GRFBL Description

I. The GRFBL project

The Grand Raiden Forward-mode (GRF) beam-line is being constructed and will be finished in this (2013) fiscal year. The beam-line will be used for a new operation mode of the high-resolution spectrometer Grand Raiden (GR) as well as the large-acceptance spectrometer (LAS) at the research center for nuclear physics (RCNP), Osaka University. The GRFBL enables transportation of the beam to a beam dump, which is located 25 meters downstream of the target position, with placing the GR spectrometer at forward angles in 4.5-19.0 degrees.

The GRF beam-line realizes 1) coincidence measurements with detectors around the target, e.g. gamma-ray detectors which are sensitive to radiation background from the beam stopper, and 2) high beam-intensity measurements up to 1000 nA.

In parallel, CAGRA project is going on, which will combine 16 clover Germanium detectors from US and Japan to be used at RCNP and RIBF. These two projects are bringing world new opportunity to combine a high-resolution spectrometer and a gamma-detector array.

Below we summarize the present plan and specification of the GRF beam line together with possible physics researches.

II. Physics Research Opportunies

The following is a summary of candidates of possible physics researches using the GRF beam-line with/without CAGRA detectros

Tagging specific excited states by gamma-ray detectors

studying proton inelastic scattering angular distribution with taggin each E1 state in PDR

Study of decay properties of excited states
- gamma strength function, Axel-Brink hypothesis
- decay property of PDR
- gamma-decay of giant resonances
Gamma-ray detection as a part of probe for spin-isospin excitations
- (α,α'γ),(⁶Li,⁶Li'γ), (⁷Li,⁷Beγ), ...
Detection of rare gamma-decay events
- radiative decay of ¹²C excited states
Achieving higher energy resolution by gamma-detection
- study of level densities
Excitation of high-spin states with gamma-ray tagging
- excitation of high-spin states by light-ion reactions with gamma-ray detection
Reaction measurements with implanted stable/unstable nuclei (the BRILLIANT project)
Background reduction (detection of rare events) by coincidence measurement with a high-intensity beam
Spin-parity determination of excited states
Study of reaction mechanism
Life-time measurement
...

III. Specification

By adding the GRFBL mode three beam-transportation modes, Zero-degree mode, GRFBL mode, and WS_LONG mode, will become available. Below each of them is described.

For the CAGRA project, a gamma-ray detector support system and a scattering chamber will be newly designed. Thus they are not shown in the figures below.

Table 1 summarizes the specification of the three modes

Table 1. Summary of the three spectrometer modes
mode	beam stopper	Max. beam intensity	GR angle (coverage)	LAS angle (coverage)
Zero-deg inel. scatt.	0-deg beam dump	~10 nA	0 deg (0-~3 deg)	61-120 deg (58-123 deg)
Zero-deg CEX or transfer	In GR-D1	~10-100 nA	0 deg (0-~3 deg)	61-120 deg (58-123 deg)
GRFBL	wall beam dump	1000 nA	4.5-19.0 deg (3.5-20.0 deg)	61-120 deg (58-123 deg)
WS_LONG	wall beam dump	1000 nA	25.5-70.0 deg (24.5-71.0 deg)	25.5-120 deg (22.5-123 deg)

2.1 Zero-Degree mode

The GR spectrometer is placed at zero-degrees. Owing to the vertical angular acceptance of the GR spectrometer, scattering angle range of 0-3 degrees can be covered. The beam will be stopped at the zero-degree beam-dump for inelastic scattering measurements and in the first dipole (GR-D1) for change-exchange (CEX) or transfer reactions.

The LAS can be placed between 61 and 120 degrees.

The maximum beam intensity is limited by the radiation safety requirement and is 10-100 nA depending on the beam particle and energy.

Figure 1. zero-deg mode. GR is placed at 0 deg.
The beam is stopped either at the 0-deg beam dump
or in the first dipole of GR.

2.2 GRFBL mode

The GR spectrometer can be placed from 4.5 to 19.0 degrees except between 11.5-12.5 degrees.

Owing to the horizontal angular acceptance of the GR spectrometer, scattering angle range from 3.5 to 20.0 degrees can be measured. The GRF beam-line is optimized for the magnetic-rigidity ratio of B rho_GR / B rho_beam = 1-2. For example, inelastic scattering B rho_GR / B rho_beam ~ 1 and (3He,t) reaction B rho_GR / B rho_beam = 2, is well suited. For reactions with B rho_GR / B rho_beam below 1 or above 2, the most-forward angle is larger than 4.5 degrees.

In addition, spatial angular spread of the beam on target should be smaller than 5 mr, approximately, for 99% of the beam in order to achieve good beam transmission from the target position to the beam dump.

The LAS can be placed from 61 to 120 degrees.

Figure 2. GRFBL mode. GR can be placed between 4.5 (left) and 19.0 (right) degrees.

2.3 WS_LONG mode

The GR spectrometer can be placed from 25.5 to 70.0 degrees. Owing to the horizontal angular acceptance of the GR spectrometer, scattering angle range from 24.5 to 71.0 degrees can be measured.

Spatial angular spread of the beam on target should be smaller than 5 mr, approximately, for 99% of the beam in order to achieve good beam transmission from the target position to the beam dump.

The LAS can be placed from 25.5 to 120 degrees.

Figure 3. WS_LONG mode. GR can be placed between 25.5 (left) and 70.0 (right) degrees.