Gamma-ray Production Cross Sections Research Articles

New γ-ray production cross sections for the 4.439 and 6.129 MeV lines of 12C and 16O. Astrophysical implications

Gamma-ray line production cross sections from nuclear reactions induced by 30 - 200 MeV protons on natC and Mylar targets have been measured at the SSC facility of iThemba LABS. Results for the 4.439 and 6.129 MeV prominent lines of 12C and 16O of astrophysical concern are reported and discussed.

Potential neutron-induced γ -ray background on natural tellurium relevant to Te130 0νββ decay searches at the CUORE and SNO+ detectors

Gamma-ray production cross-section data have been obtained for the inelastic neutron scattering reactions $^{126,128,130}\mathrm{Te}(n,{n}^{\ensuremath{'}}\ensuremath{\gamma})$ at five neutron energies between 3.6 and 10 MeV. We report data for the $\ensuremath{\gamma}$-ray energy region relevant to $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay of $^{130}\mathrm{Te}$ with a ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}$ value of 2527.515 keV, assuming natural-abundance tellurium, as used at CUORE and $\mathrm{SNO}+$. The natural abundance of $^{130}\mathrm{Te}$, $^{128}\mathrm{Te}$, and $^{126}\mathrm{Te}$ is 34%, 32%, and 19%, respectively. For CUORE the $\ensuremath{\gamma}$-ray cascades from the excited state in $^{130}\mathrm{Te}$ at 2527.06 keV and in $^{126}\mathrm{Te}$ at 2533.85 keV are of concern. For $\mathrm{SNO}+$, accounting for its inferior energy resolution, an additional four levels are important in $^{130}\mathrm{Te}$, an additional nine levels in $^{128}\mathrm{Te}$, and an additional eight levels in $^{126}\mathrm{Te}$. Of these, we report neutron-induced $\ensuremath{\gamma}$-ray production cross sections for the strongest transitions: the 2581.15 keV level in $^{130}\mathrm{Te}$, the 2494.20, 2508.06, and 2630.14 keV levels in $^{128}\mathrm{Te}$, and the 2496.83 and 2585.46 keV level in $^{126}\mathrm{Te}$. The largest cross-section values were found for cascade $\ensuremath{\gamma}$-ray transitions to the ground state, while direct transitions to the ground state are very weak and were not observed in the present work. Both the CUORE and $\mathrm{SNO}+$ detectors, however, may not be able to distinguish between cascade transitions and direct transitions to the ground state, making the neutron-induced excitation of the 2527.06 keV state of $^{130}\mathrm{Te}$ in particular a potential problem for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay searches of $^{130}\mathrm{Te}$, because it matches its ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}$ value.

Measurement and analysis of nuclear γ -ray production cross sections in proton interactions with Mg, Si, and Fe nuclei abundant in astrophysical sites over the incident energy range E=30–66 MeV

Gamma-ray production cross section excitation functions have been measured for $30$, $42$, $54$ and $66$ MeV proton beams accelerated onto targets of astrophysical interest, $^{nat}$C, C + O (Mylar), $^{nat}$Mg, $^{nat}$Si and $^{56}$Fe, at the Sector Separated Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with 8 Compton suppressed HPGe clover detectors was used to record $\gamma$-ray data. For known, intense $\gamma$-ray lines the previously reported experimental data measured up to $E_{p}\simeq$ $25$ MeV at the Washington and Orsay tandem accelerators were extended to higher proton energies. Our experimental data for the last 3 targets are reported here and discussed with respect to previous data and the Murphy \textit{et al.} compilation [ApJS 183, 142 (2009)], as well as to predictions of the nuclear reaction code TALYS. The overall agreement between theory and experiment obtained in first-approach calculations using default input parameters of TALYS has been appreciably improved by using modified optical model potential (OMP), deformation, and level density parameters. The OMP parameters have been extracted from theoretical fits to available experimental elastic/inelastic nucleon scattering angular distribution data by means of the coupled-channels reaction code OPTMAN. Experimental data for several new $\gamma$-ray lines are also reported and discussed. The astrophysical implications of our results are emphasised.

Proton induced differential cross sections on 14N and 28Si from 3 to 4 MeV

In this work commercially available self-supporting thin silicon-nitride films were applied to measure the differential cross sections for the reactions 28Si(p,p′γ)28Si (Eγ = 1779 keV) and 14N(p,p′γ)14N (Eγ = 2313 keV) in the proton energy range of 3–4 MeV. For an additional validation of the data, the cross section from the present work and from the literature were integrated and compared to experimental thick target yields. Gamma-rays were detected simultaneously with backscattered particles using a HPGe detector at 55° and an ion implanted Si detector at 135° with respect to the beam direction. As a by-product, differential gamma-ray and particle production cross sections were measured for the first time in the 29Si(p,p′γ)29Si (Eγ = 1273 keV) reaction at 55°, as well as in the natN(p,po)natN, natSi(p,po)natSi and 28Si(p,p1)28Si elastic and inelastic scatterings at 135° from 3 to 4 MeV proton energies.

Characterizing near-surface elemental layering on Mars using gamma-ray spectroscopy: A proof-of-principle experiment

Abstract Gamma-ray spectroscopy investigations characterize the chemical composition of planetary surfaces by measuring element-characteristic gamma rays with energies of ∼100 keV to ∼9 MeV. Over this energy range, the mean free path of a gamma ray varies from about 1 to 25 cm, therefore gamma-ray measurements sample subsurface composition. Many elements emit gamma rays at multiple, often widely spaced energies, so gamma-ray measurements can in principle also be used to identify depth-dependent variations in subsurface composition. We report results from laboratory measurements and radiation transport modeling designed to demonstrate this capability. The laboratory measurements verified the presence of depth-dependent gamma-ray signatures, and were then used to benchmark radiation transport simulations that were used to model realistic Mars-like scenarios. The models indicate that compositionally distinct subsurface deposits, buried to depths of ∼80 cm (125 g/cm2), can be identified using gamma-ray measurements. Going beyond identification to characterization (burial depth, relative composition of the layers) of the deposits requires knowledge of the vertical and horizontal variability in the water content of the near-surface surface materials, the local Galactic Cosmic Ray environment (magnitude and energy distribution), the depth-dependent neutron flux, gamma-ray production cross sections, and knowledge of the composition and column density of the atmosphere. The results of our experiments and models provided a basis for examining the utility of using orbiter- and lander-based gamma-ray measurements to identify subsurface deposits on Mars.

Measurement of gamma-ray production cross sections in Li and F induced by protons from 810 to 3700 keV

Differential cross sections for the reaction channels 7Li(p,nγ1-0)7Be (Eγ=429keV), 7Li(p,pγ1-0) (Eγ=478keV), 19F(p,pγ1-0)19F (Eγ=110keV), 19F(p,pγ2-0)19F (Eγ=197keV) have been measured in the proton energy range 810–3700keV, with an energy step of 10keV. The reactions channels 19F(p,pγ3-1)19F (Eγ=1236keV), 19F(p,pγ4-1)19F (Eγ=1349keV), 19F(p,pγ5-2)19F (Eγ=1357keV) have also been investigated in the proton energy range 1915–3225keV. The experimental set-up, the uncertainty budget, the comparison with other data and the progress assured by new data in the analytical use of standard-less Particle Induced Gamma-ray Emission (PIGE) are discussed.

Deuteron nuclear data for the design of accelerator-based neutron sources: Measurement, model analysis, evaluation, and application

A comprehensive research program on deuteron nuclear data motivated by development of accelerator-based neutron sources is being executed. It is composed of measurements of neutron and gamma-ray yields and production cross sections, modelling of deuteron-induced reactions and code development, nuclear data evaluation and benchmark test, and its application to medical radioisotopes production. The goal of this program is to develop a state-of-the-art deuteron nuclear data library up to 200 MeV which will be useful for the design of future (d ,xn ) neutron sources. The current status and future plan are reviewed.

The evaluation of experimental data in fast range for n + 56Fe(n,inl)

Iron is one of the five materials selected for evaluation within the pilot international evaluation project CIELO. Analysis of experimental data for n+56 Fe reaction is the basis for constraining theoretical calculations and eventual creation of the evaluated file. The detail analysis was performed for inelastic cross sections of neutron induced reactions with 56 Fe in the fast range up to 20 MeV where there are significant differences among the main evaluated libraries, mainly caused by the different inelastic scattering cross section measurements. Gamma-ray production cross sections provide a way to gain experimental information about the inelastic cross section. Large discrepancies between experimental data for the 847-keV gamma ray produced in the 56 Fe(n,n1 'γ) reaction were analyzed. In addition, experimental data for elastic scattering cross section between 9.41∼11 MeV were used to deduce the inelastic cross section from the unitarity constrain.

Proton induced gamma-ray production cross sections and thick-target yields for boron, nitrogen and silicon

The excitation functions for the reactions 14N(p,p′γ)14N, 28Si(p,p′γ)28Si and 29Si(p,p′γ)29Si were measured at an angle of 55° by bombarding a thin Si3N4 target with protons in the energy range of 3.6–6.9MeV. The deduced γ-ray production cross section data is compared with available literature data relevant for ion beam analytical work. Thick-target γ-ray yields for boron, nitrogen and silicon were measured at 4.0, 4.5, 5.0, 5.5, 6.0 and 6.5MeV proton energies utilizing thick BN and Si3N4 targets. The measured yield values are put together with available yield data found in the literature. The experimental yield data has been used to cross-check the γ-ray production cross section values by comparing them with calculated thick-target yields deduced from the present and literature experimental excitation curves. All values were found to be in reasonable agreement taking into account the experimental uncertainties.

Measurement of gamma-ray production cross sections for nuclear reactions 14N(d,pγ)15N and 28Si(d,pγ)29Si

In this work the differential cross sections for gamma-ray emission from the 14N(d,pγ)15N (Eγ=1885, 2297, 7299 and 8310keV) and from the 28Si(d,pγ)29Si (Eγ=1273, 2028, 2426 and 4934keV) were measured simultaneously with the 14N(d,p4,5,6,7)15N differential cross sections and 14N(d,d)14N elastic scattering cross section using a HPGe detector at 55° and an ion implanted Si detector at 135° with respect to the beam direction in the deuteron energy range 0.65–2.0MeV. The target was a thin silicon-nitride film. Gamma-ray angular distribution measurements were performed to determine the possible anisotropy of the gamma-ray emission, and the measured cross section values were converted into total gamma-ray producing cross sections for most of the gamma-ray emissions. The average uncertainties of nitrogen and silicon gamma-ray production cross sections are 5% and 12%, respectively and 8% concerning the particle production cross section of natN(d,d0)natN and 14N(d,p4,5,6,7)15N reactions.

PIGE: A Useful Technique for the Study of Innovative Energy Related Materials. Technical Note on the Measurement of Gamma-ray Production Cross Sections

Particle induced gamma-rays are used more and more in materials quantitative characterization with ion beams, being absolutely competitive to other techniques, when low Z elements are involved and when dynamic processes are produced and monitored. Energy production involves such kind of materials, whose composition needs to be known and controlled under diverse and sometimes extreme conditions. This paper reviews some technical aspects associated with the knowledge of production cross sections, which is fundamental to any quantitative analysis, and the use of gamma detectors like their absolute efficiency.

GAMMA-RAY OBSERVATIONS OF THE ORION MOLECULAR CLOUDS WITH THEFERMILARGE AREA TELESCOPE

We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between \sim100 MeV and \sim100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to \sim10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity integrated CO intensity (WCO) at a 1{\deg} \times1{\deg} pixel level. The correlation is found to be linear over a WCO range of ~10 fold when divided in 3 regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The Wco-to-mass conversion factor, Xco, is found to be \sim2.3\times10^20 cm-2(K km s-1)-1 for the high-longitude part of Orion A (l > 212{\deg}), \sim1.7 times higher than \sim1.3 \times 10^20 found for the rest of Orion A and B. We interpret the apparent high Xco in the high-longitude region of Orion A in the light of recent works proposing a non-linear relation between H2 and CO densities in the diffuse molecular gas. Wco decreases faster than the H2 column density in the region making the gas "darker" to Wco.

Data Acquisition and Analysis of the UNCOSS Underwater Explosive Neutron Sensor

The purpose of the FP7 UNCOSS project (Underwater Coastal Sea Surveyor, http://www.uncoss-project.org) is to develop a neutron-based underwater explosive sensor to detect unexploded ordnance lying on the sea bottom. The Associated Particle Technique is used to focus the inspection on a suspicious object located by optical and electromagnetic sensors and to determine if there is an explosive charge inside. This paper presents the data acquisition electronics and data analysis software which have been developed for this project. A field programmable gate array that digitizes and processes the signal allows to perform precise time-of-flight and gamma-ray energy measurements. The gamma-ray spectra are unfolded into pure elemental count proportions, mainly C, N, O, Fe, Al, Si, and Ca. The C, N, and O count fractions are converted into chemical proportions, taking into account the gamma-ray production cross sections, as well as neutron and photon attenuation in the different shields between the ROV (Remotely Operated Vehicle) and the explosive, such as the explosive iron shell, seawater, and ROV envelop. A two-dimensional (2D) barycentic representation of the C, N, and O proportions is built from their chemical ratios, and a 2D likelihood map is built from the associated statistical and systematic uncertainties. The threat level is evaluated from the best matching materials of a database including explosives.

Partialγ-ray production cross sections for (n,xnγ) reactions in natural argon at 1–30 MeV

Background: Neutron-induced backgrounds are a significant concern for experiments that require extremely low levels of radioactive backgrounds such as direct dark matter searches and neutrinoless double-beta decay experiments. Unmeasured neutron scattering cross sections are often accounted for incorrectly in Monte Carlo simulations. Purpose: Determine partial gamma-ray production cross sections for (n,xng) reactions in natural argon for incident neutron energies between 1 and 30 MeV. Methods: The broad spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used used for the measurement. Neutron energies were determined using time-of-flight and resulting gamma rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE). Results: Partial gamma-ray cross sections were measured for six excited states in Ar-40 and two excited states in Ar-39. Measured (n,xng) cross sections were compared to the TALYS and CoH3 nuclear reaction codes. Conclusions: These new measurements will help to identify potential backgrounds in neutrinoless double-beta decay and dark matter experiments that use argon as a detection medium or shielding. The measurements will also aid in the identification of neutron interactions in these experiments through the detection of gamma rays produced by (n,xng) reactions.

Exact nuclear data uncertainty propagation for fusion neutronics calculations

Recently, we have presented an exact method (now called “Total Monte Carlo”) to propagate uncertainties of fundamental nuclear physics experiments, models and parameters to different types of criticality-safety benchmarks. We now show that such exact uncertainty calculations are directly relevant to the optimal and safe design of fusion reactors by applying this methodology to a series of fusion shielding benchmarks, namely those connected to the Oktavian, Fusion Neutronics Source and LLNL Pulsed Sphere experiments. Uncertainties on neutron and gamma leakage fluxes for 13 shielding benchmarks are obtained, in the mass range from natMg to natW. Uncertainties for cross-sections, angular distributions, single- and double-differential emission spectra, and gamma-ray production cross-sections are considered in this uncertainty propagation scheme.

Determination of new k0 values for prompt gamma activation analysis at Budapest

A series of measurements were carried out at the PGAA facilities of the Budapest Research Reactor and at the FRM-II, Garching, Germany, to re-determine the k 0 values and the partial gamma-ray production cross-sections of prompt gamma lines for 19 elements. Different stoichiometric compounds and water solutions were irradiated in cold neutron beams. The new values are compared with the old ones measured at the Budapest facility and others in the literature.

Measurement of partial gamma-ray production cross-sections and k0-factors for radionuclides with chopped-beam PGAA—Part II

As a continuation of our previously reported experiments, the partial gamma-ray production cross-sections ( σ γ) and k 0-factors of 12 short- and medium-lived radionuclides were determined using a chopped beam of cold neutrons. This technique avoids several problems associated with epithermal activation, sample transportation and dead-time effects in neutron activation analysis (NAA) measurements. Our k 0-values were determined with internal standardization, using stoichiometric compounds or water solutions of known compositions.

Recent developments of prompt gamma activation analysis at Budapest

The PGAA facility at the Budapest Research Reactor has been continually upgraded and developed since its start-up in 1996, as a result of which its performance has improved considerably. The installation of the cold neutron source, the partial change to supermirror neutron guides and their realignment increased the flux by almost two orders of magnitude. The data acquisition has been modernized as well; digital spectrometers were tested and implemented in novel forms of gamma-ray spectrum collection. This year a higher-efficiency HPGe detector and a new data acquisition module were put into operation. Most recently all the neutron guides were changed to supermirror-coated ones to further increase the neutron flux. The improved evaluation software makes possible a more reliable elemental analysis of the samples. In this progress report these developments are critically reviewed. The characteristics of the latest system are also described. It is the first time that a set of new partial gamma-ray production cross sections are presented, which are based on the new intensity values of 14N(n,γ)15N calibration standard.

Gamma-Ray Production Cross Sections in Multiple Channels for Neutron-Induced Reaction on 48Ti for En = 1 to 200 MeV

Prompt γ-ray production cross sections were measured on a 48Ti sample for incident neutron energies from 1 to 200 MeV. Partial γ-ray cross sections for transitions in 45-48Ti, 45-48Sc, and 43-45Ca were determined. The observation of about 130 transitions from 11 different isotopes in the present work provides a demanding test of reaction model calculations, and is the first study in this mass region to extract partial γ-ray cross sections for many different reaction channels over a wide range of incident neutron energies. The neutrons were produced by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center/Weapons Neutron Research facility. The prompt-reaction γ rays were detected with the large-scale Compton-suppressed GErmanium Array for Neutron Induced Excitations (GEANIE). Event neutron energies were determined by the time-of-flight technique. The γ-ray excitation functions were converted to partial γ-ray cross sections and then compared with model calculations using the enhanced GNASH reaction code. Compound nuclear, preequilibrium emission, and direct reaction mechanisms are included. Overall, the model calculations of the partial γ-ray cross sections are in good agreement with measured values.

Data acquisition with a fast digitizer for large volume HPGe detectors

A 12-bits and 420 MSample/s waveform digitizer was used with large volume High Purity Germanium (HPGe) detectors for measurements of gamma-ray production cross-section from inelastic neutron scattering. For these time-of-flight measurements at the GELINA white neutron source, the use of a fast digitizer significantly increases the efficiency compared with a conventional data acquisition system. First, the pulse processing time required to obtain the amplitude with high resolution is significantly reduced so that pulse pile-up with the prompt gamma-burst is eliminated for neutron-induced events. Second, an improved time response is obtained for which the amplitude and rise time dependence is strongly reduced compared to that of a conventional constant fraction discriminator. Excellent energy and time resolution is obtained with algorithms suitable for on-line signal processing, so that data storage is under control. Bench tests are presented that compare methods of signal processing. For the best method, the data acquisition system based on the fast digitizer was tested during measurements of gamma production cross-sections for Pb 206 and Pb 208 . A direct comparison was made with results obtained with conventional electronics operated in parallel.