Short-lived Nuclei Research Articles

NMR of short-lived nuclei implanted in crystals and a new isol for projectile fragments in relativistic heavy-ion reaction

Hyperfine interactions of substitutional and interstitial impurities in crystals were studied by use of the asymmetric β decay and NMR detection, following recoil implantation. A new ISOL for the projectile fragments produced in relativistic heavy-ion reaction separated radioactive isotopes. Their high kinetic energies obtained in the reaction enabled us to created spin polarization artificially in the isotopes and to implant them deep in any material.

Synthesis and study of atomic nuclei with Z > 100

The studies of atomic nuclei with Z > 100 are closely related to the synthesis of new chemical elements and to the investigation of stability limits for the heaviest nuclides. From the mid-50s these studies have been carried out using intense heavy-ion beams and highly sensitive techniques designed for the physical and chemical identification of rare short-lived nuclei. The studies proceeded in two stages, the first one being characterized by the use of hot-fusion reactions between the U, Pu, Am, Cm and Cf target nuclei and the C, N, O, and Ne projectiles and the second being based on the use of the cold-fusion reactions induced by Cr, Mn, and Fe projectiles on Pb and Bi target nuclei. As a result, the chemical elements with atomic numbers from 102 to 109 have first been synthesized. The radioactive properties of over 40 isotopes of these elements have been investigated and unambiguous evidence has been obtained that shell effects play a decisive role for the stability of the Z ≳ 104 nuclei against spontaneous fission. This provides an experimental substantiation for the known hypothesis that the island of nuclear stability should lie around Z ⋍ 114 and N ⋍ 178 or 184. It has been proposed to synthesize elements with Z ≥ 110 by the complete fusion reactions of uranium and adjacent element nuclei with projectile nuclei such as Ar and Ca. The spontaneous fission of a product nucleus (a total of 26 events) has been observed in Dubna experiments with the 232Th + 44Ca and 236U + 40Ar reactions. The authors of those studies tentatively assigned this activity to the decay of the nuclei of element 110.

A Penning trap for studying cluster ions

We propose to use a Penning trap for spectroscopy of stored cluster ions. A similar device has been built for the purpose of mass measurements of short-lived nuclei produced at the on-line isotope separator ISOLDE/CERN. A resolving power of 500,000 in a mass measurement of39K and an accuracy of 2 × 10−7 for the85Rb/39K mass ratio were obtained. An efficiency for in-flight capture as high as 70% was achieved. The method provides very high sensitivity since typically only 10 to 100 ions are stored in the trap. We intend to perform laser spectroscopy on trapped Na clusters as a first application of the trap technique.

A high-speed target-rotation system (taro) for the study of short-lived nuclei

We describe the design and performance of a high-speed target-rotation system for the study of nuclei far from stability, by which targets can be transported to the detector position in 60 ms after irradiation (90° rotation). The rotor movement and the cyclotron beam pulsing, as well as the data acquisition, are controlled by a microcomputer. Using this device 54 Co (T 1 2 = 193 ms) and 58 Cu (T 1 2 = 3.2 s) were observed in a test experiment with a transport efficiency of 71 and 98%, respectively (180° rotation).

Possibilities for studying short-lived nuclei produced at lampf

We present results of a study of the feasibility of using a He-jet coupled on-line mass separator system at LAMPF. He-jet transport-line characteristics, and estimates for the production of nuclei far from stability are given. Some specific areas of interest for potential studies are also presented. 18 refs.

Optical measurements of ground-state properties of short-lived nuclei in resonance cells

Hyperfine structure and isotope shift of radioactive Hg, Au and Cd isotopes have been determined by optical spectroscopy. In all cases the atoms were confined in a resonance cell. The various variants of the cell technique and alternative methods as the resonance ionization spectroscopy related to the investigation of short-lived nuclei are described, and some results are discussed.

Nuclear spectroscopy from on-line nuclear orientation

Low-temperature nuclear orientation is well established as a technique for gaining spectroscopic information from radioactive decays. A new development in this field has been the on-line coupling of a dilution refrigerator to an isotope separator, which permits the direct implantation of any desired nuclide. If the isotope separator is itself on-line to a heavy-ion accelerator, it is possible to produce, implant and orient a variety of short-lived nuclei, especially those far from stability. Technological details of such facilities are discussed and examples of recent results from three operating facilities are given.

Nuclear orientation and quadrupole interaction

In quadrupole-interaction nuclear-orientation experiments (QI-NO) the quadrupole interaction frequency VQ=e2qQ/h is determined from the angular distribution of γ-rays emitted in the decay of radioactive nuclei oriented at low temperatures as impurities in noncubic single-crystal matrices. This means that either the spectroscopic quadrupole moment Q of radioactive isotopes or the crystal electric field gradient eq can be determined from QI-NO experiments. Recent developments in QI-NO are discussed, especially with regard to the investigation of nuclei far from stability, with the following main topics: (1) Experimental aspects; (2) Quadrupole moments of short-lived nuclei; (3) Systematics of electric field gradients; (4) QI-NO with “new” host lattices, such as dichalcogenides; (5) Resonance techniques.

Optical pumping and unstable nuclei

The paper reviews the application of optical pumping to short-lived nuclei, where either the nuclear polarisation is detected by the β-decay asymmetry or the atomic polarisation by Stern-Gerlach-analyzer. Moreover the paper deals with collinear laser spectroscopy on beams of short-lived, mass-separated isotopes. The aim of the experiments is the systematic investigation of nuclear structure through the determination of spin, moments and charge radii from the hyperfine structure and isotopic shift of the atomic spectra. The impact of these experiments on the theory of nuclear forces and structure is discussed by means of a few examples.

From radop to laser spectroscopy and back

The paper reviews some techniques in optical spectroscopy of short-lived nuclei, their results regarding nuclear moments and isotopic shift, and their relation to the work of Professor K. Sugimoto.

Search for Short-Lived Mirror Nuclei and the β-Decay

Search for Short-Lived Mirror Nuclei and the β-Decay

The study of short-lived nuclei in the regionZ=59?68

β + -ray endpoint energies for mass-separated samples of neutron deficient Rare-Earth isotopes have been measured using an intrinsic germanium detector. QEC values have been obtained and new isomeric states have been identified for the first time.

Nuclear orientation of neutron deficient isotopes in the Z = 50 region

The first low temperature nuclear orientation measurements on electromagnetically separated short lived nuclei (5.1 min. ⩽ t 1 2 ⩽ 58 min.) are presented. A systematic magnetic moment study of the series 105–108In and of 101–102Ag has been performed. This investigation permitted to deduce ground state characteristics. The spin values of the high spin isomers of the odd-odd indiums have been fixed.

Characteristics of a gas-jet transport system for an on-line isotope separator

Basic characteristics of a gas-jet transport system for an on-line isotope separator have been investigated using a 252Cf source and a 235U fission source. The transport efficiency of fission products through a capillary has been measured to be about 60% for the 235U fission source. The sweep-out time of fission products through a target chamber and the transit time through a capillary have been measured for He, N 2 and CO 2 gases at several pressures. The measured sweep-out times have been almost equal to the exchange over time of the gas. The transit times have been found to be reasonably predicted by calculations. The transport system has been incorporated into the KUR-ISOL and is used for the study of short-lived nuclei.

Neutron activation cross section of molybdenum isotopes at 14.8MeV.

The neutron activation cross sections of Mo isotopes have been measured for the 14.8 MeV neutron. The cross sections have been determined with reference to the known 27A1 (n, α)24Na and the 27Al(n, p)27Mg reactions. The cyclic activation method was employed for the γ-ray measurement of short-lived nuclei. A 55 cm3 Ge(Li) detector was used for the measurement of γ-ray spectra. Cross section data are presented for (n, 2n), (n, p) and (n, a) reactions on Mo isotopes. The cross sections of (n, np) reactions on 98Mo are also presented. The exponential dependence on (N-Z)/A of the (n, p) reaction cross sections are discussed.

Nuclear orientation of on-line separated isotopes

Abstract On-line techniques have proven to be successful for the study of nuclei far from stability in performing spectroscopy. Further information on these short-lived nuclei can be obtained by measuring anisotopy coefficients of β- and γ-transitions. These measurements permit the clarifying of decay schemes and the study of nuclear moments. We thus propose the combination of on-line mass-separation with low temperature nuclear orientation. A system for this is being set up at the LISOL facility. The main part consists of a 3 He- 4 He dilution cryostat with high cooling power. It features a side-access port to allow direct implantation on the cold finger. A liquid helium cooled transport line with adjustable baffles makes the connection to the isotope separator. Nuclei with a lifetime down to a few minutes can be continuously implanted into a ferromagnetic host and oriented by the hyperfine field at temperatures lower than 30 mK. The limit of the lifetime is set by the spin-lattice relaxation time. In order to study shorter lived nuclei an “on-line” immediate orienting mechanism is installed: the beam line includes a UHV-chamber, where polarization is achieved by scattering at grazing incidence on a magnetized nickel single crystal. For preserving the obtained orientation during measurement the low temperature implantation is still required. Both mentioned orienting mechanisms completement each other for a nuclear study of short-lived isotopes. Sets of deflection plates and a movable part of the beam line allow a quick transition from one mode to another. Furthermore the cooled collecting foils can be changed in a short time without breaking the cooling cycle it removal of the daughter activities is requested.

The physical and chemical aspects of the search for superheavy elements

Abstract

A simple, inexpensive tape system for on-line studies of short-lived nuclei transported by He-jet

A simple tape transport system is described which is used for the collection of short-lived nuclides emerging from a He-jet recoil transport system. It is based on pistons driven by compressed air and is both inexpensive and reliable, and allows accurate and reproducible positioning of the radioactive sources at the counting position.

A simple, inexpensive tape system for on-line studies of short-lived nuclei transported by He jet

A simple, inexpensive tape system for on-line studies of short-lived nuclei transported by He jet

An on-line system of ionization chambers for the observation of short-lived fissionable nuclei

An on-line system of six ionization chambers designed for observing short-lived spontaneously fissioning isotopes has been developed and tested. In the test experiments using an Ar ion beam spontaneous fissioning fragments from 244Fm have been detected. It has been shown that the performance rate of the system can amount to 5 μs at a beam intensity of 0.1 μA.