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in the last few years , nuclear reactions involving weakly bound nuclei became a subject of interest due to the observation of flux enhancement for processes like nucleon transfer and breakup . through the study of these processes @xcite , it is possible to obtain information about nuclear structure , such as single - particle states and nuclear cluster structure , as well as information about the influence of continuum states in the nuclear reaction dynamics @xcite . additionally , the investigation on how these properties change from the stability line to regions far from the stability valley can also be addressed . in this context , the elastic scattering measurement and coupled channel analysis @xcite are very important tools to investigate nucleon transfer and breakup , as they appear as competing mechanisms in the reproduction of the measured angular distributions .    in this work , elastic scattering cross section measurements were performed for the @xmath3be+@xmath1c reaction to study anomalies @xcite in the extracted optical parameters values and the contribution of inelastic channels , transfer and compound nucleus formation in the elastic scattering process . the experimental data show an enhancement in the elastic cross sections at intermediate and backward angles . this behavior is typically observed in systems where projectile and target present the same core structure @xcite . this effect can be understood in terms of a @xmath4he transfer process , assuming that @xmath1c has a @xmath4he+@xmath0be cluster structure . the elastic scattering angular distributions were analyzed in a four steps procedure . distinctively of previous works , our experimental elastic scattering data have been compared to optical model predictions using a empirical double folding potential @xcite . in this process , the normalization parameters for the real and imaginary potentials were adjusted to describe the data at forward angles ( @xmath5@xmath680@xmath7 ) . the normalization of the real part of the potential shows a decrease as a function of the bombarding energy , and the normalization of the imaginary part of the potential is approximately constant . during the following two steps , we investigate the importance of the coupling to inelastic and transfer channels respectively , and finally in the fourth step we analyse the compound elastic contribution . the experiment was performed at the university of so paulo physics institute . the @xmath3be beam was delivered by the 8ud pelletron accelerator with energies e@xmath2=13.0 , 14.5 , 17.3 , 19.0 and 21.0 mev ( e@xmath8=7.4 , 8.3 , 9.9 , 10.8 and 12.0 mev respectively ) and hit a 40 @xmath9g/@xmath10 thick @xmath1c target . the charged particles produced in the @xmath3be+@xmath1c reaction were detected by means of 13 triple telescopes @xcite separated by @xmath11 = 10@xmath7 in the reaction plane , which covered the angular range from @xmath12 = 10@xmath7 to @xmath12 = 140@xmath7 . the triple telescopes were composed of an ionization chamber , filled with 20 _ torr _ of isobutane gas , followed by a 150 @xmath9 m silicon detector and a 40 mm csi scintillator crystal . the identification of the elastic events was done by means of two - dimensional spectra like the one shown in fig . [ biparametrico]-a . the elastic yields were obtained by projecting the z = 4 region on the e@xmath13 axis ( energy measured by the silicon detector ) and identifying the elastic processes as shown in fig . [ biparametrico]-b . as ilustraded in this figure , we can see a considerable number of events due to target contamination . in order to subtract the contributions in the energy spectra from this target contamination , we have assumed rutherford scattering for the involved cross sections . this is a good approximation in our experimental conditions . the uncertainties in the differential cross section were estimated considering the statistical uncertainty in the yield and the systematic uncertainty of 5% in the target thickness . in the present work , the experimental data were analyzed using the fresco code @xcite in the framework of the so paulo potential ( spp ) @xcite due to the recent success of this approach in describing nuclear reactions involving weakly bound nuclei @xcite . clearly , there are other options for the scattering potential , as shown in recent works by a. t. rudchick _ et . _ @xcite and j. carter _ et . @xcite who have used a woods - saxon shape and a double folding potential , respectively , and the effects of coupled channels to describe the @xmath3be+@xmath1c scattering data .    for the so paulo potential , the radial dependence is a folding potential and the energy dependence takes non - local effects into account , in the form @xmath14 where @xmath15=v / c , @xmath16 is the local relative velocity between the two nuclei and @xmath17 is a folding potential obtained by using the matter distributions of the nuclei involved .    in detail , the folding potential depends on the matter densities in the form    @xmath18    where @xmath19 is a physical nucleon - nucleon interaction given by    @xmath20    with @xmath21 mevfm@xmath4 and the usage of a delta function corresponds to the zero range approach . extensive systematics were performed in ref . @xcite , to provide a good description of matter and charge distribution .    in the present work , we adopt the matter and charge diffuseness @xmath23 fm and @xmath24 fm respectively , and the matter and charge distribution radius given by @xmath25 and @xmath26 respectively . in this first step of the analysis , we considered the real and imaginary potential normalizations as free parameters that are adjusted in order to describe the forward angles of the angular distribution ( @xmath5 @xmath6 80@xmath7 ) . in this case the nuclear potential is given by the equation @xmath27 where the normalization coefficients @xmath28 and @xmath29 are reaction energy dependent . the results for the first step are shown as solid lines in fig . [ elastico ] . we observe a good agreement for the forward angular region . however , a pronounced disagreement at backward angles for 17.3 , 19.0 and 21.0 mev , is an indication of the importance of other reaction mechanisms , not taken into account in the optical potential . for 13.0 and 14.5 mev , the optical model description is reasonable . finally , fig . [ elastico ] also shows an angular distribution for e@xmath2=19.0 mev extracted from ref . these data are in good agreement with our data and with the optical model calculation at forward angles . the @xmath28 and @xmath29 energy dependence is depicted in fig . the uncertainties are determined by a @xmath30 analysis . one can notice that n@xmath31 increases in the vicinity of the coulomb barrier energy ( e@xmath8 @xmath32 9 mev @xcite ) . the values of n@xmath33 are approximately constant for all energies , and they are in agreement with the results obtained in ref . @xcite . the increase of the n@xmath31 parameter near the coulomb barrier suggests the presence of a threshold anomaly @xcite . however , no strong statement about this anomaly can be made due to the constant behavior of n@xmath33 . the results from the first step of the analysis were used to perform the coupling of the inelastic and transfer channels presented in the next sections . be + @xmath1c system at e@xmath2 = 13.0 , 14.5 , 17.3 , 19.0 and 21.0 mev . the solid lines correspond to optical model fits , the dashed and dash dotted lines represent the same optical potential including the inelastic and elastic transfer mechanisms respectively ( color online ) . ]     and n@xmath33 as a function of the bombarding energy obtained from fits using the so paulo potential ( equation [ sppotential ] ) for the @xmath0be + @xmath1c system . the lines are just to guide the eyes ( color online ) . ]      with the optical potentials previously obtained , we are able to take into account the effects of other channels . the second step of the analysis consisted in calculating the effects of inelastic channels in the theoretical elastic cross section , by considering 5/2@xmath34 and 7/2@xmath34 states of @xmath35be and 2@xmath36 of @xmath1c .    in our study the transitions to excited states of @xmath35be and @xmath1c were calculated using the rotational model approach , where the coupling interaction v@xmath37(*r * ) of the multipole @xmath38 is    @xmath39    the coulomb excitations are included by considering deformations on the charge distributions in the form    @xmath40    where    @xmath41    therefore , to take into account the effects of inelastic process in the theoretical elastic cross section , we take from the literature @xcite the nuclear deformation parameters @xmath42 and the reduced transition probabilities b(e@xmath38:j@xmath43@xmath44j@xmath45 ) , in order to calculate the deformations on the symmetrical central potential . the parameters for each channel included in the calculations and the reduced transition probabilities are presented in table [ tabela1 ] . p2 cm p2 cm p2 cm p2 cm p2 cm nucleus & transition & @xmath38 & b(e@xmath38 ) & @xmath42 + @xmath3be & @xmath46 @xmath44 @xmath47 & 2 & 46.0@xmath480.5 & 2.4 +   + @xmath3be & @xmath46 @xmath44 @xmath49 & 2 & 33@xmath48 1 & 2.4 +   + @xmath1c & @xmath50 @xmath44 @xmath51 & 2 & 42@xmath48 1 & 1.52 +   +     + [ tabela1 ]    the results are shown as dashed lines in fig . [ elastico ] . in general , we observed that the inclusion of these channels decreases the theoretical cross section when compared to the results obtained only with the optical potential .    comparing with the experimental data , we observed that the curves show a good description at forward angles . for intermediate and backward angles , the theoretical prediction underestimates the cross section . this demonstrates that the inclusion of these inelastic channels is not sufficient to explain the experimental results at intermediate and backward angles .      in order to improve the description of experimental elastic distributions at intermediate and backward angular region , a coupling to the @xmath52he transfer was included in the third step of the analysis . p3 cm p1.75 cm p1.5 cm p1.5 cm systems & v@xmath53(mev ) & r@xmath53(fm ) & a@xmath53(fm ) +   + @xmath3be+@xmath0be@xmath54 & 189.3 & 1.0 & 0.63 +   + @xmath4he+@xmath3be & 55.8@xmath55 & 1.35 & 0.65 +   +     +    p3 cm p1.75 cm p1.5 cm p1.5 cm a = c+v & j@xmath56 & @xmath57 & a +   + @xmath1c=@xmath0be @xmath58 @xmath52he & 0@xmath59 & 2p@xmath60@xmath61 & 1.224@xmath61 +   + [ parametrospotencialoptico ]     +    .optical parameters for dwba calculations and spectroscopic factor for a a = c+v system . [ cols= " < " , ]      +    the calculation was performed using the hauser - feshbach statis code @xcite . the nuclear level density has been described by means of a level density expression given by lang @xcite , and the transmission coefficients were determined by an internal fermi parametrization @xcite . the levels considered in this calculations are listed on table [ tabela3 ] and are quite similar to those used in the ref . @xcite . = 19.0 and 21.0 mev . the calculated points , were normalized to agree with behavior of data from @xcite ( color online ) . ] finally the angular distributions are normalized in such a way that the total cross section agree with the results presented in the excitation function from ref . @xcite ( figure [ secaototalcompound ] ) . when the obtained angular distributions are incoherently added to the @xmath52he transfer results , we can see that the contribution of this reaction mechanisms is not relevant , even for our highest energies , as shown in fig . [ total ] for the two highest energies e@xmath2 = 19.0 and 21.0 mev . be + @xmath1c system at e@xmath2 = 19.0 and 21.0 mev . the dot lines are the ce angular distributions from hf calculations . we can notice that the contribution of ce to differential cross section enhancement at backward angles is not significante ( color online ) . ] in this work we measured elastic scattering angular distributions for the @xmath35be+@xmath1c light system at bombarding energies ranging from 13.0 mev to 21.0 mev . the double folding so paulo potential was used in the analysis that was performed in four steps .    in the first one we considered n@xmath53 and n@xmath43 as free parameters for the fits to the angular distributions at the forward angular region . the angular distributions calculated with the optical model have shown a good agreement with the 13.0 and 14.5 mev experimental data . for 17.3 , 19.0 and 21.0 mev the agreement is reasonable at forward angles . however , the description at backward angles is not good , suggesting that the coupling to other mechanisms is important .    in the second step of the analysis , no evidence of the coupling to inelastic channels was observed . using the spectroscopic factors extracted from the literature for @xmath1c=@xmath4he@xmath58 @xmath3be , in the third step we took into account the @xmath4he elastic transfer channel . for the @xmath4he transfer we see a pronounced improvement in the description of the data for 17.3 , 19.0 and 21.0 mev , which suggests that this process is important at intermediate and backward angles . finally in the fourth step , corresponding to the compound elastic calculation , the results suggest that this mechanism is not an important process at the energies studied in this work .      finally , to obtain information about the effects of the elastic transfer process and check the values of spectroscopic factors , it would be important to perform a more carefully analysis and measurements of the elastic scattering angular distributions at more backward angles .
in this work , angular distribution measurements for the elastic channel were performed for the @xmath0be+@xmath1c reaction at the energies e@xmath2=13.0 , 14.5 , 17.3 , 19.0 and 21.0 mev , near the coulomb barrier . 
 the data have been analyzed in the framework of the double folding so paulo potential . 
 the experimental elastic scattering angular distributions were well described by the optical potential at forward angles for all measured energies . however , for the three highest energies , an enhancement was observed for intermediate and backward angles . 
 this can be explained by the elastic transfer mechanism . 
 @xmath0be+@xmath1c , elastic scattering , so paulo potential 24.10