1. Isochronous Mode of the CR
Sergey Litvinov
Novosibirsk, 17 November 2015

2. Introduction
National Research Council's board on physics and astronomy
The 11 Greatest Unanswered Questions of Physics
“Resolution of these profound questions could unlock the secrets of existence and deliver a new age of science within several decades”
3. How were the heavy elements from
iron to uranium made?
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by Eric Haseltine,
llustrations by Dan Winters & Gary Tanhauser

3. Stellar nucleosynthesis: fusion until iron
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4. s-only rp-process rp-only r-process r-only neutron number
s process: slow n-capture and β- decay near valley of β stability
(from Rene Reifarth)
s-only
rp-process
neutron number
proton number Zr
80Br, t1/2=17 min, 92% (b-), 8% (b+) Y Sr
(n,g) Rb
rp-only Kr Br
85Kr, t1/2=11 y
(b-) Se As
r-process
79Se, t1/2=65 ky
(b+) Ge Ga Zn
r-only Cu Ni
64Cu, t1/2=12 h, 40% (b-), 60% (b+) Co
63Ni, t1/2=100 y Fe

5. The r (rapid neutron capture) - process:
termination point:
fission of very heavy nuclei
waiting points
Rolfs & Rodney:
Cauldrons in the Cosmos, 1988
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typical lifetimes for unstable nuclei far from the valley of b stability: – 10-2 s
Requiring n capture time:
tn ~ 10-4 s  Nn ~ 1020 n/cm3
explosive scenarios needed to account for such high neutron fluxes
The r–process creates about 50% of nuclei; its site is still unknown 5

6. Are Supernovae IIa the sites of the r-process?
A possible scenario:
Supernovae IIa provide in the
second of their outbreak a huge
neutron flux creating a plenty of
unstable neutron-rich nuclei
that decay by a
chain of beta decays
towards the valley of stability
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7. Why do we need the Isochronous Mode?
To determine the r-process we have to measure masses of neutron-rich exotic nuclei with a high
accuracy of (Δm/m~10-6).
1. Revolution frequency difference (or revolution time)
of two particles with different m/q ratio
circulating in the ring can be written as:
2. Transition energy gt is:
3. Isochronous condition:
g = gt
Thus, all nuclei with the same m/q at different velocities
travel around the ring with equal revolution times.
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Isochronous Mass Spectrometry (IMS) is one and only quick and sensitive enough technique for mass measurements of large number of extremely short exotic nuclei.
H. Wollnik et al., “Experiment Proposal for the SIS-FRS-ESR Facilities”, (1986). 8

8. Collector Ring (CR)
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9. Different CR Isochronous Settings
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r-process can be reached at Bρ~9-10 Tm, the dipole
B-Field has to be stable for different magnetic rigidity. 10

10. Isochronicity curve +Magnets errors 10xZoom Zoom 10xZoom
Super-FRS + CR
CR is coupled to the Super-FRS facility and will among other tasks operate as an isochronous storage ring. As I mentioned before my task was to investigate and design the isochronous mode of the CR
Zoom 11

11. One has to cut tails (reduce momentum acceptance)!
Bρ Tagging
Experimental isochronicity curves in the ESR
Good isochronous conditions are fulfilled only in a small range.
One has to cut tails (reduce momentum acceptance)!

12. Solution: measurement of Bρ or v in addition
Bρ Tagging
Isochronous experiments at the ESR
With tagging the resolution is improved but transmission of exotic nuclei is worst.
Solution: measurement of Bρ or v in addition
H. Geissel et al., Hyper. Inter. 173 (2006).

13. 2 TOF detectors εx= εy=100 mm mrad from Super-FRS
x/y (TOF2) = 59/42 mm
ΔL=18m
TOF detectors are not symmetric
regarding to the middle quarupole
TOF signals depend from the detectors‘ position.
x/y (TOF1) = 56/42 mm

14. Thank You
For Your Attention!

15. Influence of octupole imperfections
To investigate the influence of high-order harmonics, the strength of octupoles was changed
by 1, 2, 5 and 10% from the calculated ones. The corresponding Monte-Carlo simulations have
been performed and TOF signals at the CR symmetry point have been plotted.
For the deviation of 1% the TOF signal width is almost not changed.
For 2% deviation the signal is already wider by factor 1.5
So, the octupole field error should not exceed 1%.