Molly Ayala
Alpha particles can be converted into electricity using a radiovoltaic (RV) device, which uses a semiconductor junction to produce electrical energy from energetic alpha particles. This process is also known as alphavoltaic (AV) or alpha-voltaic power. The direct conversion of alpha particles into electricity has been attempted with limited success due to poor planning and improper device designs. However, recent studies have proposed the use of semiconductors that are stable at high temperatures, such as GaAs or SiC, with curium-244 as the alpha particle source. These long-lived, low-power cells could operate for years at extreme temperatures and are expected to be useful as power sources for low-power electronic circuits that require long-term operation without recharging or external power connections.
| Characteristics | Values |
|---|---|
| Technique | Betavoltaics |
| Materials | Tritium capsule, sealed-in potassium-40 layer, silicon solar arrays, diamond semiconductor diodes, liquid gallium, GaAs, SiC, curium-244, Am-241, plutonium-238, InGaP diodes, etc. |
| Temperature range | -250 to 600 °C |
| Voltage | 1.62 V, a few hundred microwatts to a few milliwatts, kilovolts, megavolts |
| Current | Very low |
| Applications | Power source for low-power electronic circuits, spacecraft, hearing aids, surgically implanted medical devices, pacemakers, etc. |
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What You'll Learn
Using a direct-charging generator
Direct-charging generators are one of the methods to convert alpha particles to electricity. This method of conversion was referenced in a 1994 paper by Kanngiesser Karl-Werner, D. Hartmut Huang, Hans Peter Lips, and Georg Wild.
Direct-charging generators use a capacitor to capture the charge created by a current of charged particles. This capacitor is charged by the current of positively charged alpha particles from a radioactive layer deposited on one of the electrodes. The charged particles create a flow of electricity as they move from the radioactive layer to the inside surface of the sphere.
The use of direct-charging generators for electricity generation from alpha particles dates back to 1913 when Henry Moseley first demonstrated a current generated by charged-particle radiation. However, due to the extremely low currents and inconveniently high voltages, direct-charging generators have found few applications.
To address the issue of high voltages, oscillator/transformer systems can be employed to reduce the voltage, and then rectifiers are used to convert the AC power back to direct current. This was first demonstrated by English physicist H. G. J. Moseley, who constructed an apparatus consisting of a glass globe silvered on the inside with a radium emitter mounted on a wire at the center.
In recent years, there have been proposals for small electric power cells based on the direct conversion of kinetic energy of alpha particles into electricity. These cells would utilize semiconductors that are stable at high temperatures, such as GaAs or SiC, and the alpha-particle sources would likely be made from curium-244, a radioactive material with a half-life of about 18 years. These proposed power cells could have a wide range of applications, including in spacecraft, hearing aids, and surgically implanted medical devices.
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$139 $148
Using a radioluminescent material
Radioluminescent materials, such as self-glowing crystals containing alpha-radionuclides, can be used to convert alpha particles into electricity. The process involves using a radioluminescent material, such as a scintillator or phosphor, to convert the alpha particles into light through radioluminescence. This light can then be converted into electricity using a photovoltaic cell.
The first step in this process is to obtain a radioluminescent material that can absorb alpha particles and emit light. This can be achieved by using crystals containing alpha-radionuclides, such as YPO4:Eu3+,238Pu, ZrSiO4:Tb3+,238Pu, or ceramics based on cubic ZrO2:Eu3+,238Pu. These materials are synthesised by activating specific crystals and ceramics with 238Pu. The synthesized materials then undergo radioactive decay, causing the emission of alpha particles that result in radioluminescence.
The radioluminescent material emits light through the phenomenon of radioluminescence. In this process, the incoming alpha particles, which are a form of ionizing radiation, collide with atoms or molecules in the material. This collision excites an orbital electron to a higher energy level, and when the electron returns to its ground energy level, it emits the extra energy as a photon of light. This emitted light is what makes the material radioluminescent.
The emitted light from the radioluminescent material can then be converted into electricity using a photovoltaic cell. This process, known as radiophotovoltaic (RPV) conversion, involves the photovoltaic cell absorbing the light and converting it into electrical energy. The photovoltaic cell is specifically designed to capture the photons of light and use their energy to generate a flow of electrons, creating an electric current.
By combining the radioluminescent material with the photovoltaic cell, alpha particles are indirectly converted into electricity. This method allows for the efficient utilisation of the energy from alpha particles, as the radioluminescent material ensures that the energy is first converted into light, which can then be effectively transformed into electrical energy by the photovoltaic cell. This approach has been explored for various applications, including long-lasting power sources and implantable medical devices.
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Using diamond as a conversion medium
Alpha particles can be converted to electricity using diamond semiconductor diodes. This method involves the direct conversion of the kinetic energy of alpha particles into electricity. The proposed power sources would be miniature in size and function over a wide range of temperatures, from -250°C to 600°C, in both terrestrial and outer-space environments. The expected operational lifetime of these sources is 10 to 20 years, with energy conversion efficiencies of over 35%.
Each device would consist of Schottky and p/n diode devices made from high-band-gap, radiation-hard diamond substrates. The n and p layers in the diode portion would be doped sparsely to maximize the volume of the depletion region and, consequently, the efficiency. The diode layers would be supported by an undoped diamond substrate. This design aims to maximize efficiency and minimize lattice damage caused by impinging alpha particles.
The use of diamond as a conversion medium for alpha particles offers several advantages. Diamond is known for its high thermal conductivity, providing effective heat dissipation, which is crucial for managing the high-energy alpha particles. Additionally, diamond's high band gap and radiation hardness make it suitable for withstanding the high-energy particle collisions without degradation, ensuring the long-term reliability of the power source.
Furthermore, diamond's mechanical strength and chemical inertness contribute to the durability and stability of the conversion medium. The proposed design also includes additional insulation or isolation to prevent damage from alpha-particle collisions. This insulation can be in the form of an undoped diamond substrate, providing a robust barrier against the energetic particles.
Overall, the use of diamond as a conversion medium for alpha particles to electricity offers promising potential due to its ability to withstand extreme conditions, high-energy particle collisions, and its long-term reliability. The development of such power sources can have applications in both terrestrial and space environments, powering electronic circuits, spacecraft, medical devices, and more.
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Using liquid gallium as a conversion medium
Gallium is a suitable candidate for use as an electrolyte and energy-conversion medium due to its unique properties in the liquid state. When gallium is heated above its melting point of 29.76 °C, it becomes a semimetal with electrical conductivity greater than that of a typical semiconductor but lower than that of metals. This property allows electrons and Ga(+) ions to exist independently and be manipulated by electric fields without immediate recombination.
In the proposed design of alpha-voltaic sources, liquid gallium serves as the energy-conversion medium within an electrolytic cell. The cell consists of an iridium cathode and a zirconium anode, with a source of alpha particles positioned to emit particles into the liquid gallium. The alpha particles, emitted by the radioactive decay of curium-244 (Cm-244), carry a kinetic energy of approximately 5.8 MeV.
As the alpha particles enter the liquid gallium, their kinetic energy is dissipated primarily through the ionization of Ga atoms, resulting in the creation of Ga(+) ions and free electrons. The presence of an electric field, resulting from the difference in work functions of the electrode metals, then moves the electrons and ions towards their respective electrodes. This process generates an electric current and converts the kinetic energy of the alpha particles into usable electricity.
One significant advantage of using liquid gallium as the conversion medium is its ability to withstand the impingement of energetic alpha particles without sustaining displacement damage. In solid-state energy conversion media, the impact of high-energy particles can cause structural damage, reducing the efficiency and lifespan of the material. However, the liquid state of gallium allows for continuous annealing of any potential lattice damage, ensuring the long-term stability and efficiency of the energy conversion process.
The proposed alpha-voltaic sources using liquid gallium are expected to offer high energy-conversion efficiencies, ranging from 70 to 90 percent. Additionally, these sources are designed to have long operational lives and function across a wide range of temperatures, making them suitable for various applications, including outer space missions and low-power electronic devices that require extended periods of operation without recharging.
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Using semiconductors
The concept of an alpha voltaic battery was first proposed in 1954 by W. G. Pfann and W. van Roosbroeck. This type of battery involves the use of a radioactive substance that emits energetic alpha particles, which are coupled to a semiconductor p/n junction diode. As the alpha particles penetrate the p/n junction, they decelerate and lose energy in the form of electron-hole pairs. These electron-hole pairs are then collected by the p/n junction and converted into electricity, similar to how a solar cell functions.
The main challenge with alpha voltaic batteries is that the alpha particles tend to damage the semiconductor material, leading to rapid degradation of electrical performance. However, recent research by Jagdishbhai Patel of Caltech for NASA's Jet Propulsion Laboratory has shown that lattice damage in the active regions of the semiconductor can be continuously annealed during ionization processes. This finding could potentially address the issue of semiconductor degradation.
To improve the efficiency of alpha voltaic batteries, various factors need to be considered, including the source of radioactive radiation, the interface between materials, and the process of converting electron-hole pairs into electric current. Computer simulations can be employed to optimize device designs and minimize lattice damage from alpha particles, thereby maximizing the lifetime and reliability of the devices.
One proposed design for an alpha voltaic battery includes at least one layer of a semiconductor material with a p/n junction, an absorption and conversion layer, and an alpha particle emitter. The absorption and conversion layer play a critical role in preventing alpha particles from damaging the p/n junction while converting the alpha particle energy into electron-hole pairs for electricity generation. This design can potentially be utilized for power sources in low-power electronic circuits, spacecraft, hearing aids, and surgically implanted medical devices.
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Frequently asked questions
Alpha particles are positively charged particles emitted by radioactive materials. They are high-energy particles that can be converted into electricity.
Alpha particles can be used to generate electricity through a process called "direct charging". This involves placing a thin sheet of radioactive material between two metal plates in a vacuum. The alpha particles emit an electric current, which can be captured and converted into usable electricity.
Alpha particle electricity generation has a wide range of applications, including in outer space and on Earth. They can be used as power sources for low-power electronic circuits, such as those in spacecraft on long interplanetary missions, hearing aids, and surgically implanted medical devices.
