Search for alpha and double alpha decays of natural Nd isotopes accompanied by gamma quanta

From 7 naturally occurring Nd isotopes, 5 are unstable in relation to α decay. If an excited level of the daughter nucleus is populated, or the daughter nucleus is unstable, γ quanta can be emitted. We used an ultra-low back- ground spectrometry system with 4 high purity germanium (HPGe) detectors (about 225 cm3 volume each) to search for such decays using a highly purified Nd-containing sam- ple with mass of 2.381 kg. Measurements were performed at the INFN Gran Sasso underground laboratory (with an overburden of about 3600 m w.e.) during 51,237 h. Half-life limits for α decays of 143 Nd and 145 Nd were determined to be T 1/2(143Nd) > 1.1 × 10^20 year and T 1/2(145Nd) > 2.7 × 10^19 year at 90% C.L. This is an increase of three and two orders of magnitude, respectively, compared with the most restrictive values currently given in literature. A limit for α decay of 144 Nd to the excited level of 140 Ce with E_exc = 1596.2 keV was determined for the first time as T 1/2 (144 Nd → 140Ce*) > 9.3 × 10^20 year. Restriction for the α decay of 146Nd to the excited level of 142Ce with E_exc = 641.3 keV was increased by 3 orders of magnitude to T 1/2 (146 Nd → 142Ce*) > 1.4 × 10^21 year. For α and 2α decays of 148Nd, first T 1/2 limits were set as 4.2 × 10^18 year and 2.1 × 10^20 year, respectively.