LVII. The ranges of the α particles from various radioactive substances and a relation between range and period of transformation

Surface-clearance levels for the normal reuse of objects for 413 radionuclides

This paper provides surface-clearance levels for 413 radionuclides for the normal reuse of objects leaving the controlled area of a nuclear facility. Four sets of surface-specific clearance levels are derived based on choices of dose coefficients (DCs) in probabilistic dose assessments using the SUrface DOse QUantification model (SUDOQU; van Dillen and van Dijk 2018J. Radiol. Prot.381147-203). The general dose criteria for clearance, extended with a suitable dose constraint for the concept of the representative person, are applied in the derivations. These clearance levels apply to the total of fixed and removable radioactive contamination on the surface of objects. The results are discussed in the context of conservatism of the exposure scenarios (parameters, DCs), and guidance is given on the selection and application of the values.

Scintillation in Low-Temperature Particle Detectors

Inorganic crystal scintillators play a crucial role in particle detection for various applications in fundamental physics and applied science. The use of such materials as scintillating bolometers, which operate at temperatures as low as 10 mK and detect both heat (phonon) and scintillation signals, significantly extends detectors performance compared to the conventional scintillation counters. In particular, such low-temperature devices offer a high energy resolution in a wide energy interval thanks to a phonon signal detection, while a simultaneous registration of scintillation emitted provides an efficient particle identification tool. This feature is of great importance for a background identification and rejection. Combined with a large variety of elements of interest, which can be embedded in crystal scintillators, scintillating bolometers represent powerful particle detectors for rare-event searches (e.g., rare alpha and beta decays, double-beta decay, dark matter particles, neutrino detection). Here, we review the features and results of low-temperature scintillation detection achieved over a 30-year history of developments of scintillating bolometers and their use in rare-event search experiments.

Partial alpha-decay half-lives for alpha-emitting Osmium isotopes: Accurate determinations by a semi-empirical model

Partial alpha-decay half-life-values for twenty-four cases of alpha-decaying Osmium isotopes (^{161-174, 184, 186-188}Os) have been obtained in the framework of a semi-empirical, one-parameter model based on the quantum mechanical tunneling mechanism through a potential barrier. Here the Coulomb, centrifugal and overlapping contributions to the barrier have been considered within the spherical nucleus approximation. The calculation method enabled to reproduce, within a factor 2, the measured half-lives for ground-state to ground-state (gs-gs) α-transitions of twelve artificially produced Osmium isotopes (^{162-172, 174}Os) and of two naturally occurring isotopes (^{184, 186}Os). In addition, a half-life prediction of T_½ = (2.0 ± 0.1) × 10¹⁶ a has been found for the gs-gs α-transition of naturally occurring ¹⁸⁷Os isotope. Two cases of gamma quanta accompanying α-decay possible of being accessed experimentally have been predicted: ¹⁸⁴Os decaying to the first level of ¹⁸⁰W, with T_½ = (0.73 ± 0.04) × 10¹⁵ a, and ¹⁸⁶Os decaying to the first level of ¹⁸²W, with T_½ = (3.9 ± 0.2) × 10¹⁶ a. New α-decay schemes for ¹⁸⁴Os, ¹⁸⁶Os, ¹⁸⁷Os isotopes have been anticipated, and estimated T_½-values for rarer cases of α-transitions of Osmium isotopes have been reported.

Predictability analysis of α decay formulae and the α partial half-lives of exotic nuclei

We examine the ability of 3 phenomenological alpha decay formulae, the Generalised Liquid Drop Model, the Sobiczewski- Parkhomenko and the Viola-Seaborg-Sobiczewski formulae, to predict the α partial half-lives Tα of 100 exotic alpha radioactive nuclei by the statistical quantification of their accuracy and precision. These quantities were derived using a method based on standard experimental quality assurance wherein the alpha spectroscopic data of 313 well-established alpha decaying nuclei (calibration and test data sets) were used. Experimental masses as well as Finite Range Droplet Model masses were used to compute Qα. Improved coefficients for the three formulae were derived resulting in modified formulae. A simple linear optimization allowed adjustment of the modified formulae for the insufficient statistics of the odd-even and odd-odd decays of the calibration data set, without changing the modified formulae. Relatively better figures of merit for the odd-odd and the SHE were obtained using the modified GLDM formula.

Geiger-Nuttall Law for Nuclei in Strong Electromagnetic Fields

We investigate the influence of a strong laser electromagnetic field on the α-decay rate by using the Hennenberger frame of reference. We introduce an adimensional parameter D=S_{0}/R_{0}, where R_{0} is the geometrical nuclear radius and S_{0}∼sqrt[I]/ω^{2} is a length parameter depending on the laser intensity I and frequency ω. We show that the barrier penetrability has a strong increase for intensities corresponding to D>D_{crit}=1, due to the fact that the resulting Coulomb potential becomes strongly anisotropic even for spherical nuclei. As a consequence, the contribution of the monopole term increases the barrier penetrability by 2 orders of magnitude, while the total contribution has an effect of 6 orders of magnitude at D∼3D_{crit}. In the case of deformed nuclei, the electromagnetic field increases the penetrability by an additional order of magnitude for a quadrupole deformation β_{2}∼0.3. The influence of the electromagnetic field can be expressed in terms of a shifted Geiger-Nuttal law by a term depending on S_{0} and deformation.

Signatures of the Z = 82 shell closure in α-decay process

In recent experiments at the velocity filter Separator for Heavy Ion reaction Products (SHIP) (GSI, Darmstadt), an extended and improved set of α-decay data for more than 20 of the most neutron-deficient isotopes in the region from lead to thorium was obtained. The combined analysis of this newly available α-decay data, of which the (186)Po decay is reported here, allowed us for the first time to clearly show that crossing the Z = 82 shell to higher proton numbers strongly accelerates the α decay. From the experimental data, the α-particle formation probabilities are deduced following the Universal Decay Law approach. The formation probabilities are discussed in the framework of the pairing force acting among the protons and the neutrons forming the α particle. A striking resemblance between the phenomenological pairing gap deduced from experimental binding energies and the formation probabilities is noted. These findings support the conjecture that both the N = 126 and Z = 82 shell closures strongly influence the α-formation probability.

Synthesis of the heaviest elements in 48Ca-induced reactions

The observation of atomic numbers Z that are 40% larger than that of Bi, the heaviest stable element, is an impressive extension of nuclear survival. Although the super heavy nuclei (SHN) are at the limits of Coulomb stability, shell stabilization lowers the ground-state energy, creates a fission barrier, and thereby enables the SHE to exist. The fundamentals of the modern theory concerning the mass limits of nuclear matter have been experimentally verified.

Universal decay law in charged-particle emission and exotic cluster radioactivity

A linear universal decay formula is presented starting from the microscopic mechanism of the charged-particle emission. It relates the half-lives of monopole radioactive decays with the Q values of the outgoing particles as well as the masses and charges of the nuclei involved in the decay. This relation is found to be a generalization of the Geiger-Nuttall law in alpha radioactivity and explains well all known cluster decays. Predictions on the most likely emissions of various clusters are presented.