Polarization enhanced NQR detection at low frequencies

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Polarization enhanced NQR detection at low frequencies

EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

Janko Luznik

Institute of Mathematics,

Physics and Mechanics, Ljubljana

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TNT, 

_Q

 850 kHz, low signal/noise ^,

RF sensitivity  

Signal intensity  N

Boltzmann distribution

N  exp(-E/kT) ; N  E/kT; E =  ^{h ;} N  

Proton polarization 

_H

 

_Q

 N

_H

 N

_Q

(3)

H H N Q

H Q

H N

N N N N

N (1 ) N N

N N

  

       



 = N

_N

/(N

_H

+N

_N

)

 

^H

 

^H

Q Q Q

N

EF N 1 1

N N

 

           

  

(4)

3e qQ

2

4h 1 3



  

    

 

3e qQ

2

4h 1 3



  

      

2 0

e qQ

  2h 

For the spin 1

¹⁴

N nuclei energy levels and allowed transitions are:

Q is the nuclear electric quadrupole moment, q the maximal component

(5)

H

2 0

H

3 0 2 0

H

( )(1 )

1( )(1 ) (1 )

2

3 3

( )(1 ) (1 )( ) (1 )

4 2



 

      

          

                

(6)

EF

^

= 

_^



_^



⁺

++/2+/2)/ 

^

EF

^-

=

_^



_^



^-

++/2)/ 

^

EF

⁰

=

_^



_^



⁰

+/2+)/ 

⁰

2 3 2 3 2

H

2 2 3 2 3

H

2 2 3 2

0

0 H 0

1 9 5 3 13 21 11 3 2 8 6

EF 8 8 8

2 4 6 5 3 5 3 1 3 3

EF 8 8 8

4 12 8 18 16 6 10 16

EF 8 8 8

 

 

 

 



                

    

 

                

    

 

            

    

 

N

H N

2 N

3 2

N N

3  



(7)

TNT

Two molecules per unit cell – 6 

⁺

, 6 

^-

and 6 

⁰

frequencies

two modifications: monoclinic and orthorhombic

(8)

Zeeman broadening of the 

⁺

lines for B  20 mT ( 

_H

 850 kHz)

and 

^-

lines for B  17.5 mT ( 

_H

 750 kHz) in TNT

(9)

For TNT  = 2/7

H

0 H

0 0

EF 0.046 0.476 0.21 E

3 EF 0.020 0.503 0.211

F 0.413 0.978 0.026

 





 

 

 

   

 



 

   



 

EF

⁺

 50/T

EF

^-

EF

⁰

(10)

proton-nitrogen spin coupling in TNT 

_NH

^{ 500 Hz}

proton NMR linewidth  

_H

is around 20 kHz (0.5 mT)

dB/dt  0,5 mT/2 ms = 250 mT/s

T

_cp

>> 1/ 

_NH

^{= 2 ms}

The signal intensity enhancement factor for the + (870 kHz) line in TNT at room temperature.

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0 5 10 15 20 25 30 -1

0 1

signal [a.u.]

time [ms]

5,0 5,2 5,4 5,6 5,8 6,0

-1 0 1

signal [a.u.]

time [ms]



₀

- (  - 

₉₀

-  - )

_n

multi-pulse pulse spin-locking sequence

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835 840 845 850 855 860 865 870 875 0,0

0,2 0,4 0,6 0,8 1,0

relative intensity [a.u.]

frequency [kHz]

+ part of

¹⁴

N NQR spectrum in an old sample of TNT where the mixture of

two phases monoclinic/orthorhombic (approx. 50%/50%) can clearly be

(13)

-20 -15 -10 -5 0 5 10 15 20 0,0

0,2 0,4 0,6 0,8 1,0

freqeency (0=855) [kHz]

(14)

-20 -10 0 10 20 0,0

0,1 0,2 0,3

Intensity [a.u.]

Frequency [kHz]

TNT

(15)

 = 1000s, 50x

 = 200s, 300x

(16)

Conclusions

Polarization enhancement can be very effective - reduction of detection time

- strong polarizing magnetic field is needed - nonhomogenous field (average field)

- ratio of protons to nitrogens - proton relaxation time

- nitrogen relaxation time

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Institute of Mathematics, Physics and Mechanics, Ljubljana

Faculty of mathematics and physics

Janez Pirnat Vojko Jazbinsek Janko Luznik

Zvonko Trontelj Janez Seliger

Tomaz Apih

Robert Blinc

Alan Gregorovic

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0 20 40 60 0

5 10 15 20

enhancement factor

polarization time [sec]

 = 16 sec

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0 5 10 15 20 0,2

0,4 0,6 0,8 1,0

tau = 7 sec

enhancement factor

trigger delay time [sec]

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The multi-pulse pulse spin-locking (PSL) 

₀

- ( - 

₉₀

-  - )

_n

50 100 150 200 250 300 350 400 450 500

0 2 4 6 8 10 12 14 16 18 20

signal/noise

number of averaged echoes n

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-20 -15 -10 -5 0 5 10 15 20 0,0

0,2 0,4 0,6 0,8 1,0

relative intensities [a.u.]

frequency (0=855) [kHz]

monoclinic orthorhombic

S(  ^{) = a O(}  ^{) + b}

M(  )

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-20 -15 -10 -5 0 5 10 15 20 0,0

0,2 0,4 0,6 0,8 1,0

-20 -15 -10 -5 0 5 10 15 20

0,0 0,2 0,4 0,6 0,8 1,0

freqeency (0=855) [kHz]

-20 -15 -10 -5 0 5 10 15 20

0,0 0,2 0,4 0,6 0,8 1,0

50:50

1937

1955

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TNT

six 

⁺

^lines

average 10000 X

 few 10 hrs

RDX



⁺

line at 5256 kHz single shot

 10 msec

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Polarization enhanced NQR detection at low frequencies