Gamma-ray Yields Research Articles

Li-glass detector response study with a 252Cf source for low-energy prompt fission neutrons

Prompt-fission-neutron spectra for neutron-induced fission reactions on uranium and plutonium isotopes are important for nuclear applications. We have used 6Li-glass scintillation detectors to measure outgoing neutron energies in the range from 10keV to 1MeV, where there is currently large uncertainty in nuclear data. To better understand the response of 6Li-glass detectors in this energy range, measurements of well-known spontaneous-fission neutrons from a 252Cf source were done in the neutron-beam flight path. Results were compared with Monte Carlo simulations and they show good agreement. Similar measurements with a 7Li-glass detector were used to assess gamma-ray background yields.

Alpha particle induced gamma yields in uranium hexafluoride

Fluorine has a relatively large (α,n) production cross-section in the MeV range, the energy range of interest for special nuclear materials. In the uranium fuel cycle enriched UF6 in particular is a reasonably prolific source of (α,n) neutrons because along with 235U, 234U becomes enriched and it has a relatively short half-life. This enables the mass content of storage cylinders containing UF6 to be verified by neutron counting methods.In association with such measurements high resolution gamma-ray spectrometry (HRGS) measurements using a high-purity Ge detector are often undertaken to determine the 235U enrichment based off the intensity of the direct 186keV line. The specific (α,n) neutron production, neutrons per second per gram of U, is sensitive to the relative isotopic composition, particularly the 234U concentration, and the traditional gross neutron counting approach is needed to quantitatively interpret the data.In addition to F(α,n) neutrons, α-induced reaction γ-rays are generated, notably at 110, 197, 582, 891, 1236 and 1275keV. If one could observe 19F(α,xγ) gamma-lines in the HRGS spectra the thought was that perhaps the α-activity could be estimated directly, and in turn the 234U abundance obtained. For example, by utilizing the ratio of the detected 197–186keV full energy peaks. However, until now there has been no readily available estimate of the expected strength of the reaction gamma-rays nor any serious consideration as to whether they might be diagnostic or not.In this work we compute the thick target yields of the chief reaction gamma-rays in UF6 using published thin target data. Comparisons are made to the neutron production rates to obtain γ/n estimates, and also to the 235U decay line at 186keV which we take as a fiducial line. It is shown that the reaction gamma-rays are produced but are far too weak for practical safeguards purposes.Now that the underlying numerical data is readily available however, it can be used to support neutron and gamma production calculations in other fluorine compounds, for example impure plutonium reference materials where fluorine may be present only at the parts per million by weight level yet still present a serious nuisance addition to the neutron production rate.

Regression analysis for a bottom-up approach to analyzing semi-prompt fission gamma yields

We present an empirical model that describes the yield of gamma rays emitted by fission in the time interval from 20 to 958ns following a fission event. The analysis is based on experimental data from neutron-induced fission of 235U and 239Pu. The model is devised by first using regression analysis to identify likely patterns in the data and to choose plausible fitting functions. We provide statistical and physical arguments in support of time and energy independence. The intensity of the emitted gamma rays can be described as a bivariate distribution that is the product of independent variates for energy and time. We test several plausible distribution families for the energy and time variates and use maximum likelihood and minimum χ2 to estimate distribution parameters. Because of the uncertainty in the experimental data, multiple combinations of variate pairs give rise to a surface that plausibly well fits the observations well. The best-fit variate turns out to be lognormal in energy and F in time. The findings illustrated in this paper can be used to simulate gamma ray de-excitation from fission in Monte Carlo codes.

Special nuclear material detection with a mobile multi-detector system

The detection of special nuclear material has been studied with a mobile inspection system used both as a high sensitivity passive neutron/gamma spectroscopic tool and as an active inspection device using tagged neutrons. The detection of plutonium samples seems to be possible with passive interrogation, even for small samples, thanks to the yield of gamma ray and neutrons. Moreover the gamma ray spectrum shows clear signatures related to 239Pu. The passive detection of uranium is much more difficult because of the low neutron yield and of the easiness of shielding the gamma ray yield of highly enriched U samples. However, we show that active interrogation with tagged neutrons is able to provide signatures for the discrimination of uranium against other heavy metals.

Electromagnetic properties of vibrational bands in 170Er

Excited states of the nucleus Er-170 have been studied by Coulomb excitation using the GASP gamma-ray detector system at the Laboratori Nazionali di Legnaro. The ground-state band along with a low-lying K-pi = 0(+) band and gamma-vibrational band were populated during the experiment. Based on the measured gamma-ray yields, a set of interband and intraband matrix elements has been extracted using the Coulomb excitation code GOSIA. The resulting E2 matrix elements are compared to collective model predictions.

“Discrepant hardenings” in cosmic ray spectra: A first estimate of the effects on secondary antiproton and diffuse gamma-ray yields

Recent data from CREAM seem to confirm early suggestions that primary cosmic ray (CR) spectra at few TeV/nucleon are harder than in the 10-100 GeV range. Also, helium and heavier nuclei spectra appear systematically harder than the proton fluxes at corresponding energies. We note here that if the measurements reflect intrinsic features in the interstellar fluxes (as opposed to local effects) appreciable modifications are expected in the sub-TeV range for the secondary yields, such as antiprotons and diffuse gamma-rays. Presently, the ignorance on the origin of the features represents a systematic error in the extraction of astrophysical parameters as well as for background estimates for indirect dark matter searches. We find that the spectral modifications are appreciable above 100 GeV, and can be responsible for ~30% effects for antiprotons at energies close to 1 TeV or for gamma's at energies close to 300 GeV, compared to currently considered predictions based on simple extrapolation of input fluxes from low energy data. Alternatively, if the feature originates from local sources, uncorrelated spectral changes might show up in antiproton and high-energy gamma-rays, with the latter ones likely dependent from the line-of-sight.

Effect of Sample Moisture and Bulk Density on Performance of the 241Am-Be Source Based Prompt Gamma Rays Neutron Activation Analysis Setup—a Monte Carlo Study

Monte Carlo simulations were carried out using the dependence of gamma ray yield on the bulk density and moisture content for five different lengths of Portland cement samples in a thermal neutron capture based Prompt Gamma ray Neutron Activation Analysis (PGNAA) setup for source inside moderator geometry using an 241Am-Be neutron source. In this study, yields of 1.94 and 6.42 MeV prompt gamma rays from calcium in the five Portland cement samples were calculated as a function of sample bulk density and moisture content. The study showed a strong dependence of the 1.94 and 6.42 MeV gamma ray yield upon the sample bulk density but a weaker dependence upon sample moisture content. For an order of magnitude increase in the sample bulk density, an order of magnitude increase in the gamma rays yield was observed, i.e., a one-to-one correspondence. In case of gamma ray yield dependence upon sample moisture content, an order of magnitude increase in the moisture content of the sample resulted in about 16–17% increase in the yield of 1.94 and 6.42 MeV gamma rays from calcium.

PIGE analysis of magnesium and beryllium

Abstract In this work, we present an alternative method for PIGE analysis of magnesium and beryllium in thick samples. This method is based on the ERYA – Emitted Radiation Yield Analysis – code, which integrates the nuclear reaction excitation function along the depth of the sample. For this purpose, the excitations functions of the 25Mg(p,p′γ)25Mg (Eγ = 585 keV) and 9Be(p,γ)10B (Eγ = 718 keV) reactions were employed. Calculated gamma-ray yields were compared, at several proton energy values, with experimental yields for thick samples made of inorganic compounds containing magnesium or beryllium. The agreement is better than 5%. Taking into consideration the experimental uncertainty of the measured yields and the errors related to the stopping power values, this agreement shows that effects as the beam energy straggling, ignored in the calculation, seem to play a minor role.

Effect of silica fume addition on the PGNAA measurement of chlorine in concrete

Pozzolanic materials, such as fly ash (FA), silica fume (SF), and blast furnace slag (BFS) are added to Portland cement in concrete to prevent reinforcement steel corrosion in concrete. Further preventive measure against reinforcement steel corrosion require monitoring of chloride salts concentration in concrete using non-destructive techniques, such as the prompt gamma-ray neutron activation analysis (PGNAA) technique. Due to interferences between gamma-rays from chlorine and calcium in PGNAA technique, detection limit of chlorine in concrete strongly depends upon calcium concentration in concrete. SF mainly contains silica and its addition to cement concrete reduces overall concentration of calcium in concrete. This may result in an improvement in detection limit of chlorine in SF-based concrete in PGNAA studies. Particularly for chlorine detection using 6.11 and 6.62 MeV prompt gamma-rays that strongly interfere with 6.42 MeV prompt gamma-rays from calcium. In this study, SF was added to Portland cement to prevent concrete reinforcement steel from corrosion. The chlorine concentration in SF cement concrete specimens containing 0.2–3.0 wt% chlorine was measured through yield of 1.16, 1.95, 6.11, 6.62, 7.41, 7.79, and 8.58 MeV chlorine gamma-rays using PGNAA technique. An excellent agreement was noted between the experimental yield of the prompt gamma-rays and the gamma-ray yield calculated through the Monte Carlo simulations. Further the minimum detectable concentration (MDC) of chlorine in SF cement concrete was calculated and compared with the MDC values of chlorine in plain concrete and concrete mixed with fly ash cement. The MDC of chlorine in SF-based concrete through 6.11 MeV, and 6.62 MeV chlorine gamma-rays was found to be improved as compared to those in plain concrete and concrete mixed with fly ash cement.

Response of a PGNAA setup for pozzolan-based cement concrete specimens

Pozzolanic materials are added to Portland cement concrete to increase its durability, particularly corrosion-resistance. In this study the elemental composition of a pozzolanic cement concrete was measured non-destructively utilizing an accelerator-based Prompt Gamma Ray Neutron Activation Analysis (PGNAA) setup. The optimum size of the pozzolanic cement concrete specimen was obtained through Monte Carlo simulations. The simulation results were experimentally verified through the gamma-ray yield measurement from the pozzolanic cement concrete specimens as a function of their radii. The concentration of the pozzolanic material in the cement concrete specimens was evaluated by measuring gamma-ray yield for calcium and iron from pozzolanic cement concrete specimens containing 5-80 wt% pozzolan. A good agreement was noted between the experimental values and the Monte Carlo simulation results, indicating an excellent response of the KFUPM accelerator-based PGNAA setup for pozzolan based concrete.

Prompt Gamma-Ray Analysis of Steel Slag in Concrete

Blast furnace slag (BFS) is added to Portland cement concrete to increase its durability, particularly its corrosion resistance. Monitoring the concentration of BFS in concrete for quality control purposes is desired. In this study, the concentration of BFS in concrete was measured by utilizing an accelerator-based prompt gamma-ray neutron activation analysis (PGNAA) setup. The optimum size of the BFS cement concrete specimen that produces the maximum intensity of gamma rays at the detector location was calculated through Monte Carlo simulations. The simulation results were experimentally validated through the gamma-ray yield measurement from BFS cement concrete specimens having different radii. The concentration of BFS in the cement concrete specimens was assessed through calcium and silicon gammaray yield measurement from cement concrete specimens containing 5 to 80 wt% BFS. The yield of calcium gamma rays decreases with increasing BFS concentration in concrete while the yield of silicon gamma rays increases with increasing BFS concentration in concrete. The calcium-to-silicon gamma-ray yield ratio has an inverse relation with BFS concentration in concrete.

Prompt gamma analysis of fly ash, silica fume and Superpozz blended cement concrete specimen

Preventive measures against corrosion of reinforcing steel require making the concrete dense by adding pozzolanic materials, such as fly ash, silica fume, Superpozz, blast furnace slag, etc. to Portland cement. In order to obtain the desired strength and durability of concrete, it is desirable to monitor the concentration of the pozzolan in the blended cement concrete. Addition of pozzolan to blended cement changes the overall concentration of calcium and silicon in the blended cement concrete. The resulting variation in calcium and silicon gamma-ray yield ratio from blended cement concrete has found to have an inverse correlation with concentration of fly ash, silica fume, Superpozz, blast furnace slag in the blended cement concrete.For experimental verification of the correlation, intensities of calcium and silicon prompt gamma-ray due to capture of thermal neutrons in blended cement concrete samples containing 5–80% (by weight of cement) silica fume, fly ash and Superpozz were measured. The gamma-ray intensity ratio was measured from 6.42MeV gamma-rays from calcium and 4.94MeV gamma-ray from silicon. The experimentally measured values of calcium to silicon gamma-ray yield ratio in the fly ash, silica fume and Superpozz cement concrete specimens agree very well with the results of the Monte Carlo simulations.

New positron spectral features from supersymmetric dark matter: A way to explain the PAMELA data?

The space-borne antimatter experiment PAMELA has recently reported a surprising rise in the positron to electron ratio at high energies. It has also recently been found that electromagnetic radiative corrections in some cases may boost the gamma-ray yield from supersymmetric dark-matter annihilations in the galactic halo by up to 3 or 4 orders of magnitude, providing distinct spectral signatures for indirect dark matter searches to look for. Here, we investigate whether the same type of corrections can also lead to sizeable enhancements in the positron yield. We find that this is indeed the case, albeit for a smaller region of parameter space than for gamma rays; selecting models with a small mass difference between the neutralino and sleptons, like in the stau-coannihilation region in mSUGRA, the effect becomes more pronounced. The resulting, rather hard positron spectrum with a relatively sharp cutoff may potentially fit the rising positron ratio measured by the PAMELA satellite. To do so, however, very large ``boost factors'' have to be invoked that are not expected in current models of halo structure. If the predicted cutoff would also be confirmed by later PAMELA data or upcoming experiments, one could either assume nonthermal production in the early universe or nonstandard halo formation to explain such a spectral feature as an effect of dark-matter annihilation. At the end of the paper, we briefly comment on the impact of radiative corrections on other annihilation channels, in particular, antiprotons and neutrinos.

Intenseγ-Ray Source in the Giant-Dipole-Resonance Range Driven by 10-TW Laser Pulses

A gamma-ray source with an intense component around the giant dipole resonance for photonuclear absorption has been obtained via bremsstrahlung of electron bunches driven by a 10-TW tabletop laser. 3D particle-in-cell simulation proves the achievement of a nonlinear regime leading to efficient acceleration of several sequential electron bunches per each laser pulse. The rate of the gamma-ray yield in the giant dipole resonance region (8<E{gamma}<17.5 MeV) was measured, through the radio activation of a gold sample, to be 4 x 10;{8} photons per joule of laser energy. This novel all-optical, compact, and efficient electron-gamma source is suitable for photonuclear studies and medical uses.

Calculation of a gigantic upward atmospheric discharge, accompanying optical phenomena, and penetrating radiations. II. Numerical simulation results

Gigantic upward atmospheric discharges have been numerically simulated. The space-time distributions of the self-consistent electric field strength and charged particle densities have been obtained. The brightness, color, and evolution in the space and time of fluorescence above a thundercloud, which agree with the data of field observations of such high-altitude optical phenomena as blue jets and red sprites, have been calculated. It has been indicated that large duration of blue jets results from the emission of a decaying ion plasma of the air. The yields of hard gamma rays and neutrons, generated by upward discharges, have been calculated.

Neutron Emission Profile of d-Be Reaction with Low-energy Deuteron Beam for Accelerator Neutron Source

The neutron emission profile of the 9Be(d,n)10B nuclear reaction using a low-energy deuteron beam (300 keV) was examined to develop an accelerator neutron source for boron neutron capture therapy (BNCT). The gamma rays corresponding to the transition from excited levels of 10B were measured using a high-purity Ge detector. By analyzing the gamma-ray yields, the transition probability to each excited state of 10B was determined and the neutron yields for the individual energies were evaluated. The emission of the 3.8 MeV neutron was approximately 42% of the total emission, and other neutron emissions from 1.1 to 4.5 MeV were clearly specified. A neutron moderator assembly using heavy water (D2O) or Be metal was designed in order to obtain thermal neutrons from the d-Be reaction with high efficiency. The simulations of neutron transport in the assembly were performed using the Monte Carlo code MCNP4C. Thermal, epithermal, and fast neutron fluxes were calculated as a function of the moderator thickness. The experimentally evaluated neutron emission property was reflected in the simulation. The results indicate that the use of the D2O moderator is suitable for thermal neutron production and shielding of fast neutrons rather than that of Be.

New gamma-ray contributions to supersymmetric dark matter annihilation

We compute the electromagnetic radiative corrections to all leading annihilation processes which may occur in the Galactic dark matter halo, for dark matter in the framework of supersymmetric extensions of the Standard Model (MSSM and mSUGRA), and present the results of scans over the parameter space that is consistent with present observational bounds on the dark matter density of the Universe. Although these processes have previously been considered in some special cases by various authors, our new general analysis shows novel interesting results with large corrections that may be of importance, e.g., for searches at the soon to be launched GLAST gamma-ray space telescope. In particular, it is pointed out that regions of parameter space where there is a near degeneracy between the dark matter neutralino and the tau sleptons, radiative corrections may boost the gamma-ray yield by up to three or four orders of magnitude, even for neutralino masses considerably below the TeV scale, and will enhance the very characteristic signature of dark matter annihilations, namely a sharp step at the mass of the dark matter particle. Since this is a particularly interesting region for more constrained mSUGRA models of supersymmetry, we use an extensive scan over this parameter space to verify the significance of our findings. We also re-visit the direct annihilation of neutralinos into photons and point out that, for a considerable part of the parameter space, internal bremsstrahlung is more important for indirect dark matter searches than line signals.

PIGE analysis and profiling of aluminium

In this work we present an alternative method for PIGE analysis of aluminium in thick samples. This method is based on the ERYA – emitted radiation yield analysis – code, which integrates the nuclear reaction excitation function along the depth of the sample. For this purpose, the excitations functions of the 27Al(p,p′γ1,2)27Al reaction (with gamma-ray energies of 844 and 1014keV) were employed. Calculated gamma-ray yields were compared, at several proton energy values, with experimental yields for thick samples made of inorganic compounds containing aluminium. The agreement is better than 5%.The 1684keV resonance of the same reaction, with a natural width of 100eV, was used to profile samples of Ti implanted with several doses of Al. We show that this resonance, stronger than the 992keV resonance of the 27Al(p,γ)28Si usually employed for aluminium profiling, leads to similar depth resolution in shorter collection time.

Cross-section measurements for (n, 2n) and (n, p) reactions on tellurium isotopes in the neutron energy range of 13.5−14.6 MeV

Cross sections for (n,2n) and (n,p) reactions have been measured on tellurium isotopes at the neutron energies of 13.5−14.6 MeV using the activation technique. Data are reported for the following reactions: 120Te(n,2n)119mTe, 120Te(n,2n)119gTe, 122Te(n,2n)121mTe, 122Te(n,2n)121gTe, 124Te(n,2n)123mTe, 128Te(n,2n)127gTe, 130Te(n,2n)129mTe, 120Te(n,p)120mSb, 122Te(n,p)122m+gSb, 124Te(n,p)124m+gSb, 126Te(n,p)126m+gSb and 128Te(n,p)128m+gSb. These new data for the cross sections of tellurium isotopes have smaller uncertainties than those reported in the previous literature. The first data for the 120Te(n,p)120mSb reaction cross sections are presented. In our experiment, natural high-purity tellurium powder was used as target material and the samples were wrapped in cadmium foil during the irradiation so the influence of the (n,γ) reactions of thermal neutrons was reduced to a low level and the interfering reactions were avoided or subtracted. The HPGe detector employed in this work has better resolution than NaI(Tl). Furthermore, while gamma-ray yields were measured and then turned into cross sections using the formula in Sect. 2.2, the most recent and accurate nuclear data available were adopted. These cumulative improvements should make our results more accurate and reliable than those reported in the previous literature. Our results are useful for verifying the accuracy of nuclear models used in the calculation of cross sections and are expected to help new evaluations of the 14 MeV neutron cross sections on isotopes of tellurium.

The sensitivity of the PIGE analytical technique

The aim of this work is to provide a basis for the estimation of fluorine and lithium contributions to the background of gamma-ray spectra and of their influence on PIGE (Proton-Induced Gamma-Ray Emission) detection limits of lithium, boron, fluorine and sodium. Results for yields and background contributions of lithium and fluorine were obtained from measurements using samples of known composition. Detection limits were determined by extrapolation of those measurements and by calculations based on the inferred background values. Yields were converted in concentrations using the ERYA (Emitted Radiation Yield Analysis) code. This code divides the sample in sublayers parallel to its surface for the integration of the partial gamma-ray yields along the depth of the target.