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NUCLEAR RELAXATION OF POLARIZED 3He DILUTED BY LIQUID 4He AT 4K IN LOW
MAGNETIC FIELDS
M. Taber
To cite this version:
M. Taber. NUCLEAR RELAXATION OF POLARIZED 3He DILUTED BY LIQUID 4He AT 4K IN LOW MAGNETIC FIELDS. Journal de Physique Colloques, 1978, 39 (C6), pp.C6-192-C6-193.
�10.1051/jphyscol:1978685�. �jpa-00218365�
JOURNAL D E PHYSIQUE Colloque C6, suppl6ment au no 8, Tome 39, aoat 1978, page C6-192
NUCLEAR RELAXATION OF POLARIZED 3He DILIJTED BY L I Q U I D 4 ~ e AT 4 K I N LOW MAGNETIC FIELDS
M.A. Taber
Department of Physz"cs, Stanford U n < ~ e ~ s $ t y , Stanford, Ca, 343Q6? USA
Rfisura6.- On a mesure le temps de relaxation naclbailre IongEtudinal des solutions de Q,Q7X de 3 ~ e polaris6 dans 4 ~ e liquide b 4.2 K en se servant d'un magn6tonStre du type SQUID dans des tHmps magn6tiques au-dessous de 3 mG. Des temps de relaxation de 5 jours ont St6 observ6s au qoyen d'une cellule en Pyrex de 1 cm de diamstre dont la paroi 6tait recouverte d'unmanteau de K2 s~li'de..
Abstract.- Longitudinal nuclear relaxation times of .07% solutrons of polarized 3 ~ e in li'quid 4 ~ e have been measured at 4.2 K by use of a SQUIB mgnetmeter inmagnetic fields belaw 3 me, Bela,xa- tion times of 5 days were obtained w?th a 1-cm-dim Pyrex cell when a wall caating of sali'd K2 was used.
Measurements of the longitudinal relaxation time (TI) were made on dilute solutions of polarized 3 ~ e in liquid '~e at 4.2 K in magnetic fields ( B ) ranging from 36 ~.IG to 2.9 mG. The 3 ~ e was polarized to Q 5% at a typical pressure of 1 torr at room tea- perature by optical pumping /I/. After mixing the polarized 3 ~ e with superleak-purif ied 4 ~ e , the mixture was condensed into a I-cm-diam Pyrex sample bulb (figure 1) via 2 m of 112 nun-bore glass capil- lary. The condensed mixture had a typical 3 ~ e con- centration of 6.9x10-' and an initial internal
LlaJlO He BATH
PYREX CbPILLARY WIDE SOCEMIO ALUMINUU c4N
HELMKlLTZ FIELD COILS SUFERmMLTTlNG COUPLING aRwlT
PYREX SAMPLE BULB
%PERamDlhTlm Pb FOIL SHIELD
Fig. 1 : Lower portion of the cryostat. The guide solenoid was used only during condensation of the sample to maintain a uniform field over the length of capillary. Not shown is a I cm x 0.1 mm diam constriction located just above the sample bulb that limited diffusion in and out of the sample.
tial 3 ~ e polarization of 2%. The sample magneti- zation was detected with an rf-biased SQUID magne- tometer /2,3/ coupled to the sample by a persis- tent superconducting pickup circuit. Magnetometer noise referred to the pickup coil was 3x10-' G H Z - ~ Q The ambient magnetic field at the sample bulb d u ~ to all field sources was Q 3 uG. The low-field region was maintained by a superconducting-Pb-foil shield lining the interior of the dewar as descri- bed by Cabrera 141.
Measurements of T1 were made by periodical- ly measuring the sampie magnetization by use of a transitory precession technique. This technique involved presetting B to a standard value and
-0
thensuddenly shifting its direction by 45'. The sample was allowed to precess through two complete cycles (the magnetic field was selected so that the Larmor frequency was 0.25 Hz during precession) after which time the precession was halted by res- toring B to its original direction. This techni-
-0
que yielded an ac signal proportional to the sam- ple magnetization that was not affected by occa- sional drift or sub-quantum jumps in the SQUID.
Because of magnetic field gradients, a few percent of the magnetization was lost through dephasing during the precession, and this had to be taken into account when estimating TI from a sequence of these measurements.
The most salient Eenture of our relaxation data was a strong dependence of T on Bo
.
The de-- 1
pendence was of the form T;' = T I + a ~ (figure ; ~ ~ ~
-3/2 "
2), and the aBo portion was attributed t~ field magnetic-flux density due to the sample magnetiza- gradients arising from a ferromagnetic contaminant tion in excess of 10 uG. Thiscorresponds to an ini- dipole lying near the sample bulb, presumably in
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1978685
8-
- -
n 6 -"o -
- L-
-8h BARE PYREX -lZh
.
H p COATlNG - I D0 I 2 3 4
-3/z, Fig. 2 : Relaxation rates as a function of Bo Left-hand intercepts yield ~i;d
.
Differences in slope are not significant 151.the pickup coil form 151. In these low magnetic fields, it can be assumed that the remaining relaxa- tion mechanisms are independent of Bo so that we may write :;T = T;; +
~~h - ,
where T:; is the in- trinsic relaxation rate in the bulk and T;; is the wall-induced relaxation rate. In the bare Pyrex sample cell with a 3 ~ e concentration of 6 . 9 ~ 1 0 ~ ~,
a least-squares fit determined that Tlo= 40f 1 h.
Following Barbs, Lalog and Brossel (BLB) 161, who found that a wall coating of solid Hz dramati- cally increased TIW for 3 ~ e gas at 4.2 K, a wall coating of % 30 molecular layers of H2 was tried with the same 3 ~ e concentration as before.
This yielded Tla = 141 f 3 h, although the longest Ti that was actually measured was 128' 8 h
(5 days). A thicker wall coating of 280 layers Hz gave a relaxation time of Tlo= 57
+
1 h. The reason for the thicker wall coating resulting in a shorter relaxation time than the thin coating has not been ascertained.An argon wall coating was also tried but resulted in a Tlo.that was identical to the uncoated cell result. This is consistent with the preliminary result reported by BLB that Ar had a significant ef- fect on TIW only in the temperature range of 14-36 K.
Although no detailed theoretical calculation of TIB that pertain to our particular experimental conditions appear to be available, an estimate may be made from the results obtained by Oppenheim and Bloom /7/ for liquid 3 ~ e :
The diffusion coefficient of 3 ~ e in liquid '~e at 4.2 K was measured by applying a series of known gradients of the form Bl (r)
-
. .. = G(-?x + 1 /2;y+1/2$z), where the z axis is defined by the direction of Bo,and fitting the expression T;~=(T;~)~,~+~/~(G/B~) 2~
/8,9/ to the measured relaxation rates. Bo was suf- ficiently large to minimize the effect of the am- bient gradient. Using the resulting value for the 3 ~ e diffusion coefficient, D = (8.4 t .08)~10-~crn~
s.-', yields the estimate TIB
"
160 h. Thus it is likely that T;; was dominant over T;; in the value of T;J obtained with the thin H2 wall coating.These results have potential for applica- tion to 3 ~ e nuclear gyroscopes 151 and measurement of the 3 ~ e nuclear electric dipole moment 15,101.
Acknowledgments. The efforts of Dr. B. Cabrera in preparing the shield used in these experiments are gratefully acknowledged. This work was supported in part by the U.S. Air Force Office of Scientific Research under Contract No F44620-75-C-0022.
References
/I/ Colegrove, F.D., Shearer, L.D. and Walters, G.K., Phys.Rev.
132
(1963) 2561 121 Zimmerman, J.E., Thiene, P. and Harding, J.T.,J.Appl.Phys. (1970) 1572
131 Giffard, R.P., Webb, R.A. and Wheatley, J.C., J. Low Temp.Phys.
2
(1972) 533141 Cabrera, B., Thesis, Stanford University (1975) Proc. 14th 1nt. ~on£.Low Temp.Phys. (1 975), Helsinki. (North-Holland Publishing Co), vo1.4, 151 Taber, M.A., Thesis, Stanford University (1978) /6/ Barb&, R., Lalo:, F. and Brossel, J.,.Phys.Rev.
Lett.
36
(1975) 1488171 Oppenheim, I. and Bloom, M., Can.J.Phys.39 (1961) 845
181 Schearer, L.D. and Walters, G.K., Phys.Rev.
139 (1965) A1398
-
191 Barb&, R., Leduc, M. et ~ a l o g , F., J. Physique 35 (1974) 699
-
/I01 Schiff
,
L.I., Phys.Rev.132
(1963) 2194Here D, y, and n are the 3 ~ e diffusion coefficient, gyromagnetic ratio and number density, respectively, and a is the Lennard-Jones radial parameter for He.
