Nuclearites search with the TLS detector S. Liang a , T. Wada a , T. Nakatsuka b , K. Okei a , O. Saavedra c , N. Takahashi d , S. Tsuji e ∗ , I. Yamamoto f , Y. Yamashita a , S. Lan a , M. Okita a , N. Takahashi a , T. Morita a , R. Ishii a , Y. Goto a , A. Iyono f , H. Matsumoto f , M. Nakagawa f , C. Noda f and M. Masuda f a Department of Physics, Okayama University, Okayama 700-8530, Japan b Okayama Shoka University, Okayama 700-8601, Japan c General Physics Department, University of Torino , 10125 Torino, Italy d Hirosaki University, Hirosaki 036-8561, Japan e Department of Information Sciences, Kawasaki Medical School, Kurashiki 701-0192, Japan f Faculty of Engineering, Okayama University of Science, Okayama 700-0005, Japan It is shown that a thermoluminescent sheet stack (TLS) detector, consisting of TL sheets and medical x-ray films, is an effective nuclearite detector. The TLS can be used for searching lighter nuclearites at sea level owing to the fact that the usual relativistic particles cannot make their tracks in the TLS unless they have a charge of larger than 50. We will report recent results of searching for lighter nuclearites at sea level. 1. Introduction Witten proposed (Witten, 1984) that quark matter consisting of aggregates of up, down and strange quarks in roughly equal proportions may exist and be stable. This strange quark matter (also called ’strangelets’) may have masses rang- ing from a few GeV to that of a neutron star. De R´ ujula and Glashow have termed such parti- cles in cosmic rays colliding with Earth, ’nucle- arites’, and suggested several experimental tech- niques to detect them (De R´ ujula and Glashow, 1984; De R´ ujula, 1985). Experiments search- ing for nuclearites have been performed using different techniques or the same technique but by different groups (see, for example Barish et al. (1987); Liu and Barish (1988); Astone et al. (1993). In the search for slow and massive nuclearites, say, velocities β ≤ 10 -3 and masses M ≥ 10 10 GeVc -2 , Ahlen, S. et al. (1992), Am- brosio et al. (2000), Okei, K. et al. (2001), Am- brosio et al. (2002) for M ≥ 10 14 GeVc -2 (Final * Corresponding author. e-mail:tsuji@med.kawasaki- m.ac.jp results; The 90% C.L. magnetic monopole flux limit of 1.4 × 10 -16 s -1 sr -2 ). 2. TLS sensitivity to nuclearites The maximum cosmic flux of nuclearites is expected to be small (De R´ ujula and Glashow, 1984; De R´ ujula, 1985). Thus a large area of the TLS should be easily read when searching for nuclearites. To solve this problem, the TLS and medical X-ray film was designed as shown in Fig- ure 1. Though the X-ray films would not respond to nuclearites immediately, they do respond to fluorescence or phosphorescence (LTL, low tem- perature luminescence) of the TLS. Therefore, we can search for evidence of nuclearites by scan- ning the X-ray films and searching for a track. The TLS are vacuum-packed doubly to make the X-ray films cling to the TLS. The two outermost X-ray films are covered with black paper in or- der to distinguish heavily nuclearite. The total thickness of the TLS is about 1 g cm -1 . We have estimated the TLS sensitivity by assuming that NTL depends on how BaSO 4 of the TLS Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 261–264 0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. www.elsevierphysics.com doi:10.1016/j.nuclphysbps.2007.11.010