multi-point observation network for thundercloud gamma-rays”(ref) FPGA/ADC board specification http://ytkyk.info/blog/2016/09/04/growth-fpga-adc-board/ (C) T. Yuasa
MIS18-05

Radiation detectors for mapping observations

Board

data acquisition

Cost >$20 k

Cost ~$4 k

Enoto

WadadDC 4
ht and detection timeth FPGAquisition withll-sized linux)
ion possible
W
2006 December
Yuasa & Shimafuji Elec.

2016 October

Front-end
Board
BGO scintillator

web camera(25x8x2.5 cm3)

PMT
DAQelectronics

cm

20 cm

ADC board

45c35mRaspberry Pi

DAQ

water proof box(Detector FY2016)

Wada, Master thesis of the University of Tokyo, “Construction of the multi-point observation network for thundercloud gamma-rays”(ref) FPGA/ADC board specification http://ytkyk.info/blog/2016/09/04/growth-fpga-adc-board/ (C) T. Yuasa
MIS18-05

bservations of neutron and positron signals after lightning. section ‘Lightning discharges’). Aa thunderstorm on 6 February 2017 in Japan, a γ-ray flash recorded an intense radiation tha
uration of less than one millisecond was detected at our The radiation-monitoring stationing
0.5–1.7 kilometresaway from at
theKashiwazakilightning. Thestation
recordedflash(see Fig. 1a aonsites
February
6, 2017, 17:34:06,
had thisthreecomponents
ent γ-ray afterglow subsided quickly, with an exponential monitors’). The analogue outputs onstant
40–60 milliseconds,
was followedby prolongedstrong‘undershoot’(that is, a neg
1. ofIntensive
initial andspike(<~a few
milliseconds,exceeds
10 MeV)ssion at about 0.511 megaelectronvolts, which lasted for a which would never happen during

Short-duration burst associated with lightning
2. Gamma-ray afterglow (<~100 ms, <10 MeV)
3. Delayed annihilation gamma rays (~minute, at 0.511 MeV)

Relative enhancement
103102

2101

3N
4aofJ

apan–Se+N

17mC

s –1D9N

B
6A
85770
70

250
50
50
40
4030
30

200
2020138.593º E

138.606º E

detector
80 C (>1.2 MeV)
100 ms60

101000− 200

150

− 100

0-1000100

100

200
Time (s)

200

80

70
300

60100
50

200

40300

300

Time (ms)
400

400

500

600

40

3. Annihilation gamma rays
detector A (0.35-0.60 MeV)
2030 50

100
2000

100

2.Gamma-ray afterglow

60
60

101 km138.580º E

80300
80

Lightning

1c

Lightning

Detectors
Monitoring stations

毎秒のカウント数

NCountsCounts
s-1 per 10-ms Countsms)-1bin Count (10(10 ms)-1b60 s
000–1000050
10050
時間 (秒) 100

100 200 300 400–100

1500Time (sec)

100 200 300

bservations of neutron and positron signals after lightning. section ‘Lightning discharges’). Aa thunderstorm on 6 February 2017 in Japan, a γ-ray flash recorded an intense radiation tha
uration of less than one millisecond was detected at our The radiation-monitoring stationing
0.5–1.7 kilometresaway from at
theKashiwazakilightning. Thestation
recordedflash(see Fig. 1a aonsites
February
6, 2017, 17:34:06,
had thisthreecomponents
ent γ-ray afterglow subsided quickly, with an exponential monitors’). The analogue outputs onstant
40–60 milliseconds,
was followedby prolonged
strong‘undershoot’(that is, a neg
1. ofIntensive
initial andspike(<~a fewmilliseconds,exceeds
10 MeV)ssion at about 0.511 megaelectronvolts, which lasted for a which would never happen during

Short-duration burst associated with lightning
2. Gamma-ray afterglow (<~100 ms, <10 MeV)
3. Delayed annihilation gamma rays (~minute, at 0.511 MeV)bDetectors
Monitoring stations

101

3N
4aofJ

apan–Se+

N

17mCs –1D9N

B
6A
85138.606º E

photonenergy

20060

Low-energy

150

10 ms

detector
40
baseline
voltage100

instrumental saturation
due to a large input
2050

0138.593º E

80

1.Intensive initial spike

71 km
138.580º E

3000

250

22000

102

High-energy

1000

Relative enhancement
103

High-energy photons
100

300

1Counts
per 10-msbinunit)
Energy(ADCN

c050–100detector
0 100A200 300 400

0100–1000Time
100 (ms)
200 300

Photonuclear reactions triggered by lightning
downward TGF(initial spike)half-life 10 min

neutrino

nitrogenradioactive
isotopecarbonisotope

14N

13N

13C

proton 7
neutron 6

proton 6
neutron 7

atmospheric

γ-raysproton 7
neutron 7

fast neutron

photonuclear reaction

γ + 14N → 13N + npositronbeta-plus decay
13N → 13C + e+ + ν(p → n + e+ + ν)

fast neutron

positronGamma rays from neutron and positrons
fast neutron

positronatmosphericnitrogen 14N(n,p) reaction

neutron capture

electron-positronannihilationelectroncarbonisotopenitrogenisotope

14C

15N

semi-stable(half-life 5730 year)
radiocarbon dating

promptgamma rays

gamma-ray afterglow

annihilation
gamma rays
at 0.511 MeV

delayed emission

bservations of neutron and positron signals after lightning. section ‘Lightning discharges’). A
a thunderstorm on 6 February 2017 in Japan, a γ-ray flash recorded an intense radiation tha
uration of less than one millisecond was detected at our The radiation-monitoring stationing
0.5–1.7 kilometresaway from attheKashiwazakilightning. Thestation
recordedflash(see Fig. 1a aonsites
February
6, 2017, 17:34:06,
had thisthreecomponents
ent γ-ray afterglow subsided quickly, with an exponential monitors’). The analogue outputs onstant
40–60 milliseconds,
was followedby prolonged
strong‘undershoot’(that is, a neg
1. ofIntensive
initial andspike(<~a few
milliseconds,exceeds
10 MeV)ssion at about 0.511 megaelectronvolts, which lasted for a which would never happen during

Short-duration burst associated with lightning
2. Gamma-ray afterglow (<~100 ms, <10 MeV)
3. Delayed annihilation gamma rays (~minute, at 0.511 MeV)

Relative enhancement
1031022101

3N
4aofJapan–Se+N

17mCs –1D9N

B
6A
85770
70

250
50
50
4040
30
30

200
2020

138.593º E

138.606º E

detector
80 C (>1.2 MeV)
100 ms60

101000− 200

150

− 100

0-100

0

100

100

200Time (s)

200

80

70
300

60100
50

200

40300

300

Time (ms)
400

400

500

600

40

3. Annihilation gamma rays
detector A (0.35-0.60 MeV)
2030 50

100
2000100

2.Gamma-ray afterglow

6060

101 km138.580º E8030080

Lightning

1c

Lightning

Detectors
Monitoring stations

毎秒のカウント数

N

CountsCounts
s-1 per 10-ms Countsms)-1bin Count (10(10 ms)-1b60 s
000–1000050
10050
時間 (秒) 100

100 200 300 400

–100

150

0Time (sec)

100 200 300

lts, which lasted for a

Neutrons make the gamma-ray afterglow
c300

detector A
decay const.
56±3 (ms)

250

100

detector B
decay const.
55±12 (ms)

80

100

detector C
decay const.
36±4 (ms)

80

200
60

60

40

40

200–100

2000

100 200 300 400
Time (ms)–100Lightning

100

Lightning

15050•dLightningb

Counts per 10-ms bin

3which would never happen during normal operation) at the beginning00

100 200 300 400
Time (ms)–100

0100 200 300 400
Time (ms)caying high-energy
averagedover the approximately
10 min before
and after thelightning.
Exponential decay
constantof the sub-second
afterglow
is consistentllow dashed circles
The arrow shows the wind speed and direction. b–d, Deadtime-corrected
withthetheoreticalprediction ~56 ms of the neutron thermalisation.
ative (‘− ’) and10-ms-binned count-rate histories with ±1σ errors, recorded by detectors
Spectrum withAa(b;sharp
MeV
is andwell
explained
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>0.35 cutoffMeV), Bat(c;10>0.35MeV)
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nitoring gamma
stations rays fromthe best-fitting
model functions
of anexponential
decay. See
Methods
atmosphericnitrogensandsurroundingmaterials.
of the circle indicating
section ‘Initial flash’ for details.

•lts, which lasted for a

Neutrons make the gamma-ray afterglow
c300

detector A
decay const.
56±3 (ms)250200150

80–1001000

00100 200 300 400
Time (ms)

検出器
C Cdetector

8010010200

検出器
A A
detectorbackground
環境バックグラウンド

40Lightning

10010010000

6050•d100-1)-1)
Spectrum (Countss-1 MeV
ガンマ線スペクトル(Countss-1 MeVbCounts per 10-ms bin

3which would never happen during normal operation) at the beginning

–100

10.1
060

40200

4 50 6 100
7 8200910300 400
1100 200 3002 400 3 –100
Time (ms)Time (ms)エネルギー(メガ電子ボルト)
Energy(MeV)

caying high-energy
averagedover the approximately
10 min before
and after thelightning.
Exponential decay
constantof the sub-second
afterglowis consistentllow dashed circles
The arrow shows the wind speed and direction. b–d, Deadtime-correctedwiththetheoreticalprediction ~56 ms of the neutron thermalisation.
ative (‘− ’) and10-ms-binned count-rate histories with ±1σ errors, recorded by detectors
Spectrum withAa(b;sharpcutoffBat
MeV
isand
well
explained
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>0.35 MeV),(c;10>0.35
MeV)
C (d;>1.2 MeV).byRedlines show
nitoring gamma
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model functions
of anexponential
decay. SeeMethods
atmosphericnitrogens
andsurrounding
materials.
of the circle indicating
section ‘Initial flash’ for details.

•lts, which lasted for aNeutrons make the gamma-ray afterglow
c300

detector A
decay const.
56±3 (ms)

250

200

150

8080

1000

40Lightning

100–100

60

100

1020000100 200 300 400
Time (ms)

100

10000

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ガンマ線スペクトル(Countss-1 MeV
Spectrum (Countss-1 MeVbCounts per 10-ms bin

3which would never happen during normal operation) at the beginning

–100

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040

Geant4 Monte Carlosimulation
20Atmospheric nitrogenSurrounding materials
BGO detectors 0
4 50 6 100
7 8200910300 400
1100 200 3002 400 3 –100
Time (ms)エネルギー(メガ電子ボルト)
Energy(MeV)Time (ms)caying high-energy
averagedover the approximately
10 min before
and after thelightning.
Exponential decay
constantof the sub-second
afterglow
is consistentllow dashed circles
The arrow shows the wind speed and direction. b–d, Deadtime-correctedwiththetheoreticalprediction ~56 ms of the neutron thermalisation.
ative (‘− ’) and10-ms-binned count-rate histories with ±1σ errors, recorded by detectorsSpectrum withAa(b;sharp
cutoffBat
MeV
isandwell
explained
prompthtning discharges’).
>0.35 MeV),(c;10>0.35MeV)
C (d;>1.2 MeV).byRedlines show
nitoring gamma
stations rays fromthe best-fitting
model functions
of anexponential
decay. See
Methods
atmosphericnitrogensandsurroundingmaterials.
of the circle indicating
section ‘Initial flash’ for details.

•bservations of neutron and positron signals after lightning. section ‘Lightning discharges’). Aa thunderstorm on 6 February 2017 in Japan, a γ-ray flash recorded an intense radiation tha
uration of less than one millisecond was detected at our The radiation-monitoring stationing
0.5–1.7 kilometresaway from at
theKashiwazakilightning. Thestation
recordedflash(see Fig. 1a aonsites
February
6, 2017, 17:34:06,
had thisthreecomponents
ent γ-ray afterglow subsided quickly, with an exponential monitors’). The analogue outputs onstant
40–60 milliseconds,
was followedby prolonged
strong‘undershoot’(that is, a neg
1. ofIntensive
initial andspike(<~a few
milliseconds,exceeds
10 MeV)ssion at about 0.511 megaelectronvolts, which lasted for a which would never happen during

Short-duration burst associated with lightning
2. Gamma-ray afterglow (<~100 ms, <10 MeV)
3. Delayed annihilation gamma rays (~minute, at 0.511 MeV)

Relative enhancement
103

102

2101

3N
4

aofJ

apan–Se+N

17m

Cs –1D9N

B
6A
8

5

770
70

250
50
50
40
4030
30200
2020

138.593º E

138.606º E

detector
80 C (>1.2 MeV)
100 ms60

101000− 200150− 1000-1000100

100200Time (s)2008070300

60100
50

200

40300

300

Time (ms)
400

400

500

600

40

3. Annihilation gamma rays
detector A (0.35-0.60 MeV)
2030 50

100
2000100

2.Gamma-ray afterglow

6060

101 km138.580º E

80300
80Lightning

1cLightning

Detectors
Monitoring stations

毎秒のカウント数

N

CountsCounts
s-1 per 10-ms Countsms)-1
bin Count (10(10 ms)-1b60 s
000–1000050
10050
時間 (秒) 100

100 200 300 400–100150

0Time (sec)

100 200 300

Positron annihilation signal at 0.511 MeV

1 km

RESEARCHfrom the lightning.
moving• The ~35 sec delay is consistent with the cloudLETTER• The duration ~13 sec (1σ) x wind speed ~17 m/s → emission size ~200 m

Positronemitting
cloud
13N

Data compared withGeant4 simulation

200 m
detector

distance tothe cloudbase 80 m• Relative intensity of the 0.511 MeV emission line and continuum below it

Extended Data Figure 6 | Observed annihilation spectrum andsimulated models. The background-subtracted spectrum in the delayedphase for detector A, accumulated over t = 11.1–62.8 s, is plotted, withblack crosses indicating ±1σ errors. The simulated model curves areoverlaid, for assumed distances to the base of the positron-emitting cloudof 0 m (that is, the detector is within the cloud; red), 40 m (green), 80 m(blue) and 160 m (magenta). The models are normalized by the total
counts in the 0.4–0.6-MeV band.

gives a distance to the base of the positron-emitting cloud: ~80 m• A lightning-triggered photonuclear event produces 4x1012 neutrons.

Discussion
102

10 MeV

10(Counts/s/MeV)1

TGF spectrum
RHESSI (Smith+05)
AGILE (Tavani+11)0.1
110Energy (MeV)TGF spectrum
exceeds 10 MeV, inwhich photonucler
reactions take place

Estimated number of neutron 4x1012 produced by photonuclear
reaction is within predicted range of 1011-15 (Babich+10, Carlson+14).

• Atmospheric oxygen also contributes to the lightning photonuclear reactions.
• Can explain past reports of 0.511 MeV (Umemoto+2016) and neutrons (Bowers+2017).
• Lightning produces atmospheric 13N, 15N, 13C, and 14C isotopes.

Summary• GROWTH project has been observing high-energy atmosphericphenomena in the Japanese winter thunderstorm and lighting
since 2006. We are also aiming at expanding to citizen science.

• We provided unequivocal evidence for the lightning-triggered
photonuclear reactions of atmospheric nitrogen 14N+γ→13N+n;(1) downward terrestrial gamma-ray flash, (2) gamma-ray
afterglow of thermalised neutrons, and (3) annihilation gammaray signal at 0.511 MeV from the beta-plus decay of 13N.

• Lightning provides channels to generate carbon isotopes.
Enoto, Wada, Furuta et al., Nature 551, 481 (2017)
Selected as one of the Top 10 Physics Breakthroughsof 2017 by Physics World magazine, IOP Publishing Ltd
Photo by Otowa Electric Co., Ltd. / Hisashi Yoshinaga