Radiation Protection Dosimetry Advance Access published February 21, 2015 Radiation Protection Dosimetry (2015), pp. 1–8
doi:10.1093/rpd/ncv013
INDOOR RADON ACTIVITY CONCENTRATION MEASUREMENTS IN THE GREAT HISTORICAL MUSEUMS OF UNIVERSITY OF NAPLES, ITALY Maria Quarto1,2,*, Mariagabriella Pugliese1,2, Filomena Loffredo1,2, Giuseppe La Verde1 and Vincenzo Roca1,2 1 Dipartimento di Fisica, Universita` di Napoli Federico II, Naples, Italy 2 Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Naples, Italy *Corresponding author:
[email protected] Received 9 September 2014; revised 27 January 2015; accepted 28 January 2015 Indoor radon activity concentrations were measured in seven Museums of University of Naples, very old buildings of great historical value. The measurements were performed using a time-integrated technique based on LR-115 solid-state nuclear track detectors. The annual average concentrations were found to range from 40 up to 1935 Bq m23 and in 26 % of measurement sites, the values were higher than 500 Bq m23 which is the limit value of Italian legislation for workplace. Moreover, we analysed the seasonal variations of radon concentrations observing the highest average in cold weather than in warm.
INTRODUCTION 222
Radon (usually called radon) is a naturally occurring gas produced by the decay of 226Ra and belonging to the decay series of 238U. It is found everywhere in the Earth’s crust, in amounts depending on geology, in rocks, soil and underground water. Radon and its decay products are the main source of natural ionising radiation and they represent the major contributor to the effective dose to human life. UNSCEAR(1) estimates that the annual effective dose from naturally ionising radiation for humans is 2.4 mSv and 1.0 mSv of this is attributable to radon exposure. Radon is considered to be the second risk factor for lung cancer after smoking(2). After inhalation, radon is completely exhaled due to its long half-life period (3.82 d), while its short half-life decay products, 218Po and 214 Po, being electrically charged, can be attached to dust or smoke particles in indoor air. When these charged particles are inhaled, a fraction of them is deposited in lungs, where they emit alpha particles that are absorbed in the nearby lung tissue damaging the pulmonary epithelium and thereby causing lung cancer(2). Indoor radon activity concentrations vary widely country-by-country and its indoor accumulation depends on many geogenic and anthropogenic factors. It is well known that the underlying geology and meteorological conditions affect the radon transport in building. Moreover the indoor radon accumulation also depends on the building characteristics and the lifestyle of the inhabitants. Worldwide, many surveys were conducted to measure radon activity concentrations in buildings and workplace and to study the correlation with the factors affecting their values(3 – 8). In this study, the results of indoor radon concentrations
in seven museums of University of Naples Federico II are reported. MATERIALS AND METHODS Measurement sites The Italian law requires the protection of workers from exposure to radon in the workplace. The obligation is extended to a wide range of work activities selected according to their location rather than to the type of work done. In particular, the sites considered are all underground workplace, tunnels, underpasses, catacombs, caves, spas and places located in areas where there is a high probability of finding high radon levels (radon prone areas). The choice to measure the radon concentration in Museums of University of Naples was determined by the observation that, although being they not hazardous locations according to the parameters taken into account by the Italian law, they are places of special interest for radon risk. They are very old buildings, constructed between 1500 and 1750, built mainly with materials containing high concentrations of radon precursor, such as the Neapolitan yellow tuff and piperno. Moreover, they are subject to particular microclimates in order to prevent the possibility of degradation of the collections. The museums monitored are as follows: Mineralogical Museum, Zoological Museum, Physics Museum and Museum of Anthropology, located in the same buildings’ complex named ‘Collegio Massimo dei Gesuiti’ (Figure 1); Museum of Paleontology (Figure 2); Museum of Veterinary Anatomy (Figure 3) based in other palaces in Naples and Museum of Agriculture (Figure 4) in Portici, a city 8 km away to the south of
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M. QUARTO ET AL.
Figure 1. ‘Collegio Massimo dei Gesuiti’ complex with description of measurement site. The complex was built in 1572 and then expanded through other purchases of Jesuits in consecutive centuries.
Naples. The planimetries of the museums are not in scale, in fact they describe only the arrangement of the rooms taking into account the localisation of windows and detectors. The ‘Collegio Massimo dei Gesuiti’ is a big square whose sides are four buildings which house
the museums. On the first floor with respect to the level of garden, in the west side (building B), there is the Physics Museum; it exist from 2005, after the last restoration of the building in 2004. In the same building, on the second floor, characterised by double
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Figure 2. ‘San Marcellino and Festo complex’, an ancient convent of 1566. The structure is very articulated by many buildings at different altitudes with respect to the ground floor.
height rooms, is located the museum of Mineralogy which extends up to the middle south-east side of complex (building C). The Zoological Museum is located on the second floor of both buildings C and D. Immediately below, in building D there is the Museum of Anthropology on the first floor. The site of Museum of Paleontology is in ‘San Marcellino and Festo complex’, an ancient convent of
1566. All rooms of the museum are on the third floor of building A, only the store room is in the other building (building B). The complex is very articulated in many buildings at different altitudes with respect to the ground floor. In fact, with respect to the southwest side of the complex, building A overlooks on a street and the museum’s rooms are on the third floor, while the storage room, located in building B, is on
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Figure 3. ‘Santa Maria degli Angeli alle Croci’s convent’ dates back to 1581 and it was the site of Franciscans until 1815, when the king, Gioacchino Murat assigned the palace to the University.
the fourth floor because the yard is under the street level. Instead, with respect to the south-east side of the complex, building A is on the yard level and so the museum’s rooms are on the first level, while the storage room, in building B, is located in the basement of yard. For this reason, the store room can be considered in the basement with respect to building A, but at the fourth floor with respect to building B. The Museum of Veterinary Anatomy is located in the ‘Santa Maria degli Angeli alle Croci’s convent’, which is 2 km away from the Museum of Paleontology. This building dates back to 1581 and the museum is at the third floor in the middle of the building and its plan follows a linear structure. Finally, the Museum of Agriculture is at the Royal Palace in Portici. The palace was built between 1738 and 1742 by order of Charles III of Borbone and since 1935 it hosts the Faculty of Agriculture of the
University of Naples. The museum is at the third floor of the north-east side of the palace. Radon activity concentration measurements The integrated measurements of indoor radon activity concentrations in Federician Museums were measured with passive radon detectors, each equipped with a pair of solid-state nuclear track detectors LR-115 (SSNTD) provided from Dosirad closed in a polyethylene bag to prevent the entry of thoron and its progeny. The number of radon detectors placed differed among the museums depending on their planimetry, in particular, one detector was placed in rooms smaller than 50 m2, while in larger ones were positioned up to a maximum of three detectors, such as in room 3 of the Mineralogical Museum and room 5 of the Museum of Paleontology. The integrated measurements of the
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Figure 4. Museum of Agriculture in the Royal Palace of Portici.
average radon activity concentration were based on the continuous and passive sampling of air by natural diffusion. In this way were generated the ‘latent tracks’ on the LR-115 detectors caused by alpha particle produced by the disintegration of the radon and its decay products. After chemical etching the latent tracks were converted into ‘visible tracks’. The survey was carried out from February 2013 to January 2014. In this period, the detectors were exposed for four consecutive quarters: spring, summer, autumn and winter. After exposure of 3 months, all detectors were chemically etched using a solution of 2.5 N NaOH at 608C for
110 min. In the LR-115 detectors, the number of tracks increases linearly as the residual thickness decreases so the determination of the residual thickness is necessary for normalising the observed track density to the nominal final thickness (6.5 mm). In this study the residual thickness was measured by using an optical method. The image of the detector has been acquired by means of a scanner with double lighting and its mean brightness in the grey scale was determined by using Image J software (Image Processing and Analysis in Java, version 1.46r, National Institutes of Health, USA). Using a calibration curve previously
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determined, the brightness was then converted into residual thickness. Also the automatic counting of tracks was performed using the ImageJ software. The background track density was estimated to be 10 tracks cm22 and it was determined by counting the tracks of unexposed LR-115. Finally, the radon activity concentration was calculated using the formula CRn ¼
N ; ET
ð1Þ
where N is the track density corrected by background and normalised to the nominal thickness of 6.5 mm, E is the calibration factor and T is the exposure time. The calibration was carried out at National Institute of Ionizing Radiation Metrology—ENEA, where LR-115 detectors were exposed to different exposures between 500 and 5000 kBq h m23. The calibration factor is the ratio between the track density and exposure. The quality assurance of the whole method was performed by an intercomparison exercise organised by German Federal Office for Radiation Protection (BfS), where the present results were included in the good category with an uncertainty by 12 % with respect to the references (data not published). The annual average indoor radon concentrations reported in Tables 1 and 2 were calculated as the time-integrated mean on four quarters using the formula Av ¼ CRn
P4
CRni Ti ; P4 i¼1 Ti
i¼1
where CRni is the radon concentration measured in the ith quarter and Ti is the exposure time. The measurement uncertainties were calculated using the formula 1 Av Þ ¼ vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi uðCRn " #; u uP4 1 t i¼1
ðuðCRni ÞÞ2
where u(CRni) is the standard deviation of the radon concentration measured in the ith quarter. RESULTS AND DISCUSSION The annual average indoor radon concentrations measured in the seven museums of University of Naples are reported in Tables 1 and 2. The yearly radon level varies from the lowest value of 40+6 Bq m23 in MV02 of Museum of Veterinary to the highest value of 1935+39 Bq m23 found in MF07 of Physics Museum. The results show that in 26 % of measurement sites, the radon activity concentrations are higher than 500 Bq m23, which is the limit level of Italian legislation for workplace. Despite the presence of high concentrations of radon in some environments, no remedial action has been applied. The Italian law imposes the control of radon concentration only in underground workplace. Considering that these environments are of great historical value and therefore there are structural constraints, the only action you can take is to educate the people who work in these rooms to ventilate daily the environments.
Table 1. Annual average radon activity concentrations in the Museums of ‘Collegio Massimo dei Gesuiti’. Physics Museum Location
MF01 MF02 MF03 MF04 MF05 MF06 MF07
Zoological Museum
Anthropology Museum
Mineralogical Museum
Radon activity concentration/ Bq m23
Location
Radon activity concentration/ Bq m23
Location
Radon activity concentration/ Bq m23
Location
Radon activity concentration/ Bq m23
883+22 904+23 940+23 972+24 989+24 989+25 1935+39
MZ01 MZ02 MZ03 MZ04 MZ05 MZ06
132+8 136+8 140+8 130+8 218+11 227+10
MA01 MA02 MA03 MA04 MA05 MA06
444+14 485+15 503+15 494+15 286+10 329+12
MM01 MM02 MM03 MM04 MM05 MM06 MM07 MM08 MM09 MM10 MM11 MM12 MM13 MM14 MM15 MM16
668+18 212+10 193+11 231+10 219+11 140+8 82+7 140+8 1057+26 804+21 414+13 511+15 183+8 181+8 191+8 198+9
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RADON CONCENTRATION MEASUREMENTS IN THE MUSEUMS Table 2. Annual average radon activity concentrations in Museums of ‘San Marcellino and Festo complex’, ‘Santa Maria degli Angeli alle Croci’s convent’ and Museum of Agriculture in the Royal Palace of Portici. Paleontology Museum Location
MP01 MP02 MP03 MP04 MP05 MP06 MP07 MP08 MP09 MP10 MP11 MP12 MP13 MP14 MP15
Veterinary Museum
Museum of Agriculture
Radon activity concentration/Bq m23
Location
Radon activity concentration/Bq m23
Location
Radon activity concentration/Bq m23
368+12 304+11 286+10 322+11 377+12 313+11 335+12 339+12 374+12 711+18 365+12 367+12 451+14 394+12 889+22
MV01 MV02 MV03 MV04 MV05 MV06 MV07
48+6 40+6 57+6 52+6 47+6 49+6 50+6
MAG01 MAG02 MAG03 MAG04 MAG05 MAG06 MAG07 MAG08
123+8 148+8 134+7 543+17 545+15 480+14 538+15 317+11
As shown in Table 1, the Museums of Physics, Zoology, Anthropology and Mineralogy, although belonging to the same building, present radon levels very different from each other ( p , 0.001). In particular, the Physics museum presents the highest radon concentrations in all its monitored premises. This result could be attributed to the fact that these rooms are located on the first floor and also they are poorly ventilated as the case of MF01 and MF07, which do not have windows. Furthermore, in the Museum of Mineralogy high radon levels were found (MM01, MM09 and MM10). The first room is an office and has no windows while the other two measurement points correspond to the side walk of the main salon with limited access to the public. The two highest levels observed in the Museum of Paleontology were found in a warehouse used to store that does not have windows (MP10) and in a room on the ground floor (MP15), respectively. In the first case, such high levels of radon may therefore be attributed to poor ventilation of the room due to the absence of windows; moreover for MP15 to its the proximity to the ground (Figure 2) and the poor state of repair of plaster and the presence of cracks on the walls. The lowest radon concentrations were found in the rooms of the Museum of Veterinary Medicine. This could be due to the fact that the museum has the linoleum floor while all other floors are made of marble or stone. Additionally, it has large windows at low seal. Regarding the Museum of Agriculture we can observe that the concentrations in rooms MAG01–03 are lower than the other, which is due to the fact that these three rooms are located in another building and are used as offices. Here very large windows with poor insulation
are present. As shown in Tables 1 and 2, the measurements relative to detectors placed in the same room are in very good agreement except for detectors MAG07 and MAG08 for which the radon concentrations differ by 59 %. This could be attributed to the fact that the detector MAG08 was placed on the library near the window with poor insulation while, the MAG07 detector has been located in a corner of the room poorly ventilated (Figure 4). So the effect of the air exchange has fostered an annual average radon concentration lower at that point of measurement. It is well known that the variation of the heating and ventilation of the internal as well as the weather conditions give rise to large fluctuations in the level of indoor radon. The seasonal variation of the indoor radon concentration in different museums is given in Figure 5. The present results show radon activity concentrations generally higher in the winter and autumn than the summer and spring. This finding is in agreement with the results of other authors who measured radon activity concentrations in confined spaces(9 – 11). This could be attributed to the fact that during the colder months the doors and windows remain closed and so the ventilation is poor. For the Physics Museum this result is not evident because the annual average radon concentration is affected by the level of room MF07 that being an office remained closed throughout the summer holiday favouring the accumulation of radon. For each room, the winter–summer ratio of indoor radon concentrations has also been computed and their frequency distribution is reported in Figure 6. This distribution of values ranges from 0.71 to 2.54 with an mean value of 1.41.
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that the concentrations were higher in winter than those in summer.
ACKNOWLEDGEMENTS The authors thank the staffs of Museums of University of Naples for their collaboration during measurements. REFERENCES
Figure 5. Indoor average radon activity concentrations measured over summer, spring, autumn and winter at Federiciani Museums.
Figure 6. Frequency distribution of winter–summer ratios of indoor radon concentrations measured in the 67 rooms of Federiciani Museums.
CONCLUSION The indoor radon activity concentrations were measured in rooms of seven museums of University of Naples and their values ranged from 40 to 1935 Bq m23. Approximately 26 % of the values are above 500 Bq m23, which is the action level for workplace imposed by the Italian law. The measurements were performed during four quarters and it was observed
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