Stepped-up development of accelerator mass spectrometry method for the detection of ^(60)Fe with the HI-13 tandem accelerator

The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae.Lunar samples retain valuable information from these events,via detectable long-lived“fingerprint”radionuclides such as^(60)Fe.In this work,we stepped up the development of an accelerator mass spectrometry(AMS)method for detecting^(60)Fe using the HI-13tandem accelerator at the China Institute of Atomic Energy(CIAE).Since interferences could not be sufficiently removed solely with the existing magnetic systems of the tandem accelerator and the following Q3D magnetic spectrograph,a Wien filter with a maximum voltage of±60 kV and a maximum magnetic field of 0.3 T was installed after the accelerator magnetic systems to lower the detection background for the low abundance nuclide^(60)Fe.A 1μm thick Si_(3)N_(4) foil was installed in front of the Q3D as an energy degrader.For particle detection,a multi-anode gas ionization chamber was mounted at the center of the focal plane of the spectrograph.Finally,an^(60)Fe sample with an abundance of 1.125×10^(-10)was used to test the new AMS system.These results indicate that^(60)Fe can be clearly distinguished from the isobar^(60)Ni.The sensitivity was assessed to be better than 4.3×10^(-14)based on blank sample measurements lasting 5.8 h,and the sensitivity could,in principle,be expected to be approximately 2.5×10^(-15)when the data were accumulated for 100 h,which is feasible for future lunar sample measurements because the main contaminants were sufficiently separated.

First proof-of-principle experiment with the post-accelerated isotope separator on-line beam at BRIF:measurement of the angular distribution of ^(23)Na+^(40)Ca elastic scattering

The reaction dynamics of exotic nuclei near the drip line is one of the main research topics of current interest.Elastic scattering is a useful probe for investigating the size and surface diffuseness of exotic nuclei.The development of rare isotope accelerators offers opportunities for such studies.To date,many relevant measurements have been performed at accelerators using the projectile fragmentation technique,while the measurements at accelerators using isotope separator on-line(ISOL)systems are still quite scarce.In this work,we present the first proof-of-principle experiment with a post-accelerated ISOL beam at the Beijing Radioactive Ion Beam Facility(BRIF)by measuring the angular distribution of elastic scattering for the stable nucleus^(23)Na from the doubly magic nucleus^(40)Ca at energies above the Coulomb barrier.The angular distribution measured by a silicon strip detector array in a scattering chamber using the ISOL beam at BRIF is in good agreement with that measured by the high-precision Q3 D magnetic spectrograph using the nonISOL beam at nearly the same energy.This work provides useful background for making BRIF a powerful tool for the investigation of the reaction dynamics of exotic nuclei.

Root hemiparasitism in Malania oleifera(Olacaceae), a neglected aspect in research of the highly valued tree species

Malania oleifera(Olacaceae)is a valued tree species,mostly because its seeds have high precious fatty acid content(particularly nervonic acid).However,seedling mortality rates are often high and regeneration of this tree has been problematic,which greatly hinders its utilization at a large scale.Cultivation difficulties of some tree species in the family Olacaceae have been attributed to their root hemiparasitic habit.Prompted by field observations and the taxonomic proximity of M.oleifera to root hemiparasites in Olacaceae,we hypothesized that tuberous structures observed on the roots of M.oleifera are parasitic organs known as haustoria.To test this hypothesis,we collected root samples from M.oleifera plants of various ages and growth conditions,investigated the morphological and anatomical features of tuberous structures and their connections to neighboring roots.Our analyses confirmed that M.oleifera are root hemiparasites.To the best of our knowledge,this is the first empirical report on root hemiparasitism in M.oleifera.Because life strategies of root hemiparasitic plants differ greatly from autotrophic plants,the root hemiparasitic habit needs to be taken into account for successful seedling regeneration of M.oleifera.This study establishes the foundation for investigations into a long-neglected but essential aspect in research of these highly valued tree species.

Preparation of large-area isotopic magnesium targets for the 25Mg(p,γ)^26 Al experiment at JUNA

To study the 25Mg(p,y)^26 Al reaction at the Jinping Underground Nuclear Astrophysics laboratory,a large-area 25Mg target with a uniform thickness is needed.A rotating unit is used to ensure the uniformity of the target thickness during evaporation.After many attempts,19 targets with diameters of 40 mm and a non-uniformity of8.4%were prepared simultaneously.The rate of material utilization was approximately 4.7 times higher than that obtained using a conventional evaporation method.

New determination of the^7Be ground state spectroscopic factor and the^6Li(p,γ)^7Be astrophysical S(E)factors

The ＇lithium problem, in Big Bang nucleosynthesis（BBN） has recently focused on reactions involving ^7 Be.The ^6 Li（p,γ）^7 Be reaction can provide us not only with information about ^6 Li destruction but also with information about ^7 Be production. In the present work, the proton spectroscopic factor in ^7 Be is extracted to be 0.70 ± 0.17 from the angular distribution of ^7 Be（d, ^3 He）^6 Li at Ec.m. = 6.7 MeV. This value is then used to compute the direct component of the astrophysical ^6 Li（p,γ）^7 Beg.s. S（E） factors and determine the resonance parameters from the total S（E） factors.

Measurement of the^2H(^7Be,^6Li)^3He reaction rate and its contribution to the primordial lithium abundance

In the standard Big Bang nucleosynthesis （SBBN） model, the lithium puzzle has attracted intense interest over the past few decades, but still has not been solved. Conventionally, the approach is to include more reactions flowing into or out of lithium, and study the potential effects of those reactions which were not previously considered. 7Be（d, 3He）6Li is a reaction that not only produces 6Li but also destroys 7Be, which decays to 7Li, thereby affecting 7Li indirectly. Therefore, this reaction could alleviate the lithium discrepancy if its reaction rate is sufficiently high. However, there is not much information available about the 7Be（d, 3He）6Li reaction rate. In this work, the angular distributions of the 7Be（d, 3He）6Li reaction are measured at the center of mass energies Ecm=4.0 MeV and 6.7 MeV with secondary 7Be beams for the first time. The excitation function of the 7Be（d, 3He）6Li reaction is first calculated with the computer code TALYS and then normalized to the experimental data, then its reaction rate is deduced. A SBBN network calculation is performed to investigate its influence on the 6Li and 7Li abundances. The results show that the 7Be（d, 3He）6Li reaction has a minimal effect on 6Li and 7Li because of its small reaction rate. Therefore, the 7Be（d, 3He）6Li reaction is ruled out by this experiment as a means of alleviating the lithium discrepancy.

Direct measurement of the resonance strengths and branching ratios of low-energy(p,γ)reactions on Mg isotopes

Proton capture reactions on Mg isotopes are significant in the Mg-Al cycle in stellar H-burning.In particular,the resonance strengths and branching ratios of low-energy resonances in 23Mg(p,γ)26Al reactions determine the production of which is one of the most important long-lived radioactive nuclei in nuclear astrophysics.In this article,we report our first experiment using the intense proton beam of approximately 2 mA provided by the JUNA accelerator ground laboratory and a new technique that can minimize the composition change of targets under intense beam irradiation.The resonance strengths and branching ratios of E=214,304,and 326 keV resonances in the reactions of 2~4Mg(p,γ)25Al,25Mg(p,γ)26Al,and 26Mg(p,γ)27Al,respectively,were measured with high accuracy.The success of this experiment provides a good calibration for the nuclear astrophysical experiment at the Jinping underground laboratory.

The angular distributions of elastic scattering of^12,13C+Zr

To obtain the neutron spectroscopic amplitudes for 90-96Zx overlaps experimental data of elastic scatter-ing with small experimental errors and precise optical potentals were anary exin othe hiohpyecision o3D magneticangular distributions of^12,^13C+^AZr(A=90,91,92,94,96)were measured using the high-precision Q3D magnetic spectrometer in the Tandem accelerator.The Sao Paulo potential was used for the optical potential.The optical mod-el and coupled channel calculations were compared with the experimental data.The theoretical results were found tobe very close to the experimental data.In addition,the possible effects of the couplings to the inelastic channels of the^AZr targets and 12,13^C projectiles on the elastic scattering were studied.It was observed that the couplings to the in-elastic channels of the^12,^13C projectiles could improve the agreement with the experimental data,while the inelasticcouplings to the target states are of minor importance.The effect of the one-neutron stripping in the^13C+^AZr elasticscattering was also studied.The one-neutron stripping channel in^13C+^AZr was found to be not relevant and did notaffect the elastic scattering angular distributions.Our results also show that in the reactions with the considered zir-conium isotopes,the presence of the extra neutron in^13C does not influence the reaction mechanism,which is gov-erned by the collective excitation of the^12C core.