Silver Activation Detectors Research Articles

Simulation study of the response of a highly sensitive silver-activation detector for neutron detection using MCNP code

In this paper, simulations were carried out using Monte-Carlo N-Particle MCNP-4C code to determine the energy dependence of the response of a highly sensitive silver-activation detector used for fast-neutron detection after moderated to thermal neutrons. The detector consists of sandwiched alternating thin-sheets of silver and crystal scintillator Anthracene. The simulations also had considered different materials and designs to get the most efficient design for detecting signals from fast-neutrons interactions with the active materials (silver) and the scintillator. The energy and charge depositions of photons and electrons created by fast-neutron interactions with detector within the detection-cell were simulated for different scenarios. Owing on the simulations, a method to maximize the response by modifying the design was identified. The optimal configurations are suitable for a wide range of monitoring and detecting neutron sources especially for big detectors implemented for security purposes, where the costs and weighs can be reduced significantly.

Optimizing of Experimental Load of PFZ-200 Plasma Focus

This article presents a study of neutron emission on the PFZ-200 plasma focus at the Department of physics on FEE CTU in Prague, Czech Republic. In order to achieve the highest and most stable neutron yields, the deuterium working gas pressure and the anode shape were systematically varied. We observed the plasma time to the pinch and the discharge current by the Rogowski coil and neutron emission by the silver activation detector and scintillation time-of-flight detectors. The imploded plasma was visualized using a fast X-ray pinhole camera with a gated microchannel plate detector. The experiment presents the z-pinch discharges with the current maximum above 200 kA and the average neutron yields of ${3 \times 10^{8}}$ neutrons/shot. Measured pinch times were in the range from 1.65 to 1.85 $\mu \text{s}$ . The hollow round anode configuration performed the most stable neutron yields with a deviation under 20%.

Gated liquid scintillator detector for neutron time of flight measurements in a gas-puff Z-pinch experiment.

Detection of secondary D(t, n)4He neutrons produced when thin argon or krypton gas shells implode on a deuterium gas target is a very challenging task because the secondary neutron yield is a small fraction of the primary neutron yield and because the implosion is often accompanied by an intense hard X-ray burst. We built a large volume neutron time of flight (nTOF) detector using liquid scintillator (xylene solvent with small quantities of wavelength shifting PPO + bis-MSB fluors) in an attempt to increase the detection probability for secondary neutrons in our staged Z-pinch experiments at the 1 MA Zebra pulsed-power generator. Two fast, gated microchannel plate photomultiplier tubes detect the light created in 21 liters of liquid. The hard X-rays were successfully suppressed in the recorded nTOF traces, but we found no evidence of secondary neutrons. The signal quality from the primary D(d, n)3He neutrons was higher compared to the signal quality from a plastic scintillator nTOF, thus providing a more reliable estimate of the deuterium ion temperature at the pinch stagnation time. Cross-calibration with a silver activation detector enables standalone neutron yield measurement.

Copper activation detector for high energy-pulsed neutron measurements

A first of its kind threshold activation proportional counter is developed using copper for the measurement of pulsed 14 MeV neutrons. The detector is of 26 mm outer diameter and 200 mm overall length. Tests at D-T facility showed that the detector is capable of measuring high-energy neutrons. The high-energy neutron sensitivity of the detector is estimated as 7.6 × 10−5 counts/neutrons cm-2/s, and pulsed neutron sensitivity is estimated as 3.3 × 107 neutrons pulse−1 count−1. The low-energy response of the detector can be discriminated by curve fitting method to the decay counts. An identical dimension silver-lined proportional counter with 0.5 counts/neutrons cm-2/s thermal neutron sensitivity is developed for comparison with the copper detector. The silver activation detectors are conventionally used for neutron yield measurement of D-T-pulsed source. Experiments confirmed that compared to silver detector which is sensitive to low-energy neutrons, the copper detector is able to measure high-energy neutrons directly by threshold reaction.

Effect of gas filling pressure and operation energy on ion and neutron emission in a medium energy plasma focus device

The effects of gas filling pressure and operation energy on deuterium ions and neutrons have been studied in a medium energy plasma focus device, MEPF-12. The deuterium gas filling pressure was varied from 1 to 10 mbar at an operation energy of 9.7 kJ. Also, the operation energy was varied from 3.9 to 9.7 kJ at a deuterium gas filling pressure of 4 mbar. Time resolved emission of deuterium ions was measured using a Faraday cup. Simultaneously, time integrated and time resolved emissions of neutrons were measured using a silver activation detector and plastic scintillator detector, respectively. Various characteristics (fluence, peak density, and most probable energy) of deuterium ions were estimated using the Faraday cup signal. The fluence was found to be nearly independent of the gas filling pressure and operation energy, but the peak density and most probable energy of deuterium ions were found to be varying. The neutron yield was observed to be varying with the gas filling pressure and operation energy. The effect of ions on neutrons emission was observed at each operation condition.

Experimental research of neutron yield and spectrum from deuterium gas-puff z-pinch on the GIT-12 generator at current above 2 MA

The Z-pinch experiments with deuterium gas-puff surrounded by an outer plasma shell were carried out on the GIT-12 generator (Tomsk, Russia) at currents of 2 MA. The plasma shell consisting of hydrogen and carbon ions was formed by 48 plasma guns. The deuterium gas-puff was created by a fast electromagnetic valve. This configuration provides an efficient mode of the neutron production in DD reaction, and the neutron yield reaches a value above 1012 neutrons per shot. Neutron diagnostics included scintillation TOF detectors for determination of the neutron energy spectrum, bubble detectors BD-PND, a silver activation detector, and several activation samples for determination of the neutron yield analysed by a Sodium Iodide (NaI) and a high-purity Germanium (HPGe) detectors. Using this neutron diagnostic complex, we measured the total neutron yield and amount of high-energy neutrons.

A 10(9) neutrons/pulse transportable pulsed D-D neutron source based on flexible head plasma focus unit.

A 17 kJ transportable plasma focus (PF) device with flexible transmission lines is developed and is characterized. Six custom made capacitors are used for the capacitor bank (CB). The common high voltage plate of the CB is fixed to a centrally triggered spark gap switch. The output of the switch is coupled to the PF head through forty-eight 5 m long RG213 cables. The CB has a quarter time-period of 4 μs and an estimated current of 506 kA is delivered to the PF device at 17 kJ (60 μF, 24 kV) energy. The average neutron yield measured using silver activation detector in the radial direction is (7.1 ± 1.4) × 10(8) neutrons/shot over 4π sr at 5 mbar optimum D2 pressure. The average neutron yield is more in the axial direction with an anisotropy factor of 1.33 ± 0.18. The average neutron energies estimated in the axial as well as in the radial directions are (2.90 ± 0.20) MeV and (2.58 ± 0.20) MeV, respectively. The flexibility of the PF head makes it useful for many applications where the source orientation and the location are important factors. The influence of electromagnetic interferences from the CB as well as from the spark gap on applications area can be avoided by putting a suitable barrier between the bank and the PF head.

Praseodymium activation detector for measuring bursts of 14 MeV neutrons

A new, accurate, neutron activation detection scheme for measuring pulsed neutrons has been designed and tested. The detection system is sensitive to neutrons with energies above 10 MeV; importantly, it is insensitive to gamma radiation <10 MeV and to lower-energy (e.g., fission and thermal) neutrons. It is based upon the use of 141Pr, an element that has a single, naturally occurring isotope, a significant n,2n cross-section, and decays by positron emission that result in two coincident 511 keV photons. Neutron fluences are thus inferred by relating measured reaction product decay activity to fluence. Specific sample activity is measured using the sum-peak method to count gamma-ray coincidences from the annihilation of the positron decay products. The system was tested using 14 and 2.45 MeV neutron bursts produced by NSTec Dense Plasma Focus Laboratory fusion sources. Lead, copper, beryllium, and silver activation detectors were compared. The detection method allows measurement of 14 MeV neutron yield with a total error of ≈18%.

Use of thermoluminescent dosimeters for measurement of fast-neutron spatial-distribution at the plasma focus device PF-1000

A system of moderators of DD-fusion neutrons emitted by the plasma focus device PF-1000 at IPPLM, Warsaw was employed for the use of thermoluminescent dosimeters (TLDs) as passive detectors of thermal neutrons. The diagnostics was derived from Monte Carlo calculations of responses of dosimeters located in spherical polyethylene moderators with different diameters. As time-integrating dosimeters coupled 6LiF:Mg,Cu,P (TLD-600H) and 7LiF:Mg,Cu,P (TLD-700H) detectors were applied. A difference in read-out signals between TLD-600H and TLD-700H dosimeters, which is directly proportional to the number of thermal neutron interactions, is compared with the response of silver activation detectors. The detectors used started to operate from a neutron yield of ∼5×109 and present a convenient method for investigation of spatial-distribution of neutron emission.

Isotropic and anisotropic components of neutron emissions at the FN-II and PACO dense plasma focus devices

The average angular distribution of neutron emissions has been measured in the Fuego Nuevo II (FN-II) dense plasma focus device (5 kJ) by means of CR-39 plastic nuclear track detectors. When pure deuterium is used as the filling gas, the data can be adjusted to a Gaussian function, related to anisotropic emission, superposed on a constant pedestal, related to isotropic emission. When deuterium–argon admixtures are used, the anisotropic contribution is best represented by a parabola. The same analysis is applied to previously reported results, for fewer shots, in pure deuterium from the PACO device, which is similar in size to the FN-II. In both devices the anisotropic component is smaller than the isotropic one, but with different features. In PACO the anisotropic component is concentrated on a large narrow beam around the axis, but its contribution to the total neutron yield is significantly smaller than in the FN-II, where the anisotropic component spreads over a wider range. The neutron flux per shot is monitored in both devices with calibrated silver activation detectors, at 20° and at 90° from the axis. The average values of the neutron flux at these two angles are used, along with the angular distributions obtained form the track detectors, in order to estimate the absolute neutron yield of both the isotropic and the anisotropic contributions. From examining different groups of shots, it is found that the shape of the angular distribution is important in the estimation of anisotropy, and that the value usually reported, as the ratio of neutron counts head-on and side-on, as measured by activation counters, may be misleading.

Influence of electrode and insulator materials on the neutron emission in a low energy plasma focus device

Insertion of internal impurities is one of the factors for the degradation of neutron output in plasma focus devices. In this context, neutron emission measurements were carried out in a 2.2 kJ (7.2 /spl mu/F, 25 kV) Mather type squirrel cage plasma focus device with various combinations of electrode and insulator materials. The neutron yield was measured by silver activation detector. The results indicate that a central electrode of low erosion rate material produces maximum neutron yield with the highest anisotropy factor. A time integrated X-ray pinhole image shows that focus corresponding to the highest neutron yield material is the most compressed. The dielectric constant of the ceramic insulators has, at best, a very weak correlation with neutron output. The nonceramic insulators like perspex, nylon, or teflon neither produce focus nor neutrons.

A highly sensitive silver-activation detector for pulsed neutron sources

A silver-activation detector has been built and calibrated to measure the neutron yield produced by pulsed D(d,n) and T(d,n) sources. The detector has three principle virtues. Its high sensitivity (registering as little as 20 n/cm 2) results from 1.7 kg of silver incorporated into a plastic scintillator. Its modular design allows several efficiency vs energy responses to be obtained, including one configuration in which the efficiency is the same at 2.5 and 14 MeV. Also, the dynamic range spans five to seven decades of useful neutron intensity. Construction details and measured efficiencies are given.

A fast-neutron activation detector for 14-MeV pulsed neutron sources

A fast-neutron activation detector is described in which the gamma rays resulting from the decay of Pb207m are observed in a plastic scintillator. The Pb207m is produced by fast-neutron activation of a lead shield which sorrounds the scintillator and photomultiplier. Following a 20-msec delay from the neutron pulse, the Pb207m activity is observed for 2.40 sec. A source of Ba133 is used to check the gain stability of the detection system. The detector is observed to have higher sensitivity than a standard silver activation detector.