Search for the ternary cluster decay of Cm isotopes using SSNTD

Investigation of the ²⁴⁶Cm spontaneous ternary decay into nearly equal clusters using polyethyleneterephthalate track detectors has been carried out. The possibility of ternary cluster decay has been found out to be of less than 10⁻⁶ with respect to all fission modes of ²⁴⁶Cm.     

Distinction between pre-formed cluster emission and heavy ion decay by fission

For studying cluster radioactivity in the actinide region as well as trans-tin region two types of models are used: the pre-cluster formation model and the unified fission model. In the case of the actinide region, the cluster-like shapes are preferred for very high asymmetry while fissioning shapes are more suitable for less asymmetry and symmetry (the line of demarcation being around A _c =31). In this work this line of demarcation is studied in the case of the trans-tin region. The results of this study show that the transition from cluster mode to fission mode takes place at A _c =16.     

Cubic potential models for cluster radioactivity

Cluster radioactivity is a process by which nuclei equal and heavier than the α-particle is emitted spontaneously. The clusters usually emitted in this process are the α-particle, carbon, oxygen, neon, magnesium, silicon etc. When the mass of the cluster becomes comparable with the mass of the daughter, symmetric fission takes place. Thus the cluster radioactivity is an intermediate process between the well known α-decay and the spontaneous fission. In earlier years such cluster radioactivity was found mostly in actinide nuclei like radium, uranium etc. Very recently it has been predicted that such decays are possible in a new region around ¹¹¹Ba. There has been an exciting experimental detection of the emission of ¹²C from ¹¹¹Ba leading to ¹⁰²Sn, which is attracting a lot of attention recently. To study the phenomenon of cluster radioactivity there are various theoretical models in vogue. The existing models generally fall under two categories: the unified fission model (UFM) and the preformed cluster model (PCM). The physics of the UFM and the PCM are completely different. The UFM considers cluster radioactivity simply as a barrier penetration phenomenon in between the fission and the α-decay without worrying about the cluster being or not being preformed in the parent nucleus. In the PCM clusters are assumed to be preborn in a parent nucleus before they could penetrate the potential barrier with a given Q-value. The basic assumption of the UFM is that heavy clusters as well as the α-particle have equal probability of being preformed. In PCM, clusters of different sizes have different probabilities of their being preformed in the parent nucleus. We have developed three fission models during the last decade using the cubic potential for the pre-scission region. The use of these models in the study of cluster radioactivity in both the actinide and barium regions will be discussed in this talk in comparison with the other existing theories.     

Use of phosphate glass detectors for study of curium-242 cluster radioactivity

The effect α particle fluences (3 × 10³−2 × 10¹⁵ cm ⁻²) on properties of the two types of phosphate glass detectors with different compositions was studied. It was shown that the registration properties of glass detectors depended on the α particle fluence, spatial distribution of the α particle paths, and glass type. The critical α particle fluences, above which the detector properties changed, were determined.     

The Determination of 222Rn in Drilling Fluids of the KTB Pilot Borehole Using SSNTD Techniques

²²²Rn dissolved in drilling fluids of the KTB (Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschland) pilot hole has been determined using solid state nuclear track detector (SSNTD) technique:The α-sensitive SSNTD CR-39 was used to measure the a-activity of ²²²Rn. Well-defined conditions for Rn-measurements could be established by employing a mica nuclear track microfilter to separate the detector containing air volume from the volume containing the water. This technique has been applied to determine quantitatively the ²²² Rn-concentration as a function of depth of the borehole down to 4000 m.     

Alpha decay of Cm

An enriched sample of ²⁴⁷Cm (99.4 %) has been used to investigate the -decay scheme of ²⁴⁷Cm. Seven -groups with energies and intensities 5.265 (13.8 %), 5.210 (5.7 %), 5.145 (1.2 %), 4.983 (2.0 %), 4.941 (1.6 %), 4.868 (71.0 %) and 4.818 (4.7 %) were observed. Gamma-singles and γ coincidence spectra showed the presence of 278.0, 287.5, 346.0 and 402.4 keV γ-rays. A two-parameter coincidence experiment established that the sources of the 402.4 and the 287.5 keV γ-rays were 4.868 and 4.983 MeV -groups, respectively. The multipolarity of the 287.5 keV transition was found to be M1. The K conversion coefficient of the 402.4 keV γ-ray indicates an E1 multipolarity for this transition. The levels at 287.5 and 402.4 keV have been assigned to the and Nilsson states, respectively. The half-life of ²⁴⁷Cm was found to be (1.56±0.05) ×10⁷ y from the pulse analysis and mass spectrometric analysis of the sample.     

Evaluation of 242Cm and 244Cm decay data

The decay data evaluation results are presented for the ²⁴²Cm and ²⁴⁴Cm radionuclides decaying to the levels in ²³⁸Pu and ²⁴⁰Pu, respectively. The evaluated data have been obtained using information published up to 2005. The text was submitted by the author in English.     

Analyse of Corrections during Measurements of Charge of a Semiconductor Detector

The amplitude of signals coming from a semiconductor detector depends on the a amplifier system filter networks, detector physical properties and energy of particles measured. The absolute measuring of detector charge requires an analysis of the influence of the mentioned parameters upon the measuring system reaction. The paper gives the theoretical concepts and correction diagrams for the optimum filter networks of CR-RC and CR-(RC)² tapes taking into consideration the existence of an undesirable integrating constant of the charge sensitive preamplifier. The application of the presented diagrams increases the accuracy and helps checking the obtained results by a pulse generator.     

Study of cluster decay of heavy nuclei

The last results of studying radioactive decay of heavy nuclei ²³²Th, ²³⁶U, ²³⁶Pu and ²⁴²Cm using different dielectric detector types and methods of their development have presented.     

New approach for alpha decay half-lives of superheavy nuclei and applicability of WKB approximation

The α decay half-lives of recently synthesized superheavy nuclei (SHN) are calculated by applying a new approach which estimates them with the help of their neighbors based on some simple formulas. The estimated half-life values are in very good agreement with the experimental ones, indicating the reliability of the experimental observations and measurements to a large extent as well as the predictive power of our approach. The second part of this work is to test the applicability of the Wentzel-Kramers-Brillouin (WKB) approximation for the quantum mechanical tunneling probability. We calculated the accurate barrier penetrability for alpha decay along with proton and cluster radioactivity by numerically solving Schrödinger equation. The calculated results are compared with those of the WKB method to find that WKB approximation works well for the three physically analogical decay modes.     

Pd2团簇结构与能级分布的理论研究

在相对论有效原子实势(RECP)近似下,用密度泛函(B3LYP/SDD)方法,计算Pd2及其±1价和±2价分子离子的结构,光谱性质和能级分布.最后讨论了最高占据轨道(HOMO)与最低空轨道(LUMO)之间的能级间隙(HLG),分析了团簇的化学活性.     

On the 34Si emission of 242Cm

A ³⁴Si-decay of ²⁴²Cm has been reported by Oglobin et al. But an interpretation of this ³⁴Si emission as a ternary high-energy particle emission accompanying the fission of ²⁴²Cm can be proposed as well. Received: 18 October 2000 / Accepted: 8 November 2000     

Study of radon diffusion from RHA-modified ordinary Portland cement using SSNTD technique

The diffusion coefficient of radon is a very important factor in estimating the rate of indoor radon inflow. The aim of this work is to develop and assess the potential of radon resistant construction materials in residential buildings. Of late, rice husk ash (RHA) has been used as a component in cement. The X-ray diffraction of RHA indicates that the RHA contains mainly amorphous materials while the X-ray fluorescence analysis shows that the major percentage of it is composed of silica. The amorphous silica present in the RHA is responsible for the pozzolonic activity of the ash. The results of the present study indicate that the RHA when mixed with cement initially reduces radon diffusion coefficient, followed by enhancement when the percentage of RHA is increased above 30% by weight.     

β衰变能量连续谱发现的历史回顾

回顾了β衰变能量连续谱的发现过程，评价了这一过程中有关的重要工作，并分析了导致这一发现长达三十多年的原因．     

Computer simulation of cluster decay

Lennard-Jones metastable clusters consisting of 5 to 1030 atoms have been studied by molecular-dynamics simulation. Evaporation rate constants and caloric equations of state have been obtained in the microcanonical ensemble and with the use of RRK theory of unimolecular reactions and a local harmonicity approximation the canonical rate constants have been evaluted. The comparison with classical nucleation theory, specifically with the liquiddrop model, shows that the calculated equilibrium vapour pressure is significantly higher than theoretical one for small clusters, whereas the microcanonical results agree with theory.     

Exotic decay in cerium isotopes

Half life for the emission of exotic clusters like ⁸Be, ¹²C, ¹⁶O, ²⁰Ne, ²⁴Mg and ²⁸Si are computed taking Coulomb and proximity potentials as interacting barrier and many of these are found well within the present upper limit of measurement. These results lie very close to those values reported by Shanmugam et al using their cubic plus Yukawa plus exponential model (CYEM). It is found that ¹²C and ¹⁶O emissions from ¹¹⁶Ce and ¹⁶O from ¹¹⁸Ce are most favorable for measurement (T _1/2<10¹⁰ s). Lowest half life time for ¹⁶O emission from ¹¹⁶Ce stress the role of doubly magic ¹⁰⁰Sn daughter in exotic decay. Geiger-Nuttall plots were studied for different clusters and are found to be linear. Inclusion of proximity potential will not produce much deviation to linear nature of Geiger-Nuttall plots. It is observed that neutron excess in the parent nuclei slow down the exotic decay process. These findings support the earlier observations of Gupta and collaborators using their preformed cluster model (PCM).     

Alpha decay and cluster decay of some neutron-rich actinide nuclei

Nuclei in the actinide region are good in exhibiting cluster radioactivity. In the present work, the half-lives of α-decay and heavy cluster emission from certain actinide nuclei have been calculated using cubic plus Yukawa plus exponential model (CYEM). Our model has a cubic potential for the overlapping region which is smoothly connected by a Yukawa plus exponential potential for the region after separation. The computed half-lives are compared with those of other theoretical models and are found to be in good agreement with each other. In this work, we have also studied the deformation effects on half-lives of cluster decay. These deformation effects lower the half-life values and it is also found that the neutron-rich parent nuclei slow down the cluster decay process. Geiger–Nuttal plots for various clusters are found to be linear and most of the emitted clusters are α-like nuclei.     

Rare cold nuclear processes — A review and some new results

The rare nuclear processes of cluster radioactivity, cold fission and cold fusion, studied on the basis of the quantum mechanical fragmentation theory (QMFT), are reviewed. This theory was advanced as early as in 1974–75 by the author and collaborators, first at Frankfurt and then developed both at Frankfurt and Chandigarh. The QMFT predicted all the three phenomena to occur most probable as cold processes, prior to their experimental observations. The success of experiments with respect to the QMFT and some new results are presented as predictions of this theory for future experiments.     

Unimolecular decay of hydrogen-bonded cluster ions

The unimolecular decay of the hydrogen-bonded phenol(H₂O)₄ ⁺ cluster ion was studied both experimentally and theoretically. The ion is formed by resonant two-color two-photon ionization of the neutral cluster. If the second color exceeds the dissociation threshold of the ion, fragmentation occurs on a microsecond time scale. By analyzing the time-of-flight (TOF) signal of the metastable ions at different excess energies the dependence of the fragmentation rate on the excess energy can be deduced. These experimental rates are compared to microcanonical decay constants k(E) calculated from Rice–Ramsperger–Kassel–Marcus (RRKM) theory based on ab initio data solely. Received: 8 March 2000 / Revised version: 28 April 2000 / Published online: 5 October 2000