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Unformatted text preview: –June 2013 Plastic track detectors such as CR39 (Enge, 1995), which
have the advantage of being insensitive to x rays and electrons, have been widely used also in multistack arrangements,
e.g., by Clark et al. (2000a). CR39 layers (typically 0.25–
1 mm in thickness) require etching in a NaOH solution after
exposure to ions, so that the damage tracks created by the
particles can be revealed thanks to the different etching rate in
the track compared to the undamaged bulk (Seguin et al.,
2003). After etching, the single tracks can be counted, which
provides a direct measurement of the number of protons
hitting the detector. CR39 works better for low particle ﬂuxes,
as at high ﬂux (typically above $108 particles cmÀ2 ) or for
long etching times the tracks start to overlap, leading to
saturation (Gaillard et al., 2007).
The interaction of laser-driven high-energy ions with
secondary targets can initiate a number of nuclear reactions
(see Sec. V.E), which can been used to diagnose the beam
properties with the ability to provide absolute particle numbers with a linear response and virtually no saturation at high
ﬂux. The 63 Cuðp; nÞ63 Zn reaction in copper stacks has been
used to quantify the proton numbers through measurement of þ decay of 63 Zn nuclei, using a NaI detector-based coincidence counting system (Santala et al., 2001; Spencer et al.,
2001). Techniques employing a single Cu layer, in which a
range of isotopes resulting from proton-induced nuclear
reactions is analyzed in order to reconstruct the proton
spectrum, have also been used (Yang et al., 2004b).
Spectral resolution is provided by a combination of ﬁltering
and known thresholds for the considered reaction. The above
described approaches provide particle ﬂux integrated over
the whole beam cross section. Contact radiography of
ðp; nÞ-generated isotopes in activation samples (where the
activated foil is placed in contact with RCF) has been Andrea Macchi, Marco Borghesi, and Matteo Passoni: Ion acceleration by superintense laser-plasma . . . developed (Clarke et al., 2008; Offermann et al., 2010) as a
way to achieve 2D images of the beam proﬁle with high
spatial resolution and extremely high-dynamic range.
Neutron spectra produced through fusion reactions of the
type Dðd; nÞ3 He have been used as a diagnostic of laserdriven deuterium ions inside a laser-irradiated target (Habara
et al., 2003, 2004a, 2004b).
Obtaining spectra with high-energy resolution requires the
use of magnetic dispersion techniques. In simple magnetic
spectrometers [see, e.g., H. Chen et al. (2008)] the ions,
spatially selected by an entrance slit or pinhole, are dispersed
along one spatial direction according to their energy by a
$1 T magnetic ﬁeld B. This arrangement, which discriminates particles according to their energy but not to their
charge-to-mass ratio, is adequate for diagnosing the highenergy proton spectrum in ‘‘standard’’ TNSA experiments in
which protons are the dominant acc...
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