低本底高分辨测量技术在^(16)N衰变的出射α粒子测量中的应用

Application of Low Background and High Resolution Measurement Method in Measurement ofβDelayedαDecay of ^(16)N

^(16)N的β延迟α衰变能谱在E_(c.m.)≈1.2 MeV处有一低能峰,该α峰的形状和高度可用于约束^(12) C(α,γ)^(16)O反应截面的E1部分,对其进行测量具有重要意义。本工作尝试采用重离子注入法对其进行测量,在兰州重离子加速器国家实验室RIBLL1放射性束流线上产生了^(16)N放射性束流并将其注入到双面硅微条探测器(DSSD)中,利用DSSD对其β延迟α能谱进行了测量。通过选用薄的DSSD探测器、DSSD正反面能量符合关系以及DSSD点火数约束等方法,显著减小了^(16)N衰变产生的电子对α能谱测量的干扰,将α能谱的测量阈值降低到800 keV左右,成功观测到了E_(c.m.)≈1.2 MeV处的低能峰。该方法为间接研究^(12)C(α,γ)^(16) O反应率开辟了一条新的实验方法。

The ^(12) C(α,γ)^(16) O reaction is the key nuclear reaction in the helium combustion phase of stars.The reaction rate not only directly determines the abundance ratio of carbon and oxygen,but also has an important influence on the subsequent stellar evolution process.However,its cross section at energy relevant for astrophysical applications is only poorly constrained by laboratory data.The cross sections at stellar helium-burning energy(E_(c.m.)≈0.3 MeV)are dominated by the tails of the Jπ=1-and Jπ=2+subthreshold resonances corresponding to the bound states at 7.12 MeV and 6.92 MeV.The reaction cross section of ^(12) C(α,γ)^(16) O in this energy region is extremely small,and it is difficult to measure directly due to the influence of cosmic ray background.Therefore,it is necessary to extrapolate the contribution of these subthreshold states by indirect measurement.Theαparticle spectrum followingβdecay of ^(16)N can improve the reliability of the extrapolation.βdelayedαenergy spectrum of ^(16)N has a low energy peak at E_(c.m.)≈1.2 MeV.The shape and height of the peak can be used to constrain the extrapolation of the E1 component of ^(12) C(α,γ)^(16) O reaction,which is considered to be of great importance to measure.This work tried to measureαspectrum of ^(16)N heavy ion injection.^(16)N beams from RIBLL1 at Lanzhou National Laboratory of Heavy Ion Accelerator were implanted in double-sided silicon micro strip detector(DSSD).In the experiment of measuringβdelayedαdecay by the injection method,in addition to theαand recoil nuclei,theβray generated by the decay will also deposit energy in the detector and lead to an exponentially tailed background,which can distort the energy spectrum and cause great interference to the low-energy alpha peak.Taking advantage of a series of advanced methods such as hit pattern constraint,obviously minimize the distortion of theαspectrum due toβsumming which are produced byβdecay of ^(16)N,and extend the threshold of theαspectrum down to 800 keV so that the low energy peak at E_(c.m.)≈1.2 MeV was measured successfully.The ^(16)Nβdelayαenergy spectrum measured in this work can see a 1.2 MeVαpeak,and its shape and relative height are basically consistent with the existing work.This shows that it is feasible to measure the ^(16)Nβdelayαenergy spectrum with the injection method.This new measurement opens up a new way to study the cross section of ^(12)C(α,γ)^(16)O.