3.3. 2017 Minkälaisen vaikutuksen jonisoiva säteily tekee elektronisten laitteiden käyttöikään.
Uusi menetelmä pohjustaa säteilylle altistuneiden elektronisten laiteiden eliniän ennustamista.
New Methodology Paves Way for Predicting the Lifetime of Electronic Devices Exposed to Radiation https://www.iaea.org/sites/default/files/17/02/nuclear-safety-and-security.pdf
- Solar technology and radiation therapy could benefit from a new methodology developed to better understand the effects of ionising radiation on electronic devices. The technique could help predict the lifetime of these devices with the aim of improving their performance. The methodology is the result of a four-year Coordinated Research Project ( CRP) supported by the IAEA, which involved 14 research groups from 13 countries.
- The problem
- Despite years of research, there are still significant gaps in the ability to predict how radiation affects and damages electronic materials and the electrical properties and performance of semi-conductors. “Because of the huge variety of devices with very different properties, it is hard to implement an effective general model to quantify the effects of radiation on electronic materials,” said Ettore Vittone, a researcher from the University of Torino. “The results of the CRP will help us better understand the effects of energetic radiation in electronic materials and improve their quality and durability for long-term use.”
- The new methodology takes into account both the immediate and long-term effects of damage on electronic materials and devices working in harsh radiation environments, said Aliz Simon, a nuclear physicist at the IAEA and coordinator of the CRP. “The performance of a detector used to measure radiation from a radiotherapy device, for example, will deteriorate over time. Knowing when its performance starts to decline will help conduct safe irradiation for cancer therapy,” she said.
- The new methodology is based on a model that groups existing techniques for investigating radiation effects on semi-conductor devices
- Experimenting on solar cells with ion accelerators
- One area where the methodology could come in handy is working on solar cells in satellites, which are exposed to – and can be damaged by – cosmic radiation.
- To know how much radiation a solar cell installed to power a satellite could endure, researchers would have to reproduce cosmic ray exposure in experiments on earth. This, however, would be a gargantuan and time consuming task, so they opted for a more practical approach: evaluating the key parameters of the device materials. To do so, they used ion accelerators—machines that convert atoms into ions and accelerate them into energies of the order of MeV (millions of electron volt), similar to the energies emitted by radioactive nuclei. The device materials are then irradiated with ions from these accelerators. The electric signal induced is analysed and the resulting damage calculated.
- The highly energetic ions from accelerators play a dual role in the experiments: they induce damage by penetrating into the material and deteriorating the electronic properties of the device. In parallel to this effect, the ions are also used as probes to measure structural changes because when they interact with the material, an electrical signal is induced and analysed.
Calculating the damage
- The electrical signal induced is due to the motion of charge carriers generated by the ions. If the material does not have defects, the charge carriers can cross the whole device and the signal is at maximum. However, if there are defects, they would act as traps along the way and reduce the number of charge carriers crossing the device. As the number of charge carriers reduces, the electric output signal decreases and the efficiency of the device degrades.
- “Since we know where and how many traps the damaging ions generated, we can extract parameters that characterise the radiation hardness of the material and use the parameters to predict how the device will behave in a traditional environment without the need to conduct additional experiments,” Vittone said.
The CRP aimed to develop an experimental and theoretical methodology accessible to any laboratory equipped with ion accelerators. However, at the current, initial stage, the methodology has been established only for low-level damage — when the radiation slightly perturbs the order for the crystalline lattice. The methodology is published in the Journal of Nuclear Instruments & Methods in Physics Research (NIM B) and can be found here.
Additional relevant studies by the project members are published in a special section of NIM B and on Science Direct.
3rd Feb. 2014. IAEA asking about Iranian polonium production
- Amano’s statement offered a hint that polonium-210 may be among topics it wants to discuss at the February 8 meeting: “Polonium can be used for civil purposes like nuclear batteries, but can also be used for a neutron source for nuclear weapons. We would like to clarify this issue too,” he said. A U.S. think-tank, the Institute for Science and International Security (ISIS), said Iran had admitted to producing small amounts of polonium-210 in a Tehran research reactor in the early 1990s. “Iran claims that the polonium was produced as part of a study of the production of neutron sources for use in radioisotope thermoelectric generators and not for use in a nuclear weapons neutron initiator,” it added on its web site.
- The IAEA-Iran deal is separate from a November 24 breakthrough accord between Iran and six world powers to curb Iran’s nuclear program in return for a limited easing of sanctions that have battered its economy. That agreement took effect on January 20.
- Iran has moved quickly since Rouhani took office in August to improve relations with the West after years of confrontation under his hardline predecessor, Mahmoud Ahmadinejad. Iran denies accusations it is seeking to develop atomic bombs.
- As the first step to be implemented under the Iran-IAEA agreement, U.N. inspectors went to the Arak heavy-water production facility in December, a plant that is linked to a nearby reactor under construction that the West fears could yield plutonium for nuclear bombs once operational.
- The other measures concerned provision of information about nuclear facilities Iran has said it plans to build.
- The IAEA says it needs such access and data to gain a better understanding of Iran’s nuclear program and to ensure there is no diversion of atomic material for military purposes.
- Iran says it is only refining uranium to fuel a planned network of nuclear power plants. But the same material can also provide the fissile core of an atomic bomb if enriched more.
- Diplomats say the six first steps are relatively easy to implement and that it will be more difficult for Iran to agree to other action sought by the IAEA, including access to the Parchin military site where the U.N. agency believes nuclear weapons-relevant explosives tests took place a decade ago.
- Iran and the IAEA will meet again in Tehran on February 8 to discuss future measures. IAEA Director General Yukiya Amano told a news conference on Friday that they should include issues related to what the U.N. agency calls the “possible military dimensions” to Iran’s nuclear program.