Interdisciplinary Science Conference in Okinawa— Physics and Mathematics meet Medical Science —ISCO 2023 @ OISTMar. 1, 2023

New Developments
in Muon-Catalyzed Fusion Researchby Precise X-ray Spectroscopy of Muonic MoleculesμtdShinji OKADA (Chubu Univ.)

Contents
1. What’s Muon-Catalyzed Fusion (μCF)?
2. New developments on μCF research(a) μCF target development(b) Advances in our understanding of μCF
elementary processes
3. Summary2

1. What’s muon-catalyzed fusion?

4

Muonic atom
What is muon?
• A member of the electron family• ~200 times heavier than the mass of an electron• short life time (~2.2 μsec)• can be made into a beam using a particle accelerator

Electron e-

x 200 mass
Muon μ-What is a muonic atom?
➡ When a negative-charged muon is stopped in a material,
it can replace an electron to form a muonic atom
➡ Muons are 200 times heavier than electrons, so they form
very compact atoms with a radius of 1/200 compared toordinary atoms.
Normal atomeμ-replacing

Nucleusradius+To a small "muon atom"with a radius of 1/200

me
Bohr radius / ⇤mµ(inversely proportional to the muon reducedm⇤µ mass)/
eme<latexit sha1_base64="WbUN5NGOFpodPYLQGpFXUT6/lyw=">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</latexit>μ-Scaled image

MuonichydrogenμH

HydrogenH
1 / 200 Å(~ 500 fm)~1Å

5

Scaled image

The smallest
molecule !!
μpp~ 500 fm

H2

8

9

Muonic molecule

The smallest
molecule !!
μpp~ 500 fm

Lookcloserμ＋＋

Two nuclei, impossibly close !!

Compared to the reach of nuclear force (a few fm), it becomes smallenough to allow nuclear reactions to occur within the molecule.

10

FusionThermonuclear fusion
Vigorous collisions in plasma
at several hundred million
degrees Celsius＋＋

Large repulsion due toelectromagnetic force

Fusion with muons
Nuclei easily approacheach otherμ＋＋

No repulsion byelectromagnetic forces
up to the size of a muonic
molecule11

Muon-Catalyzed Fusion (μCF)
Interestingly,
it causes a chain reaction!

Fusion cycle withmuons as “catalysts"

Muonic atom

eμ-

μ-

Note : 200x
magnification

replaceμ-tNormal atom

Note : 200x
magnificationdMuonic molecule
free muon (re-emitted after nuclear fusion)
can re-create muonic atom & molecules.

%

.7
99

The phenomenon ofsome muons going out
of cycle is known as“α sticking problem”.

α

μ-

n
μ-

0.3%

μ-4He
atom

4He

This cycle continues
until the muon lifetime(~2 μs) is over.

12

Brief history of μCF research๏1947 F.C. Frank : Hypothesis of the μCF cyclic reaction๏1957 L.W. Alvarez : First observation of the μCF cyclic
reaction๏

1967 E.A. Vesman : Theory of Resonant Molecule Formation

๏1980 - 2000 Significant progresses in both experimental andtheoretical studies- LAMPF (US, Los Alamos)- SIN, PSI (Swiss, Villigen)- TRIUMF (Canada, Vancouver)- KEK (Japan, Tsukuba)- RIKEN-RAL (UK, Chilton)

L.W. Alvarez et al., Phys Rev 105 (1957) 1127

muon
decay

μCF

➡ found that the maximum number of μCF cycles is about 150➡ Since it takes about 5 GeV of energy to make one muon, thescientific breakeven can be exceeded if more than 300
cycles/μ (~5000 MeV / 17.6 MeV) are performed.
➡ The bottlenecks are the molecular production rate and the αsticking problem, and μCF research has not progressed since2000.
๏2016 Reexamination has been initiated by Y. Kino (Tohoku
Univ) and M. Sato (Chubu Univ).

μCF

μCF reaction in a bubble chamber
observed by Alvarez et al.
→ “AB”, “CD” followed by μCF,
and Muons turn into electrons
and neutrinos at “E”.

Since 2016
Two research funding programs :(1) ImPACT (Impulsing Paradigm Change through Disruptive Technologies Program)
Substantial reduction and recycling of high-level radioactive waste through nuclear
transmutation (PM : Reiko Fujita)• Theoretical calculations of elementary processes of muon-catalyzed fusion
reactions in high-temperature plasmas (Yasushi KINO)• Application of fusion neutrons to the separation and transmutation of LLFPs(Motoyasu SATO)(2) Grant-in-Aid for Scientific Research on Innovative Areas (2018-2022)
Toward new frontiers : Encounter and synergy of state-of-the-art astronomical
detectors and exotic quantum beams (PI : Tadayuki Takahashi)• Program B02 : Basic research of in-flight muon catalyzed fusion in the Machshock wave interference region (Yasushi KINO)
New elementary process

μCF research is gaining momentum, again!

13

2. New developments on μCF research

New developments of μCF① Proposed a “Muon Fusion Reactor”

15②Advances in our understanding of elementary→ This is a circulating μCF target, which is
at a level that can be developed with existing
technology.

processes→ proposed a new μCF elementary process andtook the first step toward its experimental verification

Circulating
D2/T2 mixed gas
muon beamtarget (high pressure gas region)

New development ①

μCF target development○ Requirement oftarget for μCF :17(1) Mixed deuterium and tritium targets(2) High density (for eﬃcient μ- rest in the target)(3) Removal of reaction products (4He)

Traditionally, solid and liquid targets have been used for μCF

Proposed a new concept of the “circulating” target
Oblique shock wave generator

Utilizing Mach shock wave buﬀer region(high-density region floating in a hollow)

Mach shock front

Muon
catalyzed
fusionLaval nozzle
Muon injectionμ-Peak pressure
10 ~ 30 atm
Subsonic zone
Subsonic zone
Subsonic zone

1 atm

Length overall 10 m

Prototypes will be built / tested.
* Motoyasu SATO
* Yoshiharu TANAHASHINew development ②
new μCF process (IFμCF)19

Muon-Catalyzed Fusion (μCF)μ-

Fusion cycle withmuons as catalysts
Muonic atom
ereplace

μ-

μ-

t

Normal atom

Muonic molecule
μ-

4He

d

n
μ-

20

μ atomic & molecular processμ-Muonic atoms have been
actively studied so far(e.g., verification of fundamental physical constants)

Muonic atom

Complex quantum
scattering processes

ereplaceμ-μ-Normal atomtdMuonic molecule

Almost no experimental knowledge ofwhat quantum states are being generated.

How μ molecules are created ?
D2
Theoretical Prediction

edchargeneutralddμe-

without destroying themolecular skeleton

If the muonic atom collide “gently” to the normal molecule,the excess energy of ddµ molecule formation is passed to
the rovibrational excitation energy of D2 molecule.
Resonant generation (Vesman mechanism)

21

Molecule in molecule !
Theoreticalprediction

ed

ddμ molecule

Matryoshka-like

d

e-

d

μ-

Forms a molecule
within a moleculeby acting as a
pseudo-nucleus
with charge +1

22Key point of the new μCF process
Ground state

Excited state

dtμ

dtμ*
tμ*

tμ(1s)(2s, 2p
mixed state)

μ-

t

μ-

d

t

d

~ 2 keV
excitation

Immediately leading
to nuclear fusion

No nuclear fusion,
but dissociates
quickly<- also will be created via Vesman mechanism

23

Dissociation of excited molecules

24• Metastable Excited Molecule
At first glance, it appears to havenothing to do with fusion because it
dissociates.
But, the high-energy “electricallyneutral” muonic hydrogen atoms
after the dissociation suggest thepossibility of direct fusion.

• Size ~10-12 m

tμ*• Structure with μ localized on one sideμ-(2s, 2p
mixed state)t~ 2 keV
excitation

non-radioactive

Precise measurement of X-rays
enables the study of molecularresonance states.

d

X-ray

radioactive

New μCF elementary
processes

1.7 ~ 2 keV

hot tμLow energy to bring up~1 keVμ-~1 keVtdInflight μCF study

μ-

t

d

X-ray precision
spectroscopy

Conventional（Vesman process）
tμ(1s)

μ-dt

μCF cycle

Intra-molecularfusion
dµ

tµ

μ-

µ

n

4He

μ-

µ4He

μCF cycle

4He, ndtµIntramolecular
nuclear fusion

New elementary process
hot tμdeuterium

Conventional（Vesman process）
tμ(1s)of D2 molecule

μ-

d

t

μ-

t

Collision at 1 keV

In-flight
fusion(IF-μCF)

Intra-molecularfusionGeneration process of hot dμ

tμ*

μ-

(2s, 2p
mixed state)

μ-

d

t
~ 2 keV
excitationn

4He

dissociation

hot tμ
μ-

1 keV

μ-

dtμ* molecularresonancetdμCF cycle considering "excited molecules”

28

In-flight μCF joins
the conventional μCF
Conventional μCF cycle（Vesman model）
dµ
µ

µ4He

tµ

μCF cycle

4He, n

tµ*
dµ*
dµ

dtµ

µ

Low
temperature
moleculetµIFμCF
BranchVesmanBranchdtµExcitedmolecule
dtµ*
dissociationµ4He

4He, nhot tµhot dµmuonic atoms
with high kinetic energy(Sidepath model)
It has been suggested that this process may reduce “α sticking”,
and the formation rate is faster than the ordinary μCF process.
→ So it is important to study the mechanism to enhance the IFμCF process.

Importance of dtμ* was demonstrated
Conventional
theory(dotted line)

New few-body many-body calculation
breaking away from adiabatic approximation: (dtμ*)e→ 4-body calculation including electrons

Succeeded in explaining thetemperature dependence

New calc.

of the μCF reaction rates,
which could not be explainedby the conventional μCF cycle.

Experiment (plot)

T. Yamashita et al.,Sci. Rep.12 (2022) 6393

Aiming for direct experimental verification

29

Strategy for IFμCF Demonstration Experiment

Step-by-step development ofdemonstration experiments

tµ*
dµ*
dµ

µ

tµ

IFμCF
BranchVesmanBranch

① Measurement of excitedmolecular X-rays

dtµ ①

X-ray

②
µ4He

4He, ndtµ*② Observation of hot dμ

excitedmolecule③ IFμCF experiment

hot tµhot dµ③30High Precision Spectroscopy of Muonic Molecules
Normal moleculeD2+0

Muonic molecule

~1 nm

e-

d

~0.005 nm

0

d

μ-

d

Energy (eV)๏ Distance between
nuclei : x 1/200

ultraviolet
ray
紫外線

15

d
0.0

0.2

0.4

D(1s) + de-dissociation
0.6

0.8

1.0

d-d distance (nm)d1.2

๏ Energy : x 200
๏ Adiabatic
approximation is not
valid due to closemasses of d and μ

Energy (keV)

dde*
dde*

10

d

dµ(n=2) + d

D(n=2) + d
5

31

1

ddµ*
ddμ*

2

XX線
ray
X線

(1.7〜1.97 keV)3d

๏ ddμ* has large zeropoint motion andsparse level spacing

0.0

1.0

2.0

dµ(1s) + d

μ-dissociation
3.0

4.0

5.0

d
6.0

d-d distance (pm)✤ Theory : Few-body calculations simultaneously solving for the motion of
nuclei and heavy negatively charged particles✤ Experimental : High energy resolution in X-ray measurements in muon beams

Scientific Research on Innovative Areas (2018-2022)

Encounter and Synergy ofState-of-the-art
Astronomical
Detectors

CdTe

TES

and

ExoticQuantum
Beams

J-PARCWe brought the detector to the muon beam experiment !

32

Innovative Spectroscopic Techniques

Conventional Detector (SDD)(FWHM ~ 150 eV)

Detector with excellent
energy resolution anddetection eﬃciency(FWHM ~ 5 eV)@ ~ 6 keVTES microcalorimeters
1. incident particles areabsorbed by the absorber
2. energy ΔE is converted tophonons
3. slight temperature rise ismeasured with highsensitivity thermometer TES

High
Sensitivity
Thermometer
TES

X-ray
absorberTransition Edge Sensor
R0~50 mΩResistance R0/Rn

TES
Microcalorimeter

Normal state

photoninjection

bias pointsuperconducting
state

Sudden increase
in resistance
Read out the change inresistance (bias current)with a SQUID

Slight temperature
increase

Temperature T [mK]heatsink

High resolution (ΔE / E ~ 10-3)

33

High Precision Spectroscopy of Muonic Molecules
ddμ* “molecule” X-raydμ “atom” X-raydµ(n=2) + d

1700

1800

1900

2000

TES

2100

2200

300

Expected
spectrum

150
100

2500

Conventional
detector(Silicon drift detector)

dissociated X-rays
from excited
muon molecules

1.6

1700

1800

1.8

1900

XX線
ray
X線

(1.7〜1.97 keV)

2000

2.0

2100

2200

2.2

2300

d

3.0

dμ atom
X-rays(2p-1s)ddμ*→ dμ(1s) + d + hν

1600

2

3

50
0
1500

ddµ*
ddμ*

ΔE = 150 eV

250
200

2400

ΔE = 5 eV

400
350

2300

1

2400 2500
2.4 [eV]
EnergyEnergy [keV]

2.5dµ(1s) + d

μ-dissociation

ddµ*

2.0
1.5

0.0

1.0

1.0

2.5
2.5
2.0
2.0

pdµ*
ddµ*

pdμ*
→ dμ(1s) + p
υ=0pdμ*→ pμ(1s) + d
υ=0

1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0
3.0

3.0

4.0

5.0

υ=2
d-d
distance
(pm)
1
υ=0

0.5
0.0
3.0
3.0

2.0

υ = 0υ = 0
1.6

pdµ*

1.7

1.8
X-ray energy (keV)

1

1
1.9

3

d

dμ(2p → 1s)

1600

ΔE : FWHM
Energy resolution

4 6.0

dμ(2p
1s)
dμ(2p
→→1s)

convoluted
by detector
responsefunction–1–1ps–1–1
Intensity(keV(keVpsIntensity))

Countscounts / 1 eV (TES), counts / 5 eV (SDD)

0
01500

d

44
3 3
υ = 22

2.0

1s)

1

1

d

pμ(2p → 1s)

2

2

μ-

1s)

3

3

–1)

arb. unit

44

Theory~0.005 nm

0Energy (keV)55(large peak)Intensity (keV–1 ps–1)

66

Muonic molecule342019MS01 : “μ molecule” experiment
Mar 9 - 19, 2022

Gas D2

Feb 5 - 11, 2023

Solid D2
w/ new TES

35

Experiment with gas D2
connected
to beam pipe

μ- beamMarch, 2022

n
ws

e

μNe
ddμ*
X-ray
X-rayscalib. X-rays

TES
detector

D2 gastargetX-ray
generator

36

Experiment with gas D2
Counts/(1.00 eV)

3
2.5
2

×106
1.5

Counts/(1.00 eV)

Cu

3.5
3.0
2.5

1

1.5

✓ Clear Lyman series dμ X-rays

1.0

3

×10
0.0
1.90 1.92 1.94 1.96 1.98 2.00 2.02 2.04 2.06 2.08 2.10

✓ No significant signal of μ
molecules

Energy [eV]

Al
Kα

2.5

Cl
Kα

1.5

2

2.5

K
Kα

Energy [eV]Responsefunction :

3

3

× 10
3.5

3

0.2
0

✓ Precise energy calib. in ~2 keV

2.0

Energy [eV]

p

1.2

0.4

2

X-ray tube
(calibration)

1.4

0.6

Gas D2

6-1

0.5

0.8

4-1

5-1

1

1.6

3-1

March, 2022

Gas D2
Solid Cu

4.0

0.5

1.5

0

μd
2-1

muonic X-ray(w/timing cut)

3.5

4.5

Counts/(1.00 eV)/hour

4

Cl
y
r
a
n
i
Kα
m
i
l
e
r
μd 2-1

3

× 10✓ “Vesman mechanism” requiresthat μ atoms collide “gently” tothe normal molecule.
➡ expecting that the Vesman
mechanism did not work well in
the low-density gas environment
due to insuﬃcient thermalization➡ Moreover, the present TES is
known to have a tail component
in the detector response function.

×103
3.5
5

Next :
tail37➡ Low tail TES➡ Solid D2 target4 (b) time-division-multiplexingshows a photograph of the 240-pixel
array.chip
Eachmounted
TES consistsof a superconducting
the readout(TDM)
on eachfour sides. Figure
bilayerof thin Mo andCu films
with anadditional
Bi absorber[19]. The
4 (b) showsa photographof the240-pixel
array.
Each4-µm
TESthickconsistsof a superconducting
absorption
this Biwith
layeranis about
80% for4-µm
6.5 keV
x rays.
Each pixel[19].
has Thebilayer ofthin Moefficiency
and Cuof films
additional
thick
Bi absorber
an effective
areaofofthis
320 µm× 300 isµm,about
thus thetotal
area xof rays.
the array
is about
absorption
efficiency
Bi layer80%
foractive
6.5 keVEachpixel has
2
23
mm
.
TES
array
is
collimatedwithagold-coated275-µm-thicksilicontoavoid
an effective area of 320 µm × 300 µm, thus the total active area of the array theis about
2 unnecessary x-ray hit on the TES stage.
23 mm . TES array is collimated with a gold-coated 275-µm-thick silicon to avoid theunnecessary x-ray hit on the TES stage.

38

New TES : Less tail component
Good ch1

Original TES

Counts/(0.25 eV)

new snout Run0019

0.8

Absorber : Bi (4.1 um)# of Pixel : 240

prev. snout Run0119

Review of
Scientific Instruments

ARTICLE

scitation.org/journal/rsi(61% for 8 keV)

0.6

0.4

New TESfor Low energy X-ray

0.2

0Figure 4: (a) A photograph of the detector package of the TES array. The array is on
top,Awould
where
each
is wire-bonded
for package
the readout
chip mounted
eachfour is on
Au absorbers as Au is a metal (Bi is aFigure
semimetal)
andcausepixel
theof
4:the(a)photographthe detectorof TDMthe TESarray. onThearraysides.
(b)A
photographofthe240-pixel
TES
array.
The
gold-coated275-µm-thicksiliconTES superconducting properties to the
be intrinsicallycoupledto those
top, where
each pixel
is wire-bonded for the readout TDM chip mounted on each four
57,58
collimatorisstackedinstalled. Photos
credit: The
D.R. gold-coatedSchmidt, NIST.
of the Au absorber through the proximity
effect,which
issides. (b) A photographinconofwhen
the 240-pixel
TES array.
275-µm-thick siliconvenient from a design tuning and collimatorfabrication isstandpoint.
Instead,stacked when installed. Photos credit: D.R. Schmidt, NIST.
the Au absorber is deposited laterally away fromTESs
the TESare thermistor
thermally isolated with the support of 100-nm thick silicon-nitride SiNx
in a “sidecar” design.
which limits
the thermal
conductance
TES andsubstrate.
The sub- SiN
TESsmembrane
are thermallyisolated
with thesupportbetweenof 100-nm
thick
silicon-nitridex
The sensor material is a sputtered MoCu
bilayerwith
215
nm
strateis a grid
structureof 275-µm-thicksilicon between
wafer, theTES
partsandbehindeach TESTheare submembrane
which
limitsthe thermal
conductancesubstrate.
of Cu on top of 65 nm of Mo. The thicknessesof CuA andMo heatare sink layer of 500-nm-thick gold is deposited on the backside ofremoved.
thermalstrate istransitiona grid structureof 275-µm-thicksilicon wafer, the parts behind each TES are
tuned to target a specific superconducting
temperature,
substrate.
Thisheatheat sink
islayerconnected
to the low temperaturethermal bath.
57,58
removed.
A
thermalsinkof500-nm-thickgold is depositedon the backside ofT C , via the proximity effect.
The sample wafer is rotated during
The
TES
array
is
operated
at
about
100
mK
aroundthecriticaltemperature,
This inheat
is connected to the low temperature thermal bath. andsputtering to maximize uniformity,substrate.
and the sensors
thissink
particuisTES
cooledwithisa operated
pulse-tube-backed
demagnetization(ADR). The and3adiabatic
array
about
100 mKaround therefrigerator
critical temperature,lar array have T C values in the range ofThe
111–112mK.
This T C was at×10
pulse
tube
cools
the
system
from
300K
to
3K
for
16
hours.
Then
4-Teslamagnetic
field Theis cooled withpulse-tube-backed
adiabatic
demagnetization refrigerator (ADR).
chosen as a trade-off between the theoreticalenergya resolution
we
∗
2.55
2.6
2.65
2.7 the2.75
is applied
to thetwo-stage
pills tothroughcoils.4-Tesla
By releasing
the field
cools
3K forsuperconducting
16 hours. Then
magnetic
could hope to achieve and cryostatpulse
hold tube
time(see Sec.
IIsystemD).
Anfromsalt300K∗
magnetic
adiabatically,
is cooleddown to 600 mK coils.
and finally75mK, theadditional Cu layer of thickness 419
is depositedon
topof thesalt theis nmappliedto thefield
two-stage
pillssystemthroughsuperconducting
By toreleasing
sensor and patterned into banks, used
to steercurrent
toward thethe system is cooled down to 600 mK and finally to 75mK,
magnetic
field
adiabatically,∗
GGG:
Gadolinium-Gallium
leads, and interdigitated stripes, used to control the transition shape Garnet, and FAA: Ferric-Ammonium Alum∗ also thermally connects theand reduce excess noise.59 This Cu layer
GGG: Gadolinium-Gallium Garnet, and FAA: Ferric-Ammonium Alum8
sensor to the absorber. In addition to its use in the sensor bilayer,
the Mo is used for superconducting leads and traces running off the8membrane.
The absorber is made from Au that is electron beam evaporated
in two separate layers, first 186 nm and then 779 nm thick, resulting in a total absorber thickness of 965 nm. The wafer is also rotatedduring this deposition, and the evaporation tool had previously beencharacterized for roughly 3% variation across a 76 mm wafer (better
than 1% variation across a single detector array chip). The absolute
thickness had been measured with a stylus profilometer with �3%
uncertainty. Section III B contains a discussion of these absorber
thickness uncertainties as they relate to the quantum efficiency (QE).
The deposition is done in two separate layers to reduce step coverFIG. 3. (a) The TES array used in NETS. The aperture chip used to prevent x-rays
age issues when coupling the absorber to the sensor through the Cufrom being absorbed by areas outside the TES absorbers is also shown (displayed
on top of a penny, for scale). (b) Pixel map indicating absorber size (rather thanand to better control the thermal conductivity. The absorber area isAbsorber : Au (965 nm)# of Pixel : 192

2.5

EnergyEnergy[keV]
[eV]

New
TES

(32% for 8 keV)

Experiment with solid D2 (2023)
connected
to beam pipe

μ- beam39

Feb 5 - 11, 2023

new TESdetector

Solid D2
targetμNe
X-rays Calib. x-rays
ddμ*

x-rayscalib. X-rays

X-ray
generator

X-ray
generator

Summary

take-home message✓ Muon-catalyzed fusion, μCF, research is entering a new phase✓ Concept of circulating gas target for μCF is ready for practical use✓ A new elementary process of μCF was proposed and indirect
evidence was obtained.
✓ The first direct evidence for the existence of “resonant Matryoshka
molecules” (= intramolecular molecules) is provided.
➡ opens a complex and diverse black box leading to μCF➡ marks the beginning of a new quantum few-body study in thefield of "exotic molecules".

41Collaborators

many researchers from diﬀerent fields
T. Osawa,
T. Hashimoto

M. Katsuragawa, S. Takeda, T. Takahashi,
P. Caradonna
C. I-Huan, K. Ninomiya, A. Shinohara
K. Terada, H. Noda
T. Azuma,
K. Ishida,
T. Isobe,
Y. UenoS. Watanabe

T. Saito,
Y. UenoK. Kubo

Y. Kino, T. Nakamura,
K. Okutsu, T. Yamashita
S. Kanda, N. Kawamura, Y. Miyake,
H. Natori, S. Nagatani, K. Shimomura,
P. Strasser, S. Takeshita, I. Umegaki,
M. Tampo

T. Okumura,
H. Tatsuno

T. K. Kouzuma
S. Okada,
Y. Toyama
A. Taniguchi

P. Indelicato, N. PaulK. Mizumoto

D. A. Bennett, W. B. Doriese, M. S. Durkin,
J. W. Fowler, J. D. Gard, G. C. Hilton,
K. M. Morgan, G. C. O'Neil, C. D. Reintsema,
D. R. Schmidt, D. S. Swetz, J. N. Ullom

R. Hayakawa,Y. Ichinohe,
S. Yamada,with graduate students.