Isotopes

18 grams are one fourth of the original sample mass of 72 grams. Accordingly, the half life is 6.2/4 = 1.55 days.

Radioactive elements are just like the other elements. They are made of neutrons, protons, and electrons. The only real difference is that they radiate matter in the form of Alpha particles (Helium nuclei, more specifically the Helium isotope with an atomic mass of four [2 Protons, 2 Neutrons]), Beta positive (positrons), and Beta negative (electrons) particles. An atom emits an Alpha particle when the ratio of neutrons to protons in its nucleus is too low. This eventually stabilizes the atom, causing it to become a smaller element. Alpha radiation/emission has the highest ionizing strength of the two forms of particle emission, but also does the worst at penetration, being possible to stop with a mere sheet of paper. Beta radiation/emission occurs when an atom has an excess of a particular nucleonic particle. Positive Beta emission occurs when an atom has an excess protons. It resolves this problem by turning the extra protons into neutrons by means of emitting a positron (the polar opposite of an electron) and an electron-type neutrino. Negative Beta emission occurs when an atom has an excess of neutrons. It solves this by converting the extra neutrons into protons. In doing this, it emits an electron (the polar opposite of an electron) and an electron-type anti-neutrino. Beta radiation doesn't have as strong an ionizing power as Alpha radiation, but it has a greater penetrating strength, requiring that a minimum of a sheet of aluminum be used to prevent it from going to someplace unwanted. Then, there are really dangerous radioactive atoms. The kind that emit Gamma rays. Gamma rays radiate from atoms when they make a dramatic shift in energy states in an incredibly short amount of time by emitting photons. Gamma radiation has the highest ionizing power of all forms of radiation and also has the strongest penetrating force, so strong that not even a whole wall of lead can stop it, just weaken it.

These particles are electrons.

Each isotope of an element has a different Atomic Mass, so an average is taken of all the isotopes, but the average is weighted because the natural abundance (%) of each isotope is factored in. If hydrogen-1 is much more abundant than deuterium and tritium, then the weighted average will be closer to 1 than 2 or 3 but not a whole number.

The following equation shows how percent abundance factors into the weighted average.

(atomic mass A)(X% abundance) + (atomic mass B)(Y% abundance)...=(weighted average of all isotopes of the element)(100% abundance)

Radioactive isotopes.

Electrolytes are substances able to be dissociated in solution or after melting.
Isotopes are atoms of chemical elements; isotopes have different number of neutrons.

This phenomenon is probable possible for hydrogen, boron, nitrogen, carbon, oxygen and lithium isotopes. Repeated cycles of chemical reactions can lead to some fractionation by ion exchange or other processes.

The numbers of protons and electrons are identical.

Isotopes of krypton are: Kr-78, Kr-80 to Kr-84, Kr-86. Kr-83 was used in magnetic resonance imaging.

Probable you think to scintimetry.

"element" is a very confusing word for what you are asking. But what I think you are asking is what part of an atom does not change with an isotope. I'll answer that question.

An isotope of an atom is a variation fo the element in which the atom has a different number of neutrons. However, the number of protons can never change in a single element. So no matter how many atoms of a certain element are gathered, no matter how many different isotopes there are, they all have the exact same number of protons.

Technetium-99 is used as standard source for beta radiation.

Radioisotopes are "radioactive isotopes"; they are not stable. Radioactive atoms will decay, or break apart into other atoms, by emitting an electron, or a neutron or a positron or an alpha particle (2 protons and two neutrons). The rate at which this happens is measured by the "half-life"; after one half-life, half of the atoms will have decayed. After another half-life, half of the remaining atoms will have decayed.

Atoms with short half-lives are highly radioactive, and can be fairly dangerous. Atoms with long half-lives are only slightly radioactive, and aren't all that dangerous.

If 42 is the atomic number then there is 42 electrons in isotope.

The symbol of gamma rays is γ.
Between the initial atom and the daughter atom from decay an arrow (→) is placed.

All carbon isotopes have the same number of neutrons.

Mercury is a metal element. Mass number of it is 201.

No. Nitrogen and oxygen are two different elements. The identity of an element is determined by the number of protons in the nucleus. A nitrogen atom has 7 protons while an oxygen atom has 8. Isotopes are variations of the atoms of a given element that differ in the number of neutrons in the nucleus.

The isotope Cr-54 has 24 electrons.

Two new isotopes are produced by fission.

Thorium-232 is an alpha emitter; rarely decay by spontaneous fission or double beta decay are possible.

Number of neutrons = atomic mass of an isotope - atomic number of the isotope The atomic number of curium is 96; for the isotopic masses read at: http://en.wikipedia.org/wiki/Isotopes_of_curium.

Potassium-41 has 19 electrons and protons and 22 neutrons.

Carbon-14

The isotopes of molybdenum have different electron configurations.