Transmission of FastH2+through Thin Foils

Abstract

Evidence recently accumulated 1 " 3 has demonstrated that simple atoms and molecules transmitted through thin solids at velocities V>v 0 , where v 0 is the Bohr velocity, can be the incident species with their original electron(s) as well as those reconstituted by the process of target electron capture after the loss of the incident electron(s). For convenience, we distinguish the two as the 0 (original) and (ft (reconstituted) transmission regimes, respectively. The 0 regime may be simply characterized by the survival of the incident projectile and this has been described in detail elsewhere. 1 " 3 The (ft regime may not be so simply understood except perhaps for the case of atomic projectiles. Indeed, data on molecular transmission in the (ft regime have been available 4 " 8 for a number of years and, to our knowledge, no quantitative account has previously been given for the yield of even the simplest case of H 2 + . We describe here a quantitative model for fast H 2 + which reproduces remarkably well the observed transmitted yield of H 2 + as well as the associated yield of H° breakup fragments.The experimental features of the H 2 + transmit-13 J. Sugar and V. Kaufman, Phys. Rev. A 21, 2096 (1980). 14 P. Shorer and A. Dalgarno, Phys. Rev. A lj>, 1502 (1977). 15 P. Shorer, Phys. Rev. A L8, 1060 (1978). This paper contains excitation energies for Zn-like Ga, Br, Mo, W, and U. Values for intermediate atoms were communicated privately by the author. 16 K. T. Cheng and Y.-K. Kim, At. Data Nucl. Data Tables 22, 547 (1978).ted fraction at 0.4, 0.8, and 1.2 MeV/amu through carbon foils 1-8 /ig/cm 2 thick are shown in Fig. 1 as a function of dwell time, t D , in the target. These new data were obtained at University Lyon-I using a procedure described elsewhere. 3 The 0 and (ft features can clearly be seen. There is the © region of t D % 1 fs which is observed to follow exp(-1 D /T) , with T = 0.17 f s, independently of the projectile velocity V. This translates into an "electron-loss" cross section o t cc 1/V which is a feature expected from binary collisions. 1 On the other hand, there is the other region of t D > 1 fs, which exhibits a strong dependence on V. Such a feature can only be reasonably understood in terms of a reconstitution process after the loss of the incident electron, and it is this process that is of principal concern here. To properly focus on the (ft regime, we subtract out the exponential 6 transmission yield from the data and display in Fig. 2(b) the (ft transmission yield F(H 2 + ) relative to twice the equilibrium neutral fraction $ 0 for incident H + of the corresponding velocity. In effect then we have made use of a previous observation 6 that the Transmission yield of fast H 2 + through carbon foils has been measured over a wide range of foil thicknesses for 0.4-1.2-MeV/amu H 2 + projectiles. A model is described which gives an excellent quantitative account of this yield as well as that of the associated H° production.

Direct detection of primordial black hole relics as dark matter

“…The corresponding mean free path in the atmosphere is microscopic. Additionally, in passing through solid overburden enroute to a detector, a bare CPR would be very likely to acquire bound charge: experiments and simulations show that the recombination timescale of molecular hydrogen ions in carbon is O(10 fs) [74][75][76]. Thus, we must consider the possibility of detecting CPRs bound into neutral "atoms".…”

Using an Electrostatic Accelerator to Determine the Stereochemical Structures of Molecular Ions

“…HCO" 1 In Table I we compare the diameters of the ring patterns obtained 18 for C 4+ , 0 3+ , and 0 5+ fragments from the foil-induced dissociation of HC0 + and CO + of the same velocity (124 keV/nucleon). A cursory glance suffices to deduce that the triatomic beam ions must have the structure H-C-0 and not C-O-H or C-H-O.…”

Simulation of the energy spectra of original versus recombinedH2+molecular ions transmitted through thin foils

“…Original and recombined H 2 + molecular ions transmitted through thin carbon foils were first identified by Poizat and Remillieux in 1971 [4]. Subsequent measurements of highenergy molecular ion yield versus target thickness by Remillieux and co-workers [2,[4][5][6][7] and others [8] have demonstrated the existence of two regimes: one corresponding to a rapid decrease of the molecular ion yield with target thickness for very short dwell times, and the other showing a slower decrease of the molecular ion transmission yield for longer dwell times. There is strong evidence that the short dwell time regime represents transmission of the original molecule; for longer dwell times, this transmission probability is negligible, and the detected molecular ions apparently result from recombination of the protons dissociated from the incident H 2 + molecular ion.…”