**4. Long term monitoring at Hatsushima station, Sagami-bay**

JAMSTEC has been carrying out multi-disciplinary real time long term observation on deep seafloor at a depth of 1175 m off Hatsushima Island in Sagami Bay. There, a cabled observatory was deployed with several kinds of sensors e.g. video cameras, a CTD sensor that measures conductivity of seawater, ambient temperature and depth of water, a seismometer, since 1993 (Momma et al., 1998). The main target of the observatory is to investigate the environmental and biological phenomena of the cold seepages around the observatory that feed a large number of chemo-synthetic biological communities which are mainly consisted of Vesicomyid clam.

In March 2000, the original observatory, which had been deployed in September 1993, was retrieved and fully renewed. The renewed observatory and the submarine cable connected were deployed at the position of approximately 40 m northward from the original one (Iwase, 2004). At the renewal, a gamma-ray sensor with NaI(Tl) scintillator was attached to the observatory. Since then, a long term environmental gamma-ray monitoring was started. The renewed observatory was retrieved again in March 2002 to repair, and re-deployed in November 2002 approximately 40 m southward from the previous position had deployed; i.e. the observatory relocated into almost the same position where the original observatory had located. Then, gamma-ray observation has resumed and continued at the same position for almost 9 years to date.

The specification of the gamma-ray sensor equipped to the station is almost the same as those for submersibles or a ROVs of JAMSTEC: three inch spherical NaI(Tl) scintillation counter and 256-channel PHA. It is stored in a titanium container (Plate 2). The output signal with a 9600 baud RS232C interface is transmitted to the shore station in Hatsushima

<sup>3</sup> Oceanic Core Complex (OCC) is a domy exposure of lower lithological units of oceanic plates. It is frequently observed along Mid-Ocean Ridges with slow spreading rate, e.g. Mid Atlantic Ridge or Southwest Indian Ridge.

In Figure 7, several points of moderately high Th-series contribution but very little U-series contributions are found: >1 μR/h and < 0.1 μR/h of respective Th-series and U-series dose rate. These data came from Indian Ocean either at the Rodriguez Triple Junction (RTJ) or at Atlantis Bank (AB). Those areas are well away from any continents or large land masses but very tectonic active area, thus very little terrigeneous sediments accumulated. RTJ is a Ridge-Ridge-Ridge type triple junction where very slow spreading Southwest Indian Ridge (SWIR) is propagating toward the junction of Central Indian Ridge and Southeast Indian Ridge. The magmatic activity of SWIR is very low due to its very slow spreading, thus numbers of active faults developed in the area. AB is one of the Oceanic Core Complex3 that tectonically exposed and consisted of gabbros and peridotites. It locates ~100km away from present-days ridge axis, but, it is regarded to be exposed tectonically near the ridge axis approx. 12 Ma. The gabbros are in the category of mafic plutonic rocks that usually contains very little radioactive nuclei. These relatively old age and the composition of seabed caused such low gamma radiations in the areas. These tendencies are in the context of the Th-series

JAMSTEC has been carrying out multi-disciplinary real time long term observation on deep seafloor at a depth of 1175 m off Hatsushima Island in Sagami Bay. There, a cabled observatory was deployed with several kinds of sensors e.g. video cameras, a CTD sensor that measures conductivity of seawater, ambient temperature and depth of water, a seismometer, since 1993 (Momma et al., 1998). The main target of the observatory is to investigate the environmental and biological phenomena of the cold seepages around the observatory that feed a large number of chemo-synthetic biological communities which are

In March 2000, the original observatory, which had been deployed in September 1993, was retrieved and fully renewed. The renewed observatory and the submarine cable connected were deployed at the position of approximately 40 m northward from the original one (Iwase, 2004). At the renewal, a gamma-ray sensor with NaI(Tl) scintillator was attached to the observatory. Since then, a long term environmental gamma-ray monitoring was started. The renewed observatory was retrieved again in March 2002 to repair, and re-deployed in November 2002 approximately 40 m southward from the previous position had deployed; i.e. the observatory relocated into almost the same position where the original observatory had located. Then, gamma-ray observation has resumed and continued at the same position

The specification of the gamma-ray sensor equipped to the station is almost the same as those for submersibles or a ROVs of JAMSTEC: three inch spherical NaI(Tl) scintillation counter and 256-channel PHA. It is stored in a titanium container (Plate 2). The output signal with a 9600 baud RS232C interface is transmitted to the shore station in Hatsushima

3 Oceanic Core Complex (OCC) is a domy exposure of lower lithological units of oceanic plates. It is frequently observed along Mid-Ocean Ridges with slow spreading rate, e.g. Mid Atlantic Ridge or

**3.1.1 Environmental gamma radiation in Mid-Ocean Ridges** 

**4. Long term monitoring at Hatsushima station, Sagami-bay** 

enrichment in tectonic active area.

mainly consisted of Vesicomyid clam.

for almost 9 years to date.

Southwest Indian Ridge.

Island through the electro-optical submarine cable. The energy spectra can be obtained by automated calculation every ten minutes at the shore station, i.e. each dataset of energy spectrum is the summation of ten minute measurement. The gamma-ray sensor unit is installed to touch its scintillator side on seabed in which scintillator is attached downward to maximize its sensitivity (Plate 3).

Plate 2. Gamma ray sensor of cabled observatory off Hatsushima Island.

Plate 3. Cabled observatory off Hatsushima Island and gamma ray sensor (denoted by circle) deployed on seafloor.

It is known that output signal of NaI(Tl) scintillator is affected by temperature variation. However, since the water temperature at the observation site on deep seafloor is approx. 3 °C and shows very small perturbation, the influence with temperature is negligible. On the other hand, some kind of signal drift associated with aging could occur. Fig. 8 shows the spectra obtained on January 1st in 2003, 2005, 2007, 2009 and 2011. Each spectrum is

Environmental Gamma-Ray Observation in Deep Sea 67

Fig. 9. Temporal change of the center position of 40K peak.

Fig. 10. Temporal change of relation between channel number and energy.

accumulated for one day. Prominent peaks of natural radiation 214Bi, 40K and 208Tl are remarked. It is obvious that each peak linearly shifts to lower channel as time passes.

Fig. 8. Gamma ray energy spectra observed with the observatory.

The correspondence between channel number and energy was calibrated by using those three peaks (214Bi of U-series, 40K and 208Tl of Th-series) in the one day averaged spectrum. The centre position of each peak was calculated by curve fitting. Fitting function is the combination of Gaussian and linear function as follows,

$$y = A \exp\left\{-4\ln 2\left[\left(x - p\right) / \text{FWHM}\right]^2\right\} + ax + b,\tag{1}$$

where *x* is channel number, *y* is the number of counts, *A* is the peak height, *p* is the centre position of the peak in units of fractional channel number, FWHM is the full width at half maximum of the peak in units of fractional channel number, *a* and *b* are the constant parameters.

As the result, the centre position of each energy peak decreased at roughly constant rate. In case of 40K (1461 keV), the centre position of the peak decreased as large as 10 channels for the period of 8 years (Fig. 9), while the relation between the channel number and energy stayed linear (Fig. 10).

On the other hand, the full width at half maximum (FWHM) of each peak, which was calculated at the same time by the curve fitting, stayed almost constant as are shown in Fig. 11 (a)-(c) for 214Bi, 40K and 208Tl, respectively.

accumulated for one day. Prominent peaks of natural radiation 214Bi, 40K and 208Tl are

remarked. It is obvious that each peak linearly shifts to lower channel as time passes.

Fig. 8. Gamma ray energy spectra observed with the observatory.

combination of Gaussian and linear function as follows,

parameters.

stayed linear (Fig. 10).

11 (a)-(c) for 214Bi, 40K and 208Tl, respectively.

The correspondence between channel number and energy was calibrated by using those three peaks (214Bi of U-series, 40K and 208Tl of Th-series) in the one day averaged spectrum. The centre position of each peak was calculated by curve fitting. Fitting function is the

where *x* is channel number, *y* is the number of counts, *A* is the peak height, *p* is the centre position of the peak in units of fractional channel number, FWHM is the full width at half maximum of the peak in units of fractional channel number, *a* and *b* are the constant

As the result, the centre position of each energy peak decreased at roughly constant rate. In case of 40K (1461 keV), the centre position of the peak decreased as large as 10 channels for the period of 8 years (Fig. 9), while the relation between the channel number and energy

On the other hand, the full width at half maximum (FWHM) of each peak, which was calculated at the same time by the curve fitting, stayed almost constant as are shown in Fig.

*<sup>y</sup>* = <sup>2</sup> *<sup>A</sup>*exp 4 2 FWHM *ln x p / ax b,* (1)

Fig. 9. Temporal change of the center position of 40K peak.

Fig. 10. Temporal change of relation between channel number and energy.

Fig. 11. Temporal change of the FWHM of respective peak: (a) 214Bi, (b) 40K and (c) 208Tl.

The respective result for 214Bi, 40K and 208Tl is shown in Fig. 12.

equation.

By using those results, long term fluctuation of net area of each peak, which corresponds to each radiation does rate, was calculated by using the same fitting function. Here, 30 day simple moving average of the above result on the centre position of the peak was used for *p* and the average of whole period on the FWHM (3.23, 5.97 and 8.10 for 214Bi, 40K and 208Tl, respectively) was used as known variables in the equation, while *A*, *a* and *b* were the unknown parameter. The net area of each peak S is obtained by the following

*S A* FWHM 2 2 */ ln /* (2)

By using those results, long term fluctuation of net area of each peak, which corresponds to each radiation does rate, was calculated by using the same fitting function. Here, 30 day simple moving average of the above result on the centre position of the peak was used for *p* and the average of whole period on the FWHM (3.23, 5.97 and 8.10 for 214Bi, 40K and 208Tl, respectively) was used as known variables in the equation, while *A*, *a* and *b* were the unknown parameter. The net area of each peak S is obtained by the following equation.

$$S = A \bullet \text{FWHM} \bullet \sqrt{\pi / \ln 2} \text{ / 2} \tag{2}$$

The respective result for 214Bi, 40K and 208Tl is shown in Fig. 12.

Fig. 12. Temporal change of the respective peak area; (a) 214Bi, (b) 40K and (c) 208Tl.

Fig. 12. Temporal change of the respective peak area; (a) 214Bi, (b) 40K and (c) 208Tl.

Environmental Gamma-Ray Observation in Deep Sea 73

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Hattori, M. & Okano, M. (2001). New results of sea bottom radioactivity measurement, *JAMSTEC J. Deep Sea Res.*, vol.18, pp.1-13 (in Japanese w/ English abstract) Hattori, M. & Okano, M. (2002). Sea bottom gamma ray measurement - Results of study and

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Iwase, R. (2004). 10 Year Video Observation on Deep Seafloor at Cold Seepage Site in Sagami Bay, Central Japan, *Proc. OCEANS'04 / TECHNO-OCEAN'04: 2200-2205* Iwase, R., Goto, T., Kikuchi, T. & Mizutani, K. (2007). Earthquake Accompanied by Mudflow

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In Fig. 12 (a), significant increase of 214Bi peak area was observed in October 2006. The reason of this fluctuation is under study at present, though it may suggest the fluctuation of seepage or may reflect some tectonic deformation. Another increases which are less significant than that in October 2006 were observed several times, many of which seem to occur in spring. Since the increase of the amount of suspended materials have been also observed in spring, those may have some relation. In Fig. 12 (b), steady increase is observed. Although the reason is yet to be investigated, it may be caused by instrumental reason, e,g drift. Episodic increase of 40K peak area was observed when M5.8 earthquake occurred east off Izu Peninsula on April 21st in 2006 which caused mudflow (Iwase et al, 2007). When M5 class earthquakes occurred on December 17th and 18th in 2009, increase of 40K peak area seems to be less significant. This difference suggests the difference of mudflow composition as their suspended materials. The peak area of 208Tl seems to be constant, though it contains somewhat periodical fluctuation which is caused by some error in calculation. Main reason is the selection of ROI (Range of Interest) channel for curve fitting calculation. While the variable *p* (the centre position of peak) in fitting function is fractional channel number, ROI is not, and then some discontinuity in the result occurs. Those preliminary results need much detailed evaluation in both technical and other environmental aspects.

## **5. Prospect and concluding remarks**

One of the ways to improve the current model as for the proto-type apparatus is to develop stand-alone type of detector with battery and data logger system likely to an onland system; it could deploy on the seabed for a year or more to accumulate the signals. Such a trial has already done by Ashi et al. (2003). Alternatively, once 10-times higher sensitivity of sensor achieved, such an apparatus may become quite powerful tool to monitor the rapid change of gamma ray intensities in deep sea environment, e.g. vibration of hydrothermal venting, tidal change of seepages. An application of plastic scintillator partly replacing the pressure hull is one of the available solutions (Shitashima et al., 2009).

#### **6. Acknowledgments**

All operations at sea had been supported numerous supports of captains, crews of research vessels, operation teams of submersibles or ROVs and technicians. Throughout the development, the authors express their thanks to colleagues of Deep Sea Research Department of JAMSTEC.

#### **7. References**

Ashi, J., Kinoshita, M., Kuramoto, S.'i., Morita, S. & Saito, S. (2003). Seafloor gamma ray measurements around active faults by standalone system, *JAMSTEC J. Deep Sea Research,* vol.22, pp.179-187 (in Japanese w/ English abstract)

In Fig. 12 (a), significant increase of 214Bi peak area was observed in October 2006. The reason of this fluctuation is under study at present, though it may suggest the fluctuation of seepage or may reflect some tectonic deformation. Another increases which are less significant than that in October 2006 were observed several times, many of which seem to occur in spring. Since the increase of the amount of suspended materials have been also observed in spring, those may have some relation. In Fig. 12 (b), steady increase is observed. Although the reason is yet to be investigated, it may be caused by instrumental reason, e,g drift. Episodic increase of 40K peak area was observed when M5.8 earthquake occurred east off Izu Peninsula on April 21st in 2006 which caused mudflow (Iwase et al, 2007). When M5 class earthquakes occurred on December 17th and 18th in 2009, increase of 40K peak area seems to be less significant. This difference suggests the difference of mudflow composition as their suspended materials. The peak area of 208Tl seems to be constant, though it contains somewhat periodical fluctuation which is caused by some error in calculation. Main reason is the selection of ROI (Range of Interest) channel for curve fitting calculation. While the variable *p* (the centre position of peak) in fitting function is fractional channel number, ROI is not, and then some discontinuity in the result occurs. Those preliminary results need much detailed evaluation in both technical

One of the ways to improve the current model as for the proto-type apparatus is to develop stand-alone type of detector with battery and data logger system likely to an onland system; it could deploy on the seabed for a year or more to accumulate the signals. Such a trial has already done by Ashi et al. (2003). Alternatively, once 10-times higher sensitivity of sensor achieved, such an apparatus may become quite powerful tool to monitor the rapid change of gamma ray intensities in deep sea environment, e.g. vibration of hydrothermal venting, tidal change of seepages. An application of plastic scintillator partly replacing the pressure hull is one of the available solutions (Shitashima

All operations at sea had been supported numerous supports of captains, crews of research vessels, operation teams of submersibles or ROVs and technicians. Throughout the development, the authors express their thanks to colleagues of Deep Sea Research

Ashi, J., Kinoshita, M., Kuramoto, S.'i., Morita, S. & Saito, S. (2003). Seafloor gamma ray

*Research,* vol.22, pp.179-187 (in Japanese w/ English abstract)

measurements around active faults by standalone system, *JAMSTEC J. Deep Sea* 

and other environmental aspects.

et al., 2009).

**6. Acknowledgments** 

Department of JAMSTEC.

**7. References** 

**5. Prospect and concluding remarks** 


**5** 

Meltem Degerlier

*Turkey* 

**Gamma Dose Rates of Natural Radioactivity** 

*Nevsehir University, Science and Art Faculty, Physics Department, Nevsehir* 

We are all exposed to ionizing radiation from natural sources at all times. This radiation is called natural background radiation. Background radiation is the radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources. Natural radioactivity is wide spread in the earth's environment; it exists in soil, plants, water and air. Exposure of radiation mainly come from natural radiation (85 %). The assessment of gamma radiation doses from natural sources is of particular importance because natural radiation is the largest contributor of external dose to the world population (UNSCEAR,2000; Narayana N. et al.,2007) The exposure of human beings to ionizing radiation from natural sources is a continuing and feature of life on earth inescapable (UNSCEAR Report 2000). Throughout the history of life on earth, organisms have been continuosly exposed to radiations from radionuclides produced by cosmic ray interaction in the atmosphere and radiations from naturally occuring substances that are spatially distributed in all living and non-living components of the biosphere.(Whicker F.W. And

Environmental natural gamma radiation is formed from terrestrial and cosmic sources (Merdanoglu and Altinsoy, 2006, M.Degerlier et al., 2008) It comes from two primary sources: cosmic radiation and terrestrial sources. The worldwide average background dose for a human being is about 2.4 millisievert (mSv) per year. This exposure is mostly from cosmic radiation and natural radionuclides in the environment (including those within the

The main sources of natural background radiation are radioactive substances in the earth's crust, emanation of radioactive gas from the earth ,cosmic rays from outer space which

Sources in the Earth include sources in water, soil and food which are incorporated to the human body, to building materials, and to products that incorporate radioactive sources from nature, sources from outer space are the radiation produced by the atomic bombardment of the upper atmosphere by high-energy cosmic rays and sources in the atmosphere, such as the radon gas released from the Earth's crust, which then decays into radioactive atoms that attach to airborne dust, and other particulate (granular, powder)

bombard the earth, trace amounts of radioactivity in the body.

**1. Introduction** 

Schultz, 1982)

body).

materials.

**in Adana Region in Turkey** 

Yoshida, N. & H. Tsukahara (1987) A γ-ray spectral survey on giant clam colonies using the submersible Shinkai2000. *JAMSTEC J. Deep Sea Res.,* Vol.3, pp.105-112 (in Japanese w/English abstract).
