Transcript Highligh in Physics 2005

Congresso del Dipartimento di Fisica
Highlights in Physics 2005
11–14 October 2005, Dipartimento di Fisica, Università di Milano
222Rn
M.
in the house in soil and in atmosphere
*
Carnevale ,
G.
*
Polla ,
*
Sesana ,
L.
U.
*
Facchini
and L. De
†
Capitani
* Istituto
•
di Fisica Generale Applicata, dipartimento di Fisica, Università di Milano
• † Dipartimento di Scienze della Terra “A. Desio”, Università di Milano
Radon measurements in Milan and in Ispra
Natural radionuclides in the rocks of Valle del Cervo Pluton
Atmospheric level of 222Rn, a natural radioactive tracer, can be used to characterize the conditions of turbulence and
stability of lower layers of the atmosphere to investigate the structure of PBL and, in some cases, to observe the
movements of air masses.
The radionuclides from 238U and 232Th series represent, with 40K, the main source of gamma radiation in the
continental crust. The specific levels are related to the rock types. Highest radiation levels are mainly associated
with felsic rocks, due to the geochemical behavior of U, Th and K. These elements are more abundant in the
continental crust than in the earth mantle and prefer the liquid phase during a process of crustal anatexis (partial
melting) and subsequent fractional crystallization. Valle del Cervo Pluton is a composite body consisting of
Monzonitic, Syenitic and Granitic Complexes formed by strongly K-enriched rocks. The areas, where these rocks
crop out, are characterized by high natural radiation background.
In particular, measurements have been carried out in Milan and Ispra on the shores of Lago Maggiore over an entire
year.
Radon concentrations were measured by means of continously Scintillator detectors which detect alpha particles
emitted by radon and its products decay.
A frequently encountered daily pattern is characterized by accumulation of radon in night until the early hours of the
morning, followed by a decrease. Nocturnal accumulation of radon occurs under stable atmospheric conditions as
the result of the formation of the ground-based temperature inversion; radon mixing takes place in increasingly
higher layers in the daily hours.
Figures on the right side show the trends in radon concentration measured at EMEP station in Ispra for the same
period shown for Milan. It can be seen that nocturnal radon accumulation is far more frequent in Ispra, indicating
greater atmospheric stability.
Nocturnal accumulation of radon indicates the formation of the Nocturnal Stable Layer, where mixing is limitated but
not completely inhibited. The Equivalent Mixing Height (EMH) can be obtained by analysing radon concentration.
Radon-Prone areas in the Lombard plain
Complex/
Sample
GC/MP 105
GC/MP 65
GC/MP 50
SC/MP 34
SC/PM 8
SC/PM 26
LB 99
MC/CG8
MC/PM22
Lithology
Altitude
white granite
monzogranite
monzogranite
syenite
syenite
syenite
syenite
monzonite
monzonite
820 m s.l.
1050 m s.l.
750 m s.l.
1010 m s.l.
1160 m s.l.
1130 m s.l.
Balma quarry
1950 m s.l.
800 m s.l.
MC/PM56
monzonite
1280 m s.l.
Gamma spectroscopy at high resolution,
with HPGe, is the most used technique
for quantitative analysis of gamma
emitters radionuclides. The following
hypothesis has been made: 1- Isotopic
ratio between 235U and 238U is 7,2 ‰. 2238U
and 226Ra are in secular
equilibrium. 3- The exhalation rate of
radon gas has been determined to be
less than 1% of the total radon
contained inside sample’s volume. This
rate is not relevant for examination of
radon’s daughters.
For all the analysed rocks the U
concentrations are lower than the Th
ones.
The rocks of the Granitic Complex
show the lowest contents in elemental
Th, whereas the elemental U values
are similar to those of the Syenitic and
Monzonitic Complexes.
Mineralogical
assemblage
Pl+Cam+Bt+Kfs+Qtz+
Spn+Ap+Zrn+Mag+Ilm
Pl+Cpx+Cam+Bt+Kfs+
Qtz+Spn+Ap+Zrn+Mag+
Ilm
Pl+Cpx+Cam+Bt+Kfs+
Qtz+Spn+Ap+Zrn+Mag+
Ilm
UP: investigated rock
samples
RIGHT: geological
sketch map of V.d.C.
Down: Map in which
location of V.d.C. is
shown
The specific activity related to syenite PM 26 is particularly
interesting: 764 Bq/kg for 238U and 478 Bq/kg for 232Th. This rock is
the most active.
Moreover, the syenite LB 99, collected at the La Balma quarry,
shows specific activities of 468 Bq/kg for 238U and 381 Bq/kg for
232Th, respectively. These values are relevant compared with those
of other granitoids used as building stones.
Study of 222Rn levels in the Angera area (Lake Maggiore)
Radon measurements were performed in a sample of 411 one-family houses in seven villages located in the
southern area of Bergamo and Brescia. This area lies in the Po plain, and is delimitated by the Adda river to the
West and the Chiese river to the East and extends southwards from the Bergamo and Brescia areas to the Po river.
This area is flat.
The location of the selected dwellings can be divided in
two areas:
Geological maps of the Lombardy administrative
region show that this area is characterized by
- In south area, situated in the alluvial plain degrading to
quaternary deposits mainly made up of loose
Po river, silt and clay are predominant.
material with granulometry varying from gravel to
- In north area sands and gravels are predominant near
sand and silt.
the hilly terrain of Bergamo and Brescia provinces.
The area near to the town of Angera, on the eastern coast of the Lake Maggiore (Lombardy), is characterized
by hills ranging from 200 to 350 m.s.l.. The main geological feature of the area is the presence of glacial
deposits (moraine) referred to the Wurm glacial episode and of post-glacial flood deposits; these form a thick
cover of sands and pebbles that make difficult the geological interpretation. The outcrops of pre-quaternary
rocks are scarce; some isolated hills of Triassic dolomitic limestone come out from the moraines and a late
Permian volcanic felsic rock (granofiro) rises out by fault near the town of Angera.
Measurements of the average radon concentration has been performed in Angera’s area, by means of a suitable
track detectors. With a ZnS scintillator detectors, variation has been monitorated continuosly over a long period.
Variation in relation to meteorological parameters has been analysed.
In particular an one-family house has been investigated because of the high-level of radon concentration (103
Bq/m3 ), connected to the presence of an hole sited in the cellar.
The following figures show the statistical distribution of the radon concentration in the investigated areas. Results
are relative to summer and winter semesters for houses without cellars.
The results of measurements performed on the ground floor confirmed the correspondence between degree of
permeability of the ground and indoor radon concentration.
Distribution of radon concentrations for ground floors
Winter
Distribution of radon concentrations for ground floors
Summer
20
10
(Bq/m3)
>600
581-600
561-580
541-560
521-540
501-520
481-500
461-480
441-460
421-440
401-420
381-400
361-380
341-360
321-340
301-320
(Bq/m3)
Distribution of radon concentrations for ground floors
Winter
Distribution of radon concentrations for ground floors
Summer
50

45
40
20
30
25
20
15

18
16
14
Frequency %
35
12
10
8
6
10
(Bq/m3)
(Bq/m3)
>600
581-600
561-580
541-560
521-540
501-520
481-500
461-480
441-460
421-440
401-420
381-400
361-380
341-360
321-340
301-320
281-300
261-280
241-260
221-240
201-220
181-200
161-180
141-160
121-140
81-100
101-120
61-80
41-60
21-40
>600
581-600
561-580
541-560
521-540
501-520
481-500
461-480
441-460
421-440
401-420
381-400
361-380
341-360
321-340
301-320
281-300
261-280
241-260
221-240
201-220
181-200
161-180
141-160
121-140
101-120
81-100
61-80
41-60
0
0-20
2
0
0-20
4
5
21-40
Frequency %
281-300
261-280
241-260
221-240
201-220
181-200
161-180
141-160
0-20
>600
581-600
561-580
541-560
521-540
501-520
481-500
461-480
441-460
421-440
401-420
381-400
361-380
341-360
321-340
301-320
281-300
261-280
241-260
221-240
201-220
181-200
161-180
141-160
0
121-140
0
101-120
2
61-80
4
5
81-100
10
41-60
6
0-20
15
121-140
8
101-120
20
12
61-80
25
14
81-100
30
21-40
Frequency %
35
16
41-60
40
Of particular interest is that the maximum radon levels have been observed during the nocturnal hours, on the
other hand minimum values have been observed during morning hours. This alternation is due to convective
movements of air connected to the difference of indoor-outdoor temperatures.

18
21-40

45
Frequency %
50
The following patterns show the variation of radon concentration over a period of 8 days.