Heavy Shielding Research Articles

Space radiation measurements during the Artemis I lunar mission

Space radiation is a notable hazard for long-duration human spaceflight1. Associated risks include cancer, cataracts, degenerative diseases2 and tissue reactions from large, acute exposures3. Space radiation originates from diverse sources, including galactic cosmic rays4, trapped-particle (Van Allen) belts5 and solar-particle events6. Previous radiation data are from the International Space Station and the Space Shuttle in low-Earth orbit protected by heavy shielding and Earth’s magnetic field7,8 and lightly shielded interplanetary robotic probes such as Mars Science Laboratory and Lunar Reconnaissance Orbiter9,10. Limited data from the Apollo missions11–13 and ground measurements with substantial caveats are also available14. Here we report radiation measurements from the heavily shielded Orion spacecraft on the uncrewed Artemis I lunar mission. At differing shielding locations inside the vehicle, a fourfold difference in dose rates was observed during proton-belt passes that are similar to large, reference solar-particle events. Interplanetary cosmic-ray dose equivalent rates in Orion were as much as 60% lower than previous observations9. Furthermore, a change in orientation of the spacecraft during the proton-belt transit resulted in a reduction of radiation dose rates of around 50%. These measurements validate the Orion for future crewed exploration and inform future human spaceflight mission design.

Study of a detector prototype for detecting special nuclear materials based on differential die-away technology

Differential die-away Analysis (DDAA) technology is a powerful analytical technique to detect fissile materials such as 235U and 239Pu. It can reveal the presence of nuclear materials even when shielded or embedded in non-fissile matrices by inducing fission through externally applied pulsed neutrons. An innovative modular system that is convenient for transportation and suitable for various application scenarios is proposed. The detection sensitivity of the system, with different structures, is studied. The data acquisition hardware, along with real-time online measurement and alerting software, have been developed. The results indicate that a detection system with a bilaterally arranged array of detectors offers enhanced sensitivity, enabling rapid detection of a single nuclear fuel rod (200.4g) under heavy shielding and at standard distances.

Radiation source terms analysis and classification of radioactive waste for the decommissioning of the first HWRR reactor in China.

Nuclear reactors will face the problem of decommissioning at the end of their operating life due to the high radioactivity of reactor components and environmental safety considerations. The Heavy Water Research Reactor (HWRR) is the first large-scale research reactor to be decommissioned in China. The second phase of HWRR decommissioning involves the main components in the reactor block, so the radiation source terms and the radioactive waste level need to be evaluated before demolition and disposal. Based on the operating history, three-dimensional geometry, materials, and other information of the HWRR, the activity of radionuclides in the main components of HWRR is calculated and analyzed, and the MCNP/ORIGEN coupling scheme is utilized for theoretical analysis. The theoretical results indicate that 14C, 54Mn, 55Fe, 60Co, 63Ni, and 152Eu are the main radioactive nuclides. The total activity of radioactive nuclides was 2.36E + 15Bq at the end of 2007, 4.27E + 13Bq at the end of 2021, and 1.83E + 13Bq at the end of 2025. Furthermore, local sampling and radiometric analyses based on the HPGe gamma-ray spectrometer are also performed to verify the theoretical results, the ratio of theoretical activity values to the measured activity of the experimental sample is within 2.5 times, so the theoretical results are conservative. According to the classification standards for radioactive waste, the inner shell, outer shell, cooling water tank, sand layer, and heavy concrete shielding layer are all low-level waste. These results and conclusions can serve as a reference for the second phase decommissioning of the HWRR and the subsequent disposal of radioactive waste.

Applicability of an Ionising Radiation Measuring System for Real-Time Effective-Dose-Optimised Route Finding Solution during Nuclear Accidents

The reduction in the effective dose of evacuated injured persons through contaminated areas of nuclear accidents is an essential emergency services requirement. In this context, there appeared a need to develop a dose-optimised route finding method for firefighting rescue vehicles, which includes the development of a real-time decision support measurement and evaluation system. This determines and visualises the radiation exposure of possible routes in a tested area. The system inside and outside of the vehicle measures the ambient dose equivalent rate, the gamma spectra, and also the airborne radioactive aerosol and iodine levels. The method uses gamma radiation measuring NaI(Tl) scintillation detectors mounted on the outside of the vehicle, to determine the dose rate inside the vehicle using the previously recorded attenuation conversation function, while continuously collecting the air through a filter and using an alpha, beta, and gamma radiation measuring NaI(Tl)+ PVT + ZnS(Ag) scintillator to determine the activity concentration in the air, using these measured values to determine the effective dose for all routes and all kinds of vehicles. The energy-dependent shielding effect of the vehicle, the filtering efficiency of the collective protection equipment, and the vehicle’s speed and travel time were taken into account. The results were validated by using gamma point sources with different activity and energy levels. The measurement results under real conditions and available real accident data used in our simulations for three different vehicles and pedestrians proved the applicability of the system. During a nuclear accident based on our model calculations, the inhalation of radioactive aerosols causes a dose almost an order of magnitude higher than the external gamma radiation caused by the fallout contamination. The selection of the appropriate vehicle and its route is determined by the spectrum that can be measured at the accident site but especially by the radioactive aerosol concentration in the air that can be measured in the area. In the case of radiation measuring detectors, the shielding effect of the carrier vehicle must be taken into account, especially in the case of heavy shielding vehicles. The method provides an excellent opportunity to reduce the damage to the health of accident victims and first responders during rescue operations.

Response optimization of a three-axis sensitive SERF magnetometer for closed-loop operation

Most triaxial-vectorial magnetic field measurements with spin-exchange relaxation free (SERF) atomic magnetometer (AM) are based on the quasi-steady-state solution of the Bloch equation. However, the responding speed of these methods is greatly limited because the frequency of the modulation signal should be slow enough to ensure the validity of the quasi-steady-state solution. In this work, a new model to describe the response of the three-axis sensitive SERF AM with high modulation frequency is presented and verified. The response of alkali-atomic spin to high-frequency modulation field is further investigated by solving the Bloch equation in a modulation-frequency-dependence manner. This solution is well verified by our experiments and can offer a reference for selection of modulation frequencies. The result shows a potential to achieve a SERF AM operating in a geomagnetic field without heavy aluminum shielding when the modulation frequencies are selected properly.

Lead-free X-Ray shielding aprons using Zn-doped SnO2 epoxy nanocomposite: A promising alternative to traditional heavy and lead-based materials

This report describes the first use of SnO2 nanoparticles with Zn dopants as a light weight and lead-free material for X-ray shielding applications. The material is environmentally friendly and offers high X-ray attenuation properties, making it a promising alternative to traditional heavy and lead-based X-ray shielding materials. The Zn-doped SnO2 nanoparticles were prepared using a sol-gel synthesis technique. This approach enabled the creation of high-quality Zn-doped SnO2 nanoparticles that were then mixed with epoxy polymer and coated onto a nylon mixed rexine cloth with the help of the drop casting technique, and they were treated for X-ray shielding applications. Micro-sized PbO particles were mixed with epoxy resin and coated onto rexine cloth to compare the X-ray shielding properties of the Zn-doped SnO2 nanoparticle. The structural properties were evaluated through X-ray Diffraction (XRD) and Raman analysis showed that the prepared SnO2 nanoparticles were in a tetragonal crystal structure. When compared to pure SnO2, the crystallite size of Zn-doped SnO2 nanoparticles was reduced (23.5–18 nm). UV–Visible spectroscopy is used to calculate the bandgap, which is increased as dopant introduced (3.41–3.57 eV). The photoluminescent (PL) study showed where the oxygen vacancy defect peaks originate. The cross-section Scanning Electron Microscopy (SEM) mapping showed a good coating of Zn doped SnO2 nanoparticle on the rexine cloth. The X-ray shielding abilities were extensively researched using various methods including percentage of attenuation (98–80 %), exposure, half value layer (0.06–0.16 mm), linear attenuation coefficient (μ), and mass attenuation coefficient (8.29–3.32 cm2/g). The findings indicated that 2% Zn-doped SnO2 has outstanding X-ray shielding properties compared to undoped SnO2 and PbO based aprons, making it a potential alternative for lead-free aprons in X-ray shielding applications.

Heavy concrete shielding properties for carbon therapy

As medical facilities are usually built at urban areas, special concrete aggregates and evaluation methods are needed to optimize the design of concrete walls by balancing density, thickness, material composition, cost, and other factors. Carbon treatment rooms require a high radiation shielding requirement, as the neutron yield from carbon therapy is much higher than the neutron yield of protons. In this case study, the maximum carbon energy is 430 MeV/u and the maximum current is 0.27 nA from a hybrid particle therapy system. Hospital or facility construction should consider this requirement to design a special heavy concrete. In this work, magnetite is adopted as the major aggregate. Density is determined mainly by the major aggregate content of magnetite, and a heavy concrete test block was constructed for structural tests. The compressive strength is 35.7 MPa. The density ranges from 3.65 g/cm3 to 4.14 g/cm3, and the iron mass content ranges from 53.78% to 60.38% from the 12 cored sample measurements. It was found that there is a linear relationship between density and iron content, and mixing impurities should be the major reason leading to the nonuniform element and density distribution. The effect of this nonuniformity on radiation shielding properties for a carbon treatment room is investigated by three groups of Monte Carlo simulations. Higher density dominates to reduce shielding thickness. However, a higher content of high-Z elements will weaken the shielding strength, especially at a lower dose rate threshold and vice versa. The weakened side effect of a high iron content on the shielding property is obvious at 2.5 μSv/h. Therefore, we should not blindly pursue high Z content in engineering. If the thickness is constrained to 2 m, then the density can be reduced to 3.3 g/cm3, which will save cost by reducing the magnetite composition with 50.44% iron content. If a higher density of 3.9 g/cm3 with 57.65% iron content is selected for construction, then the thickness of the wall can be reduced to 174.2 cm, which will save space for equipment installation.

Determination of resistance against the transmission of charged particles of Rhenium-Boron (Re-B) based alloys

In this study, the resistance of the Rhenium-Boron (Re-B) based alloys against the transmission of charged particles such as electron, proton, alpha, carbon and oxygen was investigated using the stopping power as the characterizing quantity. For this, the collision, radiative/nuclear, total stopping powers and projected range of the charged particles in the Re40-B60, Re50-B50, Re58-B42 and Re60-B40 alloys were calculated using the ESTAR, and the the Stopping and Range of Ions in Materials (SRIM) Monte Carlo code. It was found that the stopping powers of the heavy charged particles tended to decrease with increasing the rhenium concentration. These results suggest that the boron element is more suitable for heavy charged particle shielding materials compared to rhenium element.

Study of Gamma-ray Shielding of Two Different Heavy Metals and their Combination for Cs-137 and Co-60 Sources

This article presents data collected by measurements of lead (Pb) and iron (Fe) and their combination as heavy shielding materials. Measurements were performed using gamma photon energies of 662, 1173, and 1332keV for the Cs-137 and Co-60 sources. The theoretical data part was calculated using WinXCom, Phy-X, and Py-MLUBF software packages. Tables and graphs of the photon Mass Attenuation Coefficient (MAC), Linear Attenuation Coefficient (LAC), Half Value Layer (HVL), Tenth Value Layer (TVL) and Mean Free Path (MFP) are presented for both heavy metals and their combination to study the shielding properties experimentally and theoretically. The results will contribute to the ongoing research as a database for future use.

A Wide Energy Range and 4π-View Gamma Camera with Interspaced Position-Sensitive Scintillator Array and Embedded Heavy Metal Bars.

(1) Background: Gamma cameras have wide applications in industry, including nuclear power plant monitoring, emergency response, and homeland security. The desirable properties of a gamma camera include small weight, good resolution, large field of view (FOV), and wide imageable source energy range. Compton cameras can have a 4π FOV but have limited sensitivity at low energy. Coded-aperture gamma cameras are operatable at a wide photon energy range but typically have a limited FOV and increased weight due to the thick heavy metal collimators and shielding. In our lab, we previously proposed a 4π-view gamma imaging approach with a 3D position-sensitive detector, with which each detector element acts as the collimator for other detector elements. We presented promising imaging performance for 99mTc, 18F, and 137Cs sources. However, the imaging performance for middle- and high-energy sources requires further improvement. (2) Methods: In this study, we present a new gamma camera design to achieve satisfactory imaging performance in a wide gamma energy range. The proposed gamma camera consists of interspaced bar-shaped GAGG (Ce) crystals and tungsten absorbers. The metal bars enhance collimation for high-energy gamma photons without sacrificing the FOV. We assembled a gamma camera prototype and conducted experiments to evaluate the gamma camera’s performance for imaging 57Co, 137Cs, and 60Co point sources. (3) Results: Results show that the proposed gamma camera achieves a positioning accuracy of <3° for all gamma energies. It can clearly resolve two 137Cs point sources with 10° separation, two 57Co and two 60Co point sources with 20° separation, as well as a 2 × 3 137Cs point-source array with 20° separation. (4) Conclusions: We conclude that the proposed gamma camera design has comprehensive merits, including portability, 4π-view FOV, and good angular resolution across a wide energy range. The presented approach has promising potential in nuclear security applications.

Laser-Driven Collimated Neutron Sources Based on Kinematic Focusing

Neutron beams are unique tools to probe samples in many fields, such as biology medicine and fusion research. Access to such sources is traditionally limited to large particle accelerators. However, laser-driven pulsed neutron sources have attracted attention in recent years due to their compactness and cost savings. Although, in practical applications, the major obstacle is terribly low neutron flux due to the isotropic scattering. Here we propose a roadmap for laser-driven neutron sources based on ``kinematic focusing,'' which is ideal for producing highly collimated neutron beams and leads to the neutron-flux enhancement by more than 1 order of magnitude. Such a good collimation is conducive to the detection of samples located several meters from neutron sources, and it becomes feasible to place sensitive detectors adjacent to the neutron sources without the necessity of heavy shielding. A theoretical model for kinematic focusing and supporting two-dimensional particle-in-cell simulations are presented. It is shown that a well-collimated neutron beam, with the maximal divergence angle of about ${30}^{\ensuremath{\circ}}$, is generated by bombardment of a hydrogen target with ${\mathrm{Li}}^{3+}$ beams, which come from a metallic lithium foil irradiated by a short laser pulse at an intensity of $5.5\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{0.2em}{0ex}}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. This proposed method can be achieved by present-day petawatt laser facilities.

Evaluation of optical transmission across the ITER hard x-ray monitor system designed for the first plasma scenarios.

Hard x-ray (HXR) spectroscopy is applied for diagnostics of runaway electrons in nuclear fusion reactors. The scintillation counter is one of the most commonly used types of detectors for HXR spectroscopy. It consists of a detector that emits light when excited by HXR radiation (scintillator) directly coupled to a PMT (Photomultiplier Tube) that converts light pulses into an electrical signal. This type of detector is commonly used in existing tokamaks, such as Joint European Torus (JET),Experimental Advanced Superconducting Tokamak (EAST),Compact Assembly (COMPASS), andAxially Symmetric Divertor Experiment (ASDEX-U). In all these cases, the scintillator is directly coupled to the PMT to provide the best possible light transmission efficiency. The Hard X-ray Monitor (HXRM) is one among the first plasma diagnostic systems at ITER that provides information about the energy distribution of runaway electrons inside a tokamak by HXR spectroscopy. This system also uses a scintillator and a PMT as a detector. Due to the heavy shielding of the blanket modules, vacuum vessel, and port-plugs, it is not possible to assemble the scintillator outside the tokamak vacuum vessel. The PMT detector cannot be installed in the close vicinity of the tokamak due to either the significant magnetic field or temperature. A possible solution is to decouple the scintillator from the PMT and place the PMT inside the port-cell. Light pulses will be transmitted to the PMT via a 12m long optical fiber bundle. Evaluation of the optical transmission was carried out to assess the performance of the HXR monitor and verify possible problems related to the PMT pulse discrimination under low light conditions.

High-dynamic-range micro-CT for nondestructive testing of titanium 3D-printed medical components.

Purpose: Industrial microcomputed tomography (micro-CT) scanners are suitable for nondestructive testing (NDT) of metal, 3D-printed medical components. Typically, these scanners are equipped with high-energy sources that require heavy shielding and costly infrastructure to operate safely, making routine NDT of medical components prohibitively expensive. Alternatively, fixed-current, low-cost x-ray units could be implemented to perform CT-based NDT of 3D-printed medical parts in a subset of cases, if there is sufficient x-ray transmission for the CT reconstruction. A lack of signal-caused by areas of high attenuation in two-dimensional-projection images of metal objects-leads to artifacts that can make an image-based NDT unreliable. We present the implementation of a dual-exposure technique devised to extend the dynamic range (DR) of a commercially available CT scanner equipped with a low-cost low-energy (80kV) x-ray unit, increasing the signal-to-noise ratio of highly attenuated areas for NDT of 3D-printed medical components. Approach: Our high-dynamic-range CT (HDR-CT) technique adequately combines projection images acquired at two exposure levels by modifying the integration times of each protocol. We evaluate the performance and limitations of this HDR-CT technique by imaging a series of titanium-alloy test-samples. One of the test-samples was a resolution and conspicuity phantom designed to assess the improvements in void visualization of the proposed methodology. The other test-samples were four porous cylinders, , with 60%, 70%, 80%, and 90% nominal internal porosities. Results: Our HDR-CT technique adequately combines projection images acquired at two exposure levels by modifying the integration times of each protocol. Our results demonstrate that the 12-bit native DR of the CT scanner was increased to effective values of between 14 and 16 bits. Conclusions: The HDR-CT reconstructions showed improved contrast-to-noise and void conspicuity, when compared with conventional CT scans. This extension of DR has the potential to improve defect visualization during NDT of medium-size, titanium-alloy, 3D-printed medical components.

Gamma, neutron, and heavy charged ion shielding properties of Er3+-doped and Sm3+-doped zinc borate glasses

AbstractThis study aimed to investigate the nuclear radiation shielding properties of erbium (Er)-reinforced and samarium (Sm)-reinforced borate glasses. In the 0.015–15 MeV photon energy range, attenuation coefficients, as well as half-value layer tenth-value layers, and the mean-free path have been calculated. Additionally, effective, and equivalent atomic numbers, effective atomic weight, electron density, and exposure and energy absorption build-up factors were also calculated. To evaluate the overall nuclear radiation attenuation competencies of Er-rich and Sm-rich glasses, effective removal cross-section values for fast neutrons and projected range/mass stopping power values for alpha and proton particles were also determined. The glass sample BZBEr2.0 had the highest linear and mass attenuation coefficients (µandµm), effective conductivity (Ceff), the effective number of electrons (Neff), and effective atomic number (Zeff) values as well as the lowest half-value layer (T1/2), tenth value layers (T1/10), mean free path (λ), exposure build-up factor, and energy absorption build-up factor values.µmvalues were reported as 2.337, 2.556, 2.770, 2.976, 2.108, 2.266, 2.421, 2.569, and 2.714 for BZBEr0.5, BZBEr1.0, BZBEr1.5, BZBEr2.0, BZBSm0.0, BZBSm0.5, BZBSm1.0, BZBSm1.5, and BZBSm2.0 glass samples at 0.06 MeV, respectively. The results showed that Er has a greater effect than Sm regarding the gamma-ray shielding properties of borate glasses. The results of this investigation could be used in further investigations and added to older investigations with the same aim, to aid the scientific community in determining the most appropriate rare-earth additive, to provide adequate shielding properties based on the requirement.

Isotope-selective radiography and material assay using high-brilliance, quasi-monochromatic, high-energy photons.

We demonstrate the possibility to directly detect microgram amounts of the isotope 7Li using a quasi-monochromatic high-energy photon beam. The isotope selective detection is based on a witness scatterer absorbing and re-emitting photons via nuclear resonance fluorescence. This enables the detection of isotopes with microgram accuracy at long distances from the actual sample. Further, we demonstrate that the technique can deliver quantitative information without specific knowledge of the photon flux and no spectral capabilities or knowledge of the resonance fluorescence cross section. Detection of low-atomic-weight isotopes screened by heavy shielding is also shown. The techniques described are applicable to all next-generation, ultrahigh brilliance, laser-Compton light sources currently under construction.

Implementation and benchmarking of an automatic global variance reduction method on OpenMC

Shielding calculation is an important but challenging part of safety analyses for nuclear facilities due to the complex geometry and heavy shielding. In this work, an automatic Global Variance Reduction (GVR) method has been developed and implemented in OpenMC, an open-source Monte Carlo (MC) code for neutron and photon transport simulation. This GVR method is based on flux-based GVR method, improving it by defining a novel “pseudo-source”, which enhances remarkably computation efficiency. In addition, the OpenMC parallel calculation is also improved with the asynchronous scheduling function to mitigate the unbalance loading on the processes. For benchmarking this automatic GVR method, a simple thick solid sphere benchmark and a heavy shielding cuboid benchmark has been employed. An application on IFMIF-DONES Test Cell has been also adopted to demonstrate the ability of this GVR method on shielding calculations of heavy-shielded facility. These benchmarks and application show the enhancement on computation efficiency, as well as some limitations, of this newly developed GVR method.

Convolutional Neural Networks for Challenges in Automated Nuclide Identification.

Improvements in Radio-Isotope IDentification (RIID) algorithms have seen a resurgence in interest with the increased accessibility of machine learning models. Convolutional Neural Network (CNN)-based models have been developed to identify arbitrary mixtures of unstable nuclides from gamma spectra. In service of this, methods for the simulation and pre-processing of training data were also developed. The implementation of 1D multi-class, multi-label CNNs demonstrated good generalisation to real spectra with poor statistics and significant gain shifts. It is also shown that even basic CNN architectures prove reliable for RIID under the challenging conditions of heavy shielding and close source geometries, and may be extended to generalised solutions for pragmatic RIID.

Verification of the on-the-fly global variance reduction technique on Monte Carlo global coupled neutron photon shielding calculations

Using Monte Carlo (MC) transport codes for fusion device shielding calculation is very challenging due to the complexity and heavy shielding of a fusion reactor. An effective on-the-fly (OTF) global variance reduction method was developed and verified before. The OTF method is designed to speed up the general-purpose MC global total neutron distribution by generating and updating the global weight window mesh (WWM) internally in the MC code. In this work, this method has been further extended for accelerating global coupled neutron photon transportation calculation. The goal of this paper is to evaluate the applicability of OTF to enhance the efficiency of the global total neutron and photon fluxes calculation of challenging problems. For verification purposes, the ITER C-model and IFMIF-DONES have been chosen as test cases. The OTF has achieved a substantial reduction in computational time comparing with analogue method.

Observations of the [C i] (3P1–3P0) emission toward the massive star-forming region RCW 38: Further evidence for highly-clumped density distribution of the molecular gas

Abstract We present observations of the 3P1–3P0 fine-structure line of atomic carbon using the ASTE 10m sub-mm telescope towards RCW 38, the youngest super star cluster in the Milky Way. The detected [C i] emission is compared with the CO J = 1–0 image cube presented in Fukui et al. (2016, ApJ, 820, 26) which has an angular resolution of 40″ (∼0.33 pc). The overall distribution of the [C i] emission in this cluster is similar to that of the 13CO emission. The optical depth of the [C i] emission was found to be τ = 0.1–0.6, suggesting mostly optically thin emission. An empirical conversion factor from the [C i] integrated intensity to the H2 column density was estimated as X[C i]$= 6.3 \times 10 ^{20}\:$cm−2 K−1 km−1 s (for visual extinction: AV ≤ 10 mag) and 1.4 × 1021 cm−2 K−1 km−1 s (for AV of 10–100 mag). The column density ratio of the [C i] to CO (N[C i]$/N_{\rm CO}$) was derived as ∼0.1 for AV of 10–100 mag, which is consistent with that of the Orion cloud presented in Ikeda et al. (2002, ApJ, 571, 560). However, our results cover an AV regime of up to 100 mag, which is wider than the coverage found in Orion, which reaches up to ∼60 mag. Such a high [C i]$/$CO ratio in a high-AV region is difficult to explain via the plane-parallel photodissociation region model, which predicts that this ratio is close to 0 due to the heavy shielding of the ultraviolet (UV) radiation. Our results suggest that the molecular gas in this cluster is highly clumpy, allowing deep penetration of UV radiation even at averaged AV values of 100 mag. Recent theoretical works have presented models consistent with such clumped gas distribution with a sub-pc clump size (e.g., Tachihara et al. 2018, arXiv:1811.02224).

Numerical analysis on a conical shaped target for laser fusion rocket

Laser fusion rocket can achieve large thrust and high specific impulse by utilizing huge amount of fusion energy to heat up a propellant. One of the issues of this system is heavy neutron shields which are heated by neutrons. The propulsion performance of a conical target that can reduce neutron radiation to the coil is calculated by numerical analysis. The impulse bits of the spherical and the conical targets are 12 Ns and 0.75 Ns, respectively, and the propellant in the conical target does not contribute to the thrust. This result suggests that the target shape should be optimized to establish both the neutron shielding and large thrust.