Описаны характеристики прототипа детектора нейтронов с энергией 1–15 МэВ, представляющего собой детектор полного поглощения и состоящего из чередующихся сцинтилляторов из пластика и стекла с примесью 6Li. Попавший в детектор нейтрон теряет всю свою энергию в пластике, замедляется до тепловых энергий и регистрируется в литиевом стекле. Измеренное время полного замедления нейтрона составляет 60 мкс. Регистрация в этом временном интервале двух сигналов – от первого акта рассеяния нейтрона в пластике до акта поглощения нейтрона литием в стекле – обеспечивает эффективное подавление фоновых тепловых нейтронов и -квантов и, как следствие, детектирование малоинтенсивных источников нейтронов. Предлагаемая конструкция детектора дает возможность определения направления на источник нейтронов.

The characteristics of the detector prototype for 1–15 MeV neutrons are described. The prototype is a full absorption detector consisting of interlaced plastic scintillators and 6 Li doped glasses. A neutron incident on the detector deposits all its energy in the plastic scintillator, is moderated to thermal energies, and detected in the lithium glass. The measured time of complete neutron moderation is ∼60 μs. Recording two signals in this time interval from the first event of neutron scattering in the plastic scintillator and from the neutron absorption by a lithium atom in the glass, it is possible to effectively suppress background thermal neutrons and γ rays and, therefore, detect low-intensity neutron sources. Owing to the proposed detector design, the direction toward the neutron source can be determined.

Between 1505 and 1506 Leonardo Da Vinci painted his masterpiece, the Battle of Anghiari, in Palazzo Vecchio’s Hall of 500 in Florence. The unfinished mural remained visible until 1563, when architect Giorgio Vasari undertook a renovation of the Hall and all traces of the Battle of Anghiari were lost. However, scholarly interpretation and scientific evidence suggest that the mural could be on the eastern wall, hidden behind a brick wall built in 1563 by Vasari. This paper discusses the possibility of using NNA/APT (Nanosecond Neutron Analysis/Associated Particle Technique) to establish the presence of the masterpiece by identifying behind the Vasari’s wall chemical elements from the gesso preparation layer of the mural and possibly from its pigments. This paper reports on the experiments run with a simple NNA/APT system and the Monte Carlo simulations that have been carried out in order to outline the experimental setup of an advanced NNA/APT able to detect and locate the tiny amount of gesso and pigments.

Nanosecond Neutron Analysis (NNA) method with spatial selection of secondary gamma-radiation, proposed at V. G. Khlopin Radium Institute as a further development of the well-known Associated Particle Technique (APT), allows one to substantially (by two orders of magnitude) reduce the level of the background radiation, making possible creation of devices for detection of small amounts of hazardous materials. A prototype APT/NNA device is based on a DT neutron generator with built-in nine-segment semiconductor detector of accompanying alpha-particles. The prototype is the basis for further development of the NNA method in order to create devices for detection of explosives and other hazardous materials in luggage, sea cargo containers, etc. A concept of a device for detection of hazardous materials in sea cargo containers “3D NNA Scanner” has been developed. Results of numerical modeling suggest, that the device will be capable of detecting 30 kg of explosives hidden anywhere inside a 40-feet cargo container within a 12 minute-long inspection cycle.

Exotic Nuclei, pp. 158-166 (2002) No AccessLATEST RESULTS FROM HENDES COLLABORATION: FINE STRUCTURE IN FRAGMENT MASS-ENERGY DISTRIBUTIONW. H. TRZASKA, YU. V. PYATKOV, YU. E. PENIONZHKEVICH, V. A. MASLOV, O. I. OSETROV, A. A. ALEXANDROV, I. A. ALEXANDROVA, J. ÄYSTÖ, K. -TH. BRINKMANN, S. V. KHLEBNIKOV, V. F. KUSHNIRUK, A. V. KUZNETSOV, V. G. LYAPIN, M. MUTTERER, Z. RADIVOJEVICH, V. A. RUBCHENYA, YU. G. SOBOLEV, V. G. TISHCHENKO, G. P. TIOURINE and D. N. VAKHTINW. H. TRZASKADepartment of Physics of University of Jyväskylä, Finland, YU. V. PYATKOVMoscow Engineering Physics Institute, Russia, YU. E. PENIONZHKEVICHFlerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia, V. A. MASLOVFlerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia, O. I. OSETROVKhlopin Radium Institute, St. Petersburg, Russia, A. A. ALEXANDROVFlerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia, I. A. ALEXANDROVAFlerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia, J. ÄYSTÖDepartment of Physics of University of Jyväskylä, Finland, K. -TH. BRINKMANNTechnical University Dresden, Germany, S. V. KHLEBNIKOVKhlopin Radium Institute, St. Petersburg, Russia, V. F. KUSHNIRUKFlerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia, A. V. KUZNETSOVKhlopin Radium Institute, St. Petersburg, Russia, V. G. LYAPINDepartment of Physics of University of Jyväskylä, Finland, M. MUTTERERTechnical University Darmstadt, Germany, Z. RADIVOJEVICHDepartment of Physics of University of Jyväskylä, Finland, V. A. RUBCHENYADepartment of Physics of University of Jyväskylä, FinlandKhlopin Radium Institute, St. Petersburg, Russia, YU. G. SOBOLEVFlerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia, V. G. TISHCHENKOMoscow Engineering Physics Institute, Russia, G. P. TIOURINEDepartment of Physics of University of Jyväskylä, FinlandKhlopin Radium Institute, St. Petersburg, Russia and D. N. VAKHTINDepartment of Physics of University of Jyväskylä, FinlandKhlopin Radium Institute, St. Petersburg, Russiahttps://doi.org/10.1142/9789812777300_0012Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: Existence of a new feature in fragment mass-energy distribution is reported. Careful analysis of the data obtained in the reaction 238U + 40Ar (275 MeV) shows that small but statistically significant ripples visible already in the gross mass spectrum come from extended and regular 2D patterns in the TKE vs. mass matrix. Intensity distributions of these patterns coincide with the location of heavy clusters such as 78Ni, 108Mo, or 132Sn. Presumably, the observed patterns show the dominant trajectories in the elongation vs. mass-asymmetry space of the decaying system. This information, unknown in the past, can shed a new light even on the previously well-studied reactions. FiguresReferencesRelatedDetails Exotic NucleiMetrics History PDF download

A position-sensitive neutron detector has been developed for use in nuclear physics research. The detector consists of a ∅5.5cm×100cm long quartz tube filled with liquid scintillator viewed from both ends by photomultipliers and enclosed in a light-tight titanium container. The properties of the detector were determined both experimentally and by Monte Carlo simulations (EFEN code). A time resolution of 0.4ns was reached resulting in the position resolution of less than 4cm. The neutron registration efficiency varies from 36% to 20% within neutron energy range 1–10MeV and is practically independent of the position along the detector length. Good n–γ separation is achieved for neutron energies greater than 0.5MeV.

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 238 U 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.

A pronounced fine structure (FS) in the form of distinct peaks was observed in neutron gated mass spectra from the decay of the 278110 composite system produced in the reaction 238U + 40Ar (243 MeV) at an initial excitation energy E* > 70 MeV. The FS peaks are located in the vicinity of mass numbers 70-80, 100, and 130, which correspond to those of magic nuclei (clusters). In the data there is also evidence for a new type of decay -- collinear cluster tripartition of an excited nucleus.

The primary fission fragment mass and kinetic energy distributions, and neutron multiplicities as function of fragment mass have been measured in the proton-induced fission of 238U at energies Ep=20,35,50 and 60MeV using time-of-flight technique. Pre-scission and post-scission neutron multiplicities have been extracted from double differential distributions. The fragment mass dependence of the post-scission neutron multiplicities reveals the gross nuclear shell structure effect even at the higher proton energies we measured. The yields of neutron-rich fission products in the fission of 238U by 25MeV protons were measured using an ion guide-based isotope separator technique. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus. The experimental results have been analysed in the framework of a time-dependent statistical model with inclusion of nuclear friction effects in the fission process.

The results of studies of fission fragment mass distributions in deuteron-induced fission of U-238 for (d,f), (d,pf), and (d,nf) reaction channels at deuteron energy E-d = 65 MeV are presented. The double differential proton and neutron spectra in coincidence with fission fragments have been measured. Enhancement of fragment yield in the highly asymmetric mass region had been observed in (d,f), (d,pf), and (d,nf) reaction channels. The U-238(d,pf) reactions channel can be used to imitate the neutron induced fission at intermediate energy.

New data on neutron, proton and alpha particle multiplicity measured for the reactions Ni-58 (340 MeV) + Sn-112,Sn-118,Sn-124, N-20, (160 MeV) + Er-162, (40)A, (243 MeV) + Nd-142, and Ni-58 (320 MeV) + Sn-124 are presented. The results are compared with new model calculations. New results on proton induced very asymmetric division of U-238 at intermediate energies are discussed. A short description of experimental set-up HENDES for investigation of fusion-fission processes is given.

V. A. Rubchenya, 1,2 A. V. Kuznetsov, 1,2 W. H. Trzaska, 1 D. N. Vakhtin, A. A. Alexandrov, I. D. Alkhazov, J. Äystö, S. V. Khlebnikov, 2 V. G. Lyapin, O. I. Osetrov, 2 Yu. E. Penionzhkevich, 3 Yu. V. Pyatkov, 3 and G. P. Tiourin Department of Physics, University of Jyva ̈skylä, FIN-40351, Jyva ̈skylä, Finland V.G. Khlopin Radium Institute, 194021, St. Petersburg, Russia Flerov Laboratory of Nuclear Reactions, 149980, Dubna, Russia ~Received 5 December 1997 !

Pre-neutron emission fragment mass distributions in fission of U-238 by protons at energies E-p = 20, 35, 50 and 60 MeV were measured by means of time-of-flight method. The results taken together with the data measured earlier at IGISOL for 25 MeV proton induced fission of U-238 indicate enhancement for superasymmetric mass division at intermediate excitation energy and show the potential of this reaction for the production oi: neutron-rich exotic nuclei below A = 80.

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.

HENDES is a new device for correlation measurements of fission fragments, neutrons and light charged particles produced in HT 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 Ar-40 + Hf-180 reaction at E-Ar = 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.

In an effort to extend the scope of basic research centred around the new K-130 heavy-ion cyclotron at the Physics Department of the University of Jyvaskyla a new experimental device called HENDES has been constructed. It is designed for correlation measurements of fission fragments, neutrons, and light charged particles produced in heavy ion induced reactions in the energy range of about 5 to 10 MeV/A. Collective dynamical parameters of nuclear matter are extracted from the data. New results were obtained from Ar-40 + Hf-180 reaction at E(Ar) = 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.