Wen-Hsien Li (李文献)
Center for Neutron Beam Applications
(中子束應用研究中心)
Department of Physics (物理系)
National Central University (中央大學)
中子散射原理、實驗設施、
與應用實例簡介
(Principles, facilities & applications
of neutron scattering techniques)
National Central University
散射概念
(Scattering process)
中子束源
(Neutron beam sources)
常用中子散射儀簡介
(Neutron instruments)
應用實例
(Examples)
Content
散射概念
Scattering process
奈米物性實驗室
Viewing atomic landscape
Solid: periodic arrangement of atoms,
consisting of unit cell blocks
Momentum and energy changes of the probes
→ Understanding the atomic arrangement and dynamics
Momentum exchange: yes
Energy exchange: no
Momentum exchange: yes
Energy exchange: yes
Elastic scattering
Inelastic scattering
Incident
neutron
ki
kf
2q ∆k
Elastic scattering (彈性散射) 4 sink = 0
q
22 2
neutron f i f iE = E - E = (k - k ) = 02m
Diffraction for structure
(繞射尋靜態結構)
Incident
neutron
ki
kf
2q ∆k
Inelastic scattering (非彈性散射) 4 sink = 0
q
22 2
neutron f i f iE = E - E = (k - k ) 02m
Excitation for dynamics
(激發尋動態組合)
Physical quantities
Energy scale
o 12.4(A)
(keV)E
Photon : Energy dispersion of
with h = 4.1310-15 eVs and c = 2.998108 m/s.
for photons.
For an x-ray photon of = 1.5 Å E = 8.3 keV.
For a laser photon of = 5145 Å E = 2.41 eV.
/E h hc
2 2 2 2
22 2 2
k pE
m m m
o 0.28 9.04(A)
(eV) (meV)E E
Neutron : Energy dispersion of
with h = 4.1310-15 eVs and m = 1.67510-24 g.
for neutrons.
For a thermal neutron of = 1.5 Å E = 36.3 meV.
Neutron: in the meV (10-3 電子伏特) range
Comparable to the dynamical energy of solids
Epithermal neutron (超熱中子): 200 meV, 0.64 Å
Thermal neutron(熱中子): 20 meV, 2 Å
Cold neutron(冷中子): 2 meV, 6.4 Å
X-ray: in the keV range
Laser: in the eV range
Electron: in the 100 eV range
Energy scale
中子束源
奈米物性實驗室
Reactor neutron source
1. Nuclear fusion processes → proving continuous
free neutrons
2. n + 235U → 36Ba + 56Kr + free n (平均2.5) + betas
3. D2O moderator: 減速核分裂所滋生中子能量
(~1 MeV)至熱中子(eV) 增加連鎖反應速率。
Beam guides
Energetic proton
以高能量質子(500MeV)
撞擊金屬靶
平均每次撞擊可滋生約10個中子
Spallation neutron source
Types of neutron source
Reactor source:
穩態,能量依Maxwellian分佈
以H2O/D2O/石墨降低能量至meV範圍
Cold neutron source:
爐内增設致冷器(液態氫: 20 K)
Spallation source:
脈衝式,瞬時通量較高,TOF techniques
Energy: meV(good for dynamics studies)
Average flux
1 MW spallation source
≈ 10 MW reactor source
Neutron:
carries no charge
small in size relative to atomic radius
heavy in weight relative to electron
mneutron = 1.675 × 10−27 kg
mproton = 1.673 × 10−27 kg
melectron = 9.109 × 10−31 kg
mneutron / melectron = 1838
Strong neutron-nucleus interaction
→ Determine the atom position with high precision
Incident
neutron
atom
What makes neutron so special for diffraction
To detect cation substitution, distribution,
site occupancies and order-disorder processes
Mn Fe Co
X-ray
Neutron
ex.: (Fe, Mn)2SiO4, Al-Mg order-disorder in spinel structure
Al-Si distribution in silicates
What makes neutron so special for diffraction
Strong neutron-nucleus interaction
→ Discriminate elements with similar atomic number
Relative Scattering Powers of the Elements
Neutrons scatter strongly from light elements,
since neutrons scatter mainly from the nuclei.
Scattering length
中子散射作用力
散射作用力:
中子–原子核:強交互作用力
(見到原子核,散射機率並非隨原子序增加而增大)
偵測原子核位置 原子排列方式(晶體結構)
中子自旋–未成對電子自旋:磁偶矩交互作用力
偵測未成對電子自旋 自旋排列方式(磁結構)
對樣品穿透力:
除少數元素(Gd、Cd、Sm、B)外,基本上全然穿透
散射長度因同位素而異:
對比調變(contrast variation)技術
中子束基本功能
˙為一非破壞性探測的工具。
˙能深入系統的內部。
˙目前唯一能探測磁性結構的工具
→ 磁性材料。
˙在重原子間判定輕原子
→ 生化分子裡氫原子的測定。
˙動力組態探討。
→ 所具能量與動力激發子相當。
˙中子影像。
→ 漸層分析,觀看動態氫。
D
H
O Ca Si
Scattering power:
中子能量: meV
中子為電中性
中子具磁耦矩
Amorphous (glass, liquid, gas…)
Elastic scattering (∆E=0)
shows where atoms are
Yarnell, J. L. et. al. Phys. Rev. A (1973) 7, 2130
Peak positions → unit cell size
Peak intensity → positions of atoms
Peak width → block size
20 30 40 50 60 70 80
0
2
4
6
8
10
12 Ho0.82
La0.18
Mn2O
5
Inte
nsi
ty (
10
3 c
ou
nts
)
Scattering angle 2q ( deg. )
T=300 K
g(r
)
0 5 10 15 20 25
r(Å )
1
3
2
0
radial distance
distribution
0 10 20 30 40 θ (deg.)
1000
3000
2000
0
Inte
nsi
ty
Liquid Ar at 85 K
Neutron powder diffraction
Neutron activation analysis
Neutron imaging Inelastic neutron scattering (TOF)
Small angle neutron diffraction
大小 形狀
Motion of H atoms
in a fuel cell
Ancient Greek
hanging bronze oil lamp
Neutron x-ray
Neutron imaging
Neutron x-ray
打火機
Small angle neutron scattering
大小 形狀
常用中子散射儀
簡介
奈米物性實驗室
*
Australian Nuclear Science and
Technology Organisation
OPAL
reactor
Guide
Hall
澳洲雪梨ANSTO
Taiwan
office
Thermal source
20 K liquid H2
cooled cold source
9.045
E meV
1 Å = 82 meV
2 Å = 20.5 meV
4 Å = 5 meV
Neutron flux of OPAL OPAL cold source
Cold head
(liquid H2)
Heat
exchanger
Opal guide and reactor halls
TOF DCS
飛逝時間散射儀
Reflectometer
反射儀
Residual stress
diffractometer
殘餘應力繞射儀
HIPD
高強度 中子繞射儀
SANS
小角度散射儀
Quasi-Laue
diffractometer
準勞厄繞射儀
Thermal-TAS
熱三軸散射儀
HRPD
高解析度 中子繞射儀
Cold-TAS
冷三軸散射儀
Neutron instruments at ANSTO
ANSTO 2nd phase projects:
3He polarizer, USANS, 2nd SANS, Back scattering, Neutron radiography
7+2+5散射儀
Opal neutron beam facility
www.ncnr.nist.gov
NCNR NBSR
TSB
美國華盛頓NIST
Center for Neutron Research
4 new guides
5 new instruments
30+ Neutron Beam Line Instruments
NBSR guide and reactor halls
SAMPLE AREA
GRANITE FLOOR
NIST BT-7 TAS
NIST guide hall
繞射
diffraction
奈米物性實驗室
1. Crystalline structure
atomic composition,
atomic separation
2. Spin arrangement
transition temperature,
magnetic moment,
correlation length,
dimensionality
3. Particle size
The interference pattern of neutrons
being diffracted by the periodic
lattice of solid.
Results of 3D interference.
Cu(2)
O(2)
Cu(1) O(1)
O(4)
Ba
2.4654(15) Å
2.7736(4) Å
74.32°(9)
O(3)
O(5)
2.4458(16) Å
Pr
104.92°(9)
105.68°(9)
75.08°(9)
Purpose
A macroscopic point of view:
Crystals are made out of
parallel planes of spacing d.
θ:Bragg angle, 2θ: scattering angle
Electric scattering:
Momentum transfer:
k k
( )K k k
Constructive interference occurs whenever nλ=2dsinθ,
which is known as the Bragg reflection law.
Bragg reflection (1913)
A, B: lattice points
X: Viewing point
A: origin
Incident wave at B :
Scattered wave at X due to scattering by B:
with
Final scattered wave due to scattering by all lattices:
jik Re
( ) - j j jik R ik r R iK Rik re e e e K k k
- -( ) j jiK R iK Rik r ik r
s
j j
r e e e e
Information on lattice structure, 含晶格結構資訊
Incident wave:
Scattered wave:
ik r
ik r
e
e
: Direct lattice vectorjR
Diffraction wave
幾何結構因子 Structure factor
Two basis at B and B
Scattered wave at X due to scattering
by B:
by B:
with is known as the geometrical structure
factor, which provides the information on the relative
positions between B and B.
( ) -j j jik R ik r R iK Rik re e e e
( ) ( ) - -j j jik R r ik r R r iK R iK rik re e e e e
- - -- -( ) j j jiK R iK R iK RiK r iK rik r ik r ik r
s Kj j j
r e e e e e e e e S
-iK r
KS e
-iK r
KS e
Structural factor of a bcc lattice
bcc lattice = sc lattice + basis at 1 2 1 2 3
10,
2r r a a a
1 2 3Recall K hb kb lb
1
2
0
2
2 2 2
K r
h k lK r h k l
( ) 0 for odd
1 2 for even
i h k lh k l
S hkl eh k l
1. No Bragg peaks at position with
h+k+l is an odd integer.
2. Bragg peaks appear at positions
with h+k+l is an even integer.
Structural factor of an fcc lattice
fcc lattice = sc lattice + basis at
1 2 2 3 3 3 1 4 1 2
1 1 10, , ,
2 2 2r r a a r a a r a a
No Bragg peaks at positions for the indices are partly
even or partly odd.
( ) ( ) ( )( ) 1
4 , , all even
4 , , all odd
0 otherwise
i k l i h l i h kS hkl e e e
h k l
h k l
Atomic form factor
Basis with internal structure
Introduce atomic form factor f so that
KiK r
KS f e
31 ( ) iK rf K d r r e
e
1. X-ray diffraction: scattered by electron density
→ f = Fourier transform of change density
→
2. Neutron nuclear diffraction: nucleus are “size less”
→ f = 1, use scattering length b to describe the
neutron-nucleus scattering probability with (4b2)
is the scattering cross section, so that biK r
KS e
22
2ˆ ˆ 1 ( )
sinθ sin2θ
h k lM Z M
MeI C F m
m c
Magnetic scattering
Scattering intensity
Magnetic moment Moment direction
2 sinθ sin2θ
h k lN N
MI C F
Nuclear scattering
2
2
j
rik
jNjebF
2
2 (0.0729) 2
(100) 774 sinθ sin2θ 0.16794(110) 1061
(0.0726) 3sinθ sin2θ 0.3195
h k lz
M
h k lN
MC
I
MIC
2 2 2
(001) (010) (001)
If points at the (001) direction:
ˆ ˆ ˆˆ ˆ ˆ1 ( ) 0, 1 ( ) 1, 1 ( ) 1
m
m m m
(1 0 0)+(0 1 0)+(0 0 1)
Moment calculation
BGive 1.07 μZ
Observations:
Nuclear {100} integrated intensity of 1061
Magnetic {110} integrated intensity of 774
應用實例
奈米物性實驗室
SAMPLE AREA
128 Position sensitive
detectors
Monochromator
shielding
GRANITE FLOOR
Neutron
guide
Dr Klaus-Dieter Liss
高解析度
粉末繞射譜圖
High Resolution Powder Diffractometer (HRPD)
- Complex crystalline structure
- Magnetic structure
- Cation ordering
- High pressure study
- Phase transition (vs T, P, H)
- Solid state chemical reaction
- Location of light anion or oxygen vacancy
2q
Neutrons
High resolution powder
diffraction pattern
Scattered by nuclei
Bi
O Cu S
20 40 60 80 100 120 140
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0Tetragonal P4/nmm
a = 3.8645(1) Å
c = 8.5493(3) Å
Rp = 3.81 %
Rwp
= 4.74 %
2 = 2.297
Neutron = 1.6208 Å
T = 293 K
Scattering angle (deg.)
Inte
nsi
ty (
103 c
oun
ts )
BiOCu0.94
S
1. Seeing nuclei 2. Well-defined Bragg profiles
3. Insignificant form factor variations
Neutron powder diffraction (粉末繞射)
Cu(2)
O(2)
Pr
Cu(1) O(1)
O(4)
Ba
2.4882(12) Å
2.7991(9) Å
76.49°(7)
103.51°(7)
c
b a
Rietveld refining analysis
General Structure Analysis System
晶體結構分析 (PrBa2Cu3O6.338)
0 20 40 60 80 100 120 140 160
0
500
1000 P 4/m m m
χ2 = 1.175
Rwp =
8.47%
Rp = 6.66%
1500
PrBa2Cu3O6.338
λ = 1.5402 Å
15'-20'-7'
Neu
tron
cou
nts
Scattering angle (deg)
50 100 150 200 250 300 350-48
-45
-42
-39
-36
-33
-30
-27
Jd
Ja
Jc
Ex
cha
nge i
nte
gra
l (
arb
. u
nit
s )
Temperature ( K )
Jb
(b)Jahn-Teller
distortion
(a)
c
a y=½ b
Mn(1) Mn(2)
Mn(3)
Mn(1) Mn(2)
O(8)
O(8)
O(7)
O(7)
O(6)
O(6)
O(5)
O(5)
O(6) O(7)
O(8) O(5)
O(8) O(7)
O(6) O(5)
Jb
Jc
Ja
Jd
50 100 150 200 250 300 3509
12
15
18
21
24
Jg
Jf
Je
Mn4+
(3)-Mn4+
(3)
Mn3+
(2)-Mn3+
(2)
Mn3+
(1)-Mn3+
(1)E
xch
an
ge i
nte
gra
l (
arb
. u
nit
s )
Temperature ( K )
Jahn-Teller distortion
(b)
(a) z=0c
b
a
Mn(2)
Mn(2) Mn(1)
3 1
Mn(1)
Bi Je Jf
z=½ c
b
a
4 3 Bi Bi
Mn(3) Mn(3)
2 2
Mn(3) Mn(3)
Bi Jg Bi Jg
Bi0.37Ca0.63Mn0.96Cr0.04O2.98
Mn-O-Mn superexchange
coupling strength
TN
Exchange integral calculation
High Intensity Powder Diffractometer (HIPD)
APPLICATIONS
• Real time: Single shot (kinetic) measurements
• Real time: Stroboscopic (cyclic, periodic) measurements
• Small sample volumes
• Magnetic studies at “long” wavelengths (2.36 Å and 4 Å)
Dr Andrew Studer
High intensity
powder diffraction
pattern
Neutron magnetic diffraction (磁繞射)
Magnetic dipole moment of neutron & unpaired electrons
→ Magnetic scattering High intensity
diffraction pattern
Polyaniline-intercalated
FeOCl 4000
3000
2000
1000
0
-1000
Inte
nsity (
co
un
ts / m
in.)
3530252015
Scattering angle 2 q (deg.)
(PANI)0.16FeOCl
{0
1}- ,
{0
0}+
{1 1
}- , {
1 0
}-
1. Coupled bi-layered quasi-2D
magnetic scattering profile.
2. No magnetic correlation
between the adjacent bilayers.
Magnetic modulation vector K=(1/3 1/2)
c
a
Along b: antiparallel
Van-der-Waals gap
• Direct exchange (DE):
Fe–Fe → Ferromagnetic
• Superexchange (SE):
Mediated through O between the Fe
ions Fe–O–Fe → Antiferromagnetic
• Competition bet. FMDE & AFMSE:
Non-collinear spin arrangement
Non-collinear spin arrangement
Fe Fe O
Bi-layer magnetic order
Calculated pattern
20 25 30 35 40 45 50 55
0
3
6
9
12
15Bi0.37Ca0.63Mn0.96Cr0.04O2.99
I30 K - I150 K
{1 1
1/2
}
{1 1
3/2
} +
{3
1 1
/2}
{3 1
0}
+ {
0 1
3/2
}
{0 1
0}{2 1
0}
+ {
0 1
1}
{2 0
0}
+ {
1 1
1/2
} +
{0
0 1
}
Inte
nsi
ty (
10
3 C
ou
nts
/ m
in.
)
Scattering angle 2q ( deg. )
{1 1
0}
+ {
0 1
1/2
}
a
c
b
θ= 45° φ=90°
101
θ= -135°
b a
c φ=90°
101
Mn4+(3), 4f
Mn3+(1), 2a
Mn4+(3), 4f
Mn3+(2), 2b Mn4+(3), 4f
Mn3+(1), 2a
Mn3+(1), 2a
Mn4+(3), 4f Mn3+(2), 2b
Ferromagnetic clusters
created by Cr-doping.
Spin-charge coupling
CMR
Bi0.37Ca0.63Mn0.96Cr0.04O2.98
Magnetic cluster
4 nm Au
1. Langevin M(H): alignment
of moment in Au by H.
2. Moments confirmed by
neutron diffraction.
3. Moments appear in the core.
0 10 20 30 40 50 60
0
1
2
3
4
MI
MP
15 K
300 K 55 K
10 K
7.5 K
Mag
net
iza
tio
n (
10
-2 e
mu
/g )
Applied magnetic field Ha (kOe)
4 nm Au 5 K
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
T = 2.1 K5
4
3
2
M (
10
-2 e
mu
/ g
)
Applied magnetic field Ha ( kOe )
4 nm Au
1
30 45 60 75 90 105 120 135
0
2000
4000
6000
Ha= 0 Oe
(420)(331)
(400)
(222)
(311)
(220)
(200)
Inte
nsi
ty (
co
un
ts /
19
0 m
in.
)
Scattering angle 2q ( deg. )
I5 K
- I100 K
4 nm Au
(111)
0 5 10 15 20 25 30
0.00
0.01
0.02
0.03
0.04
1.15
1.20
1.25
1.30
1.35
1.40
1.45(b)
Magn
eti
zati
on
( e
mu
/g )
Applied magnetic field Ha ( kOe )
T = 5 K
4 nm Au
Inte
grated
inte
nsity
( arb
. un
it )
(400) 0 50 100 150 200 250 300
1.10
1.15
1.20
1.25
1.30
1.16
1.20
1.24
1.28
1.32
(220)
Inte
gra
ted
inte
nsity
(arb
. un
it)
(200)
(111)
(400)
Ha = 1 kOe
Inte
gra
ted
in
ten
sity
(a
rb
. u
nit
)
Temperature (K)
4 nm Au
Confirmation of magnetic moment
X-rays are best (synchrotrons) for solving structures
Easier to find the heavy atoms first
Neutrons are best for refining structures
All atoms are ‘equal’ for neutrons
Few systematic errors (average over big samples etc…)
Easier sample environment (low temperatures etc…)
Interest of very precise structure measurements
Precise bond lengths
Study charge ordering, metal-insulator transitions…
Magnetic structures: difficult with x-ray powders
Best combinations for structural analysis
APPLICATIONS
• Complex fluids under flow
• Polymer coatings and interdiffusion
• Protein adsorption in biological membranes
• Magnetic multilayers
掠角反射(干涉)譜圖
Time-of-flight Reflectometer (反射儀)
PolymerProtein
Air
Water
Neutron Beam
Lipid
Layer thickness
Interface roughness
Mass density
Spin arrangement
Interference pattern
Reflectivity & grazing-incident scattering
磁性薄膜:鐵磁雙交換
與反鐵磁超交換建構成
canted spin arrangement
HIV protein and how it
penetrates a lipid monolayer
Protein penetration Spin exchange
Dr Elliot Gilbert
APPLICATIONS
• Large scale structures (1-100 nm)
• Colloids/emulsions/micelles
• Nanomagnetic materials
• Polymers and polymer processing
• Biomineralisation & biomimetics
• Biomembrane physics
• Zeolites & mesoporous materials
Small Angle Neutron Scattering (小角度散射儀)
Information may be obtained by neutrons
˙ Structure - exact arrangement of atoms.
˙ Overall shape - related to their function.
˙ Dynamic changes within a molecular
structure - correct functioning. 1
10
100
1000
0.004 0.007 0.01 0.04
Wave vector transfer Q(Å -1)
Inte
nsi
ty
Shape
Size
Small angle scattering (小角度散射)
Hydrogen/Deuterium contrast matching
H與D對中子的散射方式
非常不同
(bH = -3.74 fm bD = 6.67 fm)
以D取代部分H來調配背
景溶液或樣品的散射強度
判定H的位置、隱藏部份
分子
Increasing %D2O in the solvent 0% 100%
結構組態&受熱分解(鄰苯二酚加氧酵素)
0.00 0.05 0.10 0.15
1.5
2.0
2.5
3.0
3.5
log
I
S,A-1
Rg = 290 Å
83oC A B
C D
C23O(SH1) thermal cycle
52.5 oC 62.5 oC 5 oC
72.5 oC 80 oC 5 oC
A B
D C
0 10 20 30 40 50 60 70 80
30
40
50
60
70
80
90
100
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
Rg
Rg (
)
Temperature ( oC )
ActivityÅ
Activ
ity (u
nit)
Enlargement of the
enzyme size: due to
partial unfolding of the
tetrameric subunits of
the enzyme.
Spins in Fe2O3 nanoparticle 極化中子小角度散射
磁性奈米顆粒的核(內部)與殼
(表面)的自旋排列方式相互垂
直,使得奈米顆粒的磁矩小於
塊材者。
Oil/surfactant mixtures, repeat layer constant,
but membrane thickness (dip) changes
Membrane thickness
Inelastic scattering (非彈性散射)
Filter
selector
Beam shutter
Collimator
exchanger
Collimator
Monochromator
Sample table
Collimator Analyser
Beam stop
Bea
m sto
p
Collimator
Detector
Beam aperture
Monochromator drum
Analyzer-detector system
1st axis
(monochromator)
2nd axis
(sample) 3rd axis
(anlyzer)
Triple-axis
spectrometer
Sika
Cold Three-Axis-Spectrometer (TAS)
Dr. Chun-Ming Wu
For low energy excitations
Thermal Three-Axis-Spectrometer (TAS)
APPLICATIONS
Inelastic scattering - excitations
• collective - phonons and magnons
• diffusive - spin fluctuations
• localised - crystal-field levels
Dr Sergey Danilkin
W. -H. Li et. al. PRB 39 4119 (1989).
1. Coexistence of antiferromagnetic
order and superconductivity.
2. Very low Neel temperature,
hence the crystalline electric
field (CEF) effects play
important roles in its magnetic
and superconducting properties.
Crystal field scheme of Ho3+ in HoPd2Sn
Powder sample
Crystal field excitations
Crystal field
level scheme
of HoPd2Sn
and
isostructures
HoPd2Sn
Crystal field scheme
Maxons
Phonons
Rotons
T=1.1 K
He-II
A. D. B. Woods & R. A. Cowley, Rep. Prog. Phys. 36 1135 (1973 .)
smdP
dEvg / 239
Phase diagram of He
Excitations in superfluid 4He
Cu
T=49 K
Cu (FCC), Bravais lattice,
no optical branches
R. M. Nickow et. al. (1967), PR 164, 922
1. 1 Longitudinal +2 Transverse modes.
2. Transverse modes degenerate alone high symmetry
directions.
3. Sound speed: VL>VT
4. Phonon density of state → calculating thermal properties
Fm3m
a=3.516 Å FBZ: Octahedron
Phonon dispersion of Crystalline field scheme
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0
20
40
60
80
q (Å -1)
Ma
gn
on
en
ergy
(m
eV)
B. Antonini & V. J. Minikiewicz, Solid State Comm. 10 203 (1972)
G. Shirane et. al., JAP 39, 383 (1968)
2cos12 kqJSkqJS
Magnon dispersion
Wetting of root
上圖左下部分的放大圖:
At day 2 the soil next to roots was darker
and probably wetter than the soil far
from the roots.
At day 6, just after rewetting, the region
next to roots appeared bright, indicating
that it was not rewetted.
Day1-5: drying period
Day 6: immediately after rewetting
中子
影像圖
Seeing
H2O
Conclusions
Welcome to
neutron
scattering
community
Thank you for your attention
CNBA Center for Neutron Beam Applications, National Central University, Taiwan