Radioacvity measurements of green tea leaves from Japan aer the Fukushima incident M. S. Pravikoff ([email protected]), Ph. Hubert ([email protected]) Centre d'Études Nucléaires de Bordeaux-Gradignan (CNRS/Université de Bordeaux) 19 Chemin du Solarium CS 10120 33175 Gradignan cedex, France H. Ohsumi Saga University, Japan Abstract A series of 32 green tea leaves samples from different Asian producers were analyzed by direct γ-ray spectrometry at the PRISNA facility in Bordeaux. All the samples contain about 500 Bq/kg of 40K and 10 Bq/kg of 210Pb. As expected, most of the recent Japanese samples contain also the 137Cs and 134Cs radio-isotopes, whose ac8vity distribu8ons are studied as a func8on of the geographical origin in order to get an insight on the outspread and fallout of radionuclides ste ing fro the 2011 9ukushi a Dai-ichi Nuclear Power Plant incident. 1. Introduction Depending on where you live, your cultural background and your habits, your favorite beverage can be wine, beer, hard or so; drinks, fruit juices or even just plain water. If we talk of war li0uids, people enjoy soup, ulled wine, coffee or tea, just to en8on a few. The last two instances part the world into two species: coffee-lovers and tea-lovers. We will focus here on the last ones. Tea and its any varie8es are to be found in all our socie8es. Its i age is al ost a trade ark of the ,ri8sh E pire and the . oAclock ritual, but who shall forget the link between the sa ovar and the Russian aristocracyB Nowadays, especially in the western he isphere, the trend to brew upper-class high 0uality tea leaves is soaring. And one of the favorite tea species is indeed green tea leaves fro 5apan and other Asian countries. ,ut, in the a;er ath of the 9ukushi a Nuclear Power Plant (9NPP) accident on March 11, 2011, tea-lovers are puzzled and worry about how safe it is to carry on drinking tea ade fro 5apanese tea leaves. This was the trigger for our 0uest. We chose to analyze available co ercial green tea leaves grown a;er the 9ukushi a accident in order to infer their radioac8ve content fro both 0ualita8ve and 0uan8ta8ve prospects. 9irst part is about the origin of the sa ples and the ga a spectro etry setup used for the radioac8vity easure ents. Results are discussed for both natural and an- ade radio-isotopes in a following chapter. ,eyond the beta-decay isotopes with a broader possible health i pact in ind, 210Pb has also been inves8gated since this isotope and its daughter, 210Po, see to be involved in so e neuro-degenera8ve diseases (Mo CiloviD et al., 2001E Mo CiloviD et al., 2006). 2. Material and methods 2.1 Samples origin Green tea leaves for aking tea are to be found in specialized bou80ues, on the internet and, so e8 es even in your local grocery or super arket. A real array of different species is at hand with a ini u of consu er advices on the best prepara8on ethod (water te perature, brewing 8 eH.) and with so e background infor a8on on the product (region of origin, harvest season, peculiari8esH.). Figure 1: Overview of the geographical origin of our tea samples (only those from Japan and Korea) – Purple dot indicates FNPP loca4on, red dots are for domes4c probes and lime-green is for the export tea samples. 2.1.1 Exported samples We bought several speci ens in 9rance. Most of the (11) ca e fro 5apan, one fro 3orea, one fro Taiwan, two fro China and one fro the Hi alaya area. Harvest year for all the tea leaves we ac0uired, e-cept one, was 2013, either spring, su er or fall. A single sa ple of 5apanese green tea was fro year 2010, which eans it dated back before the 9ukushi a incident. The loca8on of the harvest region for each of these sa ples was precisely known in very few instances. Most of the 8 e, the ain indica8on was the tea deno ina8on, which, co bined with so e infor a8on retrieved on the web sites of the i porters1retailers or by direct discussion with the sellers, helped us deter ine roughly the geographical origin of the leaves. In a few cases, assu p8ons based on general internet infor a8on retrieval were ade. Harvest year, on the opposite, was at hand, albeit not en8oning if it was an early, iddle or late harvest season. We were lucky to have two le;-over vintage tea cans, albeit not fro the green type, fro Darjeeling (India) and Ii en (China), harvested ost probably in 1987, a few onths a;er the Chernobyl accident on April 26, 1986. All those sa ples will be referred in the following as Le-portM teas. 2.1.2 Japanese (domes4c) samples To ensure a beNer deter ina8on of the origin area of the leaves and to ini ize possible traceability uncertain8es associated with e-ported green tea leaves fro 5apan, one of us (HO) bought 12 sa ples directly in 5apan, at local groceries and producersA outlets, fro Morioka in the North to 3yushu in the South. A Orst batch of . sa ples was obtained in April 2012 with harvest year being 2013. It included sa ples fro a couple of hundred kilo eters fro the 9NPP to up to ore than one thousand kilo eters to the south-west down to the 3yushu island. A second batch of 9 sa ples corresponding to harvest year 2012 (or aybe end of 2013) was received in su er 2012. In this lot we had sa ples closer to 9NPP, but either inland west of the Power Plant or to the North. ,y directly collec8ng those tea sa ples in 5apan, the geographical origin was a liNle bit ore precise, even though there re ained doubts as to the e-act source of the leaves we obtained. These green tea leaves are labeled in this paper as Ldo es8cM teas. ,oth sa ple types (do es8c and e-port), e-cept for the two vintage ones and the one fro Hi alaya, are pin-pointed on the ap of 5apan according to the assu ed region, with contour lines of the country fro 3D Geography ( 5apan blank ap P 2012 by 3D Geography ). The large purple dot indicates the 9NPP loca8on, red dots correspond to the Ldo es8cM 5apanese teas, and all the Le-portM tea leaves are li e-green. 2.2 Description of the HP Ge detectors 9or the ga a easure ents, we have at our disposal both low-background high-purity well-type 300 c 3 Ge detectors and a co-a-ial 100 c 3 Ge detector in our PRISNA facility on the pre ises of the Centre dAQtudes NuclRaires de ,ordeau--Gradignan (CEN,G) ca pus in Gradignan, a suburb of ,ordeau-. 9ull details about PRISNA and the spectro eters are reported on the relevant web pages ( P late-for e R Rgionale Interdisciplinaire de S pectro Rtrie N uclRaire en A 0uitaine ) and in a previous paper (Perrot et al., 2012). The ger aniu detectors are encased in lead and polyethylene coSns against environ ental background and the resul8ng spectro eters are installed in a easure ent hall built par8ally underground with a cover of . eter water-e0uivalent of concrete and soil. Added are also large plas8c scin8llators ac8ng as electronic vetoes against re aining e-ternal cos ic radia8ons. Figure 2- installing a sample in the spectrometer 9igure 2 shows one of the spectro eters opened in order to install a sa ple. The sa ples are put in . c 3 tubes atching the inner di ensions of the well-type detectors. Depending on the leaves te-ture and density, 2 to 2 gra s can be s0ueezed into these tubes. Data ac0uisi8on for each sa ple was of the order of 2 days. 9or so e rela8vely very ac8ve sa ples, this easuring 8 e was reduced to 1 day and, conversely, for weakly ac8ve sa ples, up to 7 days were necessary to reach suScient precision and low uncertainty values. 9or brewing e-peri ents, processed tea leaves are infused ho e-styled ethod with plain water, a teapot and Olters. ,oth well- type and co-a-ial Ge detectors are used. 9or the easure ent of the ini8al processed tea leaves, the ethod is the one described previously. A;er brewing tea, the used leaves and the li0uor are either reduced in volu e in order to Ot the tubes e ployed with the well-type detector or transferred in a Marinelli beaker and easured by a co-a-ial Ge detector. 9or all the spectro eters the e-peri ental para eters, notably eSciency values, have been controlled and acknowledged through Geant 2 si ula8ons (Geant2, 2003, 2006) which take into account the geo etrical para eters of the apparatus, the co posi8on and density of the sa ple and so on. Cer8Oed IAEA reference radioac8ve sources are also used for calibra8on purposes (Shakhashiro et al., 2012). 3. Results and discussion 3.1 Gamma Spectra Figure 3- 8 spectrum of a typical sample of Japanese green tea leaves Tery clean spectra are obtained in our easure ents. The one in 9ig. 3 is typical of our easure ents of green tea leaves. Most re arkable is that only two natural isotopes are to be found: 210Pb and 203. The laNer one, with a period over one billion years, is well-known.