On the absence of appreciable half-life changes in alpha emitters cooled in metals to 1 Kelvin and below

Abstract

The recent suggestion that dramatic changes may occur in the lifetime of alpha and beta decay when the activity, in a pure metal host, is cooled to a few Kelvin, is examined in the light of published low temperature nuclear orientation (LTNO) experiments on such sources cooled to as low as 25 mK, with emphasis here on alpha decay. In LTNO observations are made of the anisotropy of radioactive emissions with respect to an axis of orientation. Correction of data for decay of activities in metallic samples held at temperatures at and below 1 Kelvin for periods of several days has been a routine element of LTNO experiments for many years. No evidence for any change of half-life on cooling, with an upper level of order 1%, has been found, in striking contrast to the predicted changes, for alpha decay, of several orders of magnitude. The proposal that such dramatic changes might alleviate problems of disposal of long-lived radioactive waste is shown to be unrealistic.

Half-life ofFr221in Si and Au at 4 K and at millikelvin temperatures

“…Because of the findings reported in [16] and [17], it comes as no surprise that our results do not support the Debye-Hücker model [1][2][3], which predicts (based on the calculations of [11,12]) a reduction of the half-life of 221 Fr in a metal at 4 K with a factor of about 50, and at 20 mK with a factor of many orders of magnitude more. No dependency on the solid-state environment and temperature of this α decaying isotope is observed up to a level of 1 × 10 −3 , which is at variance with the reported 6% change of the activity of 213 Po nuclei implanted in Cu at 12 K [4].…”

“…[21][22][23][24]). In LTNO experiments on α-decaying isotopes implanted in Fe, no half-life changes at the percent level were observed between room temperature and 1 K [17], and between 4 K and 50 mK [16].…”

“…Further, it was argued [16,17] that if the Debye plasma model would be applicable to α decays, the effect should have been observed previously in Low Temperature Nuclear Orientation (LTNO) experiments [18]. In this type of experiment, radioactive isotopes are implanted in a metallic foil, typically Fe, and cooled to millikelvin temperatures.…”

The on-line low temperature nuclear orientation facility NICOLE

“…Angular distributions of alpha emission from different members of the decay chains of the 224 Ra, 225 Ra and 227 Ac, and their temperature dependence, between 1 K and ∼25 mK, were extensively studied at the NICOLE facility. Detailed modeling including necessary correction for decay of the samples, showed no evidence for any modification of either alpha-or beta-decay half lives in the decay chains from normal accepted values [31]. The NICOLE collaboration is preparing for a new experiment, for the world first study of the angular distribution of beta-delayed neutrons emitted by nuclei oriented at low temperatures [32].…”

Nuclear astrophysics with light nuclei at GANIL

“…For example, the β + decay half-life of 22 Na implanted in the Pd metallic environment cooled to T = 12 K was observed to be shorter by 1.2 %. But, contradictory results were also obtained [10]. It is of high interest to investigate such effects, not only because of the possible theoretical implications but also because of the possible applications (nuclear astrophysics, nuclear fusion, waste disposal management).…”