Light Charged Particles Research Articles

A single-chip telescope for heavy-ion identification

A ΔE-E telescope exploiting a single silicon chip for both ΔE measurement and scintillation light collection has been tested. It is a Si - CsI (Tl) telescope tailored for mass identification of light charged particles and intermediate mass fragments. A procedure based on two different shaping filters allows for extraction of the ΔE-E information from the single silicon signal. The quality of the obtained fragment identification is expressed in terms of a figure of merit and compared to that of a standard ΔE-E telescope. The presented configuration could be a good candidate for the basic cell of a large solid angle array of ΔE-E telescopes, given the reduction in complexity and cost of the front-end electronics.

New excited states in the halo nucleus 6He

The low-lying spectroscopy of 6He was investigated via the 2-neutron transfer reaction p(He8,t) with the 8He beam delivered by the SPIRAL facility at 15.4 AMeV. The light charged particles produced by the direct reactions were measured using the MUST2 Si-strip telescope array. Above the known 2+ state, two new resonances were observed: at E⁎=2.6±0.3 MeV (width Γ=1.6±0.4 MeV) and at 5.3±0.3 MeV with Γ=2±1 MeV. Through the analysis of the angular distributions, they correspond to a 2+ state and to an L=1 state, respectively. These new states, challenging the nuclear theories, could be used as benchmarks for checking the microscopic inputs of the newly improved structure models, and should trigger development of models including the treatments of both core excitation and continuum coupling effects.

Study of fission dynamics in fusion–fission reactions

One-dimensional Langevin equations were applied to study the fission dynamics of compound nucleus 200Pb formed in heavy ion-induced fusion reactions in an intermediate range of excitation energies. A modified wall and window dissipation with a reduction coefficient, ks, has been used in the Langevin equations. The average pre-fission multiplicities of neutrons, light charged particles and fission probabilities were calculated for 200Pb and results compared with the experimental data. It was shown that the results of the calculations are in good agreement with the experimental data of neutron and charged particles (p and alphas) multiplicities and fission probabilities by using values of ks in the range 0.27⩽ks⩽0.48.

Correlations with projectile-like fragments and emission order of light charged particles

Correlations with projectile-like fragments and emission order of light charged particles

Nuclear data measurements at the new NFS facility at GANIL

The NFS (Neutrons For Science) facility is part of the SPRIAL 2 project at GANIL, Caen, France. The facility is currently under construction and the first beam is expected in early 2013. NFS will have a white neutron source covering the 1–40 MeV energy range with a neutron flux higher than comparable facilities. A quasi-mono-energetic neutron beam will also be available. In these energy ranges, especially above 14 MeV, there is a large demand for neutron-induced data for a wide range of applications involving dosimetry, medical therapy, single-event upsets in electronics and nuclear energy. Today, there are a few or no cross section data on reactions such as (n, fission), (n, xn), (n, p), (n, d) and (n, α). We propose to install experimental equipment for measuring neutron-induced light-charged particle production and fission relative to the H(n, p) cross section. Both the H(n, p) cross section and the fission cross section for 238U are important reference cross sections used as standards for many other experiments. Nuclear data for certain key elements, such as closed shell nuclei, are also of relevance for the development of nuclear reaction models. Our primary intention is to measure charged particle production (protons, deuterons and alphas) from 12C, 16O, 28Si and 56Fe and neutron-induced fission cross sections from 238U and 232Th.

Calculations of (n,α) Cross Sections on Some Structural Fusion Materials for Fusion Reactor Technology

The knowledge of cross section for emission of light charged particles (p, d, t, andα) induced by fast neutrons on structural fusion materials has a critical importance on fusion reactors. The gas production arising from (n,p) and (n,α) reactions causes seriously radiation damage in fusion reactor structure. The radiation damage in fusion related materials is a large problem need to be overcome for development of fusion reactor technology. Particularly, the (n,α) reaction cross section data are required to estimation of the radiation damage effects on structural fusion materials. Therefore, the cross section data for (n,α) reaction induced by fast neutrons are of increasing importance for the success of future fusion reactors. In this study, reaction model calculations of the cross sections of neutron induced reactions on structural fusion materials such as 29Si,30Si,48Ti,50Ti,50Cr,54Cr,54Fe and 58Fe have been investigated. The new calculations on the excitation functions of 29Si (n,α) 26Mg,30Si (n,α) 27Mg,48Ti (n,α) 45Ca,50Ti (n,α) 47Ca,50Cr (n,α) 47Ti,54Cr (n,α) 51Ti,54Fe (n,α) 51Cr and 58Fe (n,α) 55Cr have been carried out for incident neutron energies up to 30 MeV. In these calculations, the pre-equilibrium and equilibrium effects for (n,α) reactions have been investigated. The pre-equilibrium calculations involve the new evaluated the geometry dependent hybrid model, hybrid model and the cascade exciton model. The equilibrium effects of the excitation functions for the investigated reactions are calculated according to the Weisskopf–Ewing model. Also in the present work, the (n,α) reaction cross sections have calculated by using evaluated empirical formulas developed by Tel et al. at 14–15 MeV energy. The calculated results have been discussed and compared with the available experimental data and found agreement with each other.

Role of energy cost in the yield of cold ternary fission of 252 Cf

The energy costs in the cold ternary fission of 252Cf for various light charged particle emission are calculated by including Wong’s correction for Coulomb potential. Energy cost is found to be higher in cold fission than in normal fission. It is found that energy cost always increases with decrease in experimental yield in all the light charged particle emissions. The higher ground state deformation of the fragments, the odd–even effect and the enhanced yield in the octupole region observed in cold fission are found to be consistent with the concept of energy cost.

Isospin observables from fragment energy spectra

The energy spectra of light charged particles and intermediate mass fragments from ${}^{112}\mathrm{Sn}+{}^{112}\mathrm{Sn}$ and ${}^{124}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ collisions at an incident energy of $E/A=50$ MeV have been measured with a large array of silicon strip detectors. We used charged-particle multiplicities detected in an array with nearly 4$\ensuremath{\pi}$ coverage to select data from the central collision events. We study isospin observables analogous to ratios of neutron and proton spectra, including double ratios and yield ratios of triton/${}^{3}$He and of asymmetries constructed from fragments with $Z=3$--8. Using the energy spectra, we can construct these observables as functions of kinetic energy. Most of the fragment asymmetry observables have a large sensitivity to sequential decays.

Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions

The two-proton removal reaction from ${}^{28}$Mg projectiles has been studied at 93 MeV/u. First coincidence measurements of the heavy ${}^{26}$Ne projectile residues, the removed protons, and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations based on the use of eikonal dynamics and $sd$-shell-model structure amplitudes.

SP-0021 TREATMENT PLANNING: INTEGRATING ROBUSTNESS IN OPTIMIZATION

irradiation. Due to the nuclear reaction characteristics, most of the resulting light charged particles have a larger range than the primaries, i.e. they can leave the patient, whereas the primary projectiles are completely stopped inside. Measuring the trajectories of the escaped particles and calculating their intersection points with the pencil beam results in a depth distribution of the nuclear reaction probability, which is correlated to the primary particle range. It should be noticed that for prompt gamma-ray as well as charged particle imaging proof-of-principle experiments have been performed. Clinically applicable systems are not available at present. However, their development is in progress at several institutions worldwide.

Multi-intruder structures in34P

The available experimental information on ${}^{34}$P has been greatly increased through the analysis of $\ensuremath{\gamma}$ decays in coincidence with protons from the interaction of an ${}^{18}$O beam at 24 MeV with an ${}^{18}$O target. Light charged particles from the reaction were detected with Microball, and multiple $\ensuremath{\gamma}$-ray coincidences with Gammasphere. Many observed $\ensuremath{\gamma}$ transitions have been identified and placed in the level scheme. Additionally, for most states, spins have been assigned based on measured $\ensuremath{\gamma}$-ray angular distributions while parities were inferred from lifetimes determined through Doppler-broadened line-shape analysis. Most of the states observed have been interpreted in terms of shell-model calculations using the WBP-a and SDPF-NR interactions having one particle in the $0{f}_{7/2}$ or $1{p}_{3/2}$ orbital. The two calculations agree almost equally well with the data resulting in root-mean-square differences of about 200 keV. However, a few high-lying states observed with long lifetimes challenge current calculations. Two of these may be associated with stretched $\ensuremath{\pi}{f}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{f}_{7/2}$ states, but the calculations overpredict their energies by 2--3 MeV. Furthermore, a long-lived 7919-keV state is established for which no explanation is available at present.

Identification of light particles by means of pulse shape analysis with silicon detector at low energy

Particle separation of 1,2,3H at energy of 3MeV has been achieved by digital pule shape analysis (DPSA) for particles fully stopped in a 500μm silicon detector. Light charged particles were produced in a nuclear reaction induced by a 34MeV beam of 7Li impinging on a 12C target. Proton–deuterium identification has also been observed at 2MeV using mono-energetic beams. A 20keV resolution neutron transmutation doped (NTD) silicon detector was employed in a low-field injection setup. The method uses the parameters obtained both from the charge and current pulses generated by a high bandwidth charge sensitive preamplifier. The simplicity of the electronic chain plus the experimental conditions allowed the team to work with very low noise achieving signal-to-noise ratio (SNR) at values greater than 10.

Sensitivity of neutron to proton ratio toward the high density behavior of the symmetry energy in heavy-ion collisions

The symmetry energy at sub- and supra-saturation densities has great importance for understanding the exact nature of asymmetric nuclear matter as well as neutron stars, but it is poorly known, especially at supra-saturation densities. We will demonstrate here whether or not the neutron-to-proton ratios from different kinds of fragments can determine the supra-saturation behavior of the symmetry energy. For this purpose, a series of Sn isotopes were simulated at different incident energies using the isospin quantum molecular dynamics (IQMD) model with either a soft or a stiff symmetry energy. It is found that the single neutron-to-proton ratio from free nucleons as well as Light Charged Particles (LCPs) is sensitive to the symmetry energy, incident energy, and isospin asymmetry of the system. However, with the double neutron-to-proton ratio, this is true only for the free nucleons. It is possible to study the high-density behavior of symmetry energy by using the neutron-to-proton ratio from free nucleons.

Optimal Application of the Betatron

The betatron is a very important instrument to impart high energy to light charged particles such as electrons. In this paper, we propose two optimal ideas to improve the efficiency of the original betatron application. With our approaches, the efficiency of betatron could be improved to nearly 100%. And the current density of the electron beam can also be improved obviously.

Clustering effects in48Cr composite nuclei produced via24Mg +24Mg reaction

In the framework of studying clustering e ects in N=Z light nuclei, an ex- periment was carried out to get information on the properties of the 48 Cr composite nuclei produced via the 24 Mg + 24 Mg reaction. In particular, the study regards the 48 Cr at 60 MeV of excitation energy where a resonance with a narrow width (170 KeV) has been found by measuring the elastic and anelastic channels. To determine the deformation of this state, evaporative Light Charged Particles (LCP) are measured and compared to the Statistical Model (SM) predictions, which are very sensitive to nuclear deformation. The experiment was performed at LNL using the 8 LP apparatus to select LCPs and a Parallel Plate Avalanche Counter (PPAC) system to detect the Evaporation Residues (ER). Pre- liminary results on the measurements of ER LCP and LCP LCP angular correlations are presented which indicate the presence of a very large deformation.The analysis will proceed with the extraction of the LCP energy spectra and with the angular correlations for high multiplicity channels to determine the deformation.

Description of light charged particle multiplicities in the framework of dinuclear system model

In the framework of dinuclear system (DNS) model we calculate the light charged particle (LCP) multiplicities produced in fusion and quasifission reactions and their kinetic energy spectra. Calculations indicate that with increasing bombarding energy the ratio of LCP multiplicity from fragments M FF to corresponding LCP multiplicity from compound nucleus (CN) M CN strongly increases.

Asymmetric Fission in the78Kr+40Ca reactions at 5.5 MeV/nucleon

The cross section, kinetic energy distribution and angular distribution of frag- ments with atomic number 3 Z 28 emitted in the reaction 78 Kr + 40 Ca at the bombard- ing energy of 5.5 MeV/nucleon and coincidence between light charged particles and frag- ments were measured by means of the 4 -INDRA array to study the decay mechanism of medium mass excited nucleus. Global features indicate a high degree of relaxation and are compatible with a binary fission from compound nucleus. The mean value of the kinetic energy distributions of fragments indicates dominance of Coulomb interaction, while the width of the distribution signals large fluctuations. Inclusive cross-section distributions of fragments with charge 3 Z 28 are bell-shaped and a strong even-odd-staggering (o-e- s) is observed for 3 Z 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical model describing the decay of compound nuclei by emission of light particles and fragments. Calculations as- suming spherical fission fragments and finite-range liquid drop fission barriers are not able to explain the experimental features. Attempts have been made to improve the agreement with experimental data. The analysis indicates the strong influence of the shape parame- terization of the potential energy surface in describing the fission process of intermediate mass compound nuclei.

Processes in massive nuclei reactions and the way to complete fusion of reactants. What perspectives for the synthesis of heavier superheavy elements?

By using the dinuclear system (DNS) model we determine the capture of reactants at the first stage of reaction, the competition between the DNS decay by the quasifission (QF) and the complete fusion (CF) process up to formation of the compound nucleus (CN) having compact shape. Further evolution of the CN is considered as its fission into two fragments or formation of evaporation residues (ER) by its cooling after emission of neutrons or/and charged light particles. Disappearance of the CN fission barrier due to its fast rotation leads to the fast fission (FF) by formation of fissionlike fragments. The results of calculations for the mass symmetric 136 Xe+ 136 Xe reaction, almost mass symmetric 108 Mo+ 144 Ba reaction, and mass asymmetric like 24 Mg+ 238 U and 34 S+ 248 Cm reactions are discussed. The fusion probability P CN calculated for many massive nuclei reactions leading to formation of superheavy nuclei have been analyzed. The reactions which can lead in perspective to the synthesis of superheavy elements in the Z = 120 − 126 range and, eventually, also to heaviest nuclei, are discussed.

A reevaluation of radiation damage cross sections

In the past years, INC models simulating spallation reactions have been undergoing considerable development, and their results are more and more scrutinized by experimental work. Recently, IAEA has led an international collaboration to independently benchmark various INC models. The preliminary results of this collaboration indicate that while the Bertini model performs well in predicting neutron production, it greatly lacks the capability to predict light charged particle emission compared to CEM’03 and INCL. This drives us to completely reevaluate the NCSU radiation damage cross section database, which was developed 7years ago using a combination of CEM2k and Bertini models for benchmarking experimental data. The reevaluation currently involves just the CEM’03 model in MCNPX due our limited code access. Our preliminary results are in reasonable agreement with the NCSU database for the helium and hydrogen production cross section, but there are obvious differences for the displacement cross section. Such similarities and differences are being investigated, and the validity of the CEM’03 model for predicting radiation damage to materials is being examined. The reevaluated radiation damage cross sections presented in this paper are used in calculating radiation damage to the target assembly currently running at SNS, and the results are compared with those of previous studies.

Small Dosimeter based on Timepix device for International Space Station

The radiation environment in space is different, more complex and more intense than on Earth. Conventional devices and detection methods used nowadays do not allow to discriminate single particle types and the energy of the single particles. The Timepix detector is a position sensitive pixelated detector developed at CERN in a frame of the Medipix collaboration that provides capability to visualize tracks and measure energy of single particles. This information can be used for sorting the particles into different categories. It is possible to distinguish light charged particles such as electrons or heavy charged particles such as ions. Moreover, the Linear Energy Transfer (LET) for charged particles can be determined. Each category is assigned a quality factor corresponding to the energy a particle would deposit in the human tissue. By summing the dose of all particles an estimate of the dose rate can be calculated. For space dosimetry purposes a miniature device with the Timepix detector and a custom made integrated USB based readout interface has been constructed. The entire device has dimensions of a USB flash memory stick. The whole compact device is connected to a control PC and is operated continuously. The PC runs a software that controls data acquisition, adjusts the acquisition time adaptively according to the particle rate, analyzes the particle tracks, evaluates the deposited energy and the LET and visualizes in a simple display the estimated dose rate. The performance of the device will be tested during a mission on International Space Station planned towards the beginning of year 2012.