Track etch rates along the trajectories of nitrogen and oxygen ions in CR-39

Experimental studies on track etch rates in CR-39 performed with protons, deuterons and alpha particles as well as ⁷Li, ¹¹B and ¹²C ions were extended to ¹⁴N and ¹⁶O ions. The results are compatible with the general systematics found for the dependence on the kind of ion and its initial energy. Analysing the etch rate ratios as function of the restricted energy loss (REL), the non-existence of a unique relationship has been confirmed. However, assuming a dependence of the etch rate ratio not only on REL, but also on the depth within the detector where a given REL value occurs, all experimental data could be adjusted. The experiments with ¹⁴N and ¹⁶O ions allow extension of the REL range studied up to about 14 000 MeV/cm. The whole area relevant to neutron-induced charged particles generated within the CR-39 detectors is covered thereby. Having added the data for ¹⁴N and ¹⁶O ions, the array of curves for the etch rate ratio could be expanded up to 14 000 MeV/cm without inconsistencies, demonstrating the compatibility of the new data set also quantitatively.     

Low energy alpha particle spectroscopy using CR-39 detector

The possibility of using CR-39 to measure the depth profile of ¹⁰B in Si is analysed. The measuring technique exploits the ¹⁰B(n, )⁷Li nuclear reaction. For this reason the track parameters (size, optical properties) of low energy alpha-particles (<1.47 MeV) were studied. The results showed that an energy resolution of about 100 keV could be obtained by an appropriate selection of etching conditions. The profile of ¹⁰B in Si at a depth as small as 1 μm can be measured.     

Stopping powers of CR-39 nuclear track material for Z=1−14 ions with 0.25–2.8 MeV/u

Experimental studies of the slowing down of ¹H, ⁴He, ⁷Li, ¹¹B, ¹²C, ¹⁴N, ¹⁶O, ²³Na, ²⁷Al and ²⁸Si ions in CR-39 nuclear track etch material in the ion energy range 0.25–2.8 MeV/u are presented. The ion stopping powers obtained are compared to the predictions of two recent semiempirical models for calculating ion stopping powers. The predictions are found to clearly underestimate the observed stopping powers for ⁷Li, ¹¹B, ¹²C, ²³Na, ²⁷Al and ²⁸Si ions.     

Photoparticle production in solid state detectors used for neutron dosimetry in the presence of photons

Photon-induced neutron, proton and alpha particle production in polyethylene and CR-39 has been estimated for the photon energy range of 2–30 MeV, using our previously established methods and photonuclear cross-section data for hydrogen, carbon and oxygen. The rarer isotopes of the constituents of CR-39 and polyethylene, namely ²H, ¹³C, ¹⁷O and ¹⁸O, have been taken into account. Neutrons and protons are produced in polyethylene and CR-39 for photon energies above 2.2 MeV, the (γ, np) threshold for ²H. Photoparticles produced in these materials may need to be taken into consideration when using them for neutron dosimetry in the presence of photons in this energy range, especially when the neutron flux is several orders of magnitude less than that of the photons.     

Experimental and Monte-Carlo studies of the spatial distribution of neutrons around extended Pb-spallation target

The spatial distribution of thermal and fast neutrons on the surface of a paraffin moderator surrounding a cylindrical lead target, irradiated with 1 GeV protons was studied. The lead target had 8 cm diameter and 20 cm length. The thickness of the paraffin around the target was 6 cm. The slow and fast neutron distributions were determined using LR 115 2B and CR-39 detectors via the ¹⁰B(n,) reaction and neutron induced nuclear recoils, respectively. The observed slow and fast neutron distributions on the surface of the paraffin were compared with Monte-Carlo simulations using the MCNPX-2.1.5 code.     

Measurement of pionic and muonic X-rays IN B

The energies of muonic 2p-1s X-rays in ¹⁰B and ¹¹B have been measured to be 52217(8) eV and 52279(5) eV, from which the rms nuclear charge radii were calculated to be 2.44(6) fm and 2.38(4) fm. The energies and widths of pionic 2p-1s X-rays have been measured in ¹⁰B to be 65901(13) eV and 1780(30) eV, and in ¹¹B to be 65120(26) and 1720(80) eV. The sensitivity of the strong interaction shift to the neutron matter distributions has been investigated using an optical-model approach. The results of these calculations are not in good agreement with the experimental results when reasonable values of the nuclear matter distributions are used.     

Cross sections for several (n, 2n) reactions at 14 Mev

Precision measurements of the cross sections of the (n, 2n) reactions to produce ^44mSc, ⁸⁸Y, ⁸⁹Zr, ⁹²Nb, ¹⁵⁰Eu(35y), ¹⁶⁸Tm, ^174m+gLu and ¹⁹⁶Au were made for a range of neutron energies from 13.7 to 15.0 MeV. The samples were irradiated at various positions on the surface of a 20 cm radius sphere centered at the ²H–³H neutron source. This allowed a range of neutron energies to be obtained with good energy resolution. The ²⁷Al(n, )²⁴Na reaction was used to monitor the neutron fluence in the target samples. Particular attention was given to the accurate measurement of the (n, 2n) products, using calibrated Ge(Li) and NaI(Tl) detectors. An uncertainty of about ±5% is assigned to the results, except those for ¹⁵⁰Eu and ¹⁷⁴Lu, which have an additional uncertainty in their decay schemes.     

Determination of slow neutron flux and spatial distribution using LR-115 2B detectors and radiochemical sensors and comparison of the results with Monte Carlo simulations

The fluence and spatial distribution of slow neutrons on the surface of a cylindrical paraffin moderator, surrounding a Pu/Be neutron source was measured using LR-115 2B detectors via ¹⁰B(n,)⁷Li reaction and ¹³⁹La radiochemical sensors. The obtained results were compared with Monte Carlo simulation using MCNP-4B2 code.     

Measurement of dose enhancement by neutron capture of boron in Cf interstitial brachytherapy

The effect of boron concentration in water on the gamma, fast and slow neutrons and alpha particles components at the central, forward and backward surfaces inside tumor phantom of 4.2 cm diameter and 4.4cm height, during brachytherapy by neutrons from ²⁵²Cf were investigated. The source was at the centre of a cubic shaped water phantom of 30 cm side. The study was carried for different concentrations of boron from H₃BO₃, Li₂B₄O₇ and H₃¹⁰BO₃. The effect of source to tumor distance on the different components of radiation was also measured. The results indicated that the use of ¹⁰B compounds enhances the damage and is recommended for successful boron neutron capture therapy (BNCT).     

贫化铀/聚乙烯球壳交替系统中铀-238中子俘获率的测量与分析

为校验次临界能源堆的概念设计,建立了贫化铀/聚乙烯球壳交替系统, 采用活化法测量²³⁸U的中子俘获率. 贫化铀片置于系统内与入射D离子束成90^o的方向上活化 ,用HPGe探测器测量²³⁸U俘获中子衰变产生的²³⁹Np 衰变产生的277.6 keV特征γ射线计数,实验修正了贫铀片对277.6 keV γ射线的自吸收, 得到了交替系统中²³⁸U (n, γ)反应率的径向分布,反应率的相对不确定度为3.5%-3.7%, 并计算得到系统上整个贫铀区中²³⁸U的总中子俘获率为2.24 ± 0.09. 用MCNP5程序在常用ENDF库下进行了模拟计算, ²³⁸U (n, γ)反应率分布计算与实验一般在5%以内符合, 总俘获率在1%以内符合.     

COULD 7Be BE DESTROYED BY NEUTRON ABSORPTION IN THE SUN? -A NOTE ON THE SOLAR NEUTRINO PUZZLE

A comparison is made between the rate of the ⁷Be(p,y) ⁸B reaction and the rate of the neutron absorption reaction ⁷Be(n,p) ⁷Li which might have been important in. destroying ⁷Be in the solar interior.     

Calibration study on the triton response of CR-39 track detector

Triton response of the CR-39 track detector has been studied at energy ranges below 2.7 MeV. Triton irradiation was made both on the top and the well polished side surface of the CR-39 sample sheets, using ⁶Li(n,t)⁴He reaction in a thermal neutron field. At large residual ranges more than 10 μm, fine results of etch rate ratio were obtained by analysing the growth curves of etch-pit radius on the top surface. But the response at near the track end-point could not be obtained well in this method, as a result of the missing track effect. Clearly resolved response at short residual ranges was attained by means of the shape analysis of the etch-pit profile observed on the side surface.     

Optimization of CR-39 for fast neutron dosimetry applications

We present the results of an experimental work aimed at improving the performances of the CR-39^® (Registered Trademark of PPG Industries Inc.) nuclear track detector for neutron dosimetry applications. The work was done in collaboration with the Intercast Europe S.p.A., producer of CR-39 for commercial and scientific applications. We compare the CR-39 made with different additives concentrations and different polymerization processes. We evaluate the response of the CR-39 to fast neutrons from three sources: ²⁴¹Am---Be, ²⁵²Cf and ²³⁸Pu---Li. Particular attention was paid to background fluctuations that limit the lower detectable dose.     

Characterization of polyalkylvinyl ether phases by solid-state and suspended-state nuclear magnetic resonance investigations

Pure organic polyalkylvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C₄VE) and n-octadecylvinyl ether (C₁₈VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and ¹H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of ¹H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the ¹H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin–lattice relaxation times (T₁) as well as accumulation of a 2D wide line separation NMR spectrum.     

应用E.COSY型的13C-1H相关谱准确测定果糖-1,6-二磷酸根离子中异核31P-1H和31P-13C偶合常数

建议了一种E.COSY型的¹³C-¹H相关实验.在相应的¹³C-¹H相关谱中,³¹P核对¹³C,¹H核的被动偶合给出E.COSY型的谱峰裂分,可用于准确测定含磷化合物中的³¹P-¹H和³¹P-¹³C偶合常数及其相对符号.测定了果糖-1,6-二磷酸根离子的³¹P-¹H和³¹P-¹³C偶合常数。     

Investigation of neutron emission from relativistic heavy ion interactions by nuclear tracks

Fast neutrons produced in 44 and 22 GeV ¹²C+Cu interactions have been recorded and analysed with a CR-39 detector stack. The irradiation of the CR-39 stack to fast neutrons was carried out at the accelerator Synchrophasotron, Joint Institute for Nuclear Research, Dubna, Russia. Areal and volume densities of tracks induced by fast neutrons in the CR-39 at different positions and for different etching time have been measured. The neutron production ratio of 44 GeV to 22 GeV ¹²C+Cu interactions has been obtained, which is 2.17 ± 0.30 by areal track density, or 2. 12±0.33 by step etch technique, or 2.03±0.34 by volume track density measurement. These results confirm that the production rate at 44 GeV ¹²C+Cu interactions is more than theoretical estimation.     

Use of CR-39 solid state nuclear track detector in neutron personnel monitoring

Neutron sources like ²⁴¹Am–Be, ²³⁹Pu–Be, ²⁵²Cf and 14.6 MeV neutron generator are being used in oil exploration industries as well as in research institutions. While handling these neutron sources, personnel may be exposed to neutrons. Also personnel working in reactors, accelerators may receive dose from neutrons. These exposed individuals need to be monitored regularly for measurement of neutron doses. The individual neutron doses can be estimated by using Kodak NTA films and CR-39 Solid State Nuclear Track Detector with a polyethylene radiator to increase sensitivity in front in holder. Nearly 1450 personnel are being monitored regularly throughout the country on a quarterly basis. In India, the monitoring system adopted for individual neutron dose estimation having energy from 100 keV and above is described in this paper. Background counts of 0.20 mSv could be measured with CR-39 SSNTD foil system and it has been successfully introduced for Fast Neutron Personnel Monitoring for the country.     

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.