Science > Physics > PHYSICS NEWS UPDATE -- Number 834 July 27, 2007 by Phillip F. Schewe,Ben Stein
| Topic: |
Science > Physics |
| User: |
"Sam Wormley" |
| Date: |
27 Jul 2007 09:46:37 AM |
| Object: |
PHYSICS NEWS UPDATE -- Number 834 July 27, 2007 by Phillip F. Schewe,Ben Stein |
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 834 July 27, 2007 by Phillip F. Schewe, Ben Stein
www.aip.org/pnu
HYDROGEN-SEVEN. An experiment at the GANIL facility in France is
the first to make, observe, identify, and characterize the heaviest
isotope yet of hydrogen, H-7, consisting of a lone proton and 6
neutrons. (An earlier experiment saw some inconclusive evidence for
this state-see Korsheninnikov et al., Physical Review Letters, 8 Feb
2003.) All of the lighter isotopes of hydrogen have previously
been seen: H-1 (ordinary hydrogen), H-2 (deuterium), H-3 (tritium),
and H-4 up to H-6. Technically speaking, the H-7 state (like H-4,
H-5, and H-6) is not a fully bound nucleus. It is considered a
resonance since (besides being very short lived) energy is required
to force the extra neutron to adhere to the other nucleons. In a
proper nucleus energy is required to remove a neutron.
In the GANIL experiment, a beam of helium-8 ions (themselves quite
rare) is smashed into a carbon-12 nucleus residing in a gas of
butane (see figure at http://www.aip.org/png/2007/283.htm). In a
few rare occurrences, the He-8 gives one of its protons to the C-12,
producing H-7 and N-13, respectively. The H-7 flies apart almost
immediately into H-3 and 4 separate neutrons. Meanwhile the N-13 is
observed in the active-target MAYA detector (named after a cartoon
character, Maya the Bee, whose honeycomb hive resembles the
hexagonal cathode pads in the experiment), a device much like a
bubble chamber, allowing its energy and trajectory to be deduced.
By taking the conservation of momentum and energy into account, the
fleeting existence of the H-7 is extracted from the N-13 data (see
the figure at www.aip.org/png). A total of 7 H-7 events was
observed. A rough lifetime for H-7 of less than 10^-21 seconds can
be inferred.
The helium-8 nucleus (2 protons plus 6 neutrons) used to make the
H-7 is interesting all by itself since it is believed to consist of
a nuclear core with two *halo* neutrons orbiting outside. This
radioactive species must carefully be gathered up from carbon-carbon
collisions (in a separate step) and then accelerated to
participating in the H-7 experiment. One of the GANIL researchers,
Manuel Caamaño Fresco (caamano@ganil.fr, 33-231-45-4435), says that
one of the chief reasons for looking at H-7 is to get a better
handle on exotic nuclear matter. The H-7 nucleus, during its brief
existence, might consist of a H-3 core and plus two 2-neutron
outriders, or maybe even a single 4-neutron blob outside. Larger
still hydrogen isotopes, such as H-8 or H-9, might be observable.
(Caamaño et al., Physical Review Letters, upcoming article; PhD
thesis at http://www.usc.es/genp/maya/)
LASER ICEMAKING. Physicists at the University of Goettingen have
for the first time gotten supercooled water to freeze using pulses
of laser light. Supercooling occurs when a sample of water is
chilled down through its normal freezing point (0 C) without
crystallization occurring. This can happen in a small sample and if
no *nucleation* site presents itself around which solid ice (a
crystal structure) can form. The incoming laser pulse brings about
an optical breakdown: some of the water molecules are ionized,
creating a momentary plasma. The hot plasma expands and forms a
vapor bubble that collapses very rapidly. It is the pressure waves
emitted by the tiny plasma and the bubble collapse which, the
Goettingen scientists believe, trigger the rapid crystallization.
Previously an acoustic equivalent of this
process---sonocrystallization-had been seen, but this is the first
time crystallization has been initiated by a laser pulse. One of the
researchers, Robert Mettin (R.Mettin@physik3.gwdg.de,
+49-551-39-2285), suggests that laser icemaking can be extended to
studying solidification of other materials. (Lindinger et al.,
Physical Review Letters, 27 July 2007)
***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.
.
|
|
|
Related Articles |
PHYSICS NEWS UPDATE -- Number 832 July 12, 2007 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 739 July 28, 2005 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 693 July 22, 2004 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 784 July 7, 2006 by Phillip F. Schewe,Ben Stein and Davide Castelvecchi
PHYSICS NEWS UPDATE -- Number 737 July 14, 2005 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 786 July 25, 2006 by Phillip F. Schewe,Ben Stein and Davide Castelvecchi
PHYSICS NEWS UPDATE -- Number 694 July 29, 2004 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 785 July 17, 2006 by Phillip F. Schewe,Ben Stein and Davide Castelvecchi
| PHYSICS NEWS UPDATE --- Number 831 July 5, 2007 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 736 July 6, 2005 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 692 July 14, 2004 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 738 July 21, 2005 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 691 July 7, 2004 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 821 April 23, 2007 by Phillip F.Schewe, Ben Stein
PHYSICS NEWS UPDATE --- Number 842 October 9, 2007 by Phillip F.Schewe
|
|
|
