Here, you can see it here. So as I put the plastic right between the source and the detector, the counts are gone. So this is an effective shield for beta particles.
So beta particles do present an external hazard, because even though clothing can offer some protection, some of the energetic beta particles can go through clothing.
But certainly if they're on skin they can go through the outer layer of skin and cause skin burns, and they're also an internal hazard. Now let's move on to gamma rays. And the source we have here is Cesium I have two sheets of lead. And let's see if I can hold this into it. I'll put it on top like that. It cuts it. But that's the effect of lead. So it takes lead to shield gamma rays. Gamma rays are obviously an external hazard, because for example first responders, if they show up on a scene and their protective clothing cannot stop penetrating gamma rays.
They will go right through that. So it's an external hazard that needs special attention. Another feature of each radionuclide is its half-life. That is the length of time it takes for half of the radioactive atoms in a population of radionuclides to decay.
And I'll show it to you in an example. After another half-life we would have And after another half-life, we would have 12, and then 6, and then 3, and then 1, and eventually all of the radioactive [ bell ] atoms that we started with have decayed to a more stable state.
So half-life. And each radionuclide has its own specific half-life. And a good rule of thumb for every radionuclide is that after seven half-lives, less than 1 percent the original number are still around. And this half-life can range from microseconds to billions of years.
So the half-life varies depending on radionuclide. Some have very short half-lives — microseconds — and some have very long half-lives measured in billions of years. To give you a couple examples, most radionuclides used in nuclear medicine have short half-lives, because we don't want them in the patient for too long. Technetium 99 is the most common radionuclide used in imaging studies.
That has a half-life of six hours. So one feature of a radionuclide with a short half-life is that later when we talk about environmental contamination, if you have an event, an incident, that involved contaminating the area or the room, but the decontaminant has a short half-life, that means it will decay really quickly and go away.
On the other hand, uranium has an extremely long half-life. Remember, that's the primordial radionuclide that's been part of the earth's crust.
It's in our soil and rock. So we still have plenty of it around, and in fact, if we take a soil sample from the backyard you're gonna find Uranium in there. Now before we leave the subject of radioactive decay, one last point to make is that some radionuclides need to go through a series of transformation before they reach a stable state.
There's more than one radioactive decay process through a series of steps. And again, the uranium we were just talking about is a good example of that, 'cause it goes through a series of transformations before it'll reach a stable state. Starts with uranium, goes through thorium, radium, then radon, bismuth, and then ultimately stable lead.
So an atom that starts as uranium finally ends up happy as a lead atom, but it takes it quite a long time sometimes. As a result of this natural process, all of these radioactive atoms are not part of our natural environment. Gamma rays can be emitted from the nucleus of an atom during radioactive decay. They are able to travel tens of yards or more in air and can easily penetrate the human body. Shielding this very penetrating type of ionizing radiation requires thick, dense material such as several inches of lead or concrete.
Neutrons can be released from the nucleus of an atom during a fission reaction, such as within a nuclear reactor, or upon detonation of a nuclear weapon. Neutrons, like gamma rays, are very penetrating and several feet of concrete is needed to shield against them. Penetration Abilities of Different Radiation Types.
Ionizing radiation can affect the atoms in living things, so it poses a health risk by damaging tissue and DNA in genes. Ionizing radiation comes from x-ray machines, cosmic particles from outer space and radioactive elements. Radioactive elements emit ionizing radiation as their atoms undergo radioactive decay.
Radioactive decay is the emission of energy in the form of ionizing radiation ionizing radiation Radiation with so much energy it can knock electrons out of atoms. The ionizing radiation that is emitted can include alpha particles alpha particles A form of particulate ionizing radiation made up of two neutrons and two protons. Alpha particles pose no direct or external radiation threat; however, they can pose a serious health threat if ingested or inhaled.
Some beta particles are capable of penetrating the skin and causing damage such as skin burns. Beta-emitters are most hazardous when they are inhaled or swallowed. Gamma rays can pass completely through the human body; as they pass through, they can cause damage to tissue and DNA. Radioactive decay occurs in unstable atoms called radionuclides.
The energy of the radiation shown on the spectrum below increases from left to right as the frequency rises. Other agencies regulate the non-ionizing radiation that is emitted by electrical devices such as radio transmitters or cell phones See: Radiation Resources Outside of EPA. Alpha particles come from the decay of the heaviest radioactive elements, such as uranium , radium and polonium. Even though alpha particles are very energetic, they are so heavy that they use up their energy over short distances and are unable to travel very far from the atom.
The health effect from exposure to alpha particles depends greatly on how a person is exposed. Alpha particles lack the energy to penetrate even the outer layer of skin, so exposure to the outside of the body is not a major concern.
Inside the body, however, they can be very harmful. If alpha-emitters are inhaled, swallowed, or get into the body through a cut, the alpha particles can damage sensitive living tissue. The way these large, heavy particles cause damage makes them more dangerous than other types of radiation. The ionizations they cause are very close together - they can release all their energy in a few cells.
This results in more severe damage to cells and DNA. These particles are emitted by certain unstable atoms such as hydrogen-3 tritium , carbon and strontium
0コメント