45. Determination of ³²P Concentration in Hair of Three Victims in JCO Criticality Accident and Estimation of the Fast Neutron Fluence on Body Surfaces

Masae Yukawa, Hiroshi Takeda, Kiriko Miyamoto, Yoshito Watanabe, Shoichi Fuma, Yoshikazu Nishimura, Fuminori Soga, Nobuhito Ishigure, Yutaka Noda and Makoto Akashi

Keywords: ³²P, hair, neutron fluence, criticality accident, beta-ray counting

³²P is generated by fast neutrons of 2.5MeV and over in sulfur with an (n, p) reaction, as well as by thermal neutron activation of stable phosphorous (n,). Human hair contains a higher amount of sulfur, approximately 5% in chemical abundance, than other human tissues, and the distribution in hair is almost uniform. Additionally, hair contains little phosphorus. Since the neutron activation cross sections of sulfur and phosphorus are essentially the same, most of the ³²P activity present in the hair is derived from fast neutron capture by sulfur. Therefore, hair samples have been used for estimation of the fast neutron dose on body surface. When hair samples are collected from different positions of the body, the distribution of neutron fluence on the body surface can be estimated. We determined ³²P and S in the hair of three workers severely exposed to neutrons in the JCO criticality accident to estimate fast neutron dose to their body surfaces.

In this work, head and pubis hair samples of workers A and B who were heavily exposed in the vicinity of the precipitation tank were analyzed by beta-ray counting, as ³²P is a beta-emitter. Hair samples of worker C who was in a room next to the precipitation tank had an obvious contamination with fissions products such as ⁹¹Sr, ⁹¹Y and ¹⁴⁰Ba. Therefore, determination of ³²P in his hair samples was not carried out.

Concentrations of neutron-induced ³²P in the hair were measured with a low background -ray spectrometer (Pico ; Fuji Electric Co, Japan) and a liquid scintillation counter. The Pico is composed of a gas flow type GM tube and plastic scintillator with an anticoincidence system to achieve low background counting. Weight of each hair sample was less than 1g, and the hair was cut into small pieces so it could be put into a counting vessel. The activities of ³²P were counted in the regions of the corresponding energy. Concentrations of ³²P were determined by comparing the activities to the reference standard, an NIST standard radioactive solution. Stable sulfur was determined by ICP-AES method after wet digestion with ultra-pure HNO₃ and a microwave digester.

Concentrations of ³²P in the hair are shown in Table 4. Pubic hair of workers A and B had higher concentrations than scalp hair. Neutron doses to the body surface for workers A and B were estimated using Maruyama's equation (D_af/a =2.92X10^-2/S, D_af: rad, a: activity of ³²P, S: concentration of sulfur) and were: worker A, 7.9Gy; worker B, 4.2Gy.

The results show that workers A and B received higher doses of irradiation to the frontal side of their body trunk than to the head.

Table 4. Concentrations of 32P and stable S in hair
(Radioactivity of 32P was decay-collected to Sep. 30, 1999.)

	Worker A		Worker B
	32P (Bq/g)	Stable S(g/g.dry)	32P(Bq/g)	Stable S(g/g.dry)
Head right side	3.9 + 0.3	43850	2.3 + 0.1	37800
Head left side	4.5 + 0.2
Pubic hair	19.8 + 0.5		8.8 + 0.2

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