Surrogate Reactions Research Articles

Study of the surrogate ratio method by determination of 56Fe(n,xp) cross sections

In recent years (n,xp) cross sections of some long-lived radionuclei which are of importance in the upcoming fusion reactor technologies have been constrained using the surrogate ratio method. But the (n,xp) cross sections for the stable nuclei for which a great wealth of data is available from the direct measurements have not been constrained using surrogate ratio method yet, so that the consistency of the surrogate ratio method can be checked. In this study we have investigated the validity of surrogate ratio method by constraining 56Fe(n,xp) cross sections and then the results are compared with the available experimental data, evaluated data and the statistical model predictions. In this study 52Cr(n,xp) reaction has been used as the reference reaction in the surrogate ratio method. It is found in this study that (n,xp) cross sections constrained using surrogate ratio method are sensitive to the spin distribution of the compound nuclei populated in the surrogate reactions. It is also presented in this study that the proton emission probabilities for 57Fe and 53Cr are highly spin dependent. It is concluded that the surrogate ratio method is not suitable for constraining the (n,xp) cross sections.

Determining neutron-induced reaction cross sections through surrogate reactions at storage rings

Determining the cross sections of neutron-induced reactions on short-lived nuclei is imperative to rate calculations in stellar nucleosynthesis and applications of nuclear physics. It is also an immense experimental challenge due to the radioactivity of the targets involved. Our goal is to circumvent this obstacle by using surrogate reactions in inverse kinematics at the heavy-ion storage rings of GSI/FAIR. We present here preliminary results from the first proof of principle experiment, where a beam of 208Pb impinged on a H2 gas jet target in the Experimental Storage Ring (ESR).

Surrogate Reactions at Heavy-Ion Storage Rings: The NECTAR Project

Surrogate Reactions at Heavy-Ion Storage Rings: The NECTAR Project

Research program of nuclear astrophysics based on the HIAF

Nuclear astrophysics is an interdisciplinary research field integrating nuclear physics, astrophysics and astronomy. It has always been an important frontier of physics in the world. This paper summarizes the current status, key research topics, and experimental approaches in nuclear astrophysics and briefly introduces its research prospect based on the High Intensity heavy-ion Accelerator Facility (HIAF), which is a large-scale scientific facility for nuclear physics that is under construction in China. HIAF has great advantages for studying the masses, half-life, and reaction cross sections of the unstable nuclides and will provide a good opportunity for understanding explosive nuclear processes as well as the origin of heavy elements in the universe. For key reactions in the nucleosynthesis process, indirect measurement methods and experimental techniques such as ANC, Oslo, surrogate reactions, and surrogate ratio methods, will be developed and used for the systematic studies on the charged-particle or neutron capture reactions. Using the HIAF storage ring, the mass of the r-process nuclides can be systematically measured. Using the HIAF secondary beam line and high-efficiency detector, the decay half-life of the r-process nuclides can be measured. Furthermore, based on HIAF, the equations of states of a neutron star and weak interaction rates can be studied. Using the above nuclear physics experimental and theoretical research, the database of the masses and reaction rates will be updated. Astronomical observations will be combined to test the astrophysical model, and to understand the evolution of stars as well as the origin of elements in the universe.

Measurement of (n, f) and (n, xn) cross sections with surrogate reaction method

Surrogate reaction method is an important approach to overcome the difficulties meet in the direct measurement of neutron induced nuclear reaction. The current existing surrogate reactions generally employ the peripheral reactions such as inelastic excitation and transfer reaction where the involved angular momenta are much larger than the neutron capture reaction, which causes a difficulty in theoretical correction of spin of compound nucleus. We proposed to use capture reaction of light charged particle as the surrogate reaction, thus the spin distributions of compound nucleus in two reactions are quite similar and therefore the spin correction is not strongly desired. Based on this idea, the 239Pu(n, f) and (n, 2n) cross sections were successfully extracted by using 236U(α,, f) and (α, 2n) reactions as the surrogate reactions. The well coincidence of the present results with the data of ENDFB7 within the error bars shows the reliability of the proposed surrogate capture reaction method.

Insight into the Fission Process from Surrogate Reactions in Inverse Kinematics

Innovative experiments are conducted to widen our approach to fission, aiming notably at a complete identification and characterization of the fragments and the study of unstable fissioning systems. In the GANIL facility, full fission-fragment distributions and fragment kinetic energies are measured, thanks to the inverse kinematics technique and the magnetic spectrometer VAMOS. The access to the scission-point information is possible thanks to the low-energy regime. The initial excitation energy of the systems is also determined due to the well-defined transfer reactions. In this work, fission yields and fission-fragment kinetic energies of 239U, as well as the evolution of the yields with the initial excitation energy of 240Pu, are presented.

The neutron within the deuteron as a surrogate for neutron-induced reactions

We propose the use of neutron poisons in reactions induced by radioactive beams as a test of theoretical models aiming to relate neutron capture in nuclei with neutron surrogate reactions such as ([Formula: see text]) reactions. We exploit the approximations necessary to obtain a direct relation between the two reactions: surrogate versus neutron capture. We also show how this is intimately related to the momentum distribution of the neutron within the deuteron. The models we use are based on the theory of inclusive breakup reactions commonly employed in the treatment of incomplete fusion and surrogate method. Such theories were developed in the 1980s by Ichimura, Austern and Vincent [Phys. Rev. C 32 (1985) 431], Udagawa and Tamura [Phys. Rev. C 24 (1981) 1348] and Hussein and McVoy [Nucl. Phys. A 445 (1985) 124]. We use these theories to derive an expression for the proton yield in the reaction [Formula: see text]. The capture reaction [Formula: see text] is then extracted using reasonable approximations. By recalling an old method proposed by Serber [Phys. Rev. 80 (1950) 1098; Proc. Roy. Soc. A 208 (1951) 559] we explain how the momentum distribution of neutrons within the deuteron will depend on the short-range dependence of the nucleon–nucleon force. The relevance of our work to nucleosynthesis in the rapid neutron capture process is emphasized.

Nonlocal interactions in the (d,p) surrogate method for (n,γ) reactions

Single-neutron transfer reactions populating states in the continuum are interesting both for structure and astrophysics. In their description often global optical potentials are used for the nucleon-target interactions, and these interactions are typically local. In our work, we study the effects of nonlocality in $(d,p)$ reactions populating continuum states. This work is similar to that of [1] but now for transfer to the continuum. A theory for computing cross sections for inclusive processes $A (d,p) X$ was explored in [2]. Therein, local optical potentials were used to describe the nucleon-target effective interaction. The goal of the present work is to extend the theory developed in [2] to investigate the effects of including nonlocality in the effective interaction on the relevant reaction observables. We implement the R--matrix method to solve the non--local equations both for the nucleon wavefunctions and the propagator. We then apply the method to systematically study the inclusive process of $(d,p)$ on $^{16}$O, $^{40}$Ca, $^{48}$Ca and $^{208}$Pb at 10, 20 and 50 MeV. We compare the results obtained when non--local interactions are used with those obtained when local equivalent interactions are included. We find that nonlocality affects different pieces of the model in complex ways. Depending on the beam energy and the target, the non-elastic breakup can either increase or decrease. While the non-elastic transfer cross section for each final spin state can change considerably, the main prediction of the model [2], namely the shape of the spin distributions, remains largely unaltered by nonlocality. [1] L. J. Titus and F. M. Nunes. Testing the Perey effect. Phys. Rev. C, 89:034609, Mar 2014. [2] G. Potel, F. M. Nunes, and I. J. Thompson. Establishing a theory for deuteron-induced surrogate reactions. Phys. Rev. C, 92:034611, Sep 2015.

Surrogate Decision Makers' Perspectives on Family Members' Prognosis after Intracerebral Hemorrhage.

Surrogate communication with providers about prognosis in the setting of acute critical illness can impact both patient treatment decisions and surrogate outcomes. To examine surrogate decision maker perspectives on provider prognostic communication after intracerebral hemorrhage (ICH). Semistructured interviews were conducted and analyzed qualitatively for key themes. Surrogate decision makers for individuals admitted with ICH were enrolled from five acute care hospitals. Fifty-two surrogates participated (mean age = 54, 60% women, 58% non-Hispanic white, 13% African American, 21% Hispanic). Patient status at interview was hospitalized (17%), in rehabilitation/nursing facility (37%), deceased (38%), hospice (4%), or home (6%). Nineteen percent of surrogates reported receiving discordant prognoses, leading to distress or frustration in eight cases (15%) and a change in decision for potentially life-saving brain surgery in three cases (6%). Surrogates were surprised or confused by providers' use of varied terminology for the diagnosis (17%) (e.g., "stroke" vs. "brain hemorrhage" or "brain bleed") and some interpreted "stroke" as having a more negative connotation. Surrogates reported that physicians expressed uncertainty in prognosis in 37%; with physician certainty in 56%. Surrogate reactions to uncertainty were mixed, with some surrogates expressing a negative emotional response (e.g., anxiety) and others reporting understanding or acceptance of uncertainty. Current practice of prognostic communication in acute critical illness has many gaps, leading to distress for surrogates and variability in critical treatment decisions. Further work is needed to limit surrogate distress and improve the quality of treatment decisions.

A Theoretical Study of Deuteron-induced Surrogate Reactions

We use the zero-range post-form DWBA approximation to calculate deuteron elastic and nonelastic breakup cross sections and estimate the breakup-fusion cross section that could serve as a surrogate for a neutron-induced reaction cross section. We compare the angular momentum dependence of the breakup-fusion compound nucleus formation cross section with that of the corresponding neutron-induced cross section.

Investigation of the surrogate-reaction method via the simultaneous measurement of gamma-emission and fission probabilities

We present the results of two experiments where we have measured for the first time simultaneously the fission and gamma-decay probabilities induced by different surrogate reactions. In particular, we have investigated the 238 U(d,p), 238 U( 3 He,t) and 238 U( 3 He, 4 He) reactions as surrogates for the neutron-induced n + 238 U, n + 237 Np and n + 236 U reactions, respectively. In the region where gamma emission, neutron emission and fission compete, our results for the fission probabilities agree fairly well with the neutron-induced data, whereas our gamma-decay probabilities are significantly higher than the neutron-induced data. The interpretation of these results is not obvious and is discussed within the framework of the statistical model with preliminary results for calculated spin-parity distributions populated in surrogate reactions. We also present future plans for surrogate-reaction studies in inverse kinematics with radioactive-ion beams at storage rings.

Role of the direct processes in low-energy deuteron interactions

An extended analysis of the key role of direct interactions, i.e., breakup, stripping and pick-up processes, has been carried out for deuteron-induced reactions. Particular comments concern the deuteron breakup which is the dominant mechanism involved in surrogate reactions on heavy nuclei, around the Coulomb barrier.

A theoretical study of deuteron-induced surrogate reactions

We use the zero-range post-form DWBA approximation to calculate deuteron elastic and nonelastic breakup cross sections and estimate the breakup-fusion cross section that could serve as a surrogate for a neutron-induced reaction cross section. We compare the angular momentum dependence of the breakup-fusion compound nucleus formation cross section with that of the corresponding neutron-induced cross section.

On deuteron interactions within surrogate reactions and nuclear level density studies

The consequences which the suitable consideration of direct interaction, namely the breakup, stripping and pick-up processes, may have for the analysis of the deuteron surrogate reacions as well as for studies of nuclear-level density models on the basis of nucleon spectra analysis in deuteron-induced reactions are discussed. An increased attention is paid to the deuteron breakup which is the dominant mechanism for the interaction processes at low incident energies around Coulomb barrier, particularly on actinides.

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.

A Comprehensive Approach to Determination of Nuclear Data of Unstable Nuclei

A comprehensive approach to determine nuclear data of unstable nuclei will be described. It consists of a measurement of fission and capture cross sections, mass distribution of fission fragments (independent fission yields) and number of prompt fission neutrons by the method of surrogate reactions. A multi-dimensional Langevin model is being developed to estimate the independent fission yields theoretically. Furthermore, the β decay properties of the fission fragments, almost all are neutron-rich unstable nuclei, are investigated systematically by improving the gross theory of β decay, which will yield information on the decay heat and delayed-neutron data

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.

Establishing a theory for deuteron-induced surrogate reactions

Background: Deuteron-induced reactions serve as surrogates for neutron capture into compound states. Although these reactions are of great applicability, no theoretical efforts have been invested in this direction over the last decade.Purpose: The goal of this work is to establish on firm grounds a theory for deuteron-induced neutron-capture reactions. This includes formulating elastic and inelastic breakup in a consistent manner.Method: We describe this process both in post- and prior-form distorted wave Born approximation following previous works and discuss the differences in the formulation. While the convergence issues arising in the post formulation can be overcome in the prior formulation, in this case one still needs to take into account additional terms due to nonorthogonality.Results: We apply our method to the $^{93}\mathrm{Nb}(d,p)X$ at ${E}_{d}=15$ and 25 MeV and are able to obtain a good description of the data. We look at the various partial wave contributions, as well as elastic versus inelastic contributions. We also connect our formulation with transfer to neutron bound states.Conclusions: Our calculations demonstrate that the nonorthogonality term arising in the prior formulation is significant and is at the heart of the long-standing controversy between the post and the prior formulations of the theory. We also show that the cross sections for these reactions are angular-momentum dependent and therefore the commonly used Weisskopf limit is inadequate. Finally, we make important predictions for the relative contributions of elastic breakup and nonelastic breakup and call for elastic-breakup measurements to further constrain our model.

Measurement of theγemission probability of173Yb using surrogate reactions

We performed the 174Yb(p,d) reaction in order to measure the gamma-emission probability of 173Yb. The identification of the ejectiles — allowing us to tag the production of 173Yb nuclei — was performed using the STARLiTeR detector system. Unusually, the “statistical“ γ-rays were used to determined the gammaemission probability and a spin distribution was extracted from it. A comparison with the spin distribution from the 174Yb(3He,α) reaction shows that the transferred angular momentum is similar in both reactions.

Development of Anti-Compton LaBr3(Ce) Spectrometer for Measurement of Surrogate Reactions

We have installed a new experimental apparatus to measure the γ rays from highly excited states produce by surrogate reactions. The apparatus consists of of two anti-Compton LaBr3(Ce) spectrometers to measure the γ rays and a Si ΔE−E detector to detect outgoing particles. We have used the apparatus to measure the deexcitation γ rays in compound nuclei produced by multinucleon transfer reactions.