X-Message-Number: 25342
Date: Thu, 16 Dec 2004 07:23:35 EST
Subject: Flea repport on brain scanner first demonstrator.

Some years ago, I have started the FLEA  (French Laser Experimental Area) 

repport. The last activity has been on laser hyperpolarizaton of helium 3 gas, 
fact I have defined such a system in the framework of a brain reader. 

The first reader generation will be a magnetic resonance imaging (MRI) using 
cold 3He in superfluid 4He. Before doing that, a first step is to build a 
demonstrator for nuclear magnetic resonance in hyperpolarized helium 3.

I'll define in this message the general setting of that demonstrator.

The gas is contained in a glass cell, because any impurity on the cell 
surface may destroy the polarized state, this cell must be heated to high 

temperature in vacuum to evaporate any harmful product. After that the cell is 
with helium 3 gas at a pressure between .5 and 1.2 mbar. I have found only two 
laboratories to do that in Europe.

The polarization process unfolds this way:

The gas is first excited by a radio wave, so that a circularly polarized 
laser beam can induce a transition between the hyperfine c8 state from the 

metastable 23P to the 23S1 orbit. The electron in the metastable orbit gets the
polarization from the infrared photon at 1083 nm produced by the laser.

When such a polarized atom collides with another atom in the fundamental 
state, the polarization is transfered to the nuclear spin of the second atom. 
After some tens of seconds, many He3 atoms are in the nuclear polarized state. 

This polarization is slowly destroyed by interaction with the cell wall, but the
half life of the polarization state is in the hours range at room temperature.

Put in a magnetic field, such spin polarized nuclei get a precession jerk at 
a frequency depending on the magnetic field : Near 3.24 kHz/gauss. This is the 
Larmor frequency detected in NMR.

I am launching orders for the components. I may go to the US and/or Canada 
next year, if there is anyone interested, I could desing the system so that it 
could be moved and I could bring it with me. Well I assume I must not tell to 
the custom that I bring a nuclear device in my luggages...?


 Content-Type: text/html; charset="US-ASCII"


Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=25342