dynamic nuclear polarization - cern · 2009. 4. 24. · on the other hand, the electron and nuclear...
TRANSCRIPT
Dynamic Nuclear Polarization
COMPASS PT- team at CERN:
• K. Kondo,
• N. Doshita,
• J. Koivuniemi,
• F. Gautheron,
• Y. Kisselev
Dynamically Polarized Targets
How the dynamically polarized targets work?
Basic apparatus required and techniques
Recent developments and topics
Elementary consideration S=I=1/2
,
,1( ) tanh( )
2e p
e p
B
Bn nP S I
n n k T
large magnetic
moment of electron
small magnetic
moment of nuclei
B
n+
n-
B=2.5 T
T=1 K
1000e p
One can see that all parameters in this formulae are fixed but the temperature
,e p
are electron and proton
magnetic moments
Dilution refrigerator may cool the nuclear spins down T~0.1 K,
but practice shows that this process takes about 1000 hour due to
excellent isolation of nuclear spins from the lattice!
with MW at with MW at
without Microwave
SS-Reservoir
Cooled down
SS-Reservoir
Heated upThermodynamic
equilibrium
SS Z LT T T 300 400
e ZSS Z
e
TT T
300 400
e ZSS Z
e
TT T
On the other hand, the electron and nuclear spins interact with electromagnetic
irradiation, therefore, to reach lower temperatures, It was elaborated very specific
method called the Dynamic Nuclear Polarization (DNP).
e
exp( )
p
B SS
B
k T
eee
exp( )e
B Z
B
k T
exp( )
p
B SS
B
k T
To realize DNP we need the free electrons in a target material
Free electron spins are induced by electron beam irradiation at about 90 K temperature with the dose of 1016~1017electrons/cm2 which generates
about 1019spins/cm2
Ammonia: NH3, ND3
Lithium Hydrides: 7LiH, 6LiH, 6LiD
6LiD: 6Li=α+ deuteron
30 Jan. 2004 Kaori KONDO, Naogya Univ. 8
THE COMPASS CAVITY FOR OD-MAGNET
Beam line
Cavity 1 Cavity 2 Cavity 3
Thermal screen
Microwave power
Coupling hole
Stainless steel
Silver
waveguides
Copper cavities
Cooling loop
Centering rim
All of cavity elements
provide
a very long use
High magnetic field, low temperature
and microwave irradiation
Polarizing magnet: 2.5T with field uniformity, ~100ppm
Overview of the COMPASS Polarized Targets
First polarization with our new set-up (measured June 14th )
D-butanol
Downstream cellCentral cellUpstream cell
P=-36±2 % in ~ 2-3 hours
NH3
NH3
6LiD
6LiD
Built-up the target polarizations
The typical signal-to-noise for
protons on the display
After the signal accumulation Kaori
receives almost an the free electrons ideal
proton signal
Q-meter circuit for polarization
measurements
Polarization measurements
Summary
• Dynamically Polarized targets have been used in many experiments.
• The techniques are well established although complicated apparatus is needed.
• The targets are still being developed for various applications.