You may wonder which naturally-occurring element has the shortest half-life. That would be francium, element 87, whose longest-lived isotope, francium-223, has a half-life of 22 minutes, decaying either into radium by beta decay or astatine by alpha emission.

Hydrogen-7

A short-lived radioisotope is usually defined as one whose half-life is reckoned in seconds, minutes or hours. By their very nature, these isotopes must be used at or near the site of production, unless it is possible to produce and ship many times the activity actually required by the user.

Istopes with shorter half-lives are more intense. In nuclear waste, isotopes with very short half-lives, say a few days or even a few weeks, are not the major concern. They will decay to negligible amounts within a year or two. Isotopes with very long half-lives, more than 1000 years, are likely to be less intense.

Radioisotopes with short half-lives are dangerous for the straightforward reason that they can dose you very heavily (and fatally) in a short time. Such isotopes have been the main causes of radiation poisoning and death after above-ground explosions of nuclear weapons.

a short half-life usually means more withdrawal problems. a long half-life usually means fewer withdrawal problems.

Depends what you mean by danger. Short half life isotopes like iodine-131 are dangerous with direct exposure. But with a half life of 8 days, it is 99% gone after a couple of months, and poses little long term environmental risk.

Transuranic wastes, sometimes called TRU, account for most of the radioactive hazard remaining in high-level waste after 1,000 years. Strontium-90 and cesium-137 have half-lives of about 30 years (half the radioactivity will decay in 30 years). Plutonium-239 has a half-life of 24,000 years.

Iodine-129

Every element does not have a halflife. Only elements with no stable isotopes–Pm, Tc, and all from Atomic Number 83 on up have no stable isotopes. Some naturally occurring elements have stable and radioactive isotopes–Such as Potassium with the radioactive isotope K-40, 0.012% abundance, 1.25E9 years halflife.

The following radioactive elements are found naturally in the environment.

• Alpha Radiation. Alpha radiation is a type of energy released when certain radioactive elements decay or break down.
• Uranium. Uranium is a radioactive element that can be found in soil, air, water, rocks, plants and food.
• Radium.
• Radon.
• Polonium.

Half-life is the expected value when half the number of atoms have decayed. Radioactive atoms have unstable nuclei. Their nuclei are unstable because the arrangement of protons and neutrons in them are unsteady.

Generally it is considered that it takes 5.5 half-lifes for a drug to be removed from the body, in that it is considered to no longer have a clinical effect. So for Ambien it would take approximately 11 hours (2 hours X 5.5) to be eliminated from your body.

These types of decay involve the nuclear capture of electrons or emission of electrons or positrons, and thus acts to move a nucleus toward the ratio of neutrons to protons that has the least energy for a given total number of nucleons. This consequently produces a more stable (lower energy) nucleus.

In terms of decay types, beta decay is predicted by looking at an isotope’s neutron to proton ratio. Alpha decay will occur frequently in elements with atomic numbers greater than 83, and gamma decay will occur when a nucleus is an excited state.

So first look at the father nucleus and list its number of protons and its atomic weight. Step 3) Now from number of neutrons subtract 2 and from number of protons subtract 2 as an alpha particle has 2 neutrons and 2 protons and in an alpha decay an alpha particle will always form in case of any any father nucleus.

Positron Emission A positron is a particle with the same mass as an electron, but with a positive charge. Like the beta particle, a positron is immediately ejected from the nucleus upon its formation. The symbol for a positron in an equation is e+01.