Ambient office  = 131 nanosieverts per hour

Ambient outside = 96 nanosieverts per hour

Soil exposed to rain water = 111 nanosieverts per hour

Cucumber from Central Market = 144 nanosieverts per hour

Tap water = 106 nanosieverts per hour

Filtered water = 89 nanosieverts per hour

Ambient office  = 129 nanosieverts per hour

Ambient outside = 88 nanosieverts per hour

Soil exposed to rain water = 81 nanosieverts per hour

Banana from Central Market = 121 nanosieverts per hour

Tap water = 78 nanosieverts per hour

Filtered water = 65 nanosieverts per hour

Dover sole – Caught in USA = 100 nanosieverts per hour

Part 3 of 5 Parts (Please read Parts 1 and 2 first)
   For three months in 2016, the team recorded the tracks of almost a half a million muons. The tracks were used to determine which of the twenty-four fuel assembly slots in the cask actually contained fuel assemblies and which of the slots were empty. They successfully identified full and empty slots in four out of six slot groupings.
     The team at Los Alamos’ ultimate goal is to use muons to determine not only whether a slot in a cask is empty but also whether a fuel assembly has been removed and replaced by a dummy assembly made of a dense material such as lead. This process would require combining muon scattering to determine atomic numbers and muon absorption to determine the density of the material.
     The team has run computer simulations that show that this combined process should be possible, but they have not verified it experimentally yet. Their tests at INL were not completely successful because strong winds moved the detectors out of alignment. They have not yet received sufficient funds from Department of Energy’s National Nuclear Security Administration to carry out the necessary experiments.
    The Los Alamos team had intentions to utilize their new technology to image the damaged reactor cores at Fukushima. The Tokyo Electric Power Company (TEPCO) wanted to use the muon detectors to find the missing nuclear fuel in the reactors that melted down at Fukushima. Between 2015 and 2017, TEPCO determined that the missing nuclear fuel had melted down through the bottom of the containment vessels. Morris said that absorption radiography is not the best solution for these tasks because nuclear fuel and water have similar density and there is water in the ground below the reactor vessels at Fukushima.
     Morris and his team worked with Toshiba physicists to develop muon scattering detectors. They have successfully tested their new technology on a small Toshiba reactor in Yokohama. Unfortunately, this particular technology is too expensive and disruptive to utilize at Fukushima. Morris said, “We were very disappointed not to make measurements.”
    Interest in muon monitoring has been rising in Europe, especially in Germany. Germany decided to close all of their nuclear power plants by 2022 following the Fukushima nuclear disaster. When all the reactors in Germany have been permanently shut down, it will not be possible to open up casks in cooling pools to run tests. It is unlikely that any of the other nuclear nations in Europe such as France will be willing to allow their cooling pools to be used for tests. Morris said, “Everybody has enough problems dealing with their own nuclear waste.”
    German scientists are researching ways to look inside dry casks such as muography which do not require opening the casks. Katharina Aymanns works at the Jülich Research Centre near Cologne, Germany. She thinks that that this research is very important because Germany will not have a permanent spent nuclear fuel repository until 2050 at the earliest. She says it is very important, “to make sure that all the fuel assemblies that you think are in a cask are actually in a cask”.
Please read Part 4

Ambient office  = 109 nanosieverts per hour

Ambient outside = 124 nanosieverts per hour

Soil exposed to rain water = 134 nanosieverts per hour

Red potato from Central Market = 68 nanosieverts per hour

Tap water = 91 nanosieverts per hour

Filtered water = 72 nanosieverts per hour

Part 2 of 5 Parts (Please read Parts 1 first)
    Muons are fundamental charged particles that are created naturally when cosmic rays collide with atomic nuclei in the atmosphere. This results in the generation of pion particles which then decay. Muons are about two hundred times as massive as electrons. They can easily pass through the atmosphere to the surface of the Earth. About a thousand muons hit every square foot of the Earth’s surface every minute. They penetrate into rock and other dense materials but lose energy as they interact with electrons. They are absorbed eventually after traveling through a thousand feet of rock. Scientists can track the variation in muon flux to measure the density of the materials they are passing through.
    British physicist Eric George first used atmospheric muons for measuring the thickness of ice above a mining tunnel in Australia in the 1950s. In 2003, Christopher Morris and his team at Los Alamos National Laboratory proposed using muon scattering as opposed to absorption to form images of dense objects, especially nuclear materials.
    Muons are deflected by the dense concentration of charge inside an atomic nucleus. The higher the atomic number of an element, the greater the muon deflection will be. Uranium and plutonium will deflect muons much more than materials such as concrete and steel with lower atomic numbers. The composition of materials can be calculated by plotting the trajectory of muons before they enter an object and after they leave it. With a sufficiently long exposure time, muons can be recorded that have a wide range of incident angles and positions. This can provide a very accurate image of the contents of the object under study.
     Morris and his team used muon detectors called drift tubes. These tubes contain gas and a wire that has a positive charge. When a muon passes through a drift tube, it liberates electrons which generate a signal at that point on the wire. Tubes are laid out in layers that are at right angles to each other. It is possible to map a trajectory of a muon by tracking a series of excited points on wires in the tubes. A minimum of two sets of perpendicular layers of drift tubes on either side of an object is required to plot the incoming and outgoing vectors of a muon.
    Researchers at Los Alamos National Laboratory first carried out muon experiments with a tungsten cylinder. After those experiments, the team created muon detectors that were designed to identify nuclear materials concealed within cargo in trucks and shipping containers. Funding for this work was made available after the 9/11 terrorist attack in New York in 2001. Los Alamos developed a prototype of such a detector for nuclear materials for Decision Sciences Corporation, a company in California which is now selling such detectors in the U.S. and abroad.
     Morris and his team then began working on monitors for spent nuclear fuel. They developed two muon trackers which each had twenty-four layers with twenty four-meter long drift tubes in each layer. They shipped these detectors to the Idaho National Laboratory (INL) for testing. The detectors were placed on either side of a dry cask containing fuel assemblies removed from a Westinghouse nuclear reactor in the 1980s.
Please read Part 3

Ambient office  = 113 nanosieverts per hour

Ambient outside = 178 nanosieverts per hour

Soil exposed to rain water = 155 nanosieverts per hour

Celery from Central Market = 67 nanosieverts per hour

Tap water = 84 nanosieverts per hour

Filtered water = 77 nanosieverts per hour

Part 1 of 5 Parts
    I have blogged about muons before. They are often generated in particle accelerators. Physicists can use them to identify more exotic particles in the debris of particle collisions. Muons are also produced by natural forces in the atmosphere and researchers have turned to them for probing dense materials. This use is referred to as muon radiography or muography. Muon detectors have been used by archeologists to probe for cavities in pyramids and by geologists to check for the rise of magma in volcanoes. Muography is especially well suited for use in probing containers of nuclear waste which are inaccessible to other forms of radiation.
    Dealing with spent nuclear fuel is complex, expensive and dangerous. The goal is to keep the public and environment safe while ensuring that the fuel can be traced. The International Atomic Energy Agency (IAEA) was establish partly to ensure that no spent nuclear fuel will fall into the hands of groups that could extract plutonium to create dirty bombs or fulling operations nuclear bombs.
    Nuclear fuel for commercial power reactors is produced in the form of pellets of uranium which are inserted in to long metal tubes that are bundled into fuel assemblies for insertion into the core of the reactors. As the uranium in the pellets undergoes fission and generates power, it also creates plutonium and other highly radioactive isotopes which generate a lot of heat.
     After a fuel assembly is removed from the core, it is placed in a cooling pool near the reactor for several years to cool off. Cooling pools in the U.S. are filling up rapidly. Some fuel assemblies are removed after cooling and placed in steel and concreate cylinders referred to as dry casks. These casks are several meters high and lined with radiation absorbing material. They are stored near the reactor or in a temporary storage facility somewhere else.
    In order to account for spent nuclear fuel, the IAEA inspectors utilize cameras to observe the process of loading and unloading the fuel assemblies. They can also use Cerenkov radiation (Cherenkov radiation is electromagnetic radiation emitted when a charged particle such as an electron passes through a dielectric medium at a speed greater than the phase velocity of light in that medium.) to check the assemblies in the cooling pool. However, once the assemblies are placed in the radiation proof casks, no direct monitoring is possible.
    All the inspectors can do is place seals on the casks to indicate if they have been tampered with. However, the seals could corrode with time or be damaged when the casks are moved. The only way find out if a damaged seal indicates tampering would be to open the casks to inspect their contents. This would be complicated, expensive and dangerous.
     Muons offer a solution to the problem of monitoring the contents of a sealed cask without opening it. Matt Durham works at the Los Alamos National Laboratory. On the matter of monitoring spent nuclear fuel, he says, “This issue is only getting worse as more plutonium piles up around the world.  Muons offer a way to establish how much waste there is in a container without having to open or move the container in question.”
Please read Part 2