25 research outputs found
Time and position sensitive single photon detector for scintillator read-out
We have developed a photon counting detector system for combined neutron and
gamma radiography which can determine position, time and intensity of a
secondary photon flash created by a high-energy particle or photon within a
scintillator screen. The system is based on a micro-channel plate
photomultiplier concept utilizing image charge coupling to a position- and
time-sensitive read-out anode placed outside the vacuum tube in air, aided by a
standard photomultiplier and very fast pulse-height analyzing electronics. Due
to the low dead time of all system components it can cope with the high
throughput demands of a proposed combined fast neutron and dual discrete energy
gamma radiography method (FNDDER). We show tests with different types of
delay-line read-out anodes and present a novel pulse-height-to-time converter
circuit with its potential to discriminate gamma energies for the projected
FNDDER devices for an automated cargo container inspection system (ACCIS).Comment: Proceedings of FNDA 201
High Resolution Heavy Ion Track Structure Imaging
The difference in the relative biological efficincy (RBE) of ions of same
linear energy transfer (LET) but different atomic number (Z) can be attributed
to the difference in the radial ionisation distribution. In this contribution
we present data from measurements of the spatial ionisation pattern of heavy
ions of various Z but similar LET and compare the results with track structure
data obtained by Monte Carlo simulations. The measurements were made with a
time projection chamber with optical readout (Optical Avalanche Chamber, OPAC)
which is able to quantitatively capture the spatial ionisation pattern of an
ion traversing the chambe
Unambiguous Identification of the Second 2+ State in 12C and the Structure of the Hoyle State
The second 2+ state of 12C, predicted over fifty years ago as an excitation
of the Hoyle state, has been unambiguously identified using the 12C(g,a_0)8Be
reaction. The alpha particles produced by the photodisintegration of 12C were
detected using an Optical Time Projection Chamber (O-TPC). Data were collected
at beam energies between 9.1 and 10.7 MeV using the intense nearly
mono-energetic gamma-ray beams at the HIgS facility. The measured angular
distributions determine the cross section and the E1-E2 relative phases as a
function of energy leading to an unambiguous identification of the second 2+
state in 12C at 10.03(11) MeV, with a total width of 800(130) keV and a ground
state gamma-decay width of 60(10) meV; B(E2: 2+ ---> gs) = 0.73(13) e2fm4 [or
0.45(8) W.u.]. The Hoyle state and its rotational 2+ state that are more
extended than the ground state of 12C presents a challenge and constraints for
models attempting to reveal the nature of three alpha particle states in 12C.
Specifically it challenges the ab-initio Lattice Effective Field Theory (L-EFT)
calculations that predict similar r.m.s. radii for the ground state and the
Hoyle state.Comment: Accepted for Publication in the Physical Review Lette