Radiation - Quia



Radiation

Dose

A Brief History

History

The Big Three.

Wilhem Conrad Roentgen’s discovery of x-rays in 1895.

Henri Becquerel’s observance of rays being given off by uranium-containing substances.

The discovery of radium by Pierre and Marie Curie.

First Occupation Death

The first U.S. x-ray fatality occurred in 1906.

Clarence Day, died from radiation effects after working with friend Thomas Edison in producing fluoroscope and fluorescent screens.

Shielding was rarely used in those times.

Law of Bergonie & Tribondeau

In 1906 exposed rodent testicles to x-rays, and observed the effects of radiation.

Noticed that immature cells were injured at a dose lower than the mature cells.

Their law maintains that actively mitotic and undifferentiated cells are most susceptible to damage from ionizing radiation.

Law of Bergonie & Tribondeau

It states

Stem cells are most radiosensitive than mature cells; The more mature a cell is, the more radioresistant.

Younger tissues and organs are more radiosensitive than older tissues and organs.

The higher the metabolic activity of a cell, the more radiosensitive it is.

The greater the proliferation and growth rate for tissues, the greater the radiosensitivity

Ancel & Vitemberger

In 1925 modified the Law of Bergonie and Tribondeau.

Suggested that the intrinsic susceptibility of damage to any cell by ionizing radiation is the same, but that the timing of manifestation of radiation-produced damage varies according to types of cells.

Ancel & Vitemberger

Two factors affect the appearance of radiation damage to the cell.

The amount of biologic stress the cell receives (division stress).

Pre- and Post-irradiation conditions that the cell is exposed to.

A given dose of radiation will cause the same damage to all cells, but only if and when the cells divides will damage be demonstrated.

Ancel & Vitemberger

Direct / Indirect Effect

Direct ionization along charged particle tracks cause direct effect.

The formation of free radicals caused indirect effects.

Fractionation Theory

1920’s & 1930’s

Sterilization of rams.

Found that if large doses where fractionated (smaller doses spread out over a period of time), the animals would still become sterile, but with considerably less damage to their skin.

Mutagenesis

1927 H. Muller discovered that ionizing radiation produced mutations through his experiments with fruit flies.

Radiation-induced mutations were the same as those produced in nature.

Mutations not only caused by radiation, but increases in frequency as radiation is introduced

Effects of Oxygen

1940’s 1950’s: Oxygen is termed a radiosensitizer because it increases the cell-killing effect of a given dose of radiation.

The higher amount of oxygen the more free radicals produced

Reproductive Failure

1956, Puck and Marcus.

Exposed human uterine cervix cells to varying doses of radiation.

Determined reproductive failure by counting the number of colonies formed by these irradiated cells.

Units of measurement were developed to quantify radiation levels and track exposure.

Now for some attention getters

Radiation Dose

One of the most confusing things about understanding radiation effects is visualizing “how much” radiation is involved. It is very difficult to keep the units which measure radiation straight. A number describing the amount of radiation means nothing without evaluating the units, but this is not easy.

For example...

...try to match the letter with the amount of radiation involved in each example

Amount of potassium 40 in the body

Dose to Atomic bomb survivors

You can safety hold this amount of alpha radiation

One coast to coast flight

A diagnostic X-ray

Commonly Used Radiation Units

Understanding Radiation Units

Activity

The number of times each second a radioactive material decays and releases radiation.

Dose (Absorbed)

The amount of radiation energy absorbed into a given mass of tissue.

Dose (Equivalent)

Measures the energy per unit mass times adjustments for the type of radiation involved (quality factor) and the biological response in the tissue (a weighting factor).

Equivalent dose converts dose into a measure of risk.

Understanding Radiation Units

Activity

Disintegration/sec=1 Becquerel (Bq)

37 billion Bq = 1 curie

Dose (Absorbed)

1 joule/kg=1 Gray(Gy)

1Gray=100 rad =100,000 mrad

Dose (Equivalent)

Gray x quality factors= Sievert (Sv)

1 Sievert =100 rem =100,000 mrem

How much is a picocurie (pCi)?

Many times the media reports excess radiation in picocuries. It takes 1,000,000,000,000 pCi to make 1 Curie. A becquerel is 1 disintegration/second. It takes 27 pCi to make one Bq, so a pCi represents less radioactivity that a Bq and results in very, very little dose.

How much is a Becquerel(Bq)?

The natural 40K activity in the body of an adult human of normal weight is 4000-6000 Bq.

There is an average of about 50 Bq per cubic meter of air inside a home from radon.

Even though a 60Co source of strong gamma radiation containing billions of Bq can kill you if you are standing 5 meters from it, it is harmless at a distance of 100 meters.

A Bq has 27 times more disintegrations than a pCi, but is still a very small amount of radiation.

How much radiation is an X-ray?

What is equivalent dose?

Radiation Weighting Factors

Tissue Weighting Factors

Radiation induced cancers have been seen in the atomic bomb survivors exposed to as low as 0.2 Sieverts.

A Sievert is a relatively large amount of radiation.

The annual background radiation exposure for a typical American is 0.0037 Sv or 370 millirem.

1 Sv = 1000 mSv = 100,000 mrem

A millirem measures the amount of radiation energy absorbed into the tissue.

1000 millirems =1 rem =0.01 Gy

The effectiveness of the dose is dependent on the dose-rate

Background Radiation

Radiation is everywhere

BACKGROUND RADIATION

The average background radiation per person is 370 millirems (mrem) per year. This varies widely depending on where someone lives, and their occupation, health and lifestyle.

Most background radiation is natural.

It is part of nature.

It has always been here.

People have always lived with it.

Radiation comes from space-

sun and cosmic rays

Background Radiation Exposure

at Different Elevations

Radiation comes from the earth

Some rocks, like Uranium are radioactive. So are coal and some building materials such as granite.

Radon is a radioactive gas that comes from inside the earth

Usually radon escapes into the air in very small amounts and does not hurt us. However, sometimes radon can get trapped in buildings. Then there is more radiation than is healthy for us.

Radiation comes from within

our own bodies.

Cells in our body contain radioactive elements, such as Potassium, which come from the food we eat

Background Radiation

Other radiation is man-made. Radiation from X-rays, medical isotopes, televisions, smoke detectors, nuclear fuel, and weapons fallout are all man-made sources of radiation.

About 70 mrem/yr

Medical procedures 53 mrems

Consumer products 10 mrems

One coast to coast airplane flight 2 mrems

Watching color TV 1 mrem

Sleeping with another person 1 mrem

Weapons test fallout less that 1 mrem

Nuclear industry less than 1 mrem

Background Radiation

The body does not distinguish between natural and man-made. Neither natural nor man-made background radiation has been shown to be harmful. The body has developed repair mechanisms to deal with negative effects of background radiation.

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