How are gamma rays measured and what is the quantity that can be harmful to humans and or pets and will a harmful amount be able to reach Denver from Japan?

Answer 1

Gamma radiation is measured in several different ways. You can use a geiger-muller detector running in avalanche mode; you can use an ion chamber in linear mode; you can use a photo scintillator running in either gross or window mode; and you can use a supercooled diode to detect it. These are just a few examples.

We don't really know how much gamma radiation at low levels can harm humans or pets. It is understood that a typical person receives about one millisievert per year from background radiation, with an additional one millisievert per year due to medical radiation. These levels are considered perfectly normal.

At higher doses, it becomes a little more certain, but it still requires a substantial amount of radiation to impact a person, on the order of 250 millisieverts before you can even detect changes in blood, and on the order of 1 sievert before significant, predictable impact.

No, the distance between Japan and Denver is such that, at that distance, there will be no measurable dose rate in Denver. However, you need to realize the distinction between radiation and radioactivity. Radiation is what comes out of radioactive material so, if the radioactive material stays in Japan, then the radiation will not be measurable outside of Japan. On the other hand, radioactive material, such as Cesium-137 and Iodine-131, both gamma emitters, can travel from Japan to Denver, even to the entire world. Problem (or salvation, depending on how you look at it) is that diffusion from the atmosphere will dilute the radioactive material so much that you still won't be able to detect it at any statistical confidence above the normal background radiation.

Yes, there are trace amounts of radioactive material coming in from flights out of Japan, and there are trace amounts in the atmosphere already reaching our west coast, but they are trace amounts that do not matter. Even in Japan, the risk is small so, by the time we reach Denver, there will be no significant risk.

Addendum:Denver lies east of The Nevada National Security Site (N2S2), essentially down wind. The significance of this is the largest nuclear test site in the continental US, and one of the largest nuclear detonation sites in the world resides at N2S2. From the 1950's into the 1990's, the US detonated over 1000 devices in the various test ranges at this site. N2S2 is one of the most radioactively contaminated sites in the world, much of the debris from detonations still lies on the surface of the desert there, free to be carried by the wind as far as it can go. The gamma emitter I-131 has been traced as far as the state of Maine as a direct result of nuclear detonations in the Nevada desert, and roughly 3% of all radioactive debris cast out by nuclear fissile detonations is I-131, a direct link to thyroid cancers.

Summary, you have more to fear from the dust blown up from Nevada, than that kicked off the shoes of Japanese refugees.

Answer 2

Gamma rays are measured using a device called a dosimeter, which quantifies radiation exposure. In terms of harmful levels for humans and pets, exposure to a high dose of gamma rays can lead to radiation sickness and potentially death. The potential harm from a nuclear event in Japan reaching Denver would depend on the distance, atmospheric conditions, and the amount of radioactive material released. Such scenarios are typically studied by radiation experts and authorities in the event of a nuclear accident.