Development of a low-level setup for gamma spectroscopy: Application for nuclear astrophysics using reverse kinematics

It is more and more necessary to improve the sensitivity of gamma-ray spectroscopy systems, especially in nuclear astrophysics. In the case of radiative proton capture reactions, one means is to avoid the reactions on the target impurities by using reverse kinematics. This technique is possible with the LARN accelerator and can provide very clean cross-section measurements. For that purpose, a hydrogen standard has been carried out by means of ion implantation in silicon. In addition, a low-level setup has been put in place on a new beam line of the accelerator. A high efficiency and high resolution germanium detector is used conjointly with a double shielding. A passive lead castle shielding system is used to reduce the natural radioactivity and an active shielding consisting of an anti-cosmic veto is provided by an anticoincidence between the plastic scintillator and the gamma-ray detector. The setup allows a reduction of 70% of the background interference and provides an approximately 200 fold sensitivity gain of between 600 and 3000 keV. Some other developments have also been carried out to optimize the setup. The entire setup and the reverse kinematics have been validated by measuring the cross-section of the ¹³C(p,γ)¹⁴N and ¹⁵N(p,γ)¹⁶O reactions that present some astrophysical interest.     

Curvilinear grids for WENO methods in astrophysical simulations

We investigate the applicability of curvilinear grids in the context of astrophysical simulations and WENO schemes. With the non-smooth mapping functions from Calhoun et al. (2008), we can tackle many astrophysical problems which were out of scope with the standard grids in numerical astrophysics. We describe the difficulties occurring when implementing curvilinear coordinates into our WENO code, and how we overcome them. We illustrate the theoretical results with numerical data. The WENO finite difference scheme works only for high Mach number flows and smooth mapping functions, whereas the finite volume scheme gives accurate results even for low Mach number flows and on non-smooth grids.     

W UMa型相接双星V523 Cas测光研究

对V523 Cas（W UMa型）相接双星系统进行了测光观测,并通过IRAF软件经行了测光处理,获得了其自转周期.双星系统的掩食过程中主极小和次主极小红化分别为0m.07和0m.06;主极大与相随的次主极大在V和B波段分别相差0m.018和0m.022,V523 Cas为非对称的短周期W UMa型相接双星.     

6He(p,γ)7Li反应的实验设计与束流准备

在HI-13串列加速器次级束流线上，使用7Li初级束，通过²H(⁷Li,⁶He)³He反应产生了能量为26、32和38MeV的放射性6He次级束，纯化并准直后，6He次级束流纯度可达99%，强度最大为900s^-1。使用该次级束可实现对²H(⁶He,⁷Li)n反应的角分布测量，并结合理论计算，间接导出⁶He(p,γ)⁷Li的天体物理S因子和反应率。     

Instructions for Manuscript Preparation

Plasma Science and Technology （PST） is a joumal reporting novel experimental and theoretical results and progress of interdisciplinary and application sciences in the fields related to Plasma Physics. Specific interested areas include： basic plasma phenomena; magnetically confined plasma; inertially confined plasma; astrophysics and space plasma; low temperature plasma; plasma technology and fusion engineering.     

Instructions for Manuscript Preparation

Plasma Science and Technology （PST） is a journal reporting novel experimental and theoretical results and progress of interdisciplinary and application sciences in the fields related to Plasma Physics. Specific interested areas include： basic plasma phenomena; magnetically confined plasma; inertially confined plasma; astrophysics and space plasma; low temperature plasma; plasma technology and fusion engineering.     

APPLICATION OF THE POSITRON ANNIHILATION TECHNIQUE

The principles of positron annihilation and four positron experimental techniques are described. The application of positron annihilation technique in material science. atomic physics and other related fields are discussed.     

Efficient tree codes on SIMD computer architectures

This paper describes changes made to a previous implementation of an N-body tree code developed for a fine-grained, SIMD computer architecture. These changes include (1) switching from a balanced binary tree to a balanced oct tree, (2) addition of quadrupole corrections, and (3) having the particles search the tree in groups rather than individually. An algorithm for limiting errors is also discussed. In aggregate, these changes have led to a performance increase of over a factor of 10 compared to the previous code. For problems several times larger than the processor array, the code now achieves performance levels of ∼ 1 Gflop on the Maspar MP-2 or roughly 20% of the quoted peak performance of this machine. This percentage is competitive with other parallel implementations of tree codes on MIMD architectures. This is significant, considering the low relative cost of SIMD architectures.     

Halo World: Tools for Parallel Cluster Finding in Astrophysical N-body Simulations

Cosmological N-body simulations on parallel computers produce large datasets--gigabytes at each instant of simulated cosmological time, and hundreds of gigabytes over the course of a simulation. These large datasets require further analysis before they can be compared to astronomical observations. The “Halo World” tools include two methods for performing halo finding: identifying all of the gravitationally stable clusters in a point-sampled density field. One of these methods is a parallel implementation of the friends of friends (FOF) algorithm, widely used in the field of N-body cosmology. The new IsoDen method based on isodensity surfaces has been developed to overcome some of the shortcomings of FOF. Parallel processing is the only viable way of obtaining the necessary performance and storage capacity to carry out these analysis tasks. Ultimately, we must also plan to use disk storage as the only economically viable alternative for storing and manipulating such large data sets. Both IsoDen and friends of friends have been implemented on a variety of computer systems, with parallelism up to 512 processors, and successfully used to extract halos from simulations with up to 16.8 million particles.