Relativistic Projectile Fragmentation Research Articles

Nuclear Track Detectors for Relativistic Nuclear Fragmentation Studies: Comparison with Other Competitive Techniques

The potential of the high resolution nuclear track detector (NTD) CR-39 is examined carefully for the measurement of relativistic nuclear projectile fragmentation cross sections and studies of related processes using the experience of many years of such measurements. The charge resolution and the charge resolving power of CR-39 detectors for the measurements of 158 A GeV 207Pb projectiles and their fragments are presented. Exposures of target-detector stacks, the chemical etching procedure and the nuclear track measurements are described in detail discussing precautions and possible errors. The procedures discussed are also valid for other NTDs. A comparison with electronic active detectors is also made considering important detection and measurement aspects. An experimental design proposing the co-use of NTDs with in-use active detectors is described.

Multipleβ−decaying states in194Re: Shape evolution in neutron-rich osmium isotopes

decays from heavy, neutron-rich nuclei with A∼190 have been investigated following their production via the relativistic projectile fragmentation of an E/A=1 GeV 208Pb primary beam on a ∼2.5 g/cm2 9Be target. The reaction products were separated and identified using the GSI FRagment Separator (FRS) and stopped in the RISING active stopper. γ decays were observed and correlated with these secondary ions on an event-by-event basis such that γ-ray transitions following from both internal (isomeric) and β decays were recorded. A number of discrete, β-delayed γ-ray transitions associated with β decays from 194Re to excited states in 194Os have been observed, including previously reported decays from the yrast Iπ=(6+) state. Three previously unreported γ-ray transitions with energies 194, 349, and 554 keV are also identified; these transitions are associated with decays from higher spin states in 194Os. The results of these investigations are compared with theoretical predictions from Nilsson multi-quasiparticle (MQP) calculations. Based on lifetime measurements and the observed feeding pattern to states in 194Os, it is concluded that there are three β−-decaying states in 194Re.

Nuclear structure “southeast” ofPb208: Isomeric states inHg208andTl209

The nuclear structure of neutron-rich N>126 nuclei has been investigated following their production via relativistic projectile fragmentation of a E/A=1 GeV U238 beam. Metastable states in the N=128 isotones Hg208 and Tl209 have been identified. Delayed γ-ray transitions are interpreted as arising from the decay of Iπ=(8+) and (17/2+) isomers, respectively. The data allow for the so far most comprehensive verification of the shell-model approach in the region determined by magic numbers Z<82 and N>126.Received 1 October 2009DOI:https://doi.org/10.1103/PhysRevC.80.061302©2009 American Physical Society

Isomeric states in neutron-deficientA~80–90nuclei populated in the fragmentation ofAg107

The relativistic projectile fragmentation of a 750 MeV per nucleon beam of Ag-107 was used to populate isomeric states in neutron-deficient nuclei around A=80-90. Reaction products were separated and unambiguously identified using the GSI FRagment Separator (FRS) and its ancillary detectors. At the final focal plane, the fragments were slowed from relativistic energies by means of an aluminium degrader and implanted in a passive stopper in the center of the high-efficiency, high-granularity Stopped Rare Isotope Spectroscopic INvestigation at GSI (RISING) germanium array. This allowed the identification of excited states in the N=Z nuclei Tc-86(43) and, for the first time, Nb-82(41). Isomeric states have also been identified for the first time in Tc-87,Tc-88, and a previously unreported isomer was observed in Nb-84. Experimental results are presented along with a discussion on the structure of these nuclei based on interpretations provided by several theoretical models. (Less)

Weakly deformed oblate structures in76198Os122

Gamma rays de-exciting isomeric states in the neutron-rich nucleus 76198Os122 have been observed following relativistic projectile fragmentation of a 1 GeV per nucleon Pb208 beam. The ground-state band has properties compatible with oblate deformation. The evolution of the structure of Os isotopes characterized by sudden prolate-oblate shape change is discussed and contrasted with the smooth change known in the Pt chain.Received 23 January 2009DOI:https://doi.org/10.1103/PhysRevC.79.031305©2009 American Physical Society

Angular momentum population in fragmentation reactions

Using a relativistic transport model followed by a statistical sequential binary emission model, the population of metastable high-spin isomeric states are studied in relativistic projectile fragmentation reactions. The initial angular momentum distribution are generated from hole excitations. We find that the angular momentum distribution of the excited prefragments are considerably broadened due to light particle evaporation. The model reproduces the experimentally measured population of relatively low-lying states and underpredicts states with high angular momentum I⩾17ℏ. We propose that coupling the spin of the excited and hole states in the prefragment will give a better understanding of the data.

Experimental details of the Stopped Beam RISING campaign

The RISING (Rare ISotope INvestigations at GSI) project constitutes a major pan-european initiative to study nuclear structure in exotic nuclei. A brief outline of the technical details specific to studies of isomeric decays following relativistic projectile fragmentation reactions is presented.

A RISING [formula omitted]-factor measurement of the 19/2 + isomer in 127Sn

The g -factor of the 19 / 2 + T 1 / 2 = 4.5 ( 3 ) μ s isomer in 127Sn, which was populated in relativistic projectile fragmentation, was measured within the g-RISING campaign at GSI, utilizing the time-differential perturbed angular distribution method. The deduced g -factor | g | ≈ 0.16 is in agreement with theoretical estimates based on the empirical g -factors.

Angular momentum population for the neutron-deficient lead nuclei produced following the relativistic projectile fragmentation of ^&lt;208&gt;Pb(International Workshop on Nuclear Structure-New Pictures in the Extended Isospin Space(NS07)-)

Angular momentum population for the neutron-deficient lead nuclei produced following the relativistic projectile fragmentation of ^&lt;208&gt;Pb(International Workshop on Nuclear Structure-New Pictures in the Extended Isospin Space(NS07)-)

Isomers in neutron-rich A ≈ 190 nuclides from 208Pb fragmentation

Relativistic projectile fragmentation of Pb-208 has been used to produce isomers in neutron-rich, A approximate to 190 nuclides. A forward-focusing spectrometer provided ion-by-ion mass and charge identification. The detection of gamma-rays emitted by stopped ions has led to the assignment of isomers in Ta-188, W-190, Re-192, Re-193, Os-195, Ir-197, Ir-198, Pt-200, Pt-201, Pt-202 and Au-203, with half-lives ranging from approximately 10 ns to 1 ms. Tentative isomer information has been found also for Er-174, Er-175, Hf-185, Re-191, Re-194 and Ir-199. In most cases, time-correlated, singles gamma-ray events provided the first spectroscopic data on excited states for each nuclide. In Pt-200 and Pt-201. the assignments are supported by gamma-gamma coincidences. Isomeric ratios provide additional information, such as half-life and transition energy constraints in particular cases. The level structures of the platinum isotopes are discussed, and comparisons are made with isomer systematics.

Angular momentum population in the projectile fragmentation ofU238at750MeV∕nucleon

A systematic study of the population probabilities of nanosecond and microsecond isomers produced following the projectile fragmentation of U-238 at 750 MeV/nucleon has been undertaken at the SIS/FRS facility at GSI. Approximately 15 isomeric states in neutron-deficient nuclei around A similar to 190 were identified and the corresponding. isomeric ratios determined. The results are compared with a model based on the statistical abrasion-ablation description of relativistic fragmentation and simple assumptions concerning gamma cascades in the final nucleus (sharp cutoff). This model represents an upper limit for the population of isomeric states in relativistic projectile fragmentation. When the decay properties of the states above the isomer are taken into account, as opposed to the sharp cutoff approximation, a good agreement between the experimental and calculated angular momentum population is obtained.

Energy and range focusing of in-flight separated exotic nuclei – A study for the energy-buncher stage of the low-energy branch of the Super-FRS

The relative momentum spread of in-flight separated exotic nuclear beams produced in fragmentation and/or fission reactions is of the order of a few percent. A new technique is presented, which reduces the momentum spread significantly, and first experimental results obtained with relativistic projectile fragments are shown. This technique is the key to experiments with slowed-down and stopped beams, in particular for the efficient stopping of relativistic exotic nuclei in gas-filled stopping cells. It will be employed at the energy-buncher stage of the low-energy branch of the Super-FRS facility. The ion-optical design of the energy buncher is presented and a brief outlook to the experimental program is given.

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.

Angular momentum population in the fragmentation of208Pbat 1 GeV/nucleon

A systematic study of the population probabilities of microsecond isomers produced following the fragmentation of 208Pb projectiles at 1 GeV/nucleon has been undertaken at the SIS/FRS facility at GSI Darmstadt. Gamma decays from approximately 20 isomeric states, mainly in the rare-earth and transitional nuclei with A∼180, were identified and the corresponding isomeric ratios deduced. The results are compared with a model based on the statistical abrasion-ablation description of relativistic fragmentation and simple assumptions concerning gamma cascades in the final nucleus (sharp cutoff). The model is found to represent an upper limit for the population of isomeric states in relativistic projectile fragmentation.

Isomer spectroscopy of neutron rich 190W 116

Gamma-rays de-exciting a millisecond isomer in the neutron-rich nucleus 190 74W 116 have been observed following relativistic projectile fragmentation of a 1 GeV per nucleon 208Pb beam. The isomeric decay populates the ground-state rotational band, with energies that indicate a significant deformation change at Z=74 for the N=116 isotones. The successful application of the projectile fragmentation technique in a region of deformed nuclei opens up the prospect of exploiting K-isomer decays to probe the evolution of collective nuclear structure far from the valley of beta stability.

Mass measurements of relativistic projectile fragments in the storage ring ESR

Two experimental methods of measuring masses of exotic nuclei in the storage ring ESR are presented. Bismuth and nickel fragments were produced via projectile fragmentation, separated and investigated with the combination of the fragment separator FRS and the ESR: (i) Direct mass measurements of relativistic projectile fragments were performed using Schottky mass spectrometry (SMS), i.e., exotic nuclei were stored and cooled in the ESR. Applying electron cooling, the relative velocity spread of circulating low intensity beams can be reduced below 10−6. Under this condition a mass resolving power of up to m/Δm=6.5·105 (FWHM) was achieved in a recent measurement. Previously unknown masses of more than 100 neutron-deficient isotopes have been measured in the range of 60≤Z≤84. Using known Q α values the area of known masses could be extended to more exotic nuclei and to higher proton numbers. The results are compared with mass models and extrapolations of experimental values. In a second experiment with 209Bi projectiles the area of the measured masses was extended to lower proton numbers. Due to various improvements at the ESR the precision of the measurements could be raised. (ii) Exotic nuclei with half-lives shorter than the time needed for SMS (present limit: T 1/2 ≈ 5 sec) can be investigated by time-of-flight measurements whereby the ESR is operated in the isochronous mode. This novel experimental technique has been successfully applied in first measurements with nickel and neon fragments where a mass resolving power of m/Δm=1.5·105 (FWHM) was achieved.

Precision experiments with relativistic exotic nuclei at GSI

Secondary beams of exotic nuclei have been produced in peripheral nuclear collisions with projectiles in the velocity range of 0.7-0.9 v/c provided by the heavy-ion synchrotron SIS at GSI. 8B, 11Be, and 19C nuclei have been studied in relativistic break-up reactions by using the projectile fragment separator FRS as a high-resolution energy-loss spectrometer. The experiments contribute to the knowledge of nuclear matter distribution for weakly-bound systems. A new era of experiments has been started with exotic nuclei separated by the FRS and stored and cooled in the experimental storage ring ESR. For instance, direct mass measurements of relativistic projectile fragments yield more than 100 previously unknown masses for isotopes in the range of54 ≤ Z ≤ 84. The data, characterized by an accuracy of about 100 keV, are compared to different mass models.

Emission of relativistic heavy fragments at wide angles from the interaction of 58 GeV 16O ions with thick copper target

Relativistic projectile fragmentation has been studied with track detection methods. Heavy fragments produced in the interaction of 58 GeV 16O with thick copper target have been investigated using 10 cm thick stacks of PADC (sometimes called CR-39) nuclear track detectors placed at 25° with respect to the direction of the incoming beam. A computer-controlled automatic scanning system was employed to “trace” the etched damaged trails in respective detectors of the PADC stack. Heavy reaction products producing “through-tracks” in consecutive sheets of 0.82 mm of PADC detectors were observed. The spatial distribution of these tracks with end points at various depths have been recorded. After calibration it has been concluded that these “through-tracks” should be due to relativistic O, N and C. These fragments are emitted from the interaction of 58 GeV 16O ions with thick copper target, their actual number is very tiny. The differential angular cross-section for their formation was found to decrease with increasing angle with respect to the incident beam direction.

The scintillation-detector equipment of the GSI projectile—fragment separator

A complete identification in mass and nuclear charge for relativistic projectile fragments up to uranium is possible at the fragment separator (FRS) at GSI by using the scintillation detector equipment described in this paper. It was successfully used in experiments with primary beams ranging from oxygen to uranium with energies from 300 to 1000 A MeV. A mass-resolving power of A/Δ A = 407 (FWHM) was obtained for 0.95 A GeV 238U fragments.

Study of transverse momentum spectrum of proton projectile fragments in 4.5A GeV/c12C-Emulsion interactions. Evidence of a single temperature

This work reports a study of transverse momentum distribution of relativistic proton fragments emerging from the interaction of12C with nuclear emulsion at 4.5A GeV/c energy. A comparison of transverse momentum spectrum with the Maxwell-Boltzmann distribution reveals a temperature of about 8 MeV. This observation does not agree with the results obtained by a similar analysis with relativistic alpha projectile fragments where there was a clear indication of two different temperatures (10 MeV and 40 MeV).