Fukushima two years later: a scientific report (2) - Gamma spectroscopy

This post appeared in Italian on wired.it. This is the secon part of a (poor) English translation. First part is here

Not only  the food is continuously monitored: also construction wood from the forests of the region is controlled. In this case too the safety limits are much more severe than that of  the volcanic pozzolans often used in the construction of houses and Italian schools.

Monitoring of radiation in a supermarket 10 km
from the coast of Fukushima

Comparison between radiation Italy (Rome) and Japan (Tokyo and Saitama). It is possible to see how radioactive background is higher in Rome than Tokyo. In  Rome the radiation environment is dominated by the peaks of Radon 222. The arrow indicates  where   the Cesium 137 (660 keV) peak should be located.

An estimation of  the amount of Cesium in food, wood or forage requires a spectrometer capable of determining the energy of each gamma ray. Since each isotope emits gamma rays of specific energies, it is possible to determine the quantities of the various isotopes present.

Among the recent devices there is a portable detector consisting of a crystal to stop the gamma  (CsI) and a Silicon Photomultiplier (MMPC or as they call them) to detect the energy measuring the light emitted in the crystal. The simplicity of this type of tools is that they do not require high voltages, are   small as a pack of cigarettes and is used as a USB device. The cost, however, is about 20 times that of a Geiger counter.

A spectrometer can  count, for each decay, the energy of the rays that strike it. In about an hour and then it is possible to obtain a spectrum which describes the type and amount of environmental radiation. To improve the statistics and better highlight the peaks is, however, advisable to wait a while longer. The picture above shows the value measured at Rome in an apartment on the fourth floor: it is 0.25microSv/hour  (with peaks of 0.35).

In the figure above it is possible to see how the spectrum in Rome (and in much of Italy) is dominated by radon 222, a noble gas source to the high amount of environmental radiation. Usually the radon comes from the soil and tuff, but in this case, since it is an apartment on the fourth floor, is more likely to come from pozzolana used in the construction materials . In figure are compared the spectra taken in Rome with those  acquired in Japan. The value of Rome is  higher (0.25microSv / h), followed by the basement workshops of Tor Vergata (0.10 microSv / h, where, however, there is much radon), Kokubunji (0.05), and the fourth floor in Wako (0035 microSv / h). Note the almost total absence of radon in Japan. It is worth mentioning that the environmental radiation at the onsen baths is higher due to the volcanic nature of the sulphurous waters.

Monitoring radiation in wood to be used for construction

In the samples collected in the hot spots, Cesium-137 is present in large quantities: this isotope decays into an excited state of barium (emitting an electron and an antineutrino). The de-excitation of barium emits a signal characteristic of this element: a gamma ray energy of 660 keV. The process is similar to that of fluorescence, only that in this case atomic electrons are excited. The return to the ground state emits light (between 2 and 3 eV), e.g. electromagnetic radiation. The energy levels in the nucleus are thousands of times more intense and therefore the electromagnetic radiation emitted has an frequency and associated energy thousands of times greater.

To the left of the peak  there is the so-called 'Compton edge', produced by gamma rays hitting an atomic electron of the Cesium crystal in the detector and accelerating it with a slightly lower energy (depending on the angle with which it is emitted). The spectroscopic analysis of a particularly contaminated sample, taken on  the side of a mountain road between the city of Fukushima and the coast. This sample shows the presence of the isotope cesium-134, which decays into barium with several peaks at 600, 790, 1400 and 1600 keV (the latter is out of range of the detector).

The cesium-134 has a decay time of two years, therefore the presence of this isotope represents the "signature" of the origin of the  Fukushima power plant. In other cases, the absence of cesium-134 was used to show how well mushrooms that had radioactivity above the threshold of 100 Bq / kg were not contaminated by the panel, but presumably from nuclear tests in the ‘60s.

Gamma spectrum from a pure Cs 137 source

Spectrum of a sample of soil containing cesium 134 and 137 of Fukushima region

The measures in the region of Fukushima were extremely interesting, but equally important on a personal level was the contact with the local population. Far from being disheartened, the people in Tohokoku did not give up and have rebuilt many of the structures destroyed by the tsunami. Although the plant has not resulted in deaths due to radiation (morbidly sought by national and international journalists), many deaths are due to poor management of the emergency in the first frantic days after the earthquake. Others are due to suicides after resettlement. The inhabitants of the regions closer to the center have been forcefully moved away and are now rebuilding the social fabric elsewhere, so sometimes it is difficult to return to their town of origin, even if it were decontaminated. The most relevant problem is economic: the damage to the primary sector and tourism are visible to all and will require years to get back to normal.

2. end  First part is here

Radon from Rome, Cesium from Fukushima: environmental radiation and gamma spectroscopy

The detector C12137, at the bottom right in the photo. 
(iaIt connects via USB to the computer for the acquisition

(Italian version here)

The Fukushima accident released large quantities of radioactive materials in the environment, especially iodine and cesium. Iodine decayed in  a few weeks, leaving  cesium-134 and 137 as potential contaminants of the environment and food. A Geiger counter is sufficient to measure the amount of environmental radiation. This detector, however, counts indistinctly each gamma ray that hits it, regardless of the energy of the particles.To estimate the amount of cesium in the environment (and especially in food) is necessary a spectrometer, capable of determining the energy of gamma rays. Since each isotope emits gamma rays of specific energies, from the analysis of the peaks, it is possible to determine the amount  of the various isotopes present.

Recently, Hamamatsu photonics, a company specializing in the development of detectors for space physics, particle and medical devices, has released a portable detector ( C12137) with a crystal to stop the gammas (CsI) and a Silicon Photmultiplier (or a MMPC as they call them) to reveal the energy by measuring the emitted light . The simplicity of this relatively new detector, invented by a Russian scientist, is that it does not requires high voltages, is as small as a pack of cigarettes and you can connect to any USB port. As all  spectrometers,  however, the cost is about 20 times that of a Geiger counter.

The  picture above   shown the radiation in Rome, in a fourth (fifth by Japanese counting) floor apartment: it is 0.25microSv/hour (with peaks of 0.35).
As mentioned, the advantage of the gamma spectrometer, however, is to count, for each decay, the energy of the rays that hit him. In about an hour and then it is possible to obtain a spectrum which describes the type and amount of ambient radiation. To improve the statistics and better highlight the peaks is, however, advisable to wait a while longer. In the figure below you can see how the spectrum in Rome (and in much of Italy) is dominated by radon 222, a noble gas source to the high amount of environmental radiation. Usually the radon comes from the subsoil and from tuff, but in this case, being a flat on the fourth floor, is more likely to come from pozzolanas of construction materials. 

Spectrum of the radiation environment in a home 
of Rome. The peaks of radon 222 are clearly visible. 
Spectrum of an hour equivalent averaged over 7 hours

The figure below compares two spectra  taken in Rome with two acquired in Japan. The value of Rome is the higher (0.25microSv /h), followed by the basement laboratories of Tor Vergata University in Rome(0.10 microSv / h, where, however, there is not much radon), Kokubunji (0.05), and the fourth floor in Wako (0035 microSv / h).Note the almost total absence of radon in Japan (in the onsen, however, may be  higher). The peak at 1460 keV is probably due to Potassium 40 (aka Calium - the same present  in bananas).

Radiation comparison between Italy and Japan. 
The radioactive background is higher in Rome than in Tokyo

The arrow marks the 660 keV regiorn where   the peak of cesium 137 should be located: as is evident there are no measurable quantities of this species above the bottom of the radiation environment. 

Cesium can be detected detected in various hotspots in the region of Fukushima and in soil samples: this topic will be discussed in a next post.

(1) continues

Previous post on this topic in english:

Let's measure Radiation: the radioactivity of everyday objects　放射線を測って見よう (also in Japanese)

Survivalism and the real radiation contamination in Japan

Nuclear Plants, Radiation and Food in Japan - updates

Previsione dei terremoti, un falso problema.

Attualmente è impossibile riuscire a prevedere  quando e  dove avrà luogo un terremoto ed  evacuare così in anticipo le zone che stanno per essere colpite.  È tuttavia possibile stimare  –  sulla base della frequenza degli  eventi passati  –  la probabilità che un sisma colpisca una regione e ridurre  i danni realizzando per tempo strutture  antisismiche.Per poter essere realmente utilizzabile, qualunque metodo di previsione basato su uno o più precursori dei terremoti    deve fornire  con un certo intervallo di confidenza tempo, luogo ed intensità del sisma che si verificherà.  Se si afferma   di essere in grado di determinare in anticipo un terremoto bisogna essere in grado  di fornire  i  dati citati  sopra prima che il sisma di verifichi. Altrimenti le affermazioni generiche a posteriori hanno la stessa validità di quelle astrologiche, con la colpa ulteriore di distogliere l’attenzione dal reale problema: la realizzazione di case ed edifici seguendo norme e criteri di costruzione antisismici.

 Il terremoto di Haicheng, verificatosi nel 1975  nel nord-est della Cina (M 7.3) è uno dei pochi casi...

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Survivalism and the real radiation contamination in Japan

Japan is catching up with the tradition of bad newspaper articles, depicting an apocalyptic,  post-nuclear vision of the life in the  island. If the term "post-nuclear" might apply to a country that has all but one nuclear reactors off the power production grid, many of the personal views expressed in one recent article were especially puzzling. This is an excerpt of the letter I sent to the editors of the daily newspaper. I hope it might be a useful recap of the situation in Japan. The letter did not contain the links (that unfortunately are in italian, but google translate does a decent job).

Dear Sirs,

in reading your article [...] I cannot help but be puzzled by the content and implications.  

[...] in the article there is no mention of real measurements of environmental or food contamination,  only hearsay and very general and unhelpful comments that would probably better find its place in a personal blog rather than on a daily newspaper that is widely read by the foreign community in Japan and by foreigners that are interested on Japan.

The risk in reading the personal comments and life-style expressed in the article is that all foreigners are mindlessly scared about radiation and/or  that the situation of the radiation in Japan after the Fukushima accident is out of control.

As you might be aware, the foreign press in general, and in particular the Italian one, has been extremely inaccurate and unprofessional in dealing with the accident, its effects and the risks of radiation in Japan and abroad.   This kind of old-maid’s tale articles can be misinterpreted or voluntarily misused by foreign press to depict an incorrect situation in Japan and on the people -  foreigners or not -  living in this country.

Some points that are worth remembering,  at least  to ease the worries of the author:

1.       Radiation in Tokyo area is roughly one third than in Rome (0.1 microSv/h vs 0.3microSv/h and 0.4 at the University of Rome Tor Vergata, near volcanic rocks – personally measured)

2.       Radiation on airplanes is 20 times higher than on the ground. Even though we spend less time on an airplane this is relevant for airline crews.

3.       Radiation in space is 1000 times higher than on ground. No ill effect have been found on astronauts who lived  for months on the International Space Station.

4.       Bananas have 125 Bq/kg of radioactive potassium 40 (higher than the Cesium safety levels of 100 Bq/kg).  It is possible that the process of eliminating cesium and potassium is different, though. (edit May 2012, here  the time of permanence of Cesium in human body).

5.       The amount of food consumed comes into play in calculating the radiation exposure.  Five grams of “radioactive” tea, even assuming  the old limit of 500Bq/kg amount to 0.5 Bq.

6.       A number of independent measurements point to no risk in the food, my colleagues in Italy have tested personally the amount of cesium in rice of Miyagi-ken and found 0.1 Bq/kg, less than 1per mil of what found in bananas.

7.        Chernobyl and Fukushima are two completely different accidents: in the former case the reactor core was exposed and radioactivity was dispersed in the air. This did not happen in Fukushima plant, where most of the radiation went in the water.

8.       Cigarettes contain polonium 210 (the same isotope used to kill the Russian dissident Litvinienko), present in the tobacco due to fertilizers. A two pack per day smoker is exposed to 250 mSv/year in the bronchial region, compared to about 1-3mSv/year of non-exposed persons.  In Europe, every year 5000 people die because of radiation induced cancers in the lungs (this is about 15% of all cancers in lungs).

9.       The highest risk of radiation in Europe is due to radon gas seeping through the underground cracks. This radioactive , but chemically inert gas, can accumulate in places where air is not changed often. 

At this point it should be mentioned that I have been living with two small children and a Japanese wife since before the fateful earthquake and accident at the power plant, and that, even though we took precautions and monitor closely the situation, we do not live in the state of fear that might be mistaken to be typical of foreigners in Japan. The same can be said of my colleagues, Japanese and foreigners  at RIKEN  and the many foreigners living in Japan, equally puzzled by the tone of the article and the discrepancy with their daily lives and behavior.  

This is not to attempt to deny the tragic events of the accident and its devastating implications, but to put them in the correct context and to analyze the situation individually and independently with real measurements.  This is the effort that has to be painstakingly pursued by everyone.  

My main research field is space physics with satellites and radiation environment studies on astronauts, but I am also struggling – for what is possible – to inform on the real situation and correct the excesses and apocalyptic visions that have been evoked in my country since the Fukushima accident.  [...]  

I sincerely hope that – in line with your excellent editorial policy and quality of the articles  that have kept us informed of the situation in Fukushima - of you might publish in the future a “review” article with more circumstantiated numbers, values and  reading, but also on the life in daily Japan,  so that the general public can be made aware of the current situation. If possible, please print the main points of this letter on your newspaper.

yours sincerelly....

-------------
It might be worth adding that very cheap and relatively precise geiger counters are available from many shops. Radiation is one of the most easily measurable quantities, also by non-specialists. If you have doubts, it is very easy to make your own measurements. 

Il latte radioattivo: aggiornamento della situazione alimentare in Giappone

Uno dei prodotti di latte
in polvere della Meiji

Lo scorso 6 dicembre la ditta  giapponese Meiji ha confermato la presenza di cesio 137 - (30.8 Bq/kg, a fronte di una soglia massima consentita di 200 Bq/kg)  nel latte in polvere da loro prodotto.  L'ammontare di materiale radioattivo è ben al di sotto della soglia di sicurezza. Considerando inoltre che una parte di latte viene disciolto in 3-4 d'acqua, la quantità di cesio per litro scenderebbe a circa 6-7 Bq/l . Il valore dunque non è tale da destare preoccupazione, soprattutto se  confrontato con la radioattività "naturale" presente nelle banane, pari a 125Bq/kg di potassio 40.
Con i neonati la prudenza non è mai troppa, anche perchè è necessario tener conto di eventuali effetti psicologici:  La compagnia ha quindi richiamato circa 400000 scatole di latte in polvere per evitare ulteriori critiche e soprattutto salvaguardare il valore delle sue azioni, sceso del 10% a seguito della diffusione della notizia. 

Quantità di cesio 137 nel latte e nel foraggio nell'america degli anni '60
I valori sono notevolmente superiori a quelli rilevati in Giappone.
Da qui

La tempistica dell'incidente (le scatole sono state confezionate ad aprile) farebbe pensare che il cesio sia stato trasportato dall'aria calda utilizzata per disidratare il latte.  

Negli anni '60, in pieni test nucleari nell'atmosfera, le quantità di cesio nel foraggio e nel latte era molto più alta che nel caso giapponese: uno studio su Public health report del 1966 riporta valori di cesio intorno a 50-70Bq/l e di foraggio  superiori a 400Bq/kg. Un altro  studio  su Health physics aveva analizzato la presenza di cesio e stronzio nel latte della California.  Chi fosse  interessato può trovare ulteriori dettagli qui.

In parallelo il governo - a seguito della notizia che la carne di mucche proveniente  da Minami-soma, prefettura di Fukushima, conteneva cesio con più di 500 Bq/kg (al di sopra della soglia di 300 Bq/kg) -   darà inizio ad uno studio per determinare quanto materiale radioattivo viene assorbito dai bovini tramite il foraggio contaminato. 

Allego anche le misure sul cibo della coop: tutti i prodotti sono sotto le soglie di sicurezza, con i funghi shiitake  che in alcuni casi raggiungono  circa 90 Bq/kg nella regione di Saitama.

Le scorie radioattive nel giardino: dai marciapiedi di Tokyo ai container di Genova.

Uno dei problemi legato all'energia  nucleare è quello dello smaltimento delle scorie.  I rifiuti radioattivi sono però presenti  non solo nel caso delle centrali, ma anche in tutte le sorgenti usati per applicazioni mediche, industriali e di ricerca. Molto spesso lo smaltimento di questi rifiuti non avviene secondo le norme, causando contaminazioni dell'area e - in alcuni casi più gravi - anche morti.

Bottiglie di radio rinvenute in
 una cantina di  Setagaya (Asahi shinbun)

Bottiglia di radio in prossimità
del supermercato di Tokyo. (Asahi shinbun)

Due recenti  allarmi di alti livelli di radiazioni a Tokyo, nel quartiere di Setagaya,  hanno fatto rinascere la preoccupazione per il fallout di Fukushima. Tuttavia in entrambi i casi sono stati ricondotti a sorgenti di radio presenti nelle vicinanze: nel primo episodio (4microSv/h, ottobre 2011) si trattava di bottiglie di radio (un tempo ampiamente usato per rendere fosforescenti i quadranti degli orologi) presenti nel seminterrato di una casa.  Successivamente (novembre 2011), scavando vicino ad un supermercato di Setagaya, sotto il marciapiede nella cui prossimità si registravano valori   di 110microSv/h,  è stato rinvenuto un vecchio contenitore arrugginito contenente radio.

I fusti nella cantina di Castelmauro

Anche l'Italia non è immune da  casi di rifiuti radioattivi smaltiti in maniera del tutto illegale e pericolosa: è di qualche anno la notizia che almeno duemila fusti di scorie radioattive sono stati trovati anni fa nella zona di Castelmauro (Molise). La ditta che li doveva smaltire li aveva semplicemente buttati in cantina e sepolti in una masseria in campagna (qui un interessante servizio di rainews24). 

Più di recente è la notizia che scorie radioattive sono state rinvenute nel sottosuolo del parcheggio di un centro sportivo. Non è chiaro quante  tonnellate di rifiuti tossici e radioattivi sono state smaltite in questa maniera, contaminando (come nel caso di metalli pesanti e sostanze tossiche) l'ambiente ed il suolo in maniera irreparabile.

Talvolta il nostro paese è un punto di transito per materiale radioattivo di cui ci si vuol liberare  di nascosto.

Letture di radiazione in prossimità
del container di Genova (da wired)

Il caso più eclatante è quello di un container scoperto nel porto di Genova: la radioattività in prossimità di esso era pari a quella che si registrava vicino agli edifici dei reattori di Fukushima nei primi giorni dopo gli incidenti: 400mSv/h (ossia centomila volte di più di quanto causato dal radio in bottiglia di Setagaya). Il container fu finalmente aperto dopo circa 6 mesi dalla scoperta. Ben nascosta tra le tonnellate di metallo, fu rinvenuta una barra di cobalto 60, probabilmente di qualche apparecchio medico per la radioterapia. La barra - opportunamente schermata -  è stata poi spedita in Germania dove una ditta specializzata si occuperà dello smaltimento e di tentare di capire da dove provenisse.

Radioattività e nucleare in Italia, nell'Italia del Giappone del dopo-Fukushima. Conferenza ad Agropoli

Lo scorso 19 settembre 2011, nell'ambito del settembre culturale di Agropoli,   si è tenuta una conferenza su

Radioattività e nucleare in Italia, nell'Italia del Giappone del dopo-Fukushima. L'incontro  è stato organizzato dall'Associazione Filippo Patella ed ha suscitato un notevole interesse tra il pubblico presente.  

A questo indirizzo è presente il video della presentazione, nel corso della quale è stata misurata la radioattività ambientale nel castello  di Agropoli e confrontata con quella del Lazio e della Campania. 

E' stata anche misurata l'attività di oggetti di uso comune che contengono materiale radioattivo, come le mantelline usate nelle lampade da campeggio (contengono torio) e collane e braccialetti di vetro di uranio. 

Il dibatitto con i partecipanti è stato molto acceso, sia sui temi che riguardano l'incidente in Giappone che sulle fonti note e meno note di radiazione in Italia, come il radon che proviene dal sottosuolo ed il polonio-210 presente nel tabacco delle sigarette.

Foto con i ragazzi del Liceo Scientifico "L. da Vinci"  di Vallo della Lucania (SA).
T appartenenti al Gruppo0g