Nuclear spin-lattice relaxation of ${}^{62}\mathrm{Cu}$ at low temperatures in iron

The nuclear spin-lattice relaxation of ${}^{62}\mathrm{Cu}$ in iron has been studied with the low temperature nuclear orientation method. At temperatures ranging from 6.5 mK to about 100 mK and a magnetic field of 0.1 $T$ the relaxation constant for ${}^{62}\mathrm{Cu}$ in Fe was found to be $C_{\mathrm{K}}[$${}^{62}\mathrm{Cu}$$]=4.34(25)\mathrm{s}\mathrm{K}$.

Figure 1

β-spectrum for unoriented (“warm”) ${}^{62}\mathrm{Cu}$ obtained in 300 s with one of the HPGe particle detectors. The 511 keV γ-line, the β-spectrum endpoint at 2926 keV and the pulser peak are indicated. The part of the β-spectrum that was used for analysis is the region between 1121 keV and the endpoint. It was subdivided in seven energy bins.

Figure 2

($a$) $W({15}^{°})/W({165}^{°})$ values versus inverse temperature for positrons from ${}^{62}\mathrm{Cu}$$\underline{\mathrm{Fe}}$ with energies between 1482 and 1723 keV (bin 3 in Fig. 1) [10]. The curve is a fit to the data varying both $f$ and $C_{\mathrm{K}}$ yielding $f=0.63(3)$ and $C_K=4.1(5)sK$ (${\chi }^2/\nu =3.0$). (b) Same data as in (a) together with the fitted curve that was obtained when $C_{\mathrm{K}}=0$ was assumed (i.e. using thermal equilibrium values for $B_1$) and with $f$ being the only free parameter. This fit yielded $f=0.412(7)$ (${\chi }^2/\nu =9.3$). Note that since the ${\chi }^2/\nu$ values are larger than unity the errors obtained from the fits have been increased by the factor $\sqrt{{\chi }^2/\nu }$.