# Presentation: 102195

## Heavy Ion Microbeam and Micron Resolution Detector

- Veljko Radeka, Kevin A. Brown, Zheng Li, Marcelo E. Vazquez
-  BNL
- Outline:
***Micron resolution detector***
***Preparations for the detector beam test***
***Progress in the design study of the microbeam***
***Plans for further system development***
-        NSBRI Technology Team Retreat JHU/APL, Sept. 15, 2003

## The Roles of the Microbeam and the Micron Resolution Detector

***The Roles of the Microbeam and the Micron Resolution Detector***

- A microbeam of heavy ions (e.g. iron) at energies up to 3 GeV/nucleon.  The microbeam would have a sufficiently small diameter (~10m) to localize the ions to a single cell.

- An electronic position sensitive detector for heavy ions with a position resolution better than 1μm, to localize the position of an ion impact within a particular region of the cell.

## Individual pixels are alternately connected by X and Y readout lines (strips) 

- Individual pixels are alternately connected by X and Y readout lines (strips)

**   **Two dimensional position sensitivity is achieved by charge sharing between X and Y pixels
-    In principle, the pixel pitch should not be larger than the size  of charge cloud caused by diffusion process

- The new concept:

## Expected effects on energetic Fe ions due to the traversal of 200 of Si. 

| Energy per nucleon | Average energy loss | RMS energy loss fluctuation | dE/dx | LET | RMS exit distance from incident ion trajectory | RMS exit angle with respect to incident ion trajectory |
| --- | --- | --- | --- | --- | --- | --- |
| (MeV/amu) | (MeV) | (MeV) | (MeV/
μm) | (MeV cm2/mg) | (μm) | (mrad) |
| 1000 |   55.4 | 3.81 | 0.277 | 1.19 | 0.024 | 0.20 |
|   800 |   58.4 | 3.41 | 0.292 | 1.26 | 0.030 | 0.28 |
|   600 |   64.0 | 2.93 | 0.320 | 1.38 | 0.048 | 0.37 |
|   400 |   75.9 | 2.51 | 0.379 | 1.63 | 0.076 | 0.56 |
|   200 | 112.1 | 2.23 | 0.561 | 2.41 | 0.131 | 1.15 |

**Expected effects on energetic Fe ions due to the traversal of 200******** of Si. **
** ****The estimates are based on TRIM simulations.**

**Signal: 8x10****4**** e-h/********m for 1 GeV iron ion**
**Diffusion:                                               for d= 200 ******** m**

**Design Considerations for the Micron-resolution Detector**

**Charge cloud covers about 9 **
**pixels to ensure sub-micron **
**position resolution in two**
**dimensions**

## A design layout of a X, Y ASD (8.5 m pitch)

**X**

**Y**

**4 ********m diameter circular **
**pixels**
**3 ********m X and Y read out **
**Strip line width**
**Sensitive area: **
**131x131 ********m****2**

##  Prototype Stripixel Detectors 

** ****Prototype Stripixel Detectors **

**FWHM for charge**
**diffusion**

**X pixels and Y**
**strips**

**X and Y pixels**

## Slide 8

## Micron Resolution Detector (“Stripixel”) Prototype

- Chip size: 4x4 mm

## Current Status of the Micron-Resolution Detectors

***Second batch***** fabrication has been completed:**
**      ****New double metal process has been used with in situ back-**
**      ****sputtering to remove oxide from the first metal before the**
**      ****sputtering of the second metal --- contact problems observed  on the *****first batch***** with 8 micron strip pitch (but not on the 20 micron strip pitch) have been resolved.**
**Assemblies of the detector chips with 8 micron pitch and 20 micron pitch, with preamplifiers, are being prepared for the beam tests with heavy ions.**
** **

***Current Status of the Micron-Resolution Detectors***

## Preparations for the detector beam test

**Booster Accelerator Facility (BAF) will become operational in the fall of 2003.**
**The micron resolution detector will be tested (following testing with a laser) at  BAF with  ~1GeV/nucleon iron ions.**
**A detector readout system will be used which includes signal   amplification, pulse shaping and *****computation of the position centroid in real time*****, as illustrated in the following three slides.**

## Micron resolution detector

**Micron resolution detector**
** ****- position centroid finding**

- Charge samples on ***x*** and ***y*** strips
- for a typical event, on a detector
- based on the same readout concept.
- The charge is shared between
- strips 8 and 9  on ***x***, and among
- strips 9,10,11 on ***y***.
- First moment computation of the
- charge samples provides the
- interpolation required to obtain a position resolution of ~1 micron with a detector strip pitch of 8.5 microns.

## New Digital Centroid Finding Module

## New Digital Centroid Finding Module

**Gated Baseline Restorers**

**Anode Trigger Logic**

**Digital Processor**

**ADCs**

## Microbeam Design Studies  (1)

- Simplified schematic representation of two microbeam systems differing by a factor 2 in length.  The longer configuration was chosen for detailed beam-optic calculations and scattering estimates. It discriminates better against scattered ions, it requires weaker lenses and it provides more than adequate intensities for a single-hit facility.

- Schematic of tungsten jaws used for defining the object aperture for the present example.

**Microbeam Design Studies  (1)**

- (studies being performed by P. Thieberger)

## Microbeam Design Studies  (2)

- Simulated X and Y projections of 20,000, 1 GeV/amu iron ions focused onto the image plane using a 1 mm diameter lens aperture and a mono-energetic beam. Focusing is achieved with a quadrupole triplet, optimized for equal and maximum demagnification in both planes.

- Defocusing effect with a 1 mm lens aperture of the 0.5% momentum sweep expected during slow beam extraction.

- The defocusing effect caused by the ***0.5%*** momentum sweep is reduced if the lens aperture is reduced to ***0.5*** mm diameter.

**Microbeam Design Studies  (2)**

- Beam FWHM ~ 8 microns

## Beam spot at the image plane showing the few scattered ions as larger, purple dots (38 ions scattered, 8000 transmitted).  Scattered ions are outside of the target area. For this simulation, the object collimator surfaces were assumed to have a peak-to-valley roughness of 5 microns. Smooth surfaces were also simulated and it was shown that further large reductions of scattered ions can be achieved. 

- Beam spot at the image plane showing the few scattered ions as larger, purple dots (***38 ions scattered, 8000 transmitted***).  Scattered ions are outside of the target area. For this simulation, the object collimator surfaces were assumed to have a peak-to-valley roughness of 5 microns. Smooth surfaces were also simulated and it was shown that further large reductions of scattered ions can be achieved.

## Plans for Future System Development

- After completing the demonstration of the detector with cell samples, and an evaluation, a proposal will be prepared for the development of a detector system for routine measurements of effects of heavy ions on single cells and biological systems.
- After completing the design study for the microbeam, a proposal will be prepared for the construction of a heavy ion (up to 3 GeV/nucleon) microbeam addition to the new facility.