The half-life of the superallowed Fermi β ^+ emitter ^14 O was determined to high precision via a direct β counting experiment performed at the Isotope Separator and Accelerator (ISAC) facility at TRIUMF. The result, T_1/2 ( ^14 O) = 70619.2(76) ms, is consistent with, but is more precise than, the world average obtained from 11 previous measurements. Combining the ^14 O half-life deduced in the present work with the previous most precise measurements of this quantity leads to a reduction in the overall uncertainty, by nearly a factor of 2. The new world average is T_1/2 ( ^14 O) = 70619.6(63) ms with a reduced χ ^2 value of 0.87 obtained from 8 degrees of freedom.

Reactions on proton-rich nuclides drive the nucleosynthesis in core collapse supernovae (CCSNe) and in x-ray bursts (XRBs). CCSNe eject the nucleosynthesis products to the interstellar medium and hence are a potential inventory of p nuclei, whereas in XRBs nucleosynthesis powers the light curves. In both astrophysical sites the Ni-Cu cycle, which features a competition between Cu-59(p, alpha) Ni-56 and Cu-59(p, gamma) Zn-60, could potentially halt the production of heavier elements. Here, we report the first direct measurement of Cu-59(p, alpha) Ni-56 using a reaccelerated Cu-59 beam and a cryogenic solid hydrogen target. Our results show that the reaction proceeds predominantly to the ground state of Ni-56, and the experimental rate has been found to be lower than Hauser Feshbach based statistical model predictions. New results hints that the vp process could operate at higher temperatures than previously inferred and therefore remains a viable site for synthesizing the heavier elements.

Zirconium and beryllium fast-neutron activation detectors are used to investigate the DD fusion neutron emission from the NX3 Plasma Focus (PF) device operated in deuterium gas. The differing energy dependence of the Zr and Be activation cross-sections enables an effective neutron energy ${E_{\mathrm{n}}}^{\text{eff}}$ to be inferred from the Zr/Be count ratio for individual PF shots. For the fast-neutron activation detector geometry, the relationship between the Zr/Be count ratio and ${E_{\mathrm{n}}}^{\text{eff}}$ is established by MCNP5 simulation. Zirconium and beryllium detector pairs are positioned at 0° and 90° to the PF axis, so that the anisotropy of the neutron energy is measured from shot to shot. The NX3 PF is operated at 12 kV, corresponding to 7.2 kJ capacitor bank energy. Shots are performed for D2 gas pressures ranging from 1.5 to 10 mbar. The highest neutron yields of ∼109 neutron/shot are observed for 5 mbar D2 gas pressure. Typical effective neutron energies ${E_{\mathrm{n}}}^{\text{eff}}$ for the 0° and 90° directions are ∼2.8 MeV and ∼2.5 MeV, respectively, and the neutron energy-anisotropy remains close to $\Delta E_{\mathrm{n}}\cong 0.3\ \text{MeV}$ over the range of D2 gas pressures investigated. The effect of blocking the forward fast-deuteron beam with an obstacle plate positioned in front of the PF anode is also studied. For this case, shots are performed for D2 gas pressures ranging from 1 to 6 mbar. Insertion of the beam-obstacle plate results in a large reduction in neutron yield, while the effective neutron energy ${E_{\mathrm{n}}}^{\text{eff}}$ increases for both the 0° and 90° directions. The results indicate that DD fusion contributions from thermonuclear or gyrating-particle processes are negligible. The collected results are entirely consistent with beam-target fusion being the dominant mechanism within the plasma pinch and throughout an extended cone on the forward (0°) axis of the NX3 PF.

Reactions on the proton-rich nuclides drive the nucleosynthesis in Core-Collapse Supernovae (CCSNe) and in X-ray bursts (XRBs). CCSNe eject the nucleosynthesis products to the interstellar medium and hence are a potential inventory of p-nuclei, whereas in XRBs nucleosynthesis powers the light curves. In both astrophysical sites the Ni-Cu cycle, which features a competition between $^{59}$Cu(p,$\alpha$)$^{56}$Ni and $^{59}$Cu(p,$\gamma$)$^{60}$Zn, could potentially halt the production of heavier elements. Here, we report the first direct measurement of $^{59}$Cu(p,$\alpha$)$^{56}$Ni using a re-accelerated $^{59}$Cu beam and cryogenic solid hydrogen target. Our results show that the reaction proceeds predominantly to the ground state of $^{56}$Ni and the experimental rate has been found to be lower than Hauser-Feshbach-based statistical predictions. New results hint that the $\nu p$-process could operate at higher temperatures than previously inferred and therefore remains a viable site for synthesizing the heavier elements.

This paper is a sequel to the 1998 review paper “Scientific status of the Dense Plasma Focus” with 16 authors belonging to 16 nations, whose initiative led to the establishment of the International Center for Dense Magnetized Plasmas (ICDMP) in the year 2000. Its focus is on understanding the principal defining characteristic features of the plasma focus in the light of the developments that have taken place in the last 20 years, in terms of new facilities, diagnostics, models, and insights. Although it is too soon to proclaim with certainty what the plasma focus phenomenon is, the results available to date conclusively indicate what it is demonstrably not. The review looks at the experimental data, cross-correlated across multiple diagnostics and multiple devices, to delineate the contours of an emerging narrative that is fascinatingly different from the standard narrative, which has guided the consensus in the plasma focus community for several decades, without invalidating it. It raises a question mark over the Fundamental Premise of Controlled Fusion Research, namely, that any fusion reaction having the character of a beam-target process must necessarily be more inefficient than a thermonuclear process with a confined thermal plasma at a suitably high temperature. Open questions that need attention of researchers are highlighted. A future course of action is suggested that individual plasma focus laboratories could adopt in order to positively influence the future growth of research in this field, to the general benefit of not only the controlled fusion research community but also the world at large.

Remediation of subsurface contamination using microbial consortium can be less toxic to the environment and ecosystems than using chemical dispersants or physical measures. But bioremediation involves complex and dynamic processes in a visually opaque medium, which can be difficult to monitor. Positron emission tomography (PET), which reveals the dynamic distribution of labeled molecules, offers a means to probe into the bioremediation process. This study evaluates and verifies the feasibility of employing a freely-rearrangeable modular PET system (BioPET) in combination with a generic tomographic image reconstruction platform, CASToR, for tracking fluid transport, as well as metabolic activities, occurrence, and distribution of subsurface microorganisms. This enables quantitative imaging of bioremediation processes in high resolution with further expanding the flexible modular system and refining the data processing algorithms.

A modular PET detector system with variable geometry, BioPET, has been constructed to specifically study plant-microorganism-environment complexes. While the modular design in combination with rotation and translation mechanics provides greater flexibility in detector arrangement, adaptive data processing and image reconstruction methods are needed for such a transformable system. In this work, we developed a data processing pipeline by making used of a generic, modular, and extensible platform for tomography reconstruction, CASToR, and applied the process to evaluate performance of BioPET in rotational and stationary modes. The NEMA NU 4-2008 image quality phantom was utilized for analysis of recovery coefficients, spillover ratios, uniformity, and their relationship to selected reconstruction parameters. The rotational mode outperforms the stationary mode in exhibiting lower spillover effect as well as in reconstructing the activity concentration of smaller features, although partial volume effect is evidenced in both modes. The behaviour of the performance indices as a function of the selected reconstruction parameters is found specific to each detection mode. The procedure and the image quality characterization presented in this work are driving the development and optimization of data processing, image reconstruction and correction framework towards quantitative image analysis for PET systems with flexible geometry.

A sub-kilo-Joule plasma focus device (FMPF-3, 14 kV/235 J) was operated with deuterium–krypton admixtures (of 1, 2 and 5 % Kr by volume) to study the influence of admixture ratio on neutron yield (Y n). Experiments were performed for different insulator sleeve lengths and cathode geometries. The results reveal that for a carefully optimized electrode geometry the highest average neutron yield is obtained with pure deuterium as the operating gas, whereas krypton seeding leads to a reduction in Y n. We argue that the electrode geometry and electrical coupling play critical roles in determining the influence of gas admixtures; and that for an optimized plasma focus device D2-Kr admixtures may give little or no neutron yield enhancement relative to pure D2 operation and so the admixture operation is an evaluation methodology to determine the level of optimization of device geometry.

The deuterium-deuterium (DD) fusion neutron yield and anisotropy were measured on a shot-to-shot basis for the NX2 plasma focus (PF) device using two beryllium fast-neutron activation detectors at 0° and 90° to the PF axis. Measurements were performed for deuterium gas pressures in the range 6–16 mbar, and positive correlations between neutron yield and anisotropy were observed at all pressures. Subsequently, at one deuterium gas pressure (13 mbar), the contribution to the fusion yield produced by the forwardly-directed D+ ion beam, emitted from the plasma pinch, was investigated by using a circular Pyrex plate to obstruct the beam and suppress its fusion contribution. Neutron measurements were performed with the obstacle positioned at two distances from the anode tip, and also without the obstacle. It was found that ~ 80% of the neutron yield originates in the plasma pinch column and just above that. In addition, proton pinhole imaging was performed from the 0° and 90° directions to the pinch. The obtained proton images are consistent with the conclusion that DD fusion is concentrated (~ 80%) in the pinch column region.

The spatial distribution of DD fusion in a 1.6 kJ plasma focus (PF) device is investigated using the coded aperture imaging (CAI) technique, enabling single shot fusion images to be obtained. Simultaneously, two beryllium fast-neutron activation detectors are employed to measure neutron yield and anisotropy. The coded mask patterns used are based on Singer cyclic difference sets with various open fractions. The physical mask patterns are laser-machined in stainless steel foil, and CR-39 nuclear track detectors record the coded image of the ~3 MeV DD protons emitted from the PF pinch region. In one series of experiments using pure deuterium, five CAI cameras were employed simultaneously: one positioned on-axis (0°) and four at 45° to the PF axis. For another series of experiments two higher-resolution CAI cameras were positioned at 90° to the PF axis, on opposite sides of the pinch. The PF was operated in either pure deuterium gas or deuterium-krypton admixtures of various concentrations1. For single PF shots, the shape of the fusion emission zone is observed to change between high and low neutron-yield shots; high and low neutron-anisotropy shots; and between pure deuterium and deuterium-krypton admixtures. These results are discussed with regard to PF fusion mechanisms.

X-ray lithography (XRL) can be a potential candidate for next generation lithography. The main objective of this study is to demonstrate XRL using fast miniature plasma focus (FMPF) device as the X-ray source. The advantage of using FMPF as X-ray source is the smaller X-ray spot size due to smaller electrode dimensions leading to higher resolution micro-components. Some of the major hurdles in the realization of XRL using FMPF device have been addressed and FMPF based XRL is demonstrated for the first time. The dosage required for sufficient crosslinking in SU8 photoresist is determined using Fourier transform infrared spectroscopy analysis.

Laser shadowgraphy has been used to investigate the plasma sheath dynamics in a miniature plasma focus device (FMPF-3, 14 kV/235 J). The occurrence of magneto-hydro-dynamics instabilities are compared for pure deuterium versus deuterium–krypton admixture operation, over the range of gas pressures 2–12 mbar. A cathode-less geometry was also tested to study the influence of cathode configuration on current sheath formation and compression. The average neutron yield, measured using 3He proportional counters, is compared for different geometries and gas pressures. The synchronization of the four pseudo-spark-gap switches was found to be a major factor influencing the plasma sheath dynamics and neutron yield. To make a fair comparison of operation with different gas pressures or admixture proportions, the level of switch synchronization must be in the same range. Laser shadowgraphs of early stage dynamics show that poorly synchronized discharges result in asymmetric plasma sheath formation, and asymmetries in the accelerated sheath typically persist till the end of the final compression.

It is known that the radius ratio of a plasma pinch depends on the specific heat ratio γ of the pinch plasma, where radius pinch ratio is defined as: radius of plasma pinch column/radius of anode. The lower the specific heat ratio the lower would be the pinch radius ratio with corresponding increased compression and pinch density. The deuterium plasma focus pinch is invariably fully ionized and has a specific heat ratio of practically the highest possible value of 5/3. If the deuterium plasma focus could have its specific heat ratio reduced below 5/3 we might expect its radius ratio to be correspondingly reduced, increasing the pinch density, thus improving the D-D fusion neutron yield. To demonstrate this effect we run the Lee model code in deuterium but hypothetically fix the specific heat ratio, reducing it at each run. The results show that indeed the radius ratio is reduced, increasing the compression, and the neutron yield is substantially increased. The effect is used to explain the observed neutron yield enhancement when a deuterium plasma focus doped with a small amount of krypton.

We classify all coded masks onto which cyclic difference sets can be wrapped periodically using a generalization of the Finger and Prince construction. In particular, we establish simple numerical criteria which determine whether any given mask can be wrapped periodically in this way and, for each mask which can, we provide explicit constructions which will produce at least one such wrapping. We show that all periodic wrappings currently reported in the literature are special cases of our explicit constructions, and we often provide simpler alternatives. Using these constructions we show that all Singer cyclic difference sets of practical size and open fraction can be wrapped exactly onto masks which are very nearly as compact and symmetrical as hexagons, without the need for pixel padding.

An investigation on the possibility of enhancement of soft X-ray (SXR) (900–1600 eV) emission from a fast miniature plasma focus (FMPF) device of 235 J (at 14 kV) storage energy through doping of operating gas was performed. Neon (Ne), the operating gaseous medium, was doped with krypton (Kr) in different volumetric ratios at various operating pressures ranging from 2 to 14 mbar. The 1% Kr doping increased the average optimum SXR emission efficiency from 0.47% to 0.6% without enhancing the hard X-ray (HXR) (>1600 eV) emission. The Kr doping influenced the major pinching characteristics such as focusing efficiency and time to pinch with consequential effect on X-ray emissions. Synchronous operation of the 4 pseudo-spark gap (PSG) switches was mandatory for efficient discharge current delivery to the electrodes. A drastic improvement in the pinching efficiency was obtained with replacement of old and worn out PSG switches with the new ones. Optical imaging of current sheath dynamics was performed using gated ICCD camera to verify the normal operation of the device after the PSGs replacement. A numerical simulation analysis on the 2 cm long stainless steel tapered anode, used in this study, was done to predict the maximum SXR emission efficiency and the peak operating gas pressure. An analysis on the amount of SXR fluence generated at the source position and the proportion of it reaching the target position is also reported.

Fast miniature plasma focus (FMPF-3), a low energy (235 J) device, is an attractive option for being a potential source for soft X-ray (SXR) (0.9 – 1.6 keV) lithography due to its smaller X-ray generation spot size and the capability of being a high repetition source. As a continuation of our work on the enhancement of SXR emission from this device, in present investigation the insulator sleeve length is optimized for efficient SXR emission. It plays a major role in the current sheath formation, which is determinant of the efficient compression and the consequent radiation emission. The influence of the presence or absence of cathode rods on the SXR emission is also investigated. It is one least explored parameter although it plays a major role in the determination of plasma sheath curvature which in turn influences the dynamic plasma inductance and the magnetic flux associated with moving current sheath. Another major highlight of this study is the time resolved laser shadowgraphy of the plasma sheath dynamics to understand the influence of the variation of these parameters on it. Through optimization of the insulator sleeve length, the highest ever obtained SXR yield of 1.8 J/shot was achieved for this device.

Plasma emissions can be intense source of high energy radiations and can serve as a source for soft x-ray lithography however; it is a complex phenomenon which is substantially influenced by the performance of the associated components such as electrical circuit parameters and filling gas parameters of the plasma focus device. Fine tuning of these parameters can determine the dominant energy emitted as well as their emission efficiency. This can be effectively accomplished when the characteristics of their influence on the plasma dynamics is well understood. For this purpose, experimental analysis were done to study the influence of synchronous operation of Pseudo Spark Gap (PSG) switches on current pinch and X-ray emission, influence of operating gas pressure, percentage of dopant added and the presence or absence of cathode rods on plasma dynamics and X-ray emission. Extensive imaging of the plasma dynamics was done using laser Shadowgraphy technique and the current derivative and X-ray signals were also simultaneously monitored using Rogowski coil and BPX65 silicon PIN photodiodes respectively. Our results deduce the tolerable extent of asynchronisation that does not deteriorate the pinching and the X-ray. The experimental results also infer that the lower operating gas pressure regime is suitable for hard X-ray (>2500 eV) (HXR) emission while higher pressure is suitable for soft X-ray (900 - 1600 eV) (SXR) emission. The obtained images evidently reveal the dependence of symmetry of plasma sheath on the proportion of dopant added and the influence of cathode rods on density, symmetry and curvature of plasma sheath with consequential effect on x-rays emitted from plasma source.

There is an increasing requirement for alternative and improved detection of fast neutrons due to the renewed interest in neutron diagnostics applications. Some applications require heavily shielded neutron sources that emit a substantial proportion of their emission as fast neutrons and so require high performance fast neutron detectors. In some applications, the detection of neutron bursts from pulsed neutron sources has to be synchronized to the repetition rate of the source. Typical fast neutron detectors incorporate scintillators that are sensitive to all kinds of ionizing radiations as well as neutrons, and their efficiency is low. In this paper, we present a device based on the principle of neutron activation coupled to solid-state p-i-n diodes connected to a charge amplifier. The charge amplifier is specially developed to operate with high capacitance detectors and has been optimized by the aid of the SPICE program. A solid-state pulse shaping filter follows the charge amplifier, as an inexpensive solution, capable to provide pulses that can be counted by a digital counter.