M. Mutterer

Followers

Following

Co-authors

Public Views

Interests

Uploads

Papers by M. Mutterer

New experimental studies on the quaternary fission of 233, 235U(nth, f ) and 252Cf (sf )

by M. Mutterer and Valery Nesvizhevsky

The European Physical Journal A, 2005

Experiments have been performed for studying quaternary fission (QF) in spontaneous fission of 25... more Experiments have been performed for studying quaternary fission (QF) in spontaneous fission of 252 Cf, on the one hand, and for the neutron-induced fission reactions 233,235 U(n th , 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 kineticenergy 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 252 Cf(sf) were found to be roughly by an order of magnitude larger than the yields found in the 233 U(n th , f) and 235 U(n th , 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.

Download

Interference effect in the angular distribution of outgoing particles in ternary fission induced by cold polarized neutrons

by Valery Nesvizhevsky and M. Mutterer

Physics of Atomic Nuclei - PHYS ATOM NUCL-ENGL TR, 1999

Download

Can time reversal invariance be tested in ternary fission?

by Valery Nesvizhevsky and M. Mutterer

ABSTRACT

Observation of a triple correlation in ternary fission: is time reversal invariance violated?

by Valery Nesvizhevsky and M. Mutterer

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2000

In ternary "ssion, besides the two main "ssion fragments, a third (usually light) charged particl... more In ternary "ssion, besides the two main "ssion fragments, a third (usually light) charged particle is emitted. A triple correlation has been studied involving the momenta for a speci"c "ssion fragment p( , the momenta of the ternary particle p( and the spin of the polarized cold neutron inducing "ssion L . The correlation observable B" L ) [p( ;p( ] reverses sign upon time reversal and thus a non-vanishing value for the expectation value 1B2 could possibly be due to TRI being violated. However, "nal-state interactions or speci"c properties of the emission mechanism for ternary particles could equally well lead to a non-zero 1B2 with TRI being perfectly conserved. The reaction chosen was U(n,f). An unexpectedly large correlation was observed. From the raw data the value for 1B2 is 1B2"!(0.78$0.02);10\ with the sign corresponding to light fragments. Corrections for neutron polarization, geometric e$ciency, resolution of detectors and background increase this "gure by a factor of (1.5$0.3).

Download

Angular Momentum in Fission

by C. Wagemans, Valery Nesvizhevsky, I. Tsekhanovich, and M. Mutterer

Seminar on Fission VI, 2008

Three novel experiments in spontaneous and thermal neutron induced fission all with a bearing on ... more Three novel experiments in spontaneous and thermal neutron induced fission all with a bearing on angular momentum in fission are reviewed. In the first experiment it was observed that, in the reaction 235U(n, f) with incident polarized cold neutrons, the nucleus undergoing scission is rotating. This was inferred from the shift in angular distributions of ternary particles being dependent on

Orbital electron capture by the nucleus

The theory of nuclear electron capture is reviewed in the light of current understanding of weak ... more The theory of nuclear electron capture is reviewed in the light of current understanding of weak interactions. Experimental methods and results regarding capture probabilities, capture ratios, and EC/Beta(+) ratios are summarized. Radiative electron capture is discussed, including both theory and experiment. Atomic wave function overlap and electron exchange effects are covered, as are atomic transitions that accompany nuclear electron capture.

Particular Aspects of Particle-Accompanied Fission

A brief survey is presented of particular recent experiments on particleaccompanied fission. Very... more A brief survey is presented of particular recent experiments on particleaccompanied fission. Very recently, a new experiment was performed to re-measure the ternary α-particle energy spectrum in 252 Cf spontaneous fission by time-of-flight techniques. Compared to many previous experiments, which entailed detection thresholds of 6 to 9 MeV α-particle energy due to the ∆E − E method applied and use of protection foils on detectors, the energy distribution of ternary α-particles could, for the first time, be measured down to 1 MeV. We, furthermore, report on experimental studies on quaternary fission in spontaneous fission of 252 Cf, on the one hand, and the neutron-induced fission reactions 233,235 U(n th ,f), on the other hand. Finally, in a third experiment, ternary fission in the reaction 235 U(n,f) with cold polarised neutrons was under investigation. From peculiar but unmistakable shifts in the α-particle angular distribution when flipping the neutron spin the fissioning nucleus was deduced to undergo rotation at scission. This startling new phenomenon was dubbed the "ROT" effect.

Download

Fragment mass distribution in superasymmetric region in proton-induced fission of U and Th

Il Nuovo Cimento A, 1998

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

Fission Time Distributions in Fusion-Fission Reactions

Dynamical Aspects of Nuclear Fission, 2002

ABSTRACT The fission time distributions have been analysed using the comparison between measured ... more ABSTRACT The fission time distributions have been analysed using the comparison between measured and calculated characteristics of neutrons, protons and alpha-particles for compound nuclei near 182Pt, 220Th and 239Np, formed in the heavy ion and proton induced fission. Theoretical calculations were carried out taking into account effects of nuclear friction which increases with nuclear temperature. The form of the extracted fission time distributions consits of short and long time components. The center position of both components decreases slowly with increasing of excitation energy of compound nucleus.

Radiative Capture of s Electrons in the Decay of Be 7

Physical Review C, 1973

ABSTRACT

Gas scintillation nuclear particle detectors

Nuclear Instruments and Methods in Physics Research, 1982

ABSTRACT

Problems and possibilities of bremsstrahlung counting

Nuclear Instruments and Methods, 1973

Better understanding of bremsstrahlung and modern experimental techniques, especially the use of ... more Better understanding of bremsstrahlung and modern experimental techniques, especially the use of GeLi detectors for the determination of weak 7-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 brems-strahlung counting and corrections for bremsstrahlung in other methods are discussed. Finally the 4:~fl-bremsstrahlung coincidence methed for the measurement of pure fl-emitters or 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.

Download

Detection of Low Energy Electrons with a Channeltron in a Magnetic Beta-Spectrometer

Inelastic deuteron breakup followed by fission at intermediate energy

Physics of Atomic Nuclei, 2002

The results of experimental and theoretical studies of the double-differential proton and neutron... more 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.

Angular Anisotropy of Prompt γ Rays and Fragment Spin Alignment in Binary and Light-Charged-Particle-Accompanied Spontaneous Fission of 252Cf

Physical Review Letters, 1999

Angular correlations of prompt gamma rays in binary and light-charged-particle (LCP)-accompanied ... more Angular correlations of prompt gamma rays in binary and light-charged-particle (LCP)-accompanied spontaneous fission of 252Cf were measured with a 4pi-crystal-ball NaI(Tl) gamma-ray spectrometer. For 3H, 4He, 6He, Li, and Be accompanied fission, gamma-ray angular distributions were deduced with respect to the motion both of the fragments and the LCPs. There is no indication for a change of the fragment spin

Energy losses of 252Cf fission fragments in thin foils

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006

The stopping power of fission fragments from 252 Cf(sf) has been measured in thin foils of C, Ni,... more The stopping power of fission fragments from 252 Cf(sf) has been measured in thin foils of C, Ni, Au, Al 2 O 3 and Mylar as a function of fragment mass and energy. The chosen stopping materials are frequently used as the backing of sources and targets or entrance windows of gas detectors. The experimental setup allowed registration of velocities of two fission fragments and energy of one of them. In this way fragment masses could be unambiguously determined and the pulse-height defect of the silicon detector verified. The measured stopping power data for fission fragments cover masses between A = 101 and A = 148. The results are compared with semi-empirical predictions of SRIM 2003 code, LSS theory and theoretical calculation by Sigmund (PASS code). The best representations of the data are achieved by a semi-empirical formula based on classical Bohr theory. The formula was successfully tested also on the available data for Ar, Ca, Kr, Xe and Au ions in the energy range 0.2-6 MeV/u slowing down in carbon, nickel and gold.

Download

Breakthrough in pulse-shape based particle identification with silicon detectors

IEEE Transactions on Nuclear Science, 2000

Identification of charged particles is an important method in nuclear spectroscopy. We have achie... more Identification of charged particles is an important method in nuclear spectroscopy. We have achieved a major breakthrough that makes pulse-shape discrimination (PSD) method with a single solid-state detector comparable to and sometimes better than traditional telescope technique. By using rear-side injection in over-biased surface barrier n-type Si detectors made from homogeneously doped n-TD silicon, and extracting the pulse-shape information already at the preamplifier level we have reached improved Z and even A discrimination over a wide dynamic range. Previously good separation with PSD technique required major degradation of time resolution and inferior energy resolution. Currently we have pushed down the dynamical time range to below 35 ns and reached time resolution of about 200 ps fwhm while maintaining good energy resolution characteristic of silicon detectors. The lowest energy threshold for Z separation of intermediate mass fragments (IMF) achieved with a 250 m thick detector is equivalent to a range of about 20 m in silicon. For IMFs with ranges higher than 80 m of silicon we got full isotope separation. Details of this study are presented, and the application of our method in recent nuclear physics experiments is briefly discussed.

Download

Investigation of the α-cluster structure of Ne22 and Mg22

by G. Chubarian, G. Rogachev, C. Spitaleri, and M. Mutterer

Physical Review C, 2004

An excitation function for resonance elastic scattering of alpha particles on 18 O and 18 Ne was ... more An excitation function for resonance elastic scattering of alpha particles on 18 O and 18 Ne was measured using the method of inverse geometry with a very thick target. Spectroscopic information was obtained for 23 levels in the excitation energy region from 11.9 to 13.7 MeV in 22 Ne . Twelve of them are new. General features of alpha -cluster bands in 22 Ne are analyzed in the framework of the potential model with a deep potential well. Predictions for the 11- level in 22 Ne , as well as for the isotopic shift of the cluster levels in 22 Mg , are given. Evidence is presented that new perspectives on the study of nuclear structure and nuclear spectroscopy can be obtained in complimentary measurements of alpha -cluster states in mirror N!=Z nuclei.

Angular Correlations between Fragment Spin and Prompt Neutron Evaporation in Spontaneous Fission of 252 Cf: CORA-DEMON

ABSTRACT A novel method to search for the anisotropic emission of prompt neutrons in the center‐o... more ABSTRACT 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 252Cf 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. © 2007 American Institute of Physics

CAST status report

M. Mutterer

Uploads

Papers by M. Mutterer

Log In