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

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

 = N N /(N H +N N ) EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

For the spin 1 14 N nuclei energy levels and allowed transitions are: Q is the nuclear electric quadrupole moment, q the maximal component of EFG tensor  is the asymmetry parameter. EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

EF  =        + +  +  /2+  /2)/  EF - =        - +  +  /2)/  EF 0 =        0 +  /2+  )/ 0 EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

TNT Two molecules per unit cell – 6 +, 6 - and 6 0 frequencies two modifications: monoclinic and orthorhombic

Zeeman broadening of the + lines for B  20 mT ( H  850 kHz) and - lines for B  17.5 mT ( H  750 kHz) in TNT EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

For TNT  = 2/7 EF +  50/T EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008 EF - EF 0

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 EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008 The signal intensity enhancement factor for the + (870 kHz) line in TNT at room temperature.

 0 - (  -  90 -  - ) n EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008 multi-pulse pulse spin-locking sequence

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

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

 = 1000  s, 50x  = 200  s, 300x EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

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

Institute of Mathematics, Physics and Mechanics, Ljubljana EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008 Faculty of mathematics and physics Janez Pirnat Vojko Jazbinsek Janko Luznik Zvonko Trontelj Janez Seliger Tomaz Apih Robert Blinc Alan Gregorovic

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

The multi-pulse pulse spin-locking (PSL)  0 - (  -  90 -  - ) n EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

S( ) = a O( ) + b M( ) EUROMAR 2008, Saint Petersburg, Russia, 6-11 July 2008

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

TNT six + lines average X  few 10 hrs RDX + line at 5256 kHz single shot  10 msec