Radiation Protection Dosimetry (2015), Vol. 164, No. 4, pp. 591 –594
doi:10.1093/rpd/ncv317
ASSESSING THE DEPOSITION OF RADON PROGENY FROM A URANIUM GLASS NECKLACE M. F. Hansen* and G. R. Moss Track Analsysis Systems Ltd, Napier House, Meadow Grove, Bristol BS11 9PJ, UK *Corresponding author: [email protected]
INTRODUCTION
MATERIALS
Uranium-doped glass is often referred to as Vaseline glass and is made by adding a small amount of uranium to the glass to make it fluoresce in the UV light. The uranium content varies between 2 and 25 %(1). It is a type of glass which has been found as far back as 79 AD(1) and which had a revival in the 19th century. Uranium glass beads are an example of popular uranium glass things. The question posed here is whether wearing a uranium glass bead necklace directly on the skin could pose a potential health risk in terms of additional skin dose. The radon progeny, 218Po and 214Po, will plateout on the skin, emitting alphas at 6.11 and 7.83 MeV, respectively. The approximate ranges for these alphas in skin are 66 and 44 mm(2). The average depth of the basal layer is 70 mm as given by the International Commission on Radiological Protection so not within a range of the these alpha particles, but the question to be asked is whether one can assume this depth for the skin around the collar bone, where the necklace would be worn? Skin depth varies from body position to body position, with age and with sex. Table 1 is a summary of the parent nuclides and their decay modes, including the energies of the alpha and beta particles. Only the decay products with the highest energies have been chosen. The relative absorbed dose as a function of tissue depth for the two alpha-emitting radon progeny and for three beta emitters have been calculated in (3) and shown in Figure 1. This illustrates the questionable effect of the alpha particles but does highlight that the skin dose from the beta-emitting daughters should be of concern.
TASTRAK(5) PADC (Poly Allyl Diglycol Carbonate) material (sometimes referred to as 39CR) was used to detect the alpha particles from the progeny decay, 214 Po and 218Po. The alpha particles will leave ionisation trails in the plastic as they travel through, the so-called latent tracks. These ‘latent tracks’ can be revealed by chemical etching and analysed under a microscope. A 1-h etch at 988C in a 6.25 M NaOH solution was used. An automated microscope-based system, a TaslIMAGE analysis system(6), was used to analyse the tracks utilising parameters such as track size, shape, optical density and more(7). A piece of pig skin was cut into thin slices of approximate thickness of 90+20 mm as a good approximation to human skin. This was wrapped around the TASTRAK plastic, and the necklace was placed on top. A GeigerMller counter with a mica window was used to assess the beta particles. Table 1. Selection of radon progeny and their decay modes for alpha particles with energies of >6 MeV and beta particles with energies of >2 MeV(4). Parent nuclide 234
Pa Po Bi 214 Po 210 Ti 218 214
Half-life
Decay mode
Decay energy (MeV)
6.7 h 3.1 min 19.9 min 164.3 ms 1.3 min
b a b a b
2.19 6.11 3.27 7.83 5.48
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
Could jewellery made from uranium glass beads pose an increased risk to skin cancer? The literature Eatough (Alpha-particle dosimetry for the basal layer of the skin and the radon progeny 218Po and 214Po. Phys. Med. Biol. 1997;42:1899 –1911.) suggests that the alphas from the short-lived radon daughters, 218Po and 214Po, may reach the basal layer of the epidermis, which is believed to be important in the induction of skin cancers. The deposition of the alphas from the 218Po and 214Po daughters was investigated using PADC detector material. The expectation would be that no alpha particles would penetrate through the dead skin layer, assuming the average of 70 microns used in radiation protection, but the skin around the collar bone could potentially be thinner than the assumed average. It should be noticed that by inserting a slice of pig skin in between the necklace and the PADC, no great excess of alpha tracks were seen after 1 week of exposure in the freezer. There was, however, a clear signal through the pig skin from beta particles, confirming the potential of a uranium bead necklace posing a health risk.
M. F. HANSEN AND G. R. MOSS
EXPERIMENTAL SET-UP A mannequin torso was used as a phantom. It was treated with antistatic paint to ensure that it was electrically conducting. A number of PADC elements were hung underneath the necklace, 2, and the
RESULTS
Figure 1. Adaptation of figure from Reference (3) illustrating the relative absorbed dose as a function of tissue depth for different energy alpha emitters.
The results presented here are of qualitative nature, and it is therefore deemed inappropriate to attempt any dose calculations. The motivation for showing what was observed was to suggest that further work into this may lead to an interesting result. The exposed PADC is clearly showing the trace of the uranium beads, illustrated in Figure 3, showing
Figure 2. The mannequin torso with TASTRAK PADC elements and uranium necklace around the neck.
592
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
necklace was left on the mannequin for 4–12 h. The chosen time for exposures was to keep it realistic in terms of how long one would wear such a piece of jewellery (Figure 2). The exposed plastics were etched and analysed after end exposure. The potential for radon progeny to penetrate pig skin, to a qualitative level given the lack of equipment to finely slice it into different thicknesses, was assessed by placing the pig skin around a piece of PADC and exposing it to the uranium bead necklace. To extend this work to look beyond the alpha decay products, a piece of pig skin was mounted around a metal ring to enable a measurement of any ionising radiation penetrating through using a GeigerMller counter.
ASSESSING THE DEPOSITION OF RADON PROGENY
the difference in track density across a piece of plastic. The uncalibrated results from all the PADC pieces are show in Figure 4. These illustrate a clear deposition of radon progeny on the surface of the PADC and also a clear increase on the pieces where the necklace is lying across with either one or two strands. The PADC pieces exposed to the uranium bead necklace through the pig skin showed no real
excess above background after 1-week exposure in a freezer. The results from the GeigerMller counter were obtained from first reading the response to the bare uranium bead necklace and then inserting the pig skin in between counter and necklace. The necklace was placed on top of the pig skin, and they were placed 5 cm from the top of the end window. A reduction of a factor of 3 was observed when inserting the pig skin between the necklace and the uranium bead necklace.
Figure 3. A PADC element showing the difference in track density across the PADC surface from the uranium bead necklace.
The results from assessing the radon progeny deposition from the uranium bead necklace are despite their qualitative nature, pointing towards a measurable signal from the daughters decaying via beta decay. The thickness of the pig skin was variable due to the lack of instruments, and the idea behind this added experiment was to assess whether or not any alpha particles could be seen and whether any beta particles would be detected. A repeat of this part for different thicknesses of pig skin would be of interest. It was assumed that the average skin depth of 70 mm would also apply to the skin on the top of the collar bone, something that could be questioned. Any conclusion regarding the potential cancer risk from a uranium bead necklace would assume that the
Figure 4. This illustrates the variation of exposure across the plastics hung underneath the uranium bead necklace. This particular set is from a 12-h exposure.
593
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
DISCUSSION
M. F. HANSEN AND G. R. MOSS
ionising radiation would have to reach the basal layer of the epidermis. CONCLUSION The potential health risk from wearing a uranium bead necklace would require further investigation to quantify. It is, however, clear that the beta particles from the decay chain of the radon progeny, 218Po and 214 Po, would be the particles of concern, in agreement with the conclusions of (8).
1. Wikipedia page on uranium glass. Available on http://en. wikipedia.org/wiki/Uranium_glass (9 April 2015, date last accessed).
594
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
REFERENCES
2. Charles, M. W. Radon exposure to the skin: I. Biological effects. J. Radiol. Prot. 27, 231– 252 (2007). 3. Charles, M. W. The skin in radiological protection-Recent advances and residual unresolved issues. Radiat. Prot. Dosim. 109, 323–330 (2004). 4. Wikipedia page on uranium. Available on http://en. wikipedia.org/wiki/Decay_chain (9 April 2015, date last accessed). 5. TASTRAK performance sheet. Available on http://www. tasl.co.uk/brochures/TASTRAK_specifications.pdf (9 April 2015, date last accessed). 6. The TaslImage radon dosimetry manual, available upon request. 7. Fews, A. P. and Henshaw, D. L. High resolution alpha particle spectroscopy using CR-39 plastic track detector. Nucl. Instr. Meth. 197, 517– 529 (1982). 8. Charles, M. W. Radon exposure to the skin: II. Estimation of the attributable risk for skin cancer incidence. J. Radiol. Prot. 27, 253– 274 (2007).
doi:10.1093/rpd/ncv317
ASSESSING THE DEPOSITION OF RADON PROGENY FROM A URANIUM GLASS NECKLACE M. F. Hansen* and G. R. Moss Track Analsysis Systems Ltd, Napier House, Meadow Grove, Bristol BS11 9PJ, UK *Corresponding author: [email protected]
INTRODUCTION
MATERIALS
Uranium-doped glass is often referred to as Vaseline glass and is made by adding a small amount of uranium to the glass to make it fluoresce in the UV light. The uranium content varies between 2 and 25 %(1). It is a type of glass which has been found as far back as 79 AD(1) and which had a revival in the 19th century. Uranium glass beads are an example of popular uranium glass things. The question posed here is whether wearing a uranium glass bead necklace directly on the skin could pose a potential health risk in terms of additional skin dose. The radon progeny, 218Po and 214Po, will plateout on the skin, emitting alphas at 6.11 and 7.83 MeV, respectively. The approximate ranges for these alphas in skin are 66 and 44 mm(2). The average depth of the basal layer is 70 mm as given by the International Commission on Radiological Protection so not within a range of the these alpha particles, but the question to be asked is whether one can assume this depth for the skin around the collar bone, where the necklace would be worn? Skin depth varies from body position to body position, with age and with sex. Table 1 is a summary of the parent nuclides and their decay modes, including the energies of the alpha and beta particles. Only the decay products with the highest energies have been chosen. The relative absorbed dose as a function of tissue depth for the two alpha-emitting radon progeny and for three beta emitters have been calculated in (3) and shown in Figure 1. This illustrates the questionable effect of the alpha particles but does highlight that the skin dose from the beta-emitting daughters should be of concern.
TASTRAK(5) PADC (Poly Allyl Diglycol Carbonate) material (sometimes referred to as 39CR) was used to detect the alpha particles from the progeny decay, 214 Po and 218Po. The alpha particles will leave ionisation trails in the plastic as they travel through, the so-called latent tracks. These ‘latent tracks’ can be revealed by chemical etching and analysed under a microscope. A 1-h etch at 988C in a 6.25 M NaOH solution was used. An automated microscope-based system, a TaslIMAGE analysis system(6), was used to analyse the tracks utilising parameters such as track size, shape, optical density and more(7). A piece of pig skin was cut into thin slices of approximate thickness of 90+20 mm as a good approximation to human skin. This was wrapped around the TASTRAK plastic, and the necklace was placed on top. A GeigerMller counter with a mica window was used to assess the beta particles. Table 1. Selection of radon progeny and their decay modes for alpha particles with energies of >6 MeV and beta particles with energies of >2 MeV(4). Parent nuclide 234
Pa Po Bi 214 Po 210 Ti 218 214
Half-life
Decay mode
Decay energy (MeV)
6.7 h 3.1 min 19.9 min 164.3 ms 1.3 min
b a b a b
2.19 6.11 3.27 7.83 5.48
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
Could jewellery made from uranium glass beads pose an increased risk to skin cancer? The literature Eatough (Alpha-particle dosimetry for the basal layer of the skin and the radon progeny 218Po and 214Po. Phys. Med. Biol. 1997;42:1899 –1911.) suggests that the alphas from the short-lived radon daughters, 218Po and 214Po, may reach the basal layer of the epidermis, which is believed to be important in the induction of skin cancers. The deposition of the alphas from the 218Po and 214Po daughters was investigated using PADC detector material. The expectation would be that no alpha particles would penetrate through the dead skin layer, assuming the average of 70 microns used in radiation protection, but the skin around the collar bone could potentially be thinner than the assumed average. It should be noticed that by inserting a slice of pig skin in between the necklace and the PADC, no great excess of alpha tracks were seen after 1 week of exposure in the freezer. There was, however, a clear signal through the pig skin from beta particles, confirming the potential of a uranium bead necklace posing a health risk.
M. F. HANSEN AND G. R. MOSS
EXPERIMENTAL SET-UP A mannequin torso was used as a phantom. It was treated with antistatic paint to ensure that it was electrically conducting. A number of PADC elements were hung underneath the necklace, 2, and the
RESULTS
Figure 1. Adaptation of figure from Reference (3) illustrating the relative absorbed dose as a function of tissue depth for different energy alpha emitters.
The results presented here are of qualitative nature, and it is therefore deemed inappropriate to attempt any dose calculations. The motivation for showing what was observed was to suggest that further work into this may lead to an interesting result. The exposed PADC is clearly showing the trace of the uranium beads, illustrated in Figure 3, showing
Figure 2. The mannequin torso with TASTRAK PADC elements and uranium necklace around the neck.
592
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
necklace was left on the mannequin for 4–12 h. The chosen time for exposures was to keep it realistic in terms of how long one would wear such a piece of jewellery (Figure 2). The exposed plastics were etched and analysed after end exposure. The potential for radon progeny to penetrate pig skin, to a qualitative level given the lack of equipment to finely slice it into different thicknesses, was assessed by placing the pig skin around a piece of PADC and exposing it to the uranium bead necklace. To extend this work to look beyond the alpha decay products, a piece of pig skin was mounted around a metal ring to enable a measurement of any ionising radiation penetrating through using a GeigerMller counter.
ASSESSING THE DEPOSITION OF RADON PROGENY
the difference in track density across a piece of plastic. The uncalibrated results from all the PADC pieces are show in Figure 4. These illustrate a clear deposition of radon progeny on the surface of the PADC and also a clear increase on the pieces where the necklace is lying across with either one or two strands. The PADC pieces exposed to the uranium bead necklace through the pig skin showed no real
excess above background after 1-week exposure in a freezer. The results from the GeigerMller counter were obtained from first reading the response to the bare uranium bead necklace and then inserting the pig skin in between counter and necklace. The necklace was placed on top of the pig skin, and they were placed 5 cm from the top of the end window. A reduction of a factor of 3 was observed when inserting the pig skin between the necklace and the uranium bead necklace.
Figure 3. A PADC element showing the difference in track density across the PADC surface from the uranium bead necklace.
The results from assessing the radon progeny deposition from the uranium bead necklace are despite their qualitative nature, pointing towards a measurable signal from the daughters decaying via beta decay. The thickness of the pig skin was variable due to the lack of instruments, and the idea behind this added experiment was to assess whether or not any alpha particles could be seen and whether any beta particles would be detected. A repeat of this part for different thicknesses of pig skin would be of interest. It was assumed that the average skin depth of 70 mm would also apply to the skin on the top of the collar bone, something that could be questioned. Any conclusion regarding the potential cancer risk from a uranium bead necklace would assume that the
Figure 4. This illustrates the variation of exposure across the plastics hung underneath the uranium bead necklace. This particular set is from a 12-h exposure.
593
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
DISCUSSION
M. F. HANSEN AND G. R. MOSS
ionising radiation would have to reach the basal layer of the epidermis. CONCLUSION The potential health risk from wearing a uranium bead necklace would require further investigation to quantify. It is, however, clear that the beta particles from the decay chain of the radon progeny, 218Po and 214 Po, would be the particles of concern, in agreement with the conclusions of (8).
1. Wikipedia page on uranium glass. Available on http://en. wikipedia.org/wiki/Uranium_glass (9 April 2015, date last accessed).
594
Downloaded from http://rpd.oxfordjournals.org/ at Stockholms Universitet on November 14, 2015
REFERENCES
2. Charles, M. W. Radon exposure to the skin: I. Biological effects. J. Radiol. Prot. 27, 231– 252 (2007). 3. Charles, M. W. The skin in radiological protection-Recent advances and residual unresolved issues. Radiat. Prot. Dosim. 109, 323–330 (2004). 4. Wikipedia page on uranium. Available on http://en. wikipedia.org/wiki/Decay_chain (9 April 2015, date last accessed). 5. TASTRAK performance sheet. Available on http://www. tasl.co.uk/brochures/TASTRAK_specifications.pdf (9 April 2015, date last accessed). 6. The TaslImage radon dosimetry manual, available upon request. 7. Fews, A. P. and Henshaw, D. L. High resolution alpha particle spectroscopy using CR-39 plastic track detector. Nucl. Instr. Meth. 197, 517– 529 (1982). 8. Charles, M. W. Radon exposure to the skin: II. Estimation of the attributable risk for skin cancer incidence. J. Radiol. Prot. 27, 253– 274 (2007).
