Australas Phys Eng Sci Med DOI 10.1007/s13246-014-0286-5

SCIENTIFIC NOTE

Background ionising radiation: a pictorial perspective Giovanni Bibbo • Lino Piotto

Received: 13 April 2014 / Accepted: 16 June 2014 Ó Australasian College of Physical Scientists and Engineers in Medicine 2014

Abstract Ionising radiation from natural sources, known as background radiation, has existed on earth since the earth’s formation. The exposure of humans and other living creatures to this radiation is a feature of the earth’s environment which is continuing and inescapable. The word ‘‘radiation’’ brings fear to many people: a fear of the unknown, as human’s senses cannot detect the presence of ionising radiation. In this study, a catalogue of images of the distribution of radioactivity in every day objects and foods has been produced using an imaging plate from a computed radiography cassette. The aim of the study is that by visually demonstrating that every day objects and foods are radioactive would alleviate the fear of ‘‘radiation’’ by becoming aware that we live in a radioactive environment and even our body is radioactive. Keywords Images of radioactivity  Images of background radiation  Radioactivity  Background radiation

Introduction People are aware that ionising radiation exposures come from X-ray machines, nuclear reactors, nuclear explosions, extraction and processing of mineral ores including uranium mining, and the use of radioactive materials. However, not everyone is aware that we are all exposed to ionising radiation because of the very nature of the environment in which G. Bibbo (&)  L. Piotto Division of Medical Imaging, Women’s and Children’s Hospital, 72 King William Road, North Adelaide, SA 5006, Australia e-mail: [email protected] L. Piotto e-mail: [email protected]

we live in. Ionising radiation consists of X-rays and gamma rays, which are part of the high energy end of the electromagnetic spectrum, and of particles such as beta, alpha and numerous other particles and subatomic particles. The radiation we are exposed to is either of natural origin or is artificially produced. The natural source of radiation is referred to as ‘‘background radiation’’ and is found everywhere. There are two main contributors to natural radiation exposures: high energy cosmic ray particles incident on the earth’s atmosphere and radioactive materials in the earth’s crust [1, 2]. Radioactive materials became part of the earth at its very formation and, therefore, radiation was present on earth before life emerged. There are small amount of radioactive materials in our bodies, in animals, plants, soil and rocks, and a variety of products used in everyday life. The main radioactive elements of concern are uranium (238U, half-life: 4.5 billion years), thorium (232Th, half-life: 13.9 billion years) and their decay products and potassium-40 (40K, half-life: 1.3 billion years) present in rocks and soils because of their long half-lives [2]. Other important radionuclides are carbon-14 (14C, half-life: 5,730 years) and tritium (3H, halflife: 12.3 years). Both carbon-14 and tritium are continuously produced in the upper atmosphere by the interaction of cosmic rays with atmospheric nitrogen and oxygen. Potassium-40 is a major contributor to background radiation as it constitutes about 0.0117 % of the natural potassium [2]. A comprehensive summary of radiation exposures to humans from different natural sources and locations on earth is reported in the UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) reports 2000 [1] and 2008 [2]. Even though we have been living in a sea of radiation since life began, we only become aware of its existence with the discovery of X-rays by Wilhelm Conrad Ro¨ntgen

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blackened with the image of the uranium salts. In 1911, Wilson [4] was able to visualise the path of particulate radiation such as alpha particles with his cloud chamber. With the advent of computed radiography and, therefore, imaging plates, it has become possible to easily image the background radiation emitted from countless objects in our daily environment. The Japanese [5–7] were the first to image the distribution of radioactivity in vegetables, meat and other objects.

Lead castle

(a)

(b)

Fig. 1 Lead castle

in 1895 and radioactivity in 1896 by Henri Becquerel because our senses cannot detect ionising radiation. However, ionising radiation can be detected and made visible by technology. Henri Becquerel was the first person to image the distribution of radioactivity with his experiment on luminescent materials [3]. He placed a sample of uranium mineral salts on a photographic plate wrapped in light-tight black paper and placed in a dark drawer. A few days later when he developed the plate, to his surprise the plate was Fig. 2 Radioactivity distribution in building materials. A Bricks and other materials. B Tiles

Methods In this study, the distribution of radioactivity in a number of samples of building materials, gemstones, vegetables, fruit, confectionaries and beverages were imaged using a Kodak GP (Carestream Health, Inc) 18 9 24 cm radiography imaging plate. The imaging plate was wrapped in a freezer plastic bag to avoid it being damaged. The samples to be imaged were placed on the wrapped image plate and kept in position with adhesive tape before being located in

A

(a) Cream brick

(b) Dark red brick

(c) Granite kitchen bench top

(d) Slate

B

(a) Floor tiles

(c) Wall tile

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(b) Wall tile with a pattern

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(a) Agate

(b) Amazonite

(c) Aventurine

(d) Carnelian

(e) Malachite

(d) Picture Jasper

(g) Red Jasper

(h) Rock Crystal

(i) Rose Quartz

(j) Sodalite

(k) Tiger Eye

Fig. 3 Radioactivity distribution in gemstones

a castle (Fig. 1) having lead walls 50 mm thick to shield it from the environment background radiation. The plate was kept in the castle for 20 days. Initially, different storage durations of the plate in the castle were used, but 20 days gave the best results. With the computed radiography imaging plate, the radioactivity that could be detected from the test samples were X-rays, gamma rays and high energy beta particles. Low energy beta particles, electrons and alpha particles would have not been detected as they would have been stopped by the protective plastic bag wrapped around the imaging plate and by the protective cover of plate itself. With the imaging system, it was not possible to quantify the amount of radioactivity in the samples. However, concentrations of uranium and thorium series radionuclides in some food samples from different countries have been reported in the UNSCEAR Report 2000 [1].

Radioactivity in building materials and gemstones Images of radioactivity detected from samples of bricks and tiles are shown in Fig. 2A and B, respectively. These building materials contain relatively large quantities of naturally occurring radionuclides, particularly, uranium, thorium and potassium-40. The concentration of radioactivity in bricks, tiles and cement vary widely with location depending on the concentration of the radionuclides in the raw material [2]. Granite has the highest radiation exposure of all the images materials and this is clearly shown in Fig. 2A(c). There is also a considerable amount of radiation in ceramic tiles (Fig. 2B). These are radioactive because mineral zircon is added during their manufacture to make them strong. The downside is that all zircon has a high concentration of uranium and thorium [2]. Most gemstones also contain a large amount of radioactivity, as shown in Fig. 3.

Results Radioactivity in food The images on the left of Figs. 2, 3 and 4 are photos of the samples imaged and, on the right, the distribution of radioactivity in the imaged objects.

Radioactive materials in the earth’s soils and water are taken up by plants and animals. Thus, everything we eat

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Australas Phys Eng Sci Med Fig. 4 Radioactivity distribution in food. A Breads. B Cheeses. C Meats. D Fruits. E Vegetables. F Nuts and seeds. G Teas and coffee. H Chocolates

A

(a) Bread

(b) Oat bread wrap

B

(a) Locally produced cheese (a) Sample 1

(c) Sample 3

(d) Imported Cheese

(b) Sample 2

(e) Wrapped sliced cheese

C

(a) Chicken

(b) Home made sausage

(c) Salami

(d) Turkey

D

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(a) Apple

(b) Banana

(c) Imported apricot

(d) Local apricot

(e) Fig

(f) Mango

Australas Phys Eng Sci Med Fig. 4 continued

(g) Prune

(h) Strawberry

(i) Sultanas

E

(a) Broccoli

(b) Carrot

(c) Cucumber

(d) Capsicum

(e) Garlic

(f) Potato

(g) Onion

(h) Mushroom

F

(a) Brazil nut

(b) Chia seeds

G

(a) Coffee beans (b) English breakfast tea (c) White tea

H

Variety of chocolates

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and drink is slightly radioactive and our bodies always contain certain amounts of radioactive substances. The main radionuclide measured in food by the imaging plate was 40K [6, 7]. Some foods contain more radioactivity than others as they concentrate certain elements more than others [2]. These foods include, but not limited to, marine food, nuts, tea, coffee, cacao, bread, milk, cheese, and rice. Even olive oil contains trace of radioactivity [8]. Radioactivity distribution in marine food has not been imaged in this study. However, it is known that shellfish and other bottom feeding marine creatures accumulate radionuclides, particularly polonium-210 in their tissues [1], but this is not the case for most fish and other swimmers. Wheat also takes up radionuclides and as a result its products bread, and other wheat-based products, contain certain amount of radioactivity (Fig. 4A). Images in Fig. 4B and C illustrate the radioactivity, respectively, in cheeses and in meats (salami). The image of the meat showed that lean meat contains most of the radioactivity while fat contains the least. Samples 1 to 3 in Fig 4B are cheeses produced in different parts of the country. The locally produced cheese (Fig. 4B(a)) has a higher content of radioactivity than the imported cheese and the sample cheeses from other parts of the country. The wrapped slice cheese, which is used in sandwiches, particularly for children’s lunch, shows no uptake of radioactivity. Of the various fruits imaged, bananas contain the highest radioactivity (Fig. 4D), while of all the vegetable varieties imaged (Fig. 4E), broccoli (Fig. 4E(a)), carrots (Fig. 4E(b)) and mushrooms (Fig. 4E(h)) contain the highest concentration of radionuclides. Radioactivity was not detected in onions (Fig. 4E(g)). Nut trees concentrate radioactivity in the kernels. A typical example is the brazil nut (Fig. 4F(a)). The brazil nut tree takes up radium as a substitute of barium since the two elements are chemically very similar and barium, an essential element for the vitality of the brazil nut tree, is lacking in the Amazon Valley where the brazil nuts are grown [9]. Chia seeds, which are considered as superfood because of their nutritional value, have also a high intake of radioactivity (Fig. 4F(b)). Coffee beans and tea leaves (Fig. 4G) also concentrate radioactivity, as does cacao, which is the raw material for chocolate (Fig. 4H). Radionuclides, particularly 40K, are present practically in all organisms and, thus, every type of food is radioactive. However, the amount of radioactivity in food is small. The radionuclide concentrations in foods vary widely from place to place depending on the local background radioactivity levels, and the uptake of the radionuclides in that environment [1, 2]. This variation is shown in Fig. 4B whereby the local produced cheese has a high content of

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radioactivity than the imported cheese and cheeses produced in other parts of Australia.

Conclusion The amount of background radiation we are exposed depends on where we live, our living style and diet. We are exposed to background radiation in our homes, at work, during leisure time or in the general environment as radiation reaches us not only from radioactive materials in the earth’s crust, in the air and water, but also from outer space in the form of cosmic rays [1, 2]. This study has demonstrated that radioactivity is uniformly distributed through the edible parts of the fruits and vegetables and uniformly through most of the materials tested except in the case of tiles shown in Fig. 2B(b) where the radioactivity has been enhanced as a result of manufacturing processing of the tile. The word ‘‘radiation’’ evokes in people all types of reactions and for many it evokes fear as to what effect it may have on them. The effects of radiation are not well understood by the layman and, particularly at low level, not even by the experts in the field. The results of the study offer a rare visual demonstration of the invisible ionising radiation emitted by virtually everything in our environment. It is hoped that an understanding that even the food we eat is radioactive would help alleviate the public perception that low-level radiation is something dangerous and should always be avoided. This should also help allay the public fear about low-level radiation doses received from diagnostic medical imaging.

References 1. United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2000 Report to the General Assembly with Scientific Annexes, Volume 1: Sources, United Nations, New York, Volume I: sources, Annex B: pp 84–156 and Volume II: Effects 2. United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2008 Report to the General Assembly with Scientific Annexes, Volume 1: Sources, United Nations, New York, Volume I, Annex B: pp 223–463 3. Becquerel J, Crowther JA (1948) Discovery of radioactivity. Nature 161(4094):609. http://www.rsc.org/pdf/radioactivity/num ber1.pdf?origin=publicationDetail. Accessed 20 Feb 2014 4. Wilson CT (1927) On the cloud method of making visible ions and the tracks of ionising particles. Noble Lecture 12. http://www. phys.sci.kobe-u.ac.jp/*sonoda/seniors_05/papers/wilson-lecture. pdf. Accessed 20 Feb 2014 5. Mori C, Suzuki T, Koido S, Miyahara H, Uritani A et al (1994) Measurement of the radioactivity distribution of material surfaces with an imaging plate. Nucl Instrum Methods A 353:371–374 6. Mori C, Suzuki T, Koido S, Uritani A, Miyahara H, Yanagida K, Wu Y et al (1996) Radioactivity distribution measurement of

Australas Phys Eng Sci Med various natural material surfaces with imaging plate. J Radioanal Nucl Chem 206(2):263–267 7. Mori C, Suzuki T, Koido S, Uritani A, Miyahara H et al (1996) Effect of background radiation shielding on natural radioactivity distribution measurements with imaging plate. Nucl Instrum Methods A 369:544–546 8. Misdaq MA, Touti R (2012) Annual committed effective dose from olive oil (due to 238U, 232Th and 222Rn) estimated fro

members of the Moroccan public from ingestion and skin application. Health Phys 102(3):335–345 9. Moeller DW (1996) Radiation sources: natural background. In: Hendee WR, Edwards FM (eds) Health effects of exposure to low level ionising radiation. Institute of Physics Publishing, Bristol, pp 269–286

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Background ionising radiation: a pictorial perspective.

Ionising radiation from natural sources, known as background radiation, has existed on earth since the earth's formation. The exposure of humans and o...
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