Radiation and human health

joeyjo100

Just been revising radiation for an upcoming exam, and was wondering which form of radiation, [tex]\alpha[/tex], [tex]\beta[/tex] or [tex]\gamma[/tex] is the worst to be exposed to?

Ionising power decreases from alpha to gamma, but penetrating power increases from alpha to gamma. Which is more important when considering how much damage each form can do to human cells?

Norman

What is exactly being held constant here? Typically, for a given dose (energy deposited per unit mass) the gammas and electrons will have the approximately the same biological response, while the alpha will tend to be more damaging.

Drakkith

Your question is too open. You need to have some specifics about how the doses were recieved. If you have alpha or beta radiation striking your skin, its pretty much harmless.

SW VandeCarr

References please. See PF rules.

fatra2

Hi there,

As Drakktih said, the harmfulness of radiation on the human body depends if you are talking about external or internal radiation.

If you are standing next to a radioactive sources, the only real danger comes from the gamma radiation. The alpha and the beta are stopped pretty much by the first layers of skin.

If you inhale or ingest some radioactive materials, then the alpha can start causing serious damage. Although, never neglecting the effects of beta and gamma, the alpha radiation will probably be the most harmful for the body.

Cheers

Xnn

The weighting factors for x-rays, gamma rays, electrons, positrons and muons is 1.
Neutrons range from 2 to 20 depending on their energy.
Alpha particles are 20!

Consequently, alpha radiation is far more dangerous to human health.

X-rays, gamma rays and electrons generally form diffused ions when they strike human cells. Normal healthy cells are well equipped to easily repair such ions.
Alpha radiation on the other hand is between 10 to 1000 times more concentrated and likely to cause chromosome damage; especially if injected or inhaled.

Radon gas (alpha radiation) is the 2nd leading cause of lung cancer while electrons and x-rays can be used to cure a wide variety of cancers.

Norman

This statement is very misleading. The rest of your post is fine.Alphas can also be used in radiation therapy. It is exactly the higher ionization that makes it effective.

fatra2

Hi there,

Alpha radiation from an external source does not penetrate the first layers of the body. How can it be dangerous if it does not penetrate, even with a weighing factor of 20???

Cheers

Norman

I believe everyone here is assuming that by "alpha radiation" one means the alpha particle emitted during radioactive decay. The energy typical of these alphas is about 5 MeV. At 5 MeV, an alpha only travels about .004 cm in water (a proxy for tissue).

The difference is that, at higher energies, the alphas can penetrate much more deeply. For instance, a 1 GeV alpha has a CSDA (continuous slowing down approximation) range of approximately 38 cm.

Drakkith

Remember that the wieght factor of 20 is for damage to biological tissue. If it isn't in your body, then it doesn't even count as exposing yourself to it.

fatra2

Hi there,

1GEV!!! Naturally occurring decays rarely decay with that much energy, firstly. Secondly, try to imagine the penetrating power and damage done by a 1GeV photon.

Why not talk about TeV or PeV as a matter of talking. Of course, if you are expose to radiation with this type of energy, it is hard to talk about radiation protection. Their penetrating power is so great that the only was to protect against, is to run a galaxy far, far away.

Cheers

Norman

Photons are low LET, that is what makes them so penetrating. But that means at high energies they do not lose as much of their energy per unit track length. So a 1 GeV photon will lose less energy (lower dose) passing through a person than a 1 GeV alpha particle. So the photon penetrates farther, but dose less damage.

A 1 GeV photon still has a weighting factor of 1 compared to 20 for an alpha. So for a given dose, the alpha is much more damaging.

You wanted to know why we would even consider an Alpha having a weighting factor of 20. It can penetrate at high energies. LBNL ran a radiotherapy beam of alphas for 30 years or so. They treated over 2000 patients here. Need weighting factors for radiotherapy. Radiotherapy uses typically uses higher energies than 5 MeV for protons and heavier ions.

In addition, there is a high energy background of heavy ions permeating the solar system called galactic cosmic rays (energies from MeV to TeV are typically considered). This radiation environment interacts with the space station and the shuttles. It contributes to the total dose received by astronauts.