Induction of tumours in intact and partially hepatectomized rats with ethyl methanesulphonate.

SINCE the suggestion was made that replicating liver cells may be especially sensitive to chemical carcinogens (Pound, 1968), much evidence has accumulated which supports this idea. As an instance of this, certain carcinogenic alkylating agents, dimethylnitrosamine (DMN) and nitrosomethylurea (NMU), which do not usually induce liver cancer by a single treatment, are hepatocarcinogens if given during the period of restorative hyper-plasia following partial hepatectomy (Craddock, 1971; Craddock and Frei, 1974). These results suggest that repli-cation of alkylated DNA is an initial event in carcinogenesis. Another methy-lating agent, methyl methanesulphonate (MMS), on the other hand, was not found to be a hepatocarcinogen, even when given after partial hepatectomy (Craddock, 1973a). Evidence suggests that this difference may be due to a difference in the nature of the reaction products formed in DNA. It appears likely that 06-alkylguanine rather than 7-alkylgua-nine is relevant in carcinogenesis (Love-less, 1969). DMN and NMU give rise to both these methylated bases, whereas no 06-methylguanine was detectable in rat liver after treatment with MMS (Craddock, 1973b). A small amount was measured after treatment of DNA with MMS in vitro (Lawley and Shah, 1972), and in mice treated with MMS in vivo (Frei and Lawley, 1976). In the case of ethy

Momentum Cleaning in the CERN LHC

This paper describes the optimization of the optics and the collimator geometry for the momentum cleaning insertion of the LHC. To collimate the off-momentum secondary halo without disturbing the circ ulating beam, the normalized dispersion in IR3 is made as large as in the arcs. The jaw locations and orientations are numerically optimized to reduce the momentum-dependent halo amplitude. The second ary halo is kept within the available aperture for momentum deviations up to 0.44%, where the horizontal aperture is 4$\sigma\, compared to 12$\sigma\ on-momentum

Initial error analysis for the LHC collimation insertion

The two cleaning insertions in the LHC, for betatron and momentum collimation, are optimized for an ideal lattice and collimator jaw setup. We have studied a collimation beam line with randomly generated jaw misalignments and quadrupole field and alignment errors, the resultant distortion of the reference orbit being corrected with the help of monitors placed near critical collimators. Different closed orbit errors and beam shapes are considered at the entrance. We report the level of errors for which no corrections are needed and the level for which corrections are not possible

Numerical Optimization of Collimator Jaw Orientations and Locations in the LHC

The collimation system of LHC will consist of flat collimator jaws distributed along the IR7 lattice with the aim of limiting the maximum combined amplitudes of secondary halo particles (born along the edges of the primary collimators). The code DJ (Distribution of Jaws) computes this amplitude using a quasi-analytic algorithm (no tracking), by which the maximum initial angles are found, corresponding to trajectories escaping all secondary jaws. We report the latest version of DJ, which contains the following enhancements: (1) the orientation of each pair of jaws is a free variable (instead of using only vertical, horizontal, or 45 degrees skew jaws); (2) the minimizing method used is "simulated annealing", which, for our case of a discontinuous function of up to 32 variables, always finds a global minimum. Different initial jaw distributions lead to different final ones, but they all give essentially the same maximum halo amplitude; this seems to depend only on the number of jaws and the lattice parameters, particularly the tune-split. We discuss lattice characteristics found favorable for collimation

Optimization of Collimator Jaw Locations for the LHC

A highly effective collimation scheme is required in the LHC to limit heating of the vacuum chamber and superconducting magnets by protons either uncaptured at injection or scattered from the collision points. The proposed system would consist of one set of primary collimators followed by three sets of secondary collimators downstream to clean up protons scattered from the primaries. Each set of collimators would consist of four pairs of jaws - horizontal, vertical, and 45 o and 135 o skew. A study is reported of the optimization of the longitudinal positions of these jaws with the aim of minimizing the maximum betatron amplitudes of protons surviving the collimation system. This is performed using an analytical representation of the action of the jaws and is confirmed by tracking. Significant improvement can be obtained by omitting inactive jaws and adding skew jaws

Optics Solutions for the Collimation Insertion of LHC

While the two collimation insertions in the LHC must have similar basic layouts and match to almost identical dispersion suppressors to respect the geometry of the existing tunnel, their different roles impose opposite requirements on the normalized dispersion within them. For betatron collimation it must be near zero, while for momentum collimation it must have a peak at the location of the primary collimator, immediately after the dispersion suppressor. The insertion lattice solution found for the latter case requires up to 30% asymmetry in the quadrupole gradients (in line with the current trend in LHC lattice development to break the exact antisymmetry within insertions). To achieve this using twin-aperture warm quadrupoles, the modules making up each quadrupole will be wired in such a way that the two beams still see the same sequence of focusing fields. We describe the optimum setup, exibility and collimation quality for the two insertions