Miscellaneous

Using the following procedure and example, estimate the anticipated activation of a sample exposed to the neutron beam in a LANSCE instrument from the table. If you cannot estimate the activation, call your LANSCE contact.

Example: For 5g YBa2Cu3O7 sample on NPD at 75mA for 24 hours (1 day).

1. Compute the mass fractions for all elements in the sample.

Example: The mass fractions are 0.13 Y, 0.4l Ba, 0.29 Cu, & 0.17 O

2. Obtain the prompt activation from the product of these mass fractions and the corresponding elemental activation values in the table. Multiply the contact dose by the sample mass that is exposed to the beam to obtain the expected contact dose from the entire sample.

Example continued:

prompt activity = 0.13x 1000 + 0.41x80 +0.29x 10000 + 0.17x0.0 = 3060nCi/g

contact dose = 5x(0.13x0.9 + 0.41x0.1 + 0.29x8.5 + 0.17x0.0) = 13.1mR/hr

3. Scale these activation values by the instrumental factor (below) and the beam current as a fraction of l00mA to obtain the estimated values for the sample and actual beam conditions.

Instrumental factors for LANSCE

HIPD 1.00 (reference) 
SCD 1.44 
FDS 0.50 
CQS 1.65 
NPD 0.025 
PHAROS 0.060 
LQD 0.033 
SPEAR 0.04 1

Example continued:

prompt activity = 3060x0.025x75/100= 57nCi/g

contact dose = 13.lx0.025x75/100 = 0.25mR/hr

4. To obtain the storage times, t, for each element in the sample, correct the appropriate times given in the table, ts, by:

t = ts(0.693+0.lxlogeC),

where C is the product of the mass fraction, instrumental factor and beam intensity ratio to l00m A. This expression assumes that the storage times given in the table are roughly 10 half-lives for the slowest decaying isotope of significant concentration in the activated element The storage time for the sample is then the largest of the resulting times.

Example continued

Y storage time = 24d(0.693+0.lxloge(0.13x0.025x75/100)) = 2.2d

Ba storage time = 150h(0.693+0.lxloge(0.41x0.025x75/100)) = 1.3d or less

Cu storage time = 7.4d(0.693+0.lxloge(0.29x0.025x75/100)) = 1.3d

O storage time = 0 (no activation expected)

Thus the storage time for this sample of YBa2Cu3O7 is determined by the decay of the Y as 2.2 days. At that time, the sample should show residual activation of less than 2nCi/g.

These estimates are based on a neutron exposure time of 1 day. The actual level of activation can drastically change if the exposure is more or less than 1 day. Determining this change cannot be accomplished using these simplistic calculations. Therefore, we require that all samples (no matter how long the neutron exposure is) be surveyed before they leave the facility.

LANSCE 12 / 1 / 92

This table allows you to calculate the activation of a sample after it has been in a neutron beam for one day and the amount of time for it to decay to 2nCi/g or less, which is the limit for shipping a sample as "nonradioactive". It also displays the anticipated exposure you may receive when removing the sample from the instrument. A sample calculation is included at the end of the table. Storage time is the time required for a sample of the pure condensed-phase element exposed to a "standard" neutron beam to decay to 2nCi/g or less. Prompt activation gives the anticipated activation for the pure solid elements 2 min after the neutron exposure ceases. Contact dose is that expected from a 1g sample of the pure element from the prompt activation. Elements with a dash for the entries in all three columns do not show any activation. Those marked with a single asterisk are radioactive before exposure to the neutron beam; apart from Tc and Pm, they are all a-particle emitters. Bismuth is a special case; it is stable before exposure to the beam, but the activation product is an a-emitter.

* These entries are derived by Mike Johnson of ISIS for decay times to 10⁵ and to 10⁴Bq/cm³ for 5-cm³ pure solid samples of the elements exposed to a neutron beam for 1 day at an intensity comparable to that on HIPD with LANSCE operating at 100mA. They are augmented by calculations from NIST of the activation from a 1-day exposure to a 10⁷n/s-cm² reactor thermal beam (marked ^†).

USING TELNET AND FTP THROUGH THE ILL/ESRF FIREWALL

(1) GOING FROM THE  ILL TO OTHER COMPUTERS OUTSIDE THE ILL

No special ID or password is needed, but you will have to pass through the firewall as described below:

TELNET 
(i) Type telnet out from whereever you are. This will put you through to the ESRF, ILL & EMBL common firewall system - you will receive the prompt telnet-proxy > 
(ii) Now type open hostname - for example 
open indy9@physics.cam.ac.uk 
or 
open 160.8.3.128.

FTP 
(i) Type ftp out from whereever you are. This will put you through to the ESRF, ILL & EMBL common firewall system. 
(ii) At the prompt, type the username & computer name of the machine that you wish to contact. For example: 
bloggs@indy9@physics.cam.ac.uk 
You will then be prompted for your password and should be able to connect and transfer in the normal way.

(2) COMING TO THE ILL FROM COMPUTERS OUTSIDE THE FIREWALL

You may have reason to need access to ILL computers after you leave Grenoble. A special firewall username and password is required to do this. If needed, this can be arranged via your local contact. Please do not divulge this username/password to anyone.

TELNET 
(i) From your outside machine, type telnet firewall.ill.fr. 
(ii) Now type telnet grill.ill.fr. When prompted, enter your firewall username & password. For example 
    v-bloggs 
    bloggspassword 
(iii) You are now inside the firewall and can access any of the computers that you could when you were on site.

FTP 
FTP access from the outside world through the firewall is not permitted. The only thing that can be done is to gain TELNET access through the firewall (as described above) and then to initiate FTP requests from within the system (as described in section 1 above).

• D19 beam monitor specification
• Available monochromators and takeoff angles
• Procedure for changing take off angle on D19
• Take off angles etc used in previous experiments
• Gold foil measurements of D19 flux
• Monitoring free data space on the d19 control computer
• The H11 casemate
• Sample alignment using camera

Available wavelengths on instrument D19

Values in red indicate those that have been commonly used in the past.

In choosing the wavlength for an experiment you have to consider a compromise between flux and resolution. An increase in wavelength gives you an effective improvement that arises from increased reflectivity in the monochromator (and in the sample). This factor  varies approximately with the square of the wavelength. Additionally the efficiency of the gas detector improves at longer wavelength. However, there is a penalty to be paid if you require high resolution.

XERAM Neutron Beam Monitors MNH 1014.2 SCAL

(This page is not for general distribution - all details given here were extracted from a scan of the PECHINEY ceramiques catalogue, which should be consulted for all definitive information)

These detectors can be put in the incident very intense primary neutron beams in order to monitor the scattering experimental data according to the fluctuations of the nuclear reactor power. The yield of detection 10^-5 to 10^-2 for thermal neutrons can be adjusted to meet the neutron flux level. Two opposite thin aluminium windows provide negligible absorption of the neutron beam. Moreover the internal structure was designed to ensure an excellent counting stability over long periods of time.  For special applications where the rectangular cross section proves useful. These detectors can be filled at a high helium 3 pressure.

Outline drawing

Specification

Monitoring free data space on the d19 control computer

1.Check the data disk on d19

Check that the data disk on the control computer d19 is not almost full (e.g. each Friday). Type: 
df /users/dat

The response will be something like: 
Filesystem   512-blocks        Used   Available Capacity  Mounted on 
/dev/rz17c     34771154    16491536    14802502    53%    /users/data

If the "capacity" field is higher than e.g. 80%, one of the IRs should delete some of the earliest scans (after checking with e.g.  msp 
that they have been transferred : that is automatic, en principe, but there is no automatic delete).

Before deleting data, do msp, and also list to be sure you are awake. For example type: 
list 
and you will get a response like: 
Taking remote .storage file 
 first found:        53000 
 last found:        55025

2.Delete files if necessary

There is a script for deleting called delete_data_script delta  (this is invoked invoked on d19 by typing "del" , then "tab") 
to make deleting easy: but be careful !! Check with the current user that he/she has finished processing, as it is slightly easier to process data on d19 than remotely.

A sample delete data files script: 
First data file local data area is  053000 
 Delete upto (and including) : 053100 
from : 053000, upto 053100 
rm /users/data/053000 
rm /users/data/053001 
.... 
Or you can simply use e.g.  rm -f  /users/dat/0530* to delete the scans 053000 to 053099