Half-lives of ${}^{132}\mathrm{La}$ and ${}^{135}\mathrm{La}$

The half-lives of ${}^{135}\mathrm{La}$ and ${}^{132}\mathrm{La}$ were determined via serial gamma spectroscopy, and the half-life of ${}^{135}\mathrm{La}$ was further determined by a high-precision ionization-chamber measurement. The results are 18.91(2) hr for ${}^{135}\mathrm{La}$ and 4.59(4) hr for ${}^{132}\mathrm{La}$ compared with the previously compiled values of 19.5(2) hr and 4.8(2) hr, respectively. These lanthanum isotopes comprise a medically interesting system with positron emitter ${}^{132}\mathrm{La}$ and Auger-electron emitter ${}^{135}\mathrm{La}$ forming a theranostic pair for internal diagnostics and therapeutics. The precise half-lives are necessary for proper evaluation of their value in medicine and for a more representative tabulation of nuclear data.

Figure 1

Decay curves for ${}^{132}\mathrm{La}$, ${}^{133}\mathrm{La}$, and ${}^{135}\mathrm{La}$. (a) Decay curves for ${}^{132}\mathrm{La}$ and ${}^{133}\mathrm{La}$, generated from the HPGe data peak sums at 302, 1909, and 2102 keV from Data Set 2. (b) Decay curves for ${}^{135}\mathrm{La}$ generated from the HPGe data peak sums at 480.5 and 874.5 keV from Data Set 1 (DS1) and Data Set 2 (DS2). The functions resulting from fitting these data points with Eq. (2) are plotted as lines for each set of points.

Figure 2

Plot of current amplitude measurements of the ionization chamber data for ${}^{135}\mathrm{La}$ with the resulting fitted function included.

Figure 3

Plot showing the five measurements for the half-life of ${}^{135}\mathrm{La}$ in this work and the Nuclear Data Sheet value. Data points A–E are the half-lives measured by using the 480.5 keV peak in Data Set 2, the 480.5 keV peak in Data Set 1, the 874.5 keV peak in Data Set 2, the 874.5 keV peak in Data Set 1, and the ionization-chamber measurement, respectively. Data point F is the previously accepted value in the NDS.