适合探测较轻粒子的一种多极平行板雪崩计数器

一种高性能多极双维位置灵敏平行板雪崩计数器(multi-plate parallel plate avalanchecounter,MPPAC)在兰州中能重离子加速器放射性次级束流线(radioactive ion beam line in lanzhou,RIBLL)上被应用,由二次雪崩带来的高增益使它很适合探测较高能量的较轻粒子,它主要由1个中心阳极,x,y位置栅极和2个阴极组成,位置信号由x,y位置栅极采用电荷分除法读出,使用异丁烷工作气体,气压650Pa,阳极+400V,阴极-350V时,对于α粒子位置分辨为0.55mm(半高全宽度,fwhm),位置线性色散远好于±0.2mm,探测效率大于99.2％,同时,也研究了位置分辨与阳极、阴极电压的关系,与放大器成形时间常数的依赖,随工作气压变化等。

Low-lying non-normal parity states in B-8 measured by proton elastic scattering on Be-7

A new measurement of proton resonance scattering on Be-7 was performed tip to the center-of-mass energy of 6.7 MeV using the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) at the Center for Nuclear Study of the University of Tokyo. The excitation function of Be-7 + p elastic scattering above 3.5 MeV was measured Successfully for the first time, providing important information about the resonance structure of the B-8 nucleus. The resonances are related to the reaction rate of Be-7(p.gamma)B-8. which is the key reaction in solar B-8 neutrino production. Evidence for the presence of two negative parity states is presented. One of them is a 2(-) state observed as a broad s-wave resonance, the existence of which had been questionable. Its possible effects on the determination of the astrophysical S-factor of Be-7(p.gamma)B-8 at solar energy are discussed. The other state had not been observed in previous measurements, and its spin and parity were determined as 1(-). (C) 2009 Elsevier B.V. All rights reserved.

Investigation of excited states in Mg-22 via resonant elastic scattering of Na-21+p and its astrophysical implications

The excited states in 22Mg have been investigated by the resonant elastic scattering of 21Na + p. A 4.0 MeV/nucleon 21Na beam was separated by the Center for Nuclear Study (CNS) radioactive ion beam separator (CRIB) and then used to bombard a thick (CH2)n target. The energy spectra of recoiled protons were measured at scattering angles of θc.m. ≈ 172◦ , 146◦, and 134◦, respectively. A wide energy-range of excitation function in 22Mg (up to Ex ∼ 8.9 MeV) was obtained simultaneously with a thick-target method, and a state at 7.06 MeV was newly observed. The resonant parameters were deduced from an R-matrix analysis of the center-of-mass (c.m.) differential cross-section data with a SAMMY-M6-BETA code. The astrophysical resonant reaction rate for the 18Ne(α,p)21Na reactionwas recalculated based on the present parameters. Generally speaking, the present rates are much smaller than the previous ones.