Precompound Models Research Articles

Estimation of production yield of 93mMo and other residues from a 7Li-induced reaction

The crux of the present work is to analyze the yield of the residues produced in the 7Li-induced reaction on 89Y target in the low energy range. The experimental yields of 93mMo, which is a significant product in the energy range considered, and other coproduced radionuclides, such as 92mNb, 89Zr, 91mY, and 90mY have been measured within 19–40 MeV energy, and are compared with the compound and pre-compound models in the framework of the statistical reaction model code EMPIRE. The maximum measured yield for 93mMo is 374 MBq/C at 31.3 MeV in a 3 mg/cm2 thick 89Y target corresponding to a cross-section of 396.8 ± 38.6 mb from the 89Y(7Li,3n)93mMo reaction. The model estimations well reproduce the experimental yields of 93mMo. The possible production of stable isotopes has also been estimated theoretically from the model over the experimental energy range. The reaction could be an alternative route for the production of no-carrier-added 93mMo radionuclide provided that the radionuclides are chemically separated from the bulk 89Y matrix.

Investigating the aberration found in 4.438 MeV 12C photo peak of the Geant4 simulated prompt gamma spectrum

The purpose of this study is to investigate the broad 4.438 MeV 12C photo-peak found in the Geant4 simulated prompt gamma spectrum from proton beam collision on a thin carbon target. The broad 4.438 MeV 12C peak has been reported in previous work using the AFRODITE clover detector performing an absolute comparison of measured and simulated prompt gamma production for a carbon target in the proton therapeutic range. The simulated prompt gamma spectrum was obtained for a 95 MeV proton beam collision on the carbon target by counting the emitted prompt gammas over a 4ˇ solid angle using a Geant4(v10.01.p3) cross-section code with the suggested physics list for inelastic scattering in the proton therapeutic range (binary cascade model). This result was compared to prompt gamma spectra from other Geant4 inelastic scattering physics models. First, the default inelastic cross-section data set (Geisha) was compared to the Tripathi data set, producing basically identical spectra, indicating that the cross-section data set has no bearing on the binary cascade inelastic scatter model. Second, comparisons of the precompound model using an exciton number of 1 and the Geisha cross-section data set provides a 4.438 MeV photo peak that is closer to the experimental result. The precompound model with an exciton number of 1 and the default (Geisha) cross-section data set significantly narrowed the 4.438 MeV photo peak, giving the peak that most closely resembled measured data.

Measurement of the cross section of the residues from the B11 -induced reaction on Y89 and Nb93 : Production of Ru97 and Rh101m

The heavy-ion induced reactions on intermediate mass targets are complex in nature, even at the low energies. To understand those nuclear reaction phenomena in detail, more experimental studies are required in a wide range of energy. Heavy-ion reactions were investigated by measuring production cross sections of the residues produced in the $^{11}$B-induced reactions on $^{89}$Y and $^{93}$Nb at low energies, near and above the barrier, and to check the effectiveness of the different nuclear models to explain them. Further, aim is also to optimize the production parameters of neutron deficient medically relevant $^{97}$Ru and $^{101m}$Rh radioisotopes produced in those reactions, respectively. The $^{11}$B-beam was allowed to impinge on $^{89}$Y and $^{93}$Nb foils supported by an aluminum catcher foil, arranged in a stack, in 27.5-58.7 and 30.6-62.3 MeV energy range, respectively. The $\gamma$-spectrometry was carried out after EOB to measure the activity of the radionuclides produced in each foil and cross sections were calculated. Measured cross-sectional data were analyzed in terms of compound and precompound model calculations. The measured cross sections of the residues showed good agreement with the model calculations based on the Hauser-Feshbach formulation and exciton model. A substantial preequilibrium contribution was noticed in the 3$n$ reaction channel in both the reactions. Theoretical estimations confirmed that major production yields are mostly contributed by the compound reaction process. Preequilibrium emissions contributed at the high energy tail of the 3$n$ channel for both the reactions. Moreover, an indirect signature of a direct reaction influence was also observed in the $^{90m}$Y production.

Experimental probe for the production ofRu97from theLi7+Nb93reaction: A study of precompound emissions

Background: Interaction of weakly bound heavy-ions with an intermediate or heavy target is not yet understood completely due to the scarcity of experimental data. In order to develop a clear understanding of breakup fusion or preequilibrium emission even at low energy range, 3--10 MeV/nucleon, more experimental investigations are necessary. Purpose: Study of reaction mechanisms involved in the weakly bound heavy-ion induced reaction, $^7$Li + $^{93}$Nb, at low energies by measuring the production cross sections of the residual radionuclides. Method: Natural niobium ($^{93}$Nb) foil, backed by aluminium (Al) catcher, arranged in a stack was bombarded by $^{7}$Li ions of 20-45 MeV energy. Activity of the residues produced in each $^{93}$Nb target was measured by off-line $\gamma$-ray spectrometry after the end of bombardment (EOB) and cross sections were calculated. Experimental cross sections were compared with those computed using compound and precompound models. Results: In general, measured excitation functions of all residues produced in $^{7}$Li + $^{93}$Nb reaction showed good agreement with the model calculations based on Hauser-Feshbach formalism and exciton model for compound and precompound processes, respectively. Significant preequilibrium emission of neutrons was observed at the relatively high energy tail of the excitation function of $^{97}$Ru. Conclusions: Preequilibrium process played an important role for the enhancement of cross-section in $xn$ reaction channel over the compound reaction mechanism at higher energies for $^{7}$Li + $^{93}$Nb reaction. Additionally, indirect evidence of incomplete or breakup fusion was also perceived.

Evaluation of proton inelastic reaction models in Geant4 for prompt gamma production during proton radiotherapy

During proton beam radiotherapy, discrete secondary prompt gamma rays are induced by inelastic nuclear reactions between protons and nuclei in the human body. In recent years, the Geant4 Monte Carlo toolkit has played an important role in the development of a device for real time dose range verification purposes using prompt gamma radiation. Unfortunately the default physics models in Geant4 do not reliably replicate the measured prompt gamma emission. Determining a suitable physics model for low energy proton inelastic interactions will boost the accuracy of prompt gamma simulations. Among the built-in physics models, we found that the precompound model with a modified initial exciton state of 2 (1 particle, 1 hole) produced more accurate discrete gamma lines from the most important elements found within the body such as 16O, 12C and 14N when comparing them with the available gamma production cross section data. Using the modified physics model, we investigated the prompt gamma spectra produced in a water phantom by a 200 MeV pencil beam of protons. The spectra were attained using a LaBr3 detector with a time-of-flight (TOF) window and BGO active shield to reduce the secondary neutron and gamma background. The simulations show that a 2 ns TOF window could reduce 99% of the secondary neutron flux hitting the detector. The results show that using both timing and active shielding can remove up to 85% of the background radiation which includes a 33% reduction by BGO subtraction.

Preequilibrium Emission of Light Fragments in Spallation Reactions

The ability to describe production of light fragments (LF) is important for many applications, such as cosmic-ray-induced single event upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams. The cascade-exciton model (CEM) and the Los Alamos version of the quark-gluon string model (LAQGSM) event generators in the LANL transport code MCNP6, describe quite well the spectra of fragments with sizes up to 4He across a broad range of target masses and incident energies (up to ∼ 5 GeV for CEM and up to ∼ 1 TeV/A for LAQGSM). However, they do not predict the high-energy tails of LF spectra heavier than 4He well. Most LF with energies above several tens of MeV are emitted during the precompound stage of a reaction. The current versions of our event generators do not account for precompound emission of LF larger than 4He. The aim of our work is to generalize the precompound model to include such processes, leading to increased predictive power of LF production. Extending the model in this way provides preliminary results that have much better agreement with experimental data.

Extension of PENELOPE to protons: Simulation of nuclear reactions and benchmark with Geant4

Describing the implementation of nuclear reactions in the extension of the Monte Carlo code (MC) PENELOPE to protons (PENH) and benchmarking with Geant4. PENH is based on mixed-simulation mechanics for both elastic and inelastic electromagnetic collisions (EM). The adopted differential cross sections for EM elastic collisions are calculated using the eikonal approximation with the Dirac-Hartree-Fock-Slater atomic potential. Cross sections for EM inelastic collisions are computed within the relativistic Born approximation, using the Sternheimer-Liljequist model of the generalized oscillator strength. Nuclear elastic and inelastic collisions were simulated using explicitly the scattering analysis interactive dialin database for (1)H and ICRU 63 data for (12)C, (14)N, (16)O, (31)P, and (40)Ca. Secondary protons, alphas, and deuterons were all simulated as protons, with the energy adapted to ensure consistent range. Prompt gamma emission can also be simulated upon user request. Simulations were performed in a water phantom with nuclear interactions switched off or on and integral depth-dose distributions were compared. Binary-cascade and precompound models were used for Geant4. Initial energies of 100 and 250 MeV were considered. For cases with no nuclear interactions simulated, additional simulations in a water phantom with tight resolution (1 mm in all directions) were performed with FLUKA. Finally, integral depth-dose distributions for a 250 MeV energy were computed with Geant4 and PENH in a homogeneous phantom with, first, ICRU striated muscle and, second, ICRU compact bone. For simulations with EM collisions only, integral depth-dose distributions were within 1%/1 mm for doses higher than 10% of the Bragg-peak dose. For central-axis depth-dose and lateral profiles in a phantom with tight resolution, there are significant deviations between Geant4 and PENH (up to 60%/1 cm for depth-dose distributions). The agreement is much better with FLUKA, with deviations within 3%/3 mm. When nuclear interactions were turned on, agreement (within 6% before the Bragg-peak) between PENH and Geant4 was consistent with uncertainties on nuclear models and cross sections, whatever the material simulated (water, muscle, or bone). A detailed and flexible description of nuclear reactions has been implemented in the PENH extension of PENELOPE to protons, which utilizes a mixed-simulation scheme for both elastic and inelastic EM collisions, analogous to the well-established algorithm for electrons/positrons. PENH is compatible with all current main programs that use PENELOPE as the MC engine. The nuclear model of PENH is realistic enough to give dose distributions in fair agreement with those computed by Geant4.

Activation cross-section measurement of deuteron induced reactions on cerium for biomedical applications and for development of reaction theory

In the frame of a systematic study of deuteron induced nuclear reactions on lanthanides we have measured the excitation functions on natural cerium for production of 142,139,138m,137Pr, 143,141,139,137m,137,135Ce and 140La up to 50MeV deuteron energy using the activation method with stacked-foil irradiation technique and high-resolution γ-ray spectrometry. The cross-sections of the investigated reactions were calculated using the modified pre-compound model codes ALICE-IPPE-D and EMPIRE-II-D. A comparison was made also with the data retrieved from the TENDL-2012 library, based on the latest version of the TALYS code system. The measured cross-section data are important for further improvement of nuclear reaction models and for practical applications in nuclear medicine and other labeling and activation studies.

OC-0438: Experimental validation of monte carlo pencil beam scanning model in heterogeneous media for proton therapy

Purpose/Objective To validate experimentally a GATE/GEANT4-based(G4) Monte Carlo (MC) model in heterogeneous media for dedicated pencil beam scanning in proton therapy. Comparisons between measurements and MC simulations using G4 and PENELOPE-proton are presented. A comparison against analytical modeling from commercial TPS is also investigated. This work evaluates the impact of heterogeneities on range prediction, beam shape and depth dose changes. Materials and Methods The MC model for pencil beam based on G4 has been validated in water and PMMA phantoms (Grevillot et al Phys. Med. Biol.(2011)) reproducing pristine Bragg peaks for a series of individual energies (from 100 to 226.7 MeV) with 0.7 mm range and 0.2 mm spot size accuracy. The same optical model was implemented in PENELOPE-proton. In order to validate the beam model in heterogeneous media, phantoms made of stacked slabs with different densities and known compositions were used. Two experimental test cases including solid water (SW), lung (LN-300) and bone (SB3) tissue-equivalent material were investigated. Depth-dose distributions for a monoenergetic single spot and 10x10cm² composite fields were measured using Gafchromic EBT3 films and the ionization chamber (IC) PPC05 in all configurations. To measure accurately the Bragg peak position, a stack of films of 2x2cm² was inserted in the last centimeter of the proton range. Results Figure 1 shows results for one heterogeneous configuration. All doses-to-medium were converted to dose to water using stopping power ratios. Dose distributions were arbitrarily normalized in the middle of the second SW region. Bragg peak positions are reproduced by MC simulations within 1mm in both configurations (Table 1). IC measurements, G4 (binary-cascade) and PENELOPE-proton simulations are within 2%/2 mm. Point-to-point mean difference of 1.2% is observed between G4 (precompound) and measurement in the first 15 cm of the phantom and increased to 7.2% after bone insert until 286.5mm depth. In lung and bone slabs, EBT3 films and G4 binary-cascade are inagreement within 0.77% while a mean point-to-point difference up to 1.26% is observed with G4 precompound model. The uncertainty (1σ) on EBT3 films was evaluated to be at 2.75% which included readout process and dose calibration against IC (TRS-398). A statistical uncertainty of 0.1% was achieved for MC simulations. Conclusions The Bragg peak position is predicted with 1mm precision for all MC simulations, even though ionization potential values for phantom slabs were calculated using classical additive rules. G4/GATE beam model reproduce depth-dose behavior of proton transport regarding both IC and EBT3 measurement in heterogeneities.

Recent Developments and Validation of Geant4 Hadronic Physics

In the past year several improvements in Geant4 hadronic physics code have been made, both for HEP and nuclear physics applications. We discuss the implications of these changes for physics simulation performance and user code. In this context several of the most-used codes will be covered briefly. These include the Fritiof (FTF) parton string model which has been extended to include antinucleon and antinucleus interactions with nuclei, the Bertinistyle cascade with its improved CPU performance and extension to include photon interactions, and the precompound and deexcitation models. We have recently released new models and databases for low energy neutrons, and the radioactive decay process has been improved with the addition of forbidden beta decays and better gamma spectra following internal conversion.As new and improved models become available, the number of tests and comparisons to data has increased. One of these is a validation of the parton string models against data from the MIPP experiment, which covers the largely untested range of 50 to 100 GeV. At the other extreme, a new stopped hadron validation will cover pions, kaons and antiprotons. These, and the ongoing simplified calorimeter studies, will be discussed briefly. We also discuss the increasing number of regularly performed validations, the demands they place on both software and users, and the automated validation system being developed to address them.

Improvements in the Geant4 Hadronic Physics

During the last five years, development of GEANT4 hadronic physics models has been driven largely by the anticipated turn-on of the LHC detectors and the subsequent comparison of new data with the simulated detector responses.Work has concentrated on three main areas: hadronic model improvement for high energy string models, intranuclear cascade models, precompound and de-excitation models, and elastic scattering which are currently used in the simulation of LHC experiments. These development are tested against a large collection of thin target data and dedicated test beam experiments using calorimeter prototypes. Salient improvements in physics and computing performance of these models will be discussed.

Geant4 hadronic physics for space radiation environment

Purpose: To test and to develop Geant4 (Geometry And Tracking version 4) Monte Carlo hadronic models with focus on applications in a space radiation environment.Materials and methods: The Monte Carlo simulations have been performed using the Geant4 toolkit. Binary (BIC), its extension for incident light ions (BIC-ion) and Bertini (BERT) cascades were used as main Monte Carlo generators. For comparisons purposes, some other models were tested too. The hadronic testing suite has been used as a primary tool for model development and validation against experimental data.Results: The Geant4 pre-compound (PRECO) and de-excitation (DEE) models were revised and improved. Proton, neutron, pion, and ion nuclear interactions were simulated with the recent version of Geant4 9.4 and were compared with experimental data from thin and thick target experiments.Conclusions: The Geant4 toolkit offers a large set of models allowing effective simulation of interactions of particles with matter. We have tested different Monte Carlo generators with our hadronic testing suite and accordingly we can propose an optimal configuration of Geant4 models for the simulation of the space radiation environment.

Excitation functions of α-particle induced reactions on enriched 123Sb and natSb for production of 124I

Excitation functions of (α,xn) reactions on 98.28% enriched (123)Sb and on (nat)Sb were measured from 9 to 40 MeV. The data could be described well in terms of statistical and precompound models using the code TALYS. The discrepancies in the literature data for the formation of (125)I and (126)I were solved. The nuclear reaction (123)Sb(α,3n)(124)I on an enriched target appears to be interesting for the production of (124)I (T(1/2)=4.18 d) over the energy range E(α)=42→32 MeV, its yield being 11.7 MBq/μAh. The levels of the radionuclidic impurities (125)I and (126)I amount to 1.8% and 0.6%, respectively. The use of (nat)Sb as target material for (124)I production is unsuitable due to the high level of (123)I impurity.

Evaluation of inelastic hadronic processes for 250 MeV proton interactions in tissue and iron using GEANT4

When high-energy protons interact in beam delivery systems and are stopped in patients, a fraction of beam will undergo nuclear interactions that release secondary particles, in particular, neutrons of different energies. The GEANT4 Monte Carlo Code was used to simulate the interaction of 250 MeV proton beam in tissue and iron to calculate the energy and angular distributions of generated protons, neutrons and photons, and thus provide H* (10), the ambient dose equivalent. A modular physics list by utilising electromagnetic interactions and hadronic interactions was constructed. Three different GEANT4 models that include the low-energy parameterisation, binary cascade and pre-compound model with Bertini cascade for proton inelastic interactions were compared. The findings suggest that the models play critical roles in terms of secondary particle generation. Further benchmarks are necessary to select the best model predicting a realistic scenario.

Progress in hadronic physics modelling in Geant4

Geant4 offers a set of models to simulate hadronic showers in calorimeters. Recent improvements to several models relevant to the modelling of hadronic showers are discussed. These include improved cross sections, a revision of the FTF model, the addition of quasi-elastic scattering to the QGS model, and enhancements in the nuclear precompound and de-excitation models. The validation of physics models against thin target experiments has been extended especially in the energy region 10 GeV and below. Examples of new validation results are shown.

GEANT4 MC simulation results of the MRPC for neutrons in the energy range of 10−10 MeV < En < 1.0 GeV

A Monte Carlo computer simulation program has been developed to investigate the neutron response of a multi-gap resistive plate chamber (MRPC). This simulation program is based on the GEANT4 software package developed at CERN. A proper physics list known as a quark–gluon string model with the pre-compound model (QGSP) and a complete geometrical configuration of the MRPC are inserted in this simulation package. Neutrons are simulated through the MRPC in an energy range from 10−10 MeV to 1.0 GeV. The simulation results obtained are presented and discussed. A comparison of the current simulation results obtained for a MRPC with the experimental results available at a few energy points for a double-gap RPC is also presented.

Non-convergence of Geant4 hadronic models for 10 and 30 MeV protons in 18O and 14N

We investigated Geant4 Monte Carlo simulation of protons interactions in 18O and 14N. With proton incident energies of 10 and 30 MeV, we compared the different Geant4 models available for proton inelastic collisions: the low-energy parameterisation, Bertini cascade and precompound models. The models produced different (1) combinations of secondary particles and (2) final states of secondary particles. The non-convergence suggests that the hadronic models, yet to be benchmarked for this energy range, are not ready for production-mode problem-solving.

Cross sections and isomeric cross-section ratios in the interactions of fast neutrons with isotopes of mercury

Excitation functions were measured for the reactions $^{196}\mathrm{Hg}$($n$, $2n)$$^{195}\mathrm{Hg}$${}^{m,g},$$^{198}\mathrm{Hg}$($n$, $2n)$$^{197}\mathrm{Hg}$${}^{m,g},$$^{204}\mathrm{Hg}$($n$, $2n)$$^{203}\mathrm{Hg}$,$^{198}\mathrm{Hg}$($n,p)$$^{198}\mathrm{Au}$${}^{g}$, and $^{199}\mathrm{Hg}$($n,p)$$^{199}\mathrm{Au}$ over the neutron energy range of 7.6--12.5 MeV. Quasimonoenergetic neutrons were produced via the $^{2}\mathrm{H}$($d,n)$$^{3}\mathrm{He}$ reaction using a deuterium gas target at the J\"ulich variable energy compact cyclotron CV 28. Use was made of the activation technique in combination with high-resolution, high-purity Ge detector $\ensuremath{\gamma}$-ray spectroscopy. All the data were measured for the first time over the investigated energy range. The transition from the present low-energy data to the literature data around 14 MeV is generally good. Nuclear model calculations using the codes STAPRE and EMPIRE-2.19, which employ the statistical and precompound model formalisms, were undertaken to describe the formation of both the isomeric and ground states of the products. The total reaction cross section of a particular channel is reproduced fairly well by the model calculations, with STAPRE giving slightly better results. Regarding the isomeric cross sections, the agreement between the experiment and theory is only in approximate terms. A description of the isomeric cross-section ratio by the model was possible only with a very low value of \ensuremath{\eta}, i.e., the ${\ensuremath{\Theta}}_{\text{eff}}$/${\ensuremath{\Theta}}_{\text{rig}}$ ratio.

Nuclear model calculations on proton and deuteron induced reactions on 122Te and 120Te with particular reference to the formation of the isomeric states 120m,gI

Nuclear model calculations were performed on (p, xn) reactions on 122Te and 120Te, and (d, xn) reactions on 120Te. The computer code used (STAPRE) incorporates statistical and precompound models as well as nuclear structure effects. The total cross-sections of (p, xn) and (d, xn) processes leading to the formation of the radioisotopes 119I, 120gI, 121I and 122I are described well by the calculations. The isomeric cross-section, however, is rather difficult to calculate. The yield of the high spin isomer ( 120mI) depends on the type of reaction involved and increases with the increasing projectile energy. From an analysis of the energy dependence of the isomeric cross-section ratio, the excitation energy of 120mI was deduced to be 550±50 keV and its spin and parity as 4 +. The experimental data reported earlier and the theoretical analysis presented in this work allow to define the optimum conditions for the production of the medically important β + emitter 120gI with enhanced confidence.

New precompound decay model: Angular distributions

A new Monte Carlo precompound decay model is used to calculate double-differential spectra using an approach based on conservation of linear momentum between an incident nucleon and the three quasiparticles activated in the collisions of the equilibration process. The angular distribution theory is presented as it is applied to the individual three-exciton cascades of the precompound model. The importance of multiple precompound decay beyond two nucleons per nucleus is illustrated for ${}^{90}$Zr$(p,xn)$ reactions for incident protons up to 256 MeV. These components are shown to be important for extending the useful range of the precompound approach to energies beyond 80 MeV. The contribution to nucleon spectra due to hole conversion processes is illustrated. We compare results of the formulation described with experimental angular distributions for ${}^{90}$Zr$(p,xn)$ reactions at incident energies of 45, 80, and 160 MeV, and for the ${}^{90}$Zr$(p,xp)$ reactions at incident energies of 80, 160, and 200 MeV. Additionally, ${}^{208}$Pb$(p,xn)$ spectra at 7.5\ifmmode^\circ\else\textdegree\fi{}, 30\ifmmode^\circ\else\textdegree\fi{}, 60\ifmmode^\circ\else\textdegree\fi{}, 120\ifmmode^\circ\else\textdegree\fi{}, and 150\ifmmode^\circ\else\textdegree\fi{} are compared with two experimental data sets for 256 MeV incident proton energy, and ${}^{90}$Zr$(p,xn)$ spectra at the same five angles are compared with predicted results for 256 MeV incident protons. At 256 MeV incident proton energy, the higher energy emission spectra are seriously overpredicted at 60\ifmmode^\circ\else\textdegree\fi{}. All other results are reproduced quite well, including back-angle yields. The quasielastic peak measured at 7.5\ifmmode^\circ\else\textdegree\fi{} at 256 MeV incident proton energy is shown to be in quite reasonable agreement with experimental results.