Investigation of7Be(n,p)7Li reaction

The⁷Be(n, p)⁷Li nuclear reaction with thermal and 2 keV neutrons was studied. For thermal neutrons the total cross section of (46 800± 4 000) b was obtained and the proton branching ratio to the first excited and ground states of⁷Li was determined to be ₁/₀ = (2±1) %. For 2 keV neutrons the upper limit of the cross section of 540 b was estimated.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.The autors thank Mr. A. Dvoák and Mrs. B. Michalcová for their manufacturing the⁶Li standards, Dr. J. Frána for his help in determining the number of⁷Be atoms and Ing. J. Hoffmann, Mr. J. Novotný and Mr. J. Badura for their careful preparation of electronics.     

The cross section of the7Be(n,p)7Li reaction at 24.5 keV neutron energy

The 24.5 keV neutrons induced reaction with the⁷Be radioactive nucleus was studied. The value of σ_np=(18±4)b was obtained for the⁷Be(n, p)⁷Li reaction cross section.     

A study of the Li(p,n)Be reaction by the neutron threshold technique

The reaction ⁶Li(p,n)⁶Be has been studied by slow-neutron detection, with particular attention to the ⁶Be ground state threshold. The detector response was calculated by a Monte Carlo technique and verified with a measurement of the ⁷Li(,n)¹⁰B threshold. An analysis of the shape of the ⁶Be threshold indicated that both s- and p-wave neutrons contribute significantly to the reaction. The results depend on what mode of decay is assumed for the ground state of ⁶Be. If a two-stage process is assumed, with either an alpha particle and an unbound diproton or ⁵Li and a proton as intermediate state, the width is found to be 95±28 keV and the Q-value obtained for the ⁶Li(p,n)⁶Be reaction is −5074±13 keV. It was not possible to detertmine which process is predominant. No higher thresholds in the slow neutron yield up to 4 MeV of excitation in ⁶Be were observed. The data above the ground state threshold are consistent with a broad excited state of ⁶Be or with the occurrence of other neutron-producing reactions.     

Be(d,n)反应中子源能谱测量及应用

利用中子飞行时间技术和BC501A液体闪烁探测器的粒子分辨特性,测量了0°方向、20 MeV氘束轰击厚金属铍靶反应产生的中子源能谱,测量的中子能谱范围为0.7～25.0 MeV。在60°方向放置芪晶体闪烁探测器,由刻度好的BC501A液体闪烁探测器归一校正后,用于中子源强度监测。利用Be(d, n) 反应中子源,采用单粒子灵敏度标定方法,实验标定了0.75~15.75 MeV能量范围内的薄膜闪烁探测器中子能量响应曲线,实验结果与蒙特卡罗模拟计算结果在8%的不确定度范围内一致。     

Be(d,n)反应中子源能谱测量及应用

 利用中子飞行时间技术和BC501A液体闪烁探测器的粒子分辨特性,测量了0°方向、20 MeV氘束轰击厚金属铍靶反应产生的中子源能谱,测量的中子能谱范围为0.7～25.0 MeV。在60°方向放置芪晶体闪烁探测器,由刻度好的BC501A液体闪烁探测器归一校正后,用于中子源强度监测。利用Be(d, n) 反应中子源,采用单粒子灵敏度标定方法,实验标定了0.75~15.75 MeV能量范围内的薄膜闪烁探测器中子能量响应曲线,实验结果与蒙特卡罗模拟计算结果在8%的不确定度范围内一致。     

Measurement of (p,n) and (n,p) reactions on 6Li and 7Li at 800 MeV

The measured ⁷Li(p,n), and ⁶Li(n,p) cross sections at 0° show a high-energy peak (≈25 MeV/c FWHM) which we attribute primarily to nuclear charge exchange leading to final states in ⁷Be, ⁶Be, and ⁶He, respectively. By contrast, the ⁷Li(n,p) cross section at O° shows a broad weak high-energy peak believed due mostly to break-up processes. At 16°, the ^6,7Li(n,p) cross sections are dominated by quasi-elastic scattering.     

Neutron beam optimization based on a ~7Li(p,n)~7Be reaction for treatment of deep-seated brain tumors by BNCT

Neutron beam optimization for accelerator-based Boron Neutron Capture Therapy(BNCT) is investigated using a7Li(p,n)7Be reaction. Design and optimization have been carried out for the target, cooling system,moderator, filter, reflector, and collimator to achieve a high flux of epithermal neutron and satisfy the IAEA criteria.Also, the performance of the designed beam in tissue is assessed by using a simulated Snyder head phantom. The results show that the optimization of the collimator and reflector is critical to finding the best neutron beam based on the7Li(p,n)7Be reaction. Our designed beam has 2.49×109n/cm2 s epithermal neutron flux and is suitable for BNCT of deep-seated brain tumors.     

Measurements of neutron energy spectra of 9Be(d,n)10B reaction with a thick beryllium target

Novel measurements of the neutron energy spectra of the 9Be(d,n)10B reaction with a thick beryllium target are performed using a fast neutron time-of-flight(TOF)spectrometer for the neutron emission angles θ=0°and 45°,and the incident deuteron energies are 250 and 300 keV,respectively.The neutron contributions from the 9Be(d,n)10B reaction are distributed relatively independently for the ground state and the first,second,and third excited states of 10B.The branching ratios of the 9Be(d,n)10B reaction for the different excited states of 10B are obtained for the neutron emission angles θ=0°and 45°,and the incident deuteron energies are 250 and 300 keV,respectively.The branching ratio of the 9Be(d,n)10B reaction for the third excited state decreases with increase in the incident deuteron energy,and the branching ratios for the ground state and the second excited state increase with increase in the neutron emission angle.     

Isovector giant resonances in light nuclei observed by (7Li, 7Be) reaction

Isovector giant resonances were studied with the (⁷Li, ⁷Be) reaction on ¹²C, ²⁴Mg, ²⁷Al, ²⁸Si and ⁴⁸Ti at an incident energy of 150 MeV. Differential cross sections were measured at forward scattering angles including 0°. We observed the octupole resonance at E_x ∽ 16 MeV and the giant dipole resonance at E_x ∽ 20 MeV in all residual nuclei.     

The4He(α,p)7Li,7Li*0.478 reaction near threshold

Differential cross sections for the reaction⁴He(α,p)⁷Li,⁷Li^{* 0.478MeV} have been obtained at nine energies between 37 and 43 MeV in the laboratory system. It is shown that these results are consistent with a non zero inelasticity in thel=4 partial wave of the entrance channel. Comparisons with the reaction cross section for the⁴He-α interaction are discussed.     

Production of a monochromatic γ-ray beam by a Li7(p, γ)Be8 reaction

A procedure is described for producing a monochromatic beam of 17.6 and 14.8 MeV -rays. Energy calibrations are reported for a single-crystal total-absorption -spectrometer and for the proton beam of an electrostatic generator during the resonant capture of protons by lithium target nuclei in a Li⁷(p, )Be⁸ reaction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 5, pp. 18–21, May, 1969.The authors thank E. M. Vasil'ev and G. V. Zinger for arranging stable operation of the ÉSG-2.5 of the Scientific Research Institute of Nuclear Physics, Tomsk Polytechnic Institute.     

快中子堆n，γ混合场中γ光子注量的测量研究

用热释光探测器对快堆堆外n,γ混合场进行了区分测量，结果表明：该方法可有效的检测出n,γ混合场的γ成分；为了更较精确地测量快堆n，γ混合场γ光子注量，提出了采用新配方的热释光探测器LiFTLD(6LiF,７LiF各占50%)与6LiFTLD成对使用的方法.考虑到LiFTLD对中子吸收剂量的响应存在LET效应，对LiF(Mg,Cu,P)TLD进行了中子响应的LET效应因子RLET的实验测定(RLET≈005)，在此基础上，对６LiF 7LiFTLD的成对使用测量快中子堆的n,γ混合场中光子注量的方法进行了实验研究.实验结果表明，混合场中的中子在7LiF(Mg,Cu,P)中产生的热释光量(TL)占n,γ产生的总TL的81%—171%.实验结果表明该方法是行之有效的.为钝化中子谱的不确定性所致的影响，进一步提高γ光子注量测量结果的精度，提出了采用新配方的LiFTLD(6LiF,7LiF各占50%)与6LiFTLD成对使用测量快堆n,γ混合场γ光子注量的方法.     

The 28Si(7Li, 7Be)28Al reaction at 36 MeV

The ²⁸Si(⁷Li, ⁷Be)²⁸Al reaction has been investigated at E_7Li = 36 MeV. States and groups of states were observed up to 5.3 MeV excitation in the ²⁸Al+⁷Be system. Experimental angular distribution for unresolved doublets of states at ≈ 0.0 and 0.44 MeV excitation, corresponding to ⁷Be in its ground state (⁷Be₀) and first excited states (⁷Be₁) with ²⁸Al in its ground state (3⁺) and first excited state (0.031 MeV, 2⁺) are compared with microscopic distorted wave approximation calculations.     

Direct and sequential processes in the 16O(7Li, 7Be)16N reaction

Calculations are presented for the ¹⁶O(⁷Li, ⁷Be)¹⁶N charge exchange reaction. For the direct reaction, the tensor interaction leads to form factors with large spin and angular momentum transfer which are important for the unnatural parity states. The (⁷Li, ⁶Li)(⁶Li,⁷Be) sequential process exhibits a strong J-dependence and is the dominant contribution to the natural parity states.     

Precision measurement of the 7Be(p,gamma)8B cross section with an implanted 7Be target

The 7Be(p,gamma)8B reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted 7Be target, a raster-scanned beam, and the elimination of the backscattering loss. The new measurement incorporates a more abundant 7Be target and a number of improvements in design and procedure. The point at E(lab)=991 keV was measured several times under varying experimental conditions, yielding a value of S17(E(c.m.)=850 keV)=24.0+/-0.5 eV b. Measurements were carried out at lower energies as well. Because of the precise knowledge of the implanted 7Be density profile, it was possible to reconstitute both the off- and on-resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of S17(0)=21.2+/-0.7 eV b.     

Measurements of the light output functions of plastic scintillator using 9Be(d,n)10B reaction neutron source

The light output functions for protons of ST-401 and BC-408 plastic scintillators were measured using white neutron source produced by the 9Be(d,n)10B reaction at the HI-13 Tandem Accelerator at China Institute of Atomic Energy(CIAE).The LOFs of plastic scintillators for protons in the energy range of 0.516.5 MeV were obtained by the time-of-flight(TOF)technique and an iterative procedure.Two parameters(kB and C)were deduced by fitting the experimental data.     

Low-energy S(E) factor of 9Be(p, α)6Li and 9Be(p,d)8Be

Excitation functions and angular distributions of the ⁹Be(p, α)⁶Li and ⁹Be(p, d)⁸Be reactions have been measured over the energy range E _p = 16 to 390 keV. The data are dominated by one broad resonance including interference effects with a direct process. The effects of electron screening have also been observed, which are however significantly larger than expected. The deduced reaction rates at T₉ ≤ 1 are in excellent agreement with values given in a compilation.     

Analysis of (n,n) and (d,p) reactions on the same target using phase-equivalent potentials

The difference between (d, p) “Stripping into Continuum” and (n, n) Elastic Scattering on the same target has been investigated and discussed in terms of a non-local force and its local equivalent. In general our results indicate an influence of non local effects. In particular with the inclusion of the non locality a possible spin assignment for the levels at the excitation energiesE _x =3.359 MeV and 3.519 MeV in the reaction¹⁵N(d, p)N¹⁶ (unbound) has been indicated.     

The d(e,e′p)n reaction and the neutron electric form factor

The cross section for the d(e, e′p)n reaction is calculated for quasi-free kinematics in the impulse approximation including the final state interaction and the pair current contributions. Its dependence on the recoil momentum agrees quite well with recent Saclay data up to p = 350 MeV/c. We also show a measurement of the cross section for quasi-elastic scattering in which one detects low energy protons may provide information on G_Eⁿ.