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New experimental data on energy loss of 4 He, 16 O, 40 Ar, 48 Ca and 84 Kr ions in thin, self-supporting foils of C, Al, Ni, Ag, Lu, Au, Pb and Th are presented. The measurements, using the TOF-E method, were done in a very broad energy range around the stopping power maximum; typically from 0.1 to 11 MeV/u. When available, the extracted stopping power values are compared with the previously published data. The overall agreement is good although a fair comparison is difficult as the covered energy range is much larger than in previous measurements. The small error bars and a broad coverage allowed us to test the predictions of theoretical codes: PASS, CasP, and semi-empirical programs: SRIM, LET, MSTAR, and the Hubert table predictions. The deviations of PASS predictions from the experimental data do not exceed 20% for all the measured combinations. CasP predictions are within 15% from the data for heavier ions but diverge up to 40% for lighter ions. Semi-empirical approaches, including SRIM, deviate from the experimental data by less than 5% for the regions already covered by previous experiments but err by about 10–20% for the ion/target combinations that were not measured before: Ca in Lu as well as Kr in Lu, Pb, and Th.

We have tested the hypothesis that for systems 24Mg + 90,92Zr, the shape of the barrier height distribution is not influenced by transfers processes. The experiment was performed using the ICARE detector system at the Warsaw Cyclotron. Having measured the transfer cross sections of the near-barrier collisions of 24Mg + 90,92Zr, we have found them to be roughly half of the value obtained for the 20Ne + 90,92Zr systems. From that observation, we conclude that in the 24Mg + 90,92Zr case, the leading cause of washing out the barrier distribution structure is the partial dissipation of relative kinetic energy into the non-collective excitation of the system. peerReviewed

Calorimetric low temperature detectors (CLTD’s) for heavy-ion detection have been combined with the LOHENGRIN recoil separator at the ILL Grenoble for the determination of nuclear charge distributions of fission fragments produced by thermal neutron-induced fission of $$^{235}$$ U. The LOHENGRIN spectrometer separates fission fragments according to their mass-to-ionic-charge ratio and their kinetic energy, but has no selectivity with respect to nuclear charges Z. For the separation of the nuclear charges, one can exploit the nuclear charge-dependent energy loss of the fragments passing through an energy degrader foil (absorber method). This separation requires detector systems with high energy resolution and negligible pulse height defect, as well as degrader foils which are optimized with respect to thickness, homogeneity, and energy loss straggling. In the present, contribution results of test measurements at the Maier Leibnitz tandem accelerator facility in Munich with $$^{109}$$ Ag and $$^{127}$$ I beams with the aim to determine the most suitable degrader material, as well as measurements at the Institut Laue–Langevin will be presented. These include a systematic study of the quality of Z-separation of fission fragments in the mass range $$82\le A \le 132$$ and a systematic measurement of $$^{92}$$ Rb fission yields, as well as investigations of fission yields toward the symmetry region.

An array of calorimetric low temperature detectors (CLTD’s) for energy sensitive detection of heavy ions was combined with time-of-flight (TOF) detectors to obtain a detector system for high resolution mass identification of low energy heavy ions. In addition the same setup was used to prove the ability of CLTD’s to be used in electronic stopping power measurements for heavy ions in matter. Experiments with 50 MeV 63Cu and 65Cu ions at the tandem accelerator at the MPI at Heidelberg, and with 25 to 250 MeV 238U ions at the UNILAC accelerator at GSI at Darmstadt have been performed. For 63,65Cu at 50 MeV a mass resolution of Δm(FWHM)=0.9 amu, and for 238U in an energy range of 65 to 150 MeV a resolution of Δm(FWHM)=1.28 amu, was obtained. The results for stopping powers of 238U in carbon and gold are presented and compared with theoretical predictions and data from the literature.

A method for the identification of energetic charged particles has been investigated based on the employment of pulse-shape discrimination (PSD) in a silicon detector in addition to conventional time-of-flight (ToF) techniques. The method makes use of the fact that, at fixed energy, the particle's velocity, or ToF, is a measure of the particle's mass A while the time structure of the current pulse in a silicon energy detector, used as the ToF stop, permits identification of nuclear charges Z. In the measurements presented here, ToF and PSD methods were applied simultaneously. We used micro-channel plate (MCP) detectors as fast time pick-offs and surface-barrier (SB) n-type Si detectors made from homogeneously neutron-transmutation-doped (n-TD) silicon. As the particles, products from the reactions of a 400 MeV 20Ne beam impinging on 12C, 27Al and 208Pb targets were employed. With using fast current-sensitive pre-amplifiers for the 250 and 800 μ m SB detectors a major progress in particle identification with respect to both, mass A and charge Z was achieved. In addition, using a stack of two closely mounted n-TD SB detectors, a timing measurement between the two detectors permitted to study PSD in the rear detector with the time trigger derived from the foremost one. Finally, the internal PSD method was implemented which determines pulse rise-time in single detectors from analyzing differentiated preamplifier timing signals.

Experiments have been performed for studying quaternary fission (QF) in spontaneous fission of 252Cf, on the one hand, and for the neutron-induced fission reactions 233, 235U(nth, f ), on the other hand. In this higher-multiplicity fission mode, by definition, four charged products appear in the final state. In other words, as a generalization of the ternary-fission process, not only one but two light charged particles (LCPs) are accompanying the splitting of an actinide nucleus into the customary pair of fission fragments. In the two sets of measurements, which have used quite different approaches, the yields of several QF reactions with α-particles and tritons as the LCPs have been determined and the corresponding kinetic-energy distributions of the α-particles measured. The QF process can appear in two basically different ways: i) the simultaneous creation of two LCPs in the act of fission (“true” QF) and ii) via a fast sequential decay of a single but particle-unstable LCP in common ternary fission (“pseudo” QF). Experimentally the two varieties of QF have been distinguished by exploiting the different patterns of angular correlations between the two outgoing LCPs. The experiments described in the present paper are the first to demonstrate that both types of reactions, true and pseudo QF, occur with quite comparable probabilities. As a new result also, the kinetic-energy distributions related to the two processes have been shown to be significantly different. For all QF reactions which could be explored, the yields for 252Cf(sf) were found to be roughly by an order of magnitude larger than the yields found in the 233U(nth, f ) and 235U(nth, f ) reactions. An interesting by-product has been the measurement of yields of excited LCPs which allows to deduce nuclear temperatures at scission by comparison to the respective yields in the ground state.

A new multiparameter experiment on ternary fission of 252Cf has recently been successfully performed by using the CODIS2 detector system and two GSI segmented Super Clover Ge γ-ray detectors. The experimental setup and the main subjects of interest are briefly described.

The results of experimental and theoretical studies of the double-differential proton and neutron spectra measured in coincidence with fission fragments in the deuteron-induced reaction on a 238U target at E d =65 MeV are presented. These spectra measured in the forward direction are analyzed in the plane-wave Born approximation by using the modified model of stripping into a continuum. The pre-neutron emission fission fragment mass distributions were measured for the (d, f), (d, pf), and (d, nf) reaction channels. The enhancement of highly asymmetric mass division in the (d, pf) channel for the low-energy part of the breakup proton spectrum was observed. The (d, pf) channel can be used to imitate the neutron-induced fission at intermediate energy. The fission characteristics were analyzed in the model taking into account nuclear friction and relevant fission modes.

Ternary fission induced by cold polarized neutrons was studied for the two isotopes 233U and 235U at the Institut Laue-Langevin in Grenoble, France. In particular two types of angular correlations between the spin of the incoming neutrons and the emission directions of both, the fission fragments (FF) and the ternary particles (TP), were investigated. For FF and TP detectors facing the target at right angles to the neutron beam, first, for longitudinally polarized neutrons a triple correlation between spin and the emission of outgoing particles was explored and, second, for transversally polarized neutrons parity violating asymmetries in the emission of FFs and TPs were analyzed. Nonzero expectation values for the triple correlation were oberserved in the present experiments for the first time.

Fission fragment mass distributions down to super-asymmetric mass region and both pre- and post-scission neutron multiplicity for238U(p,fission) reaction atEp = 20, 35, 50, 60 MeV and for232Th(p, fission) reaction atEp = 50, 60 MeV were measured using HENDES set-up. The results indicate enhancement for super-asymmetric mass division at intermediate excitation energies.

An experiment was performed on prompt γ-ray emission in binary and α-particle accompanied spontaneous fission of 252C f using the Darmstadt-Heidelberg 4π NaI Crystal Ball spectrometer. The enhancement in γ-ray yield, denoted as the “high-energy component”, which appears between 3.5 and 8 MeV and in the region of near-symmetric fragment mass splits, was observed to be equally pronounced in both fission modes. Analyzing the fragment mass dependence of the mean γ-ray multiplicity in both fission modes clearly identifies the disintegration of equilibrated fission fragments in a narrow mass range around the double-magic 132Sn as the source of these γ-rays.

High-spin states in 22Ne have been studied using the 14C(12C,α)22Ne(α)18O reaction at E(12 C)= 44MeV. The spin assignments were obtained as results of the analysis of double (α, α) angular correlations with the residual 18O nucleus in the 0+ ground state. The obtained values of spin and parity of five levels are: 20.0 MeV (9−), 20.7 MeV (11−), 21.6 MeV (9−), 22.2 MeV (12+), 25.0 MeV (9−).

Inducing fission by polarized neutrons allows studying subtle effects of the dynamics of the process. In the present experiments ternary fission of 235U and 239Pu was investigated with cold neutrons in the (n,f) reaction at the Institut Laue‐Langevin, Grenoble. Asymmetries in the emission of ternary particles were discovered by making use of the neutron spin flipping. It was found that two effects are interfering. There is first an asymmetry in the total yields of ternary particles having been called the TRI‐effect. Second, it was observed that the angular distributions of ternary particles are shifted back and forth when flipping the neutron spin. This shift was named ROT effect. Guided by trajectory calculations of the three‐body decay, the signs and sizes of the ROT effect are interpreted in terms of the K‐numbers of the transition states at the saddle point of fission.

In the present paper we describe an experiment performed on the reaction 238U + 4He (40 MeV) using a two‐arm TOF‐E (time‐of‐flight vs. energy) spectrometer with micro‐ channel plate detectors and mosaics of PIN diodes. This experiment has aimed at searching for fine structures in the total kinetic energy vs. fragment mass (TKE ‐ M) distributions of binary events, and disclosing rare ternary decay modes others than already known from ternary fission. Details of the procedures of data handling are briefly described as well.

International audience; A novel method to search for the anisotropic emission of prompt neutrons in the center-of-mass system of fission fragments is presented. The anisotropy is conjectured to be due to the large spins of fission fragments are known to carry. Triple neutron- neutron-fragment correlations in spontaneous fission of $^{252}$Cf were investigated in an exploratory experiment dubbed CORA-DEMON experiment. Fission fragments were intercepted in a double ionization chamber while neutrons were spotted in 2 two-dimensional cylindrical walls of Demon detectors with the target on the vertical cylinder axis. A new method of analysis of triple angular correlations between 2 neutrons and a fission fragment was applied. Preliminary results are reported.

P‐odd and T‐odd asymmetries in the emission of fragments and light particles have been investigated in ternary fission induced by polarized neutrons. P‐odd asymmetries unambiguously point to a violation of parity in the fission process. By contrast, T‐odd asymmetries do not necessarily imply a violation of time reversal invariance. The asymmetries observed are rather due to a final state interaction between the light ternary particle and the nucleus from which they are ejected. New results with interesting information on the ternary fission process are presented.

In recent multi‐parameter studies of spontaneous and thermal neutron induced fission, 252Cf(sf) and 235U(nth,f) respectively, the energies and emission angles of fission fragments and light charged particles were measured. Fragments were detected by an energy and angle sensitive twin ionization chamber while the light charged particles were identified by a series of ΔE‐Erest telescopes. Up to Be the light particle isotopes could be disentangled. In addition, in the 252Cf(sf) experiment, gammas emitted by the fragments were analyzed by a pair of large‐volume segmented clover Ge detectors. Here the main interest is to study the γ‐decay and the anisotropy of gammas emitted by fragments and light particles. On the other hand, the high count rates achieved in the U‐experiment performed at the high flux reactor of the ILL, Grenoble, should allow to explore fragment‐particle correlations in very rare events like quaternary fission. At the present stage of data evaluation, yields and energy distributions of light particles are available. For the present contribution in particular the yields of Be‐isotopes for the two reactions studied are compared and discussed. For 252Cf(sf) these isotopic yields were hitherto not known.

The study of neutron-rich light nuclei near the drip line has attracted much attention as they exhibit a particular nuclear structure, namely an extended distribution of the valence neutrons surrounding a compact core. Recently the elastic proton scattering from 6,8He and 8,9,11Li at 700 MeV/u using an inverse kinematics was successfully measured at GSI [1,2]. A high-pressure hydrogen-filled ionization chamber was used as the target and a proton detector. The previous experiments were performed in the small range 0.002 ≤| t |≤ 0.05 (GeV/c)2 of the four-momentum transfer squared t and have yielded valuable information on the nuclear sizes and radial structure of nuclear matter density distributions with the aid of the Glauber multiple scattering theory. Recently, a novel experimental approach has been accomplished with the aim to deduce the differential p 6,8He cross sections in the t-range 0.05 ≤| t |≤ 0.25 (GeV/c)2 close to the expected first diffraction minimum.

Neutron-rich light nuclei near the neutron drip line have attracted much attention in recent years as they feature a particular nuclear structure, namely an extended distribution (so-called halo) of the valence neutrons surrounding a compact nuclear core. Elastic proton scattering is known as a suitable technique for exploring the nuclear matter distributions in the stable nuclei. It was successfully employed at GSI also for the radioactive nuclei 6,8He and 8,9,11Li [1–3]. The experimental technique of inverse kinematics was applied using radioactive beams with energies near 700 MeV/u. The elastic differential cross section for small-angle scattering (3° ≤ θCM ≤ 10°) was deduced from the data taken with the ionization chamber IKAR, as an active target, and a forward spectrometer. The method has been demonstrated to be very effective for obtaining valuable information on the nuclear matter distribution in the halo nuclei under investigation, such as 6He, 8He and 11Li. The previous measurements at small momentum transfer have been highly sensitive on the nuclear sizes and the radial distributions of the nuclear matter density. Recently, a novel experimental approach has been accomplished with the aim to deduce the differential p6,8He cross sections for larger angles (10≤ ± θCM ≤ 30°) that correspond to a higher momentum transfer which covers the region of the first diffraction minimum.

The CAST experiment is being mounted at CERN. It will make use of a decommissioned LHC test magnet to look for solar axions through its conversion into photons inside the magnetic field. The magnet has a field of 9.6 Tesla and length of 10 m and is installed in a platform which allows to move it +-8° vertically and +-40° horizontally. According to these numbers we expect a sensitivity in axion-photon coupling g_alpha gamma gamma

Fission of 233U induced by thermal neutrons and with detectors for fission fragments and ternary particles covering large solid angles has been studied. Evidence has been found for events where two light charged particles are emitted in coincidence with fission fragments.

Ternary fission of 233U and 235U induced by cold polarized neutrons has been investigated. Several correlations between neutron spin and the momenta of fission fragments and ternary particles were analyzed. These correlations are probing time reversal invariance, parity non-conservation and left-right asymmetries. Results for all three correlations from the reaction 233U(n,f) are presented. Especially the outcome in the searches for time reversal correlations and left-right asymmetries is unexpected. A huge effect observed formally as a violation of time reversal is most probably simulated by specific properties of the emission mechanism for ternary particles.

HENDES is a new device for correlation measurements of fission fragments, neutrons and light charged particles produced in HI induced reactions. Double differential neutron spectra are measured with the help of Position Sensitive Neutron Detectors, fission fragment spectra are recorded with large Position Sensitive Avalanche Counters, and light charge particle spectra are measured with arrays of dE-E telescopes. Collective dynamical parameters of nuclear matter are extracted from the data. New results were obtained from 40Ar+180Hf reaction at EAr=190–250 MeV. Work is in progress to study the influence of neutron excess on the fusion-fission dynamics in different combinations of Ni beams on Sn targets.

The yield of light fission products from the reaction 241Am(2nth,f) were measured as function of mass A, atomic number Z, and kinetic energy E, using the recoil mass separator LOHENGRIN of the Institute Laue-Langevin at Grenoble. Mass distributions summed over ionic charge states were determined within the mass range 85 ≤ A ≤ 110 at seven kinetic energies between 86.9 and 117.0 MeV. For the same range of masses, nuclear charge distributions were measured for five energy values between 98.0 and 116.2 MeV. From the data, we have also evaluated the energy integrated nuclear charge and mass yields, as well as isotonic and isotopic yields and their odd-even effects.

Left–Right Asymmetry of the Angular Distribution of Long-Range Alpha Particles from Ternary 235U Fission Induced by Cold Polarized Neutrons* G. V. Danilyan1), A. M. Fedorov1), A. M. Gagarski2), F. Goennenwein3), P. Jesinger3), J. von Kalben4), A. Koetzle3), Ye. I. Korobkina5), I. T. Krasnoshchekova2), M. Mutterer4), V. V. Nesvizhevsky6), S. R. Neumaier4), Yu. B. Novozhilov1), V. S. Pavlov1), G. A. Petrov2)

At the recoil spectrometer “Lohengrin” of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of 239 Pu were measured as a function of A , Z , the kinetic energy E and the ionic charge states q . The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct kinetic energies between 93 and 112 MeV. The proton odd-even effect which was measured to be (11.6 ± 0.6)% causes considerable fine structure in the yields. The average kinetic energy of even- Z elements in the light fission-product group is 0.3 ± 0.1 MeV larger than for odd- Z elements. The neutron odd-even effect is (6.5 ± 0.7)%. The comparison with previously published data 1 ) for thermal-neutron-induced fission of 235 U reveals a correlation between the proton odd-even effect in the yield and in the kinetic energy of the elements. The dependence of the proton odd-even effect on the fragmentation is very similar for 235 U and 239 Pu when it is considered as a function of the nuclear charge of the heavy fission products. The isobaric variances σ z 2 . for thermal-neutron fission of 235 U and 239 Pu coincide at all kinetic energies if the influence of the proton odd-even effect is averaged out. This supports the hypothesis that the magnitude of σ z 2 is determined only by quantum-mechanical zero-point fluctuations. The influence of the spherical shells Z = 50 and N = 82 on the fragmentation is discussed.

The actual situation of the research on ternary fission, mainly α-particle accompanied fission, is reviewed, with the accentuation on recent experimental and theoretical investigations. The results of multiparameter experiments are discussed in more detail, and the role of fragment deformation for a correct description of the ternary fission process is outlined.

Angular and energy distributions of ternary fission products of 252 Cf have been measured with a position sensitive ionization chamber. Most of the observed triple coincidences are light-charged-particle accompanied fission events. The few events registered with relative angles near 120° allow to deduce an upper limit of 10 −8 per binary fission for a symmetric ternary fragmentation, in contradiction to previous counting experiments yielding ternary-to-binary fission ratios between 10 −4 and 10 −6 .

Recent results with gas-scintillation detectors for heavy charged particles are summarized and a heavy-ion detector telescope is described, with a multiparameter gas scintillator as the main detector component.

The yields of light fission products from thermal-neutron induced fission of 233U are measured as a function of their mass A, their nuclear charge Z, their kinetic energy E and their ionic charge state q at the recoil spectrometer Lohengrin of the Institut Laue-Langevin in Grenoble. The mass yields are determined by intercepting the fragments with an ionization chamber of high energy resolution positioned at the focal plane of the spectrometer. The nuclear charges and their yields are determined with the same ionization chamber by measuring the residual energy of fission products, selected monoenergetically by Lohengrin, behind a passive absorber made of parylene-C. The nuclear charge resolution enabled by this detector device is considerably improved to Z/dZ = 58. The nuclear charge and mass distributions summed over all ionic charge states are listed within the mass range 79 ⩽ A ⩽ 106 at 6 energies: E = 85.34, 90.41, 95.46, 100.50, 105.55 and 110.55 MeV. The energy-integrated nuclear charge and mass yields are also given. The isotonic and isotopic yields are shown. An odd-even effect in the yields is found for the protons as well as for the neutrons at all kinetic energies. The yield weighted total odd-even effect for the protons is found to be (22.1 ± 2.1)%, for the neutrons (5.4 ± 1.7)%. An odd-even effect for the protons in the mean kinetic energy is also observed. The displacement of the mean isobaric nuclear charges from the unchanged charge-density values and the variances of the isobaric nuclear-charge distributions reveal fine structures in their mass dependences.

In thermal neutron induced fission of 245Cm a fine structure in mass distribution is observed in cold and “hot” fragmentation regions for light as well as for heavy fragments. The complementarity of the light and heavy fragment masses in the fine structures is discussed.

Different types of noble-gas scintillation counters are described, which were advantageously applied to the detection of energetic heavy ions: (a) a low-pressure gas scintillator, operated with Xe, Ar and Ar-N2 mixtures, (b) a photo-diode gas scintillator, (c) a gas scintillator with built-in bidimensional position-sensitive drift chamber, and (d) a solid-Xe scintillator. Details of design and performance are presented.

A multiplate ionization chamber for absolute photofission cross section measurements with monoenergetic γ radiation is described. Physical, electronic, and mathematical methods for background elimination are presented as well as a procedure to take fission-fragment absorption in the target layers into account. The chamber is tested under conditions typical for the photofission of bismuth.

A systematic study of light charged particle (Z≤10) accompanied fission has been undertaken using the very intense neutron beams at the High Flux Reactor of the Institute Laue Langevin.

Cross sections for strongly damped collisions of 40Ar on 40Ca have been measured at energies Elab = 191, 236 and 272 MeV. The angular distribution and energy loss of the reaction fragments as well as the charge spread of the element distribution are reported. Furthermore, the measured data are compared to the already existing 40Ca-40Ca data at similar bombarding energies. An attempt to explain the energy and angular distribution of the reaction fragments is made by applying a trajectory calculation which employs the one-body window friction as the dissipative mechanism.

Better understanding of bremsstrahlung and modern experimental techniques, especially the use of GeLi detectors for the determination of weak γ-impurities, may today allow to make wider use of bremsstrahlung counting in the metrology of radionuclides. Therefore, present theoretical and experimental knowledge of the different types of bremsstrahlung is first briefly reviewed. Then some known or possible applications of bremsstrahlung counting and corrections for bremsstrahlung in other methods are discussed. Finally the 4π β-bremsstrahlung coincidence method for the measurement of pure β-emitters of nuclides decaying by pure electron capture is described and some new experimental results are presented. Conclusions concerning fundamental principles of coincidence counting can be drawn from these results.

A new detector system for the comprehensive investigation of light charged particle accompanied fission is described. First experimental results obtained on neutron induced fission of 235U at the high-flux reactor of the ILL are used to discuss the properties of the system.

The absolute photofission cross section of 209 Bi has been measured with monoenergetic γ-radiation between 40 and 65 MeV photon energy. Cross-section data have been obtained with an accuracy between 9 and 20%. The experimental result is compared with the excitation function calculated on the basis of the statistical model. In order to reproduce the measured data on σ γf , the (γ, n) cross section must decrease with increasing photon energy faster than the experimental total (γ, n) cross section. This behaviour can possibly be explained by the assumption that after photon absorption a compound nucleus is formed only for a small, and with photon energy decreasing, fraction of all decays.