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Dans ce travail sont presentees quelques activites des groupes SADVI (Service d’Application des Detecteurs Visuels), LAM (Laboratoire d’Analyses et de Mesures) et RaMsEs (Radioprotection et Mesures environnementales) qui se sont succedes a l’IPHC de Strasbourg ces dernieres annees. Les resultats concernent : la R&D en metrologie des rayonnements ionisants, les applications des detecteurs solides de traces, les emulsions nucleaires en biologie spatiale, la thermoluminescence pour la datation archeologique, la dosimetrie neutron et les mesures de la radioactivite dans l’environnement par spectrometrie α , β et γ .

High spallation neutron fluxes were produced by irradiating massive heavy targets with proton beams in the GeV range. The experiments were performed at the Dubna High Energy Laboratory using the nuclotron accelerator. Two different experimental set-ups were used to produce neutron spectra convenient for transmutation of radioactive waste by (n,x) reactions. By a theoretical analysis neutron spectra can be reproduced from activation measurements. Thermal-epithermal and fast-super-fast neutron fluxes were estimated using the 197Au, 238U (n,gamma) and (n,2n) reactions, respectively. Depleted uranium transmutation rates were also studied in both experiments.

SummaryExperimental studies on the transmutation of some long-lived radioactive waste nuclei, such as129I,237Np, and239Pu, as well as on natural uranium and lanthanum were carried out at the Synchrophastron of the Laboratory for High Energies at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. The radioactive targets (I, Np and Pu) were contained in weld-sealed aluminium holders produced by the Institute of Physics and Power Engineering, Obninsk, Russia. Spallation neutrons were produced by relativistic protons with energies in the range of 0.5 GeV≤Ep≤1.5 GeV interacting with 20 cm long uranium or lead target stacks. The metallic targets were surrounded by 6 cm thick paraffin moderators. The uranium and lanthanum samples were positioned on the outside of the moderator surface and typically contained approximately 0.5 to 1.0 gram of uranium or lanthanum. The highest fluence of spallation neutrons was observed in the region of 5 to 10 cm downstream the entrance of the primary beam into the metallic target, rather independent of the target material or the proton energy. The results obtained by nuclear chemistry methods were supplemented by SSNTD (Solid State Nuclear Track Detector) studies. Consistent and systematic results ofB-values and spectral distributions for neutrons have been found. From the experimentally observed transmutation rates one can extrapolate that in a subcritical nuclear power assembly (or "energy amplifier") using a 10 mA proton beam of 1 GeV onto a Pb-target as used here, one can transmute within one month in one gram of sample about 3 mg129I, 21 mg237Np, 3.3 mg238U, and 200 mg239Pu. Rather similar results have been found by another group for129I and239Pu. Observations show that the transmutation rates increase almost linearly with the proton energy in the energy interval 0.5 GeV up to 7.4 GeV. These findings are largely confirmed by model calculations using the LAHET- and DCM/CEM-codes.

Small samples of 129I and 237Np, two long-lived radwaste nuclides, were exposed to spallation neutron fluences from relatively small metal targets of lead and uranium, that were surrounded with a 6 cm thick paraffin moderator, and irradiated with 1.5, 3.7 and 7.4 GeV protons. The (n,γ) transmutation rates were determined for these nuclides. Conventional radiochemical La- and U-sensors and a variety of solid-state nuclear track detectors were irradiated simultaneously with secondary neutrons. Compared with results from calculations with well-known cascade codes (LAHET from Los Alamos and DCM/CEM from Dubna), the observed secondary neutron fluences are larger.

A code for the numerical analysis of images from a CCD camera, including correction of acquisition system defects, has been written and applied to the visualization of α-particle tracks in the solid state nuclear track detectors CR39 and LR115. A standard mask having different diameter holes permitted the calibration of the imaging system. Comparison of manual scanning results with those given by the automatic system are presented for detectors exposed to α-particles of 241Am source. As application, the system was used to measure specific activities of 238U in the Moroccan phosphates and their phosphogypsums samples by contact autoradiography.

LR115 track detectors were exposed to samples of Moroccan phosphate and phosphogypsum to measure their α-particle radioactivity. Then two formalisms were used for the dosimetry: simulation by a Monte Carlo method and determination of concentrations from a numerically integrated track registration equation. The results were compared with those deduced γ-ray spectrometry.

A cylindrical lead target of diameter 8 cm and length 20 cm was irradiated with 7.4 GeV protons along the axis of the cylinder. The lead target was surrounded with a paraffin layer of thickness 6 cm to moderate the neutrons produced in p + Pb reactions. The spatial distribution of the slow and fast neutrons on different surfaces of the moderator were determined using LR 115 2B detectors (through 10 B(n,α) 7 Li reactions) and CR39 detectors (through proton recoils) respectively. Such results can be valuable in the studies and design of Accelerator Driven Subcritical Nuclear Reactors and Nuclear Waste Incinerators.

Extended targets were irradiated for transmutation studies with relativistic heavy ions. For this, a metal core was surrounded by a paraffin moderator. The metal is either copper or lead and it was irradiated with deuterium, alpha, or carbon beams of 1.5 or 3.7 GeV/u at the SYNCHROPHASOTRON, LHE, JINR, Dubna, Russia. During this irradiation copious amounts of secondary neutrons are produced and studied with SSNTD detectors and radiochemical sensors, for example: 139 La (n,γ) 140 La→ B- . The yield of reaction products allows an estimation of secondary neutron fluxes. The yields of all kinds of reactions produced with deuterium and alpha beams obey to some extent the law of limiting fragmentation, i.e. they show little influence on the energy and the kind of incoming particles. However, one observes with 44 GeV 12 C ions always enhanced nuclear cross-sections induced by secondary particles. This behavior could not be confirmed with theoretical estimations based on the Dubna Cascade Model in its Cascade Evaporation Model version (DCM-CEM). Finally, some results for transmutation studies on 127 I and Cu will be presented.

The $^{238}\mathrm{U}$+$^{197}\mathrm{Au}$ reaction has been studied at 15 MeV/nucleon bombarding energy. Correlations between two to seven final fragments with $Zg~8$ have been measured using CR-39 nuclear track detectors. An event-by-event kinematic analysis was carried out for three-body exit channel reactions which exhaust about half of the final fragment production cross section. Most of these ternary processes can be associated with intermediate and peripheral impact parameters. The dominant reaction mechanism is shown to be that of a first binary quasielastic or dissipative collision followed by the sequential binary fission of the excited quasi-$U$ (or to a lesser extent of the excited target remnant). We observe also a net drift of nucleons from the target to the projectile prior to its decay.

Events with 2, 3 and 4 heavy fragments (A≥20) detected in the reactions100Mo +100Mo at 18.7, 23.7 A·MeV and120Sn +120Sn at 18.4 A·MeV were analyzed by means of an improved version of the kinematic coincidence method. The phase-space distributions prove that 3- (and possibly 4-) body events predominantly originate from a two-step mechanism and are compatible with the hypothesis of a binary deep-inelastic interaction followed by the further fissionlike decay of one (or both) of the primary fragments. The characteristics of the fission step — mass asymmetry, relative velocity, in-plane and out-of-plane angles — have been reconstructed for the 3-body events and indications are found that nonequilibrium effects at the end of the deep-inelastic phase may influence the fissionlike decay.

An extended Cu-target was irradiated with 22 and 44 GeV carbon ions, The target was in contact with a (CH2)(n)-block for the moderation of secondary neutrons. Small holes in the moderator were filled with either lanthanium salts or uranium oxide. The reaction La-139 (n,gamma) La-140 -->/(beta) was studied via the decay of La-140 (40 h), and the reaction U-238 (n, gamma) U-239 -->/(beta) Np-239 -->/(beta) was studied via the decay of Np-239 (2.3 d). In addition, a variety of solid state nuclear track detectors (SSNTD) were used. Results will be presented. The yields for the formation of (n, gamma) products agree essentially with other experiments on extended targets carried out at the Synchrophasotron LHE, JINR (Dubna). To a first approximation, the breeding rate of (n, gamma) products, as well as the specific track density, seen with several SSNTDs, doubles when the carbon energy is increased from 22 to 44 GeV. If, however, results at 44 GeV are compared in detail to those at 22 GeV, we observe an excess of (37 +/- 9) % in the experimentally observed Np-239-breeding rate over theoretical estimations. Experiments using solid state nuclear track detectors are giving similar results. We also observed in the past such excess in the yield of other secondary particles in relativistic heavy ion interactions above a total energy of approximately 35-40 GeV.

We have studied the fragmentation of Au projectiles interacting with targets of C, Al, Cu and Pb at an incident energy of E/A = 600 MeV. The experiment was performed with the ALADiN forward spectrometer at SIS. The employed inverse kinemantics allowed nearly complete detection of projectile fragments with charge Z ≥ 2. In addition, the number of light particles for each collision was measured. We compare different observables characterizing the event and investigate the impact parameter dependence of the fragmentation process. It is found that the correlation between the mean multiplicity of intermediate mass fragments 〈Mimf〉 and Zbound, the sum charges of all projectile fragments with Z≥2, is independent of the target nucleus. This universal behavior is consistent with an - at least partial - equilibration of the projectile fragment prior to its decay. Finally we compare to two classes of statistical models, the sequential decay code GEMINI and statistical multifragmentation models.

Reactions of 15 MeV/n 238 U on Ag have been studied by means of CR 39 detector. Analysis of 3 pronged events was done and classified as a function of impact parameter. For 4 and 5 pronged events, two and three steps mechanisms were found.

The mean multiplicity of intermediate mass fragments (IMF) {l angle}{ital M}{sub IMF}{r angle} produced by fragmentation of Au projectiles interacting with targets of C, Al, Cu, and Pb at an incident energy of {ital E}/{ital A}=600 MeV is compared to predictions of statistical multifragmentation and sequential evaporation models. The initial conditions for the calculations were provided by Boltzmann-Uehling-Uhlenbeck simulations. In the high excitation energy regime where the IMF multiplicity reaches its maximum the observed universal correlation between {l angle}{ital M}{sub IMF}{r angle} and the total charge {ital Z}{sub bound} of projectile fragments with charges {ital Z}{ge}2 cannot be reproduced by a sequential evaporation code. In this regime the data are better described by statistical decay calculations which assume the formation of an expanded nuclear system and a rather fast breakup.

Triple and four-fold coincidences among fragments have been measured in the reaction 84 Kr+Au at 43 MeV/u. All events showing the projectile-like nucleus and fission fragments of the target-like nucleus, and all events with one additional intermediate-velocity fragment, were analysed in the frame of a dissipative collision and a participant-spectator model. The mechanism is basically that of a dissipative collision but the emission of the intermediate velocity fragment by the target differs from an equilibrated evaporation.

We have studied the transition from the evaporation to the vaporization regime in 197Au induced reactions on C, Al, and Cu targets at a beam energy of 600 MeV per nucleon. The experiment was performed with the ALADIN forward spectrometer at SIS. We find that with increasing violence of the collision the mean multiplicity of intermediate mass fragments first increases to a maximum ⋍ 3.5 and then decreases again. Calculations using the BUU model suggest that the fragmentation is governed by the energy Edep deposited into the Au nucleus and that the maximum of is reached around Edep = 8 MeV/nucleon.

XYZt is a multidetector specially designed to measure intermediate-mass fragments emitted at small angles (2° E A > 20 MeV/u . It consists of 12 independent modules which can be placed in any geometry. Each module is composed of an avalanche counter measuring time and position, and an ionisation chamber measuring an energy-loss. XYZt allows coincidence measurements in an angular range extending below the grazing angle. In experiments performed at GANIL, it detects Z > 4 fragments, separates the charges up to Z = 15, has a time resolution better than 1 ns and is transparent to light particles.

We have studied the fragmentation of Au projectiles interacting with targets of C, Al and Cu at an incident energy ofE/A=600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with chargeZ≧2. The recorded fragmentation events were sorted according to three observables, the multiplicityMlp of light charged particles, the largest atomic numberZmax within an event, and a new observable,Zbound, representing the sum of the atomic numbersZ of all fragments withZ≧2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for theC target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity andZbound, extending from evaporation type processes (largeZbound) to the total disassembly of the projectile (smallZbound), is independent of the target nucleus. This universal behaviour may suggest an — at least partial — equilibration of the projectile fragment prior to its decay.

Reactions of 15 MeV/n 238 U on Au have been studied by means of CR 39 solid state nuclear track detectors. Among the different events observed, all 3-pronged events were selected and examined. It is found that at final state the quasi totality of these events, say 87%, proceed by fission reactions. Analysis in the context of participant-spectator model has shown evidence for two different fission processes. Fission events derived from the break-up of the participant nuclei represent ∼78% of the events, whereas ∼9% issue from the spectator. The mean kinetic energy loss is ∼11 % of the incident energy.

CR 39 solid state nuclear track detectors have been used to study the reaction products of 17.7, 27, and 35 MeV/nucleon $^{84}\mathrm{Kr}$ on Au and Ag. The visual detectors allow studying interactions producing two or more correlated intermediate mass fragments in the final state. The characteristics of these events are such that they probably arise from a fragmentation process of the quasitarget or some intermediate zone. The cross sections of 3, 4, and (5+6) correlated fragments increase with increasing $^{84}\mathrm{Kr}$ incident energy for both targets.

High-energy protons in the range of 0.5–7.4 GeV have irradiated an extended Pb target covered with a paraffin moderator. The moderator was used in order to shift the hard Pb spallation neutron spectrum to lower energies and to increase the transmutation efficiency via (n,γ) reactions. Neutron distributions along and inside the paraffin moderator were measured. An analysis of the experimental results was performed based on particle production by high-energy interactions with heavy targets and neutron spectrum shifting by the paraffin. Conclusions about the spallation neutron production in the target and moderation through the paraffin are presented. The study of the total neutron fluence on the moderator surface as a function of the proton beam energy shows that neutron cost is improved up to 1 GeV. For higher proton beam energies it remains constant with a tendency to decline.

With the ALADiN forward spectrometer the fragmentation of gold nuclei at 600 MeV per nucleon after interaction with carbon, aluminum, copper and lead targets has been investigated. The results are compared to Quantum Molecular Dynamics calculations using soft and hard equations of state.

Experiments using 1.5 GeV, 3.7 GeV and 7.4 GeV protons from the Synchrophasotron, LHE, JINR, Dubna, Russia, on extended Pb- and U-targets were carried out using SSNTD and radiochemical sensors for the study of secondary neutron fluences. We also carried out first transmulation studies on the long-lived radwaste nuclei 129I and 237Np. In addition, we carried out computer code simulation studies on these systems using LAHET and DCM/CEM codes. We have difficulties to understand rather large transmutation rates observed experimentally when they are compared with computer simulations. There seems to be a rather fundamental problem understanding the large transmutation rates as observed experimentally in Dubna and CERN, as compared to those theoretical computer simulations mentioned above.

Momenta and masses of heavy projectile fragments (Z >= 8), produced in collisions of 197Au with C, Al, Cu and Pb targets at E/A = 600 MeV, were determined with the ALADIN magnetic spectrometer at SIS. An analysis of kinematic correlations between the two and three heaviest projectile fragments in their rest frame was performed. The sensitivity of these correlations to the conditions at breakup was verified within the schematic SOS-model. The data were compared to calculations with statistical multifragmentation models and to classical three-body calculations. Classical trajectory calculations reproduce the dynamical observables. The deduced breakup parameters, however, differ considerably from those assumed in the statistical multifragmentation models which describe the charge correlations. If, on the other hand, the analysis of kinematic and charge correlations is performed for events with two and three heavy fragments produced by statistical multifragmentation codes, a good agreement with the data is found with the exception that the fluctuation widths of the intrinsic fragment energies are significantly underestimated. A new version of the multifragmentation code MCFRAG was therefore used to investigate the potential role of angular momentum at the breakup stage. If a mean angular momentum of 0.75$\hbar$/nucleon is added to the system, the energy fluctuations can be reproduced, but at the same time the charge partitions are modified and deviate from the data. PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.Ld, 25.75.-q, 38 pages, RevTeX with 21 included figures; Also available from http://www-kp3.gsi.de/www/kp3/aladin_publications.html

Spallation neutrons produced from 12 C ions at 18 and 44 GeV on Cu and Pb targets were studied as well as thermalization in appropriate moderators. The irradiation were performed at the Dubna LHE Synchrophasotron. Results are given for thermal and fast neutrons estimated and compared with different experimental methods.

We investigate the charge changing collisions for 16 O and 32 S beams at 3.65 GeV/n on several targets, by using Solid State Nuclear Track Detectors (SSNTD). Track measurements were performed by an automatic measurement system. We determined the total charge changing cross sections and the elemental cross sections for the production of fragments of charge 9 ≤ Z ≤ 14. Comparison with theoretical models as well as with experimental data are given.

Coincident light particles and fragments produced in Kr+Au reactions at 27, 44 and 60 MeV/u have been measured with a large solid-angle set-up. Energy spectra of Z=1, 2 and 3 particles sequentially emitted by the slowed-down projectile-like nucleus evolve between an evaporation and a fragmentation pattern, suggesting a saturation in the thermalisation process.

We review the recent results on the multi-fragment decay of heated nuclear systems that are formed in asymmetric heavy-ion collisions. Particular emphasis is placed on those observables that are sensitive to the fluctuations in the decaying system and their possible role in extracting the physics of phase transitions in nuclear systems.

Total reaction cross sections of C-12, O-16 and Mg-24 projectiles were determined in several targets, by means of Nuclear Track Detectors. The beams at 4.5 GeV/N for C-12 and Mg-24 and 3.65 GeV/N for O-16 were taken from Dubna accelerator. Our results exhibit the geometrical dependence on nuclear radii. They are in good agreement with Vary's cross sections (Vary, 1975) taking the overlap parameter to be dependent on interacting masses.

We have studied multifragment decays of Au projectiles after collisions with C, Al, and Cu targets at a bombarding energy of 600 MeV nucleon. We find that with increasing violence of the collision, measured via the multiplicity of light particles, the mean multiplicity of intermediate-mass fragments originating from the projectile first increases to a maximum {l angle}{ital M}{sub IMF}{r angle}{congruent}3 and then decreases again. Calculations using the Boltzmann-Uehling-Uhlenbeck model suggest that the fragmentation is governed by the energy {ital E}{sub dep} deposited into the projectile spectator and that {l angle}{ital M}{sub IMF}{r angle} reaches its maximum around {ital E}{sub dep}{congruent}8 MeV/nucleon.

Events with 2, 3 and 4 heavy-fragments (A≧20) have been detected in the reactions100Mo+100Mo atE/A =18.7, 23.7 MeV and120Sn+120Sn atE/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilitiesP 3 andP 4 of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of theP 3 andP 4 curves at high energy losses. Small deviations of theP 3 andP 4 curves at 23.7A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter.

Backward-angle cross sections for the reactions /sup 24/Mg(/sup 16/O, /sup 12/C)/sup 28/Si(g.s.; 1.78 MeV) and /sup 24/Mg(/sup 16/O, /sup 16/O)/sup 24/Mg(g.s.; 1.37 MeV) were obtained for 17 MeV < or = E/sub c.m./ < or = 31 MeV, theta-bar/sub c.m./ approx. = 176/sup 0/. The first reaction shows gross and fine resonant structures; the second shows mainly gross structures. Angular distribution measurements give L values of 15 and 21, respectively, at E/sub c.m./ = 21.6 and 28.0 MeV. The resonant gross structures for /sup 24/Mg(/sup 16/O,/sup 12/C) /sup 28/Si(g.s.) are governed by the entrance channel and are discussed from the shape-resonance point of view.

A new method was used to measure $E0$ $\ensuremath{\pi}$-decay branching ratios. A plastic scintillator pair spectrometer of high efficiency (3%) was used. It consists of four detectors. Two of them, very thin, select the electrons; the other two, thick, help to measure their energies. An annular counter ($\ensuremath{\Omega}=0.10$ sr), working in coincidence with the spectrometer, allows the selection of the $\ensuremath{\pi}$ decay relevant to the ${0}^{+}$ excited state and the determination of its population yield. The reactions $^{23}\mathrm{Na}(\ensuremath{\alpha},p)^{26}\mathrm{Mg}$(3.58 MeV)($\ensuremath{\pi}$) and $^{27}\mathrm{Al}(\ensuremath{\alpha},p)^{30}\mathrm{Si}$(3.79 MeV)($\ensuremath{\pi}$) have been used to study the $E0$ $\ensuremath{\pi}$ decay of the first excited ${0}^{+}$ state in $^{26}\mathrm{Mg}$ and $^{30}\mathrm{Si}$. Pair spectra from the spectrometer were recorded in coincidence with protons in two-dimensional arrays. From the coincidence spectra the values for $\frac{{\ensuremath{\Gamma}}_{\ensuremath{\pi}}}{\ensuremath{\Gamma}}$ are found to be (5.1 \ifmmode\pm\else\textpm\fi{} 0.7) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ and (2.6 \ifmmode\pm\else\textpm\fi{} 0.6) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$, respectively, for $^{26}\mathrm{Mg}$(3.58 MeV) and $^{30}\mathrm{Si}$(3.79 MeV). When combined with the available lifetimes of these states, these ratios yield ${〈M〉}_{\ensuremath{\pi}}=(3.0\ifmmode\pm\else\textpm\fi{}0.25)$ ${\mathrm{fm}}^{2}$ ($^{26}\mathrm{Mg}$ and (1.4 \ifmmode\pm\else\textpm\fi{} 0.2) ${\mathrm{fm}}^{2}$ ($^{30}\mathrm{Si}$) for the monopole matrix elements.

Energy and angular correlations of ..cap alpha.. particles in coincidence with deeply inelastic ejectiles from /sup 16/O+/sup 58/Ni collisions at 6 and 9 MeV/nucleon reveal ..cap alpha.. emission processes which cannot be explained by sequential emission from the fragments.

Energy and angular distributions of products with 3⩽Z⩽22 from 32 S + 93 Nb reactions at 10 MeV/N were measured and the cross section for deep-inelastic reactions was deduced. Energy and angular correlations between α-particles and deep-inelastic fragments were measured and analysed in terms of sequential emission from the detected projectile-like fragment ( M α = 0.30± 0.06) and sequential emission from the target-like fragment α = 0.90±0.10). For sequential emission from the target-like fragment shadowing was observed due to the proximity of the two fragments at the time of emission. Three-body Coulomb trajectory (TBCT) calculations give a lifetime of (1–3)×10 −21 s for the target-like fragment, in good agreement with statistical-model calculations. It is shown that the shadow effect is sensitive to the charge/size of the projectile-like fragment as predicted by the TBCT calculations. In the forward hemisphere nonsequential emission of beam-velocity α-particles is observed α = 0.20±0.06). At backward angles another component is observed α = 0.05±0.01) which appears to be emission from the neck region of the scissioning fragments. It is shown that the two nonsequential emission processes have a different dependence on the exit-channel mass split.

Light charged particles and nuclei (1⩽Z⩽8) have been detected in a large forward plastic multidetector (3° < θ

The reaction /sup 2/H(/sup 13/C,p)/sup 14/C has been used to measure the lifetime of the /sup 14/C(6.59 MeV,0/sup +/) state. From recoil distance and Doppler shift attenuation measurements a value tau4.6=(ts +- 0.7) ps was found. The reaction /sup 13/C(d,p)/sup 14/C has been used to study the E0 ..pi.. decay of the 0/sup +/ state. The branching ratio GAMMA/sub ..pi..//GAMMA was measured to be (1.1 +- 0.1) x 10/sup -2/. When this value is combined with the determined lifetime an E0 matrix element /sub ..pi../0.36=(ts +- 0.06) fm/sup 2/ is obtained.

The particle decays of the first $T=\frac{3}{2}$ state in $^{9}\mathrm{Be}$ ($^{9}\mathrm{B}$) have been studied by the $^{7}\mathrm{Li}(^{3}\mathrm{He},pn)$ reaction at $E(^{3}\mathrm{He})=10.0$ MeV (8.7 and 7.95 MeV). Protons (neutrons) emitted at 0\ifmmode^\circ\else\textdegree\fi{} were detected in coincidence with decay neutrons (protons). Neutron energy was determined by the associated-particle time-of-flight technique. The ratios of partial neutron (proton) widths to the ground and first excited states of $^{8}\mathrm{Be}$ to the ground-state radiative width ${\ensuremath{\Gamma}}_{{\ensuremath{\gamma}}_{0}}$ are found to be, respectively, 6.4 \ifmmode\pm\else\textpm\fi{} 2.0 and 20.4 \ifmmode\pm\else\textpm\fi{} 4.6 for the $^{9}\mathrm{Be}$ analog state (1.5 and 13.9 \ifmmode\pm\else\textpm\fi{} 2.1 for $^{9}\mathrm{B}$). Taking ${\ensuremath{\Gamma}}_{{\ensuremath{\gamma}}_{0}}=10.5\ifmmode\pm\else\textpm\fi{}1.5$ eV, these results give ${\ensuremath{\Gamma}}_{{n}_{0}}=67\ifmmode\pm\else\textpm\fi{}26$ eV, ${\ensuremath{\Gamma}}_{{n}_{1}}=213\ifmmode\pm\else\textpm\fi{}56$ eV, ${\ensuremath{\Gamma}}_{{p}_{0}}18$ eV, and ${\ensuremath{\Gamma}}_{{p}_{1}}=147\ifmmode\pm\else\textpm\fi{}30$ eV for the mirror decays.

Cu and Pb targets were irradiated by 3.7 GeV/n 12 C ions and 1.8 GeV/n ions respectively at the Dubna (USSR) and Berkeley (USA) accelerators. CR 39 track detectors were placed up- and downstream of 2.0 cm Cu and 0.8 cm Pb foils. Important attenuation of the number of beam particles passing through the targets was observed allowing for direct total reaction cross section measurements. Good agreement with theoretically calculated cross section was found.

To see whether ’’Molecular Resonances’’ may be observed for A≳32 systems, the 16O+24Mg reaction has been investigated in the 17–31 MeV (CM) energy range. Despite the broad structure behavior of the 24Mg+16O outgoing channels, several rather narrow (Γtot≲500 keV) correlated resonances were observed for the 28Si+12C channels at backward angles. The angular distributions of two of these resonances at ECM = 21.6 MeV and 28.0 MeV show Jπ= (15−) and (21−) respectively.

We have measured the mass, the atomic number and the kinetic energy of the fragments emitted between 8 and 23° in the 35 MeV/u Kr+Au reaction. We found few products with the velocity of the projectile and α lot of fragments with Z ~20–28. Their kinetic energy (≲ 1 GeV) is substantially smaller than the one corresponding to the beam energy. It is not clear that these products correspond to a two-body reaction and they could arise from a three-body mechanism.

The reaction 7 Li( 3 He, α) 6 Li∗(5.36 MeV) (d) 4 He has been used to search for the isospinforbidden decay of the 5.36 MeV, T = 1 state of 6 Li into α +d. An upper limit of 2 % is placed on the deuteron branching ratio from this state, implying a reduced width for deuteron emission of less than 0.5 % of the Wigner limit (2/mR 2 , with R = 3.7 fm).

Agreement between theoretical and experimental track densities in LR115 cellulose nitrate detectors shows that α-particles can be detected quantitatively in air, solutions, and finely divided solids. For general use, a readily applicable form of the numerically integrated track registration equation for LR115 contact autoradiography is presented.

The transition probability of the transition 9.85 MeV ( J π = 2 + ) → 6.06 MeV ( J π = 0 + ) has been determined with the aid of the 12 C (α, γ, π) 16 O reaction. The width Γ 9.85 MeV → 6.06 MeV = 1.89 ± 0.42 MeV corresponds to a reduced probability B ( E 2) = 2.95 ± 0.66 e 2 fm 4 .

La mesure du rapport d'embranchement 11.52 → 6.0611.52 → 0 nous permet d'attribuer la valeur B(E2) = 7.6 ± 1.7 e2fm4 a la probabilite reduite de la transition 11.52 → 6.06 MeV dans 16O. L'accord est remarquable avec la prediction theorique de Bron et Green.

Coincidences between fragments (z = 8--36, theta = 3--30/sup 0/) emitted in the Kr + Au reaction at 35 and 44 MeV/u have been measured. On the basis of final-state interactions, the coincidence events can be divided into two distinct groups. In one group, products with near beam velocity are identified with the remaining part of the projectile; they are detected in coincidence with much slower fragments emitted by the target or by a hot zone common to the projectile and the target. The fragments of the second group have intermediate velocity and may be emitted by a much slowed-down projectile.