Kinds of radiation and their characteristics (Vol. 4)

Hello, everyone. My name is Daichi, an expert providing the information on the radiation issues in an easy-to-understand manner.

Today, I would like to respond to the following questions:

– How much the difference of three kinds of radiation (alpha, beta and gamma ray) on human health is?
– Are there any difference for kinds of radiation needed to be cared about for external/internal exposure?
– How can the three kinds of radiation (alpha, beta and gamma ray) be shielded?

Table of contents of this article

I have been involved with the radiation-relevant issues, like the policy on the decontamination activities and the management of the Interim Storage Facility, after the accident of the Fukushima Daiichi Nuclear Power Plant in 2011.

I received a doctorate in the field of radiation, while working in Fukushima.

Kinds of radiation and their characteristics (Vol. 4)

In the previous articles, (Kinds of radiation and their characteristics (Vol. 1)) (Kinds of radiation and their characteristics (Vol. 2)) (Kinds of radiation and their characteristics (Vol. 3)), basic characteristics of alpha, beta and gamma ray (e.g. approach for ionization, mass, charge and energy), as well as penetration power relevant to the characteristics are covered.

This article especially covers difference of impact on human health caused by the difference of penetration power, as well as relationship between the kinds of radiation and kinds of exposure (external and internal exposure).

And at last, shielding materials for each kind of radiation will also be covered.

Distances each kind of radiation can travel

So, difference of penetration power of each kind of radiation has been already explained, but how long can each kind of radiation specifically travel before disappearing?

As explained in this article for alpha ray, as well as in this article for beta and gamma ray, travel distance of each radiation depends on to be exact kind of radionuclide emitting the radiation with specific energy.

However, all in all it greatly depends on kind of radiation, so let’s look at them in detail, when they travel in the air, as well as they collide with human body individually.

In the air

First, travel distance in the air.

As already mentioned, penetration power of radiation is basically: ‘Alpha ray < Beta ray < Gamma ray', and although depending on their energy, but their specific travel distances are:

– Alpha ray: around a couple of centimeters
– Beta ray: around a couple of meters
– Gamma ray: around a couple of tens of meters or a couple of hundreds of meters

When colliding with human body

For the next, when colliding with human body, they react with a lot of organs or tissues in human body, so travel distances would be definitely shorter, compared with travel in the air.

Specifically speaking, they would be:

– Alpha ray: around a couple of micrometers, or tens of micrometers
– Beta ray: around a couple of milli meters
– Gamma ray: around a couple of centimeters or more

By the way, gamma ray has strong penetration power, therefore it could be possible for it to pass through human body and travel farther.

Difference of impact on human health caused by each kind of radiation

So, what would the above-mentioned difference of penetration power cause difference on impact on human health?

Let’s look at the difference for external and internal exposure individually.

For the detail of internal and external exposure, please visit this article.

External exposure

First, regarding alpha ray, its penetration power is very weak, and it stops travelling at stratum corneum at surface of human body(so to say groups of dead cells accumulating protein and protect body from various kinds of external stimuli), and won’t reach cells underneath.

For the next, regarding beta ray, it also sometimes stops at stratum corneum when its energy is relatively low (regarding energy of beta ray please visit the previous article), as is the case with alpha ray.

When its energy, however, is to some extent high, it sometimes passes through stratum corneum, and reaches skin, or subcutaneous tissues.

And when dose is quite high, it makes impact on human body with burn, for example.

When it comes to gamma ray, penetration power is very strong, compared with alpha and beta ray and it reaches deeper part of body, or sometimes travels farther.

So it means, that especially for external exposure, beta ray with high energy as well as gamma ray need to be cared about.

Internal exposure

So, what about the case of internal exposure?

First, regarding alpha ray, unlike the case of external exposure, there are no substances to shield alpha ray like stratum corneum, organs and tissues will be directly impacted by alpha ray.

As aforementioned, penetration power of alpha ray is lower compared with other kinds of radiation, therefore, impacted range will be very limited, but on the impacted spots, human body will be severely impacted rather than beta and gamma ray.

Regarding the difference of impact on human health caused by each kind of radiation, please also visit this article.

Of course, beta ray also directly makes an impact on human organs and tissues through internal exposure, as is the case with alpha ray.

Its penetration power is larger than alpha ray, so impacted area will be larger, but magnitude of impact will be smaller.

Gamma ray also directly makes an impact on human organs and tissues, as is the case with alpha and beta ray.

Magnitude of impact will be smaller than alpha ray, but it makes an impact on whole body.

And sometimes it travels through human body from inside to outside of the body, because its penetration power is strong.

In other words, when considering internal exposure, all kinds of radiation: alpha, beta as well as gamma ray need to be cared about.

Needless to say, scale or magnitude of impact will depend on a lot of kinds of factors like dose, as covered in this article.

Shielding materials for each kind of radiation

At last, for your information, let me introduce shielding materials, which are often cited for better understanding of the difference of penetration power of radiation.

Alpha ray

Regarding alpha ray, as aforementioned, its penetration power is very weak, compared with beta and gamma ray, therefore it can be shielded by only a piece of paper.

Beta ray

On the other hand, penetration power of beta ray is stronger than that of alpha ray, so it passes through a piece of paper, but it can be shielded by a thin plastic or aluminum plate with width of from a couple of millimeters to a couple of centimeters.

Gamma ray

At last, gamma ray has the strongest penetration power of the three kinds of radiation.

Therefore, it passes through both a piece of paper and a thin plastic or metal plate, but its energy can be weakened, or it can be sometimes extinguished by thick lead or iron plates.

Especially, regarding gamma ray, appropriate thickness, as well as kinds of shielding material need to be considered, taking account of its strong penetration power.

Summary

This article covers travel distance of each kind of radiation (alpha, beta and gamma ray), in the air as well as when colliding with human body.

And kinds of radiation to be cared about are also explained., both for external and internal exposure.

By the way, above-mentioned contents are summarized in the following videos.

It would be appreciated to visit them at your convenience.

– Japanese version

– English version

You can read the same article in Japanese here.

Thank you very much for reading this article.

See you next time!