Short-lived Nuclei Research Articles

The motion of particle spin in a nonuniform electromagnetic field

We have applied the Foldy-Wouthuysen transformation to spin-1 particles interacting with a non- uniform electromagnetic field. This allowed us to simultaneously confirm that the Pomeransky-Khriplovich- Sen'kov theory is valid and that the interaction of spin 1-particles with a weak field is properly described by the Corben-Schwinger equation. We analyzed the possibilities for experimentally testing theoretical conclusions by observing spin oscillations for the planar channeling of particles or nuclei in straight crystals. By carrying out such experiments, we can also detect the spin oscillations produced by electromagnetic interaction and mea- sure the quadrupole moments of short-lived nuclei. © 2003 MAIK "Nauka/Interperiodica".

Mass measurements and nuclear physics—recent results from ISOLTRAP

The Penning trap mass spectrometer ISOLTRAP is a facility for high-precision massmeasurements of short-lived radioactive nuclei installed at ISOLDE/CERN in Geneva.More than 200 masses have been measured with relative uncertainties of 1 × 10−7 or even closeto 1 × 10−8in special cases. This publication gives an overview of the measurementsperformed with ISOLTRAP and discusses some results.

Ion beam coolers in nuclear physics

Cooling techniques for low-energy radioactive ion beams are reviewed togetherwith applications on high-precision measurements of ground state properties ofexotic nuclei. The emphasis in the presentation is on cooling, bunching andimproving the overall characteristics of ion beams by RFQ-driven buffer gascooling devices. Application of cooled and bunched beams in collinear laserspectroscopy to extract isotope shifts and hyperfine structure are presented withexamples on radioactive Ti, Zr and Hf isotopes. The impact of the new-generationcoolers on mass measurements of short-lived nuclei is discussed with examples onprecision measurements of masses of super-allowed beta emitters. As a newconcept, decay spectroscopy of radioactive ions trapped in a cooler Penning trapis presented.

The proposed TITAN facility at ISAC for very precise mass measurements on highly charged short-lived isotopes

One of the necessary experimental quantities required for the test of unitarity of the fundamental Cabbibo–Kobayashi–Maskawa (CKM) quark mixing matrix can be gained from nuclear beta decay. However, the short-lived beta-decaying nuclei have to be produced on-line in order to provide a large enough sample to carry out the experiments. At the new ISAC (Isotope Separator and Accelerator) facility at the TRIUMF national laboratory in Vancouver, Canada, ideal conditions are provided for the production of some of the most interesting nuclides in that respect. The experimental information that is needed are branching ratio, half-life and Q-value of the specific beta decay. For the first two components experiments have already been carried out or are in preparation at ISAC (Ball et al., Phys. Rev. Lett. 86 (2001) 1454, and experiments E823 and E909 approved at TRIUMF), for the third one, we are proposing to set up a unique facility capable of high accuracy mass measurements δ m/ m⩽1×10 −8 on very short-lived isotopes (T 1/2⩽50 ms) employing a Penning trap spectrometer coupled to an electron beam ion trap (EBIT) for charge breeding. The main goal of TITAN is mass measurements, however, the unique combination of the systems will allow to carry out high precision measurements in other fields of nuclear and also atomic physics.

Short-Lived Nuclei in the Early Solar System: A Low Mass Stellar Source?

AbstractWe discuss possible stellar origins of short-lived radioactive nuclei with meanlife τ ≤ 100 Myr, which were shown to be alive in the Early Solar System (ESS). We first review current ideas on the production of nuclides having 10 ≤ τ ≤ 100 Myr, which presumably derive from the continuous interplay of galactic astration, nucleosynthesis from massive supernovae and free decay in the interstellar medium. The abundance of the shorter lived 53Mn might be explained by this same scenario. Then we consider the nuclei 107Pd, 26Al, 41Ca and 60Fe, whose early solar system abundances are too high to have originated in this way. Present evidence favours a stellar origin, particularly for 107Pd, 26Al and 60Fe, rather than an in situ production by energetic solar particles. The idea of an encounter (rather close in time and space) between the forming Sun and a dying star is therefore discussed: this star may or may not have also triggered the solar formation. Recent nucleosynthesis calculations for the yields of the relevant short-lived isotopes and of their stable reference nuclei are discussed. Massive stars evolving to type II supernovae (either leaving a neutron star or a black hole as a remnant) seem incapable of explaining the four most critical ESS radioactivities in their observed abundance ratios. An asymptotic giant branch (AGB) star seems to be a viable source, especially if of relatively low initial mass (M ≤ 3 M⊙) and with low neutron exposure: this model can provide a solution for 26Al, 41Ca and 107Pd, with important contributions to 60Fe, which are inside the present uncertainty range of the 60Fe early solar system abundance. Such a model requires that 26Al is produced substantially on the AGB by cool bottom processing. The remaining inventory of short-lived species in the solar nebula would then be attributed to the continuous galactic processing, with the exception of 10Be, which must reflect production by later proton bombardment at a low level during early solar history.

Recent Results from ESR

The ESR storage ring has been designed for high resolution and high precision experiments with highly charged ions, both stable and radioactive species. Stochastic and electron cooling provide fast and powerful cooling for the preparation of cold ion beams. For small ion beam intensities beams of unprecedented quality can be obtained by electron cooling. The internal gas jet target allows operation with a variety of gases. The highly charged ions can be decelerated to reduce the resolution limitation originating from Doppler effects. The decelerated ions are either used for internal experiments or extracted to a fixed target area with an ultraslow extraction mode. For the determination of the masses of radioactive nuclei two methods have been developed. Schottky mass spectrometry of cooled ions with nuclear lifetimes of the order of seconds or longer allows mass measurements by determination of the revolution frequency from the Schottky noise with a mass resolution of 1 ppm. Tuning of the focusing structure of the storage ring to the transition energy of 344 MeV/u is applied to measure the masses of short–lived nuclei by a time of flight method.

Measurement method of activation cross-sections of reactions producing short-lived nuclei with 14 MeV neutrons

We describe a method for obtaining reliable activation cross-sections in the neutron energy range between 13.4 and 14.9 MeV for the reactions producing short-lived nuclei with half-lives between 0.5 and 30 min. We noted neutron irradiation fields and measured induced activities, including (1) the contribution of scattered low-energy neutrons, (2) the fluctuation of the neutron fluence rate during the irradiation, (3) the true coincidence sum effect, (4) the random coincidence sum effect, (5) the deviation in the measuring position due to finite sample thickness, (6) the self-absorption of the γ-ray in the sample material and (7) the interference reactions producing the same radionuclides or the ones emitting the γ-ray with the same energy of interest. The cross-sections can be obtained within a total error of 3.6%, when good counting statistics are achieved, including an error of 3.0% for the standard cross-section of 27Al (n, α) 24Na. We propose here simple methods for measuring γ-rays efficiently at a close source-to-detector distance and for measuring β+ activities emitting almost no γ-rays.

Charged-particle spectroscopy in the microsecond range following projectile fragmentation

We present a new approach to charged-particle spectroscopy of short-lived nuclei produced by relativistic projectile fragmentation. The system based on digital DGF-4C CAMAC modules and newly developed fast-reset preamplifiers was tested at the Fragment Separator of GSI. We were able to detect low-energy (≈1 MeV ) decay signals occurring a few microseconds after a heavy-ion implantation accompanied by a release of ≈1 GeV energy. Applications for the study of one- and two-proton radioactivity are discussed.

Accurate mass measurements of very short-lived nuclei

Mass measurements of 34Ar, 73–78Kr, and 74,76Rb were performed with the Penning-trap mass spectrometer ISOLTRAP. Very accurate Q ec -values are needed for the investigations of the Ft-value of 0+ → 0+ nuclear β-decays used to test the standard model predictions for weak interactions. The necessary accuracy on the Q ec -value requires the mass of mother and daughter nuclei to be measured with δm/m ≤ 3 · 10−8. For most of the measured nuclides presented here this has been reached. The 34Ar mass has been measured with a relative accuracy of 1.1 · 10−8. The Q ec -value of the 34Ar 0+ → 0+ decay can now be determined with an uncertainty of about 0.01%. Furthermore, 74Rb is the shortest-lived nuclide ever investigated in a Penning trap.

Development of a Nuclear Spin Dewar: Hyperfine Interactions of the Short-Lived Emitter 12B in TiO2

The β-NMR detection of 12B ( Iπ= 1+, T1/2 = 20.2 msec) implanted in a TiO2 (rutile) single crystal following a nuclear reaction showed that its spin polarization produced in the reaction is totally maintained during its lifetime. Two implantation sites with relative populations 9:1 were identified. The electric field gradients (EFGs) were determined to be q = +(37.1 0.5) 1015 V/cm2 with η< 0.03 and q = +(185 5) 1015 V/cm2 with η= 0.62 0.02 for the major (90%) and minor (10%) sites, respectively. The EFGs were compared with the theoretical values given by the band-structure calculation in the framework of the KKR method. TiO2 crystals with proper treatment can be a good “Spin Dewar” in which any short-lived nuclei can be implanted, and their spin polarizations as produced in nuclear reactions can be maintained during their lifetime

Cross-section measurements for the (n,p) and (n,α) reactions on 23Na and for the (n,p) reaction on 26Mg at the neutron energies from 13.6 to 14.9 MeV

Cross sections were measured at neutron energies from 13.6 to 14.9 MeV for the reactions 23Na(n,p) 23Ne and 23Na(n,α) 20F, and 26Mg(n,p) 26Na leading to short-lived products. The production of short-lived nuclei and the spectra accumulation have been carried out by cyclic activation method. Corrections were made for the effects of gamma ray attenuation, coincidence summing, pulse pile-up, dead time, neutron flux fluctuations and scattered low energy neutrons.

Rearrangements in neutron shell closures far from stability

A survey of experimental results obtained at GANIL (Caen, Prance) on the study of the properties of very neutron-rich nuclei (Z = 6–20, A = 20–60) near the neutron drip line and resulting in an appearance of further evidence for the new magic number N = 16 is presented. Very recent data on mass measurements of neutron-rich nuclei at GANIL and some characteristics of binding energies in this region are discussed. Nuclear binding energies are very sensitive to the existence of nuclear shells and together with the measurements of instability of doubly magic nuclei 10He and 280 they provide information on changes in neutron shell closures of very neutron-rich isotopes. The behaviour of the two-neutron separation energies S2n derived from mass measurements gives a very clear evidence for the existence of the new shell closure N = 16 for Z = 9 and 10 appearing between 2s1/2 and ld3/2 orbitals. This fact, strongly supported by the instability of C, N and O isotopes with N > 16, confirms the magic character of N = 16 for the region from carbon up to neon while the shell closure at N = 20 tends to disappear for Z ≤ 13. Decay studies of these hardly accessible short-lived neutron-rich nuclei from oxygen to silicon using the in-beam γ-ray spectroscopy are also reported.

Progress in the calculation of parton distributions in QCD

The secondary-beam facility of GSI provided the technical equipment for a new kind of fission experiment. Fission properties of short-lived neutron-deficient nuclei have been investigated in inverse kinematics. The measured element distributions reveal new kinds of systematics on shell structure and even–odd effects and lead to an improved understanding of structure effects in nuclear fission. The relevance of these studies for some presently considered applications is described. Prospects for future experiments are discussed.

Penning trap at IGISOL

The IGISOL facility at the Department of Physics of the University of Jyväskylä (JYFL) is delivering radioactive beams of short-lived exotic nuclei, in particular the neutron-rich isotopes from the fission reaction. These nuclei are studied with the nuclear spectroscopy methods. In order to substantially increase the quality and sensitivity of such studies, the beam should undergo beam handling: cooling, bunching and isobaric purification. The first two processes are performed with the use of an RFQ cooler/buncher. The isobaric purification will be made by a Penning trap placed after the RF-cooler element. This contribution describes the current status of the Penning trap project and its future prospects. The latter comprise the precise nuclear mass measurements, nuclear spectroscopy in the Penning trap interior as well as the laser spectroscopy on the extracted beams.

Storage rings for radioactive, highly charged ions

After a condensed survey on the basics of ion storage–cooler rings, Schottky mass spectrometry on unstable nuclei at the ion cooler-ring ESR is discussed, emphasizing efficiency, resolving power, and sensitivity of this method. Then the extension of in-ring mass spectrometry to short-lived nuclei by a newly developed time-of-flight technique will be outlined. Cooler rings are the only tools to address beta decay of highly charged ions which has an obvious connection to nucleosynthesis in hot stellar plasmas. That is elucidated for the cases of electron capture and bound-state beta decay, whose astrophysical impact will be finally discussed at the example of the galactic chronometer 187Re/ 187Os.

In-flight spectrometers status and new developments

In-flight spectrometers have been successfully used for the investigation of exotic nuclei from low energies near the Coulomb barrier up to the A GeV regime. The in-flight method takes advantage of the reaction kinematics to efficiently separate short-lived nuclei at the limits of stability down to a sensitivity of single atoms. Modern in-flight separators are combined with high-resolution devices such as electromagnetic spectrometers, storage-cooler rings, and ion traps. Atomic interaction in matter is a versatile tool to tailor the phase space of nuclear reaction products for efficient separation in flight.

Release studies of a thin foil tantalum target for the production of short-lived radioactive nuclei

Measurements have been made at ISOLDE, of the release curves and yields of radioactive beams of lithium, sodium and beryllium from a target constructed from 2 μm thick foils. The release curves have been analysed by fitting to a mathematical model to determine the coefficients of diffusion of the particles in the foils and effusion through the target and ionizer at several temperatures. Through a better understanding of the rate of transport of the particles, it is possible to design targets and ionizers with improved yields. This is most important for the rare, short-lived isotopes in which there is considerable interest for physics experiments. This target has demonstrated large increases in the yields of 11Li and 12Be, in agreement with the predictions of the model.

NUCLEARASTROPHYSICSMEASUREMENTS WITHRADIOACTIVEBEAMS

▪ Abstract Radioactive nuclei play an important role in a diverse range of astrophysical phenomena including the early universe, the sun, red giant stars, nova explosions, X-ray bursts, supernova explosions, and supermassive stars. Measurements of reactions with beams of short-lived radioactive nuclei can, for the first time, probe the nuclear reactions occurring in these cosmic phenomena. This article describes the astrophysical motivation for experiments with radioactive beams, the techniques to produce these beams and perform astrophysically relevant measurements, results from recent experiments, and plans for future facilities.

High-sensitivity delayed-coincidence spectrometer to search for short-lived nuclear states

A high-sensitivity four-dimensional triple-coincidence spectrometer with two detectors is developed on the basis of an autocorrelation single-crystal scintillation time 4 π spectrometer and a semiconductor HPGe detector. The delayed-coincidence spectrometer is designed to search for isomeric nano- and micro-second states in short-lived nuclei and for their related γ-rays. Half-lives of short-lived states are measured in the range from 4 ns to 4 μs. The sufficient activity of the monoisotopic source for the investigations does not exceed 0.01 μCi.

Measurement of activation cross-sections of (n, np+d) reactions producing short-lived nuclei in the energy range between 13.4 and 14.9 MeV using an intense neutron source OKTAVIAN

Activation cross-sections for 17 (n, np+d) reactions producing short-lived nuclei with half-lives between 42 s and 23 min, were measured in the energy range between 13.4 and 14.9 MeV by an activation method. The measured target isotopes were 26Mg, 29, 30Si, 53, 54Cr, 67Zn, 87Sr, 98, 100Mo, 102Ru, 105, 106, 108Pd, 123Te, 163Dy, 179Hf and 189Os. Eleven cross-sections for 26Mg, 30Si, 87Sr, 100Mo, 102Ru, 105, 106Pd, 123Te, 163Dy, 179Hf and 189Os were obtained for the first time, and four cross-sections for 53, 54Cr, 67Zn and 108Pd were obtained at six-point energies for the first time. An intense 14 MeV neutron source, OKTAVIAN at Osaka University was used for irradiation. All cross-section values were relatively obtained on the basis of the standard cross-section of 27Al(n, α) 24Na reaction (ENDF/B-VI). To obtain reliable neutron activation cross-sections, careful attention was paid to neutron irradiation and induced activity measurement. The present results were compared with the evaluated data in JENDL-3.2, JENDL-Activation File and ENDF/B-VI. The cross-sections are underestimated for 102Ru and 108Pd in JENDL-3.2.