Japanese Title: 共創型サイエンスのアプローチによる高エネルギー大気物理学・天文学の開拓 Author: Teruaki Enoto, Extreme Natural Phenomena RIKEN Hakubi Research Team (榎戸輝揚 @ 極限自然現象理研白眉研究チーム)

1. FY2020 4th CSA meeting @ 2020 July 9 (20 min +10 min)
Teruaki Enoto (Extreme Natural Phenomena RIKEN Hakubi Research Team)
Photo of a lightning discharge along the Sea of Japan
at Fukui, Japan by Otowa Electric Co., Ltd. / Masako Tanaka
Collective Power of Science: High-Energy Atmospheric Science

2. • Neutron stars are remnants of supernova explosions of massive stars.
• Magnetars are a subgroup of neutron stars which magnetic field is 1010-11 T.
Original research field is X-ray astronomy and physics of neutron stars
(image by Takeshige)
2
Magnetars are the ideal laboratory
in our Universe to study the dense
nuclear matter, strong magnetic
field, and intense radiation field.

3. (image: NASA/GSFC)
• Observational determination of the equation of state inside neutron stars
• A chair of the science group for magnetars since 2017
Working as a member of the NICER X-ray observatory onboard the ISS
3

4. • Radiation from electrons accelerated by strong electric fields at lightning?
• “What triggers lightning discharges?” → Cosmic ray induced lightning?
• Methods of radiation measurements of the X-ray astronomy is essential!
Gamma rays have been unexpectedly detected from lightning!
4 Filmed in Ogden, Utah provided by Dustin Farrell. Shot in camera at 1000fps and displayed at 23.976fps

5. 2017/2/6 15:00 JST
Himawari-8 / NICT
http://himawari8.nict.go.jp
Wind
Siberian
airmass
2006 (master thesis)
at Kashiwazaki
Kashiwazaki
Kanazawa
• Observation campaigns with our own-developed & on-ground small detectors
• Gamma rays can fly up to ~(a few) 100 m in the atmosphere.
Winter thunderstorm along the sea of Japan is an ideal target
5

6. • Observation campaigns with our own-developed & on-ground small detectors
• Gamma rays can fly up to ~(a few) 100 m in the atmosphere.
Winter thunderstorm along the sea of Japan is an ideal target
6

7. Energy (MeV)
1 10
-1
MeV-1
s-2
Photonscm
4−
10
3−
10
2−
10
1−
10
1
1 2 5 10
Energy (MeV)
Photonscm-2s-1MeV-1
1
10-1
10-2
10-4
10-3
Flux = 0.65 ± 0.05 cm-2 s-1
(0.04-10 MeV)
Bremsstrahlung gamma rays emitted from winter thunderstorms
7 Date (JST)
16:00 16:10 16:20 16:30 16:40 16:50
CountRate(count/sec)
0
5
10
15
20
25
30
35
40
45
50
:50 0
10
20
30
40
:50 16:10 16:30 16:50
03:20
Date (JST)
02:30 02:40 02:50 03:00 03:10 03:20
0
5
0
10
3:20 02:40 03:00 03:20
3:20
Date (JST)
02:30 02:40 02:50 03:00 03:10 03:20
CountRate(count/sec)
0
5
10
15
20
25
30
35
40
45
50
0
10
20
30
40
:20 02:40 03:00 03:20
50
50
Rate(count/sec)
Time
cosmic-ray
background
December 2016
Komatsu
high school
Thundercloud
Gamma rays
(a few minute)
:
Upstream
+
+
+
-
-
-
Bremsstrahlung
gamma rays up
to 10 MeV
Wada, Enoto et al., Comm. Phys. (2019)

8. Energy (MeV)
1 10
-1
MeV-1
s-2
Photonscm
4−
10
3−
10
2−
10
1−
10
1
1 2 5 10
Energy (MeV)
Photonscm-2s-1MeV-1
1
10-1
10-2
10-4
10-3
Flux = 0.65 ± 0.05 cm-2 s-1
(0.04-10 MeV)
Bremsstrahlung gamma rays emitted from winter thunderstorms
8 Date (JST)
16:00 16:10 16:20 16:30 16:40 16:50
CountRate(count/sec)
0
5
10
15
20
25
30
35
40
45
50
:50 0
10
20
30
40
:50 16:10 16:30 16:50
03:20
Date (JST)
02:30 02:40 02:50 03:00 03:10 03:20
0
5
0
10
3:20 02:40 03:00 03:20
3:20
Date (JST)
02:30 02:40 02:50 03:00 03:10 03:20
CountRate(count/sec)
0
5
10
15
20
25
30
35
40
45
50
0
10
20
30
40
:20 02:40 03:00 03:20
50
50
Rate(count/sec)
Time
cosmic-ray
background
December 2016
Komatsu
high school
Thundercloud
Gamma rays
(a few minute)
:
Electric field
+ + +
+
− −
−
−
−
++
+
Bremsstrahlung
gamma rays up
to 10 MeV
Wada, Enoto et al., Comm. Phys. (2019)

9. Energy (MeV)
1 10
-1
MeV-1
s-2
Photonscm
4−
10
3−
10
2−
10
1−
10
1
1 2 5 10
Energy (MeV)
Photonscm-2s-1MeV-1
1
10-1
10-2
10-4
10-3
Flux = 0.65 ± 0.05 cm-2 s-1
(0.04-10 MeV)
Bremsstrahlung gamma rays emitted from winter thunderstorms
9 Date (JST)
16:00 16:10 16:20 16:30 16:40 16:50
CountRate(count/sec)
0
5
10
15
20
25
30
35
40
45
50
:50 0
10
20
30
40
:50 16:10 16:30 16:50
03:20
Date (JST)
02:30 02:40 02:50 03:00 03:10 03:20
0
5
0
10
3:20 02:40 03:00 03:20
3:20
Date (JST)
02:30 02:40 02:50 03:00 03:10 03:20
CountRate(count/sec)
0
5
10
15
20
25
30
35
40
45
50
0
10
20
30
40
:20 02:40 03:00 03:20
50
50
Rate(count/sec)
Time
cosmic-ray
background
December 2016
Komatsu
high school
Thundercloud
Gamma rays
(a few minute)
:
+ + +
+
− −
−
−
−
++
+
Cosmic rays
e
e
e
e e
e
Avalanche
e
Electron acceleration
Gamma rays
Bremsstrahlung
gamma rays up
to 10 MeV
Wada, Enoto et al., Comm. Phys. (2019)

10. Failure of my KAKENHI proposal, and academic crowdfunding : )

11. Discovery of photonuclear reactions triggered by lightning
11
0 50 100 150
0
100
200
300
Lightning
Enhancement of
radiation
!
0.4 0.5 0.6 0.8 1 2
16
14
12
10
8
6
4
2
0
0.511 MeV
Annihilation line
Time (sec)
(0.35-0.60 MeV)
Energy (MeV)
Countrate(countsec-1)
Spectrum(103countMeV-1)
Radiation after a lightning Gamma-ray spectrum
(1-63 sec after a lightning)
Signature of positron ( ) from a lightning discharge?
Enoto, Wada et al., Nature (2017)

12. Discovery of photonuclear reactions triggered by lightning
12
beta-plus decay
13N → 13C + e+ + ν
(p → n + e+ + ν)
positron
neutrino
carbon
isotope
13C
proton 6
neutron 7
atmospheric
nitrogen
14N
fast neutron
γ-rays
proton 7
neutron 7
photonuclear reaction
γ + 14N → 13N + n
radioactive
isotope
13N
proton 7
neutron 6
half-life 10 min
downward TGF
(initial spike, ~ms)
Enoto, Wada et al., Nature (2017)

13. Discovery of photonuclear reactions triggered by lightning
13 Enoto, Wada et al., Nature (2017)

14. Discovery of photonuclear reactions triggered by lightning
atmospheric
nitrogen 14N
prompt
gamma rays
nitrogen
isotope
15N
neutron capture
carbon
isotope
14C
semi-stable
(half-life of 5730 years)
radiocarbon dating
(n,p) reaction
electron
electron-positron
annihilation
annihilation
gamma rays
at 0.511 MeV
gamma-ray afterglow
(~0.2 s)(~0.2 s)
delayed emission
(~60 s)
14 Enoto, Wada et al., Nature (2017)

15. What the nuclear reactions of lightning imply?
LETTER doi:10.1038/nature24630
Photonuclear reactions triggered by lightning
discharge
Teruaki Enoto1
, Yuuki Wada2,3
, Yoshihiro Furuta2
, Kazuhiro Nakazawa2,4
, Takayuki Yuasa5
, Kazufumi Okuda2
,
Kazuo Makishima6
, Mitsuteru Sato7
, Yousuke Sato8
, Toshio Nakano3
, Daigo Umemoto9
& Harufumi Tsuchiya10
Lightning and thunderclouds are natural particle accelerators1
.
Avalanchesofrelativisticrunawayelectrons,whichdevelopinelectric
fields within thunderclouds2,3
, emit bremsstrahlung γ-rays. These
γ-rays have been detected by ground-based observatories4–9
, by
airborne detectors10
and as terrestrial γ-ray flashes from space10–14
.
The energy of the γ-rays is sufficiently high that they can trigger
atmospheric photonuclear reactions10,15–19
that produce neutrons
and eventually positrons via β+
decay of the unstable radioactive
isotopes, most notably 13
N, which is generated via 14
N+γ→13
N+n,
where γ denotes a photon and n a neutron. However, this reaction
has hitherto not been observed conclusively, despite increasing
observational evidence of neutrons7,20,21
and positrons10,22
that are
presumably derived from such reactions. Here we report ground-
based observations of neutron and positron signals after lightning.
During a thunderstorm on 6 February 2017 in Japan, a γ-ray flash
with a duration of less than one millisecond was detected at our
monitoring sites 0.5–1.7 kilometres away from the lightning. The
subsequent γ-ray afterglow subsided quickly, with an exponential
decay constant of 40–60milliseconds, and was followed by prolonged
line emission at about 0.511 megaelectronvolts, which lasted for a
minute. The observed decay timescale and spectral cutoff at about
10 megaelectronvolts of the γ-ray afterglow are well explained by
de-excitation γ-rays from nuclei excited by neutron capture.
The centre energy of the prolonged line emission corresponds to
electron–positron annihilation, providing conclusive evidence of
positrons being produced after the lightning.
With the aim of detecting γ-rays from powerful and low-altitude
winter thunderclouds along the coast of the Sea of Japan, we have been
operating radiation detectors since 20066,22,23
at the Kashiwazaki-
Kariwa nuclear power station in Niigata (see Methods section
‘GROWTH collaboration’). On 6 February 2017, a pair of lightning
discharges occurred at 08:34:06 utc, 0.5–1.7 km away from our
four radiation detectors (labelled ‘A’ to ‘D’, see Fig. 1 and Methods
section ‘Lightning discharges’). All four detectors simultaneously
recorded an intense radiation that lasted for about 200ms (Fig. 1).
The radiation-monitoring stations operated by the power plant also
recorded this flash (see Fig. 1a and Methods section ‘Radiation
monitors’). The analogue outputs of the phototube amplifier exhibited
strong ‘undershoot’ (that is, a negative voltage output was detected,
which would never happen during normal operation) at the beginning
Time (ms)
–100 0 100 200 300 400
Countsper10-msbin
0
50
100
150
200
250
300
b
Time (ms)
–100 0 100 200 300 400
0
20
40
60
80
100
c
Time (ms)
–100 0 100 200 300 400
0
20
40
60
80
100
da
6
Detectors
Monitoring stations
Relative enhancement
103
102
101
SeaofJapan
1 km
17
m
s –1
1
2
3
4
5
789
B
C
A
D
–
+
138.580º E 138.593º E 138.606º E
37.415º N
37.425º N
37.435º N
37.445º N
Figure 1 | Lightning discharges and subsecond decaying high-energy averaged over the approximately 10min before and after the lightning.
• Methodology of the high-energy physics becomes a key to
understand lightning. We can use neutron and positrons!
• The carbon isotope 14C is used for radioactive dating. How many
carbon isotopes 14C are produced from lightning discharges?15

16. gamma-ray
lightning
TGF
strong
electric
field
positive
charge
negative
charge
relativistic
electron
acceleration
Gamma-ray
beam
Radiation
detector network
Radio
antennas
Photonuclear
reactions
Neutron
detection
• Gamma-ray glow from thunderstorms & photonuclear reactions at lightning
• Radiation measurements, radio observation, and optical measurements
An interdisciplinary new field of “High-Energy Atmospheric Physics”!
16

17. Thundercloud Project: multi-point mapping measurement campaign
17
• Radiation detectors and low frequency radio stations have been deployed on
high schools, universities, and private companies. Goal is ~50 observation sites.
• High-performance one-button detectors to be distributed to citizen supporters.
CsI (Tl) 50 x 50 x 150 mm3
Data collection via internet
and automatic alerts to citizen
supporters for taking photos
(new crystals.. CeBr, EJ-270)

18. • Promote citizen supporters to join in observations and analyses
• Several successful citizen science projects in US for professional researches
Citizen science approach and the new trend of “Open Science”
18
In 2016, we launched “Open Science” community with colleagues at
Kyoto University, and has organized monthly “meetups” both for
professional researchers and citizen scientists (http://kyoto-open.science)

19. 19
Collective Power of Science
•
•
Collective Power of Science
•
•
• Large scientific projects are limited in budget and human resources. Will our
generation not be allowed to have large projects as previous generations?
We will try the “Collective Power of Science” approach to advance and enjoy
science, even under the limited resources. We can use not a single large
device, but a network of a large number of decentralized devices, supported
by the citizen science for our collaboration.

20. • On 2017 June 3, I was invited to see the launch of SpaceX falcon 9 rocket for
the NICER project, and was shocked at seeing landing of the reusable rocket.
Re-usable rockets by SpaceX and a new era of space developments
20
Credit: NASA/SpaceX

21. • Science by a fleet of CubeSats is the “collective power of science”.
• Continuous gravitational wave from a fast spinning neutron star is one of targets
of the LIGO project. The spin ephemeris of the neutron star is needed for LIGO.
• CubeSat can monitor a spin ephemeris (via QPOs) of the neutron star in the
brightest X-ray source in the sky, Sco X-1. Large observatories can not try this.
Companion star
Fast spinning neutron star
Search for the continuous gravitational wave using CubeSats.
21

22. NinjaSat
CubeSat “NinjaSat” project with the RIKEN Tamagawa group
22 3D CG by
• A small X-ray observatory to be flexibly used to monitor Sco X-1
and to observe bright transient objects discovered by MAXI.
• The main detector is X-ray sensors utilizing
the gas electron multiplier foils, which have
been developed by the Tamagawa lab.
• The first public observatory open to citizen
in X-rays, used for educational purposes.
© NASA
NinjaSat
(6U ; 100 x 200 x 300 mm3)
©
X-rays from black holes
and neutron stars

23. • Lunar neutrons, produced by cosmic rays, have signals for hidden water.
• We will develop a new type of neutron monitors using neutron sensitive plastic
scintillators collaborating with the RIKEN RAP Otake’s RANS group and JAXA.
• This technique will be also used for astronomy and industrial purposes.
Lunar exploration to search for water and astronomy from the moon
23
Cosmic ray
p, He…)
Nuclear
reactions
(~1m)
Fast
neutron
Thermal
neutron
Gamma
rays
Lunar surface
Neutron
capture
Water?

24. • We have 8 members: 2 staffs (RIKEN Hakubi), 1 staff (KAKEN Kibun A), 2 SPDRs,
1 guest researcher, and 1 research assistant. Weekly zoom virtual meetings.
Team members of the Extreme Natural Phenomena RIKEN Hakubi Team
Teruaki Enoto Mariko Kimura
Yo Kato
Gabriel DinizYuuki Wada
Kaori Fukaya Chin-Ping Hu Masaki Numazawa
Ryusuke Hamazaki

25. Summary: What we will try in five years?
25
• Collective Power of Science (
• Thundercloud Project:
• NinjaSat Project: 2021-22
• Lunar exploration: