Surrogate Reaction Research Articles

Incorporating a two-step mechanism into calculations of (p,t) reactions used to populate compound nucleus spin-parity distributions in support of surrogate measurements

The surrogate reaction method may be used to determine the cross section for neutron-induced reactions not accessible through standard experimental techniques by creating the same compound nucleus which the desired reaction would pass through, but via a different entrance channel. A variety of direct reactions have been employed in order to generate the required compound nuclei for surrogate studies. In this work, a previously developed (p,t) reaction model has been extended to incorporate a two-step reaction mechanism, which takes the form of sequential neutron transfer. This updated model is applied to the 92Zr(p,t)90Zr reaction and is found to modify the strengths of the previously predicted populated levels. It is planned that this improved (p,t) model will be used to attempt to constrain cross section predictions for a number of (n,γ) reactions in future, as well as provide a possible comparison against other surrogate studies utilising different direct reactions such as (p,d).

Determination of Mn53(n,xp) cross sections using the surrogate reaction ratio method

The $^{54}\mathrm{Mn}^{*}$ (surrogate of $n+^{53}\mathrm{Mn}$) and $^{61}\mathrm{Ni}^{*}$ (surrogate of $n+^{60}\mathrm{Ni}$) compound systems have been populated at overlapping excitation energies by transfer reactions $^{52}\mathrm{Cr}(^{6}\mathrm{Li},\ensuremath{\alpha})^{54}\mathrm{Mn}^{*}$ at ${E}_{\mathrm{lab}}=33.0\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and $^{59}\mathrm{Co}(^{6}\mathrm{Li},\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{61}\mathrm{Ni}^{*}$ at ${E}_{\mathrm{lab}}=40.5\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, respectively. The proton decay probabilities of the compound systems have been determined by measuring evaporated protons at backward angles in coincidence with projectilelike fragments detected around the grazing angle. The $^{53}\mathrm{Mn}(n,xp)$ cross sections in the equivalent neutron energy range of 8.2--16.4 MeV have been determined within the framework of the surrogate reaction ratio method using $^{60}\mathrm{Ni}(n,xp)$ cross-section values from the literature as a reference. The measured $^{53}\mathrm{Mn}(n,xp)$ cross-section values are found to be consistent with the predictions of the talys-1.8 statistical model code using microscopic level densities and results of various evaluated nuclear data libraries: eaf-2010, rosfond-2010, and jeff-3.3 within the experimental uncertainties.

Amino-Acid-Based Ionic Liquids for the Improvement in Stability and Activity of Cytochrome c: A Combined Experimental and Molecular Dynamics Study.

The demand for long-term storage and stability of proteins has increased substantially in the pharmaceutical industries, yet the sensitivity of proteins toward the environment has become a cardinal task for researchers. To deal with this, we have selected a multifunctional enzyme Cytochrome-c (Cyt-c) involved in many chemical and biochemical reactions as model protein, which is very sensitive and loses structural integrity on exposure to the environment. The remarkable features of ionic liquids (ILs) have entitled them as alternatives to aqueous and organic solvents for solubility, storage, and surrogate reaction medium. Hence, we have adapted the biocompatible and nontoxic cation and anion based amino acid ILs (CAAAILs) as potential solvents for storage and stability of Cyt-c. Herein, we report the molecular insights and thermodynamics of interaction between CAAAILs and Cyt-c with the help of isothermal titration calorimetry (ITC), transmission electron microscopy (TEM), UV-vis, CD, and fluorescence spectroscopy as well as molecular docking and molecular dynamics (MD) simulations. The structure and stability of Cyt-c remain unchanged in the presence of CAAAILs. Both electrostatic and hydrophobic interactions are accountable for the binding of CAAAILs in the region between terminal helices and the loop of Cyt-c through nonspecific multiple binding sites, which can be exploited for storage and stability of proteins and will be helpful in designing new biobased ILs for biochemical applications.

Predictors and reproducibility of exercise-induced bronchoconstriction in cold air

BackgroundPhysical activity is an important part of life, and hence exercise-induced bronchoconstriction (EIB) can reduce the quality of life. A standardized test is needed to diagnose EIB. The American Thoracic Society (ATS) guidelines recommend an exercise challenge in combination with dry air. We investigated the feasibility of a new, ATS guidelines conform exercise challenge in a cold chamber (ECC) to detect EIB. The aim of this study was to investigate the surrogate marker reaction to methacholine, ECC and exercise challenge in ambient temperature for the prediction of a positive reaction and to re-evaluate the reproducibility of the response to an ECC.MethodsSeventy-eight subjects aged 6 to 40 years with suspected EIB were recruited for the study. The subjects performed one methacholine challenge, two ECCs, and one exercise challenge at an ambient temperature. To define the sensitivity and specificity of the predictor, a receiver-operating characteristic curve was plotted. The repeatability was evaluated using the method described by Bland and Altman (95% Limits of agreement).ResultsThe following cut-off values showed the best combination of sensitivity and specificity: the provocation dose causing a 20% decrease in the forced expiratory volume in 1 s (PD20FEV1) of methacholine: 1.36 mg (AUC 0.69, p < 0.05), the maximal decrease in FEV1 during the ECC: 8.5% (AUC 0.78, p < 0.001) and exercise challenges at ambient temperatures: FEV1 5.2% (AUC 0.64, p = 0.13). The median decline in FEV1 was 14.5% (0.0–64.2) during the first ECC and 10.7% (0.0–52.5) during the second ECC. In the comparison of both ECCs, the Spearman rank correlation of the FEV1 decrease was r = 0.58 (p < 0.001). The 95% limits of agreement (95% LOAs) for the FEV1 decrease were − 17.7 to 26.4%.ConclusionsThe surrogate markers PD20FEV1 of methacholine and maximal decrease in FEV1 during ECC can predict a positive reaction in another ECC, whereas the maximal FEV1 decrease in an exercise challenge at an ambient temperature was not predictive. Compared with previous studies, we can achieve a similar reproducibility with an ECC.Clinical trial registrationNCT02026492 (retrospectively registered 03/Jan/2014).

Assessment of the validity of RANS knock prediction using the resonance theory

Following the resonance theory by Bradley and co-workers, engine knock is a consequence of an auto-ignition in the developing detonation regime. Their detonation diagram was developed using direct numerical simulations and was applied in the literature to engine knock assessment using large eddy simulations. In this work, it is analyzed if the detonation diagram can be applied for post-processing and evaluation of predicted auto-ignitions in Reynolds-averaged Navier–Stokes simulations even though the Reynolds-averaged Navier–Stokes approach cannot resolve the fine structures resolved in direct numerical simulations and large eddy simulations that lead to the prediction of a developing detonation. For this purpose, an engine operating point at the knock limit spark advance is simulated using Reynolds-averaged Navier–Stokes and large eddy simulations. The combustion is predicted using the G-equation and the well-stirred reactor model in the unburnt gases based on a detailed gasoline surrogate reaction scheme. All the predicted ignition kernels are evaluated using the resonance theory in a post-processing step. According to the different turbulence models, the predicted pressure rise rates and gradients differ. However, the predicted ignition kernel sizes and imposed gas velocities by the auto-ignition event are similar, which suggests that the auto-ignitions predicted by Reynolds-averaged Navier–Stokes simulations can be given a meaningful interpretation within the detonation diagram.

Expansion of the surrogate method to measure the prompt fission neutron multiplicity for Pu241

Fission neutron multiplicity data are imperative for nuclear models that support criticality safety, nuclear nonproliferation, and stockpile stewardship. This work presents the first experimental measurement to determine the average neutron multiplicity ($\overline{\ensuremath{\nu}}$) and the neutron multiplicity distribution using a surrogate reaction. $^{241}\mathrm{Pu}$ has a short half-life of 14.3 yr. To circumvent experimental difficulties, inelastic scattering of 53.96-MeV $\ensuremath{\alpha}$ particles on $^{242}\mathrm{Pu}$ served as a surrogate for $^{241}\mathrm{Pu}(n,f)$. The present text reports and discusses the average neutron multiplicity, in addition to the neutron multiplicity moments and distribution for equivalent neutron energies up to 20 MeV. The $\overline{\ensuremath{\nu}}$ measured in this experiment agrees with previous measurements until 12 MeV, where discrepancies arise due to preequilibrium neutron emission.

Determination of Ni59(n,xp) reaction cross sections using surrogate reactions

The $^{59}\mathrm{Ni}(n,xp)$ reaction cross sections have been measured following the surrogate reaction ratio method in the equivalent neutron energy range of 11.9--15.8 MeV by populating the compound nucleus $^{60}\mathrm{Ni}^{*}$ through transfer reaction $^{56}\mathrm{Fe}(^{6}\mathrm{Li},d)$ at ${E}_{\text{lab}}=35.9$ MeV. The $^{59}\mathrm{Co}(^{6}\mathrm{Li},\ensuremath{\alpha})^{61}\mathrm{Ni}^{*}$ transfer reaction at ${E}_{\text{lab}}=40.5$ MeV has been used as the reference reaction which is the surrogate of $^{60}\mathrm{Ni}(n,xp)$ reaction populating the compound nucleus $^{61}\mathrm{Ni}^{*}$. The proton decay probabilities have been determined by measuring evaporated protons at backward angles in coincidence with projectile like fragments (PLFs, either $d$ or $\ensuremath{\alpha}$) detected around grazing angles. The cross sections for the reference reaction $^{60}\mathrm{Ni}(n,xp)$ are taken from jendl-4.0 library, which closely reproduce the available experimental data. The cross sections for the desired $^{59}\mathrm{Ni}(n,xp)$ reaction so obtained compare well with the nuclear-reactions-model code talys-1.8 using microscopic level densities. The present experimental data are consistent with the evaluated data library of rosfond-2015 but not with tendl-2015 and endf/b-viii, indicating the need of new evaluations for this reaction of importance to fusion technology.

Evolution of dolomite composition and reactivity during biomass gasification

Dolomite is a cheap and robust catalyst used for biomass gasification, but its deactivation under relevant conditions of pilot-scale gasifiers has still been poorly understood. For this reason, the catalytic activity of fresh and used dolomites produced from an industrial air-blow fluidized bed was investigated. Fresh and used dolomites were characterized by BET, SEM-EDX, XPS, ICP-MS, XRD, TPD and TPO. Benzene steam reforming was selected as a surrogate reaction of tar conversion in order to probe the reactivity of the two dolomites. The activity of used dolomite was 25% lower than that of fresh dolomite. This difference could be explained by: (1) the deposition of a Si-based layer from biomass ashes at the surface of used dolomite, and (2) the production of coke during gasification. The reaction mechanism of benzene steam reforming over fresh and used dolomites was discussed. For used dolomite, the Si and coke depositions reduced the availability of the active sites (CaO, MgO) thus lowering the conversion of benzene. These deposits could also inhibit the interactions between CaO and MgO and enhance the formation of a stable coke.

Constraining Neutron Capture Cross Sections for Unstable Nuclei with Surrogate Reaction Data and Theory.

Obtaining reliable data for nuclear reactions on unstable isotopes remains an extremely important task and a formidable challenge. Neutron capture cross sections-crucial ingredients for models of astrophysical processes, national security applications, and simulations of nuclear energy generation-are particularly elusive, as both projectile and target in the reaction are unstable. We demonstrate a new method for determining cross sections for neutron capture on unstable isotopes, using ^{87}Y(n,γ) as a prototype. To validate the method, a benchmark experiment is carried out to obtain the known ^{90}Zr(n,γ) cross section analogously. Our approach, which employs an indirect ("surrogate") measurement combined with theory, can be generalized to a larger class of nuclear reactions. It can be used both with traditional stable-beam experiments and in inverse kinematics at rare-isotope facilities.

Restoring ZSM-5 performance for catalytic fast pyrolysis of biomass: Effect of regeneration temperature

Zeolite catalysts used for biomass catalytic fast pyrolysis (CFP) deactivate rapidly, similar to a fluidized catalytic cracking (FCC) catalyst used in refining. To operate effectively when there is rapid deactivation, biomass CFP can take place in a riser FCC-style reactor in which the catalyst has a short contact time (seconds) with reactants before it is regenerated. The regeneration, therefore, has two major needs for effective operation: 1) heat balance, since the heat required for the CFP reactions is brought into the reactor by the hot catalyst and 2) relatively short (minutes) regeneration to restore the catalyst activity to be near its initial state. In order to understand effective conditions to regenerate zeolites used for CFP, a series of experiments were performed to determine the effect of regeneration temperature on the activity of ZSM-5 (SiO2/Al2O3 = 30). After use for pine pyrolysis vapor upgrading, the catalyst was oxidized in 4% O2 at temperatures between 500–700 °C and reevaluated for the upgrading of pine pyrolysis vapors to assess the extent of regeneration. Additional testing was performed using ethylene aromatization as a surrogate reaction to probe regeneration efficiency. Regeneration experiments were performed for either a fixed length of time (20 min) or until there was no further CO2 measured in the effluent gas. Results from the ethylene aromatization reactions were shown to serve as an excellent surrogate for CFP reactivity and indicated that the use of model compound studies can effectively be used to understand reaction and regeneration processes from biomass CFP. Both sets of results indicate that a spent ZSM-5 used for biomass CFP could be fully regenerated at 650°C and 700°C within 20 min, whereas regeneration temperatures of 550 °C and 600 °C required longer regeneration temperatures and in the case of regeneration at 500 °C, there may be coke species that are not removed and the catalyst activity may never be fully restored. Characterization by pyridine diffuse reflectance infrared spectroscopy, thermogravimetric analysis coupled with infrared spectroscopy, and N2 physisorption showed that higher regeneration temperatures are more effective for restoring Brønsted acid sites and catalyst mesoporosity by rapidly removing aromatic coke deposits. Additionally, regeneration at 650 °C and 700 °C led to a slightly higher total porosity as compared to the pristine catalyst, which was attributed to the formation of additional mesoporosity from catalyst steaming.

An optimization method for formulating model-based jet fuel surrogate by emulating physical, gas phase chemical properties and threshold sooting index (TSI) of real jet fuel under engine relevant conditions

Two jet fuel surrogates (S1 and S2) were proposed in this work, aimed at improving the quantitative accuracy of fuel properties that affect both premixed and spray-guided combustion modes under engine relevant conditions by emulating real jet fuel properties including physical, gas phase chemical properties and threshold sooting index (TSI). An intelligent optimization approach was employed to calculate the composition that inherently satisfies both the physical and gas phase chemical characteristics as well as sooting tendency. The jet fuel surrogate S1 was composed of five components including decalin, n-dodecane, iso-cetane, iso-octane and toluene (0.005/0.4011/0.1249/0.098/0.371 by mole fraction), while surrogate S2 is a mixture of the same components but different in proportions (0.1449/0.3706/0.2059/0.0195/0.2591 by mole fraction). Based on the newly proposed surrogates, a skeletal jet fuel surrogate chemical reaction mechanism was developed by describing the chemistries for the oxidation of large molecules C4Cn and smaller H2/CO/C1 molecules respectively. The skeletal jet fuel surrogate mechanism was significantly compacted into 74 species and 189 reactions, making it practical to be used in 3-dimensional (3-D) engine combustion simulations. This newly developed mechanism was verified against the experimental results of ignition delay times, species concentrations and laminar flame speed under a wide range of conditions, while 3-D validations were conducted for spray liquid and vapor penetrations in a constant volume chamber. As a result, the proposed fuel surrogate is capable of predicting the spray and combustion characteristics and main species profiles under engine relevant circumstance. Due to the stringent target properties used in this work, the surrogate S1 performed best in assessing ignition characteristics attributed to its elaborate chemical properties, making it the most suitable candidate for chemical dominated combustion like premixed engine combustion. Alternatively, S2 displayed outstanding spray-guided combustion behavior because of the stringent chemical and physical target properties assigned. It is worthwhile to note that this new method of formulating surrogates for different applications was efficient and time-saving. Finally, we aim to perform experimental validation tests for CN, density, viscosity, surface tension, TSI, sooting tendency and particle size distribution to further support the validity of the current proposed jet fuel surrogates (S1 and S2) in the future.

Neutron capture on short-lived nuclei via the surrogate (d,pγ) reaction

Rapid r-process nucleosynthesis is responsible for the creation of about half of the elements heavier than iron. Neutron capture on shortlived nuclei in cold processes or during freeze out from hot processes can have a significant impact on the final observed r-process abundances. We are validating the (d,pγ) reaction as a surrogate for neutron capture with measurements on 95Mo targets and a focus on discrete transitions. The experimental results have been analyzed within the Hauser-Feshbach approach with non-elastic breakup of the deuteron providing a neutron to be captured. Preliminary results support the (d,pγ) reaction as a valid surrogate for neutron capture. We are poised to measure the (d,pγ) reaction in inverse kinematics with unstable beams following the development of the experimental techniques.

Three-dimensional computational fluid dynamics engine knock prediction and evaluation based on detailed chemistry and detonation theory

Engine knock is an important phenomenon that needs consideration in the development of gasoline-fueled engines. In our days, this development is supported using numerical simulation tools to further understand and predict in-cylinder processes. In this work, a model tool chain which uses a detailed chemical reaction scheme is proposed to predict the auto-ignition behavior of fuels with different octane ratings and to evaluate the transition from harmless auto-ignitive deflagration to knocking combustion. In our method, the auto-ignition characteristics and the emissions are calculated using a gasoline surrogate reaction scheme containing pathways for oxidation of ethanol, toluene, n-heptane, iso-octane and their mixtures. The combustion is predicted using a combination of the G-equation based flame propagation model utilizing tabulated laminar flame speeds and well-stirred reactors in the burned and unburned zone in three-dimensional Reynolds-averaged Navier–Stokes. Based on the detonation theory by Bradley et al., the character and the severity of the auto-ignition event are evaluated. Using the suggested tool chain, the impact of fuel properties can be efficiently studied, the transition from harmless deflagration to knocking combustion can be illustrated and the severity of the auto-ignition event can be quantified.

Energy dependence of the promptγ-ray emission from the(d,p)-induced fission ofU*234andPu*240

Prompt fission $\gamma$-rays are responsible for approximately 5\% of the total energy released in fission, and therefore important to understand when modelling nuclear reactors. In this work we present prompt $\gamma$-ray emission characteristics in fission, for the first time as a function of the nuclear excitation energy of the fissioning system. Emitted $\gamma$-ray spectra were measured, and $\gamma$-ray multiplicities and average and total $\gamma$ energies per fission were determined for the $^{233}$U(d,pf) reaction for excitation energies between 4.8 and 10 MeV, and for the $^{239}$Pu(d,pf) reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra $\sim$5 MeV of energy is potentially available in the excited fragments for $\gamma$-decay. The measured results are compared to model calculations made for prompt $\gamma$-ray emission with the fission model code GEF. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.

Constraining the rp-process by measuring 23Al(d,n)24Si with GRETINA and LENDA at NSCL

The 23 Al(p, γ)24 Si stellar reaction rate has a significant impact on the light-curve emitted in X-ray bursts. Theoretical calculations show that the reaction rate is mainly determined by the properties of direct capture as well as low-lying 2+ states and a possible 4+ state in 24 Si. Currently, there is little experimental information on the properties of these states.In this proceeding we will present a new experimental study to investigate this reaction, using the surrogate reaction 23 Al(d,n) at 47 AMeV at the National Superconducting Cyclotron Laboratory (NSCL). We will discuss our new experimental setup which allows us to use full kinematics employing the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to detect the γ-rays following the de-excitation of excited states of the reaction products and the Low Energy Neutron Detector Array (LENDA) to detect the recoiling neutrons. The S800 was used for identification of the 24 Si recoils. As a proof of principle to show the feasibility of this concept the Q-value spectrum of 22 Mg(d,n)23 Al is reconstructed.

First simultaneous measurement of fission and gamma probabilities of237U and239Np via surrogate reactions

Fission and gamma decay probabilities of 237 U and 239 Np have been mea- sured, for the first time simultaneously in dedicated experiments, via the surrogate re- actions 238 U( 3 He, 4 He) and 238 U( 3 He,d), respectively. While a good agreement between our data and neutron-induced data is found for fission probabilities, gamma decay prob- abilities are several times higher than the corresponding neutron-induced data for each studied nucleus. We study the role of the different spin distributions populated in the surrogate and neutron-induced reactions. The compound nucleus spin distribution popu- lated in the surrogate reaction is extracted from the measured gamma-decay probabilities, and used as input parameter in the statistical model to predict fission probabilities to be compared to our data. A strong disagreement between our data and the prediction is ob- tained. Preliminary results from an additional dedicated experiment confirm the observed discrepancies, indicating the need of a better understanding of the formation and decay processes of the compound nucleus.

Calculations of Compound Nucleus Spin-Parity Distributions Populated via the (p,t) Reaction in Support of Surrogate Neutron Capture Measurements

The surrogate reaction method may be used to determine the cross section for neutron induced reactions not accessible through standard experimental techniques. This is achieved by creating the same compound nucleus as would be expected in the desired reaction, but through a different incident channel, generally a direct transfer reaction. So far, the surrogate technique has been applied with reasonable success to determine the fission cross section for a number of actinides, but has been less successful when applied to other reactions, e.g. neutron capture, due to a ‘spin-parity mismatch’. This mismatch, between the spin and parity distributions of the excited levels of the compound nucleus populated in the desired and surrogate channels, leads to differing decay probabilities and hence reduces the validity of using the surrogate method to infer the cross section in the desired channel. A greater theoretical understanding of the expected distribution of levels excited in both the desired and surrogate channels is therefore required in order to attempt to address this mismatch and allow the method to be utilised with greater confidence. Two neutron transfer reactions, e.g. (p,t), which allow the technique to be utilised for isotopes further removed from the line of stability, are the subject of this study. Results are presented for the calculated distribution of compound nucleus states populated in 90Zr, via the 90Zr(p,t)90Zr reaction, and are compared against measured data at an incident proton energy of 28.56 MeV.

Exploring the spin states of90Zr populated by (p,p’), (p,d), and (p,t) reactions

The 90 Zr nucleus was produced by three different reactions: 90 Zr( p , p ’), 91 Zr( p , d ), and 92 Zr( p , t ), and the spin-parity ( J π ) population of the 90 Zr states produced by these reactions was studied to investigate the surrogate reaction approach, which aims at indirectly determining cross sections for compound-nuclear reactions involving unstable targets such as 89 Zr( n , γ ). Discrete γ-rays, associated with the de-excitation of 90 Zr and 89 Zr, were measured in coincidence with light ions at 90 Zr excitation energies extending above the neutron separation energy. Low-lying states populated by ( p , d ) and ( p , t ) reactions agreed well with the previous measurements. The measured γ transition systematics were used to gain insights into the J π distribution of 90 Zr around the neutron separation energy and it was found that the ( p , p ’) reaction preferentially produces lower J states than ( p , d ) and ( p , t ) reactions in the studied energy region.

Spin differences in the Zr90 compound nucleus induced by (p,p′) , (p,d) , and (p,t) surrogate reactions

The effect of the production mechanism on the decay of a compound nucleus is investigated. The nucleus $^{90}\mathrm{Zr}$ was produced by three different reactions, namely $^{90}\mathrm{Zr}(p,{p}^{\ensuremath{'}})^{90}\mathrm{Zr}$, $^{91}\mathrm{Zr}(p,d)^{90}\mathrm{Zr}$, and $^{92}\mathrm{Zr}(p,t)^{90}\mathrm{Zr}$, which served as surrogate reactions for $^{89}\mathrm{Zr}(n,\ensuremath{\gamma})$. The spin-parity $({J}^{\ensuremath{\pi}})$ distributions of the states populated by these reactions were studied to investigate the surrogate reaction approach, which aims at indirectly determining cross sections for compound-nuclear reactions involving unstable targets such as $^{89}\mathrm{Zr}$. Discrete $\ensuremath{\gamma}$ rays, associated with transitions in $^{90}\mathrm{Zr}$ and $^{89}\mathrm{Zr}$, were measured in coincidence with light ions for scattering angles of ${25}^{\ensuremath{\circ}}--{60}^{\ensuremath{\circ}}$ and $^{90}\mathrm{Zr}$ excitation energies extending above the neutron separation energy. The measured transition systematics were used to gain insights into the ${J}^{\ensuremath{\pi}}$ distributions of $^{90}\mathrm{Zr}$. The $^{90}\mathrm{Zr}(p,{p}^{\ensuremath{'}})$ reaction was found to produce fewer $\ensuremath{\gamma}$ rays associated with transitions involving high spin states $(J=6--8\phantom{\rule{4.pt}{0ex}}\ensuremath{\hbar})$ than the other two reactions, suggesting that inelastic scattering preferentially populates states in $^{90}\mathrm{Zr}$ that have lower spins than those populated in the transfer reactions investigated. The $\ensuremath{\gamma}$-ray production was also observed to vary by factors of 2--3 with the angle at which the outgoing particle was detected. These findings are relevant to the application of the surrogate reaction approach.

Development of a measurement system for the determination of ([formula omitted]) cross-sections using multi-nucleon transfer reactions

We have installed a new experimental apparatus to measure γ-rays from highly excited states populated by the multi-nucleon transfer reactions with heavy-ion projectiles to determine the (n, γ) cross-sections by means of the surrogate reaction method. An apparatus consists of two anti-Compton LaBr3(Ce) spectrometers to measure the γ-rays and a Si ΔE–E detector system to detect outgoing projectile-like particles. Reactions of 153-MeV 18O beams with 155Gd and 157Gd targets were used to study the performance of apparatus. By using the LaBr3(Ce) scintillators with relatively large volume (101.6mm in diameter and 127mm in length), we have successfully measured γ-rays from the compound nuclei, which have excitation energy above neutron separation energy, populated by 155Gd(18O, 16O)157Gd and 157Gd(18O, 16O)159Gd two-neutron transfer reactions. To measure in-beam γ-rays through heavy-ion-induced transfer reaction, it is important to assign the reaction channel clearly, since the cross-sections of the transfer reactions are much smaller than those of competing reactions such as Coulomb excitation and fusion reactions. The Si ΔE–E detector system was used to separate outgoing particles. The present study has demonstrated high capability of apparatus to measure the de-excitation γ-rays in the compound nuclei produced by the multi-nucleon transfer reactions for determination of the (n, γ) cross-sections by using the surrogate reaction method.