H 1 Hydrogen 1.00794 | Periodic Table | He 2 Helium 4.002602 | |||||||||||||||

Li 3 Lithium 6.941 | Be 4 Beryllium 9.012182 | of the Elements | B 5 Boron 10.811 | C 6 Carbon 12.0107 | N 7 Nitrogen 14.0067 | O 8 Oxygen 15.9994 | F 9 Fluorine 18.9984032 | Ne 10 Neon 20.1797 | |||||||||

Na 11 Sodium 22.98976... | Mg 12 Magnesium 24.305 | mouse/touch for more information | Al 13 Aluminum 26.9815386 | Si 14 Silicon 28.0855 | P 15 Phosphorus 30.973762 | S 16 Sulfur 32.065 | Cl 17 Chlorine 35.453 | Ar 18 Argon 39.948 | |||||||||

K 19 Potassium 39.948 | Ca 20 Calcium 40.078 | Sc 21 Scandium 44.955912 | Ti 22 Titanium 47.867 | V 23 Vanadium 50.9415 | Cr 24 Chromium 51.9961 | Mn 25 Manganese 54.938045 | Fe 26 Iron 55.845 | Co 27 Cobalt 58.933195 | Ni 28 Nickel 58.6934 | Cu 29 Copper 63.546 | Zn 30 Zinc 65.38 | Ga 31 Gallium 69.723 | Ge 32 Germanium 72.63 | As 33 Arsenic 74.9216 | Se 34 Selenium 78.96 | Br 35 Bromine 79.904 | Kr 36 Krypton 83.798 |

Rb 37 Rubidium 85.4678 | Sr 38 Strontium 87.62 | Y 39 Yttrium 88.90585 | Zr 40 Zirconium 91.224 | Nb 41 Niobium 92.90628 | Mo 42 Molybdenum 95.96 | Tc 43 Technetium (98) | Ru 44 Ruthenium 101.07 | Rh 45 Rhodium 102.9055 | Pd 46 Palladium 106.42 | Ag 47 Silver 107.8682 | Cd 48 Cadmium 112.411 | In 49 Indium 114.818 | Sn 50 Tin 118.71 | Sb 51 Antimony 121.76 | Te 52 Tellurium 127.6 | I 53 Iodine 126.90447 | Xe 54 Xenon 131.293 |

Cs 55 Caesium 132.9054 | Ba 56 Barium 132.9054 | Hf 72 Hafnium 178.49 | Ta 73 Tantalum 180.94788 | W 74 Tungsten 183.84 | Re 75 Rhenium 186.207 | Os 76 Osmium 190.23 | Ir 77 Iridium 192.217 | Pt 78 Platinum 195.084 | Au 79 Gold 196.966569 | Hg 80 Mercury 200.59 | Ti 81 Thallium 204.3833 | Pb 82 Lead 207.2 | Bi 83 Bismuth 208.9804 | Po 84 Polonium (209) | At 85 Astatine (210) | Rn 86 Radon (222) | |

Fr 87 Francium (223) | Ra 88 Radium (226) | Rf 104 Rutherfordium (267) | Db 105 Dubnium (268) | Sg 106 Seaborgium (271) | Bh 107 Bohrium (272) | Hs 108 Hassium (270) | Mt 109 Meitnerium (276) | Ds 110 Darmstadium (281) | Rg 111 Roentgenium (280) | Cn 112 Copernicium (285) | Uut 113 Unutrium (284) | Uuq 114 Flerovium (289) | UuP 115 Ununpentium (288) | Lv 116 Livermorium (293) | Uus 117 Ununseptium (294) | Uuo 118 Ununoctium (294) | |

La 57 Lanthanum 138.90547 | Ce 58 Cerium 140.116 | Pr 59 Praseodymium 140.90765 | Nd 60 Neodymium 144.242 | Pm 61 Promethium (145) | Sm 62 Samarium 150.36 | Eu 63 Europium 151.964 | Gd 64 Gadolinium 157.25 | Tb 65 Terbium 158.92535 | Dy 66 Dysprosium 162.5 | Ho 67 Holmium 164.93032 | Er 68 Erbium 167.259 | Tm 69 Thulium 168.93421 | Yb 70 Ytterbium 173.054 | Lu 71 Lutetium 174.9668 | |||

Ac 89 Actinium (227) | Th 90 Thorium 232.03806 | Pa 91 Protactinium 231.0588 | U 92 Uranium 238.02891 | Np 93 Neptunium (237) | Pu 94 Plutonium (244) | Am 95 Americium (243) | Cm 96 Curium (247) | Bk 97 Berkelium (247) | Cf 98 Californium (251) | Es 99 Einstenium (252) | Fm 100 Fermium (257) | Md 101 Mendelevium (258) | No 102 Nobelium (259) | Lr 103 Lawrencium (262) |

Radioactive elements undergo decay, and the speed at which the decay occurs used to be measured in curies. The International Council of Scientific Unions on Standards, Units and Constants of Radioactivity defined the curie as the "quantity of any radioactive substance in which 3.7 × 10^10 disintegrations occur each second." Decay rates vary between the different radioactive elements, so the conversion of grams to curies, abbreviated to Ci, is possible only when the source material is known.

Establish the atomic weight of the element by checking the periodic table. For example, the atomic weight of Cobalt-60 is 59.92 and Uranium-238 has the atomic weight 238.

Convert the mass into moles, using the formula moles = mass of the element / atomic mass of the element, and then convert moles to atoms by multiplying the mole value by Avogadro's number, 6.02 x 10^23. For example, to establish the number of atoms in 1 gram of Cobalt-60, calculate (1 / 59.92) x (6.02 x 10^23). This resolves to 1.01 x 10^22 atoms.

## Sciencing Video Vault

Substitute the activity of the element, for example 1.10 x 10^3 Ci for Cobalt-60, into the formula: r = activity rate x (3.700 x 10^10 atoms/s/Ci). The result is "r," the number of atoms decaying per second. For example, 1.10 x 10^3 x 3.700 x 10^10 = 4.04 x 10^13 atoms decaying per second, so r = 4.04 x 10^13.

Use the first-order rate equation, r = k[number of atoms]1, to determine the value for k. For example, using the values for "r" and the number of atoms previously determined for Cobalt-60, the equation becomes: 4.04 x 10^13 atoms decaying per second = k[1.01 x 10^22 atoms]. This resolves to k = 4.1 x 10^-9 s^-1

Determine the decay activity, in atoms / second, for the element. To do this, substitute the number of atoms in the sample into the equation: (4.1 x 10^-9 s^-1) x (number of atoms in the sample). For example, with 1.01 x 10^22 atoms the equation becomes : (4.1 x 10^-9 s^-1) x (1.01 x 10^22). This resolves to 4.141 x 10^13 atoms / second.

Calculate the value in curies by dividing the decay rate per second by 3.7 x 10^10, the decay rate equal to 1 curie. For example, 1 gram of Cobalt-60 is equivalent to 1,119 curies because 4.141 x 10^13/ 3.7 x 10^10 = 1,119 Ci.

#### Tip

Use a scientific calculator and perform all the calculations using scientific notation. This eliminates potential errors generated by incorrect numbers of zeros in very large numbers.

#### Warning

Step 4 involves calculus and will not be possible without advanced mathematical knowledge.