Does your body contain more neutrons than protons?

Answer 1

Short Answer:

There are more protons than neutrons in the human body.

This is primarily because we are mostly water and H2O is mostly hydrogen. Hydrogen is a single proton and is 25% of all the atoms in the body.

Of the six elements that make up 99% of the mass of the human body (oxygen 65%, carbon 18%, hydrogen 10%, nitrogen 3%, calcium 1.4%, phosphorous 1.1%), all but hydrogen and phosphorous have an equal number protons and neutrons in the dominant isotope and hydrogen, be 25% of all atoms, overwhelms the balance giving more protons than neutrons.

Long Answer:

The human body (and other living things) contains a much greater number of protons than neutrons. Consider the data from the "related links" below which describe the elemental composition of the human body. This data allows one to calculate the number of neutrons and protons for each element and determine that there are about 4.15*10^27 protons more than the number of neutrons.

Perform the following calculations for each of the elements on the list: determine the difference between number of neutrons and protons in the atomic nucleus and call it N-P ('N' minus 'P') for each element; divide the mass in grams of the element in the human body by the Atomic Mass of the element to get the moles of the element in the human body; multiply the moles by Avagadro's constant (~6.022*10^23) to get the number of atoms; multiply the number of atoms with N-P to get the net neutrons for the element.

The list at the cited webpage is conveniently in order of most abundant to least abundant. If we look at only the first fifteen elements at the ones that have N-P not equal to zero we find that the net neutrons is on the order of -(10^27). This is due to the fact that Hydrogen has 1 proton and 0 neutrons (N-P = -1), and with a mass contribution of 7 kilograms to the human body, adds nearly 7000 moles of protons. Note, I'm ignoring the rest of the elements on the list after Cadmiun (the fifteenth with N-P != 0) since the mass contribution after Cadmium is less than 0.050 grams, none of the remaining elements should be able to contribute enough neutrons to increase the net neutrons into positive range. (The trend is much more clear if you perform the calculations and list the elements.)

Additionally, although Carbon makes up ~16 kilograms of the body, the amount of isotopic carbon is only about 1% of that value at most, so the contribution from isotopic carbon would be only about 160 grams, which if it were all C14, would only add 1.38*10^25 neutrons.

Answer 2

Short Answer:

The human body contains a large number of neutrons.

This is because every atom in the universe, except hydrogen, contains neutrons.

About 45% of the mass of the human body is due to neutrons and of the remaining 55%, that is mostly protons, but 0.027% of the mass, just about 20 grams, is electrons.

Long Answer:

Atoms are the building blocks of matter, and neutrons make up about half of the mass of most atoms. (Hydrogen is the exception and does not have a neutron.) The other half of the mass comes from protons. We have as many electrons as protons, but the mass of electrons is just over 1/2000th the mass of the proton or neutron.

An adult human with a mass of 70 kg (154 lbs) has about 6.7 x 1027 atoms in their body. Only the hydrogen atoms, which make up about 10% of that mass, do not have neutrons. (Almost two thirds, 63%, of the atoms in a human are hydrogen, but they don't weigh much.) The rest of the atoms, are mostly 4 elements, oxygen, carbon, nitrogen and calcium which together account for another (24+12+.6+.25=) 37% of the atoms, but almost (65+18+3+1.4=) 87.4% of the mass. Almost all of those atoms (Ca,C,N,O) have the same number of protons and neutrons. Only about 0.25% of the atoms in a human have one or more extra neutrons in excess of the number of protons.

Average Human:

Since protons and neutrons are pretty much the same mass (1 amu) and an electron is 0.0005 times their mass, the weight of the human body is 0.027% electrons 55% protons 45% neutrons. For that average sized human that is 20 grams (0.7 oz) of electrons, 31.5 kg (70 lbs) neutrons, 38.5 kg (85 lbs) protons.